Nrf2-and PPARα-Mediated Regulation of Hepatic Mrp Transporters after Exposure to Perfluorooctanoic Acid and Perfluorodecanoic Acid

Perfluorooctanoic acid and perfluorodecanoic acid (PFDA) are commonly used as emulsifiers and surfactants in fluoropolymer manufacturing and are known peroxisome proliferator-activated receptor alpha (PPAR alpha) agonists. PPAR alpha activation induces beta- and omega-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, PPAR alpha-null mice, and mice pretreated with gadolinium chloride, a Kupffer cell-depleting chemical capable of inhibiting the inflammatory cytokine response. In both PPAR alpha- 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-alpha 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 PPAR alpha and Nrf2, markedly increasing Mrp3 and Mrp4 expression, with corresponding increases in serum of known Mrp3 and Mrp4 substrates.