Decreased exhaled nitric oxide as a marker of postinsult immune paralysis

Abstract

Nitric oxide (NO) regulates neutrophil migration and alveolar macrophage functions such as cytokine synthesis and bacterial killing, both of which are impaired in immune paralysis associated with critical illness. The aim of this study was to determine whether NO is involved in immune paralysis and whether exhaled NO measurement could help to monitor pulmonary defenses. NO production (protein expression, enzyme activity, end products, and exhaled NO measurements) was assessed in rats after cecal ligation and puncture to induce a mild peritonitis (leading to approximately 20% mortality rate). An early and sustained decrease in exhaled NO was found after peritonitis (from 1 to 72 h) compared with healthy rats [median (25th-75th percentile), 1.5 parts per billion (ppb) (1.2-1.7) vs. 4.0 ppb (3.6-4.3), P < 0.05], despite increased NO synthase-2 and unchanged NO synthase-3 protein expression in lung tissue. NO synthase-2 activity was decreased in lung tissue. Nitrites and nitrates in supernatants of isolated alveolar macrophages decreased after peritonitis compared with healthy rats, and an inhibitory experiment suggested arginase overactivity in alveolar macrophages bypassing the NO substrate. Administration of the NO synthase-2 inhibitor aminoguanidine to healthy animals reproduced the decreased neutrophil migration toward alveolar spaces that was observed after peritonitis, but L-arginine administration after peritonitis failed to correct the defect of neutrophil emigration despite increasing exhaled NO compared with D-arginine administration [4.8 (3.9-5.7) vs. 1.6 (1.3-1.7) ppb, respectively, P < 0.05]. In conclusion, the decrease in exhaled NO observed after mild peritonitis could serve as a marker for lung immunodepression.

Decrease in lung nitric oxide production after peritonitis in mice with sickle cell disease*

“…The defect in NO synthesis may favor both vasoocclusive and infectious events. The decrease in exhaled NO in SAD mice could be an indirect measure of innate immunity impairment occurring after peritonitis, as previously suggested (15), justifying the enhanced mortality rate compared with control mice. Accordingly, Holtzclaw and colleagues (14) showed that intraperitoneal endotoxin challenge was associated with significant increase in mortality in transgenic sickle mice compared with control animals.…”

“…Immunoblotting for iNOS and endothelial NOS (eNOS) proteins was performed as described elsewhere (15). Briefly, the primary antibody against eNOS 3 protein (eNOS or NOS 3, Transduction Laboratory, Lexington, KY) or iNOS 2 protein (iNOS or NOS 2, Transduction Laboratories.…”

“…NOS activities were measured using transformation of [H 3 ]L-arginine to [H 3 ]L-citrulline as described elsewhere (15). Due to limited tissue homogenate availability and the low level of activities, these activities were assessed only in tissue supernatants reflecting mainly the activity of cytosolic enzyme, namely iNOS.…”

“…Accordingly, Holtzclaw and colleagues (14) showed that transgenic sickle mice had an enhanced response to inflammatory challenge compared with control animals. We recently demonstrated that NO production is reduced after peritonitis in rats, partly due to increased arginase activity (15). Induction of arginase, which is a competitive enzymatic system with NO synthase (NOS) for L-arginine use, could limit Larginine bioavailability as a substrate for NOS and thereby influence NO production (16).…”

Prediction of Nosocomial Infection Acquisition in Ventilated Patients by Nasal Nitric Oxide

“…NO is a broad-spectrum messenger involved in all biological processes including immunity (4) and also has direct antimicrobial activity (5). Some arguments suggest its usefulness for predicting immunosuppression and consequently the risk of nosocomial infection: (a) its fraction has been shown to be decreased in upper and lower respiratory tracts of patients with cystic fibrosis, and its deficiency has experimentally been shown to favor Pseudomonas aeruginosa infection (6,7); (b) a beneficial effect of NO inhalation on bacterial clearance of P. aeruginosa has been shown in animals (8); (c) immunonutrition using nutriments with L-arginine, the precursor of NO synthesis, has been associated with a reduction of nosocomial infections in surgical patients (3); and (d) we demonstrated that a decrease in exhaled NO constitutes a marker of postaggressive immunosuppression in an experimental model of sepsis (9). Besides this biological plausibility, NO measurement in the respiratory tract can be easily and immediately obtained at the bedside and is already used to assess various respiratory diseases (10).…”