Cysteamine in combination with N-acetylcysteine prevents acetaminophen-induced hepatotoxicity.

N-Acetylcysteine (NAC) is protective against acetaminophen-induced hepatotoxicity primarily by providing precursor for the glutathione synthetase pathway, while cysteamine has been demonstrated to alter the cytochrome P-450 dependent formation of toxic acetaminophen metabolite. Mice administered acetaminophen (500 mg/kg) had elevations of serum alanine aminotransferase (ALT) to 273.0 +/- 37.5 and 555.8 +/- 193.4 U/mL at 12 and 24 h, respectively, after injection. Administration of cysteamine (100 mg/kg) or NAC (500 mg/kg) significantly reduced serum ALT activity (p less than 0.001). Reducing the dose of NAC or cysteamine by 50% greatly reduced their hepatoprotective effect while the co-administration of the reduced doses of NAC (250 mg/kg) and cysteamine (50 mg/kg) following acetaminophen overdose prevented elevation of serum ALT activity (39.2 +/- 1.17 and 32.5 +/- 5.63 U/mL at 12 and 24 h post-injection, p less than 0.001) and preserved normal mouse hepatic histology. Neither NAC (500 mg/kg), cysteamine (100 mg/kg), or the lower doses in combination of both agents were found to alter the half-life or peak levels of acetaminophen. Liver microsomal aryl hydrocarbon hydroxylase activity measured 24 h after drug administration was not significantly different between treatment groups and controls receiving only saline. These results indicate a possible role for the concomitant use of NAC and cysteamine in the prevention of hepatic necrosis following toxic doses of acetaminophen. Neither decrease in plasma acetaminophen levels nor depression of cytochrome P-450 enzyme activity appears to be the mechanism of protection when these doses of NAC, cysteamine, or both drugs together are administered with a toxic dose of acetaminophen in mice.