OBJECTIVESTo explore the dynamic changes and interactions between MMP-2 and TIMP-2 during experimental liver fibrosis.

METHODSWistar rats were randomly allocated into a normal group and a model group. To induce liver fibrosis, rats were injected intraperitoneally with dimethylnitrosamine (DMN) three consecutive times in the first week, then two consecutive times per week, totally for 6 weeks. In the normal control group, rats were injected with saline by the same method as the model group. Animals were sacrificed 1, 4, 10, 17, 28, 42, 56 days after starting DMN injections. Conventional histological examinations of the livers were performed with hematoxylin and eosin and Masson staining. The fibrosis was classified into 0 to 4 stages. Hydroxyproline content was determined after liver tissues were hydrolyzed in HCl at 160 degree C for 2 hrs and then measured with spectrometry at 560 nm wavelength. mRNA levels of MMP-2 and TIMP-2 were determined by semi-quantitive RT-PCR. Gelatinase activity of MMP-2 was examined by zymography using gelatin substrate.

RESULTSIn the model group the hepatic MMP-2 mRNA expression started to increase 10 days after DMN administration and remained at a much higher level than in the normal group throughout the study period, while TIMP-2 mRNA expression started to be lower than in the normal group 17 days after DMN administration and reached the lowest level on the 28th day. Then it rapidly rebounded and remained higher than that in the normal group from the 42nd day to the end of the study period. TIMP-2/MMP-2 began to be lower by several days than that of the normal group after DMN administration through the remaining study period. Zymography showed that the enzymatic activities of both latent MMP-2 and active MMP-2 were increased during the process of liver fibrosis.

CONCLUSIONIn liver fibrosis, MMP-2 expression increases, while TIMP-2 expression relatively decreases. The enzymatic activities of MMP-2 increase as the liver fibrosis develops.