Inactivation of aflatoxin b 1 mutagenicity by thiols

Abstract

The mutagenicity of aflatoxin B 1 to Salmonella typhimurium strain TA98 decreased rapidly upon exposure of aflatoxin B 1 to various thiols in aqueous solution. Mutagenic activity was reduced to control values within 24 hr with N-acetyl- l-cysteine (NAC), N-2-mercaptopropionylglycine (MPG), mercaptoethanol, reduced glutathione or mercaptopropionic acid at pH values near 4. Mercaptoacetic acid, mercaptosuccinic acid, cysteine, acetyl- d, l-homocysteine thiolactone, cysteine methyl ester, d-penicillamine and β-mercaptoethylamine were less effective. Relatively high thiol concentrations ( ⪖ 0.25 m) were required to achieve complete inactivation within 24 hr with the thiols tested. The inactivation rate was strongly dependent on thiol concentration and pH, but was relatively independent of the aflatoxin concentration under the conditions examined. With MPG and NAC reaction rates were much slower at neutral pH values than at pH's between 3 and 4. HPLC and thin-layer Chromatographic examination of aflatoxin B 1 solutions partially inactivated with NAC revealed the formation of a new product at a rate that correlated with the disappearance of aflatoxin B 1 and the loss of mutagenic activity. This reaction product has not yet been identified, but the evidence suggests that it is the product of an addition of the thiol at the difuran region of the aflatoxin.