[Show abstract][Hide abstract] ABSTRACT: Protein C inhibitor is a heparin-dependent serine protease inhibitor present in plasma at about 0.08 mumol l-1. Protein C inhibitor inhibits activated protein C and other coagulation factors. Previously, we described the presence of high protein C inhibitor levels in human semen (3.1 mumol l-1) and showed potential roles of the inhibitor in human reproduction. Here, we show that protein C inhibitor is present in an active form in follicular fluid at about 0.1 mumol l-1 and that purified, functionally active human plasma-derived and inactive, semen-derived protein C inhibitor and a synthetic peptide derived from its sequence inhibited both binding and penetration of zona-free hamster oocytes by human sperm. The binding inhibition by protein C inhibitor was dose dependent, with 50% inhibition at 0.037 mumol l-1 inhibitor (45 +/- 17 sperm per egg versus 90 +/- 23 in control experiments). The inhibitor also blocked in a dose-dependent manner the penetration of zona-free hamster eggs by human sperm (20 +/- 7% fertilized eggs at 0.1 mumol l-1 protein C inhibitor versus 55 +/- 10% in control experiments). Polyclonal antiprotein C inhibitor or antipeptide antibodies partially abolished the effect of protein C inhibitor and peptide on the inhibition of the binding and penetration of zona-free hamster oocytes by human sperm. The effect of the protein C inhibitor was not dependent on its antiprotease activity since purified semen-derived protein C inhibitor which did not have antiprotease activity gave comparable results. We conclude that protein C inhibitor may be involved in human reproduction at several steps, including the fertilization process.
[Show abstract][Hide abstract] ABSTRACT: Since the serine protease inhibitor, protein C inhibitor (PCI), is present in seminal plasma at approximately 3 microM, complexes of PCI with urokinase (uPA) and tissue type (tPA) plasminogen activator were quantitated using sandwich enzyme-linked immunosorbent assays (ELISA's). Seminal plasma (N = 10) collected in the absence of extrinsic inhibitors had a mean of 25 +/- 5 ng/ml uPA:PCI, 76 +/- 23 ng/ml tPA:PCI, and 4 +/- 2 ng/ml of tPA complexes with plasminogen activator inhibitor-1 (tPA:PAI-1). 93% of the uPA and 17% of the tPA antigen in seminal plasma was in complex with PCI and, when complexation was inhibited by collecting semen into an 1,10-phenanthrolinium solution, 33% of the uPA and 7% of the tPA was complexed to PCI. Urine (N = 10) contained 4 +/- 1 ng/ml uPA:PCI. In purified system, complexation of uPA and tPA to PCI paralleled the inhibition of the enzymes. In vitro studies in blood and seminal plasma showed that heparin stimulated complexation of uPA and tPA with PCI, suggesting that negatively charged glycosaminoglycans in blood vessels and in the reproductive system may regulate PCI reactions with uPA and tPA. These results suggest that PCI is a physiologic regulator of uPA and tPA in male reproductive tissues and raises questions about a potential role of PCI in human fertility and in uPA-dependent cell invasiveness.
No preview · Article · Jan 1994 · Thrombosis and Haemostasis