Novel insights into the organic solute transporter alpha/beta, OSTα/β: From the bench to the bedside

Organic solute transporter alpha/beta (OST alpha/beta) is a heteromeric solute carrier protein that transports bile acids, steroid metabolites and drugs into and out of cells. OST alpha/beta protein is expressed in various tissues, but its expression is highest in the gastrointestinal tract where it facilitates the recirculation of bile acids from the gut to the liver. Previous studies established that OST alpha/beta is upregulated in liver tissue of patients with extrahepatic cholestasis, obstructive cholestasis, and primary biliary cholangitis (PBC), conditions that are characterized by elevated bile acid concentrations in the liver and/or systemic circulation. The discovery that OST alpha/beta is highly upregulated in the liver of patients with nonalcoholic steatohepatitis (NASH) further highlights the clinical relevance of this transporter because the incidence of NASH is increasing at an alarming rate with the obesity epidemic. Since OST alpha/beta is closely linked to the homeostasis of bile acids, and tightly regulated by the nuclear receptor farnesoid X receptor, OST alpha/beta is a potential drug target for treatment of cholestatic liver disease, and other bile acid-related metabolic disorders such as obesity and diabetes. Obeticholic acid, a semi-synthetic bile acid used to treat PBC, under review for the treatment of NASH, and in development for the treatment of othermetabolic disorders, induces OST alpha/beta. Some drugs associated with hepatotoxicity inhibit OST alpha/beta, suggesting a possible role for OST alpha/beta in drug-induced liver injury (DILI). Furthermore, clinical cases of homozygous genetic defects in both OST alpha/beta subunits resulting in diarrhea and features of cholestasis have been reported. This review article has been compiled to comprehensively summarize the recent data emerging on OST alpha/beta, recapitulating the available literature on the structure-function and expression-function relationships of OST alpha/beta, the regulation of this important transporter, the interaction of drugs and other compounds with OST alpha/beta, and the comparison of OST alpha/beta with other solute carrier transporters as well as adenosine triphosphate-binding cassette transporters. Findings from basic to more clinically focused research efforts are described and discussed. (c) 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).