Effects of salvianolic acid-B on TGF-beta 1 stimulated hepatic stellate cell activation and its intracellular signaling.

OBJECTIVE

To investigate hepatic stellate cells (HSC) responses at different differentiation stages on transforming growth factor-beta 1, and to elucidate the mechanisms of salvianolic acid - B (SA-B), a water soluble compound from Salvia miltiorrhiza, against hepatic fibrosis, relating to interference with TGF-beta 1 stimulated HSC activation and intracellular signal transduction via Smads.

METHODS

HSC was isolated from rat by in situ perfusion of liver and 8.2% nycondenz gradient centrifugation, and primarily cultured on uncoated plastic for 1 d, 4 d and 7 d respectively, which represented quiescent, intermediate and activated phenotypes. The cells were stimulated with 100 pmol/L TGF-beta 1, cell phenotypes were observed under inverted microscope, alpha-actin expression was checked by Western blot, and collagen secretion was measured with [(3)H] proline incorporation and collangenase digestion, then HSC at one definite differentiation stage that responded most sensitively to TGF-beta 1 was selected as the cell model for the following study. 0.1 micromol/L - 1 mmol/L SA-B was incubated with HSC and the cell proliferation was measured by intracellular [(3)H] thymidine pulse. SA-B was also incubated with TGF-beta 1 stimulated HSC, the collagen secretion was measured as above, alpha-actin and plasmin activator inhibitor-1 (PAI-1) were checked with Western blot, and alpha1 (I) procollagen mRNA levels were analyzed with Northern blot. The cytoplasmic and nuclear proteins were extracted, and cytoplasmic and nuclear Smad2, 3 expression and phosphorylation levels were measured with Western blot.

RESULTS

As culture duration prolonged, HSC phenotypes underwent activation gradually, accompanied by the increase of alpha-actin expression and collagen secretion. TGF-beta 1 increased the basal collagen levels at d1, d4 and d7 by 128.6%, 207.7% and 188.2% of the control respectively, while d4 HSC had the most sensitive response, and this intermediate HSC was used as cell model for the following study. Except 0.1 mmol/L-1 mmol/L SA-B caused parts of HSC death, 0.1 micromol/L-10 micromol/L SA-B had no influence on cell shape, but decreased HSC proliferation in a dose depend manner, by 76%, 60.1% and 47.8% of the control respectively. 1 micromol/L-10 micromol/L SA-B remarkably inhibited the collagen secretion of TGF-beta 1 stimulated HSC by 68.6% and 56.1% of the control, PAI-1 and alpha-actin expression, and down-regulated alpha 1 (I) pro-collagen gene expression. 0.1 micro mol/L approximately 10 micro mol/L SA-B decreased the cytoplasmic and nuclear Smad2, 3 protein expression, especially inhibited Smad2 phosphorylation and nuclear translocation.

CONCLUSIONS

SA-B obviously inhibits intermediate HSC proliferation, decreases TGF-beta 1 stimulated HSC activation and matrix protein and gene expression, and inhibited stimulated HSC Smad2, 3 protein expression, phosphorylation and nuclear translocation. The inhibition of TGF-beta 1 signaling in HSC and its biological responses is the important mechanism of SA-B against hepatic fibrosis.