Objective: Nicotinamide has been shown to inhibit proliferation and induce apoptosis in a variety of cells. Moreover, nicotinamide treatment attenuates collagen accumulation and fibrogenesis in the bleomycin model of lung fibrosis. We hypothesized that nicotinamide may be useful as an antifibrotic agent in liver fibrosis and we investigated the in vitro effect of nicotinamide on hepatic stellate cells proliferation, apoptosis and collagen I expression.
Material and methods: Transforming growth factor beta1 (TGF-beta1) was used for activation of the rat HSC-T6 cell line. Apoptosis was determined by fluorescence activated cell sorter (FACS) analysis after propidium iodide staining and by immunohistochemistry showing presence of the active form of caspase 3. Expression of activation marker alpha-smooth muscle actin (alpha-SMA), apoptotic and cell cycle markers cyclin D1, P53 and caspase 3 was determined by Western blotting. Collagen I expression was assessed by Northern blotting.
Results: Nicotinamide inhibits hepatic stellate cell proliferation and induces apoptosis with caspase-3 activation. There is no effect of nicotinamide on the levels of cell cycle stimulator cyclin D1. Expression of p53 is induced in the presence of nicotinamide. Nicotinamide reduces activation marker alpha-SMA and decreases both basal and TGFbetaepsilon-induced collagen I expression. Moreover, in TGFbeta-activated cells, nicotinamide reduces expression of pro-inflammatory and pro-fibrotic cytokines TGFbeta2, IL-1beta, TNFalpha and macrophage chemotactic protein-1.
Conclusions: The in vitro effect of nicotinamide on activation and proliferation of hepatic stellate cells suggests that nicotinamide may have a potential beneficial role in attenuation of liver fibrogenesis.