0099-2399/91[1707-0316/$03.00/0 JOURNAL OF ENDOOONTICS Copyright 9 1991 by The American Association of Endodontists
Printed in U.S.A.
MOL. 17, NO. 7, JULY 1991
Copper-Zinc Superoxide Dismutase Activity in Normal and Inflamed Human Dental Pulp Tissue Walter L. Davis, PhD, MD, Bennett H. Jacoby, DDS, MS, Kathleen R. Craig, DDS, MS, Gary Wagner, DDS, and John W. Harrison, DMD, MS
Information regarding the presence of the free radical scavenging (inactivating, dismutating) enzyme superoxide dismutase in human dental pulp was sought. Free radicals, such as the superoxide anion radical (02-) and the hydroxyl anion radical (OH'), are powerful biological oxidants produced by phagocytes during the normal tissue response to injury and infection. Also produced is hydrogen peroxide (H202), an aggressive oxygen species formed by the reaction of superoxide with itself, i.e., a dismutation in which one molecule of 02- is oxidized by the other. These three reactive oxygen intermediates serve as part of the normal host biological defense mechanism for the inactivation of microorganisms and the breakdown of their toxic products. Both normal and inflamed dental pulps were assayed for the presence of this enzyme. Superoxide dismutase activity was identified in the normal pulpal tissues. There was a slight decrease in activity with age. In the inflamed pulpal tissues, enzyme activity was markedly and significantly increased in comparison to that in the normal tissues. These observations indicate that human dental pulp possesses an endogenous defense mechanism designed to protect the tissue components (cells and matrix) from the toxic effects of the reactive oxygen intermediates. In this regard, the inflammatory response of this specialized and somewhat isolated (compartmentalized) tissue is not unlike that seen in other connective tissues.
mation. Such ROI include: (a) the superoxide anion radical (02-), formed by the one-electron reduction of oxygen in the presence of NADPH (202 + NADPH ~ 202- + NADP + H+); and (b) the hydroxyl anion radical (OH'), produced by the Haber-Weiss reaction (02- + H202 ~ OH" + O H - + 02). A third aggressive (but nonradical) oxygen species is also formed. The latter is hydrogen peroxide (H202) and is produced by the reaction of superoxide with itself (02- + 02- + 2H § ~ H202 + 02). H202 has a very long half-life and is known to cause considerable cell and tissue damage. These aggressive oxygen species represent a group of highly reactive and powerful biological oxidizing agents that are normally and routinely produced by phagocytes at sites of inflammation and infection (4). Such oxygen intermediates can destroy most biologic molecules, including those of bacterial origin, i.e., Nformylated oligopeptides (4, 5). In so doing however, ROI also destroy normal components of the surrounding cells and matrices. To protect against the latter, biological defense mechanisms have evolved which dismutate or inactivate these oxidants. Probably the most common defense against the ROI-induced breakdown of normal tissues involves dismutation by the enzyme SOD. The latter has been identified in most eukaryotic cells as well as in the extracellular matrices (1, 2, 6-8). Excellent reviews of free radicals, free radical chemistry, free radicals and tissue injury, and free radicals and inflammation can be found in references 1, 2, and 4. Because dental pulp is characterized by both acute and chronic inflammatory responses, the tissue was examined for the presence of SOD activity. The primary objective was to determine if a relationship existed between the activity of this enzyme and the inflammatory state of the human tissue. MATERIALS AND METHODS Both normal and inflamed intact human dental pulps were removed for either prosthetic or endodontic purposes at the graduate endodontic clinic at the Baylor College of Dentistry. Routine clinical examination techniques were used to assess the status of the pulps including subjective findings, thermal testing, and electrical testing. For this study, a total of 14 pulps were collected, 7 inflamed and 7 normal. Patients ranged in age from 19 to 47 yr. On removal, the tissues were vigorously washed three to five times over a 10-min period in chilled (4~ heparinized,
Superoxide dismutase (SOD) or superoxidoreductase (EC 1.15.1.1) is a primary oxygen radical scavenging enzyme for eukaryotic, aerobic cells and tissues (1-3). Because of this, SOD (primarily the copper, zinc SOD or Cu,ZN-SOD) represents the major enzymatic defense mechanism against toxic/aggressive oxygen species or reactive oxygen intermediates (ROI) generated during normal oxidative metabolism as well as during the respiratory burst associated with inflam-
316
Vol. 17, No. 7, July 1991
SOD in Human Dental Pulp
TABLE 1. Cu,Zn-SOD activity in normal human dental pulp
TABLE 2. Cu,Zn-SOD activity in inflamed human dental pulp
SOD Activity Patient (age) 1 (33) 2 (27) 3 (44) 4 (29) 5 (47) 6 (24) 7 (30)
317
SOD Activity
units/g wet
units/mg
wt*
tein
1680 2700 7500 1150 990 2100 1460
463 746 207 317 273 579 402
of pro-
* Mean _+ SD, 1547 _+678.
