S c a d J Gastroenterol 1992;27:529-537.
REVIEW
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Experimental Colitis in Animal Models Despite extensive research on their immunologic, biochemical, microbiologic, and epidemiologic aspects, the etiology and pathogenesis of ulcerative colitis and Crohn's disease (inflammatory bowel disease (IBD)) are still not known. Consequently, the therapeutic approach remains empiric. Nor do we know the ideal animal model for study of IBD. Nevertheless. important insight into the nature of the human disease may be obtained from the study in animals. In this article we discuss pathogenetic mechanisms of experimental colitis in various animal models.
IDEAL ANIMAL M O D E L OF INFLAMMATORY BOWEL DISEASE The ideal model should be a naturally occurring or inducible animal disease that is identical in every aspect to the human disease. This means that the animal disease is induced and maintained by the same primary and secondary factors (same etiology and pathophysiology), has an equivalent clinical spectrum, and is treatable with therapeutic agents (1). In addition, the ideal model must be a practical study tool (easy accessibility, easy experimental manipulation, and not too expensive).
CATEGORIES OF ANIMAL MODELS There are two broad categories of animal models of IBDone in which the disease arises naturally and one in which the disease is induced experimentally either by exposure to dietary substances or pharmacologic agents or by exposure to materials derived from patients or by manipulation of the animal's immune system (1).
colony-maintained CTTs develop active colitis not associated with identifiable pathogens and, as in human, the activity of the disease process spontaneously waxes and wanes (3,4). Histologically, the colonic inflammation is characterized by hemorrhages and crypt abscesses and an increase in the density of lymphocytes and plasma cells in the lamina propria (3). Biochemically, there is a reduction in colonic mucin glycoprotein analogous to that in human ulcerative colitis ( 5 ) . In addition, significant histologic improvement occurs when CTTs are treated with sulfasalazine (3). These striking similarities between CTT colitis and human ulcerative colitis provide a unique opportunity to unveil the etiopathogenesis of spontaneously occurring chronic colitis. Unfortunately, this endangered species is not widely available, thus limiting its usefulness as a research tool. The inflammatory mediators in plasma (6) show low levels of prostaglandin E2 (PGEJ and increased levels of plateletactivating factor (PAF), which may result in tissue destruction in acute C'IT colitis. However, no P A F was detected in the plasma of chronic-phase tamarins. Serial measurements of eicosanoids in the CTT by rectal dialysis (7) showed normal leukotriene B4 (LTB4) content but elevated P G E z content in active compared with inactive colitis. Oral administration of a lipoxygenase inhibitor prevented spontaneous relapses, possibly mediated by inhibition of lipoxygenase products other than LTB, (7). Recently, the presence of cross-reactive epitope(s) related to mol. wt. 40,000 protein (8), which acts as autoantigen(s) in human colon in patients with ulcerative colitis, was demonstrated (9). Sera from C'IT with colitis contain autoantibodies reactive to this unique epitope(s) (9).
There are many naturally occurring intestinal inflammations in animals (such as boxer dog and equine colitis, porcine enteritis, and proliferative ileitis in the hamster), but these diseases cannot be called animal models of IBD, because in most instances a causal organism is found.
Juvenile rhesus macaques Recently, another spontaneous chronic colitis was identified in juvenile rhesus macaques (lo), which may have recurrent episodes of persistent non-bloody liquid stool, weight loss, and/or growth retardation. Pathologic examination showed uniform, continuous inflammation of the cecum, the colon, and the rectum. Histologically, there was chronic inflammation with crypt abscesses, goblet cell depletion, and surface cell alterations. Colonic tissue interleukin 1 (IL-1) and LTB, levels were increased.
Cotton-top tamarin Recently, an interesting model was found in the cotton-top tamarin ( C P ) . This New World primate species, Saguinus oedipus, has a high prevalence of spontaneous colitis and may develop adenocarcinoma of colon (2). As many as 50% of
Intestinal inflammation produced by physical or pharmacologic agents Acetic acid. Intrarectal instillation of diluted acetic acid
NATURALLY OCCURRING INTESTINAL INFLAMMATION
EXPERIMENTALLY I N D U C E D COLITIS
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(410%) induces acute colitis in rats, rabbits, and guinea produces colonic lesions in various laboratory animals, pigs (11,12). Tissue levels of myeloperoxidase, a marker including guinea pigs, mice, rats, rabbits, and monkeys (30enzyme of polymorphonuclear leukocytes (PMN), cor- 32). The lesions are initially seen in the cecum and progress related well with histologic assessment of the severity of distally. There are no lesions in the small intestine and no colitis. In addition, the pattern of the arachidonic acid metab- remission/exacerbation of the colitis. The mechanisms of inflammation involve uptake of carolism was strikingly similar to that in human IBD (13, 14). The concentration of the potent chemotactic agent LTB, in rageenan by intestinal macrophages, followed by leakage of acetic acid-treated mucosa was 50 times higher than in nor- lysosomal enzymes into the mucosal tissue and consequent mal mucosa (13, IS). There were diffuse ulceration of the tissue destruction and inflammation (33). Histologic examdistal colon, pseudo-polyp like structures, alterations in crypt ination showed the presence of free carrageenan and carradepth and mucus secretion, and a transmural non-specific geenan-laden macrophages in the lamina propria of guinea pig colon after 2 days of carrageenan administration (34). inflammatory response ( I 1). The colitis induced by acetic acid is not simply due to the PGE2 levels in colonic tissue were elevated earlier than physical effect of acid per se, since intrarectal instillation of LTB4 levels, suggesting that PGE2 production is involved in diluted HCI with the same pII as the acetic acid does not initiating the inflammatory response, whereas LTB4 may be important in maintaining the inflammation (34). Local result in colonic inflammation (16). The severity of inflammation of acetic acid-induced colitis injection of carrageenan produced acute inflammation folcould be reduced with various agents, including 16,161- lowed by protracted granuloma formation, suggesting that macrophages contribute to phagocytosis of carrageenan (3.5). dimethyl PGE2 (17). indomethacin (17), misoprostol (18), sucralfate (19), sulfasalazine (20). phenidone (20), nordihy- Immunologic mechanisms are also involved, since carradroguaiaretic acid (20), and LTB4-receptor antagonists (12). geenan activates the complement system (36). Several investigators have tried to modify carrageenanPhorbol ester. Ethanol in concentrations above 30% acts as a mucosal barrier breaker and causes widespread acute induced inflammation with antibiotics. Pretreatment with mucosal damage when instilled into the distal colon of rats antimicrobials directed against coliforms failed to attenuate ( 2 I ) . Phorbol esters (PMA) are tumor-promoting agents the disease process (37). O n the other hand, pretreatment derived from the croton plant. A single intrarectal instillation with metronidazole, an antimicrobial primarily active against of phorbol-12-myristate-13-acetatein ethanol vehicle into anaerobic bacteria, prevented carrageenan-induced colitis male rats (10 mg/kg in 1 ml 40% ethanol solution) or male in most animals. Metronidazole treatment of established rabbits (1 .Smg/kgin 10 ml20% ethanol) causescolitis within colitis showed no salutary benetit. The results suggest that 24 h, with an increased colonic tissue myeloperoxidase level anaerobic bacteria play a role in the initial events of carra(22). The mechanism(s) of PMA-induced colitis is under geenan-induced colitis in the guinea pig model but d o not intensive investigation (22). Upregulation of LTA, hydrolase alter the course of the disease once the lesions have formed may beonemechanism. Phorbolestersactivate protein kinase (37). Oral administration of carrageenan changes the intestinal C (PKC) in several tissues (23). PKC seems to stimulate the release of LTB,, as well as PAF, from human neutrophils microflora, particularly increasing gram-negative anaerobes (24). Indeed, PKC upregulates LTA4 hydrolase, the enzyme (3638), and Bacteroide.s oulgatus has been incriminated i n responsible for the hydrolysis of the LTB, precursor, LTA4 the pathogenesis of carrageenan-induced colitis in the guinea (25). Other explanations, such as upregulation of the his- pig (38). Further, an immunologicreaction against B. uulgarus tamine response through PKC activation of PMA (26), modu- isolated from the colon in animals has been suggested (39). h. Amylopectin sulfate. Ulceration of the colon develops lation of cell adhesion (27), stimulation of the neutrophil oxidative burst (28), induction of cellular toxicity through in rabbits when they are fed sulfated amylopectin, even in interleukin-2 production, receptor expression and lympho- low concentrations (0.1 %). in the drinking water over 2 to cyte activation (29), or P A F release (24), are also possible 4 weeks (40). The deleterious effect appears similar to that of degraded carrageenan, consistent with the similarities in mechanisms of injury. Sulfated polysaccharides. Several sulfated polysaccharides structure (sulfated polysaccharide of high molecular weight) are known t o induce colitis in animals after oral adminis- and polyanionic behavior of sulfated amylopectin and degraded carrageenan (30). tration (30). c. Dextran sulfate. Ulcerative colitis can be induced in a. Carrageenan. This model was originally described by Marcus & Watt in 1969 (30). Carrageenan is a sulfated hamsters (41) and mice (42) by giving dextran sulfate sodium polysaccharide obtained by aqueous extraction of red sea- (DSS) in their drinking water. DSS causes a change in the weeds (Chondrus crispus, Eucheuma spinosum). Mild acid intestinal microflora, and particularly an increase in the hydrolysis yields degraded carrageenan, which has increased number of gram-negative anaerobes, including Bactersolubility while retaining the sulfate content and polyanionic oidaceae, has been noted as in the case of carrageenaninduced colitis (41,42). O n postmortem examination, mulproperties of the native compound. Oral administration of degraded carrageenan in water tiple erosions and inflammatory changes including crypt
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abscesses were found on the left side of the large intestine (the descending and sigmoid colon and the rectum). Mice (42) developed chronic colitis, including dysplasia, shortening of the large intestine, and prominent lymphoid follicles after five administration cycles, each cycle consisting of 7 days with 5% dextran sulfate sodium in the drinking water followed by 10 days’ consumption of distilled water. Morphologic observations showed swollen macrophages in the inflamed colonic wall (42), a finding consistent with carrageenan- or amylopectin sulfate-induced colitis (43). The macrophages had enlarged lysosomes and contained a metachromasia-positive substance on toluidine blue staining. Accordingly, this intralysosomal substance is thought to be a polysaccharide sulfate (44). In vitro phagocytosis of DSS by macrophages was also observed. Consequently, DSS appeared to have been phagocytosed by the mononuclear phagocytic system in the colonic mucosa. DSS-containing macrophages may have reduced phagocytic ability against the normal intestinal flora (45). Alternatively, DSS may have caused injury to the colonic epithelium leading to increased uptake of toxic luminal bacterial products such as endotoxin and peptidoglycan-polysaccharide polymers (46). In summary, inappropriate macrophage function, alterations of luminal bacteria flora, or toxic effects on colonic epithelium (47) are possible mechanisms by which enteral DSS induces ulcerative colitis in experimental animals. Chernotuctic peptide. Chemotactic peptides constitute a recently described class of attractants that may display selectivity for PMNs, eosinophils (EOSs), or monocytes (MONs) in vitro (48-51). The oligopeptides come from various sources, including aerobic and anaerobic bacteria normally found in the distal bowel (52). n-Formyl-methionyl-leucylphenylalanine (n-FMLP) is the most potent chemotactic peptide known for PMN (53). All chemotactic peptides appear to exert their effects by binding to cell-surface receptors. Granulocytes isolated from blood and tissue exudates in humans and rats have been shown to possess specific receptors for FMLP (54,55). FMLP activation of phospholipase C (56), which releases diacylglyceride (DAG) and inositol triphosphate (1P3), may be mediated by guanine nucleotide-binding proteins. DAG stimulates PKC, whereas IP3 participates in calcium ion mobilization (57). The interaction of FMLP with receptors results in neutrophil aggregation and adherence, superoxide production, enzyme secretion, and chemotaxis (55). PMN function is partially regulated through the expression of high- and low-affinity receptors for FMLP. High-affinity receptor binding by small amounts of FMLP activates PMN migration toward the bacteria (58,59). As the PMNs approach the bacteria, the higher concentrations of FMLP activates the low-affinity receptors to induce cytotoxic functions (59,60), including degranulation with lysosomal release (50,61) and superoxide anion production from a cellular respiratory burst (61-63). Aggregation (64) and increased phagocytosis (65) are additional effects of FML.P.
