Inhaled nitric oxide reduces human lung allograft dysfunction

Long-Term Survival Following Primary Graft Dysfunction Development in Lung Transplantation

INTRODUCTION

Primary graft dysfunction (PGD) is a known risk factor for early mortality following lung transplant (LT). However, the outcomes of patients who achieve long-term survival following index hospitalization are unknown. We aimed to determine the long-term association of PGD grade 3 (PGD3) in patients without in-hospital mortality.

METHODS

LT recipients were identified from the United Network for Organ Sharing Database. Patients were stratified based on the grade of PGD at 72 h (No PGD, Grade 1/2 or Grade 3). Groups were assessed with comparative statistics. Long-term survival was evaluated using Kaplan-Meier methods and a multivariable shared frailty model including recipient, donor, and transplant characteristics.

RESULTS

The PGD3 group had significantly increased length of stay, dialysis, and treated rejection post-transplant (P < 0.001). Unadjusted survival analysis revealed a significant difference in long-term survival (P < 0.001) between groups; however, following adjustment, PGD3 was not independently associated with long-term survival (hazard ratio: 0.972; 95% confidence interval: 0.862-1.096). Increased mortality was significantly associated with increased recipient age and treated rejection. Decreased mortality was significantly associated with no donor diabetes, bilateral LT as compared to single LT, transplant in 2015-2016 and 2017-2018, and no post-transplant dialysis.

CONCLUSIONS

While PGD3 remains a challenge post LT, PGD3 at 72 h is not independently associated with decreased long-term survival, while complications such as dialysis and rejection are, in patients who survive index hospitalization. Transplant providers should be aggressive in preventing further complications in recipients with severe PGD to minimize the negative association on long-term survival.

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Primary graft dysfunction following lung transplantation: From pathogenesis to future frontiers

Lung transplantation is the treatment of choice for patients with end-stage lung disease. Currently, just under 5000 lung transplants are performed worldwide annually. However, a major scourge leading to 90-d and 1-year mortality remains primary graft dysfunction. It is a spectrum of lung injury ranging from mild to severe depending on the level of hypoxaemia and lung injury post-transplant. This review aims to provide an in-depth analysis of the epidemiology, pathophysiology, risk factors, outcomes, and future frontiers involved in mitigating primary graft dysfunction. The current diagnostic criteria are examined alongside changes from the previous definition. We also highlight the issues surrounding chronic lung allograft dysfunction and identify the novel therapies available for ex-vivo lung perfusion. Although primary graft dysfunction remains a significant contributor to 90-d and 1-year mortality, ongoing research and development abreast with current technological advancements have shed some light on the issue in pursuit of future diagnostic and therapeutic tools.

Critical Care Management of the Lung Transplant Recipient

Lung transplantation is often the only treatment option for patients with severe irreversible lung disease. Improvements in donor and recipient selection, organ allocation, surgical techniques, and immunosuppression have all contributed to better survival outcomes after lung transplantation. Nonetheless, lung transplant recipients still experience frequent complications, often necessitating treatment in an intensive care setting. In addition, the use of extracorporeal life support as a means of bridging critically ill patients to lung transplantation has become more widespread. This review focuses on the critical care aspects of lung transplantation, both before and after surgery.

An electrochemical nitric oxide generator for in-home inhalation therapy in pulmonary artery hypertension

BACKGROUND

Inhaled NO is a selective pulmonary vasodilator proven to be therapeutic for patients with pulmonary artery hypertension (PAH). The most common NO delivery system in clinical practice is cylinder-based, but unfortunately limited by its high costs, complicated delivery, and the requirement of an extensive supply chain, leaving vast unmet medical needs globally.

METHODS

To address the need for rapid, affordable, and safe production of nitric oxide (NO) for in-home inhalation therapy in patients with PAH. We developed a novel portable device to derive NO from a nitrite complex solution with a copper(II)-ligand catalyst, and further examined its effectiveness in a porcine model of PAH. This model was established by using female Bama miniature pig and induced by monocrotaline (MCT) administration.

RESULTS

This generator could rapidly and safely produce therapeutic NO at concentrations ranging from 0 to 100 parts per million (ppm) with the least disproportionated nitrogen dioxide (NO2) and byproducts. It could effectively alleviate pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) in piglets with PAH, without causing major physiologic disruptions.

