Background & aims: The organic solute transporter α-β (OSTα-OSTβ) mainly facilitates transport of bile acids across the basolateral membrane of ileal enterocytes. Therefore, inhibition of OSTα-OSTβ might have similar beneficial metabolic effects as intestine-specific agonists of the major nuclear receptor for bile acids, the farnesoid X receptor (FXR). However, no OSTα-OSTβ inhibitors have yet been identified.
Methods: Here, we developed a screen to identify specific inhibitors of OSTα-OSTβ using a genetically encoded Förster Resonance Energy Transfer (FRET)-bile acid sensor that enables rapid visualization of bile acid efflux in living cells.
Results: As proof of concept, we screened 1280 Food and Drug Administration-approved drugs of the Prestwick chemical library. Clofazimine was the most specific hit for OSTα-OSTβ and reduced transcellular transport of taurocholate across Madin-Darby canine kidney epithelial cell monolayers expressing apical sodium bile acid transporter and OSTα-OSTβ in a dose-dependent manner. Moreover, pharmacologic inhibition of OSTα-OSTβ also moderately increased intracellular taurocholate levels and increased activation of intestinal FXR target genes. Oral administration of clofazimine in mice (transiently) increased intestinal FXR target gene expression, confirming OSTα-OSTβ inhibition in vivo.
Conclusions: This study identifies clofazimine as an inhibitor of OSTα-OSTβ in vitro and in vivo, validates OSTα-OSTβ as a drug target to enhance intestinal bile acid signaling, and confirmed the applicability of the Förster Resonance Energy Transfer-bile acid sensor to screen for inhibitors of bile acid efflux pathways.
Keywords: ASBT, apical sodium-dependent bile acid transporter; BAS, bile acid sensor; Bile Acids; FACS, fluorescence-activated cell sorting; FDA, Food and Drug Administration; FGF15/19, fibroblast growth factor 15/19; FRET, fluorescent resonance energy transfer; FXR; FXR, farnesoid X receptor; Fluorescence Resonance Energy Transfer (FRET); MDCKII, Madin–Darby canine kidney epithelial cells; OSTα-OSTβ; OSTα-OSTβ, organic solute transporter α-β; TCDCA, taurochenodeoxycholic acid; TICE, transintestinal cholesterol excretion; U2OS, human bone osteosarcoma epithelial cells; mRNA, messenger RNA; nucleoBAS, nucleus-localized bile acid sensor.