LY255283, a novel leukotriene B4 receptor antagonist, limits activation of neutrophils and prevents acute lung injury induced by endotoxin in pigs

Background: Polymorphonuclear neutrophils (PMNs) have been implicated in the pathogenesis of the adult respiratory distress syndrome (ARDS). Because leukotriene B4 (LTB4) is a potent activator of PMNs, we sought to determine whether LY255283, an LTB4 receptor antagonist, could block PMN activation and lung injury in a porcine model of lipopolysaccharide-induced ARDS.

Methods: Eighteen hours before being studied, pigs were injected with lipopolysaccharide (20 micrograms/kg). From 0 to 60 minutes, pigs received either Ringer's lactate solution (n = 5) or lipopolysaccharide (250 micrograms/kg). Among the pigs that were infused with lipopolysaccharide, nine received no other treatment, six received a low dose of LY255283 (30 mg/kg loading dose; 3 mg/kg-hr infusion), and six received a high dose of LY255283 (30 mg/kg loading dose; 30 mg/kg-hr). In vivo PMN activation was assessed with an automated chemiluminescence assay wherein results are expressed as CORE/MORE (i.e., the ratio of complement-opsonized zymosan receptor expression on circulating cells [CORE] divided by the maximal complement-opsonized zymosan receptor expression induced by incubating the cells in vitro with LTB4 or platelet-activating factor [MORE]).

Results: In control pigs, lipopolysaccharide induced hypoxemia, pulmonary hypertension, and neutrophil activation (increased CORE/MORE ratio). These changes were attenuated by LY255283, particularly when pigs were infused with the higher dose of the compound. The drug also blunted lipopolysaccharide-induced recruitment of PMNs in pulmonary air spaces, as assessed by bronchoalveolar lavage performed at 240 minutes, although the degree of pulmonary leukosequestration caused by lipopolysaccharide was not affected.

Conclusions: In a dose-dependent fashion, LY255283 ameliorated lipopolysaccharide-induced ARDS in pigs, possibly by blocking the recruitment of activated PMNs into alveoli.