Plasma prolidase activity: a possible index of collagen catabolism in chronic liver disease

We describe here an easy method of determining prolidase (EC 3.4.13.9) in plasma after preincubation with Mn2+ for 24 h at 37 degrees C to maximize prolidase activity. The mean activity in 338 patients who were either in hospital or outpatients was 900 U/L +/- 520 (2 SD), unrelated to sex or age. In 25 of these 338 samples tested, prolidase activity was between 1500 and 2000 U/L. It exceeded 2000 U/L in eight, all of whom were patients with chronic liver disease. Plasma prolidase activity was normal in cytolytic syndromes such as liver or heart disease. Of the 27 patients with cirrhosis, only five exhibited prolidase activity greater than 2000 U/L. Plasma prolidase activity was uncorrelated with six biochemical indexes to liver function (the aminotransferases, alkaline phosphatase, glutamyltransferase, total bilirubin, and serum albumin) or with the degree of cirrhotic fibrosis. We believe that plasma prolidase activity may be high only in the early stage of fibrosis. This hypothesis would be consistent with the data on rat-liver collagenolytic activities during CCl4 administration. Monitoring of plasma prolidase activity might be useful in evaluating fibrotic processes in chronic liver disease in the human.