METHYL-DONOR DEFICIENCY DUE TO CHEMICALLY-INDUCED GLUTATHIONE DEPLETION

Dietary deficiency of methionine (Met) is known to deplete cellular Me t and cause DNA hypomethylation, hut depletion of Met and impairment i n methylation due to chemically induced glutathione (GSH) depletion ha s escaped recognition. In this study, the effect of GSH depletion on t he Met pool and methylation capability was examined after bromobenzene (BB), a model GSH-depleting hepatotoxin, was administered to the Syri an hamster. An i.p. dose of BB (800 mg/kg) caused a rapid and extensiv e depletion of liver GSH; approximately 68% of the initial concentrati on was depleted during the first hour. The lowest level of GSH, only 4 % of the control, was detected at 5 h. GSH depletion was accompanied b y a prompt increase in liver Met during the first hour. This initial i ncrease was followed by an extensive depletion during the next 4 h. At 5 h after BB, Liver Met was 12% below the control value, and it remai ned around this concentration throughout the 24-h experiment. To furth er confirm these results, the endogenous Met pool was labeled with deu terated Met. The administration of L-Met-methyl-d(3) to the Syrian ham ster after GSH had been depleted by BB resulted in a significant prote ction of the liver against necrosis. The protection was accompanied by a marked incorporation of deuterated Met into the liver Met pool. The incorporation, which was determined by gas chromatography-mass spectr ometry, shows BB dose dependence. Approximately 53% of the liver Met w as labeled when a toxic BB dose (800 mg/kg) was used, while only 25% i ncorporation was found for the nontoxic dose (100 mg/kg). These result s were different from the controls, where only 15% incorporation was f ound. The differences in the incorporation indicate that there are dif ferences in the degree of utilization and/or depiction of Met in these hamsters, and these differences apparently are dependent upon the deg ree of toxicity and GSH depletion. The marked incorporation of deutera ted Met in the high-dose group was accompanied with a striking increas e in the methylation capability. Urinary excretion of the O- and S-met hylated 4- and 5-bromo-2-hydroxythiophenols and S-methylated 4- and 5- bromo-2-hydroxy-1,2-dihydrobenzenethiols was significantly increased w hen compared with the BB treated alone. Approximately 40-45% of the me thyl groups in these methylated BB metabolites were methyl-d(3). These results provide direct evidence that depletion of GSH leads to Met de pletion and also impairs the methylation processes.