Type IV collagen-degrading enzyme activity in hepatocellular carcinoma

Type IV collagen-degrading enzyme activity was measured in liver homogenate obtained from 10 patients with hepatocellular carcinomas. Type IV collagen, the enzyme substrate, was extracted from human placenta with pepsin digestion, and labeled with [1-14C] acetic anhydride. The homogenate was preincubated with p-aminophenylmercuric acetate to activate the latent form of the enzyme, and then the enzyme activity was measured at pH 7.5 by adding a substrate mixture. Referring to previous reports, the enzyme measured seemed to be a neutral metalloprotease. The enzyme activity of the homogenate was markedly reduced by omitting the p-aminophenylmercuric acetate pretreatment, indicating that the enzyme was present mainly in the latent form. The activity seemed to be higher in the peripheral portion of hepatocellular carcinoma than in the center. Further the activity was found to be the highest in a hepatocellular carcinoma patient with many metastatic nodules in the lung. The results might suggest that type IV collagen-degrading enzyme participates in tumor invasion and intrahepatic or remote metastasis.