sterile saline. Tissues were then quick-frozen in liquid nitrogen and subsequently stored at -160~ before being assayed for SOD. For the biochemical analysis of tissue SOD activity, previously reported techniques were used (6, 7). Pulps were first homogenized in a Potter-Elvehjem homogenizer in l0 volumes of chilled, 50 mM sodium acetate buffer (pH 5.5) containing 0.3 M KBr. The homogenates were subsequently sonicated and extracted for 30 min at 4~ A supernatant was prepared by centrifugation at 20,000 x g for 15 min. This supernatant was used for further enzyme analysis. SOD activity was determined by its ability to catalyze the disproportionation of 02- in an alkaline (pH 9.5) aqueous solution. This reaction was studied in a spectrophotometer as previously described by Marklund (6, 7). By this procedure, 1 unit in the assay corresponds to approximately 8.3 ng of human Cu,Zn-SOD (6, 7). For control assays, the cyanide (CN-) sensitivity of Cu,Zn-SOD was used to separate this enzyme from Mn-SOD, a mitochondrial SOD. Thus, all assays were carried out in the presence of CN-. Protein was determined according to the method of Lowry et al. (9). Human serum albumin was used for standardization. Statistical analyses were performed by using Student's t test. RESULTS The results of the assays of normal human dental pulp for Cu,Zn-SOD activity are shown in Table 1. Note that in the normal tissues, the content of this enzyme ranges from a low of 750 units/g wet weight to a high of 2,700 units/g wet weight (units/g wet wt column). This translates to a range of approximately 207 to 746 units/mg of protein, respectively (units/ mg of protein column). In the inflamed tissues, however, the content of SOD was markedly and significantly (p < 0.0001) increased, ranging from 4700 to 7600 units/g wet weight for the seven different tissues analyzed (Table 2, units/g wet wt column). These values correspond to a range of 1296 to 2095 units/mg of protein, respectively (units/mg of protein). Incubation in the presence of CN- depressed SOD activity by more than 98% (data not shown). Figure 1 shows a possible inverse relationship or correlation between age and tissue SOD activity, i.e., a decrease in the activity of this enzyme with increasing age (Tables 1 and 2). The data shown in both the point graph (Fig. 1A) and the
Patient (age)
units/g wet wt*
units/mg of protein
8(19) 9(45) 10(36) 11 (43) 12(23) 13(28) 14(39)
7600 5400 6850 4700 7050 6250 5570
2095 1489 1889 1296 1944 1723 1536
* Mean _+ SD, 6202 ___1032. t value, -8.9927; statistics, normal versus inflamed, 0.0001.