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Another effect of FMLP is the stimulation of synthesis and release of eicosanoids, including PGE2 and PGF2-alpha and thromboxane (66). The synthesis of the lipoxygenase products 5-hydroxyeicosatetraenoic acid (5-HETE) (66,67) and LTB4 (68) is also stimulated. The leukotrienes released may amplify the effects of FMLP by direct stimulation of PMN aggregation (69), chemotaxis (70), degranulation (71), and superoxide anion production (62). FMLP also stimulates active C1 secretion and inhibits electroneutral C1 absorption in both the small and the large intestine (72). Ex vivo perfused rabbit colons released LTB4 in response to chemotactic factors for neutrophils (n-FMLP), mononuclear cells (f-MLP-methyl ester, f-MLP-me), and eosinophils (Ala-Gly-Ser-Glu (AGSG)) (73). Intracolonic administration of chemotactic peptides induced dose-related mucosal infiltration of neutrophils and eosinophils in vivo (73). n-FMLP-methyl ester was most potent. n-FMLP and AGSG induced comparable degrees of inflammation, although in ex vivo perfused colons AGSG produced no eicosanoid release, whereas n-FMLP released both PGEz and LTB4 and LTC4 products. Thus, AGSG produces colitis independent of proinflammatory eicosanoids, whereas eicosanoid release could contribute to colitis produced by nFMLP and n-FMLP methyl ester. In contrast to formalin immune complex and dinitrochlorobenzene (DNCB) hypersensitivity colitis (see below), acute colitis induced by chemotactic peptides has less necrosis and more localized and consistent degree of mucosal inflammation, which may be mediated by enhanced leukotriene production (73). Magnusson et al. (74) were the first to demonstrate that luminal perfusion of the distal rat ileum with either FMLP or n-formyl methionyl phenylalanine increases mucosal permeability to fluoresceinated dextran (mol. wt., 3000). It has been shown by Teir et al. (75) that some resident granulocytes in the rat intestinal mucosa normally occupy positions between epithelial cells, where they are in direct contact with luminal fluid. Nash et al. (76) demonstrated that human neutrophils migrate across intestinal epithelial monolayers in response to FMLP, and they suggested that the physical opening of intercellular junctions by transmigrating neutrophils accounts for the FMLP-induced increase in mucosal permeability. However, it is also possible that activation and degranulation of granulocytes lead to a chemically mediated increase in mucosal permeability during luminal perfusion with FMLP (77). In the rat, gut mucosal permeability measured by blood-to-lumen clearance of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) during luminal perfusion with FMLP was significantly increased only in the terminal lOcm of the ileum (77). The increased mucosal permeability in response to FMLP could be prevented by depletion of circulating granulocytes with anti-neutrophil serum (77) or the glutathione peroxidase mimetic, PZ 5 (78). However, pretreatment with the superoxide radical scavenger superoxide dismutase or with catalase had no effect, suggesting that hydrogen peroxide is not a mediator
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of the increased mucosal permeability induced by formylated peptides (78). The observations that the most distal segment of ileum had both the highest basal clearance o f EDTA (a molecule similar in size to FMLP) and the greatest clearance in response to FMLP suggest that the size o r the number of exchange pathways is greater in the distal ileum, thus predisposing this region to the inflammatory actions of FMLP. The high sensitivity of the distal ileum to luminal perfusion with FMLP (77) may have important clinical implications. Ilollander et 211. (79) noted that thc permeability of the gut niucosa was higher not only in patients with C h h n ’ s disease hut also in their relatives, who are known to have a higher risk of developing terminal ileitis than other individuals. This suggests that basal mucosal permeability may be a predisposing factor for inflammatory bowel disease. The particularly high mucosal permeability of the terminal ileum may explain why this segment is predominantly affected in Crohn’s disease. FMLP in the colon could induce mucosal inflammation by further increase of mucosal permeability, direct activation of granulocytes, and/or release o f proinflammatory mediators such as eicosanoids (73). Healthy colon tissue can produce proinflammatory LTs in response to bacterial peptides (go), but most animals d o not develop colitis in response to luminal chemotactic peptides. I t is reasonable to that effective mucosal defenses normally block access of these agents to their target cells. Such defenses may include efficient rnucosal protease activity (81), mucosal barriers of mucin (82), and limited mucosal permeability (83). If the mucosal barrier is broken, chemotactic peptides may stimulate resident colonic niucosal cells to release leukotriene B4 and C4. These proinflammatory leukotrienes will enhance the effect of chemotactic peptides, attracting circulating PMNs and induce aggregation. degranulation, and release of reactive oxygen metabolites. The net result of these stimuli would be acute colonic inflammation. The possibility that defective mucosal permeability may constitute a predisposing factor while bacterial-derived chemotactic peptides, such as FMLP, constitute triggering factors is an attractive hypothesis for the pathogenesis of IBD. Free rudiculs. Recently, colitis was induced in rats by means of the free radical initiator 2,2’-azobis (Zamidinopropane) hydrochloride (AAPH), which decomposes to N2 and free radicals with subsequent generation of peroxyradicals. The development of colitis was prevented by sulfasalazine, 5-aminosalicylic acid (5-ASA), and the antiinflammatory drug SC-41930 (84). Intestinul inflammation induced by materials derived from patients Another experimental approach is to induce intestinal inflammation in animals by using materials obtained from
IBD patients in an attempt to a) utilize animals as culture tubes in which causative organisms can be expanded and identified, or b) establish an IBD-like disease in the animal (1). Mitchell & Rees (85) injected homogenized filtered Crohn’s disease tissue into the footpads of mice and obtained granuloma. Subsequent studies aiming to prove the existence of transmissible agents have, however, shown equivocal results (86). It seems to be accepted now that IBD lesions cannot be passed to animals by injection of homogenized, filtered materials acquired from patients. Manipulution of’ animul’s immune system Intestinal inflammation induced by immunologic mechanisms falls into two categories. The first mechanism involves antibodies or immune complexes (B-cell models), and the second involves activation of lymphocytes (T-cell models). B-cell models. In their initial work Kirsner (87) and Goldgraber & Kirsner (88) induced intestinal inflammation by local induction of the Arthus and Schwartzman reactiotis. In an Arthus-type reaction rabbits are first sensitized to an antigen (egg albumin) by systemic antigen administration. Subsequently, severe local inflammation and hemorrhagic necrosis are induced by mucosal injections of the sarne antigen. In the Schwartzman reaction the animals are given bacterial lysates in a similar sequential systemic and local fashion. Auer (89) demonstrated in 1920 that massive inflaniniation could be induced at the site of a previously mild, local, nonspecific inflammatory reaction by the parenteral administration of a large dose o f antigen to a sensitized animal. Kirsner et al. (90,91) thus induced severe colitis in rabbits which had previously been sensitized to egg albumin and had mild colonic inflammation induced by intrarectal instillation of a small amount of diluted formalin. The principle involves sensitization to a soluble antigen, a generalized antibody response, attraction of non-specifically mildly irritated tissue for circulating antigen and antibody on the basis of an increased vascular permeability in these areas, and a resultant antigen-antibody reaction leading to tissue injury. Specific antigen and antibody have been identified in (.he diseased colon by immunohistochemical methods (91). Hodgson et al. (92) induced colitis in rabbits by a modified Auer technique. Preformed immune complex of human serum albumin (HSA) and anti-HSA with antigen excess was injected intravenously to non-sensitized rabbits after provocation of mild inflammation in the colon with diluted fornialin (1%, 1 ml instilled intrareetally). The procedure produced severe colitis, including mucosal ulceration, mixed inflammatory cell infiltration in the lamina propria. and crypt abscess formation, suggesting that whatever the primary cause of the colonic inflammation, further tissue damage may be induced by immunologic mechanisms. A chronic colitis has also been induced in rabbits (93) and rats (94) by a modified Auer technique. The animals were
