AIM: To investigate the effect of herbal compound 861 (Cpd861) on the transforming growth factor-beta 1 (TGF beta 1)/ activin receptor-like kinase 1 (ALK1, type I receptor) signaling-pathway-related gene expression in the LX-2 cell line, and the inhibitory mechanism of Cpd861 on the activation of LX-2 cells. METHODS: LX-2 cells were treated with TGF beta 1 (5 ng/mL) Cpd861 (0.1 mg/mL), TGF beta 1 (5 ng/mL) plus Cpd861 (5 ng/mL) for 24 h to investigate the effect of Cpd861 on the TGF beta 1/ALK1 pathway. Real-time PCR was performed to examine the expression of alpha-SMA (alpha-smooth muscle actin), ALK1, Id1 (inhibitor of differentiation 1). Western blotting was carried out to measure the levels of alpha-SMA and phosphorylated Smad1 and immunocytochemical analysis for the expression of a-SMA. RESULTS: In LX-2 cells, TGF beta 1/ALK1-pathway-related gene expression could be stimulated by TGF beta 1, which led to excessive activation of the cells. Cpd861 decreased the activation of LX-2 cells by reducing the expression of a-SMA mRNA and protein expression. This effect was related to inhibition of the above TGF beta 1/ALK1-pathway-related expression of genes such as Id1 and ALA1, and phosphorylation of Smad1 in LX-2 cells, even with TGF beta 1 co-treatment for 24 h. CONCLUSION: Cpd861 can restrain the activation of LX-2 cells by inhibiting the TGF beta 1/ALK1/Smad1 pathway. (C) 2008 WJG. All rights reserved.