Nitric oxide from the inducible nitric oxide synthase (iNOS) increases theexpression of cytochrome P450 2E1 in iNOS-null hepatocytes in the absence of inflammatory stimuli

Nitric oxide (NO) can modulate numerous genes through several pathways, yet some genes may be modulated only in the presence of the inflammatory stimu li that upregulate the inducible nitric oxide synthase (iNOS) rather than b y NO alone. Furthermore, the role of prior expression of iNOS in the modula tion of genes by NO is unknown. We addressed these issues in hepatocytes ha rvested from iNOS-null (iNOS(-/-)) mice exposed to NO by treatment with NO donors or by infection with an adenovirus-expressing human iNOS (Ad-iNOS), rather than by stimulation with inflammatory cytokines, Differential displa y and gene array analyses performed on mRNA derived from iNOS(-/-) hepatocy tes demonstrated that infection with Ad-iNOS, but not infection with a cont rol adenovirus expressing the beta -galactosidase gene (Ad Lac Z), induced a gene fragment identical to cytochrome P450 2E1 (CYP2E1), Northern analysi s performed with this fragment demonstrated that treatment of iNOS(-/-) hep atocytes with Ad-iNOS or with the NO donor S-nitroso-N-acetyl-D,L-penicilla mine (SNAP), but not control treatment or infection with Ad-Lac Z, resulted in increased expression of CYP2EI, Inhibition of soluble guanylyl cyclase partially blocked the induction of CYP2E1 mRNA by Ad-iNOS, Rat hepatocytes treated with SNAP also exhibited increased expression of CYP2E1 mRNA, Preli minary studies, however, suggest that the induction of CYP2E1 in the rat he patocytes treated with cytokines was not reduced in the presence of a NOS i nhibitor. Our results suggest that CYP2E1 can be induced solely by NO deriv ed from iNOS, at least partly in a cyclic GMP-dependent manner and independ ently of inflammatory stimuli or of prior exposure to NO. (C) 2001 Academic Press.