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preimmunized with the common enterobacterial antigen of Kunin (93) or E . coli 0 1 4 : K 4 : H - (94). The latter is a lipopolysaccharide that resembles structures in the human intestinal wall (95). The antibodies cross-reacted with colonic mucosa. Colitis was induced by topical irritation of the colonic mucosa with diluted formalin, followed by intravenous injection of soluble immune complexes (bovine serum albumin (BSA) and anti-BSA) with antigen excess. The rabbits developed acute colitis within the first week, but, in contrast t o unsensitized rabbits, the inflammation persisted and was still present at 6 months. The results suggest that hypersensitivity to colonic bacterial antigens may be one mechanism whereby an acute colitis becomes chronic. T-cell model.$.Sensitization with haptens and subsequent challenge o f the cell-mediated immune system in guinea pigs, rats, and rabbits may induce inflammation of the gut. DNCB and trinitrobenzene sulfonic acid (TNBS) are chemical haptens that bind to tissue proteins and are capable of stimulating cell-mediated immunity ( 9 6 9 7 ) . a. f)inifrochlorohenzene. Administration of DNCB produces a delayed hypersensitivity response of T lymphocytes against this hapten (98). To sensitize the rabbits to DNCB, diluted DNCB (0.1 ml DNCB dissolved in acetone at a concentration of 2000 mg/O.l ml) was placed on the rabbit’s skin in ;I I-cm circle. Ten days later 100mg of DNCB in 0.5 ml of acetone were introduced into the colon. Three days after challenge the colonic mucosa was ulcerated with crypt abscesses and inflammatory infiltrate. However, the inflammation was not sustained (96,97). Sensitivity to DNCB can he p ively transferred by lymphocytes (99), and immunosuppression mitigates the bowel injury in DNCB-induced colitis. The lamina propria lymphocytes isolated from the colon had a greater percentage of T cells and a greater capacity to mediate mitogen-induced cellular cytotoxicity with phytohemagglutinin than lamina propria lymphocytes from the normal colon (97). PGEz levels both in inflamed mucosa and in adjacent uninflamed muscularis propria were increased i n DNCB colitis (100). Increased PGE2 production may contribute to the smooth-muscle dysfunction seen in colitis. b. 7rinitrohenzene sulfonic acid. Intrarectal administration of TNBS in ethanol vehicle resulted in acute inflammation with ulcers that evolved into chronic inflammation of the distal colon in rats (101-104). Even at a dose of 30 mg of TNBS the ulceration and thickening of the bowel wall persisted for at least 8 weeks (101). Interestingly, granulomas and Langhans-type giant cells were also observed with segmental ulceration and inflammation. The inflammation was characterized by high myeloperoxidase and decreased glutathione levels (101, 105). TNBS can bind covalently to the E-amino group of lysine and modify cell surface proteins. Colitis may develop when presensitized T lymphocytes lyse hapten-modified autologous cells (106,107). Whereas T lymphocytes will lyse
hapten-modified autologous cells only if the animal has been presensitized, macrophages will destroy TNBS-modified autologous cells in the absence of presensitization (108). In addition, TNBS may be metabolized (enzymatically and non-enzymatically) to yield 0,- and H202from the interaction between ascorbate and TNBS (109). suggesting that TNBS-induced colitis may partly be mediated by cytotoxic, reactive oxygen metabolites generated by the oxidative metabolism of TNBS. Various inflammatory mediators such as PGEz, TXB,. prostacyclin, LTB4, LTC4, PAF, and IL may be involved in TNBS colitis, as in human I B D (110). The predominant arachidonate metabolites found in TNBS colitis are LTB, and the monohydroxy fatty acids 5-HETE, 12-HETE, and 15-HETE. LTB4 in particular is likely to be a product of neutrophils (103, 104,106, 111). According to Wallace et al. (103), LTB4 synthesis increased already within 4 h and peaked 24-72 h after administration of TNBS. The increase correlated with colonic myeloperoxidase activity. Treatment with a specific 5-lipoxygenase inhibitor resulted in significant reductions of colonic LTB4 synthesis and colonic damage. Pretreatment with 16,16’-dimethyl PGEz resulted in a lower inflammation index, a lower level of colonic tissue myeloperoxidase, and decreased production of LTB4 (106). LTB,, but not other leukotrienes, P A F , or n-FMLP, augmented colonic damage (1 11). Quantification of luminal eicosanoid release in vivo using a dialysis bag placed in the distal colon of rats showed a highly significant increase in PGE2, 6-keto PGF,-alpha, TXB2, and LTB, levels 3 days after intracolonic instillation of TNBS (104). Remarkably, the release of TXB, continued to increase during the stage of chronic inflammation (up to 21 days), whereas the levels of the other eicosanoids decreased. Treatment with prednisone or 5-ASA reduced TXB, levels in the chronic stage and improved the colitis both macroscopically and histologically. Moreover, selective thromboxane synthetase inhibitors significantly reduced the development of chronic inflammation and reduced the release of TXB2 (104). These results suggest that eicosanoids (prostaglandin, leukotriene, thromboxane) play an important role in the pathogenesis of TNBS-induced colitis. P A F is also thought to play a role in TNBS-induced colitis. Wallace et al. (112) demonstrated that PAF-acether production by the colon was increased as much as 16-fold above control levels in TNBS-induced colitis in the rat. High PAF-acether production was not seen during the time of maximal neutrophil infiltration (1-4 days after TNBS) but was seen 1-3 weeks after induction of colitis. Thus, PAFacether is unlikely to play an important role in the acute inflammatory response but may be important in the prolongation of the inflammation in this model. However, significant acceleration of healing can be achieved by treatment with a specific PAF-acether antagonist when given on days 4-7 after TNB administration. Among various inflammatory mediators in TNBS-induced
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colitis IL-1 may be the most significant indicator of mucosal useful information on the origin, regulation, and function of inflammation because its level correlated with myelo- inflammatory mediators. However, with the possible excepperoxidase activity (102). In chronic TNBS-induced colitis tion of the cotton-top tamarin, no animal model of induced in the rat, the mucosal histamine level increased in parallel or spontaneous inflammation of the colon is analogous to human ulcerative colitis in etiology, course of disease with the score of damage (113). activity, or histology (114). Several features of this model are attractive (101): The observation that two different immune-mediated 1. The inflammation is induced by one single intraluminal instillation, and the severity and persistence of damage are models gave similar results suggests that the colitis is not a specific response to delayed-type hypersensitivity or very reproducible. immune-complex-mediated reactions but rather an unspe2. The rat model is relatively inexpensive. 3. The inflammation results in thickening of the colonic cific, stereotype response (125). The original disturbance wall associated with cellular infiltration and ulcers persisting may not determine the nature of the lesions ultiniately for at least 8 weeks. This relatively long duration of the produced but may instead serve as an initiator of a final inflammation makes assessment of treatment effects poss- common immunologic pathway. ible. 4. Finally, this model is histologically relevant, in that several of the features of human IBD, particularly Crohn's Acknowledgement disease, are present. Thus transmural inflammation with This work was carried out while Dr. Hak-San Kim worked 6 granuloma and Langhans-type giant cells, skip-segment months at Haukeland University Hospital, Norway, financed ulceration and inflammation, cobblestone-like appearance by a grant from the Korean-Scandinavian Foundation in of the mucosa, mast cell and lymphoid infiltrates, and crypt Korea. HAK-SANKIM distortion are seen. Dept. of Internal Medicine Smooth-muscle hyperplasia of the muscularis mucosa and National Medical Centre narrowed segments of colon were seen 3 weeks after intraSeoul, South Korea rectal administration of TNBS (106). Generally, the intensity of the acute inflammatory response induced by TNBS is less ARNOLDBERSTAD pronounced than that induced by acetic acid. Acetic acidinduced colitis is also more difficult to modify pharmacoSection of Gastroenterology logically (106). Medical Dept . Haukeland University Hospital Bergen, Norway MODELS CURRENTLY USED A survey of the abstracts of the papers presented at the Digestive Disease Week in New Orleans, USA, in 1991, showed that animal models of experimental colitis were used in altogether 21 studies; TNBS was used in 9 studies, acetic acid (or citric acid) in 6, DSS in 2 , amylopectin sulfate in 1, peptidoglycan polysaccharide in 3, immune complexes in 2, an infectious agent in 1, mitomycin in 1, and spontaneous colitis (CTI') in 1. Thus, most of the models discussed in this paper are currently in use in various laboratories. SUMMARY Colitis may be induced in animals by oral administration of sulfated polysaccharides (carrageenan, amylopectin sulfate, dextran sulfate), chemical irritation by rectal instillation of diluted acetic acid, delayed hypersensitivity reaction after sensitization to DNCB or after one single administration of TNBS, and Arthus reaction induced by intravenous injection of immune complexes after chemical irritation of the colon, and by chemoattractant peptides such as FMLP. It appears that all models of colon inflammation in the rat, mouse, or rabbit produce increased amounts of eicosanoids similar to that found in human colitis. Thus, animal studies provide
REFERENCES
1. Stroher W. Animal models of inflammatory bowel diseasean overview. Dig Dis Sci 1985; 30 Suppl:3-10. 2 . Chalifoux LV, Bronson RT. Colonic adenocarcinorna associated with chronic colitis in cotton-top marmosets, Sagiiinus oedipus. Gastroenterology 1981;80:942-6. 3 , Madara JL, Podolsky DK, King NW, Sehgal PK, Moore R , Winter HS. Characterization of spontaneous colitis in cottontop tarnarin (Saguinus oedipus) and its response to sulfasalazine. Gastroenterology 1985;88:13-9. 4. Lushhach C, Humason G, Clapn N. Histology of colitis: Saguinus oedipus and other marmosets. Dig Dis Sci 1985;30 Suppl:45-51. 5. Podolsky DK, Madara JL, King NW, Sehgal PK, Moore R, Winter HS. Colonic rnucin composition in primates: selective alterations associated with spontaneous colitis in the cottontop tamarin. Gastroenterology 1988;88:2C-5. 6 . Clapp NK, Walsh RE, Fretland DJ, Henke MA, Gaginella TS, Inflammatorymediators in the plasma of cotton-top tarnarins with acute and chronic colitis [abstract]. Gastrocntcrology 1990;98:A442. 7. Panzini B, King N , Sehga P, Podolsky DK. Role of leukotrienes in the colitis of the cotton-top tamarin: effect of a 5 lipoxygenase inhibitor [abstract]. Gastroenterology 1990;98:A468. 8. Takahashi F, D ~ KM. s Isolation and characterization of a colonic autoantigen specifically recognized by colon tissuebound immunoglobulin idiopathic ulcerative colitis, Clin Invest 1985;76:311-8.
