In vitro activity: Lithocholic acid (LCA) is a hydrophobic secondary bile acid that is primarily formed in the intestine by the bacterial 7α-dehydroxylation of chenodeoxycholic acid. LCA causes intrahepatic cholestasis (cessation or impairment of bile flow). LCA activates PXR (pregnane X receptor), and the LCA-induced severe liver damage can be protected by the activation of PXR. LCA is a ligand for farnesoid X receptor (FXR) with EC50 of 3.8 μM. LCA directly binds VDR (vitamin D receptor) with Ki of 29μM, activates VDR (vitamin D receptor) 30 μM, with much more sensitivity than the other nuclear receptors (eg. PXR, FXR), and its toxic effect is thus protected. LCA has tumor-promoting activity, inhibits mammalian DNA Polymerase β with IC50 of 15 μM

Kinase Assay: Ligand binding is performed using lysates from COS-7 cells transfected with expression plasmids for VDR or RXRα. Binding is performed overnight at 4°C in lysate buffer with 0.71 nM (18 Ci/mmol) [3H]1,25(OH)2D3 and bile acid competitor. Unbound [3H]1,25(OH)2D3 is removed by adsorption to dextran-coated charcoal and the supernatant removed for scintillation counting. Ki values are calculated from a computer fit of competition curves from triplicate assays.