In vitro effects of pregnancy-associated plasma protein-A: artifacts due to heparin

Pregnancy-associated plasma protein-A (PAPP-A) has been reported to inhibit elastase activity, lymphoblastogenesis, complement activity, and thrombin-induced coagulation of fibrinogen. Since some of these results are controversial, we reevaluate here the effects of PAPP-A in these last two systems. By molecular sieve chromatography, PAPP-A immunoreactivity and inhibitory activity on thrombin and complement were dissociated. A PAPP-A-free washing of the heparin-Sepharose column used during the purification of PAPP-A showed inhibitory activities similar to those of purified PAPP-A. Furthermore, a preparation of PAPP-A that had not been submitted to heparin-Sepharose chromatography during purification was not active in either assays. Thus, the anticoagulant and anti-complement effects previously attributed to PAPP-A were due to a contaminant of low molecular mass. We believe that this contaminant is probably heparin. A protocol to eliminate free and PAPP-A-bound heparin is presented herein, and implications for other previously reported in vitro effects of PAPP-A are discussed.