Cytotoxicity, thiol depletion and inhibition of O6-methylguanine-DNA methyltransferase by various aldehydes in cultured human bronchial fibroblasts.

Lipid peroxidation aldehydes of the 4-hydroxy-alpha, beta-unsaturated type, as well as the tobacco-smoke related alpha, beta-unsaturated aldehyde, acrolein, were highly cytotoxic and decreased the intracellular thiol content in cultured human bronchial fibroblasts after treatment with micromolar concentrations. In comparison, formaldehyde and acetaldehyde were less toxic and 100- to 300-fold higher doses were required to affect cell survival or thiol levels. The unsaturated aldehydes also markedly inhibited the DNA repair enzyme O6-methylguanine-DNA methyltransferase known to have a cysteine residue in its active site, but had no effect on the activity of uracil-DNA glycosylase. Our results indicate that reactive aldehydes of either exogenous or endogenous origin have direct cytotoxic effects and may also make cells more susceptible to other toxic chemicals due to an impairment in cellular defense mechanisms, e.g., DNA repair and detoxification by systems requiring glutathione.