Hepatic collagenase activity during carbon tetrachloride induced fibrosis

Abstract

The contribution of collagen degradation, as measured by collagenase activity, to the accumulation of collagen during hepatotoxic fibrogenesis was examined using a carbon tetrachloride rat model. Both active and inactive enzyme forms were determined with the inactive form quantitated following activation by limited trypsin digestion of the liver homogenate. The rate of collagen biosynthesis was monitored by quantitating hepatic prolyl hydroxylase activity and accumulation of collagen. In one study CCI4 was administered twice weekly, i.p. (0.2 mL, 33% v/v in light mineral oil) for sixteen weeks, with animals sacrificed every two weeks. Histologic examination of liver sections and serum alanine transaminase levels indicated a progressive necrosis and fibrosis which was confirmed by the increase in hepatic hydroxyproline content from 0.303 to 4.84 micrograms/mg wet wt. tissue. Prolyl hydroxylase activity increased in a time dependent manner to a maximum of 3.7 X control. This increase was accompanied by a large increase in both active collagenase (15.0-40.8 mU/g protein) and latent collagenase activity (69.8-191.7 mU/mg protein). These increases were maintained through the transition to irreversible fibrosis. The increase in active collagenase activity was positively correlated with collagen content. A second short term CCI4 treatment study confirmed a transient alteration in the active to latent collagenase ratio early in the fibrotic process. These results demonstrate the dynamic changes in hepatic collagenase levels and indicate that the fibrotic lesion is not dependent on decreased collagenase levels for collagen accumulation.