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9. Das KM, Squillante L, Henke M. Clapp N. The presence of circulating antibodies in cotton top tamarins (C'IT) with spontaneous colitis against an epitope(s) on MR 40,000 protein shared by human and CTT colon epithelial cells [abstract]. Gastroenterology 1990;98:A444. 10. Adler R, Hendrickx A, Rush J , Fondacaro JD. Chronic colitis of Juvenile Rhesus Macaques: mucosal tissue levels of interleukin-l (IL-1) and leukotriene B4 (LTB-4) [abstract]. Gastroenterology 1990;98:A436. 11. MacPherson BR, Pfeiffer CJ. Experimental production of diffuse colitis in rats. Digestion 1978;17:135-SO. 12. Fretland DJ, Widomski DL, Tsai BS, et al. Effect of leukotriene B4 receptor antagonist SC-41930 on colonic inflammation in rat, guinea pig and rabbit. J Pharmacol Exp Ther 1990;255:572-6. 13. Sharon P, Stenson WF. Metabolism of arachidonic acid in acetic acid colitis in rats: similarity to human inflammatory bowcl disease. Gastroenterology 1985;88:55-63. 14. Fretland DJ, Levin S, Tsai BS, et al. The effect of leukotrieneB4 receptor antagonist, SC-41730. on acetic acid-induced colonic inflammation. Agents Actions 1989;27:225-7. 15. Goetzl EJ, Pickett WC. The human PMN leukocyte chemotactic activity of complex hydroxy-eicosatetraenoic acids (HETEs). J Immunol 1980;125:1789-91. 16. Zeitlin IJ, Norris AA. Animal models of colitis. In: Chadwick VS, editor. Mechanisms of gastrointestinal inflammation. Wclwyn Garden City, UK: Smith Klinc and French, 1984:703. 17. Rcber S. Su K, Leung FW. Guth PH. Exogenous prostaglandin and indomethacin protect against the development of acetic acid colitis in the rats [abstract]. Clin Res 1989;37:113A. 18. Fedorak RN, Espey LR, MacArthur C, Jewel1 LD. Misoprostol provides a colonic mucosal protective effect during acetic acid-induced colitis in rats. Gastroenterology 1990; 9X:h15-25. 19. Waisman Y , Zahavi I. Marcus H. Ligumsky M. Roscnbach Y, Dinari G. Sucralfate is protcctivc against indomcthacininduced intestinal ulceration in the rat. Digestion 1088;41:7882. 20. Conzcntino P, Will PC, Lin A, Gaginella TS. Effect of 5lipoxygenase inhibitors on acetic acid colitis in the rat. Pharmacologist 1986;28:163. 21. Wallace JL, Whitlc BJR, Boughton-Smith NK. Prostaglandin protection of rat colonic mucosa from damage induced by ethanol. Dig Dis Sci 1985;30:86&76. 22. Fretland DJ. Widomski DL, Levin S. Gaginella TS. Colonic inflamm;ition in the rabbit induced by phorbol-l2-myristate13-acetate. Inflammation 1990;14:143-50. 23. Ashendel CL. The phorbol ester receptor: a phospholipidregulated protein kinase. Biochim Biophys 198S;822:219-42, 24. McJntyrc TM. Reinhold SL, Prescott SM. Zimmerman GA. Protein kinase C activity appears to be required for the synthesis of platelet-activating factor and leukotriene B4 by human neutrophils. J Biol Chem 1987;262:15370-6. 25. McColl SR, Ilurst NP, Betts WH, Cleland LG. Modulation of human neutrophil LTA hydrolase activity by phorbol myristate acetate. Biochem Biophys Res Commun 1987;147:622-46. 26. Leurs R. Go JNL, Bast A. Timmerman H. Involvement of protein kinase C in the histamine H1-receptor mediated contraction of guinea pig lung parenchymal strips. Agents Actions 1989;27:18(k3. 27. Danilov YN, Juliano RL. Phorbol ester modulation of integrinmediated cell adhesion: a postreceptor event. J Cell Biol 1989;108:1925-33. 28. Gerard C. McPhail LC, Marfat A, Stimler-Gerard NP, Bass DA. McCall CE. Role of protein kinases in stimulation of human polymorphonuclear leukocyte oxidative metabolism by various agonists. J Clin Invest 1986;77:61-5. 29. Aparico-Pagcs MN, Wcrspaget HW, Pena AS, et al. Natural, lectin and phorbolester-induced cellular cytotoxicity in Crohn's disease and ulcerative colitis. J Clin Lab Immunol 1988;27:10913.
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30. Marcus R, Watt J. Seaweeds and ulcerative colitis in laboratory animals. Lancet 1969;2:489-90. 31. Watt J , Marcus R. Progress report, experimental ulcerative disease of the colon in animals. Gut 1973;14:50&10. 32. Benitz KF, Goldberg L, Coulston F. Intestinal effects of carrageenan in the rhesus monkeys. Food Cosmet Toxicol 197331565-75. 33. Abraham R, Fabian RJ, Goldberg L, Coulston F. Role of lysosomes in carrageenan-induced cecal ulceration. Gastroenterology 1974;67:1169-81. 34. Marcus SN, Kline TJ, Pothoulakis H, et al. Role of inflammatory mediators in the pre-ulcerative phase of carrageenaninduced ulcerative disease of the colon (CIUDC) [abstract]. Gastroenterology 1990;98:A461. 35. Bores DL. Granulomatous inflammations. Prog Allergy 1978; 24~183-267. 36. Thomson AW, Fowler EF. Carrageenan: a review of its effects on the immune system. Agents Actions 1981;11:265-73. 37. Onderdonk AB, Hermos JA, Dzink JL, Bartlett JG. Protective effect of metronidazole in experimental ulcerative colitis. Gastroenterology 1978;74:521-6. 38. Onderdonk AB, Bartlett JG. The role of bacteria in experimental ulcerative colitis. Am J Clin Nutr 1979;32:25%65. 39. Onderdonk AB, Cisneros RL, Bronson RT. Enhancement of experimental ulcerative colitis by immunization with Bacteroides vulgatus. Infect Immun 1983;42:783-8. 40. Watt J, Marcus R. Ulceration of the colon in rabbits fed sulfated amylopectin. J Pharm Pharmacol 1972;24:68-9. 41, Ohkusa T. Production of experimental ulcerative colitis in hamsters by dextran sulfate sodium and change in intestinal microflora. Jpn J Gastroenterol 1985;82:1327-36. 42. Okayasu I, Hatakeyama S, Yamada M, Ohkusa T, Inagaki Y, Nakaya R. A novel method in the induction of reliable experimental acute and chronic ulcerative colitis in mice. Gastroenterology 1990;98:694-702. 43. Marcus R, Watt J. Ulcerative disease of the colon in laboratory animals induced by pepsin inhibitors. Gastroenterology 1974; 67:473-83. 44. Ohno S, Notsuki 1 , Kawai T. Histochemical studies on acid mucopolysaccharide. I. Histochemical detection of hyalulonic acid. Med Biol 1951;19:326-8. 45. Ohkusa T, Okayasu I, Ozaki 1, Yamada M, Nakaya R. Changes in bacterial phagocytosis of macrophage in experimental ulcerative colitis [abstract]. Gastroenterology 1990;98:A467. 46. Sartor RB, Anderle SK, Rifai N, Goo DAT. Cromartie WJ, Schwab JH. Protracted anemia associated with chronic, relapsing systemic inflammation induced by arthropathic peptidoglycan-polysaccharide polymers in rats. Infect Immun 1989; 57: 1177-8s. 47. Ling K-Y, Bhalla D , Hollander D. Mechanisms of carrageenan injury of IEC18 small intestinal epithelial cell monolayers. Gastroenterology 1988;95:1487-95. 48. Schiffmann E, Showell HV, Corcoran BA, Ward PA, Smith E, Becker EL. The isolation and partial characterization of neutrophil chemotactic factors from Escherichia coli. J Immuno1 1975;114:1831-7. 49. Schiffmann E, Corcoran BA, Wahl SM. N-Formylmethionyl peptides as chemoattractants for leukocytes. Proc Natl Acad Sci USA 1975;72:1059-62. 50. Showell HJ, Freer RJ, Zigmon SH, et al. The structure-activity relations of synthetic peptides as chemotactic factors and inducers of lysosomal enzyme secretion for neutrophils. J Exp Med 1976;143:1154-69. 51. Ho PPK, Young AL, Southard GL. Methyl ester of N-formylmethionyl-leucyl-phenylalanine. Arthritis Rheum 1978;21: 133-6. 52. Chadwick VS, Mellor DM, Myers DB, et al. Production of peptides inducing chemotacsis and lysosomal enzyme release in human neutrophils by intestinal bacteria in vitro and in vivo. Scand J Gastroenterol 1988;23:121-8. 53. Marasco WA, Phan SH, Krutzch H, et al. Purification and as the identification of formyl-methionyl-leucyl-phenylalanine
Scand J Gastroenterol Downloaded from informahealthcare.com by Bausch & Lomb IOM on 01/12/15 For personal use only.
536
Review
major peptide neutrophil chcmotactic factor produced by Escherichia coli. J Riol Chem 1984;259:5430-9. 54. Williams LT, Synderman R, Pike MC, Lefkowitz RJ. Specific receptor site for chemotactic pcptides on human polymorphonuclear leukocytes. Proc Natl Acad Sci USA 1977;
the elimination of granulocytes in the intcstinal tract in rat. Acta Pathol Microbiol Scand 1963;59:311-24. 76. Nash S, Stafford J, Madara JL. Effects of polymorphonuclear lymphocyte transmigration on the barrier function of cultured intestinal epithelial monolayers. J Clin Invest 1987;80: 1104-
74: 1204-8. 55. Painter GR, Sklar LA, Jesatis AJ, Schmitt M, Cochrane CG. Activation of neutrophils by N-formyl chemotactic peptides. Fed Proc 19X4;43:2737-42. 56. Bradlord PG, Rubin RP. Pertussis toxin inhibits chemotactic factor-induced phospholipase C stimulation and lysosomal enzyme sccrction in rabbit neutrophils. FEBS Lett 1985; 18:3 17-20, 57. Naccache PH, Molski TFP, Bargeat P, White JR, Sha’afi RI. Phorbol esters inhibit the f-Mct-Lcu-Phe and leukotriene 8 4 stimulated calcium mobilization and enzyme secretion in rabbit neutrophils. J Biol Chem 1985;260:2125-31. 58. ‘l‘urncrSR, Campbell JA, Lynn WS. Polymorphonuclear leukocyte chemotaxis toward oxidized lipid components of cell membranes. J Exp Med 1975;141:1437-41. 59. Yuli 1, Tomonaga A, Snyderman R. Chemoattractant receptor functions in human polymorphonuclear leukocytes are divergently altered hy membrane fluidizers. Proc Natl Acad Sci USA lY82;7Y:SY0610. 60. Snyderman R. Regulatory mechanisms of a chemoattractant reccptor on leukocytes. Fed Proc 1984;43:2743-8. 61. Korchak HM, Vienne K, Rutherford LE. Weissman G. Neutrophil stimulation: rcccptor, membrane, and metabolic events. Fed Proc 1984;43:2749-54. 62. Palhlad J , Gyllenhammer H, Lindgren JA, Malmsten CT. Effects of leukotrienes and f-Met-Leu-Phe on oxidative metaholisin of neutrophils and eosinophils. J Immunol 19843132: 3041-5. 63. Beckman J K , Gay JC, Brash AR, Lukcns J N , Oates JA. Stimulation hy lipoxygenase products of superoxide anion produclion in FMLP-treated neutrophils. Lipids 1985;20:318-21. 64. Beckman J K , Gay JC, Brash AR, Lukcns J N , Oatcs JA. Different effects of lipoxygenase products on FMLP and LTB4 evoked neutrophil aggregation. Lipids 1985;20:357-60. 65. Goetzl EJ, Austen KF. Purification and synthesis of eosinophilic tetrapeptides of human lung tissue: identification as eosinophil chemotactic factor of anaphylaxis. Proc Natl Acad Sci lJSA 1975:72:4123-7. 66. Bokoch GM, Reed PW. Stimulation of arachidonic acid metaho h m in the polymorphonuclear leukocyte by an N-formylated peptide. .I Biol
REVIEW
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Experimental Colitis in Animal Models Despite extensive research on their immunologic, biochemical, microbiologic, and epidemiologic aspects, the etiology and pathogenesis of ulcerative colitis and Crohn's disease (inflammatory bowel disease (IBD)) are still not known. Consequently, the therapeutic approach remains empiric. Nor do we know the ideal animal model for study of IBD. Nevertheless. important insight into the nature of the human disease may be obtained from the study in animals. In this article we discuss pathogenetic mechanisms of experimental colitis in various animal models.
