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Alpha-naphthylisothiocyanate (ANIT) causes intrahepatic cholestasis by injuring biliary epithelial cells. Adaptive regulation of hepatobiliary transporter expression has been proposed to reduce liver injury during cholestasis. Recently, the oxidative stress transcription factor Nrf2 (nf-e2–related factor 2) was shown to regulate expression of hepatobiliary transporters. The purpose of this study was to determine whether ANIT-induced hepatotoxicity and regulation of hepatobiliary transporters are altered in the absence of Nrf2. For this purpose, wild-type and Nrf2-null mice were administered ANIT (75 mg/kg po). Surprisingly, ANIT-induced hepatotoxicity was similar in both genotypes at 48 h. Accumulation of bile acids in serum and liver was lower in Nrf2-null mice compared with wild-types treated with ANIT. Transporter mRNA profiles differed between wild-type and Nrf2-null mice after ANIT. Bsep (bile salt export pump), Mdr2 (multidrug resistance gene), and Mrp3 (multidrug resistance–associated protein) efflux transporters were increased by ANIT in wild-type, but not in Nrf2-null mice. In contrast, mRNA expression of two hepatic uptake transporters, Ntcp (sodium-taurocholate cotransporting polypeptide) and Oatp1b2 (organic anion transporting peptide), were decreased in both genotypes after ANIT, with larger declines in Nrf2-null mice. mRNA expression of the transcriptional repressor of Ntcp, small heterodimeric partner (SHP), was increased in Nrf2-null mice after ANIT. Furthermore, hepatocyte nuclear factor 1α (HNF1α), which regulates Oatp1b2, was downregulated in ANIT-treated Nrf2-null mice. Preferential upregulation of SHP and downregulation of HNF1α and uptake transporters likely explains why Nrf2-null mice exhibited similar injury to wild-types after ANIT. A subsequent study revealed that treatment of mice with the Nrf2 activator oltipraz protects against ANIT-induced histological injury. Despite compensatory changes in Nrf2-null mice to limit ANIT toxicity, pharmacological activation of Nrf2 may represent a therapeutic option for intrahepatic cholestasis. [ABSTRACT FROM AUTHOR]

Alpha-naphthyl isothiocyanate (ANIT) is a hepatotoxicant that produces acute intrahepatic cholestasis in rodents. Farnesoid X receptor (FXR) and pregnane X receptor (PXR) are two major bile acid sensors in liver. The purpose of this study was to characterize the regulation of hepatic transporters by FXR and PXR during ANIT-induced liver injury. Wild-type, FXR-null, and PXR-null mice were administered ANIT (75 mg/kg, po) and evaluated 48 h later for hepatotoxicity and messenger RNA (mRNA) expression of basolateral uptake (sodium taurocholate–cotransporting polypeptide, organic anion transporting polypeptide [Oatp] 1a1, Oatp1a4, Oatp1b2) and efflux transporters (organic solute transporter [Ost] α, Ostβ, multidrug resistance–associated protein [Mrp] 3, Mrp4), as well as canalicular transporters (bile salt export pump [Bsep], Mrp2, multidrug resistance protein 2 [Mdr2], ATPase, class I, type 8B, member 1 [Atp8b1]). Livers from wild-type and PXR-null mice had comparable multifocal necrosis 48 h after ANIT. However, ANIT-treated FXR-null mice have fewer and smaller necrotic foci than wild-type mice but had scattered single-cell hepatocyte necrosis throughout the liver. Serum alanine transaminase, alkaline phosphatase (ALP), and direct bilirubin were increased in all genotypes, with higher ALP levels in FXR-null mice. Serum and liver unconjugated bile acids were higher in ANIT-treated FXR-null mice than the other two genotypes. ANIT induced mRNA expression of Mdr2, Bsep, and Atp8b1 in wild-type and PXR-null mice but failed to upregulate these genes in FXR-null mice. mRNA expression of uptake transporters declined in livers of all genotypes following ANIT treatment. ANIT increased Ostβ and Mrp3 mRNA in livers of wild-type and PXR-null mice but did not alter Ostβ mRNA in FXR-null mice. In conclusion, FXR deficiency enhances susceptibility of mice to ANIT-induced liver injury, likely a result of impaired induction of hepatobiliary efflux transporters and subsequent hepatic accumulation of unconjugated bile acids. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid and perfluorodecanoic acid (PFDA) are commonly used as emulsifiers and surfactants in fluoropolymer manufacturing and are known peroxisome proliferator–activated receptor alpha (PPARα) agonists. PPARα activation induces β- and ω-oxidation enzymes such as Cyp4a14 and acyl-CoA oxidase, which are a likely cause of subsequent oxidative stress and peroxisome proliferation. Conversely, NF-E2-related factor-2 (Nrf2) is a transcription factor that protects against oxidative stress and inflammation by regulating several detoxification and xenobiotic transporter genes. Because PFDA markedly induces hepatic metabolism and oxidative stress, we hypothesized that PFDA exposure would increase expression of hepatic efflux multidrug resistance–associated protein (Mrp) transporters. A single PFDA dose (80 mg/kg) administered to mice increased hepatic Mrp3 (fourfold) and Mrp4 (31-fold) mRNA expression. Upregulation of Mrp3 and Mrp4 correlated with elevated serum-conjugated bilirubin and bile acids, respectively. To determine the mechanism of Mrp3 and Mrp4 induction, PFDA was administered to Nrf2-null mice, PPARα-null mice, and mice pretreated with gadolinium chloride, a Kupffer cell–depleting chemical capable of inhibiting the inflammatory cytokine response. In both PPARα- and Nrf2-null mice, maximal induction of Mrp3 and Mrp4 mRNA after PFDA administration was attenuated. Gadolinium chloride pretreatment reduced serum and hepatic tumor necrosis factor-α levels after PFDA treatment, as well as Mrp4 mRNA expression by 30%, suggesting that Kupffer cell–derived mediators may contribute to Mrp induction. Thus, after PFDA administration, the liver mounts a compensatory hepatoprotective response via PPARα and Nrf2, markedly increasing Mrp3 and Mrp4 expression, with corresponding increases in serum of known Mrp3 and Mrp4 substrates. [ABSTRACT FROM AUTHOR]

Hepatic ischemia-reperfusion (IR) injury during liver transplantation can lead to cholestasis and remote organ dysfunction. Multidrug resistance–associated proteins (Mrps) are efflux transporters known to transport a diverse set of substrates, such as amphipathic chemicals, organic anions, and endogenous molecules. The purpose of this study was to determine the effect of hepatic IR injury on the expression of Mrps in rat liver and kidney. Male Sprague-Dawley rats were subjected to 60 min of partial hepatic ischemia. At various times after reperfusion (0, 3, 6, 24, and 48 h), the ischemic lobes were harvested as well as kidneys. RNA and protein expression of Mrps in livers and kidneys were determined by the branched DNA method, Western blot analysis, and tissue immunofluorescence. Mrp2 mRNA and protein expression in livers decreased after IR. Conversely, Mrp2 mRNA and protein expression in kidneys increased after IR. Mrp3 mRNA expression, and Mrp4 mRNA and protein expression in kidneys transiently increased after IR. The intensity of immunofluorescent staining of Mrp2 corresponded to changes in Mrp2 expression in livers and kidneys after IR as detected by Western blot analysis and was localized to the apical membrane domain in both tissues. These results demonstrate that after hepatic IR, downregulation of hepatic Mrp2 and upregulation of renal Mrp2 occur. These decreases in hepatic Mrp2 may contribute to cholestasis, yet increases in kidney may protect from oxidative stress and/or inflammation after hepatic IR. [ABSTRACT FROM AUTHOR]