CONCLUSIONS

Our electrochemical NO generator is able to produce the desired NO doses for pulmonary vasodilation in a safe and sustainable way, with low costs, which paves the way for its subsequent clinical trials in the patient with PAH and other common cardiopulmonary conditions with a high disease burden around the world.

Review of outcomes of delayed chest closure following lung transplantation: a meta-analysis

Purpose

The clinical outcomes of delayed chest closure (DCC) compared with primary chest closure (PCC) following lung transplantation, including perioperative outcomes and long-term survival, remained controversial. This was the first systematic review and meta-analysis aimed to identify the short- and long-term outcomes of DCC following lung transplantation.

Methods

We comprehensively searched electronic literature from 4 databases up to April 1st, 2022. Dichotomous data and continuous data were pooled with odds ratio and weighted mean difference, respectively. The quality of included studies was assessed with the Newcastle–Ottawa Scale.

Results

Ten studies were included in the systematic review and 4 studies were included in the meta-analysis. Pooled analysis showed that DCC was associated with an increased risk of surgical site infection, prolonged hospital stays, and higher risk of primary graft dysfunction compared to PCC. The 30 day and 5 year survival were higher in PCC cohort compared with DCC cohort while differences in survival at 6 months was insignificant.

Conclusion

Our findings do not support the aggressive application of DCC. DCC should be cautiously applied since its association with worse perioperative outcomes and higher mortality. But it remains the life-saving steps under dangerous circumstances.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury after transplantation characterized by hypoxemia and the development of alveolar infiltrates on chest radiograph that occurs within 72 hours of reperfusion. PGD is among the most common early complications following lung transplantation and significantly contributes to increased short-term morbidity and mortality. In addition, severe PGD has been associated with higher 90-day and 1-year mortality rates compared with absent or less severe PGD and is a significant risk factor for the subsequent development of chronic lung allograft dysfunction. The International Society for Heart and Lung Transplantation released updated consensus guidelines in 2017, defining grade 3 PGD, the most severe form, by the presence of alveolar infiltrates and a ratio of PaO₂:FiO₂ less than 200. Multiple donor-related, recipient-related, and perioperative risk factors for PGD have been identified, many of which are potentially modifiable. Consistently identified risk factors include donor tobacco and alcohol use; increased recipient body mass index; recipient history of pulmonary hypertension, sarcoidosis, or pulmonary fibrosis; single lung transplantation; and use of cardiopulmonary bypass, among others. Several cellular pathways have been implicated in the pathogenesis of PGD, thus presenting several possible therapeutic targets for preventing and treating PGD. Notably, use of ex vivo lung perfusion (EVLP) has become more widespread and offers a potential platform to safely investigate novel PGD treatments while expanding the lung donor pool. Even in the presence of significantly prolonged ischemic times, EVLP has not been associated with an increased risk for PGD.

Current status of inhaled nitric oxide therapy for lung transplantation in Japan: a nationwide survey

OBJECTIVES

Currently, inhaled nitric oxide (NO) therapy for lung transplantation is not covered by public health insurance in Japan. In this study, we evaluated the perioperative use and safety of inhaled NO therapy for lung transplantation.

METHODS

Data regarding the duration of treatment and adverse events of inhaled NO therapy were collected for all lung transplantations performed from January 1, 2015, to December 31, 2019, at nine lung transplant facilities in Japan.

RESULTS

During the study period, lung transplants were performed in 357 patients, among whom inhaled NO therapy was administered to 349 patients (98%). The median initial and median maximum inhaled NO doses were 10 and 20 ppm, respectively. Inhaled NO therapy was introduced during surgery and continued postoperatively in 313 patients (90%) for a median of 4 days. Significant improvements in oxygenation and decreases in pulmonary arterial pressure were observed in patients receiving inhaled NO therapy. Side effects of inhaled NO therapy, such as methemoglobinemia, were observed in 15 patients (4%), with a significant incidence in patients aged < 18 years.

CONCLUSIONS

Inhaled NO therapy was performed in almost all patients who underwent lung transplantation in Japan and showed reasonable efficacy. Therefore, public health insurance coverage for inhaled NO therapy during lung transplantation is recommended.

Review 2: Primary graft dysfunction after lung transplant-pathophysiology, clinical considerations and therapeutic targets

Primary graft dysfunction (PGD) is one of the most common complications in the early postoperative period and is the most common cause of death in the first postoperative month. The underlying pathophysiology is thought to be the ischaemia–reperfusion injury that occurs during the storage and reperfusion of the lung engraftment; this triggers a cascade of pathological changes, which result in pulmonary vascular dysfunction and loss of the normal alveolar architecture. There are a number of surgical and anaesthetic factors which may be related to the development of PGD. To date, although treatment options for PGD are limited, there are several promising experimental therapeutic targets. In this review, we will discuss the pathophysiology, clinical management and potential therapeutic targets of PGD.

