Glutathione depletion modulates methanol, formaldehyde and formate toxicity in cultured rat conceptuses

Abstract

The proposed use of methanol (H₃COH) as an alternative to fossil fuels has prompted concern about potential health risks resulting from widespread environmental exposure. Methanol is teratogenic in rodents and, although the exact toxic species is not known, teratogenesis may result from the enzymatic biotransformation of H₃COH to formaldehyde (CH₂O) and formic acid causing increased biological reactivity and toxicity. A protective role for the antioxidant glutathione (GSH) has been described for H₃COH, CH₂O and formic acid toxicity in various biological systems but has yet to be evaluated in the developing conceptus. Whole embryo culture studies were conducted using GD 10-11 rat conceptuses to elucidate the relationship between H₃COH and its metabolites and GSH status. Methanol exposure produced a decrease in normal growth parameters and a dose-dependent loss of viability. CH₂O had deleterious effects on embryo growth and viability. Sodium formate (HCOONa) exposure resulted in a high mortality rate but viable embryos did not manifest any abnormalities. Methanol, CH₂O, and HCOONa all produced a significant depletion of GSH in both embryo and VYS. Inhibition of GSH synthesis by L-buthionine-S,R-sulfoximine (BSO) treatment exacerbated H₃COH, CH₂O and HCOONa embryotoxicity. Interestingly, only H₃COH/BSO and CH₂O/BSO co-treatments caused increased malformation, while embryos treated with HCOONa/BSO did not produce any developmental deformities. These results implicate CH₂O as the most embryotoxic H₃COH metabolite, on a molar basis, in terms of causing dysmorphogenesis, alterations of normal growth parameters and embryolethality. HCOONa was selectively embryolethal and did not produce dysmorphogenesis. CH₂O toxicity is potentiated by GSH depletion, indicating that GSH may be more directly involved in its detoxication in the embryo.