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Rationale: Inhalation of nitric oxide (NO) exerts selective pulmonary vasodilation. Nitric oxide also has an antimicrobial effect on a broad spectrum of pathogenic viruses, bacteria and fungi. Objectives: The aim of this study was to investigate the effect of inhaled NO on bacterial burden and disease outcome in a murine model of Klebsiella pneumonia. Methods: Mice were infected with Klebsiella pneumoniae and inhaled either air alone, air mixed with constant levels of NO (at 80, 160, or 200 parts per million (ppm)) or air intermittently mixed with high dose NO (300 ppm). Forty-eight hours after airway inoculation, the number of viable bacteria in lung, spleen and blood was determined. The extent of infiltration of the lungs by inflammatory cells and the level of myeloperoxidase activity in the lungs were measured. Atomic force microscopy was used to investigate a possible mechanism by which nitric oxide exerts a bactericidal effect. Measurements and main results: Compared to control animals infected with K. pneumoniae and breathed air alone, intermittent breathing of NO (300 ppm) reduced viable bacterial counts in lung and spleen tissue. Inhaled NO reduced infection-induced lung inflammation and improved overall survival of mice. NO destroyed the cell wall of K. pneumoniae and killed multiple-drug resistant K. pneumoniae in-vitro. Conclusions: Intermittent administration of high dose NO may be an effective approach to the treatment of pneumonia caused by K. pneumoniae.

Objectives: To test the feasibility, safety, and efficacy of intratracheal delivery of nitric oxide (NO) generated from air by pulsed electrical discharge via a Scoop catheter. Study design: We studied healthy 3- to 4-month-old lambs weighing 34 ± 4 kg (mean ± SD, n = 6). A transtracheal Scoop catheter was inserted through a cuffed tracheostomy tube. U46619 was infused to increase mean pulmonary arterial pressure (mPAP) from 16 ± 1 to 32 ± 3 mmHg (mean ± SD). Electrically generated NO was delivered via the Scoop catheter to awake lambs. A sampling line, to monitor NO and nitrogen dioxide (NO2) levels, was placed in the distal trachea of the lambs. The effect of varying doses of electrically generated NO, produced continuously, on pulmonary hypertension was assessed. Results: In awake lambs with acute pulmonary hypertension, NO was continuously delivered via the Scoop catheter at 400 ml/min. NO induced pulmonary vasodilation. NO2 levels, measured in the trachea, were below 0.5 ppm at intratracheal NO doses of 10–80 ppm. No changes were detected in the levels of methemoglobin in blood samples before and after 5 min of NO breathing. Conclusions: Continuously delivering electrically generated NO through a Scoop catheter produces vasodilation of the pulmonary vasculature of awake lambs with pulmonary hypertension. Transtracheal NO delivery may provide a long-term treatment for patients with chronic pulmonary hypertension as an outpatient without requiring a mask or tracheal intubation.

BACKGROUND: Rescue therapies to treat or prevent progression of coronavirus disease 2019 (COVID-19) hypoxic respiratory failure in pregnant patients are lacking. METHOD: To treat pregnant patients meeting criteria for severe or critical COVID-19 with high-dose (160-200 ppm) nitric oxide by mask twice daily and report on their clinical response. EXPERIENCE: Six pregnant patients were admitted with severe or critical COVID-19 at Massachusetts General Hospital from April to June 2020 and received inhalational nitric oxide therapy. All patients tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A total of 39 treatments was administered. An improvement in cardiopulmonary function was observed after commencing nitric oxide gas, as evidenced by an increase in systemic oxygenation in each administration session among those with evidence of baseline hypoxemia and reduction of tachypnea in all patients in each session. Three patients delivered a total of four neonates during hospitalization. At 28-day follow-up, all three patients were home and their newborns were in good condition. Three of the six patients remain pregnant after hospital discharge. Five patients had two negative test results on nasopharyngeal swab for SARS-CoV-2 within 28 days from admission. CONCLUSION: Nitric oxide at 160-200 ppm is easy to use, appears to be well tolerated, and might be of benefit in pregnant patients with COVID-19 with hypoxic respiratory failure.