IDEAL ANIMAL M O D E L OF INFLAMMATORY BOWEL DISEASE The ideal model should be a naturally occurring or inducible animal disease that is identical in every aspect to the human disease. This means that the animal disease is induced and maintained by the same primary and secondary factors (same etiology and pathophysiology), has an equivalent clinical spectrum, and is treatable with therapeutic agents (1). In addition, the ideal model must be a practical study tool (easy accessibility, easy experimental manipulation, and not too expensive).
CATEGORIES OF ANIMAL MODELS There are two broad categories of animal models of IBDone in which the disease arises naturally and one in which the disease is induced experimentally either by exposure to dietary substances or pharmacologic agents or by exposure to materials derived from patients or by manipulation of the animal's immune system (1).
colony-maintained CTTs develop active colitis not associated with identifiable pathogens and, as in human, the activity of the disease process spontaneously waxes and wanes (3,4). Histologically, the colonic inflammation is characterized by hemorrhages and crypt abscesses and an increase in the density of lymphocytes and plasma cells in the lamina propria (3). Biochemically, there is a reduction in colonic mucin glycoprotein analogous to that in human ulcerative colitis ( 5 ) . In addition, significant histologic improvement occurs when CTTs are treated with sulfasalazine (3). These striking similarities between CTT colitis and human ulcerative colitis provide a unique opportunity to unveil the etiopathogenesis of spontaneously occurring chronic colitis. Unfortunately, this endangered species is not widely available, thus limiting its usefulness as a research tool. The inflammatory mediators in plasma (6) show low levels of prostaglandin E2 (PGEJ and increased levels of plateletactivating factor (PAF), which may result in tissue destruction in acute C'IT colitis. However, no P A F was detected in the plasma of chronic-phase tamarins. Serial measurements of eicosanoids in the CTT by rectal dialysis (7) showed normal leukotriene B4 (LTB4) content but elevated P G E z content in active compared with inactive colitis. Oral administration of a lipoxygenase inhibitor prevented spontaneous relapses, possibly mediated by inhibition of lipoxygenase products other than LTB, (7). Recently, the presence of cross-reactive epitope(s) related to mol. wt. 40,000 protein (8), which acts as autoantigen(s) in human colon in patients with ulcerative colitis, was demonstrated (9). Sera from C'IT with colitis contain autoantibodies reactive to this unique epitope(s) (9).
There are many naturally occurring intestinal inflammations in animals (such as boxer dog and equine colitis, porcine enteritis, and proliferative ileitis in the hamster), but these diseases cannot be called animal models of IBD, because in most instances a causal organism is found.
Juvenile rhesus macaques Recently, another spontaneous chronic colitis was identified in juvenile rhesus macaques (lo), which may have recurrent episodes of persistent non-bloody liquid stool, weight loss, and/or growth retardation. Pathologic examination showed uniform, continuous inflammation of the cecum, the colon, and the rectum. Histologically, there was chronic inflammation with crypt abscesses, goblet cell depletion, and surface cell alterations. Colonic tissue interleukin 1 (IL-1) and LTB, levels were increased.
Cotton-top tamarin Recently, an interesting model was found in the cotton-top tamarin ( C P ) . This New World primate species, Saguinus oedipus, has a high prevalence of spontaneous colitis and may develop adenocarcinoma of colon (2). As many as 50% of
Intestinal inflammation produced by physical or pharmacologic agents Acetic acid. Intrarectal instillation of diluted acetic acid
NATURALLY OCCURRING INTESTINAL INFLAMMATION
EXPERIMENTALLY I N D U C E D COLITIS
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(410%) induces acute colitis in rats, rabbits, and guinea produces colonic lesions in various laboratory animals, pigs (11,12). Tissue levels of myeloperoxidase, a marker including guinea pigs, mice, rats, rabbits, and monkeys (30enzyme of polymorphonuclear leukocytes (PMN), cor- 32). The lesions are initially seen in the cecum and progress related well with histologic assessment of the severity of distally. There are no lesions in the small intestine and no colitis. In addition, the pattern of the arachidonic acid metab- remission/exacerbation of the colitis. The mechanisms of inflammation involve uptake of carolism was strikingly similar to that in human IBD (13, 14). The concentration of the potent chemotactic agent LTB, in rageenan by intestinal macrophages, followed by leakage of acetic acid-treated mucosa was 50 times higher than in nor- lysosomal enzymes into the mucosal tissue and consequent mal mucosa (13, IS). There were diffuse ulceration of the tissue destruction and inflammation (33). Histologic examdistal colon, pseudo-polyp like structures, alterations in crypt ination showed the presence of free carrageenan and carradepth and mucus secretion, and a transmural non-specific geenan-laden macrophages in the lamina propria of guinea pig colon after 2 days of carrageenan administration (34). inflammatory response ( I 1). The colitis induced by acetic acid is not simply due to the PGE2 levels in colonic tissue were elevated earlier than physical effect of acid per se, since intrarectal instillation of LTB4 levels, suggesting that PGE2 production is involved in diluted HCI with the same pII as the acetic acid does not initiating the inflammatory response, whereas LTB4 may be important in maintaining the inflammation (34). Local result in colonic inflammation (16). The severity of inflammation of acetic acid-induced colitis injection of carrageenan produced acute inflammation folcould be reduced with various agents, including 16,161- lowed by protracted granuloma formation, suggesting that macrophages contribute to phagocytosis of carrageenan (3.5). dimethyl PGE2 (17). indomethacin (17), misoprostol (18), sucralfate (19), sulfasalazine (20). phenidone (20), nordihy- Immunologic mechanisms are also involved, since carradroguaiaretic acid (20), and LTB4-receptor antagonists (12). geenan activates the complement system (36). Several investigators have tried to modify carrageenanPhorbol ester. Ethanol in concentrations above 30% acts as a mucosal barrier breaker and causes widespread acute induced inflammation with antibiotics. Pretreatment with mucosal damage when instilled into the distal colon of rats antimicrobials directed against coliforms failed to attenuate ( 2 I ) . Phorbol esters (PMA) are tumor-promoting agents the disease process (37). O n the other hand, pretreatment derived from the croton plant. A single intrarectal instillation with metronidazole, an antimicrobial primarily active against of phorbol-12-myristate-13-acetatein ethanol vehicle into anaerobic bacteria, prevented carrageenan-induced colitis male rats (10 mg/kg in 1 ml 40% ethanol solution) or male in most animals. Metronidazole treatment of established rabbits (1 .Smg/kgin 10 ml20% ethanol) causescolitis within colitis showed no salutary benetit. The results suggest that 24 h, with an increased colonic tissue myeloperoxidase level anaerobic bacteria play a role in the initial events of carra(22). The mechanism(s) of PMA-induced colitis is under geenan-induced colitis in the guinea pig model but d o not intensive investigation (22). Upregulation of LTA, hydrolase alter the course of the disease once the lesions have formed may beonemechanism. Phorbolestersactivate protein kinase (37). Oral administration of carrageenan changes the intestinal C (PKC) in several tissues (23). PKC seems to stimulate the release of LTB,, as well as PAF, from human neutrophils microflora, particularly increasing gram-negative anaerobes (24). Indeed, PKC upregulates LTA4 hydrolase, the enzyme (3638), and Bacteroide.s oulgatus has been incriminated i n responsible for the hydrolysis of the LTB, precursor, LTA4 the pathogenesis of carrageenan-induced colitis in the guinea (25). Other explanations, such as upregulation of the his- pig (38). Further, an immunologicreaction against B. uulgarus tamine response through PKC activation of PMA (26), modu- isolated from the colon in animals has been suggested (39). h. Amylopectin sulfate. Ulceration of the colon develops lation of cell adhesion (27), stimulation of the neutrophil oxidative burst (28), induction of cellular toxicity through in rabbits when they are fed sulfated amylopectin, even in interleukin-2 production, receptor expression and lympho- low concentrations (0.1 %). in the drinking water over 2 to cyte activation (29), or P A F release (24), are also possible 4 weeks (40). The deleterious effect appears similar to that of degraded carrageenan, consistent with the similarities in mechanisms of injury. Sulfated polysaccharides. Several sulfated polysaccharides structure (sulfated polysaccharide of high molecular weight) are known t o induce colitis in animals after oral adminis- and polyanionic behavior of sulfated amylopectin and degraded carrageenan (30). tration (30). c. Dextran sulfate. Ulcerative colitis can be induced in a. Carrageenan. This model was originally described by Marcus & Watt in 1969 (30). Carrageenan is a sulfated hamsters (41) and mice (42) by giving dextran sulfate sodium polysaccharide obtained by aqueous extraction of red sea- (DSS) in their drinking water. DSS causes a change in the weeds (Chondrus crispus, Eucheuma spinosum). Mild acid intestinal microflora, and particularly an increase in the hydrolysis yields degraded carrageenan, which has increased number of gram-negative anaerobes, including Bactersolubility while retaining the sulfate content and polyanionic oidaceae, has been noted as in the case of carrageenaninduced colitis (41,42). O n postmortem examination, mulproperties of the native compound. Oral administration of degraded carrageenan in water tiple erosions and inflammatory changes including crypt
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abscesses were found on the left side of the large intestine (the descending and sigmoid colon and the rectum). Mice (42) developed chronic colitis, including dysplasia, shortening of the large intestine, and prominent lymphoid follicles after five administration cycles, each cycle consisting of 7 days with 5% dextran sulfate sodium in the drinking water followed by 10 days’ consumption of distilled water. Morphologic observations showed swollen macrophages in the inflamed colonic wall (42), a finding consistent with carrageenan- or amylopectin sulfate-induced colitis (43). The macrophages had enlarged lysosomes and contained a metachromasia-positive substance on toluidine blue staining. Accordingly, this intralysosomal substance is thought to be a polysaccharide sulfate (44). In vitro phagocytosis of DSS by macrophages was also observed. Consequently, DSS appeared to have been phagocytosed by the mononuclear phagocytic system in the colonic mucosa. DSS-containing macrophages may have reduced phagocytic ability against the normal intestinal flora (45). Alternatively, DSS may have caused injury to the colonic epithelium leading to increased uptake of toxic luminal bacterial products such as endotoxin and peptidoglycan-polysaccharide polymers (46). In summary, inappropriate macrophage function, alterations of luminal bacteria flora, or toxic effects on colonic epithelium (47) are possible mechanisms by which enteral DSS induces ulcerative colitis in experimental animals. Chernotuctic peptide. Chemotactic peptides constitute a recently described class of attractants that may display selectivity for PMNs, eosinophils (EOSs), or monocytes (MONs) in vitro (48-51). The oligopeptides come from various sources, including aerobic and anaerobic bacteria normally found in the distal bowel (52). n-Formyl-methionyl-leucylphenylalanine (n-FMLP) is the most potent chemotactic peptide known for PMN (53). All chemotactic peptides appear to exert their effects by binding to cell-surface receptors. Granulocytes isolated from blood and tissue exudates in humans and rats have been shown to possess specific receptors for FMLP (54,55). FMLP activation of phospholipase C (56), which releases diacylglyceride (DAG) and inositol triphosphate (1P3), may be mediated by guanine nucleotide-binding proteins. DAG stimulates PKC, whereas IP3 participates in calcium ion mobilization (57). The interaction of FMLP with receptors results in neutrophil aggregation and adherence, superoxide production, enzyme secretion, and chemotaxis (55). PMN function is partially regulated through the expression of high- and low-affinity receptors for FMLP. High-affinity receptor binding by small amounts of FMLP activates PMN migration toward the bacteria (58,59). As the PMNs approach the bacteria, the higher concentrations of FMLP activates the low-affinity receptors to induce cytotoxic functions (59,60), including degranulation with lysosomal release (50,61) and superoxide anion production from a cellular respiratory burst (61-63). Aggregation (64) and increased phagocytosis (65) are additional effects of FML.P.
