OBJECTIVETo study the role of changes of matrix metalloproteinase-2, 9 (MMP-2, 9) activity in the development of dimethylnitrosamine (DMN)-induced liver fibrosis in rats.

METHODSThe rat liver fibrosis model was established by peritoneal injection of DMN (at a dose of 10 mg/kg, 3 times a week, for 4 weeks). The dynamic changes of liver fibrosis were observed at different time points (1d, 2d, 3d, 1 week, 2 weeks, 4 weeks, 6 weeks and 8 weeks). The MMP-2, 9 activity was measured by zymogram method. Liver ultrastructure was observed by electron microscope. The expressions of type IV collagen (CIV), laminin (LN), type I collagen (CI) and alpha-smooth muscle actin (alpha-SMA) were examined by immunohistochemistry. The tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) content was measured by Western blot method.

RESULTSThe MMP-2, 9 activity (gray value) significantly increased in the 2d and 3d DMN model rats (2d: normal/model group, MMP-2: 54.72+/-4.56/70.76+/-7.63; F = 16.27, P < 0.05; MMP-9: 25.72+/-4.29/51.76+/-15.33, F=13.38, P < 0.05). The positive staining area percentage of CIV in the sinusoidal walls decreased in the 2d, 3d and 1 weeks model rats (2d: normal/model group, 6.06+/-1.35/2.86+/-0.63, F=69.12, P < 0.05), but significantly increased in the 4w model rats (normal/model group, 6.06+/-1.35/8.04+/-1.50, F=14.42, P < 0.05). There was a remarkable negative correlation between the MMP-9 activity and expression of CIV in the sinusoidal walls (r = -0.729, P < 0.05). Positive expressions of LN and CI increased, and the strongest positive staining of them displayed in the 4w model rats. The formation of basement membrane was also observed in the 4 weeks model rats. Expression of TIMP-2 significantly increased in the late stage of fibrosis.

CONCLUSIONSThe increase of MMPs activity, especially MMP-9 which degrades the CIV normally distributed under the sinusoidal endothelium is the important factor in the formation of sinusoidal capillarization. The deposition and reconstitution of LN and new synthetic CIV, adding the deposition of CI constitute the high density basement membrane. The increase of TIMP-2 expression in the late stage of the fibrosis may be one of reasons why natural resolution of DMN-induced liver fibrosis is difficult.