1,25-(OH)₂-vitamin D₃ prevents activation of hepatic stellate cells in vitro and ameliorates inflammatory liver damage but not fibrosis in the Abcb4(-/-) model

Abstract

Background/purpose of the study: Vitamin D3-deficiency is common in patients with chronic liver-disease and may promote disease progression. Vitamin D3-administration has thus been proposed as a therapeutic approach. Vitamin D3 has immunomodulatory effects and may modulate autoimmune liver-disease such as primary sclerosing cholangitis. Although various mechanisms of action have been proposed, experimental evidence is limited. Here we test the hypothesis that active 1,25-(OH)2-vitamin D3 inhibits activation of hepatic stellate cells (HSC) in vitro and modulates liver-injury in vivo.

Methods: Proliferation and activation of primary murine HSC were assessed by BrdU- and PicoGreen(®)-assays, immunoblotting, immunofluorescence-microscopy, quantitative-PCR, and zymography following calcitriol-treatment. Wild-type and ATP-binding cassette transporter b4(-/-) (Abcb4(-/-))-mice received calcitriol for 4 weeks. Liver-damage, inflammation, and fibrosis were assessed by serum liver-tests, Sirius-red staining, quantitative-PCR, immunoblotting, immunohistochemistry and hydroxyproline quantification.

Results: In vitro, calcitriol inhibited activation and proliferation of murine HSC as shown by reduced α-smooth muscle actin and platelet-derived growth factor-receptor-β-protein-levels, BrdU and PicoGreen®-assays. Furthermore, mRNA-levels and activity of matrix metalloproteinase 13 were profoundly increased. In vivo, calcitriol ameliorated inflammatory liver-injury reflected by reduced levels of alanine aminotransferase in Abcb4(-/-)-mice. In accordance, their livers had lower mRNA-levels of F4/80, tumor necrosis factor-receptor 1 and a lower count of portal CD11b positive cells. In contrast, no effect on overall fibrosis was observed.

Conclusion: Calcitriol inhibits activation and proliferation of HSCs in vitro. In Abcb4(-/-)-mice, administration of calcitriol ameliorates inflammatory liver-damage but has no effect on biliary fibrosis after 4 weeks of treatment.

Keywords: Abcb4; Calcitriol; Cholestasis; Fibrosis; Primary sclerosing cholangitis; Vitamin D.