Injbrma tion Section ARTICLES
OF GENERAL
MSG-FOOD
INTEREST
FOR THOUGHT
Monosodium glutamate (MSG) has been suspected of causing brain damage in neonates of various species (Cited in F.C.7: 1977, 15, 347) and hypothalamic damage resulting in multiple endocrine dysfunction in adult mice that had been treated neonatally with MSG has also been reported (ibid 1978, 16, 393). However, factors such as species, age, route of administration and experimental design have introduced wide variations into the results of experiments (ibid 1977. 15, 348) and the dietary threshold level at which MSG exerts neurotoxicity has yet to be established (ibid 1979. 17, 83). In the following studies, the effects of orally administered MSG on various species are described. Oral administration of 1 g MSGjkg body weight in a lo”,, (wjv) solution produced similar overall plasma levels of glutamic acid (GA) in adult mice and rats. Peak plasma levels and apparent half-lives of GA were also similar in both species. However, when the same dose was administered to adult guinea-pigs, the overall plasma levels and the apparent half-lives were higher (Bizzi et al. Toxicology Lett. 1977, 1, 123). After a dose of 1 g MSGjkg in 100; (w/v) solution, the overall plasma levels were higher in neonatal (7-day-old) mice and rats than in the adults, but the reverse was true for guinea-pigs. The GA levels in mouse and guinea-pig brains were not altered by orally administered MSG until the peak plasma-GA levels exceeded the basal concentrations by about 20 times. The concentration at which MSG was administered influenced plasma-GA levels. When a dose of MSG was administered to 7-day-old animals (mice: @5 g,‘kg; rats: 1.0 g/kg) in solutions of differing concentration (mice: 2-20”/& w/v; rats: 2-IO%, w/v), the peak plasma-GA levels and overall plasma levels, but not the apparent half-life of GA, increased with increasing concentration (B&i er ul. lot. cit.). Gimilar effects occurred in adult animals. Overall and peak plasma levels also increased with increasing doses of MSG given at the same concentration. The effect of concentration on plasma-GA levels was observed also in human volunteers, in whom 60mg MSGikg produced higher peak and overall plasma levels when given at 8”;, (w/v) than at 2:;, (Bizzi et cd. lot. cir.). Contradictory evidence comes, though, from a study in mice by James et ul. (Tmicology Left. 1978. 1. 195). In 43-day-old male mice given a single oral dose of I.5 g MSG/kg at various concentrations (2 ~700,) in aqueous solution, plasma-GA levels were increased at all concentrations given, the highest values being attained 15 min after dosing. However, the increase in GA level was not related to the concentration of the solution used, although the sodium concentration in the plasma did vary with the concentration of the MSG solution. Between 15 and 90 min
after dosing, significantly lower plasma-sodium concentrations were produced by the 2?, MSG soluti~~o than by the other concentrations. At 15 min. the 5”,, MSG solution produced lower plasma-sodium concentrations than IO or 20”/, MSG. and at 90 min. 20”,, MSG produced a higher plasma-sodium COIICCI‘Itration than the lower strengths. After 120 min. thsrc was no difference, however. and the values for sod~nm concentration were within the normally acccptcd range at all times, Although the plasma-GA ii.\cl\ were increased by dosing with MSG. no histolog~c~rl damage was induced in the hypothalamus. and 11 1s assumed that the blood-brain barrier in adult nlrci~ protects against such damage. It has been suggested that considerable annom~t~ of MSG appear to be harmless when ingested a\ p.ir\ of an otherwise normal diet (Cited in F.C.7: lOTi. 13, 125). Further support for this view comes from \tut~~cs on beagle dogs (Owen e’t ul. Toxicwlog~~ Lerr. 1’)‘s. 1, 217) and rats (i&m ibid 1978. 1. 221). Beaplc claim\ were fed Purina Dog Chow containing either 5.1: ,, (w/w) sodium propionate or 2.5. 