Expression of type I and type III collagens during the course of dimethylnitrosamine‐induced hepatic fibrosis in rats

Abstract

— Aims/Background: We wished to clarify the mechanisms that account for the increase in hepatic collagen accumulation during hepatic fibrosis. Methods: The gene expression of type I and type III procollagens and matrix metalloproteinase‐1 (MMP‐1) was measured by Northern blot analysis; immunolocalization of both types of collagen was estimated by indirect immunohistochemical assay; and the hepatic content of collagen and malondialdehyde (MDA), a product of lipid peroxidation, were assayed in hepatic fibrosis induced in rats with a single dose of dimethylnitrosamine (DMN). Results: During the experimental period, more type I procollagen mRNA was found than type III procollagen mRNA. The immunoreactive intensity of type I collagen was greater in necrotic areas near central veins 3 days after DMN treatment than it was on day 9, whereas the type III collagen immunodeposition for the latter period of the hepatic fibrosis was stronger than it was on day 3. As compared with controls, hepatic collagen content increased significantly after 3 days and continued, increasing gradually, as did type I and III procollagen mRNA levels. On day 14, fibrosis was greatest and both types of procollagen gene expression were at their highest, and type I and III procollagen mRNA levels and hepatic collagen content increased as the dosage of DMN was raised. MMP‐1 mRNA levels increased early in hepatic fibrogenesis, and increased on day 14 when DMN dosages were low. Hepatic MDA levels increased rapidly for 3 days after DMN treatment, remaining significantly higher than control values and showing a significant increase even in response to low DMN doses on day 14. Conclusions: Our results suggested that fibrotic liver collagen content may make its first notable increase due in part to the balance between type I collagen and MMP‐1 expression rates. Also, lipid peroxidation may be important in the mechanism of hepatofibrogenesis.