Sphingosine 1-phosphate receptor 2/adenylyl cyclase/protein kinase A pathway is involved in taurolithocholate-induced internalization of Abcc2 in rats.

Taurolithocholate (TLC) is a cholestatic bile salt that induces disinsertion of the canalicular transporter Abcc2 (Mrp2, multidrug resistance-associated protein 2). This internalization is mediated by different intracellular signaling proteins such as PI3K, PKCε and MARCK but the initial receptor of TLC remains unknown. A few G protein-coupled receptors interact with bile salts in hepatocytes. Among them, sphingosine-1 phosphate receptor 2 (S1PR2) represents a potential initial receptor for TLC. The aim of this study was to evaluate the role of this receptor and its downstream effectors in the impairment of Abcc2 function induced by TLC. In vitro, S1PR2 inhibition by JTE-013 or its knockdown by small interfering RNA partially prevented the decrease in Abcc2 activity induced by TLC. Moreover, adenylyl cyclase (AC)/PKA and PI3K/Akt inhibition partially prevented TLC effect on canalicular transporter function. TLC produced PKA and Akt activation, which were blocked by JTE-013 and AC inhibitors, connecting S1PR2/AC/PKA and PI3K/Akt in a same pathway. In isolated perfused rat liver, injection of TLC triggered endocytosis of Abcc2 that was accompanied by a sustained decrease in the bile flow and the biliary excretion of the Abcc2 substrate dinitrophenyl-glutathione until the end of the perfusion period. S1PR2 or AC inhibition did not prevent the initial decay, but they accelerated the recovery of these parameters and the reinsertion of Abcc2 into the canalicular membrane. In conclusion, S1PR2 and the subsequent activation of AC, PKA, PI3K and Akt is partially responsible for the cholestatic effects of TLC through sustained internalization of Abcc2.

Role of ERK1/2 in TNFα-induced internalization of Abcc2 in rat hepatocyte couplets.

TNFα is a cytokine whose levels are increased in inflammatory pathologies that are associated with cholestasis. Endocytic internalization of Abcc2 (multidrug resistance-associated protein 2), a canalicular transporter of organic anions that is implicated in the clearance of clinically important drugs, is a phenomenon that occurs in inflammatory liver diseases, and it has been established that cytokines act as mediators. However, the intracellular mechanism involved in this effect remains unknown. The aim of the present work was to characterize the internalization of Abcc2 induced by TNFα and to study the role of ERK1/2 and reactive oxygen species as signaling mediators of transporter internalization. Using rat hepatocyte couplets, we found that TNFα (6.25 pg/ml) induced a decrease in Abcc2 activity estimated by the accumulation of the Abcc2 substrate glutathione methylfluorescein in the canalicular vacuole that was accompanied by internalization of Abcc2 from the canalicular membrane. Inhibition of MEK1/2 (upstream of ERK1/2) partially prevented TNFα effects on Abcc2 internalization and activity impairment. Reactive oxygen species (ROS) scavengers such as vitamin C and mannitol partially prevented both TNFα-induced decrease in Abcc2 activity and ERK1/2 phosphorylation. Apocynin, a NADPH oxidase inhibitor, prevented the increase in ROS and the phosphorylation of ERK1/2 produced by TNFα. Taken together, these results indicate that TNFα activates a pathway involving NADPH oxidase, ROS and MEK1/2-ERK1/2 that is partially responsible for the internalization of Abcc2. This internalization leads to an altered transport activity of Abcc2 that could impair drug disposal, enhancing drug toxicity in patients suffering from inflammatory liver diseases.

Hepatotoxicity induced by coxibs: how concerned should we be?

INTRODUCTION: The selective inhibitors of COX-2, coxibs, are nonsteroidal anti-inflammatory drugs (NSAIDs) that have much better gastrointestinal safety profile as compared with non-selective NSAIDs. In this review, we analyze both the epidemiological features of coxib-induced hepatotoxicity and the clinical impact of coxib-associated liver damage, based on literature data. Areas covered: We carried out a search of the databases MEDLINE (PubMed), LILACS and SCIELO, from December 1999 to January 2016, to retrieve studies exploring the real impact of coxibs in liver toxicity as compared to non-selective COX-2 inhibitor NSAIDs. Expert opinion: Although reliable data on the incidence of celecoxib- and etoricoxib-induced hepatotoxicity are lacking, because of cohort studies have been generally underpowered to detect hepatic events, coxibs have been scarcely related to hepatotoxicity. Hence, coxib-induced liver injury seems to be an uncommon event, yet exhibits a wide spectrum of damage. Increasing COX-2 drug selectivity, as for rofecoxib, valdecoxib, parecoxib, and lumiracoxib, has been associated with higher cardiovascular risk, as well as dermatological and serious hepatic reactions. The actual risk of liver toxicity from the currently approved coxibs compared with non-selective NSAIDs will be discussed. Finally, classical and novel molecular mechanisms of coxib-induced hepatotoxicity are also described.

Is ursodeoxycholic acid detrimental in obstructive cholestasis? A propos of a case of malignant biliary obstruction.

Ursodeoxycholic acid (UDCA) is the first choice medication for most cholestatic hepatopathies, due to its capability to counteract inflammation and bile-acid-induced liver damage, two common features in cholestasis. However, UDCA is usually contraindicated in obstructive cholestasis, due to the alleged risk of biliary integrity disruption due to its choleretic effect. We report on an 83-year-old man with an unsuspected malignant biliary obstruction who received moderate doses of UDCA (8-12 mg/kg/day) for 5 weeks, because the preliminary evidence suggested he had chemotherapy-induced cholestasis. Liver integrity was extensively protected by UDCA, as indicated by a marked decrease in serum liver enzymes, despite a steady increase in the levels of bilirubin and serum bile acids due to the obstructive process. In conclusion, this report shows, for the first time in humans, that moderate UDCA doses can reduce liver injury associated with complete biliary obstruction. This may contribute to a better understanding of the risk-benefit ratio of the use of UDCA in obstructive cholangiopathies.