Abstract
Acetaminophen (APAP) is a widely available antipyretic and analgesic; however, overdose of the drug inflicts severe damage to the liver. It is well established that the hepatotoxicity of APAP is initiated by formation of a reactive metabolite, N‑acetyl‑p‑benzoquinone imine (NAPQI), which can be detoxified by conjugation with reduced glutathione (GSH), a typical antioxidant. We recently found that the blood mRNA expression level of glutathione peroxidase 3 (Gpx3), which catalyzes the oxidation of GSH, is associated with the extent of APAP‑induced hepatotoxicity in mice. The present study was carried out to determine the in vivo and in vitro role of GPx3 in APAP‑induced hepatotoxicity. In in vivo experiments, oral administration of APAP to mice induced liver injury. Such liver injury was greater in males than in females, although no gender difference in the plasma concentration of APAP was found. Female mice had a 2‑fold higher expression of Gpx3 mRNA and higher plasma GPx activity than male mice. 17β‑estradiol, a major female hormone, decreased APAP‑induced hepatotoxicity and increased both the expression of blood Gpx3 mRNA and plasma GPx activity, suggesting that the cytoprotective action of this hormone is mediated by the increase in GPx3. To further clarify the role of GPx3 in APAP‑induced hepatotoxicity, we evaluated the effect of a change in cellular GPx3 expression resulting from transfection of either siRNA‑GPx3 or a GPx3 expression vector on NAPQI‑induced cellular injury (as assessed by a tetrazolium assay) in in vitro experiments using heterogeneous cultured human cell lines (Huh‑7 or K562). NAPQI‑induced cell death was reduced by increased GPx3 and was enhanced by decreased GPx3. These results suggest that GPx3 is an important factor for inhibition of APAP‑induced hepatotoxicity both in vivo and in vitro. To our knowledge, this is the first report to show a hepatoprotective role of cellular GPx3 against APAP‑induced liver damage.