Background: There is an increasing interest in safely delivering high dose of inhaled nitric oxide (NO) as an antimicrobial and antiviral therapeutics for spontaneously breathing patients. A novel NO delivery system is described. Methods: We developed a gas delivery system that utilizes standard respiratory circuit connectors, a reservoir bag, and a scavenging chamber containing calcium hydroxide. The performance of the system was tested using a mechanical lung, assessing the NO concentration delivered at varying inspiratory flows. Safety was assessed in vitro and in vivo by measuring nitrogen dioxide (NO2) levels in the delivered NO gas. Lastly, we measured the inspired and expired NO and NO2 of this system in 5 healthy subjects during a 15-min administration of high dose NO (160 parts-per-million, ppm) using our delivery system. Results: The system demonstrated stable delivery of prescribed NO levels at various inspiratory flow rates (0–50 L/min). The reservoir bag and a high flow of entering air minimized the oscillation of NO concentrations during inspiration on average 4.6 ppm for each 10 L/min increment in lung inspiratory flow. The calcium hydroxide scavenger reduced the inhaled NO2 concentration on average 0.9 ppm (95% CI -1.58, −0.22; p =.01). We performed 49 NO administrations of 160 ppm in 5 subjects. The average concentration of inspired NO was 164.8±10.74 ppm, with inspired NO2 levels of 0.7±0.13 ppm. The subjects did not experience any adverse events; transcutaneous methemoglobin concentrations increased from 1.05±0.58 to 2.26±0.47%. Conclusions: The system we developed to administer high-dose NO for inhalation is easy to build, reliable, was well tolerated in healthy subjects.

Rationale: No medical intervention has been identified that decreases acute kidney injury and improves renal outcome at 1 year after cardiac surgery. Objectives: To determine whether administration of nitric oxide reduces the incidence of postoperative acute kidney injury and improves long-term kidney outcomes after multiple cardiac valve replacement requiring prolonged cardiopulmonary bypass. Methods: Two hundred and forty-four patients undergoing elective, multiple valve replacement surgery, mostly due to rheumatic fever, were randomized to receive either nitric oxide (treatment) or nitrogen (control). Nitric oxide and nitrogen were administered via the gas exchanger during cardiopulmonary bypass and by inhalation for 24 hours postoperatively. Measurements and Main Results: The primary outcome was as follows: oxidation of ferrous plasma oxyhemoglobin to ferric methemoglobin was associated with reduced postoperative acute kidney injury from 64% (control group) to 50% (nitric oxide group) (relative risk [RR], 0.78; 95% confidence interval [CI], 0.62-0.97; P = 0.014). Secondary outcomes were as follows: at 90 days, transition to stage 3 chronic kidney disease was reduced from 33% in the control group to 21% in the treatment group (RR, 0.64; 95% CI, 0.41-0.99; P = 0.024) and at 1 year, from 31% to 18% (RR, 0.59; 95% CI, 0.36-0.96; P = 0.017). Nitric oxide treatment reduced the overall major adverse kidney events at 30 days (RR, 0.40; 95% CI, 0.18-0.92; P = 0.016), 90 days (RR, 0.40; 95% CI, 0.17-0.92; P = 0.015), and 1 year (RR, 0.47; 95% CI, 0.20-1.10; P = 0.041). Conclusions: In patients undergoing multiple valve replacement and prolonged cardiopulmonary bypass, administration of nitric oxide decreased the incidence of acute kidney injury, transition to stage 3 chronic kidney disease, and major adverse kidney events at 30 days, 90 days, and 1 year.

The most common pediatric mitochondrial disease is Leigh syndrome, an episodic, subacute neurodegeneration that can lead to death within the first few years of life, for which there are no proven general therapies.Mice lacking the complex I subunit, Ndufs4, develop a fatal progressive encephalopathy resembling Leigh syndrome and die at ≈60 d of age. We previously reported that continuously breathing normobaric 11% O2 from an early age prevents neurological disease and dramatically improves survival in these mice. Here, we report three advances. First, we report updated survival curves and organ pathology in Ndufs4 KO mice exposed to hypoxia or hyperoxia. Whereas normoxia-treated KO mice die from neurodegeneration at about 60 d, hypoxia-treated mice eventually die at about 270 d, likely from cardiac disease, and hyperoxia-treated mice die within days from acute pulmonary edema. Second, we report that more conservative hypoxia regimens, such as continuous normobaric 17% O2 or intermittent hypoxia, are ineffective in preventing neuropathology. Finally, we show that breathing normobaric 11% O2 in mice with late-stage encephalopathy reverses their established neurological disease, evidenced by improved behavior, circulating disease biomarkers, and survival rates. Importantly, the pathognomonic MRI brain lesions and neurohistopathologic findings are reversed after 4 wk of hypoxia. Upon return to normoxia, Ndufs4 KO mice die within days. Future work is required to determine if hypoxia can be used to prevent and reverse neurodegeneration in other animal models, and to determine if it can be provided in a safe and practical manner to allow in-hospital human therapeutic trials.

