Vitamin D and S-Farnesylthiosalicylic Acid Have a Synergistic Effect on Hepatic Stellate Cells Proliferation

Hepatic stellate cells (HSCs) have a key role in the formation of hepatic fibrosis. The active form of vitamin D, 1,25(OH)₂D₃, has been found to have antiproliferative and antifibrotic effects in various tissues including liver. Farnesylthiosalicylic acid (FTS), a novel Ras antagonist, was also found to inhibit hepatic fibrosis.

The purpose of this study was to examine the antiproliferative and antifibrotic effects of the combined treatment of 1,25(OH)₂D₃ and FTS on primary cultured HSCs.

Primary HSCs, isolated from rat’s livers, were treated with 1,25(OH)₂D₃, FTS or a combination of both. Proliferation was assessed by bromodeoxyuridine. Expression of p-ERK, ERK, Ras-GTP, total-Ras, CyclinD1 and fibrotic markers was measured by western blotting analysis and real-time PCR. Cytotoxicity was assessed by lactate dehydrogenase method.

The combined treatment inhibited HSCs proliferation by threefold. The effect was synergistic and non-cytotoxic. In concordance, the combined treatment suppressed CyclinD1 expression by ~2-fold, whereas 1,25(OH)₂D₃ or FTS alone showed a significantly lower inhibitory effect. The effect of the combined treatment on CyclinD1 expression was mediated via Ras-GTP and p-ERK signal transduction pathway. The effect on fibrotic markers showed that 1,25(OH)₂D₃ decreased collagen Iα1 expression by ~40 %, FTS by ~50 % and the combined treatment by ~60 %. 1,25(OH)₂D₃ inhibited tissue inhibitor of metalloproteinases-1 (TIMP-1) expression by 20 %. FTS alone or 1,25(OH)₂D₃ + FTS inhibited TIMP-1 expression by 60 %. FTS inhibited transforming growth factor-β (TGF-β) expression by 25 %, while 1,25(OH)₂D₃ had no effect.

Although the combination of 1,25(OH)₂D₃ and FTS did not demonstrate an additive antifibrotic effect, it showed a synergistic antiproliferative effect on primary HSCs. Therefore, the combined treatment may have a potential therapeutic value in the initiation of fibrotic process.