Bone Abstracts

Introduction: Osteoporosis is a common complication in patients with chronic cholestasis, usually characterized by reduced bone formation. Ursodeoxycholic acid (UDCA) improves differentiation and mineralization and counteracts the damaging effects of bilirubin and lithocholic acid (LCA) in osteoblastic cells. Moreover, UDCA decreases apoptosis in a number of cell lines, but this antiapoptotic effect has not been investigated in bone cells.

Aims: To assess the antiapoptotic effects of UDCA on osteoblastic cells.

Material and methods: Primary human osteoblasts (hOB) and Saos-2 cell cultures were incubated with UDCA (100 μM), with and without bilirubin (50 μM) and LCA (10 μM) – the highest concentrations with no major effects on osteoblast viability –, and camptothecin (0.5 μM) as a proapoptotic agent. Apoptosis was assessed by DNA fragmentation, flow cytometry analysis (annexin V-FITC labeling), and gene expression of Bcl-2–associated X protein (BAX) and BCL2-like 1 protein (BCL2L) as antiapoptotic and proapoptotic genes respectively.

Results: LCA and bilirubin resulted in a significant (P<0.01) 4.5-and 5.7-fold induction of DNA fragmentation, respectively, with parallel effects in the flow cytometry analysis in Saos-2 cells. Similar results were found in hOB. UDCA alone had no consequences on apoptosis, but UDCA significantly (P<0.01) decreased the apoptotic effects of LCA and bilirubin by 71 and 75%, respectively, as observed by DNA fragmentation in Saos-2 cells, and with lower effects in hOB. These results were found with flow cytometry as well. Moreover, UDCA neutralized the effects of LCA and bilirubin on the up-regulated BAX, and on the down-regulated BCL2L gene expression.

Conclusions: Bilirubin and lithocholic acid stimulate apoptosis in osteoblastic cells. Ursodeoxycholic acid has clear antiapoptotic effects counteracting the consequences of these two substances increased in cholestasis. These results suggest that ursodeoxycholic acid may have further benefitial effects on bone formation in patients with cholestasis.