Increased Arginase Expression and Decreased Nitric Oxide in Pig Donor Lungs after Normothermic Ex Vivo Lung Perfusion

An established pig lung transplantation model was used to study the effects of cold ischemia time, normothermic acellular ex vivo lung perfusion (EVLP) and reperfusion after lung transplantation on l-arginine/NO metabolism in lung tissue. Lung tissue homogenates were analyzed for NO metabolite (NOx) concentrations by chemiluminescent NO-analyzer technique, and l-arginine, l-ornithine, l-citrulline and asymmetric dimethylarginine (ADMA) quantified using liquid chromatography-mass spectrometry (LC-MS/MS). The expression of arginase and nitric oxide synthase (NOS) isoforms in lung was measured by real-time polymerase chain reaction. EVLP preservation resulted in a significant decrease in concentrations of NOx and l-citrulline, both products of NOS, at the end of EVLP and after reperfusion following transplantation, compared to control, respectively. The ratio of l-ornithine over l-citrulline, a marker of the balance between l-arginine metabolizing enzymes, was increased in the EVLP group prior to reperfusion. The expression of both arginase isoforms was increased from baseline 1 h post reperfusion in EVLP but not in the no-EVLP group. These data suggest that EVLP results in a shift of the l-arginine balance towards arginase, leading to NO deficiency in the lung. The arginase/NOS balance may, therefore, represent a therapeutic target to improve lung quality during EVLP and, subsequently, transplant outcomes.

Postoperative management of lung transplant recipients

Despite advances in surgical technique, lung transplantation is associated with worse survival when compared with other solid organ transplantations. Graft dysfunction and infection are the leading causes of mortality in the first 30 days following transplantation. Primary graft dysfunction (PGD) is a form of reperfusion injury that occurs early after transplantation. Management of PGD is mainly supportive with use of lung protective ventilation. Inhaled nitric oxide (iNO) and extracorporeal membrane oxygenation may be used in severe cases. Bacterial pneumonias are the most common infectious complication in the immediate post transplant period, but invasive fungal infections may also occur. Other potential complications in the postoperative period include atrial arrhythmias and neurologic complications such as stroke. There is a lack of multicenter, randomized trials to guide ventilation strategies, infection prophylaxis, and treatment of atrial arrhythmias, therefore prevention and management of post-transplant complications vary by transplant center.

Historical perspectives of lung transplantation: connecting the dots

Lung transplantation is now a treatment option for many patients with end-stage lung disease. Now 55 years since the first human lung transplant, this is a good time to reflect upon the history of lung transplantation, to recognize major milestones in the field, and to learn from others' unsuccessful transplant experiences. James Hardy was instrumental in developing experimental thoracic transplantation, performing the first human lung transplant in 1963. George Magovern and Adolph Yates carried out the second human lung transplant a few days later. With a combined survival of only 26 days for these first 2 lung transplant recipients, the specialty of lung transplantation clearly had a long way to go. The first "successful" lung transplant, in which the recipient survived for 10.5 months, was reported by Fritz Derom in 1971. Ten years later, Bruce Reitz and colleagues performed the first successful en bloc transplantation of the heart and one lung with a single distal tracheal anastomosis. In 1988, Alexander Patterson performed the first successful double lung transplant. The modern technique of sequential double lung transplantation and anastomosis performed at the mainstem bronchus level was originally described by Henri Metras in 1950, but was not reintroduced into the field until Pasque reported it again in 1990. Since then, lung transplantation has seen landmark changes: evolving immunosuppression regimens, clarifying the definition of primary graft dysfunction (PGD), establishing the lung allocation score (LAS), introducing extracorporeal membrane oxygenation (ECMO) as a bridge to transplant, allowing donation after cardiac death, and implementing ex vivo perfusion, to name a few. This article attempts to connect the historical dots in this field of research, with the hope that our effort helps summarize what has been achieved, and identifies opportunities for future generations of transplant pulmonologists and surgeons alike.

