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Updated: Jul 31, 2026
Bronchoalveolar Lavage Exosomes in Lipopolysaccharide-induced Septic Lung Injury
Published on: May 21, 2018
Effects of macrophage inducible nitric oxide synthase in murine septic lung injury
K S Farley1, L F Wang, H M Razavi
1Centrre for Critical Illness Research, Division of Respirology, Department of Medicine, London Health Sciences Center, University of Western Ontario, South St. Campus, 375 South Street, London, Ontario, Canada.
Abstract:
Inducible nitric oxide synthase (iNOS) contributes importantly to septic pulmonary protein leak in mice with septic acute lung injury (ALI). However, the role of alveolar macrophage (AM) iNOS in septic ALI is not known. Thus we assessed the specific effects of AM iNOS in murine septic ALI through selective AM depletion (via intratracheal instillation of clodronate liposomes) and subsequent AM reconstitution (via intratracheal instillation of donor iNOS+/+ or iNOS-/- AM). Sepsis was induced by cecal ligation and perforation, and ALI was assessed at 4 h: protein leak by the Evans blue (EB) dye method, neutrophil infiltration via myeloperoxidase (MPO) activity, and pulmonary iNOS mRNA expression via RT-PCR. In iNOS+/+ mice, AM depletion attenuated the sepsis-induced increases in pulmonary microvascular protein leak (0.3 +/- 0.1 vs. 1.4 +/- 0.1 microg EB.g lung(-1).min(-1); P < 0.05) and MPO activity (37 +/- 4 vs. 67 +/- 8 U/g lung; P < 0.05) compared with that shown in non-AM-depleted mice. In AM-depleted iNOS+/+ mice, septic pulmonary protein leak was restored by AM reconstitution with iNOS+/+ AM (0.9 +/- 0.3 microg EB.g lung(-1).min(-1)) but not with iNOS-/- donor AM. In iNOS-/- mice, sepsis did not induce pulmonary protein leak or iNOS mRNA expression, despite increased pulmonary MPO activity. However, AM depletion in iNOS-/- mice and subsequent reconstitution with iNOS+/+ donor AM resulted in significant sepsis-induced pulmonary protein leak and iNOS expression. Septic pulmonary MPO levels were similar in all AM-reconstituted groups. Thus septic pulmonary protein leak is absolutely dependent on the presence of functional AM and specifically on iNOS in AM. AM iNOS-dependent pulmonary protein leak was not mediated through changes in pulmonary neutrophil influx.
Insights
Alveolar macrophage inducible nitric oxide synthase (iNOS) is essential for septic acute lung injury (ALI) protein leak in mice. Depleting macrophages or their iNOS function prevents lung injury, highlighting iNOS in macrophages as a key factor.
Area of Science:
- Pulmonary Medicine
- Immunology
- Critical Care
Background:
- Inducible nitric oxide synthase (iNOS) plays a role in septic acute lung injury (ALI) by contributing to pulmonary protein leak.
- The specific contribution of iNOS within alveolar macrophages (AMs) to septic ALI remains unclear.
Purpose of the Study:
- To investigate the specific role of AM iNOS in the development of murine septic ALI.
- To determine if iNOS expression in AMs is necessary for sepsis-induced pulmonary protein leak.
Main Methods:
- Selective depletion of AMs using clodronate liposomes in mice.
- Reconstitution of AMs with either iNOS+/+ or iNOS-/- donor cells.
- Induction of sepsis via cecal ligation and perforation, followed by assessment of ALI markers (protein leak, neutrophil infiltration, iNOS mRNA) at 4 hours.
Main Results:
- AM depletion significantly attenuated sepsis-induced pulmonary protein leak and neutrophil infiltration in iNOS+/+ mice.
- Restoration of protein leak in AM-depleted mice required reconstitution with iNOS+/+ AMs, but not iNOS-/- AMs.
- Septic protein leak and iNOS expression were dependent on the presence of functional AMs and specifically iNOS within these cells, independent of neutrophil influx.
Conclusions:
- Septic pulmonary protein leak is critically dependent on the presence of functional alveolar macrophages.
- Inducible nitric oxide synthase (iNOS) specifically within alveolar macrophages is essential for mediating sepsis-induced pulmonary protein leak.
- The mechanism of AM iNOS-dependent protein leak does not involve alterations in pulmonary neutrophil infiltration.
