Acetaminophen (AAP) overdose causes severe liver injury and is the leading cause of acute liver injury in humans. The mechanisms participating in its toxic effect are glutathione depletion, oxidative stress and mitochondrial dysfunction. S-adenosylmethionine (SAMe) is the principal biological methyl donor and is also a precursor of glutathione. In our previous studies we have documented a protective action of SAMe against various toxic injuries of rat hepatocytes in primary cultures. The aim of this study was to evaluate a possible protective effect of SAMe against AAP-induced toxic injury of primary rat hepatocytes. Hepatocytes were exposed to AAP (2.5 mM) or AAP together with SAMe at the final concentrations of 5, 25 or 50 mg/l for 24 h. Incubation of hepatocytes with AAP caused a significant increase of the leakage of lactate dehydrogenase (LDH) (p < 0.001) and decline of the activity of cellular dehydrogenases (WST-1) (p < 0.001). Co-incubation of hepatocytes with SAMe at any dose did not improve these markers of cellular integrity. The functional indicators improved in hepatocytes co-cultured with SAMe -urea production was significantly increased when using the highest dose of SAMe (p < 0.05); albumin synthesis was higher in all cultured hepatocytes exposed to SAMe (p < 0.05). SAMe did not influence AAP-induced decrease of cellular content of glutathione. Mitochondrial respiration of harvested digitonin-permeabilized hepatocytes was measured; Complex II was more sensitive to toxic action of AAP, respiration was decreased by 20%. This decrease was completely abolished by SAMe.
Hepatotoxicity, hepatoprotective effect, mitochondrial membrane potential, urea, albumin, glutathione, LDHAcetaminophen (AAP) is a widely used, relatively safe analgesic/antipyretic drug. Nevertheless, AAP overdose causes centrilobular necrosis of the liver and is the leading cause of acute liver injury in humans in the United States and most of Europe (Lee 2007). The primary metabolic pathway for AAP is glucuronidation and sulphation in the liver; this yields relative non-toxic metabolites, which are excreted into bile (Mitchell et al. 1973). AAP hepatotoxicity is dependent on another metabolic pathway. The remaining part of AAP dose, which is not directly conjugated with the hydrophylic group, is biotransformed by the cytochrome P450 family to an electrophilic, highly reactive metabolite N-acetylp-benzoquinone imine (NAPQI), which is detoxified by glutathione (Jaeschke and Bajt 2006). However, if the formation of NAPQI exceeds the capacity of liver glutathione (GSH), this reactive metabolite forms covalent adducts primarily with cysteine residues on various cellular proteins (Nelson and Bruschi 2003; Allameh and Alikhani 2006). The most important mechanism of AAP-induced cell death seems to be a change in the function of critical cellular proteins due to covalent bindings. Numerous cytosolic, mitochondrial, ribosomal, microsomal, and nuclear proteins bound to AAP have been identified. Nevertheless, the primary cellular targe...