5.0 or IOXt,, II\ \\ I MSG for 104 wk. No adverse effects were ohscricd on weight gain. food consumption. ehiciencq of food conversion, or behaviour: nor were any d~tTct-cncc~ noted between the electrocardiograms. ophthatm~>l+ gical findings. haematology and serum chemistr-!. organ weights or mortality of experimental and control dogs. Both the dietary additives slightlv incrc;r\cd urine volume and sodium excretion. but urinary c(~rcentration ability was not impaired. Tissue samples. including kidney. taken after treatment for I3 or104 wk showed no histopathological changes attributable to the additives. The medullary tubular lumen in both treated and control dogs showed I’OCI of mineralization. Similarly, in rats fed 2-05”~~ sodrum propionate or 1.0, 2.0 or 4.00, MSG in the diet for 104 wk there were no adverse effects on weight gain (except for a slight lowering in males given 40”,, MSG or 2.05% sodium propionate after wk 60). or on food consumption, efficiency of food conversion. blood. organ weights or mortality (with the exception of females receiving I”/, MSG, who survived better than the controls). The highest feed levels of MSG and sodium propionate increased water consumption. urine volume and sodium excretion; an increased incidence and earlier onset of spontaneous subepithelial basophilic deposits in the renal pelvis may have been related to the increased urine volume and sodrum excretion but were not thought to be specifically axsociated with MSG. As in dogs, focal mineralization in the medullary tubules was equally incident in treated rats and in controls. O’Hara et al. (J. toxicol. Sci., Japm 1977. 2. 2X1) investigated the effects of the route of MSG adminis541
542
Articles
of general Interest
Fd Co\mc,f. To\-id. Vol. 17. no. 5
tration on plasma-GA levels in mice. A single dose of I g MSG/kg in IO:! (w/v) aqueous solution was given ip. SC or by gastric intubation to mice aged IO days, 23 days or 4 months. Plasma-GA levels reached a peak 1@30min after the dose was given and returned to basal values after 90min. After oral doses, the GA peaks were lower than after ip or SC injection, particularly in the IO-day-old and 23-dayold animals. Single doses of 1 g MSG/kg, mixed into humanInfant formula feed or clear soup to give concentrations of 10% (w/v), were administered, respectively. to IO-day-old or adult mice by gastric intubation. The peak plasma-GA levels were reduced by some 50% in mice given the dose in either of the two foods, compared with the levels in mice given the same dose in an aqueous solution. When 1 g MSG/kg was administered to 23-day-old and adult mice as part of
VINYL
CHLORIDE-PART
In the last issue (p. 403). we reviewed the more important metabolic studies on vinyl chloride (VC). Now we turn to mutagenicity. This aspect of Vc’s biological profile has been extensively investigated, particularly in bacteria. Mutagenicity
in Salmonella
typhimurium
The preliminary studies of mutagenicity involved the Ames test. When VC, at a concentration of 20% (v/v) in air, was incubated with Sulnwnellu typhimurium strain TA1535 and a mammalian metabolizing system, namely a fortified post-mitochondrial rat-liver supernatant, the number of histidine revertants was increased to three times the spontaneous mutation rate (Rannug et al. AMBIO 1974, 3, 194). An increase over the spontaneous mutation rate also occurred in strains TA1535, TA1530 and G46 when they were exposed to a similar VC atmosphere in the presence of a 9000-g mouse-liver supernatant (S-9 fraction) fortified with an NADPH-generating system (Bartsch et al. Int. J. Cancer 1975, 15, 429). The greatest response was seen with TA1530, VC treatment (for 48 hr) being associated in this case with a 28-fold increase in the number of histidine revertants. The VC concentration of the incubation medium below the 20% atmosphere was found to be @004 M at equilibrium. Although exposure to 20% VC in air proved to be mutagenic towards TA1530 in the absence of metabolic activation, mutagenic activity was doubled by the addition of liver fractions from phenobarbital-treated mice. The highest mutagenic responses occurred in the presence of a 9000-g supernatant or with the recombined microsomal and soluble protein fraction in the presence of an NADPH-generating system. Purified microsomal fractions were less efficient activators, and soluble liver proteins (100,000-g supernatant) alone were almost without effect. The addition of alcohol dehydrogenase and NAD+ to either the fortified post-mitochondrial or the 100,000-g liver supernatant did not increase the mutation rate (Bartsch et al. lot. cit.).
a normal diet, only slight elevations in plasma-GA levels occurred and peak values were less than 45 ~~mol/lOOml compared with 219 and 344,umol: 100 ml in 23-day-old and 4-month-old mice. respectively. given the dose by gastric intubation in aqueous solution. Other studies in rats (Cited in F.C.T. 1971. 9, 719) and in neonatal pigs (ibid 1975. 13, 125) however. did not show any reduction in peak GA levels in the plasma when MSG was administered with food rather than alone in solution. Nevertheless, the rates of increase to the peak level were slower, and on balance these studies do suggest that the effects of MSG may be influenced to a significant degree by accompanying feeding patterns or by other dietary components.
