Relationships between formaldehyde metabolism and toxicity and glutathione concentrations in isolated rat hepatocytes

Abstract

The metabolism and toxicity of formaldehyde (CH 2O) in isolated rat hepatocytes was found to be dependent upon the intracellular concentration of glutathione (GSH). Using hepatocytes depleted of GSH by treatment with diethyl maleate (DEM), the rate of CH 2O (5.0 mM) disappearance was significantly decreased. Formaldehyde decreased the concentration of GSH in hepatocytes, probably by the extrusion of the CH 2O-GSH adduct, S-hydroxymethylglutathione. Formaldehyde toxicity was potentiated in cells pretreated with 1.0 mM DEM as measured by the loss of membrane integrity (NADH stimulation of lactate dehydrogenase (LDH) activity) and an increase in lipid peroxidation (formation of thiobarbituric acid-reactive compounds). This potentiation of toxicity was both CH 2O concentration-dependent and time-dependent. There was an excellent correlation between the increase in lipid peroxidation and the decrease in cell viability. L-Methionine (1.0 mM) both protected the cells from toxicity caused by the combination of 8.0 mM CH 2O and 1.0 mM DEM and increased the cellular GSH concentration. The antioxidants, ascorbate, butylated hydroxytoluene (BHT) and α-tocopherol (10, 25 and 125 μM), all exhibited dose-dependent protection against toxicity produced by 8.0 mM CH 2O and 1.0 mM DEM. At toxic concentrations of CH 2O (10.0–13.0 mM), administered by itself, lipid peroxidation did not increase concomitantly with the decrease in cell viability and the addition of antioxidants (125 μM) did not influence CH 2O toxicity. These results suggest that CH 2O toxicity in GSH-depleted hepatocytes may be mediated by free radicals as a result of the effect of CH 2O on a critical cellular pool of GSH. However, cells with normal concentrations of GSH are damaged by CH 2O by a different mechanism.