Induction of hepatic Bach1 mRNA expression by carbon tetrachloride-induced acute liver injury in rats

Hepatic oxidative stress is a major contributor to the pathogenesis of several acute liver diseases. Diagnostic markers of hepatic oxidative stress may facilitate early detection and intervention. Bach1 is an oxidative stress-responsive transcription factor that represses heme oxygenase 1 (HO-1), the rate-limiting enzyme in the catabolism of heme, a potent pro-oxidant. We previously demonstrated that carbon tetrachloride (CCl 4 ) causes oxidative hepatic injury in rats, exacerbated by free heme, suggesting that CCl 4 may affect Bach1 gene expression. In the present study, we used northern blot analysis to measure Bach1, HO-1 and δ-aminolevulinate synthase (ALAS1; a heme biosynthesis enzyme) mRNA expression levels during acute hepatic injury induced by CCl 4 (at doses of 0.1, 1.0 and 2.0 ml/kg body weight). Oxidative injury was assessed by measuring serum alanine aminotransferase (ALT), hepatic malondialdehyde (MDA) and glutathione (GSH) content. Treatment with CCl 4 induced a significant dose-dependent increase in Bach1 mRNA 1-3 h after administration. Bach1 mRNA peaked at 6 h after CCl 4 treatment (1 ml/kg), followed by a rapid decrease and gradual return to baseline by 12 h after treatment. The timecourse of transient Bach1 mRNA induction roughly mirrored that of HO-1 mRNA, while ALAS1 mRNA was inversely downregulated. Serum ALT levels and hepatic MDA concentration were significantly increased at 24 h after CCl 4 treatment, while the hepatic GSH content was significantly reduced within 3 h of treatment. Serum ALT levels were positively correlated with Bach1 mRNA levels. These findings indicate that Bach1 mRNA is transiently induced in rat liver by CCl 4 , possibly as a regulatory mechanism to restore HO-1 to baseline following free heme catabolism. Our findings also suggest that Bach1 mRNA expression may be a novel indicator of the extent of oxidative hepatic injury caused by free heme.