Modulation of acetaminophen-induced alterations of antioxidant defense enzymes by antioxidants or glutathione precursors in cultured hepatocytes

It has been shown that acetaminophen [(N-acetyl-p-aminophenol) (APAP)]- induced hepatocyte injury involves depression of antioxidant defenses and oxidative stress. The purpose of this study was to investigate possible protective effects of two antioxidants and two glutathione (GSH) precursors against APAP-induced alterations of antioxidant defense enzymes using hepatocyte culture system as a toxicity model. Rat hepatocyte culture plates were divided into five groups, and pretreated with none, alpha-tocopheryl succinate [(vitamin E succinate) (TS)], L-ascorbic acid [(vitamin C), (AA)], N-acetylcysteine (NAC) and S-adenosyl methionine (SAM). After 24 hours of pretreatment, one half of the plates in each group were treated with 5 mM APAP for another 24 hours. The cells were harvested, homogenized and biochemical analyses were performed. The results showed that pretreatment with each of the four compounds partially protected against lactic dehydrogenase leakage from the cells, partially prevented the decline of cellular GSH levels and completely prevented the depression of glutathione reductase (GR) activity caused by APAP. In addition, AA, NAC or SAM partially prevented the decline of APAP-induced protein-thiol levels, and NAC or SAM also completely prevented the depression of glutathione peroxidase (GPx) activity. The results suggest that vitamin E, vitamin C, NAC or SAM can modulate APAP-induced depression of antioxidant defense enzymes, and thus, may contribute to the attenuation of APAP toxicity.