Inhaled nitric oxide

Nitric Oxide in Post-cardiac Arrest Syndrome

Sudden cardiac arrest is a leading cause of death worldwide. Although the methods of cardiopulmonary resuscitation have been improved, mortality is still unacceptably high, and many survivors suffer from lasting neurological deficits due to the post-cardiac arrest syndrome (PCAS). Pathophysiologically, generalized vascular endothelial dysfunction accompanied by platelet activation and systemic inflammation has been implicated in the pathogenesis of PCAS. Because endothelial-derived nitric oxide (NO) plays a central role in maintaining vascular homeostasis, the role of NO-dependent signaling has been a focus of the intense investigation. Recent preclinical studies showed that therapeutic interventions that increase vascular NO bioavailability may improve outcomes after cardiac arrest complicated with PCAS. In particular, NO inhalation therapy has been shown to improve neurological outcomes and survival in multiple species. Clinical studies examining the safety and efficacy of inhaled NO in patients sustaining PCAS are warranted.

Implication of inhaled nitric oxide for the treatment of critically ill COVID-19 patients with pulmonary hypertension

Aims

This study aims to analyse whether inhaled nitric oxide (iNO) was beneficial in the treatment of coronavirus disease 2019 (COVID‐19) patients with pulmonary hypertension.

Methods and results

Five critically ill COVID‐19 patients with pulmonary hypertension designated Cases 1–5 were retrospectively included. Clinical data before and after iNO treatment were serially collected and compared between patients with or without iNO treatment. The five cases experienced pulmonary artery systolic pressure (PASP) elevation (≥50 mmHg) at 30, 24, 33, 23, and 24 days after illness onset (d.a.o), respectively. Cases 1–3 received iNO treatment on the 24th, 13th, and 1st day after the first elevation of PASP, with concentrations varied from 10 to 20 ppm based on the changes of PASP and blood pressure for 10, 9, and 5 days, respectively. Upon iNO treatment, PASP of Cases 1 and 2 returned to normal on the 10th day and 1st day, and maintained between 50 and 58 mmHg in Case 3. Pa0₂/Fi0₂ increased from 88 to 124, 51 to 118, and 146 to 244, respectively. SPO₂ increased from 91% to 97% for Case 1 and maintained a high level above 97% for Case 2. Cardiac function remained normal in the three patients after treatment. Moreover, Cases 1 and 3 survived from severe acute respiratory syndrome coronavirus 2 infection, while Case 2 finally died on the 36th day after the first elevation of PASP due to severe complications. Both cases who did not receive iNO treatment experienced a sudden decrease of PASP and Pa0₂/Fi0₂ due to right heart failure and then died.

Conclusions

Inhaled nitric oxide treatment was beneficial in reducing and stabilizing the PASP and might also reduce the risk of right heart failure in COVID‐19 with pulmonary hypertension.

Mitigation of the replication of SARS-CoV-2 by nitric oxide in vitro

The ongoing SARS-CoV-2 pandemic is a global public health emergency posing a high burden on nations' health care systems and economies. Despite the great effort put in the development of vaccines and specific treatments, no prophylaxis or effective therapeutics are currently available. Nitric oxide (NO) is a broad-spectrum antimicrobial and a potent vasodilator that has proved to be effective in reducing SARS-CoV replication and hypoxia in patients with severe acute respiratory syndrome. Given the potential of NO as treatment for SARS-CoV-2 infection, we have evaluated the in vitro antiviral effect of NO on SARS-CoV-2 replication. The NO-donor S-nitroso-N-acetylpenicillamine (SNAP) had a dose dependent inhibitory effect on SARS-CoV-2 replication, while the non S-nitrosated NAP was not active, as expected. Although the viral replication was not completely abolished (at 200 μM and 400 μM), SNAP delayed or completely prevented the development of viral cytopathic effect in treated cells, and the observed protective effect correlated with the level of inhibition of the viral replication. The capacity of the NO released from SNAP to covalently bind and inhibit SARS-CoV-2 3CL recombinant protease in vitro was also tested. The observed reduction in SARS-CoV-2 protease activity was consistent with S-nitrosation of the enzyme active site cysteine.

Pharmacological management of adult patients with acute respiratory distress syndrome

INTRODUCTION

There is still no definite drug for acute respiratory distress syndrome (ARDS) that is capable of reducing either short-term or long-term mortality. Therefore, great efforts are being made to identify a pharmacological approach that can be really effective.

AREAS COVERED

This review focuses on current challenges and future directions in the pharmacological management of ARDS, regardless of anti-infective treatments. The authors have excluded small randomized controlled trials (RCTs) with less than 60 patients because those studies do not have statistical power for outcome data, and also anecdotal trials but have considered the last meta-analysis on any drug.

EXPERT OPINION

There has been substantial progress in our knowledge of ARDS over the past two decades and many drugs have been used in its treatment. Nevertheless, effective targeted pharmacological treatments for ARDS are still lacking. The likely reason why a pharmacological approach is beneficial for some patients, but harmful for others is that ARDS is an extremely heterogeneous syndrome. To overcome this issue, a precision approach for ARDS, whereby therapies are specifically targeted to patients most likely to benefit, has been proposed. At present, however, the application of this approach seems to be a difficult task.

