NR1H4 and primary biliary cholangitis: Obeticholic acid (6α-ethyl-chenodeoxycholic acid, 6-ECDCA), a semi-synthetic bile acid analog with highly potent FXR agonistic activity (EC50 = 0.099 μM) (Pellicciari et al., 2002), is the first FDA-approved drug that is used for treating primary biliary cholangitis (PBC) (Nevens et al., 2016).