[P. Cooper---BIBRAJ
2: MUTAGENICITY In the TA1535 and TAlOO strains, McCann er al. (Proc. nutn. Acad. Sci. U.S.A. 1975, 72, 3190) found that although a VC atmosphere (20:; v/v) gave evidence of direct mutagenic activity, its activity was doubled by the addition of the S-9 fraction from a PCB-treated rat. The results of a similar study by Andrews et al. (Mutation Res. 1976, 40, 273) seem to be anomalous, in that VC at levels of up to 15~~~, in air were shown to be directly mutagenic in TA I535 and an S-9 fraction from PCB-treated rats produced only a slight enhancement. However, the differences between these two sets of results may partly be explained by the different incubation times involved. Vinyl chloride is not thought to be mutagenic per se. The increase in the number of histidine revertants seen when VC is incubated with strains TAl530, TA 1535 or TAlOO in the absence of any mammalian metabolizing system is thought to be a result of the non-enzymic breakdown products of VC or of compounds formed by the bacterial enzyme system (Bartsch et ul. lot. cit.). Aqueous solutions of VC (initial concentration 0.083 M) gave no evidence of mutagenicity when incubated with S. typhimurium strains TA1530, TAl535 or G46 together with a fortified 9000-g liver supernatant from phenobarbital-treated mice (Bartsch er al. lot. cit.). A similar lack of activity of VC in solution (at an initial concentration of PO22 M) was reported by Elmore et al. (Biochim. biophys. Actcl 1976, 442, 405) in TAlOO. It was thought that the inactivity of VC in these systems may have been caused by rapid diffusion of monomer from the liquid phase into the atmosphere. S. typhimurium strains TAl530, TA1535. TAlOO and G46 respond with varying sensitivity to monofunctional alkylating agents (base-pair substitutions or deletions). Strains TA1536, TA1537 and TA1538. which are specifically reverted by frameshift mutagens, were unaffected by 207/, VC atmospheres even in the presence of liver fractions from rats or mice (Bartsch et ul. lot. cit.; Rannug et al. lot. cit.).
OF GENERAL
MSG-FOOD
INTEREST
FOR THOUGHT
Monosodium glutamate (MSG) has been suspected of causing brain damage in neonates of various species (Cited in F.C.7: 1977, 15, 347) and hypothalamic damage resulting in multiple endocrine dysfunction in adult mice that had been treated neonatally with MSG has also been reported (ibid 1978, 16, 393). However, factors such as species, age, route of administration and experimental design have introduced wide variations into the results of experiments (ibid 1977. 15, 348) and the dietary threshold level at which MSG exerts neurotoxicity has yet to be established (ibid 1979. 17, 83). In the following studies, the effects of orally administered MSG on various species are described. Oral administration of 1 g MSGjkg body weight in a lo”,, (wjv) solution produced similar overall plasma levels of glutamic acid (GA) in adult mice and rats. Peak plasma levels and apparent half-lives of GA were also similar in both species. However, when the same dose was administered to adult guinea-pigs, the overall plasma levels and the apparent half-lives were higher (Bizzi et al. Toxicology Lett. 1977, 1, 123). After a dose of 1 g MSGjkg in 100; (w/v) solution, the overall plasma levels were higher in neonatal (7-day-old) mice and rats than in the adults, but the reverse was true for guinea-pigs. The GA levels in mouse and guinea-pig brains were not altered by orally administered MSG until the peak plasma-GA levels exceeded the basal concentrations by about 20 times. The concentration at which MSG was administered influenced plasma-GA levels. When a dose of MSG was administered to 7-day-old animals (mice: @5 g,‘kg; rats: 1.0 g/kg) in solutions of differing concentration (mice: 2-20”/& w/v; rats: 2-IO%, w/v), the peak plasma-GA levels and overall plasma levels, but not the apparent half-life of GA, increased with increasing concentration (B&i er ul. lot. cit.). Gimilar effects occurred in adult animals. Overall and peak plasma levels also increased with increasing doses of MSG given at the same concentration. The effect of concentration on plasma-GA levels was observed also in human volunteers, in whom 60mg MSGikg produced higher peak and overall plasma levels when given at 8”;, (w/v) than at 2:;, (Bizzi et cd. lot. cir.). Contradictory evidence comes, though, from a study in mice by James et ul. (Tmicology Left. 1978. 1. 195). In 43-day-old male mice given a single oral dose of I.5 g MSG/kg at various concentrations (2 ~700,) in aqueous solution, plasma-GA levels were increased at all concentrations given, the highest values being attained 15 min after dosing. However, the increase in GA level was not related to the concentration of the solution used, although the sodium concentration in the plasma did vary with the concentration of the MSG solution. Between 15 and 90 min
