Nitric oxide potentiates acute lung injury in an isolated rabbit lung model

Gaseous therapeutics in acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) remain major causes of morbidity and mortality in critical care medicine despite advances in therapeutic modalities. ALI can be associated with sepsis, trauma, pharmaceutical or xenobiotic exposures, high oxygen therapy (hyperoxia), and mechanical ventilation. Of the small gas molecules (NO, CO, H₂S) that arise in human beings from endogenous enzymatic activities, the physiological significance of NO is well established, whereas that of CO or H₂S remains controversial. Recent studies have explored the potential efficacy of inhalation therapies using these small gas molecules in animal models of ALI. NO has vasoregulatory and redox-active properties and can function as a selective pulmonary vasodilator. Inhaled NO (iNO) has shown promise as a therapy in animal models of ALI including endotoxin challenge, ischemia/reperfusion (I/R) injury, and lung transplantation. CO, another diatomic gas, can exert cellular tissue protection through antiapoptotic, anti-inflammatory, and antiproliferative effects. CO has shown therapeutic potential in animal models of endotoxin challenge, oxidative lung injury, I/R injury, pulmonary fibrosis, ventilator-induced lung injury, and lung transplantation. H₂S, a third potential therapeutic gas, can induce hypometabolic states in mice and can confer both pro- and anti-inflammatory effects in rodent models of ALI and sepsis. Clinical studies have shown variable results for the efficacy of iNO in lung transplantation and failure for this therapy to improve mortality in ARDS patients. No clinical studies have been conducted with H₂S. The clinical efficacy of CO remains unclear and awaits further controlled clinical studies in transplantation and sepsis.

Pre-emptive and continuous inhaled NO counteracts the cardiopulmonary consequences of extracorporeal circulation in a pig model

Cardiopulmonary bypass (CPB) activates a systemic inflammatory response characterized clinically by alterations in cardiovascular and pulmonary function. The aim of this study was to measure the cardiopulmonary consequences in sham-operated pigs, and in animals subjected to CPB in the presence or absence of lipopolysaccharide (LPS). We also investigated, if the perioperative administration of inhaled NO exerts significant cardiopulmonary effects in an anaesthetized and mechanically ventilated pig model of extracorporeal circulation. Thirty pigs were randomized into six equal groups (sham; sham+INO; CPB; CPB+INO; CPB+LPS; CPB+LPS+INO) and subjected to anaesthesia with mechanical ventilation for up to 24h. We found that CPB+LPS group has the highest degree of lung injury. We also demonstrated that there was a significant difference on the cardiovascular parameters (heart rate, central venous pressure, stroke volume index, and mean systemic arterial blood pressure) between the CPB groups and the sham groups. The deteriorated lung mechanics was associated with a decrease in active subfraction of surfactant (LA) with time during the procedure (P=0.0003), on which inhaled NO had only an initial beneficial effect. In our model, inhaled NO had no long-term beneficial effect on lung mechanics and surfactant homeostasis despite improving lung haemodynamics, inflammation, and oxygenation. We conclude from this study that the use of pre-emptive and continuous inhaled NO therapy has protective and safe effects against lung ischemia/reperfusion associated with CPB.

Adjuncts to Mechanical Ventilation in ARDS

Since its first description, acute respiratory distress syndrome has been characterized by abnormal physiologic and gas exchange properties of the lungs. Many adjunctive therapies have been developed to reduce the stresses of mechanical ventilation on already damaged lungs. We examined the mechanism of action and the latest clinical trial information of several adjunctive therapies including prone positioning, nitric oxide, extracorporeal membrane oxygenation, arterial venous carbon dioxide removal, and liquid ventilation. While all of these therapies have demonstrated short-term improvements in arterial blood gases and in the limitation of lung injury, none have shown an evidence-based survival benefit.

Modulation of pulmonary cytochrome P4501A1 expression by hyperoxia and inhaled nitric oxide in the newborn rat: implications for lung injury

Inhaled nitric oxide (iNO), with supplemental oxygen, is used in the treatment of hypoxic respiratory failure of the newborn. In this study, we tested the hypothesis that exposure of newborn rats to iNO, hyperoxia, or iNO + hyperoxia would modulate the expression of pulmonary cytochrome P450 (CYP)1A1 in relation to acute lung injury. Newborn Fischer 344 rats were maintained in room air, or exposed to iNO, hyperoxia (>95%), or iNO (20 or 40 ppm) + hyperoxia for up to 168 h, and lung injury parameters and CYP1A1 expression were studied. Animals given iNO (40 ppm) + hyperoxia were more susceptible to lung injury than those exposed to hyperoxia or iNO alone. On the other hand, animals exposed to iNO (20 ppm) + hyperoxia did not elicit lung damage. Pulmonary CYP1A1 protein and mRNA expression were induced by hyperoxia, iNO (20 or 40 ppm), or iNO (20 ppm) + hyperoxia for up to 168 h, compared with air-breathing controls. In animals given iNO (40 ppm) + hyperoxia, pulmonary CYP1A1 was enhanced at 48 h, followed by down-regulation at later time points. Immunohistochemistry experiments showed localization of CYP1A1 in the pulmonary epithelial and endothelial cells. In conclusion, because previous studies have shown beneficial effects of CYP1A1 induction in hyperoxic lung injury, our current observations showing maintenance of pulmonary CYP1A1 induction by iNO (20 ppm) + hyperoxia through the 168-h period support the hypothesis that this phenomenon may contribute to the protective effects of iNO against hyperoxic injury.

