LEXIPAFANT INHIBITS PLATELET-ACTIVATING-FACTOR ENHANCED NEUTROPHIL FUNCTIONS

Platelet activating factor (PAF) enhances polymorphonuclear leukocyte (PMN) superoxide (O-.(2)-) production, CD11b expression, and elastase release, all essential components in the pathophysiology of multiple-o rgan failure. This study was designed to determine the effects of Lexi pafant, a PAF receptor antagonist, on PAF-mediated PMN functions. PMNs from 10 healthy volunteers were isolated and pretreated with various concentrations of Lexipafant (0-100 mu M). PMNs were then incubated fo r 5 min with 200 nM PAP for O-.(2)- detection or 2000 nM PAF for elast ase measurement and activated with 1 mu M N-formylmethionylleucylpheny lalanine. The mean rate of O-.(2)- production was determined by a cyto chrome c reduction assay (nmole O-.(2)-/min/1.33 X 10(6) PMN +/- SEM). Elastase release was measured by the cleavage of the synthetic elasta se substrate Meo-Suc-Ala-Ala-Pro-Val-pNA (mean elastolytic activity +/ - SEM). In parallel experiments, PMNs were incubated with 200 nM PAF f or 30 min following pre-treatment with Lexipafant and CD11b expression was determined by flow cytometry (mean fluorescence intensity +/- SEM ). Statistical analysis was performed using repeated-measures ANOVA (P < 0.05). Lexipafant inhibited PAF-enhanced PMN O-.(2)- generation, CD 11b expression and elastase release in a dose dependent fashion. The I C50 of Lexipafant for O-.(2)- production, CD11b expression, and elasta se release was 0.046, 0.285, and 0.05 mu M, respectively. Lexipafant a ttenuated the PAF-mediated upregulation of PMN O-.(2)- production, CD1 1b expression, and elastase release in a dose dependent fashion. These data support the hypothesis that Lexipafant may reduce the severity o f the inflammatory response to injury produced by PAF-enhanced activat ion of PMNs. (C) 1997 Academic Press.