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FIG 1. A, Point graph showing a possible correlation between patient age and pulp SOD activity. The data are suggestive of an inverse relationship between age and pulp SOD activity in inflamed tissues (the greater the age, the less the enzyme activity). However, a similar correlation is not as apparent in the normal pulps. B, Trend graph also showing a possible correlation between patient age and pulp SOD activity. The interpretation is the same as that for the point graph in A.
trend graph (Fig. 1B) are suggestive of this inverse relationship (> age < SOD activity), especially with regard to the inflamed tissues presented here. DISCUSSION The study presented here shows, for the first time, the presence of the free radical scavenging enzyme Cu,Zn-SOD in normal human dental pulp. No attempt was made to localize the enzyme. Preliminary immunohistochemical studies indicate that Cu,Zn-SOD is found in association with the
318
Davis et al.
cytoplasm and glycocalyx of both pulpal fibroblasts and macrophages, as well as in the extracellular matrix where the enzyme is found in close proximity to collagen fibrils (W. L. Davis, unpublished observation). Cu,Zn-SOD is one component of a complex antioxidant defense system which converts toxic free radicals such as 02- (the superoxide anion free radical) to oxygen and H202 (4, 5, 8, 10). H202 is subsequently detoxifled by the enzyme catalase as well as by the glutathionedependent H202-detoxifying system--both of which reduce H20_, to water (8, 11). The study presented here also reports that Cu,Zn-SOD activity is significantly increased in inflamed human pulpal tissues. The latter observation is not surprising because it has been known for many years that, during inflammation, the phagocytes (macrophages) of the host tissues (including neutrophils, mononuclear phagocytes, and eosinophils) all produce multiple, powerful oxidizing agents in response to specific stimuli (microbes, the toxic breakdown products of microbes, etc.). Unfortunately, the highly reactive oxidants produced by stimulated phagocytes not only destroy (inactivate) microorganisms and their toxic products, etc., but also cause irreparable damage to the normal surrounding cells (fibroblasts) and extracellular matrix molecules (collagen, proteoglycans) present in the involved tissues (1-5). Those bacterial products that stimulate the respirator)' burst include Nformylated oligopeptides, lipopolysaccharides, and endotoxins (4). In addition, endogenously produced chemoattractants, present at sites of inflammation and infection, can also trigger the release of aggressive oxygen species. These include complement C5a, leukotrienes, and opsonized bacteria (15). From the data in the present report, it appears that human dental pulp, a site of frequent inflammation, possesses an inherent biological defense mechanism for the scavenging of reactive oxidants produced during the typical inflammatory response. This mechanism involves the enzyme Cu,Zn-SOD and serves to protect the components of this tissue from cell necrosis and matrix degradation, thus affording adequate tissue repair. However, with severe (acute) or repetitive (chronic) tissue insult, or quite possibly as a result of the aging process, this mechanism may be overwhelmed and/or inactivated, resulting in decreased tissue protection from locally generated ROI as well as a compromised healing response. Thus, a deficiency in the endogenous synthesis of SOD may be associated with chronic inflammation, aging, or both. These concepts are supported by currently ongoing studies which have shown that during induced, chronic, canine pulpitis, the inflamed tissue shows a temporal decrease in SOD (and catalase) activity (W. L. Davis, unpublished observation). The latter may also be true for other chronically inflamed tissues (periodontal disease, osteoarthritis) (W. L. Davis, unpublished observation). Along these lines, preliminary bioassays for SOD activity in normal pulps removed from elderly human patients (over 60 yr of age) showed significantly reduced levels of SOD activity when compared with that in
Journal of Endodontics
tissues from younger patients (20 to 40 yr of age) (W. L. Davis, unpublished observation). In summary, it has been previously shown that there is an increase in the activity of the yon Willebrand factor (clotting factor VII1) during pulpal inflammation (12). Here, we report an elevation in SOD activity. In addition, we also know that there is an elevation in arachidonic acid metabolites in inflamed human pulp (13), as well as an increase in certain tissue growth factors or cytokines (13). Taken together, this information would seem to support the original contention that this highly specialized and virtually isolated tissue is endowed with a dramatic capacity for healing and repair (12, 13). As hinted in the communication reported here, there may be an age-related competency associated with these activities. This research was supported by the Thomas and Ernestine Bedford Foundation of Fort Worth, TX, by the A. Martindale Foundation of Fort Worth, TX, by The General Dynamics Corporation of Fort Worth, TX, and by The K. M. Davis Trust, Princeton, NJ. The authors would like to acknowledge R. M Kipnis, Yale Medical School, and L. Boirnbaumer, University of Texas Health Science Center, Dallas, TX, for their assistance with the SOD assays. Dr. Davis is professor, Department of Cell Biology, The Baylor Research Foundation, Baylor University Medical Center, Dallas, TX. Dr. Harrison is professor, Department of Endodontics, Baylor College of Dentistry, Dallas, TX. Dr. Jacoby is affiliated with the Department of Periedontics, Baylor College of Dentistry. Drs. Craig and Jacoby are affiliated with the Department of Endodontics, Baylor College of Dentistry. Address requests for reprints to Dr. Bennett Jacoby, Department of Periodontic Baylor College of Dentistry, 3302 Gaston Avenue, Dallas, TX 75246.