Primary Graft Dysfunction After Lung Transplantation

Primary graft dysfunction is a form of acute injury after lung transplantation that is associated with significant short- and long-term morbidity and mortality. Multiple mechanisms contribute to the pathogenesis of primary graft dysfunction, including ischemia reperfusion injury, epithelial cell death, endothelial cell dysfunction, innate immune activation, oxidative stress, and release of inflammatory cytokines and chemokines. This article reviews the epidemiology, pathogenesis, risk factors, prevention, and treatment of primary graft dysfunction.

Early postoperative management after lung transplantation: Results of an international survey

INTRODUCTION

Little data exist regarding optimal therapeutic strategies postoperatively after lung transplant (LTx). Current practice patterns rely on expert opinion and institutional experience resulting in nonuniform postoperative care. To better define current practice patterns, an international survey of LTx clinicians was conducted.

METHODS

A 30-question survey was sent to transplant clinicians via email to the International Society of Heart and Lung Transplantation open forum mailing list and directly to the chief transplant surgeon and pulmonologist of all LTx centers in the United States.

RESULTS

Fifty-two clinicians representing 10 countries responded to the survey. Sedatives use patterns included: opiates + propofol (57.2%), opiates + dexmedetomidine (18.4%), opiates + intermittent benzodiazepines (14.3%), opiates + continuous benzodiazepines (8.2%), and opiates alone (2%). About 40.4% reported no formal sedation scale was followed and 13.5% of programs had no formal policy on sedation and analgesia. A lung protective strategy was commonly employed, with 13.8%, 51.3%, and 35.9% of respondents using tidal volumes of <6 mL/kg ideal body weight (IBW), 6 mL/kg IBW, and 8 mL/kg IBW, respectively.

CONCLUSION

Practice patterns in the early postoperative care of lung transplant recipients differ considerably among centers. Many of the reported practices do not conform to consensus guidelines on management of critically ill patients.

Pediatric Recipients of Living Donor Lobar Lung Transplants: Postoperative Care

Bilateral living donor lobar lung transplantation is a treatment option for selected children and adults with end-stage lung disease. Careful donor evaluation, skilled intraoperative management and surgical technique, and diligent immediate postoperative care and follow-up all contribute to better outcomes. Although medical management of whole lung transplant recipients in the immediate postoperative period is similar to that of lobar lung transplant recipients, there are specific differences. Anatomical distinctions, such as the entire cardiac output flowing to 2 lobes instead of 5, and thoracic space issues with simultaneous mechanical ventilation and chest tube suction, contribute to these differences. Early postoperative care, including initial postoperative stabilization, ventilation, fluid management, rejection/infection surveillance and prophylaxis, and beginning rehabilitation, can be adapted to ensure successful outcomes in these patients.

Pulmonary Hypertensive Crisis on Induction of Anesthesia

Anesthesia for lung transplantation remains one of the highest risk surgeries in the domain of the cardiothoracic anesthesiologist. End-stage lung disease, pulmonary hypertension, and right heart dysfunction as well as other comorbid disease factors predispose the patient to cardiovascular, respiratory and metabolic dysfunction during general anesthesia. Perhaps the highest risk phase of surgery in the patient with severe pulmonary hypertension is during the induction of anesthesia when the removal of intrinsic sympathetic tone and onset of positive pressure ventilation can decompensate a severely compromised cardiovascular system. Severe hypotension, cardiac arrest, and death have been reported previously. Here we present 2 high-risk patients for lung transplantation, their anesthetic induction course, and outcomes. We offer suggestions for the safe management of anesthetic induction to mitigate against hemodynamic and respiratory complications.

Critical Care Aspects of Lung Transplant Patients

Major strides have been made in lung transplantation during the 1990s and it has become an established treatment option for patients with advanced lung disease. Due to improvements in organ preservation, surgical techniques, postoperative intensive care, and immunosuppression, the risk of perioperative and early mortality (less than 3 months after transplantation) has declined [1]. The transplant recipient now has a greater chance of realizing the benefits of the long and arduous waiting period.

Despite these improvements, suboptimal long-term outcomes continue to be shaped by issues such as opportunistic infections and chronic rejection. Because of the wider use of lung transplantation and the longer life span of recipients, intensivists and ancillary intensive care unit (ICU) staff should be well versed with the care of lung transplant recipients.

In this clinical review, issues related to organ donation will be briefly mentioned. The remaining focus will be on the critical care aspects of lung transplant recipients in the posttransplant period, particularly ICU management of frequently encountered conditions. First, the groups of patients undergoing transplantation and the types of procedures performed will be outlined. Specific issues directly related to the allograft, including early graft dysfunction from ischemia-reperfusion injury, airway anastomotic complications, and infections in the setting of immunosuppression will be emphasized. Finally nonpulmonary aspects of posttransplant care and key pharmacologic points in the ICU will be covered.

