Pathological comparison of hepatic-fibrosis models induced by porcine serum and carbon tetrachloride in rats

Establishment of a rat model of alcoholic liver fibrosis and detection of hepatic expression of Smad7/TGF-β

AIM: To develop a suitable rat model of alcoholic liver fibrosis, which is easily available and low in cost with a high success rate, and to detect the alteration of expression of genes involved in the pathogenesis of alcoholic liver disease.

METHODS: Rats were raised individually in respective cages and were fed ad libitum. Rats were divided into two groups: a normal control group and an experimental group. The normal control group was given a normal diet with alcohol-free water. The experimental group was further divided into three subgroups, namely, a normal diet subgroup, a high fat diet subgroup and a limited high fat diet subgroup. Commercially available Chinese spirit was diluted into different concentrations (6%, 9%, 12%, 20%) using distilled water and used as the source of alcohol consumption for rats in the experimental group. Rats in the experimental group were fed distilled water containing 6% (v/v) alcohol at the beginning of the experiment, and the concentration of alcohol was gradually increased to 20% within 4 wk. Ultimately, water containing 20% alcohol was maintained towards the end of the study. At the end of the experiment, livers of rats were dissected for histological studies whereas serum samples were taken to detect the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). The mRNA and protein expression of transforming growth factor β1 (TGF-β1) and Smad7 in liver tissues was detected by real-time PCR and Western blot, respectively.

RESULTS: No pathological changes were observed in the liver of rats in the normal control group. However, rats in the experimental group demonstrated histopathological changes such as fatty change, inflammation as well as fibrosis. The histopathological changes were most severe in the subgroup fed a limited high fat diet, followed by those fed a high fat diet. Fatty changes were observed in the liver of rats in the experimental subgroup fed a normal diet. A small amount of collagen fibrils, inflammation and a more severe fatty change were found in the liver of rats fed a high fat diet. Bundles of closely packed collagen fibrils, inflammation, and fatty change were observed in rats fed a limited high fat diet. Serum levels of AST and ALT were higher in the experimental group compared to the normal control group. The subgroup fed a normal diet had lower levels of AST and ALT compared to the other two subgroups, although no significant difference was seen between subgroups fed a high fat diet and a limited high fat diet. Protein expression of TGF-β1 and Smad7 was positively correlated with their mRNA levels, respectively. TGF-β1 expression level in the normal control group was lower compared to the three experimental subgroups, and the level was positively correlated with the severity of hepatic pathological changes. Smad7 expression was shown to be higher in the normal control group compared to the experimental subgroups. However, there was no correlation between the level of Smad7 and hepatic pathological changes.

CONCLUSION: Feeding a limited high fat diet with alcohol ad libitum in rats is a convenient, low cost method for developing an animal model of alcoholic liver disease with a high rate of success. Inability of Smad7 to inhibit the TGF-β1 pathway contributes to the development of alcoholic liver fibrosis.