References 1. Fridovich I. The biology of oxygen radicals: the superoxide radical is an agent of oxygen toxicity--Superoxide dismutases provide an important defense. Science 1979;201:875-80. 2. Freeman BA, Crapo JD. Biology of disease: free radicals and tissue injury. Lab invest 1982;47:412-46. 3. McCord JM, Fridovich I. Superoxide dismutase, an enzymic funtion for erythrocuprein. J Biol Ghem 1969;244:6049-55. 4. Babior BM. Oxidants from phagocytes: agents of defense and destruction. Blood 1984;64:959-66. 5. Goldstein IM, Roos D, Kaplan HB, Weissmann G. Complement and immunoglobulins stimulate superoxide production by granulocytes. J Clin Invest 1974;53:1622-3. 6. Marklund SL. Spectrophotometric study of spontaneous disproportionation of superoxide anion radical and sensitive direct assay for superoxide dismutase. J Biol Chem 1976;251:7504-7. 7. Marklund SL. Extracellular superoxide dismutase and other superoxidase isoenzymes in tissue from nine mammalian species. Biochem J 1984;222:649-55. 8. Roos D, Weening RS, Wyss SR, Aebi HE. Protection of human neutrophils by endogenase catalase. Studies with cell from catalase-deficient individuals. J Clin Invest 1980;65:1415-21. 9. Lowry OH, Rosebrough NJ, Farr AL, Randall RJ. Protein measurements with the Folin phenol reagent. J Biol Chem 1951 ;193:265-73. 10. Salin ML, McCord JM. Superoxide dismutase in polymorphonuclear leukocytes. J Clin Invest 1974;54:1005-11. 11. Houpert Y, Tarallo P, Siest G. Quantitative determination of granulocytic amino acids in healthy men and women. Clin Chim Acta 1976;69:383-90. 12. Jacoby BH, Craig KR, Harrison JW, Davis WL. Immunocytochemistry of mammalian pulp: localization of cytokines. J Dent Res 1990;669:171. 13. Jacoby BH, Davis WL, Craig KR, Wagner G, Farmer GR, Harrison JW. An ultrastructural and immunohistochemical study of human dental pulp: identification of WeibeI-Palade bodies and yon Willebrand factor in pulp endothelial cells. J Endodon (in press).
Printed in U.S.A.
