Detoxification of Reactive Oxygen Species by A Nonpeptidyl Mimic of Superoxide Dismutase Cures Acetaminophen–Induced Acute Liver Failure in the Mouse

Abstract

Drug–induced acute liver failure (ALF) is a devastating and often fatal disease mainly caused by poisoning by acetaminophen (APAP). The toxic metabolite, N–acetyl–p–benzoquinone–imine (NAPQI), that leads to gluthatione depletion has been suspected to be the main effector of hepatocyte apoptosis during APAP–induced ALF. We have investigated whether reactive oxygen species (ROS) also play a role in APAP–induced ALF, and whether manganese III tetrakis (5,10,15,20 benzoic acid) (MnTBAP), a mimic of superoxide dismutase (SOD) with catalase–like activity, can treat the disease in mice. The effects of MnTBAP were tested on APAP–intoxicated mice and on isolated hepatocytes incubated with APAP. MnTBAP preventively and curatively administered significantly improved survival times, and dramatically reduced serum transaminase activity levels and parenchymal lesions in APAP–intoxicated mice. Whereas pretreatment with N–acetyl–l–cysteine (NAC) prevented ALF in a dose–dependent manner, the molecule was ineffective when curatively administered. The significant increase in glutathione peroxidase (Gpx) activity following APAP administration, and the beneficial effects of MnTBAP suggested that ROS were produced during APAP–induced ALF. A direct evidence of ROS generation was provided by flow cytometry of isolated hepatocytes incubated with APAP. In vitro, ROS production was associated with mitochondrial damage characterized by the collapse of transmembrane potential and the loss of cardiolipin content. In livers of intoxicated mice, ALF was associated with cytochrome c release that led to the activation of caspases–9 and –3. The capacity of MnTBAP to abrogate all those alterations suggests that ROS play a role in APAP–induced apoptosis of hepatocytes, and explains the beneficial effects of MnTBAP, which could be of interest in APAP–induced ALF in humans.