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Another effect of FMLP is the stimulation of synthesis and release of eicosanoids, including PGE2 and PGF2-alpha and thromboxane (66). The synthesis of the lipoxygenase products 5-hydroxyeicosatetraenoic acid (5-HETE) (66,67) and LTB4 (68) is also stimulated. The leukotrienes released may amplify the effects of FMLP by direct stimulation of PMN aggregation (69), chemotaxis (70), degranulation (71), and superoxide anion production (62). FMLP also stimulates active C1 secretion and inhibits electroneutral C1 absorption in both the small and the large intestine (72). Ex vivo perfused rabbit colons released LTB4 in response to chemotactic factors for neutrophils (n-FMLP), mononuclear cells (f-MLP-methyl ester, f-MLP-me), and eosinophils (Ala-Gly-Ser-Glu (AGSG)) (73). Intracolonic administration of chemotactic peptides induced dose-related mucosal infiltration of neutrophils and eosinophils in vivo (73). n-FMLP-methyl ester was most potent. n-FMLP and AGSG induced comparable degrees of inflammation, although in ex vivo perfused colons AGSG produced no eicosanoid release, whereas n-FMLP released both PGEz and LTB4 and LTC4 products. Thus, AGSG produces colitis independent of proinflammatory eicosanoids, whereas eicosanoid release could contribute to colitis produced by nFMLP and n-FMLP methyl ester. In contrast to formalin immune complex and dinitrochlorobenzene (DNCB) hypersensitivity colitis (see below), acute colitis induced by chemotactic peptides has less necrosis and more localized and consistent degree of mucosal inflammation, which may be mediated by enhanced leukotriene production (73). Magnusson et al. (74) were the first to demonstrate that luminal perfusion of the distal rat ileum with either FMLP or n-formyl methionyl phenylalanine increases mucosal permeability to fluoresceinated dextran (mol. wt., 3000). It has been shown by Teir et al. (75) that some resident granulocytes in the rat intestinal mucosa normally occupy positions between epithelial cells, where they are in direct contact with luminal fluid. Nash et al. (76) demonstrated that human neutrophils migrate across intestinal epithelial monolayers in response to FMLP, and they suggested that the physical opening of intercellular junctions by transmigrating neutrophils accounts for the FMLP-induced increase in mucosal permeability. However, it is also possible that activation and degranulation of granulocytes lead to a chemically mediated increase in mucosal permeability during luminal perfusion with FMLP (77). In the rat, gut mucosal permeability measured by blood-to-lumen clearance of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) during luminal perfusion with FMLP was significantly increased only in the terminal lOcm of the ileum (77). The increased mucosal permeability in response to FMLP could be prevented by depletion of circulating granulocytes with anti-neutrophil serum (77) or the glutathione peroxidase mimetic, PZ 5 (78). However, pretreatment with the superoxide radical scavenger superoxide dismutase or with catalase had no effect, suggesting that hydrogen peroxide is not a mediator
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of the increased mucosal permeability induced by formylated peptides (78). The observations that the most distal segment of ileum had both the highest basal clearance o f EDTA (a molecule similar in size to FMLP) and the greatest clearance in response to FMLP suggest that the size o r the number of exchange pathways is greater in the distal ileum, thus predisposing this region to the inflammatory actions of FMLP. The high sensitivity of the distal ileum to luminal perfusion with FMLP (77) may have important clinical implications. Ilollander et 211. (79) noted that thc permeability of the gut niucosa was higher not only in patients with C h h n ’ s disease hut also in their relatives, who are known to have a higher risk of developing terminal ileitis than other individuals. This suggests that basal mucosal permeability may be a predisposing factor for inflammatory bowel disease. The particularly high mucosal permeability of the terminal ileum may explain why this segment is predominantly affected in Crohn’s disease. FMLP in the colon could induce mucosal inflammation by further increase of mucosal permeability, direct activation of granulocytes, and/or release o f proinflammatory mediators such as eicosanoids (73). Healthy colon tissue can produce proinflammatory LTs in response to bacterial peptides (go), but most animals d o not develop colitis in response to luminal chemotactic peptides. I t is reasonable to that effective mucosal defenses normally block access of these agents to their target cells. Such defenses may include efficient rnucosal protease activity (81), mucosal barriers of mucin (82), and limited mucosal permeability (83). If the mucosal barrier is broken, chemotactic peptides may stimulate resident colonic niucosal cells to release leukotriene B4 and C4. These proinflammatory leukotrienes will enhance the effect of chemotactic peptides, attracting circulating PMNs and induce aggregation. degranulation, and release of reactive oxygen metabolites. The net result of these stimuli would be acute colonic inflammation. The possibility that defective mucosal permeability may constitute a predisposing factor while bacterial-derived chemotactic peptides, such as FMLP, constitute triggering factors is an attractive hypothesis for the pathogenesis of IBD. Free rudiculs. Recently, colitis was induced in rats by means of the free radical initiator 2,2’-azobis (Zamidinopropane) hydrochloride (AAPH), which decomposes to N2 and free radicals with subsequent generation of peroxyradicals. The development of colitis was prevented by sulfasalazine, 5-aminosalicylic acid (5-ASA), and the antiinflammatory drug SC-41930 (84). Intestinul inflammation induced by materials derived from patients Another experimental approach is to induce intestinal inflammation in animals by using materials obtained from
IBD patients in an attempt to a) utilize animals as culture tubes in which causative organisms can be expanded and identified, or b) establish an IBD-like disease in the animal (1). Mitchell & Rees (85) injected homogenized filtered Crohn’s disease tissue into the footpads of mice and obtained granuloma. Subsequent studies aiming to prove the existence of transmissible agents have, however, shown equivocal results (86). It seems to be accepted now that IBD lesions cannot be passed to animals by injection of homogenized, filtered materials acquired from patients. Manipulution of’ animul’s immune system Intestinal inflammation induced by immunologic mechanisms falls into two categories. The first mechanism involves antibodies or immune complexes (B-cell models), and the second involves activation of lymphocytes (T-cell models). B-cell models. In their initial work Kirsner (87) and Goldgraber & Kirsner (88) induced intestinal inflammation by local induction of the Arthus and Schwartzman reactiotis. In an Arthus-type reaction rabbits are first sensitized to an antigen (egg albumin) by systemic antigen administration. Subsequently, severe local inflammation and hemorrhagic necrosis are induced by mucosal injections of the sarne antigen. In the Schwartzman reaction the animals are given bacterial lysates in a similar sequential systemic and local fashion. Auer (89) demonstrated in 1920 that massive inflaniniation could be induced at the site of a previously mild, local, nonspecific inflammatory reaction by the parenteral administration of a large dose o f antigen to a sensitized animal. Kirsner et al. (90,91) thus induced severe colitis in rabbits which had previously been sensitized to egg albumin and had mild colonic inflammation induced by intrarectal instillation of a small amount of diluted formalin. The principle involves sensitization to a soluble antigen, a generalized antibody response, attraction of non-specifically mildly irritated tissue for circulating antigen and antibody on the basis of an increased vascular permeability in these areas, and a resultant antigen-antibody reaction leading to tissue injury. Specific antigen and antibody have been identified in (.he diseased colon by immunohistochemical methods (91). Hodgson et al. (92) induced colitis in rabbits by a modified Auer technique. Preformed immune complex of human serum albumin (HSA) and anti-HSA with antigen excess was injected intravenously to non-sensitized rabbits after provocation of mild inflammation in the colon with diluted fornialin (1%, 1 ml instilled intrareetally). The procedure produced severe colitis, including mucosal ulceration, mixed inflammatory cell infiltration in the lamina propria. and crypt abscess formation, suggesting that whatever the primary cause of the colonic inflammation, further tissue damage may be induced by immunologic mechanisms. A chronic colitis has also been induced in rabbits (93) and rats (94) by a modified Auer technique. The animals were