MOL. 17, NO. 7, JULY 1991
Copper-Zinc Superoxide Dismutase Activity in Normal and Inflamed Human Dental Pulp Tissue Walter L. Davis, PhD, MD, Bennett H. Jacoby, DDS, MS, Kathleen R. Craig, DDS, MS, Gary Wagner, DDS, and John W. Harrison, DMD, MS
Information regarding the presence of the free radical scavenging (inactivating, dismutating) enzyme superoxide dismutase in human dental pulp was sought. Free radicals, such as the superoxide anion radical (02-) and the hydroxyl anion radical (OH'), are powerful biological oxidants produced by phagocytes during the normal tissue response to injury and infection. Also produced is hydrogen peroxide (H202), an aggressive oxygen species formed by the reaction of superoxide with itself, i.e., a dismutation in which one molecule of 02- is oxidized by the other. These three reactive oxygen intermediates serve as part of the normal host biological defense mechanism for the inactivation of microorganisms and the breakdown of their toxic products. Both normal and inflamed dental pulps were assayed for the presence of this enzyme. Superoxide dismutase activity was identified in the normal pulpal tissues. There was a slight decrease in activity with age. In the inflamed pulpal tissues, enzyme activity was markedly and significantly increased in comparison to that in the normal tissues. These observations indicate that human dental pulp possesses an endogenous defense mechanism designed to protect the tissue components (cells and matrix) from the toxic effects of the reactive oxygen intermediates. In this regard, the inflammatory response of this specialized and somewhat isolated (compartmentalized) tissue is not unlike that seen in other connective tissues.
mation. Such ROI include: (a) the superoxide anion radical (02-), formed by the one-electron reduction of oxygen in the presence of NADPH (202 + NADPH ~ 202- + NADP + H+); and (b) the hydroxyl anion radical (OH'), produced by the Haber-Weiss reaction (02- + H202 ~ OH" + O H - + 02). A third aggressive (but nonradical) oxygen species is also formed. The latter is hydrogen peroxide (H202) and is produced by the reaction of superoxide with itself (02- + 02- + 2H § ~ H202 + 02). H202 has a very long half-life and is known to cause considerable cell and tissue damage. These aggressive oxygen species represent a group of highly reactive and powerful biological oxidizing agents that are normally and routinely produced by phagocytes at sites of inflammation and infection (4). Such oxygen intermediates can destroy most biologic molecules, including those of bacterial origin, i.e., Nformylated oligopeptides (4, 5). In so doing however, ROI also destroy normal components of the surrounding cells and matrices. To protect against the latter, biological defense mechanisms have evolved which dismutate or inactivate these oxidants. Probably the most common defense against the ROI-induced breakdown of normal tissues involves dismutation by the enzyme SOD. The latter has been identified in most eukaryotic cells as well as in the extracellular matrices (1, 2, 6-8). Excellent reviews of free radicals, free radical chemistry, free radicals and tissue injury, and free radicals and inflammation can be found in references 1, 2, and 4. Because dental pulp is characterized by both acute and chronic inflammatory responses, the tissue was examined for the presence of SOD activity. The primary objective was to determine if a relationship existed between the activity of this enzyme and the inflammatory state of the human tissue. MATERIALS AND METHODS Both normal and inflamed intact human dental pulps were removed for either prosthetic or endodontic purposes at the graduate endodontic clinic at the Baylor College of Dentistry. Routine clinical examination techniques were used to assess the status of the pulps including subjective findings, thermal testing, and electrical testing. For this study, a total of 14 pulps were collected, 7 inflamed and 7 normal. Patients ranged in age from 19 to 47 yr. On removal, the tissues were vigorously washed three to five times over a 10-min period in chilled (4~ heparinized,
Superoxide dismutase (SOD) or superoxidoreductase (EC 1.15.1.1) is a primary oxygen radical scavenging enzyme for eukaryotic, aerobic cells and tissues (1-3). Because of this, SOD (primarily the copper, zinc SOD or Cu,ZN-SOD) represents the major enzymatic defense mechanism against toxic/aggressive oxygen species or reactive oxygen intermediates (ROI) generated during normal oxidative metabolism as well as during the respiratory burst associated with inflam-
316
Vol. 17, No. 7, July 1991
SOD in Human Dental Pulp
TABLE 1. Cu,Zn-SOD activity in normal human dental pulp
TABLE 2. Cu,Zn-SOD activity in inflamed human dental pulp
SOD Activity Patient (age) 1 (33) 2 (27) 3 (44) 4 (29) 5 (47) 6 (24) 7 (30)
317
SOD Activity
units/g wet
units/mg
wt*
tein
1680 2700 7500 1150 990 2100 1460
463 746 207 317 273 579 402
of pro-
* Mean _+ SD, 1547 _+678.
