Formation of polymorphonuclear leukocyte elastase: α1 proteinase inhibitor complex and Aα(1–21) fibrinopeptide in human blood stimulated with the calcium ionophore A23187 : A model to characterize inhibitors of polymorphonuclear leukocyte elastase

Incubation of human blood with the secretagogue A23187 resulted in the formation of increased plasma concentrations of polymorphonuclear leukocyte (PMN) elastase: α 1 proteinase inhibitor (PMNE: α 1PI) complex as well as Aα(1–21) fibrinopeptide [Aα(1–21)]. The formation of these species was both time and A23187 concentration dependent. Using a sandwich ELISA and a radioimmunoassay, we determined the comparative potencies of several compounds to inhibit the formation of PMNE: α 1PI complexes and Aα(1–21), respectively. L-658,758, a substituted cephalosporin, essentially irreversible elastase inhibitor, inhibited the formation of PMNE: α 1PI and Aα(1–21) with ic 50 values of 38 and 15 μM, respectively. L-683,845, a monocyclic β-lactam, was much more potent against isolated PMNE than L-658,758. However in this system it was approximately equivalent to L-658,758 with an ic 50 of 15 μM against both species. ICI-200,880, a competitive slow-binding elastase inhibitor, was significantly less potent to inhibit Aα(1–21), having an ic 50 of 75 μM, while Declaben, a reversible noncompetitive inhibitor, was inactive at concentrations as great as 200 μM. We propose that evaluating inhibitors in the complex milieu of blood will provide a useful method to predict their therapeutic potential in vivo.