Our previous research has proved that baicalin can inhibit the expression of Matrix metalloproteinases (MMPs) in periodontal ligament cells (PDLC) by cell immunocytochemistry. Therefore, the purpose of this study was to address the effects of baicalin on the total protein amount and Collagen I mRNA expression in PDLC, and the regulatory effects on Matrix metalloproteinase-1/tissue inhibitors of metalloproteinase-1(MMP-1/TIMP-1) expression. PDLC were incubated with 0-1000 ng/ml baicalin for 1,3 and 5 days. Coomasie brilliant blue staining was used to detect the synthesis of the total protein, and the collagen I mRNA expression was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). PDLC were treated with phorbol 12-myristate 13-acetate (PMA) or interleukin-1 beta (IL-1 beta) with or without 100 ng/ml baicalin and then mRNA levels for MMP-1 and TIMP-1 were detected. Enzyme linked immunosorbent assay (ELISA) was used to assess the MMP-1 protein. The range of 1-1000 ng/ml baicalin can enhance the amount of the total protein of PDL cells and the response had a dose-dependent manner in the range of 1-100 ng/ml baicalin. And 0-1000 ng/ml baicalin also significantly increased the Collagen I mRNA expression of PDLC 1-100 pmol/ml PMA and 0.01-1 ng/ml IL-1 beta significantly (p<0.05) stimulated the production of MMP-1 by PDLC at both the transcriptional and the translational level. Different concentration PMA enhanced TIMP-1 mRNA expression, but IL-1 beta did not affect the TIMP-1 mRNA expression. Moreover, in the presence of 100 ng/ml baicalin, both the MMP-1 and TIMP-1 mRNA expression were down regulated. The present study suggests that baicalin inhibits IL-1 beta induction of MMP-1 by altering the mRNA and protein levels. In addition, baicalin may increase Collagen I mRNA and total protein levels in PDLC. (C) 2010 Elsevier B.V. All rights reserved.