sterile saline. Tissues were then quick-frozen in liquid nitrogen and subsequently stored at -160~ before being assayed for SOD. For the biochemical analysis of tissue SOD activity, previously reported techniques were used (6, 7). Pulps were first homogenized in a Potter-Elvehjem homogenizer in l0 volumes of chilled, 50 mM sodium acetate buffer (pH 5.5) containing 0.3 M KBr. The homogenates were subsequently sonicated and extracted for 30 min at 4~ A supernatant was prepared by centrifugation at 20,000 x g for 15 min. This supernatant was used for further enzyme analysis. SOD activity was determined by its ability to catalyze the disproportionation of 02- in an alkaline (pH 9.5) aqueous solution. This reaction was studied in a spectrophotometer as previously described by Marklund (6, 7). By this procedure, 1 unit in the assay corresponds to approximately 8.3 ng of human Cu,Zn-SOD (6, 7). For control assays, the cyanide (CN-) sensitivity of Cu,Zn-SOD was used to separate this enzyme from Mn-SOD, a mitochondrial SOD. Thus, all assays were carried out in the presence of CN-. Protein was determined according to the method of Lowry et al. (9). Human serum albumin was used for standardization. Statistical analyses were performed by using Student's t test. RESULTS The results of the assays of normal human dental pulp for Cu,Zn-SOD activity are shown in Table 1. Note that in the normal tissues, the content of this enzyme ranges from a low of 750 units/g wet weight to a high of 2,700 units/g wet weight (units/g wet wt column). This translates to a range of approximately 207 to 746 units/mg of protein, respectively (units/ mg of protein column). In the inflamed tissues, however, the content of SOD was markedly and significantly (p < 0.0001) increased, ranging from 4700 to 7600 units/g wet weight for the seven different tissues analyzed (Table 2, units/g wet wt column). These values correspond to a range of 1296 to 2095 units/mg of protein, respectively (units/mg of protein). Incubation in the presence of CN- depressed SOD activity by more than 98% (data not shown). Figure 1 shows a possible inverse relationship or correlation between age and tissue SOD activity, i.e., a decrease in the activity of this enzyme with increasing age (Tables 1 and 2). The data shown in both the point graph (Fig. 1A) and the
Patient (age)
units/g wet wt*
units/mg of protein
8(19) 9(45) 10(36) 11 (43) 12(23) 13(28) 14(39)
7600 5400 6850 4700 7050 6250 5570
2095 1489 1889 1296 1944 1723 1536
* Mean _+ SD, 6202 ___1032. t value, -8.9927; statistics, normal versus inflamed, 0.0001.
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FIG 1. A, Point graph showing a possible correlation between patient age and pulp SOD activity. The data are suggestive of an inverse relationship between age and pulp SOD activity in inflamed tissues (the greater the age, the less the enzyme activity). However, a similar correlation is not as apparent in the normal pulps. B, Trend graph also showing a possible correlation between patient age and pulp SOD activity. The interpretation is the same as that for the point graph in A.
trend graph (Fig. 1B) are suggestive of this inverse relationship (> age < SOD activity), especially with regard to the inflamed tissues presented here. DISCUSSION The study presented here shows, for the first time, the presence of the free radical scavenging enzyme Cu,Zn-SOD in normal human dental pulp. No attempt was made to localize the enzyme. Preliminary immunohistochemical studies indicate that Cu,Zn-SOD is found in association with the
318
Davis et al.
