Effects of inhaled nitric oxide on intrapulmonarynitric oxide production and expression of plasminogen activator inhibitor-1 in lipopolysaccharide-induced acute lung injury

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Objective To explore the effects of inhaled nitric oxide(NO) on expression of plasminogen activator inhibitor-1 (PAI-1) mRNA and protein in the early-stage of experimental acute lung injury (ALI) in a rat model.And to investigate the relationship between endogenous NO system including inducible nitric oxide synthase (iNOS) and intrapulmonary NO production and expressions of PAI-1 in ALI. Methods In the study, endotoxemia followed by the second attack due to intratracheal injection of lipopolysaccharide (LPS) in rats caused ALI.Male SD rats aged 4-5 weeks (clean conventional rats, 180-200 g) were randomly assigned to 2 groups: saline control (C) group, LPS-treated (LPS) group, and the 2 groups were randomly allocated to subgroups exposed to air (A) or 20×10-6 NO.They were sacrificed for 24 h. Expressions of PAI-1 mRNA of the lung tissue were evaluated by real-time polymerise chain reaction; PAI-1 proteins were determined by immunohistochemistry.NO production in the lung tissues and pulmonary iNOS activity were measured.Meanwhile, histopathological lung injury scores were evaluated and modified martius acid fuchsin brilliant blue(MSB) stains was performed to evaluate fibrin of the lung tissues. Results At 24 h time point with intervention of iNO, PAI-1 mRNA and protein levels in LPS-NO subgroup were decreased compared with those in LPS-A subgroup(4.94±0.52 vs 5.56±0.27; 1.31±0.40 vs 1.69±0.16, all P<0.05). Meanwhile, iNOS activity and NO productions in LPS-NO subgroup were lower than those of LPS-A subgroup [(0.84±0.36)U/mg prot vs (2.30±0.25)U/mg prot; (1.90±0.84) μmol/g prot vs (3.38±0.73) μmol/g prot, all P<0.05]. iNOS activity had significant correlation with expression of PAI-1 mRNA and protein in lung tissue(r=0.481, P=0.005; r=0.667, P=0.000); NO production had significant correlation with expression of PAI-1 mRNA and protein in lung tissue(r=0.532, P=0.002; r=0.784, P=0.000). At 24 h time point, the histopathologic lung injury scores in LPS-NO subgroup were decreased in contrast to LPS-A subgroup (4.28±0.94 vs 6.12±1.51, P<0.05). Fibrin deposition eva-luated by modified MSB stains in LPS subgroups was found in alveolar space, lumen of blood vessel and mesenchymal; LPS subgroup with NO appeared a decreasing trend in contrast to LPS subgroup with air. Conclusions Inhaled nitric oxide of 20×10-6 can suppress elevated expression of PAI-1 in ALI induced by endotoxin.This inhaled NO can improve the imba-lance of plasminogen activation system and alleviate lung injury.Meanwhile, inhaled NO down-regulates intrapulmonary iNOS activity as well as endogenous NO productions in rats with 2 hits of LPS induced ALI.These changes also have a close correlation with down-regulation of PAI-1 mRNA and protein.Thus, regulation of endogenous NO system on the expression of PAI-1 will be the future direction of new therapies for ALI. Key words: Acute lung injury; Plasminogen activator inhibitor-1; Nitric oxide; Nitric oxide synthase