Ursodeoxycholic acid decreases bilirubin-induced osteoblast apoptosis.

Background: Low bone turnover osteoporosis is common in cholestatic diseases. Ursodeoxycholic acid (UDCA) counteracts the damaging effects of bilirubin or lithocholic acid (LCA) on osteoblast viability, proliferation and mineralisation. UDCA is anti-apoptotic in various cell lines, but this effect in bone cells is unknown. Therefore, the consequences of bilirubin and LCA on apoptosis, and whether UDCA has anti-apoptotic effects have been assessed on osteoblasts.

Materials And Methods: Human osteoblasts (hOB) and osteosarcoma cell line (Saos-2) were treated with camptothecin as a pro-apoptotic agent, and UDCA, LCA and bilirubin. Apoptosis was determined by DNA fragmentation, flow cytometry, caspase-3 activity and expression of pro-apoptotic (Bcl-2-associated X protein BAX) and anti-apoptotic (BCL2 and BCL2-like 1 protein, BCL2L) genes.

Results: Both LCA (10 μM) and bilirubin (50 μM) induced apoptosis as indicated by DNA fragmentation (4·7- and 3·7-fold, respectively, P < 0·001), caspase-3 activity and flow cytometry in Saos-2 and hOB. UDCA (10 μM) reduced the apoptotic effects of camptothecin (0·5 μM) by 61%, (P < 0·001) and counteracted the apoptotic effects of LCA and bilirubin determined by DNA fragmentation (56% and 60%, respectively, P < 0·001), cytometry and caspase-3 activity in Saos-2, with lower effects in hOB. UDCA (10 μM) downregulated BAX (75%), upregulated BCL2L (10-fold, P < 0·01) genes, and neutralised BAX upregulation (P < 0·01) and BCL2L downregulation (P < 0·01) induced by LCA and bilirubin.

Conclusions: Bilirubin and LCA induce apoptosis in osteoblastic cells. UDCA counteracts the apoptotic consequences of these two substances, and therefore, it may have further beneficial effects on the decreased bone formation in the cholestasis.