Methylene Blue for Vasoplegia When on Cardiopulmonary Bypass During Double-Lung Transplantation

Vasoplegia syndrome, characterized by hypotension refractory to fluid resuscitation or high-dose vasopressors, low systemic vascular resistance, and normal-to-increased cardiac index, is associated with increased morbidity and mortality after cardiothoracic surgery. Methylene blue inhibits inducible nitric oxide synthase and guanylyl cyclase, and has been used to treat vasoplegia during cardiopulmonary bypass. However, because methylene blue is associated with increased pulmonary vascular resistance, its use in patients undergoing lung transplantion has been limited. Herein, we report the use of methylene blue to treat refractory vasoplegia during cardiopulmonary bypass in a patient undergoing double-lung transplantation.

Primary graft dysfunction: lessons learned about the first 72 h after lung transplantation

PURPOSE OF REVIEW

In 2005, the International Society for Heart and Lung Transplantation published a standardized definition of primary graft dysfunction (PGD), facilitating new knowledge on this form of acute lung injury that occurs within 72 h of lung transplantation. PGD continues to be associated with significant morbidity and mortality. This article will summarize the current literature on the epidemiology of PGD, pathogenesis, risk factors, and preventive and treatment strategies.

RECENT FINDINGS

Since 2011, several manuscripts have been published that provide insight into the clinical risk factors and pathogenesis of PGD. In addition, several transplant centers have explored preventive and treatment strategies for PGD, including the use of extracorporeal strategies. More recently, results from several trials assessing the role of extracorporeal lung perfusion may allow for much-needed expansion of the donor pool, without raising PGD rates.

SUMMARY

This article will highlight the current state of the science regarding PGD, focusing on recent advances, and set a framework for future preventive and treatment strategies.

Overview of clinical lung transplantation

Since the first successful lung transplant 30 years ago, lung transplantation has rapidly become an established standard of care to treat end-stage lung disease in selected patients. Advances in lung preservation, surgical technique, and immunosuppression regimens have resulted in the routine performance of lung transplantation around the world for an increasing number of patients, with wider indications. Despite this, donor shortages and chronic lung allograft dysfunction continue to prevent lung transplantation from reaching its full potential. With research into the underlying mechanisms of acute and chronic lung graft dysfunction and advances in personalized diagnostic and therapeutic approaches to both the donor lung and the lung transplant recipient, there is increasing confidence that we will improve short- and long-term outcomes in the near future.

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.

Primary graft dysfunction

Primary graft dysfunction (PGD) is a syndrome encompassing a spectrum of mild to severe lung injury that occurs within the first 72 hours after lung transplantation. PGD is characterized by pulmonary edema with diffuse alveolar damage that manifests clinically as progressive hypoxemia with radiographic pulmonary infiltrates. In recent years, new knowledge has been generated on risks and mechanisms of PGD. Following ischemia and reperfusion, inflammatory and immunological injury-repair responses appear to be key controlling mechanisms. In addition, PGD has a significant impact on short- and long-term outcomes; therefore, the choice of donor organ is impacted by this potential adverse consequence. Improved methods of reducing PGD risk and efforts to safely expand the pool are being developed. Ex vivo lung perfusion is a strategy that may improve risk assessment and become a promising platform to implement treatment interventions to prevent PGD. This review details recent updates in the epidemiology, pathophysiology, molecular and genetic biomarkers, and state-of-the-art technical developments affecting PGD.

Comparing beneficial effects of inhaled nitric oxide to L-arginine in necrotizing enterocolitis model in neonatal rats

OBJECTIVE

Necrotizing enterocolitis (NEC) is a common and devastating gastrointestinal condition of neonatal infants. The pathophysiology of NEC remains poorly understood. We tried to evaluate the effectiveness of inhaled NO compared to L-arginine usage in necrotizing enterocolitis model in rats.

MATERIAL-METHODS

46 newborn pups from 4 time-mated Sprague-Dawley pregnant rats were divided equally into 4 groups as follows: NEC (subjected to NEC), NEC + L-arginine, NEC + inhaled NO and control.