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preimmunized with the common enterobacterial antigen of Kunin (93) or E . coli 0 1 4 : K 4 : H - (94). The latter is a lipopolysaccharide that resembles structures in the human intestinal wall (95). The antibodies cross-reacted with colonic mucosa. Colitis was induced by topical irritation of the colonic mucosa with diluted formalin, followed by intravenous injection of soluble immune complexes (bovine serum albumin (BSA) and anti-BSA) with antigen excess. The rabbits developed acute colitis within the first week, but, in contrast t o unsensitized rabbits, the inflammation persisted and was still present at 6 months. The results suggest that hypersensitivity to colonic bacterial antigens may be one mechanism whereby an acute colitis becomes chronic. T-cell model.$.Sensitization with haptens and subsequent challenge o f the cell-mediated immune system in guinea pigs, rats, and rabbits may induce inflammation of the gut. DNCB and trinitrobenzene sulfonic acid (TNBS) are chemical haptens that bind to tissue proteins and are capable of stimulating cell-mediated immunity ( 9 6 9 7 ) . a. f)inifrochlorohenzene. Administration of DNCB produces a delayed hypersensitivity response of T lymphocytes against this hapten (98). To sensitize the rabbits to DNCB, diluted DNCB (0.1 ml DNCB dissolved in acetone at a concentration of 2000 mg/O.l ml) was placed on the rabbit’s skin in ;I I-cm circle. Ten days later 100mg of DNCB in 0.5 ml of acetone were introduced into the colon. Three days after challenge the colonic mucosa was ulcerated with crypt abscesses and inflammatory infiltrate. However, the inflammation was not sustained (96,97). Sensitivity to DNCB can he p ively transferred by lymphocytes (99), and immunosuppression mitigates the bowel injury in DNCB-induced colitis. The lamina propria lymphocytes isolated from the colon had a greater percentage of T cells and a greater capacity to mediate mitogen-induced cellular cytotoxicity with phytohemagglutinin than lamina propria lymphocytes from the normal colon (97). PGEz levels both in inflamed mucosa and in adjacent uninflamed muscularis propria were increased i n DNCB colitis (100). Increased PGE2 production may contribute to the smooth-muscle dysfunction seen in colitis. b. 7rinitrohenzene sulfonic acid. Intrarectal administration of TNBS in ethanol vehicle resulted in acute inflammation with ulcers that evolved into chronic inflammation of the distal colon in rats (101-104). Even at a dose of 30 mg of TNBS the ulceration and thickening of the bowel wall persisted for at least 8 weeks (101). Interestingly, granulomas and Langhans-type giant cells were also observed with segmental ulceration and inflammation. The inflammation was characterized by high myeloperoxidase and decreased glutathione levels (101, 105). TNBS can bind covalently to the E-amino group of lysine and modify cell surface proteins. Colitis may develop when presensitized T lymphocytes lyse hapten-modified autologous cells (106,107). Whereas T lymphocytes will lyse
hapten-modified autologous cells only if the animal has been presensitized, macrophages will destroy TNBS-modified autologous cells in the absence of presensitization (108). In addition, TNBS may be metabolized (enzymatically and non-enzymatically) to yield 0,- and H202from the interaction between ascorbate and TNBS (109). suggesting that TNBS-induced colitis may partly be mediated by cytotoxic, reactive oxygen metabolites generated by the oxidative metabolism of TNBS. Various inflammatory mediators such as PGEz, TXB,. prostacyclin, LTB4, LTC4, PAF, and IL may be involved in TNBS colitis, as in human I B D (110). The predominant arachidonate metabolites found in TNBS colitis are LTB, and the monohydroxy fatty acids 5-HETE, 12-HETE, and 15-HETE. LTB4 in particular is likely to be a product of neutrophils (103, 104,106, 111). According to Wallace et al. (103), LTB4 synthesis increased already within 4 h and peaked 24-72 h after administration of TNBS. The increase correlated with colonic myeloperoxidase activity. Treatment with a specific 5-lipoxygenase inhibitor resulted in significant reductions of colonic LTB4 synthesis and colonic damage. Pretreatment with 16,16’-dimethyl PGEz resulted in a lower inflammation index, a lower level of colonic tissue myeloperoxidase, and decreased production of LTB4 (106). LTB,, but not other leukotrienes, P A F , or n-FMLP, augmented colonic damage (1 11). Quantification of luminal eicosanoid release in vivo using a dialysis bag placed in the distal colon of rats showed a highly significant increase in PGE2, 6-keto PGF,-alpha, TXB2, and LTB, levels 3 days after intracolonic instillation of TNBS (104). Remarkably, the release of TXB, continued to increase during the stage of chronic inflammation (up to 21 days), whereas the levels of the other eicosanoids decreased. Treatment with prednisone or 5-ASA reduced TXB, levels in the chronic stage and improved the colitis both macroscopically and histologically. Moreover, selective thromboxane synthetase inhibitors significantly reduced the development of chronic inflammation and reduced the release of TXB2 (104). These results suggest that eicosanoids (prostaglandin, leukotriene, thromboxane) play an important role in the pathogenesis of TNBS-induced colitis. P A F is also thought to play a role in TNBS-induced colitis. Wallace et al. (112) demonstrated that PAF-acether production by the colon was increased as much as 16-fold above control levels in TNBS-induced colitis in the rat. High PAF-acether production was not seen during the time of maximal neutrophil infiltration (1-4 days after TNBS) but was seen 1-3 weeks after induction of colitis. Thus, PAFacether is unlikely to play an important role in the acute inflammatory response but may be important in the prolongation of the inflammation in this model. However, significant acceleration of healing can be achieved by treatment with a specific PAF-acether antagonist when given on days 4-7 after TNB administration. Among various inflammatory mediators in TNBS-induced
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colitis IL-1 may be the most significant indicator of mucosal useful information on the origin, regulation, and function of inflammation because its level correlated with myelo- inflammatory mediators. However, with the possible excepperoxidase activity (102). In chronic TNBS-induced colitis tion of the cotton-top tamarin, no animal model of induced in the rat, the mucosal histamine level increased in parallel or spontaneous inflammation of the colon is analogous to human ulcerative colitis in etiology, course of disease with the score of damage (113). activity, or histology (114). Several features of this model are attractive (101): The observation that two different immune-mediated 1. The inflammation is induced by one single intraluminal instillation, and the severity and persistence of damage are models gave similar results suggests that the colitis is not a specific response to delayed-type hypersensitivity or very reproducible. immune-complex-mediated reactions but rather an unspe2. The rat model is relatively inexpensive. 3. The inflammation results in thickening of the colonic cific, stereotype response (125). The original disturbance wall associated with cellular infiltration and ulcers persisting may not determine the nature of the lesions ultiniately for at least 8 weeks. This relatively long duration of the produced but may instead serve as an initiator of a final inflammation makes assessment of treatment effects poss- common immunologic pathway. ible. 4. Finally, this model is histologically relevant, in that several of the features of human IBD, particularly Crohn's Acknowledgement disease, are present. Thus transmural inflammation with This work was carried out while Dr. Hak-San Kim worked 6 granuloma and Langhans-type giant cells, skip-segment months at Haukeland University Hospital, Norway, financed ulceration and inflammation, cobblestone-like appearance by a grant from the Korean-Scandinavian Foundation in of the mucosa, mast cell and lymphoid infiltrates, and crypt Korea. HAK-SANKIM distortion are seen. Dept. of Internal Medicine Smooth-muscle hyperplasia of the muscularis mucosa and National Medical Centre narrowed segments of colon were seen 3 weeks after intraSeoul, South Korea rectal administration of TNBS (106). Generally, the intensity of the acute inflammatory response induced by TNBS is less ARNOLDBERSTAD pronounced than that induced by acetic acid. Acetic acidinduced colitis is also more difficult to modify pharmacoSection of Gastroenterology logically (106). Medical Dept . Haukeland University Hospital Bergen, Norway MODELS CURRENTLY USED A survey of the abstracts of the papers presented at the Digestive Disease Week in New Orleans, USA, in 1991, showed that animal models of experimental colitis were used in altogether 21 studies; TNBS was used in 9 studies, acetic acid (or citric acid) in 6, DSS in 2 , amylopectin sulfate in 1, peptidoglycan polysaccharide in 3, immune complexes in 2, an infectious agent in 1, mitomycin in 1, and spontaneous colitis (CTI') in 1. Thus, most of the models discussed in this paper are currently in use in various laboratories. SUMMARY Colitis may be induced in animals by oral administration of sulfated polysaccharides (carrageenan, amylopectin sulfate, dextran sulfate), chemical irritation by rectal instillation of diluted acetic acid, delayed hypersensitivity reaction after sensitization to DNCB or after one single administration of TNBS, and Arthus reaction induced by intravenous injection of immune complexes after chemical irritation of the colon, and by chemoattractant peptides such as FMLP. It appears that all models of colon inflammation in the rat, mouse, or rabbit produce increased amounts of eicosanoids similar to that found in human colitis. Thus, animal studies provide
REFERENCES
1. Stroher W. Animal models of inflammatory bowel diseasean overview. Dig Dis Sci 1985; 30 Suppl:3-10. 2 . Chalifoux LV, Bronson RT. Colonic adenocarcinorna associated with chronic colitis in cotton-top marmosets, Sagiiinus oedipus. Gastroenterology 1981;80:942-6. 3 , Madara JL, Podolsky DK, King NW, Sehgal PK, Moore R , Winter HS. Characterization of spontaneous colitis in cottontop tarnarin (Saguinus oedipus) and its response to sulfasalazine. Gastroenterology 1985;88:13-9. 4. Lushhach C, Humason G, Clapn N. Histology of colitis: Saguinus oedipus and other marmosets. Dig Dis Sci 1985;30 Suppl:45-51. 5. Podolsky DK, Madara JL, King NW, Sehgal PK, Moore R, Winter HS. Colonic rnucin composition in primates: selective alterations associated with spontaneous colitis in the cottontop tamarin. Gastroenterology 1988;88:2C-5. 6 . Clapp NK, Walsh RE, Fretland DJ, Henke MA, Gaginella TS, Inflammatorymediators in the plasma of cotton-top tarnarins with acute and chronic colitis [abstract]. Gastrocntcrology 1990;98:A442. 7. Panzini B, King N , Sehga P, Podolsky DK. Role of leukotrienes in the colitis of the cotton-top tamarin: effect of a 5 lipoxygenase inhibitor [abstract]. Gastroenterology 1990;98:A468. 8. Takahashi F, D ~ KM. s Isolation and characterization of a colonic autoantigen specifically recognized by colon tissuebound immunoglobulin idiopathic ulcerative colitis, Clin Invest 1985;76:311-8.
Scand J Gastroenterol Downloaded from informahealthcare.com by Bausch & Lomb IOM on 01/12/15 For personal use only.