Objectives Prolonged cardiopulmonary bypass (CPB) is associated with hemolysis, resulting in increased plasma oxyhemoglobin and vascular nitric oxide depletion. The authors hypothesized that hemolysis associated with CPB would reduce nitric oxide bioavailability, resulting in high pulmonary and systemic vascular resistances that after CPB would normalize gradually over time, due to clearance of plasma oxyhemoglobin. The authors also investigated whether prolonged CPB (≥140 min) produced increased levels of hemolysis and greater pulmonary and systemic vasoconstriction. Design Prospective cohort study. Setting Single-center university hospital. Patients The study comprised 50 patients undergoing elective cardiac surgery requiring CPB. Interventions Plasma hemoglobin and plasma nitric oxide consumption were measured before surgery and after CPB. Pulmonary and systemic hemodynamics were measured after CPB. The effects of short (<140 min) and prolonged (≥140 min) CPB on these parameters were considered. Measurements and Main Results Pulmonary and systemic vascular resistances and plasma hemoglobin and nitric oxide consumption were highest at 15 minutes after CPB and then decreased over time. Pulmonary and systemic vascular resistances and plasma hemoglobin and plasma nitric oxide consumption were higher in patients requiring prolonged CPB. The reduction in plasma nitric oxide consumption from 15 minutes to 4 hours after CPB was correlated independently with the reductions in pulmonary and systemic vascular resistances. Conclusions Prolonged CPB was associated with increased plasma hemoglobin and plasma nitric oxide consumption and pulmonary and systemic vascular resistances. The reduction in plasma nitric oxide consumption at 4 hours after CPB was an independent predictor of the concomitant reductions in pulmonary and systemic vascular resistances.

Intravascular hemolysis produces injury in a variety of human diseases including hemoglobinopathies, malaria, and sepsis. The adverse effects of increased plasma hemoglobin are partly mediated by depletion of nitric oxide (NO) and result in vasoconstriction. Circulating plasma proteins haptoglobin and hemopexin scavenge extracellular hemoglobin and cell-free heme, respectively. The ability of human haptoglobin or hemopexin to inhibit the adverse effects of NO scavenging by circulating murine hemoglobin was tested in C57Bl/6 mice. In healthy awake mice, the systemic hemodynamic effects of intravenous coinfusion of cell-free hemoglobin and exogenous haptoglobin or of cell-free hemoglobin and hemopexin were compared with the hemodynamic effects of infusion of cell-free hemoglobin or control protein (albumin) alone. We also studied the hemodynamic effects of infusing hemoglobin and haptoglobin as well as injecting either hemoglobin or albumin alone in mice fed a high-fat diet (HFD) and in diabetic (db/db) mice. Coinfusion of a 1:1 weight ratio of haptoglobin but not hemopexin with cell-free hemoglobin prevented hemoglobin-induced systemic hypertension in healthy awake mice. In mice fed a HFD and in diabetic mice, coinfusion of haptoglobin mixed with an equal mass of cell-free hemoglobin did not reverse hemoglobin-induced hypertension. Haptoglobin retained cell-free hemoglobin in plasma, but neither haptoglobin nor hemopexin affected the ability of hemoglobin to scavenge NO ex vivo. In conclusion, in healthy C57Bl/6 mice with normal endothelium, coadministration of haptoglobin but not hemopexin with cell-free hemoglobin prevents acute hemoglobin-induced systemic hypertension by compartmentalizing cell-free hemoglobin in plasma. In murine diseases associated with endothelial dysfunction, haptoglobin therapy appears to be insufficient to prevent hemoglobin-induced vasoconstriction. New & Noteworthy Coadministraton of haptoglobin but not hemopexin with cell-free hemoglo

Defects in the mitochondrial respiratory chain (RC) underlie a spectrum of human conditions, ranging from devastating inborn errors of metabolism to aging. We performed a genome-wide Cas9-mediated screen to identify factors that are protective during RC inhibition. Our results highlight the hypoxia response, an endogenous program evolved to adapt to limited oxygen availability. Genetic or small-molecule activation of the hypoxia response is protective against mitochondrial toxicity in cultured cells and zebrafish models. Chronic hypoxia leads to a marked improvement in survival, body weight, body temperature, behavior, neuropathology, and disease biomarkers in a genetic mouse model of Leigh syndrome, the most common pediatric manifestation of mitochondrial disease. Further preclinical studies are required to assess whether hypoxic exposure can be developed into a safe and effective treatment for human diseases associated with mitochondrial dysfunction., National Institute of Mental Health (U.S.) (Grant 5DP1-MH100706), National Institute of Mental Health (U.S.) (Grant 1R01-MH110049), National Institute of Neurological Diseases and Stroke (U.S.) (Grant 5R01DK097768-03)

Contains research objectives and reports on six research projects., U.S. Public Health Service (B-3055), U.S. Public Health Service (B-3090), Office of Naval Research (Nonr-1841 (70)), Air Force (AF33(616)-7588), Air Force (AFAFOSR-155-63), Army Chemical Corps (DA-18-108-405-Cml-942), National Science Foundation (Grant G-16526)