METABOLIC ALTERATIONS IN HEPATOCYTES PROMOTED BY THE HERBICIDES PARAQUAT, DINOSEB AND 2,4-D

The cytotoxic effects of the herbicides paraquat (1,1'-dimethyl-4,4'-b ipyridylium dichloride), dinoseb (2-sec-butyl-4,6-dinitrophenol) and 2 ,4-D (2,4-dichlorophenoxyacetic acid) on freshly isolated rat hepatocy tes were investigated. Paraquat and 2,4-D (1-10 mM) caused a dose and time dependent cell death accompanied by depletion of intracellular gl utathione (GSH) and mirroring increase of oxidized glutathione (GSSG). Dinoseb, the most effective cytotoxic compound under study (used in c oncentrations 1000 fold lower than paraquat and 2,4-D), exhibited mode rate effects upon the level of GSH and GSSG. These limited effects are at variance with significant effects upon the adenine and pyridine nu cleotide contents. ATP and NADH levels are rapidly depleted by herbici de metabolism. This depletion is observed in the millimolar range for paraquat and 2,4-D and in the micromolar range for dinoseb. 2,4-D comp letely depletes cellular ATP, with subsequent cell death, as detected by LDH leakage. Paraquat rapidly depletes NADH, according to the redox cycling of the herbicide metabolism. The most effective compound is d inoseb since it exerts similar effects as described for paraquat and 2 ,4-D at concentrations 1000 fold lower. Simultaneously with NADH and A TP depletion, the levels of ADP, AMP and NAD+ increase in hepatocytes incubated in the presence of the herbicides. In contrast to NADH, the time course and extent of ATP depletion and fall in energy charge corr elate reasonably with the time of onset and rate of cell death. It is concluded that the herbicides, paraquat and 2,4-D are hepatotoxic and initiate the process of cell death by decreasing cellular GSH. As a co nsequence of this primary disturbance, alteration of adenine and pyrid ine nucleotides contents is a critical event in the induction of irrev ersible cell injury.