Abstract: Objective To investigate the characteristics of oxidative stress and extracellular signal-regulated kinase (ERK) signaling pathway during the formation and regression of liver fibrosis.Methods Rats were injected intraperitoneally with dimethyl nitrosamine (DMN) to establish the rat liver fibrosis model.Normal rats were used as control group.The activity of superoxide dismutase (SOD)/glutathione S-transferase (GST),reduced glutathione (GSH) content,collagen deposition,hydroxyproline content,α-smooth muscle actin (α-SMA) expression and collagen I messenger RNA (mRNA) level in liver tissue were observed at 1 day,3 days,1 week,2 weeks,3 weeks,4 weeks after the initiation of injection and 1 week (5 weeks),2 weeks (6 weeks),4 weeks (8 weeks) after the last injection.Gelatin zymography was used to determine the activity of matrix metalloproteinase 2/9 (MMP2/9).The protein expressions of MMP2/9,tissue inhibitor of metalloproteinase 1/2 (TIMP1/2),ERK and phosphorylated ERK1/2 (p-ERK1/2) were analyzed by western blot.Results As DMN intoxication continued,the collagen deposition and α-SMA expression in the liver of the model rats increased,with marked fibrous septum and pseudo-lobule formation.After stopping the intoxication,the collagen deposition,fibrous septum,and the positive staining area of α-SMA reduced.Western blot showed that with the formation of liver fibrosis,the activity of MMP2/9 was enhanced,and the expressions of TIMP1/2 and p-ERK protein increased gradually.During the regression of liver fibrosis,the expressions of these proteins decreased,but still maintained a relatively high level.Compared with the normal group (287.12±97.15,8.17±0.59),the trends of SOD activity and GST activity in each model group were consistent,which decreased significantly from the first week (277.81±27.40,8.19±1.26),reached the lowest point at the forth week (121.83±21.69,5.95±2.21),and recovered after stopping exposure (255.69±109.51,6.53±1.67),but remained a relatively low level.The GSH content (53.71±17.07) showed a transient increase on the day 1 and 3 of exposure (63.33±16.94,70.72±21.46),then decreased gradually during exposure,and recovered to the normal level gradually after stopping exposure (42.32±18.25).Conclusion The formation and regression of hepatic fibrosis induced by DMN presents corresponding oxidative stress changes,which are related to ERK signaling pathway.

Key words: Liver fibrosis, Hepatic stellate cells, Oxidative stress, Extracellular signal-regulated kinase signaling pathway