Blood nitrate and nitrite modulating nitric oxide bioavailability: Potential therapeutic functions in COVID-19

Most outcomes of COVID-19 are associated with dysfunction of the vascular system, particularly in the lung. Inhalation of nitric oxide (NO) gas is currently being investigated as a treatment for patients with moderate to severe COVID-19. In addition to the expected vasodilation effect, it has been also suggested that NO potentially prevents infection by SARS-CoV-2. Since NO is an unstable radical molecule that is easily oxidized by multiple mechanisms in the human body, it is practically difficult to control its concentration at lesions that need NO. Inorganic nitrate and/or nitrite are known as precursors of NO that can be produced through chemical as well enzymatic reduction. It appears that this NO synthase (NOS)-independent mechanism has been overlooked in the current developing of clinical treatments. Here, I suggest the missing link between nitrate and COVID-19 in terms of hypoxic NO generation.

Clinical use of inhaled nitric oxide: Local and systemic applications

Upon the FDA approval for inhaled nitric oxide (iNO) in 1999 to treat persistent pulmonary hypertension in neonates, iNO has proven to be a beneficial therapeutic in multiple diseases. We aim to review applications of iNO that have modeled its protective and therapeutic attributes, as well as highlight preliminary studies that could allude to future avenues of use. Numerous publications have reported specific incidences where iNO therapy has proved advantageous, while some applications have potential after further validation. Establishing guidelines on dosing, duration, and defined clinical uses are crucial for the future of iNO. Delivery of iNO has been controlled by a sole distributor, and comes with high cost, and lack of portability. A shift in patents has allowed for new designs for iNO device synthesis, with many new developments of iNO medical devices that will likely change the future of iNO in a medical setting.

Controlled release of H2S and NO gases through CO2-stimulated anion exchange

Difficulties related to handling gases are a common bottleneck for applications. Although solid materials that release gas molecules under external stimuli exist, they require an external energy or a device for reliable operation. Herein, we report a CO₂ stimulus for controlled release of p.p.m.-level functional gases from solid materials. A CO₂-preferential anion-exchange property of layered double hydroxides and redox reactions in gas molecules are combined to release various gases (including H₂S and NO) under ambient air from HS⁻ and NO₂⁻-incorporated layered double hydroxides, respectively. The profiles of gas release are mainly governed by the difference of pK_a between H₂CO₃ and resulting acids (formed through protonation of interlayer anions), and are not so susceptible to the variation of relative humidity in air. Moreover, structural modulation of solid materials enables fine control of the gas release profiles. The use of safe, ubiquitous, and nearly constant (~400 p.p.m. in atmosphere) CO₂ stimulus offers broad applications for functional gases.

Solid materials releasing gas molecules under external stimuli usually require external energy for reliable operation. Here the authors synthesize layered double hydroxides for the autonomous release of H₂S and NO gases in response to CO₂-stimulus.

A pilot study on the kinetics of metabolites and microvascular cutaneous effects of nitric oxide inhalation in healthy volunteers

RATIONALE

Inhaled nitric oxide (NO) exerts a variety of effects through metabolites and these play an important role in regulation of hemodynamics in the body. A detailed investigation into the generation of these metabolites has been overlooked.

OBJECTIVES

We investigated the kinetics of nitrite and S-nitrosothiol-hemoglobin (SNO-Hb) in plasma derived from inhaled NO subjects and how this modifies the cutaneous microvascular response.

FINDINGS

We enrolled 15 healthy volunteers. Plasma nitrite levels at baseline and during NO inhalation (15 minutes at 40 ppm) were 102 (86-118) and 114 (87-129) nM, respectively. The nitrite peak occurred at 5 minutes of discontinuing NO (131 (104-170) nM). Plasma nitrate levels were not significantly different during the study. SNO-Hb molar ratio levels at baseline and during NO inhalation were 4.7E-3 (2.5E-3-5.8E-3) and 7.8E-3 (4.1E-3-13.0E-3), respectively. Levels of SNO-Hb continued to climb up to the last study time point (30 min: 10.6E-3 (5.3E-3-15.5E-3)). The response to acetylcholine iontophoresis both before and during NO inhalation was inversely associated with the SNO-Hb level (r: -0.57, p = 0.03, and r: -0.54, p = 0.04, respectively).

CONCLUSIONS

Both nitrite and SNO-Hb increase during NO inhalation. Nitrite increases first, followed by a more sustained increase in Hb-SNO. Nitrite and Hb-SNO could be a mobile reservoir of NO with potential implications on the systemic microvasculature.

Inhaled Pulmonary Vasodilators and Thoracic Organ Transplantation: Does Evidence Support Its Use and Cost Benefit?

In heart transplantation, pulmonary hypertension and increased pulmonary vascular resistance followed by donor right ventricular dysfunction remain a major cause of perioperative morbidity and mortality. In lung transplantation, primary graft dysfunction remains a major obstacle because it can cause bronchiolitis obliterans and mortality. Pulmonary vasodilators have been used as an adjunct therapy for heart or lung transplantation, mainly to treat pulmonary hypertension, right ventricular failure, and associated refractory hypoxemia. Among pulmonary vasodilators, inhaled nitric oxide is unique in that it is selective in pulmonary circulation and causes fewer systemic complications such as hypotension, flushing, or coagulopathy. Nitric oxide is expected to prevent or attenuate primary graft dysfunction by decreasing ischemia-reperfusion injury in lung transplantation. However, when considering the long-term benefit of these medications, little evidence supports their use in heart or lung transplantation. Current guidelines endorse inhaled vasodilators for managing immediate postoperative right ventricular failure in lung or heart transplantation, but no guidance is offered regarding agent selection, dosing, or administration. This review presents the current evidence of inhaled nitric oxide in lung or heart transplantation as well as comparisons with other pulmonary vasodilators including cost differences in consideration of economic pressures to contain rising pharmacy costs.

Nitric oxide is not just blowing in the wind

LINKED ARTICLES

This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.