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Mast cells and leukotrienes mediate neutrophil sequestration and lung edema after remote ischemia in rodents
G Goldman1, R Welbourn, J M Klausner
1Departments of Surgery, Brigham and Women's Hospital, Boston, MA 02115.
Abstract:
Reperfusion of ischemic hindlimbs leads to leukotriene B4 (LTB4) and polymorphonuclear neutrophil (PMN)-dependent lung injury. Pulmonary mast cells are capable of synthesizing LTB4 and are potential mediators of this inflammatory response. This study tests their role in PMN sequestration and pulmonary edema after hindlimb ischemia. Anesthetized, mast cell-sufficient mice (n = 8) or their congeneic mast cell-deficient strain (n = 8) were subjected to 3 hours of hindlimb ischemia. After another 3 hours of reperfusion, plasma LTB4 levels rose to 651 pg/ml, higher than sham ischemic control (n = 8) values of 202 pg/ml (p less than 0.05). At this time there was sequestration of neutrophils in the pulmonary microcirculation (54 PMN/10 high-power fields [HPF]) and an increase in lung wet/dry weight ratio (W/D) of 4.4. Both these values were higher (p less than 0.05) than those in sham ischemic animals that showed sequestration of 18 PMN/10 HPF and a lung W/D of 3.1. In contrast, mast cell-deficient mice showed an attenuation of ischemia- and reperfusion-induced rise in plasma LTB4 (507 pg/ml), fewer sequestered neutrophils (34 PMNs/10 HPF), and a reduction in lung W/D to 3.9 (all p less than 0.05). To test the role of lung LTB4 in determining PMN sequestration, rats (n = 78) were subjected to 3 hours of hindlimb ischemia. After 3 hours of reperfusion, plasma and bronchoalveolar lavage (BAL) LTB4 concentrations rose to 956 and 211 pg/ml, respectively--higher than sham values of 460 and 121 pg/ml (both p less than 0.05). After 4 hours, plasma LTB4 levels had returned to baseline, whereas BAL LTB4 had increased further to 658 pg/ml, indicating lung origin. Treatment of other rats by localized lung lavage of the lipoxygenase inhibitor diethylcarbamazine (80 mg/kg in 0.1 ml twice) prevented the ischemia- and reperfusion-induced rise in BAL LTB4 (267 pg/ml) and limited local neutrophil sequestration (from 51 PMN/10 HPF after saline aspiration to 36 PMN/10 HPF) and lung W/D (from 4.5 to 4.1) (all p less than 0.05). The data indicate that after hindlimb ischemia pulmonary mast cells and localized LTB4 synthesis mediate, in part, the lung inflammatory response.
Insights
Hindlimb ischemia reperfusion causes lung injury mediated by leukotriene B4 (LTB4) and neutrophils. Pulmonary mast cells contribute to this inflammatory response by synthesizing LTB4.
Area of Science:
- Inflammation and Immunology
- Pulmonary Medicine
- Vascular Surgery
Background:
- Reperfusion following ischemic events, such as hindlimb ischemia, can paradoxically trigger inflammatory lung injury.
- Leukotriene B4 (LTB4) and polymorphonuclear neutrophils (PMNs) are implicated in this injury.
- Pulmonary mast cells are a potential source of LTB4 and may play a role in mediating this response.
Purpose of the Study:
- To investigate the role of pulmonary mast cells in LTB4 synthesis and subsequent PMN sequestration and lung edema after hindlimb ischemia and reperfusion.
- To determine the contribution of localized LTB4 production in the lungs to the inflammatory response.
Main Methods:
- Comparison of mast cell-sufficient and mast cell-deficient mice subjected to hindlimb ischemia and reperfusion.
- Measurement of plasma LTB4 levels, pulmonary neutrophil sequestration (PMN/HPF), and lung wet/dry weight ratio (W/D).
- Induction of hindlimb ischemia in rats, with measurements of plasma and bronchoalveolar lavage (BAL) LTB4, neutrophil sequestration, and lung W/D, with and without lipoxygenase inhibitor treatment.
Main Results:
- Mast cell-deficient mice exhibited significantly reduced plasma LTB4, neutrophil sequestration, and lung edema compared to controls.
- Ischemia-reperfusion increased plasma and BAL LTB4 levels in rats, with BAL LTB4 rising further over time, suggesting lung origin.
- Inhibition of local LTB4 synthesis in rats significantly reduced neutrophil sequestration and lung edema.
Conclusions:
- Pulmonary mast cells are key mediators in the inflammatory lung response to hindlimb ischemia-reperfusion, partly through LTB4 synthesis.
- Localized LTB4 production in the lungs plays a significant role in driving neutrophil sequestration and edema formation.
- Targeting LTB4 synthesis may offer a therapeutic strategy to mitigate lung injury following ischemic events.