Nitric oxide mimics transcriptional and post-translational regulation during α-Tocopherol cytoprotection against glycochenodeoxycholate-induced cell death in hepatocytes

Background & Aims: Reactive oxygen species (ROS) and nitric oxide (NO) exert a relevant role during bile acid-induced hepatotoxicity. Whether alpha-Tocopherol regulates oxidative and nitrosative stress, bile acid transporter expression and their NO-dependent post-translational modifications, and cell death were assessed in vitro and in vivo. Methods: alpha-Tocopherol and/or NO donors (DETA-NONOate or CSNO, and V-PYRRO/NO) were administered to glycochenodeoxycholic acid (GCDCA)-treated cultured human hepatocytes or to bile duct obstructed rats. Cell injury, superoxide anion (O-2(.-)) production, as well as inducible nitric oxide synthase (NOS-2), cytochrome P4507A1 (CYP7A1), heme oxygenase-1, (H0-1) and bile acid transporter expression were determined. Cysteine S-nitrosylation and tyrosine nitration of Na+-taurocholate co-transporting polypeptide (NTCP), as well as taurocholic acid (TC) uptake were also evaluated. Results: GCDCA-induced cell death was associated with increased (O-2(.-)) production, NTCP and HO-1 expression, and with a reduction of CYP7A1 and NOS-2 expression. alpha-Tocopherol reduced cell death, (O-2(.-)) production, CYP7A1, NTCP, and HO-1 expression, as well as increased NOS-2 expression and NO production in GCDCA-treated hepatocytes. alpha-Tocopherol and NO donors increased NTCP cysteine S-nitrosylation and tyrosine nitration, and reduced TC uptake in hepatocytes. alpha-Tocopherol and V-PYR-RO/NO reduced liver injury and NTCP expression in obstructed rats. Conclusions: The regulation of CYP7A1, NTCP, and HO-1 expression may be relevant for the cytoprotective properties of alpha-Tocopherol and NO against mitochondrial dysfunction, oxidative stress and cell death in GCDCA-treated hepatocytes. The regulation of NO-dependent post-translational modifications of NTCP by alpha-Tocopherol and NO donors reduces the uptake of toxic bile acids by hepatocytes. 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.