SPECIES DIFFERENCES IN THE 'IN VITRO' METABOLISM OF AFLATOXIN B₁ AND PALMOTOXINS B₀ AND G₀

Abstract

An initial experiment was carried out on the variation in the production of toxins with days of incubation by Aspergillus flavus link grown on palm sap medium. This was compared with the production of toxins by the fungus grown under identical conditions on the yeast extract sucrose medium. The attendant variations in pH and weight of mycelial matt were recorded. Peak production of toxin on palm sap medium was observed on the 5th day of incubation while peak production on yeast-extract medium was on the sixth day. Further investigation of some physical characteristics of palmotoxins B₀ and G₀ have been carried out. Ultraviolet, Infra-red, Nuclear magnetic resonance and fluorescence spectra of palmotoxins B₀ and G₀ have been obtained. When compared with known aflatoxins, similar features are discernible. The susceptibility of 20-day old rats to sub-lethal doses of palmotoxins B₀ and G₀ were tested. Decrease in weight in relation to dosage; increase in the value of serum glutamic-oxaloacetic acid transaminase and serum alkaline phosphatase, when compared with control animals injected a carrier solvent, were observed in the case of palmotoxin B₀. There was however, no remarkable difference in the above indices of toxicity for animals treated with palmotoxin G₀. Animals treated with aflatoxin were also used for comparison. The metabolism of Aflatoxin B₁ and aflatoxin G₁ in

the rat in vitro have been compared. Two metabolites of aflatoxin B₁ believed to correspond to aflatoxins M₁ and B₂ₐ respectively were observed on t.l.c. Similarly, two isolates from aflatoxin G₁ - probably the 'GM' and G₂ₐ were also observed on thin layer plates. The rat liver microsomal fraction hydroxylated and demethylated aflatoxin B₁ at a higher rate than aflatoxin B₁.

The effect of variation of co-factors on the enzyme activity of the microsomal-plus-soluble fractions of rat liver with respect to the metabolism of palmotoxin B₀ and palmotoxin G₀ were investigated. Effects of variation of the concentration of NADP and changes in the pH of incubation medium on the demethylation of palmotoxins B₀ and G₀ were also investigated. Optimal conditions for the metabolism of palmotoxins B₀ and G₀ were thus obtained. Species variation in the 'in vitro metabolism of aflatoxin B₁ have been confirmed using eleven commonly available species. Using methods identical to those for the study of aflatoxin B₁ metabolism, the metabolism of palmotoxins B₀ and G₀ have been in the same animals, using both liver slices and microsomal-plus-soluble fractions of their livers. In general, a higher rate of metabolism was recorded for aflatoxin B₁ in all test animals than for palmotoxins B₀ and G₀ . The trend in metabolite formation from aflatoxin B₁ and palmotoxin B₀ appear similar. Evidence was obtained to show a great variation in the amount of isolates and the demethylation by test animals. The effect of phenobarbitone treatment of animals on the enzyme activities has been studied. Pretreated animals showed a higher rate of hydroxylation and demethylation in all three toxins. Carbon monoxide inhibited the hydroxylation and demethylation of the toxins.