Inhaled nitric oxide exacerbated phorbol-induced acute lung injury in rats

In this study, we determined the effect of inhaled nitric oxide (NO) on the acute lung injury induced by phorbol myristate acetate (PMA) in isolated rat lung. Typical acute lung injury was induced successfully by PMA during 60 min of observation. PMA (2 microg/kg) elicited a significant increase in microvascular permeability, (measured using the capillary filtration coefficient Kfc), lung weight gain, lung weight/body weight ratio, pulmonary arterial pressure (PAP) and protein concentration of the bronchoalveolar lavage fluid. Pretreatment with inhaled NO (30 ppm) significantly exacerbated acute lung injury. All of the parameters reflective of lung injury increased significantly except PAP (P<0.05). Coadministration of Nomega-nitro-L-arginine methyl ester (L-NAME) (5 mM) attenuated the detrimental effect of inhaled NO in PMA-induced lung injury, except for PAP. In addition, L-NAME (5 mM) significantly attenuated PMA-induced acute lung injury except for PAP. These experimental data suggest that inhaled NO significantly exacerbated acute lung injury induced by PMA in rats. L-NAME attenuated the detrimental effect of inhaled NO.

Inhaled nitric oxide attenuates acute lung injury via inhibition of nuclear factor-kappa B and inflammation

The effect of inhaled nitric oxide (NO) on inflammatory process in acute lung injury (ALI) is unclear. The aims of this study were to 1) examine whether inhaled NO affects the biochemical lung injury parameters and cellular inflammatory responses and 2) determine the effect of inhaled NO on the activation of nuclear factor-kappa B (NF-kappa B) in lipopolysaccharide (LPS)-induced ALI. Compared with saline controls, rabbits treated intravenously with LPS showed increases in total protein and lactate dehydrogenase in the bronchoalveolar lavage (BAL) fluid, indicating ALI. LPS-treated animals with NO inhalation (LPS-NO) showed significant decreases in these parameters. Neutrophil numbers in the BAL fluid, the activity of reactive oxygen species in BAL cells, and the levels of interleukin (IL)-1 beta and IL-8 in alveolar macrophages were increased in LPS-treated animals. In contrast, neutrophil numbers and these cellular activities were substantially decreased in LPS-NO animals, compared with LPS-treated animals. NF-kappa B activation in alveolar macrophages from LPS-treated animals was also markedly increased, whereas this activity was effectively blocked in LPS-NO animals. These results suggest that inhaled NO attenuates LPS-induced ALI and pulmonary inflammation. This attenuation may be associated with the inhibition of NF-kappa B activation.

Hemodynamic effects of S-nitrosocysteine, an intravenous regional vasodilator

BACKGROUND

S-nitrosocysteine is a carrier form of nitric oxide that can be delivered intravenously. S-nitrosocysteine is rapidly metabolized by plasma (half-life = 2-3 seconds), forming nitric oxide and cysteine. With its short half-life and potent vasodilatory properties, S-nitrosocysteine may be useful as a pulmonary vasodilating agent in cases of postoperative and chronic pulmonary hypertension.

OBJECTIVE

Our objective was to determine the hemodynamic properties of S-nitrosocysteine on the pulmonary and systemic circulations to assess its potential utility as a pulmonary vasodilatory agent.

METHODS

Eleven adult swine were anesthetized. Thermodilution (Swan-Ganz; Baxter International, Inc, Deerfield, Ill) and arterial catheters were inserted. Flow probes were placed around the coronary, renal, superior mesenteric, and iliac arteries. Incremental infusion doses of S-nitrosocysteine (5-80 nmol. kg(-1). min(-1)) were delivered into the right atrium. Cardiac output, right and left heart pressures, heart rate, Pao(2), and iliac, renal, coronary, and mesenteric blood flow rates were recorded at baseline and at each infusion dose of S-nitrosocysteine.