after dosing, significantly lower plasma-sodium concentrations were produced by the 2?, MSG soluti~~o than by the other concentrations. At 15 min. the 5”,, MSG solution produced lower plasma-sodium concentrations than IO or 20”/, MSG. and at 90 min. 20”,, MSG produced a higher plasma-sodium COIICCI‘Itration than the lower strengths. After 120 min. thsrc was no difference, however. and the values for sod~nm concentration were within the normally acccptcd range at all times, Although the plasma-GA ii.\cl\ were increased by dosing with MSG. no histolog~c~rl damage was induced in the hypothalamus. and 11 1s assumed that the blood-brain barrier in adult nlrci~ protects against such damage. It has been suggested that considerable annom~t~ of MSG appear to be harmless when ingested a\ p.ir\ of an otherwise normal diet (Cited in F.C.7: lOTi. 13, 125). Further support for this view comes from \tut~~cs on beagle dogs (Owen e’t ul. Toxicwlog~~ Lerr. 1’)‘s. 1, 217) and rats (i&m ibid 1978. 1. 221). Beaplc claim\ were fed Purina Dog Chow containing either 5.1: ,, (w/w) sodium propionate or 2.5. 5.0 or IOXt,, II\ \\ I MSG for 104 wk. No adverse effects were ohscricd on weight gain. food consumption. ehiciencq of food conversion, or behaviour: nor were any d~tTct-cncc~ noted between the electrocardiograms. ophthatm~>l+ gical findings. haematology and serum chemistr-!. organ weights or mortality of experimental and control dogs. Both the dietary additives slightlv incrc;r\cd urine volume and sodium excretion. but urinary c(~rcentration ability was not impaired. Tissue samples. including kidney. taken after treatment for I3 or104 wk showed no histopathological changes attributable to the additives. The medullary tubular lumen in both treated and control dogs showed I’OCI of mineralization. Similarly, in rats fed 2-05”~~ sodrum propionate or 1.0, 2.0 or 4.00, MSG in the diet for 104 wk there were no adverse effects on weight gain (except for a slight lowering in males given 40”,, MSG or 2.05% sodium propionate after wk 60). or on food consumption, efficiency of food conversion. blood. organ weights or mortality (with the exception of females receiving I”/, MSG, who survived better than the controls). The highest feed levels of MSG and sodium propionate increased water consumption. urine volume and sodium excretion; an increased incidence and earlier onset of spontaneous subepithelial basophilic deposits in the renal pelvis may have been related to the increased urine volume and sodrum excretion but were not thought to be specifically axsociated with MSG. As in dogs, focal mineralization in the medullary tubules was equally incident in treated rats and in controls. O’Hara et al. (J. toxicol. Sci., Japm 1977. 2. 2X1) investigated the effects of the route of MSG adminis541
542
Articles
of general Interest
Fd Co\mc,f. To\-id. Vol. 17. no. 5
tration on plasma-GA levels in mice. A single dose of I g MSG/kg in IO:! (w/v) aqueous solution was given ip. SC or by gastric intubation to mice aged IO days, 23 days or 4 months. Plasma-GA levels reached a peak 1@30min after the dose was given and returned to basal values after 90min. After oral doses, the GA peaks were lower than after ip or SC injection, particularly in the IO-day-old and 23-dayold animals. Single doses of 1 g MSG/kg, mixed into humanInfant formula feed or clear soup to give concentrations of 10% (w/v), were administered, respectively. to IO-day-old or adult mice by gastric intubation. The peak plasma-GA levels were reduced by some 50% in mice given the dose in either of the two foods, compared with the levels in mice given the same dose in an aqueous solution. When 1 g MSG/kg was administered to 23-day-old and adult mice as part of
VINYL
CHLORIDE-PART
In the last issue (p. 403). we reviewed the more important metabolic studies on vinyl chloride (VC). Now we turn to mutagenicity. This aspect of Vc’s biological profile has been extensively investigated, particularly in bacteria. Mutagenicity
in Salmonella
typhimurium
