Lithocholic acid (3α-Hydroxy-5β-cholanic acid) is a toxic secondary bile acid produced from chenodeoxycholic acid by intestinal bacteria. It is usually conjugated with glycine or taurine and used as a choleretic agent to dissolve fats and promote absorption. It can be reabsorbed and exhibits FXR antagonist and PXR/SXR agonist activities. Lithocholic acid is commonly used to induce cholestasis models.

HCT116 cells (wt):46.8 ± 2.6 μM (LD50), HCT116 cells (p53−/−):37.4 ± 3.8 μM (LD50), USP2a:31.1 ± 3.4 µM, DU-145 cells:30.4 µM, PC-3 cells:32.0 µM

In a mouse cancer model induced by DMH (dimethylhydrazine), LCA effectively inhibits apoptosis almost completely in the precancerous colon. When administered to rodents, LCA and its conjugates cause intrahepatic cholestasis, a pathological state characterized by reduced bile flow and the accumulation of bile components in the liver and blood. Lithocholic acid activates the vitamin D receptor, inducing the expression of CYP3A, a cytochrome P450 enzyme that detoxifies LCA in the liver and intestines.

Lithocholic acid exhibits tumor-promoting activity and inhibits mammalian DNA polymerase β with an IC50 of 15 μM. It causes cholestasis (cessation or obstruction of bile flow) within the liver. Furthermore, lithocholic acid activates the Pregnane X Receptor (PXR), and the severe liver damage induced by LCA can be mitigated by the activation of PXR. Additionally, lithocholic acid directly binds to the vitamin D receptor with a Ki of 29 μM, activating it with a sensitivity higher than that for other nuclear receptors (e.g., PXR, FXR), with a Ki of 30 μM. This activation offers protection from its toxic effects.

Competitive ligand binding 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.