RESULTS

Low-dose S-nitrosocysteine infusion decreased mean pulmonary artery pressure (15%, P =.013) without a significant reduction in mean systemic artery pressure. Higher dose infusions produced further dose-dependent declines in pulmonary vascular resistance and measurable reductions in systemic vascular resistance (P =.01). At an S-nitrosocysteine dosage of 40 nmol. kg(-1). min(-1), there was a significant reduction in renal (P <.001) and mesenteric (P =.003) blood flow but no change in iliac (P >.2) or coronary (P >.2) blood flow. Cardiac output remained constant up to infusion rates of 40 nmol. kg(-1). min(-1) (P >.2). Doses higher than 5 nmol. kg(-1). min(-1) resulted in a substantial dose-dependent reduction in Pao(2) (P <.001), suggesting dilation of atelectatic areas of the lung.

CONCLUSION

S-nitrosocysteine is a potent vasodilatory agent capable of overcoming the hypoxic vasoconstrictive response of the lung. Our results suggest it may prove useful as a pulmonary vasodilatory agent at low doses. Higher dose infusions reduce mean systemic pressure and lead to compensatory reductions in renal and mesenteric blood flow without a decrease in cardiac output.

Long-term inhalation of high-dose nitric oxide increases intraalveolar activation of coagulation system in mice

Inhalation of nitric oxide (NO) is useful for the treatment of patients with pulmonary hypertension. However, the potential toxicity of inhaled NO is still unclear. Coagulation activation plays an important role in lung injury. We assessed the effect of low- and high-dose inhaled NO on the coagulation system in the intraalveolar space of mice. The animals were assigned to five groups (n = 6): [RA] group, mice exposed to fresh air alone; [RA+2 ppm NO] group, fresh air and 2 ppm NO; [RA+40 ppm NO] group, fresh air and 40 ppm NO; [RA+2 ppm NO+O(2)] group, fresh air, 2 ppm NO and O(2); and [RA+40 ppm NO+O(2)] group, fresh air, 40 ppm NO and O(2). Each group was treated for 3 wk. Lung specimens of [RA+40 ppm NO] and [RA+40 ppm NO+O(2)] groups showed significant nitrotyrosine immunoreactivity. BALF concentrations of total protein, thrombin and soluble tissue factor were significantly increased in mice of [RA+40 ppm NO] and [RA+40 ppm NO+O(2)] groups compared with [RA] group. However, BALF concentrations of total protein, thrombin, and soluble tissue factor were not significantly increased in mice of [RA+2 ppm NO] and [RA+2 ppm NO+O(2)] groups compared with [RA] group. Lung tissue factor mRNA expression was higher in the high-dose NO group than in the low-dose NO group. NO donor increased significantly tissue factor activity on alveolar epithelial cells. This study has shown for the first time that long-term inhalation of high, but not low, concentration of NO may activate the clotting system by increasing the lung expression of tissue factor.

Sodium nitroprusside mitigates oleic acid-induced acute lung injury

BACKGROUND

Acute lung injury (ALI) is associated with pulmonary hypertension, intrapulmonary shunting, and increased microvascular permeability, leading to altered oxygenation capacity. Oleic acid (OA) creates a significant ALI that physiologically mimics human adult respiratory distress syndrome (ARDS). It has been hypothesized that pulmonary vasodilatation may improve ALI. Studies in our laboratory using this model and nitric oxide (NO) have shown that NO inhalation is detrimental and worsens the effects of OA. We studied the effect of pretreatment with a potent vasodilator, sodium nitroprusside (SNP), on ALI induced by OA in an isolated lung model. We hypothesized that pretreatment with SNP will worsen pulmonary hypertension and oxygenation in OA-induced ALI, similar to the effects seen with inhaled NO in this model.

METHODS

Rabbit heart lung blocks were isolated, flushed in vivo, harvested, immediately perfused with whole blood, and ventilated with 50% oxygen. Pulmonary artery pressure was determined every 15 seconds for 90 minutes of perfusion. Oxygenation was determined by blood gas analysis of pulmonary venous effluent at 0, 20, 40, 60, and 90 minutes after initiation of OA infusion. Four groups were studied: saline control (SC), oleic acid control (OAC; 20-minute infusion of 50% OA/ethanol into pulmonary circulation), SNP control (NPC; 10 microg/ kg/min SNP infused without subsequent OA infusion), and SNP treatment (NPRx); 10 microg/kg/min SNP infused before OA/ethanol. Pulmonary artery pressure (PAP), oxygenation (arterio-venous oxygen difference [AVO2], compliance (CPL), and wet/dry lung weight were determined.

RESULTS

No significant differences were found between the NPRx group and SC. Pretreatment with SNP eliminated the detrimental effects of OA infusion.

CONCLUSIONS

Contrary to our hypothesis, pretreatment with SNP eliminates the decrease in oxygenation and increase in lung weight, and ameliorates pulmonary hypertension in our isolated lung model of OA-induced ALI.