The preliminary studies of mutagenicity involved the Ames test. When VC, at a concentration of 20% (v/v) in air, was incubated with Sulnwnellu typhimurium strain TA1535 and a mammalian metabolizing system, namely a fortified post-mitochondrial rat-liver supernatant, the number of histidine revertants was increased to three times the spontaneous mutation rate (Rannug et al. AMBIO 1974, 3, 194). An increase over the spontaneous mutation rate also occurred in strains TA1535, TA1530 and G46 when they were exposed to a similar VC atmosphere in the presence of a 9000-g mouse-liver supernatant (S-9 fraction) fortified with an NADPH-generating system (Bartsch et al. Int. J. Cancer 1975, 15, 429). The greatest response was seen with TA1530, VC treatment (for 48 hr) being associated in this case with a 28-fold increase in the number of histidine revertants. The VC concentration of the incubation medium below the 20% atmosphere was found to be @004 M at equilibrium. Although exposure to 20% VC in air proved to be mutagenic towards TA1530 in the absence of metabolic activation, mutagenic activity was doubled by the addition of liver fractions from phenobarbital-treated mice. The highest mutagenic responses occurred in the presence of a 9000-g supernatant or with the recombined microsomal and soluble protein fraction in the presence of an NADPH-generating system. Purified microsomal fractions were less efficient activators, and soluble liver proteins (100,000-g supernatant) alone were almost without effect. The addition of alcohol dehydrogenase and NAD+ to either the fortified post-mitochondrial or the 100,000-g liver supernatant did not increase the mutation rate (Bartsch et al. lot. cit.).
a normal diet, only slight elevations in plasma-GA levels occurred and peak values were less than 45 ~~mol/lOOml compared with 219 and 344,umol: 100 ml in 23-day-old and 4-month-old mice. respectively. given the dose by gastric intubation in aqueous solution. Other studies in rats (Cited in F.C.T. 1971. 9, 719) and in neonatal pigs (ibid 1975. 13, 125) however. did not show any reduction in peak GA levels in the plasma when MSG was administered with food rather than alone in solution. Nevertheless, the rates of increase to the peak level were slower, and on balance these studies do suggest that the effects of MSG may be influenced to a significant degree by accompanying feeding patterns or by other dietary components.
[P. Cooper---BIBRAJ
2: MUTAGENICITY In the TA1535 and TAlOO strains, McCann er al. (Proc. nutn. Acad. Sci. U.S.A. 1975, 72, 3190) found that although a VC atmosphere (20:; v/v) gave evidence of direct mutagenic activity, its activity was doubled by the addition of the S-9 fraction from a PCB-treated rat. The results of a similar study by Andrews et al. (Mutation Res. 1976, 40, 273) seem to be anomalous, in that VC at levels of up to 15~~~, in air were shown to be directly mutagenic in TA I535 and an S-9 fraction from PCB-treated rats produced only a slight enhancement. However, the differences between these two sets of results may partly be explained by the different incubation times involved. Vinyl chloride is not thought to be mutagenic per se. The increase in the number of histidine revertants seen when VC is incubated with strains TAl530, TA 1535 or TAlOO in the absence of any mammalian metabolizing system is thought to be a result of the non-enzymic breakdown products of VC or of compounds formed by the bacterial enzyme system (Bartsch et ul. lot. cit.). Aqueous solutions of VC (initial concentration 0.083 M) gave no evidence of mutagenicity when incubated with S. typhimurium strains TA1530, TAl535 or G46 together with a fortified 9000-g liver supernatant from phenobarbital-treated mice (Bartsch er al. lot. cit.). A similar lack of activity of VC in solution (at an initial concentration of PO22 M) was reported by Elmore et al. (Biochim. biophys. Actcl 1976, 442, 405) in TAlOO. It was thought that the inactivity of VC in these systems may have been caused by rapid diffusion of monomer from the liquid phase into the atmosphere. S. typhimurium strains TAl530, TA1535. TAlOO and G46 respond with varying sensitivity to monofunctional alkylating agents (base-pair substitutions or deletions). Strains TA1536, TA1537 and TA1538. which are specifically reverted by frameshift mutagens, were unaffected by 207/, VC atmospheres even in the presence of liver fractions from rats or mice (Bartsch et ul. lot. cit.; Rannug et al. lot. cit.).
