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Objective: Inhaled nitric oxide is used to treat hypoxia associated with acute lung injury. Endogenous nitric oxide regulates inflammatory responses, but the effect of inhaled nitric oxide therapy is unknown. We hypothesized that inhaled nitric oxide may alter inflammatory responses and endogenous nitric oxide synthase activity., Design: A randomized, prospective interventional study., Setting: A university hospital's general intensive care unit., Patients: Thirty-two patients with acute lung injury., Interventions: Patients who responded to test doses of nitric oxide were randomized to ventilator therapy with and without inhaled nitric oxide. The inhaled concentration of nitric oxide was determined by dose titration at 0, 2, 10, and 40 ppm and the minimum concentration used, which resulted in an increase in the PaO2/FIO2 ratio of at least 25%., Measurements and Main Results: Patients were followed up for 30 days or until death, and bronchoalveolar lavage (BAL) was performed at 0, 24, and 72 hrs. Nitric oxide synthase activity was measured spectrophotometrically, and myeloperoxidase, elastase, interleukin-8, and leukotrienes were measured in BAL fluid by enzyme immunoassay. Total nitrite and lipid peroxides in serum were measured colorimetrically. Nitric oxide synthase activity decreased (p = .01) and total nitrite increased (p = .02) in patients receiving inhaled nitric oxide. Other markers of inflammation in BAL fluid did not change. Lipid peroxide concentrations also did not alter., Conclusions: The decrease in activity of nitric oxide synthase in patients receiving nitric oxide is likely to be the result of feedback inhibition of the enzyme. This study shows that inhaled nitric oxide has no effect on several markers of the inflammatory response system and does not lead to increased oxidant stress.

In acute lung injury, neutrophil apoptosis may be important in regulating the inflammatory process by controlling neutrophil numbers and thus activity. Exogenous inhaled nitric oxide is now a widely used therapy in patients with acute lung injury, and its effects on apoptosis may be important. We investigated the effect of nitric oxide and peroxynitrite on apoptosis in lipopolysaccharide stimulated polymorphonuclear leukocytes as a model of nitric oxide-treated lung injury. Cells were incubated for up to 16 h with and without 1.7 microg/ml lipopolysaccharide and the nitric oxide donor GEA-3162 or the peroxynitrite donor SIN-1. Apoptosis was assessed using flow cytometry following annexin-V staining, after 4, 6, 8, and 16 h. Data were assessed using Kruskal-Wallis analysis of variance or Mann-Whitney U-test as appropriate. Annexin-V staining increased spontaneously over 16 h in untreated cells (p = .0002) and incubation with either 1000 microM SIN-1 or 10 microM GEA-3162 increased annexin staining at early time points in nonactivated cells. Apoptosis was attenuated when cells were exposed to lipopolysaccharide and both nitric oxide and peroxynitrite dose dependently inhibited this suppression at all time points and was most apparent at 16 h (p = .004 and .001, respectively). Exposure of activated neutrophils to exogenous nitric oxide or peroxynitrite has marked influences on apoptosis. This work has implications for the modulation of neutrophil function within the lung in patients with lung injury who receive inhaled nitric oxide therapy.

Unlabelled: Inhaled nitric oxide is now widely used in the treatment of hypoxemia and pulmonary hypertension in critically ill patients. Interleukin-8 (IL-8) and neutrophil elastase are important markers of the onset and severity of acute lung injury. We studied the effects of nitric oxide and peroxynitrite on IL-8) and elastase accumulation in lipopolysaccharide-activated whole blood. The nitric oxide donor (GEA-3162) did not affect IL-8 accumulation (P = 0.195) but did cause an increase in elastase accumulation (P = 0.007). The peroxynitrite donor (SIN-1) caused an increase in both IL-8 accumulation (P = 0.0004) and elastase accumulation (P = 0.007). The lack of effect of nitric oxide could be explained by the scavenging of nitric oxide by hemoglobin. These results suggest that modulation of the inflammatory response may occur during inhaled nitric oxide therapy in the critically ill., Implications: Inhaled nitric oxide, used in lung injury, reacts within the lung, forming peroxynitrite. We investigated the effect of nitric oxide and peroxynitrite on interleukin-8 and elastase release by white cells during inflammation. Nitric oxide and peroxynitrite had marked effects on elastase and interleukin-8, which suggests modulation of the inflammatory response.

Patients with acute inflammatory lung injury are commonly treated with inhaled nitric oxide. Nitric oxide has profound immunoregulatory effects. Increased concentrations of the cytokine interleukin-8 (IL-8) in bronchoalveolar lavage fluid has been associated with disease severity. We have investigated the effects of a nitric oxide donor and a combined nitric oxide-superoxide donor on lipopolysaccharide-mediated accumulation of IL-8 from cultured human neutrophils. Interleukin-8 was measured in culture supernatant after 20 h using enzyme immunoassay. The combined nitric oxide-superoxide donor, 3-morpholinosydnonimine (SIN-1), dose-dependently decreased lipopolysaccharide-mediated IL-8 accumulation (P < 0.01). SIN-1 also decreased IL-8 accumulation from unstimulated neutrophils (P < 0.001). In contrast, the pure nitric oxide donor, 1,2,3,4-oxatriazolium 5-amino chloride (GEA-3162), increased stimulated IL-8 accumulation (P < 0.01) and also increased IL-8 accumulation in unstimulated cells (P < 0.002). Nitric oxide and superoxide have profound effects on IL-8. These results have important implications for the treatment of patients with acute lung injury with inhaled nitric oxide.

Background and objective: The glutamate-nitric oxide-cyclic guanosine monophosphate pathway has been identified as a potential target for anaesthetic agents. However, mice deficient in neuronal nitric oxide synthase have a similar susceptibility to volatile anaesthetic agents to wild-type mice and are not affected by non-isoform selective inhibitors. We hypothesized that the neuronal nitric oxide synthase selective inhibitor, 7-nitroindazole, would also reduce the propofol requirements in wild-type mice but would have no effect in neuronal nitric oxide synthase knockout mice. Methods: We determined the time to loss of righting reflex, time to painful stimulus and time to regaining the righting reflex in neuronal nitric oxide synthase knockout and wild-type mice following the intraperitoneal injection of propofol in untreated, 7-nitroindazole and vehicle only treated animals (n = 6 per group). Propofol (200 mg kg-1) resulted in loss of righting reflex in the untreated and vehicle only groups but was lethal in 7-nitroindazole pre-treated mice, requiring a reduced dose of propofol (100 mg kg-1). Results: 7-nitroindazole pre-treatment significantly reduced the loss of righting reflex (P < 0.001) in both wild-type and knockout mice when compared to untreated and vehicle only pre-treated animals, but had no effect on time to painful stimulus or regaining of the righting reflex. 7-nitroindazole reduced the propofol requirements in knockout mice to the same extent as in wild-type animals. Conclusions: Propofol exerts its anaesthetic effects at least partially via the glutamate-nitric oxide-cyclic guanosine monophosphate pathway. The neuronal nitric oxide synthase knockout mice are sensitive to neuronal nitric oxide synthase selective inhibition suggesting that compensatory pathways in neuronal nitric oxide synthase knockout mice exist. [ABSTRACT FROM AUTHOR]