Therapeutic doses of acetaminophen stimulate the turnover of cysteine and glutathione in man

Abstract

In spite of the importance of glutathione (GSH) in the detoxification of toxic metabolites of drugs, virtually nothing is known about the regulation of hepatic GSH homeostasis in man. In order to estimate the turnover of hepatic GSH and to assess the effect of different doses of acetaminophen (paracetamol) on the synthesis of GSH in man, [3H]cystine and varying doses of acetaminophen were administered to healthy volunteers, and the time course of the specific activity of the cysteine moiety of N-acetylcysteinyl-acetaminophen excreted in urine was followed. The fractional rate of turnover of the tracer in N-acetylcysteinyl-acetaminophen increased significantly from 0.031 +/- 0.007 h-1 after doses of acetaminophen ranging from 50 to 300 mg to 0.045 +/- 0.011 and 0.121 +/- 0.027 h-1 following 600 and 1200 mg of acetaminophen, respectively. The data indicate that therapeutic doses of acetaminophen markedly stimulate the rate of turnover of the pool of cysteine available for the synthesis of GSH, most likely due to an increased rate of synthesis of GSH which is required to detoxify the toxic metabolite of acetaminophen. Patients who are not able to respond to a similar demand on their stores of GSH by increasing the synthesis of GSH may be at higher risk of developing hepatic injury from drugs that require GSH for their detoxification.