Effects of macrophage inducible nitric oxide synthase in murine septic lung injury

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.

Akt2 Deficiency Protects from Acute Lung Injury via Alternative Macrophage Activation and miR-146a Induction in Mice

“…In this study, we used the model of acid-induced lung injury, a model of aseptic ARDS (2). Similarly to septic lung injury, we found that alveolar macrophages in acid-induced lung injury acquire a classical (M1) activation phenotype in the early phase that is characterized by increased iNOS expression and accumulation of NO metabolites, which are known to contribute to the pathogenesis of ARDS (4,13,(15)(16)(17)(18). Furthermore, we identified the onset of the resolving phase of inflammation, during which suppression of iNOS and predominance of Arg-1, Fizz1, and Ym1 expression, features of M2 polarization, take place.…”

“…Most of the studies using animal models examined the role of macrophages in LPS-induced lung injury, a model that resembles septic ARDS (11,18,20). In this study, we used the model of acid-induced lung injury, a model of aseptic ARDS (2).…”

“…Classically activated or M1 macrophages express high levels of inducible NO synthase (iNOS), generate NO, secrete IL-12b, and are prominent in the acute phase of inflammation (14). Genetic depletion or pharmacologic inhibition of iNOS was shown to confer protection against lung injury in several animal models (4,13,(15)(16)(17)(18), suggesting a crucial role for M1 macrophages in the pathogenesis of acute lung injury (ALI). Alternative macrophage activation, or M2, is characterized by high levels of arginase-1 (Arg-1), found-in-inflammatory zone-1 (Fizz1), chitinase-3-like-3 (Ym1), and macrophage galactose C-type lectin 1 and 2 (MGL1, MGL2) (8,9,19).…”

Effects of pneumonectomy on nitric oxide synthase expression and perivascular edema in the remaining lung of rats

“…Regarding iNOS, there are no studies that correlate it with the operation and with postpneumonectomy pulmonary edema. However, iNOS is related to acute pulmonary lesion and to ARDS (34,35). Since PPPE is considered to be a variant of ARDS, whose triggering factor is the operation, the operation is expected to cause a possible increase in iNOS levels.…”

Meconium-induced release of nitric oxide in rabbit alveolar cells

“…It has been shown in the lungs of septic murine to have high levels of NO produced by iNOS. [3][4][5][6] NO is also a known regulator of apoptosis and has been shown to inhibit the activity of many caspases both in vivo and in vitro conditions in endotoxin-induced lung injury. 7 High levels of NO can react with superoxide to produce a highly oxidative peroxynitrate.…”