cytoplasm and glycocalyx of both pulpal fibroblasts and macrophages, as well as in the extracellular matrix where the enzyme is found in close proximity to collagen fibrils (W. L. Davis, unpublished observation). Cu,Zn-SOD is one component of a complex antioxidant defense system which converts toxic free radicals such as 02- (the superoxide anion free radical) to oxygen and H202 (4, 5, 8, 10). H202 is subsequently detoxifled by the enzyme catalase as well as by the glutathionedependent H202-detoxifying system--both of which reduce H20_, to water (8, 11). The study presented here also reports that Cu,Zn-SOD activity is significantly increased in inflamed human pulpal tissues. The latter observation is not surprising because it has been known for many years that, during inflammation, the phagocytes (macrophages) of the host tissues (including neutrophils, mononuclear phagocytes, and eosinophils) all produce multiple, powerful oxidizing agents in response to specific stimuli (microbes, the toxic breakdown products of microbes, etc.). Unfortunately, the highly reactive oxidants produced by stimulated phagocytes not only destroy (inactivate) microorganisms and their toxic products, etc., but also cause irreparable damage to the normal surrounding cells (fibroblasts) and extracellular matrix molecules (collagen, proteoglycans) present in the involved tissues (1-5). Those bacterial products that stimulate the respirator)' burst include Nformylated oligopeptides, lipopolysaccharides, and endotoxins (4). In addition, endogenously produced chemoattractants, present at sites of inflammation and infection, can also trigger the release of aggressive oxygen species. These include complement C5a, leukotrienes, and opsonized bacteria (15). From the data in the present report, it appears that human dental pulp, a site of frequent inflammation, possesses an inherent biological defense mechanism for the scavenging of reactive oxidants produced during the typical inflammatory response. This mechanism involves the enzyme Cu,Zn-SOD and serves to protect the components of this tissue from cell necrosis and matrix degradation, thus affording adequate tissue repair. However, with severe (acute) or repetitive (chronic) tissue insult, or quite possibly as a result of the aging process, this mechanism may be overwhelmed and/or inactivated, resulting in decreased tissue protection from locally generated ROI as well as a compromised healing response. Thus, a deficiency in the endogenous synthesis of SOD may be associated with chronic inflammation, aging, or both. These concepts are supported by currently ongoing studies which have shown that during induced, chronic, canine pulpitis, the inflamed tissue shows a temporal decrease in SOD (and catalase) activity (W. L. Davis, unpublished observation). The latter may also be true for other chronically inflamed tissues (periodontal disease, osteoarthritis) (W. L. Davis, unpublished observation). Along these lines, preliminary bioassays for SOD activity in normal pulps removed from elderly human patients (over 60 yr of age) showed significantly reduced levels of SOD activity when compared with that in
Journal of Endodontics
tissues from younger patients (20 to 40 yr of age) (W. L. Davis, unpublished observation). In summary, it has been previously shown that there is an increase in the activity of the yon Willebrand factor (clotting factor VII1) during pulpal inflammation (12). Here, we report an elevation in SOD activity. In addition, we also know that there is an elevation in arachidonic acid metabolites in inflamed human pulp (13), as well as an increase in certain tissue growth factors or cytokines (13). Taken together, this information would seem to support the original contention that this highly specialized and virtually isolated tissue is endowed with a dramatic capacity for healing and repair (12, 13). As hinted in the communication reported here, there may be an age-related competency associated with these activities. This research was supported by the Thomas and Ernestine Bedford Foundation of Fort Worth, TX, by the A. Martindale Foundation of Fort Worth, TX, by The General Dynamics Corporation of Fort Worth, TX, and by The K. M. Davis Trust, Princeton, NJ. The authors would like to acknowledge R. M Kipnis, Yale Medical School, and L. Boirnbaumer, University of Texas Health Science Center, Dallas, TX, for their assistance with the SOD assays. Dr. Davis is professor, Department of Cell Biology, The Baylor Research Foundation, Baylor University Medical Center, Dallas, TX. Dr. Harrison is professor, Department of Endodontics, Baylor College of Dentistry, Dallas, TX. Dr. Jacoby is affiliated with the Department of Periedontics, Baylor College of Dentistry. Drs. Craig and Jacoby are affiliated with the Department of Endodontics, Baylor College of Dentistry. Address requests for reprints to Dr. Bennett Jacoby, Department of Periodontic Baylor College of Dentistry, 3302 Gaston Avenue, Dallas, TX 75246.
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