Cysteinyl leukotrienes impair hypoxic pulmonary vasoconstriction in endotoxemic mice

Abstract

Background: Sepsis impairs hypoxic pulmonary vasoconstriction (HPV) in patients and animal models, contributing to systemic hypoxemia. Concentrations of cysteinyl leukotrienes are increased in the bronchoalveolar lavage fluid of patients with sepsis, but the contribution of cysteinyl leukotrienes to the impairment of HPV is unknown.

Methods: Wild-type mice, mice deficient in leukotriene C(4) synthase, the enzyme responsible for cysteinyl leukotriene synthesis, and mice deficient in cysteinyl leukotriene receptor 1 were studied 18 h after challenge with either saline or endotoxin. HPV was measured by the increase in left pulmonary vascular resistance induced by left mainstem bronchus occlusion. Concentrations of cysteinyl leukotrienes were determined in the bronchoalveolar lavage fluid.

Results: In the bronchoalveolar lavage fluid of all three strains, cysteinyl leukotrienes were not detectable after saline challenge; whereas endotoxin challenge increased cysteinyl leukotriene concentrations in wild-type mice and mice deficient in cysteinyl leukotriene receptor 1, but not in mice deficient in leukotriene C(4) synthase. HPV did not differ among the three mouse strains after saline challenge (120 ± 26, 114 ± 16, and 115 ± 24%, respectively; mean ± SD). Endotoxin challenge markedly impaired HPV in wild-type mice (41 ± 20%) but only marginally in mice deficient in leukotriene C(4) synthase (96 ± 16%, P < 0.05 vs. wild-type mice), thereby preserving systemic oxygenation. Although endotoxin modestly decreased HPV in mice deficient in cysteinyl leukotriene receptor 1 (80 ± 29%, P < 0.05 vs. saline challenge), the magnitude of impairment was markedly less than in endotoxin-challenged wild-type mice.

Conclusion: Cysteinyl leukotrienes importantly contribute to endotoxin-induced impairment of HPV in part via a cysteinyl leukotriene receptor 1-dependent mechanism.

Figure 1

(A) Occlusion of the left mainstem bronchus-induced increase of left pulmonary vascular resistance in WT, LTC₄S^-/-, and CysLT₁^-/- mice at 18 hours after challenge with either saline or lipopolysaccharide (n=9 in each group). (B) Values of oxygen in the arterial blood during occlusion of the left mainstem bronchus at the end of the HPV measurements. *P<0.05 differs vs. saline-challenged mice of the respective genotype, # P<0.05 differs vs. lipopolysaccharide-challenged WT mice, § P<0.05 differs vs. lipopolysaccharide-challenged CysLT₁^-/- mice. CysLT₁^-/-, mice congenitally deficient in the cysteinyl leukotriene receptor 1; LPS, lipopolysaccharide; LPVR, left pulmonary vascular resistance; LTC₄S^-/-, mice congenitally deficient in leukotriene C₄ synthase; mmHg, millimeters of mercury; PaO₂, level of oxygen in the arterial blood; WT, wild type mice. All data mean ± SD.

Figure 2

(A) In WT (n=6), LTC₄S^-/-(n=6), and CysLT₁^-/- mice (n=7) the circulating leukocyte concentrations were markedly reduced after lipopolysaccharide challenge compared with WT (n=6), LTC₄S^-/- (n=7), and CysLT₁^-/- (n=6) mice after saline challenge. (B) Lung tissue myeloperoxidase activity was greater in lipopolysaccharide-treated WT (n=5), LTC₄S^-/- (n=7), and CysLT₁^-/- (n=7) mice than in saline-treated WT (n=6), LTC₄S^-/- (n=6), and CysLT₁^-/- (n=6) mice. Blood and tissue samples were taken 18 hours after lipopolysaccharide-challenge. *P<0.05 differs vs. saline-challenged mice of the respective genotype. CysLT₁^-/-, mice congenitally deficient in the cysteinyl leukotriene receptor 1; LPS, lipopolysaccharide; LTC₄S^-/-, mice congenitally deficient in leukotriene C₄ synthase; MPO, myeloperoxidase; WBC, white blood cell count; WT, wild type mice. All data mean ± SD.

Figure 3

The concentration of LTB₄ in bronchoalveolar lavage fluid did not differ between saline-challenged WT (n=4), LTC₄S^-/-(n=5), and CysLT₁^-/- (n=5) mice and lipopolysaccharide-challenged WT (n=6), LTC₄S^-/-(n=6), and CysLT₁^-/- (n=6) mice 18 hours after challenge. (B) In the same mice, levels of cysLTs (LTC₄/D₄/E₄) in the bronchoalveolar lavage fluid were higher in WT and CysLT₁^-/- mice after lipopolysaccharide challenge than in saline-challenged WT and CysLT₁^-/- mice. As expected, no cysLTs were detectable in bronchoalveolar lavage fluid from the LTC₄S^-/- mice after challenge with either saline or lipopolysaccharide. * P<0.05 differs vs. saline-challenged mice of the respective genotype, # P<0.05 differs vs. lipopolysaccharide-challenged WT mice, § P<0.05 differs vs. lipopolysaccharide-challenged CysLT₁^-/- mice. B₄, cysteinyl leukotriene B₄; C₄/D₄/E₄, cysteinyl leukotriene C₄/D₄/E₄; CysLT₁^-/-, mice congenitally deficient in the cysteinyl leukotriene receptor 1; LPS, lipopolysaccharide; LTC₄S^-/-, mice congenitally deficient in leukotriene C₄ synthase; WT, wild type mice. The levels of LTB₄ and cysLT are depicted as individual values with arithmetic means.