SYNTHESIS RATES OF GLUTATHIONE AND ACTIVATED SULFATE (PAPS) AND RESPONSE TO CYSTEINE AND ACETAMINOPHEN ADMINISTRATION IN GLUTATHIONE-DEPLETED RAT HEPATOCYTES

The effects of cysteine and acetaminophen (AA) on the synthesis rates of glutathione (GSH), adenosine 3'-phosphate 5'-phosphosulphate (PAPS, activated sulphate) and the AA metabolites, AA-GSH and AA-sulphate were studied in rat hepatocytes depleted of GSH by diethyl maleate (DEM). The synthesis rates were determined simultaneously by a previously described radioactive tracer method. Preincubation of the hepatocytes with 0.7 mM DEM for 30 min depleted GSH by 59% (P < 0.05) and PAPS by 28% (P < 0.05). Incubation with a toxic AA concentration resulted in GSH synthesis at a rate of 95 nmol/(10(6) cells - min) which increased to 281 nmol/(10(6) cells - min) (P = 0.05) after addition of cysteine. However, increased GSH synthesis was not followed by increased AA-GSH synthesis [4.7 vs 4.8 nmol/(10(6) cells.hr)]. Also, PAPS synthesis increased after cysteine administration 110.2 to 19.1 nmol/(10(6) cells . min)] (P < 0.05) without any change in AA-sulphate synthesis 18.5 vs 18.3 nmol/(10(6) cells . hr)]. Thus, in contrast to hepatocytes with normal GSH concentration, cysteine stimulated both GSH and PAPS synthesis rates in GSH-depleted rat hepatocytes incubated with a toxic AA concentration without stimulation of AA-GSH or AA-sulphate synthesis rates, indicating that the hepatoprotective effect of cysteine on AA toxicity is primarily due to stimulation of a GSH-mediated reduction of the reactive AA metabolite N-acetyl-p-benzoquinoneimine back to AA.