The nitroxide stable radical tempo prevents metal-induced inhibition of CYP1A1 expression and induction.

Heavy metals are known to provoke oxidative stress in fish liver cells. Because H2O2, OH*- and intracellular superoxide are involved in this oxidation, we investigated the effect of nitroxide radical, 2,2,6,6-tetramethylpiperidinyl-N-oxyl (abbreviated as TEMPO), a cell-permeable agent possessing antioxidant properties, on CYP1A expression in trout (Oncorhynchus mykiss) hepatocytes. 3-methylcholanthrene (3-MC) induced the CYP1A-related EROD activity. This induction was inhibited by concomitant exposure to Cd (II), Cu (II), Pb (II) or Zn (II). CYP1A mRNA levels were also reduced. Simultaneous treatment with 3-MC, a heavy metal and TEMPO suppressed both the inhibition of EROD activity and the decrease of CYP1A mRNA expression. These results suggest a working hypothesis that heavy metals produce multiple oxidative effects, including generation of hydroxyl radicals, which could down-regulate CYP1A1 expression. This metal-induced inhibition was prevented by TEMPO, which might protect trout hepatocytes by scavenging free radicals and thus preventing their inhibitory effects on CYP1A induction and expression.