EFFECTS OF VITAMINN C ON THE IN VTRO AND IN VIVO METABOLISM OF SOME AFLATOXINS

Abstract

In view of the role of vitamin C in the etiology of cancer, we have undertaken the study of some carcinogenic toxins: the aflatoxins. Male and female weaning rats, rabbits or guinea pigs, divided into three groups were maintained for thirty days on an experimental diet either with or without vitamin C. twenty-four hours after the last feeding, the animals were decapitated, and the liver 9000 x g supernatant or liver slices were prepared from the three animals species. While the O-demethyletion of AFB1 , AFB2, AFG1 and AFG2 with liver slices was reduced with high level of vitamin C intake in female rabbits and rats, or increased in male of the same species, the O-demethylation of aflatoxin B1 (AFB1) and G1 (AFG1) by genuine pigs showed that increase in vitamin C in the diet also increased the production of formaldehyde from those toxins in both sexes. Though the demethyletion of aflatoxin G1 was higher than aflatoxin B1 in both male and female, the two toxins O-demethylation activity in females was more sensitive to the effect of vitamin C high level intake than in males. However, using hepatic 9000 x g supernatant of the rabbits, the demethylase activity with respect to AFB1, AFB2, AFG1 and AFG2 decreased in females with high consumption of vitamin C, and increased with males with the same regime. The effect of dietary vitamin C on the in vitro demethylation with 9000 x g supernatant of male and female Wistar rats was identical to that female rabbits on control diet. The high level dietary vitamin C group, male increased activity while female decreased. To ascertain whether the effect of various levels of vitamin C on the in vitro metabolism could modified after a long period of feeding, 9000 x g supernatant of male and female Wistar rats fed for sixty and ninety days were used for in vitro metabolism. The production of formaldehyde from AFB1 , AFB2, AFG1 and AFG2 increased with increase in vitamin C consumption at the level of 1.88mg/ml after sixty days, ninety days in the drinking water for females, and decreased at a level of 5.4 mg/ml after sixty days, ninety days, with same sex. The formaldehyde produced by male rats O-demethylation of to AFB1, and AFB2 after sixty days increased in the group on the high level of dietary vitamin C as at thirty days. But a decrease was observed with AFG1 and AFG2 at sixty days and ninety days. At this later period, vitamin C consumption seemed to reduce the O-demethylation of AFB1 and AFB2 in both male and female rats. The aflatoxin B1 (AFB1) hydroxylase-activity using 9000x g supernatant of rats, increased in both sexes with the increased intake of vitamin C. In rabbits, the amount of AFB1 metabolized was less affected by the increased dose of vitamin C. some hydroxylated metabolites obtained, aflatoxicol (R0) essentially AFM1 decreased with the increased in vitamin C consumption in both sexes. The female sub-groups fed without vitamin C, produced more aflatoxicol and aflatoxin M1 (AFM1) than male. With guinea pigs, the intake of 1.88mg/ml of vitamin C increased the amount of AFB1 metabolized or the production of metabolites by male, while there was a decreased with female. On the other hand, the high intake 5.4 mg/ml of vitamin C decreased the hydroxylase activity in both sexes; the metabolism was higher with male than female in all groups. The hydroxylation activity evaluated by the quantity of AFB1 metabolized was quite different in male and female rats at sixty and ninety days. The AFB1 metabolized increased in the group of male rats maintained on a high level of dietary vitamin C at sixty days and decreased at ninety days. In female maintained on high vitamin C diet or on the control diet, there was an increased metabolism of AFB1 evident at thirty days. However at sixty days and ninety days, in the female rats fed with the same level of vitamin C, the 9000 x g supernatant showed a decreased activity. The hydroxylase activity was higher in male than female. The liver, the large and small intestine wall and contents of rats fed thirty days with experimental diet either devoid of or with vitamin C, and to which AFG1 (2mg/kg b.w.) was injected were extracted and analysed on TLC for the presence of aflatoxin B1 and its metabolites. The appearance of fluorescent metabolites was more obvious with the group of female rats fed without vitamin C. The bile extract collected by biliary intubation for ninety minutes from male rats fed with various levels of vitamin C showed that AFM1 was often the only metabolite found in group of rats on high level of vitamin C, while animals deficient in dietary vitamin C produced several unknown metabolites of parent toxin.