Review
9. Das KM, Squillante L, Henke M. Clapp N. The presence of circulating antibodies in cotton top tamarins (C'IT) with spontaneous colitis against an epitope(s) on MR 40,000 protein shared by human and CTT colon epithelial cells [abstract]. Gastroenterology 1990;98:A444. 10. Adler R, Hendrickx A, Rush J , Fondacaro JD. Chronic colitis of Juvenile Rhesus Macaques: mucosal tissue levels of interleukin-l (IL-1) and leukotriene B4 (LTB-4) [abstract]. Gastroenterology 1990;98:A436. 11. MacPherson BR, Pfeiffer CJ. Experimental production of diffuse colitis in rats. Digestion 1978;17:135-SO. 12. Fretland DJ, Widomski DL, Tsai BS, et al. Effect of leukotriene B4 receptor antagonist SC-41930 on colonic inflammation in rat, guinea pig and rabbit. J Pharmacol Exp Ther 1990;255:572-6. 13. Sharon P, Stenson WF. Metabolism of arachidonic acid in acetic acid colitis in rats: similarity to human inflammatory bowcl disease. Gastroenterology 1985;88:55-63. 14. Fretland DJ, Levin S, Tsai BS, et al. The effect of leukotrieneB4 receptor antagonist, SC-41730. on acetic acid-induced colonic inflammation. Agents Actions 1989;27:225-7. 15. Goetzl EJ, Pickett WC. The human PMN leukocyte chemotactic activity of complex hydroxy-eicosatetraenoic acids (HETEs). J Immunol 1980;125:1789-91. 16. Zeitlin IJ, Norris AA. Animal models of colitis. In: Chadwick VS, editor. Mechanisms of gastrointestinal inflammation. Wclwyn Garden City, UK: Smith Klinc and French, 1984:703. 17. Rcber S. Su K, Leung FW. Guth PH. Exogenous prostaglandin and indomethacin protect against the development of acetic acid colitis in the rats [abstract]. Clin Res 1989;37:113A. 18. Fedorak RN, Espey LR, MacArthur C, Jewel1 LD. Misoprostol provides a colonic mucosal protective effect during acetic acid-induced colitis in rats. Gastroenterology 1990; 9X:h15-25. 19. Waisman Y , Zahavi I. Marcus H. Ligumsky M. Roscnbach Y, Dinari G. Sucralfate is protcctivc against indomcthacininduced intestinal ulceration in the rat. Digestion 1088;41:7882. 20. Conzcntino P, Will PC, Lin A, Gaginella TS. Effect of 5lipoxygenase inhibitors on acetic acid colitis in the rat. Pharmacologist 1986;28:163. 21. Wallace JL, Whitlc BJR, Boughton-Smith NK. Prostaglandin protection of rat colonic mucosa from damage induced by ethanol. Dig Dis Sci 1985;30:86&76. 22. Fretland DJ. Widomski DL, Levin S. Gaginella TS. Colonic inflamm;ition in the rabbit induced by phorbol-l2-myristate13-acetate. Inflammation 1990;14:143-50. 23. Ashendel CL. The phorbol ester receptor: a phospholipidregulated protein kinase. Biochim Biophys 198S;822:219-42, 24. McJntyrc TM. Reinhold SL, Prescott SM. Zimmerman GA. Protein kinase C activity appears to be required for the synthesis of platelet-activating factor and leukotriene B4 by human neutrophils. J Biol Chem 1987;262:15370-6. 25. McColl SR, Ilurst NP, Betts WH, Cleland LG. Modulation of human neutrophil LTA hydrolase activity by phorbol myristate acetate. Biochem Biophys Res Commun 1987;147:622-46. 26. Leurs R. Go JNL, Bast A. Timmerman H. Involvement of protein kinase C in the histamine H1-receptor mediated contraction of guinea pig lung parenchymal strips. Agents Actions 1989;27:18(k3. 27. Danilov YN, Juliano RL. Phorbol ester modulation of integrinmediated cell adhesion: a postreceptor event. J Cell Biol 1989;108:1925-33. 28. Gerard C. McPhail LC, Marfat A, Stimler-Gerard NP, Bass DA. McCall CE. Role of protein kinases in stimulation of human polymorphonuclear leukocyte oxidative metabolism by various agonists. J Clin Invest 1986;77:61-5. 29. Aparico-Pagcs MN, Wcrspaget HW, Pena AS, et al. Natural, lectin and phorbolester-induced cellular cytotoxicity in Crohn's disease and ulcerative colitis. J Clin Lab Immunol 1988;27:10913.
535
30. Marcus R, Watt J. Seaweeds and ulcerative colitis in laboratory animals. Lancet 1969;2:489-90. 31. Watt J , Marcus R. Progress report, experimental ulcerative disease of the colon in animals. Gut 1973;14:50&10. 32. Benitz KF, Goldberg L, Coulston F. Intestinal effects of carrageenan in the rhesus monkeys. Food Cosmet Toxicol 197331565-75. 33. Abraham R, Fabian RJ, Goldberg L, Coulston F. Role of lysosomes in carrageenan-induced cecal ulceration. Gastroenterology 1974;67:1169-81. 34. Marcus SN, Kline TJ, Pothoulakis H, et al. Role of inflammatory mediators in the pre-ulcerative phase of carrageenaninduced ulcerative disease of the colon (CIUDC) [abstract]. Gastroenterology 1990;98:A461. 35. Bores DL. Granulomatous inflammations. Prog Allergy 1978; 24~183-267. 36. Thomson AW, Fowler EF. Carrageenan: a review of its effects on the immune system. Agents Actions 1981;11:265-73. 37. Onderdonk AB, Hermos JA, Dzink JL, Bartlett JG. Protective effect of metronidazole in experimental ulcerative colitis. Gastroenterology 1978;74:521-6. 38. Onderdonk AB, Bartlett JG. The role of bacteria in experimental ulcerative colitis. Am J Clin Nutr 1979;32:25%65. 39. Onderdonk AB, Cisneros RL, Bronson RT. Enhancement of experimental ulcerative colitis by immunization with Bacteroides vulgatus. Infect Immun 1983;42:783-8. 40. Watt J, Marcus R. Ulceration of the colon in rabbits fed sulfated amylopectin. J Pharm Pharmacol 1972;24:68-9. 41, Ohkusa T. Production of experimental ulcerative colitis in hamsters by dextran sulfate sodium and change in intestinal microflora. Jpn J Gastroenterol 1985;82:1327-36. 42. Okayasu I, Hatakeyama S, Yamada M, Ohkusa T, Inagaki Y, Nakaya R. A novel method in the induction of reliable experimental acute and chronic ulcerative colitis in mice. Gastroenterology 1990;98:694-702. 43. Marcus R, Watt J. Ulcerative disease of the colon in laboratory animals induced by pepsin inhibitors. Gastroenterology 1974; 67:473-83. 44. Ohno S, Notsuki 1 , Kawai T. Histochemical studies on acid mucopolysaccharide. I. Histochemical detection of hyalulonic acid. Med Biol 1951;19:326-8. 45. Ohkusa T, Okayasu I, Ozaki 1, Yamada M, Nakaya R. Changes in bacterial phagocytosis of macrophage in experimental ulcerative colitis [abstract]. Gastroenterology 1990;98:A467. 46. Sartor RB, Anderle SK, Rifai N, Goo DAT. Cromartie WJ, Schwab JH. Protracted anemia associated with chronic, relapsing systemic inflammation induced by arthropathic peptidoglycan-polysaccharide polymers in rats. Infect Immun 1989; 57: 1177-8s. 47. Ling K-Y, Bhalla D , Hollander D. Mechanisms of carrageenan injury of IEC18 small intestinal epithelial cell monolayers. Gastroenterology 1988;95:1487-95. 48. Schiffmann E, Showell HV, Corcoran BA, Ward PA, Smith E, Becker EL. The isolation and partial characterization of neutrophil chemotactic factors from Escherichia coli. J Immuno1 1975;114:1831-7. 49. Schiffmann E, Corcoran BA, Wahl SM. N-Formylmethionyl peptides as chemoattractants for leukocytes. Proc Natl Acad Sci USA 1975;72:1059-62. 50. Showell HJ, Freer RJ, Zigmon SH, et al. The structure-activity relations of synthetic peptides as chemotactic factors and inducers of lysosomal enzyme secretion for neutrophils. J Exp Med 1976;143:1154-69. 51. Ho PPK, Young AL, Southard GL. Methyl ester of N-formylmethionyl-leucyl-phenylalanine. Arthritis Rheum 1978;21: 133-6. 52. Chadwick VS, Mellor DM, Myers DB, et al. Production of peptides inducing chemotacsis and lysosomal enzyme release in human neutrophils by intestinal bacteria in vitro and in vivo. Scand J Gastroenterol 1988;23:121-8. 53. Marasco WA, Phan SH, Krutzch H, et al. Purification and as the identification of formyl-methionyl-leucyl-phenylalanine
Scand J Gastroenterol Downloaded from informahealthcare.com by Bausch & Lomb IOM on 01/12/15 For personal use only.
536
Review
major peptide neutrophil chcmotactic factor produced by Escherichia coli. J Riol Chem 1984;259:5430-9. 54. Williams LT, Synderman R, Pike MC, Lefkowitz RJ. Specific receptor site for chemotactic pcptides on human polymorphonuclear leukocytes. Proc Natl Acad Sci USA 1977;
the elimination of granulocytes in the intcstinal tract in rat. Acta Pathol Microbiol Scand 1963;59:311-24. 76. Nash S, Stafford J, Madara JL. Effects of polymorphonuclear lymphocyte transmigration on the barrier function of cultured intestinal epithelial monolayers. J Clin Invest 1987;80: 1104-
74: 1204-8. 55. Painter GR, Sklar LA, Jesatis AJ, Schmitt M, Cochrane CG. Activation of neutrophils by N-formyl chemotactic peptides. Fed Proc 19X4;43:2737-42. 56. Bradlord PG, Rubin RP. Pertussis toxin inhibits chemotactic factor-induced phospholipase C stimulation and lysosomal enzyme sccrction in rabbit neutrophils. FEBS Lett 1985; 18:3 17-20, 57. Naccache PH, Molski TFP, Bargeat P, White JR, Sha’afi RI. Phorbol esters inhibit the f-Mct-Lcu-Phe and leukotriene 8 4 stimulated calcium mobilization and enzyme secretion in rabbit neutrophils. J Biol Chem 1985;260:2125-31. 58. ‘l‘urncrSR, Campbell JA, Lynn WS. Polymorphonuclear leukocyte chemotaxis toward oxidized lipid components of cell membranes. J Exp Med 1975;141:1437-41. 59. Yuli 1, Tomonaga A, Snyderman R. Chemoattractant receptor functions in human polymorphonuclear leukocytes are divergently altered hy membrane fluidizers. Proc Natl Acad Sci USA lY82;7Y:SY0610. 60. Snyderman R. Regulatory mechanisms of a chemoattractant reccptor on leukocytes. Fed Proc 1984;43:2743-8. 61. Korchak HM, Vienne K, Rutherford LE. Weissman G. Neutrophil stimulation: rcccptor, membrane, and metabolic events. Fed Proc 1984;43:2749-54. 62. Palhlad J , Gyllenhammer H, Lindgren JA, Malmsten CT. Effects of leukotrienes and f-Met-Leu-Phe on oxidative metaholisin of neutrophils and eosinophils. J Immunol 19843132: 3041-5. 63. Beckman J K , Gay JC, Brash AR, Lukcns J N , Oates JA. Stimulation hy lipoxygenase products of superoxide anion produclion in FMLP-treated neutrophils. Lipids 1985;20:318-21. 64. Beckman J K , Gay JC, Brash AR, Lukcns J N , Oatcs JA. Different effects of lipoxygenase products on FMLP and LTB4 evoked neutrophil aggregation. Lipids 1985;20:357-60. 65. Goetzl EJ, Austen KF. Purification and synthesis of eosinophilic tetrapeptides of human lung tissue: identification as eosinophil chemotactic factor of anaphylaxis. Proc Natl Acad Sci lJSA 1975:72:4123-7. 66. Bokoch GM, Reed PW. Stimulation of arachidonic acid metaho h m in the polymorphonuclear leukocyte by an N-formylated peptide. .I Biol