RESULTS

SOD, GSH-Px and NOx levels were significantly higher and MDA levels were significantly lower in NEC + inhaled NO group compared to NEC + L-arginine group. There was significantly lower intestinal injury and apoptosis index scoring in NEC + inhaled NO group compared to NEC + L-arginine group.

CONCLUSION

We think that inhaled NO can be used as a novel therapeutic agent like L-arginine in NEC, like using in pulmonary hypertention in newborns but much more studies are needed.

Nebulized nitrite protects rat lung grafts from ischemia reperfusion injury

OBJECTIVES

Nebulization is a potential method for delivering therapeutic agents to lung grafts. Recent evidence suggests that nitrite may mitigate ischemia-reperfusion injury via a nitric oxide-dependent pathway.

METHODS

Syngeneic orthotopic left lung transplantation was performed in rats after 7 hours of cold ischemia. Sodium nitrite (3 mg) or phosphate-buffered saline (controls) was delivered before procurement via nebulization.

RESULTS

Nitrite treatment was associated with better oxygenation, lower peak airway pressure, lower wet/dry ratio, reduced myeloperoxidase level and macrophage infiltration, increased cyclic guanosine monophosphate (cGMP) levels, and decreased levels of interleukin 6, interleukin 1-β, inducible nitric oxide synthase, and intercellular adhesion molecule-1 at 2 hours after reperfusion. Treatment with 2-(4-carboxypheny)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a nitric oxide scavenger, reversed the beneficial effects of nitrite and decreased cGMP concentration in grafts. A dose-response curve of nitrite was performed at the following doses: 0.3 mg (N0.1), 3.0 mg (N1.0), 5.25 mg (N1.75), 7.5 mg (N2.5), and 15.0 mg (N5.0). All treatments, excluding N1.0, resulted in poorer oxygenation, higher peak airway pressures, and higher wet/dry ratio. Higher dosage groups (N1.75, N2.5, and N5.0) exhibited positive immunostaining of nitrotyrosine and increased the intensity of nitrotyrosine in immunoblotting.

CONCLUSIONS

These data suggest that nebulized nitrite limits lung ischemia-reperfusion injury and may prove a clinically useful strategy but requires appropriate dosing to limit oxidative injury at high doses.

Nitrite reduces acute lung injury and improves survival in a rat lung transplantation model

Ischemia/reperfusion injury (IRI) is the most common cause of early mortality following lung transplantation (LTx). We hypothesized that nitrite, an endogenous source of nitric oxide (NO), may protect lung grafts from IRI. Rat lung grafts were stored in preservation solution at 4°C for 6 hours. Both grafts and recipients were treated with nitrite. Nitrite treatment was associated with significantly higher levels of tissue oxygenation, lower levels of cytokines and neutrophil/macrophage infiltration, lower myeloperoxidase activity, reduced oxidative injury and increased cGMP levels in grafts than in the controls. Treatment with either a nitric oxide scavenger or a soluble guanylyl cyclase (sGC) inhibitor diminished the beneficial effects of nitrite and decreased cGMP concentrations. These results suggest that nitric oxide, generated from nitrite, is the molecule responsible for the effects of nitrite via the nitric oxide/sGC/cGMP pathway. Allopurinol, a xanthine oxidoreductase (XOR) inhibitor, abrogated the protective effects of nitrite, suggesting that XOR is a key enzyme in the conversion of nitrite to nitric oxide. In vitro experiments demonstrated that nitrite prevented apoptosis in pulmonary endothelial cells. Nitrite also exhibits longer survival rate in recipients than control. In conclusion, nitrite inhibits lung IRI following cold preservation and had higher survival rate in LTx model.

[Primary graft dysfunction after lung transplantation]

Lung transplantation is a therapeutic option for pulmonary diseases in which the other treatment options have failed or in cases of rapid disease progression. However, transplantation is not free from complications, and primary graft dysfunction is one of them. Primary graft dysfunction is a form of acute lung injury. It characteristically develops during the immediate postoperative period, being associated to high morbidity and mortality, and increased risk of bronchiolitis obliterans. Different terms have been used in reference to primary graft dysfunction, leading to a consensus document to clarify the definition in 2005. This consensus document regards primary graft dysfunction as non-cardiogenic pulmonary edema developing within 72 hours of reperfusion and intrinsically attributable to alteration of the lung parenchyma. A number of studies have attempted to identify risk factors and to establish the underlying physiopathology, with a view to developing potential therapeutic options. Such options include nitric oxide and pulmonary surfactant together with supportive measures such as mechanical ventilation or oxygenation bypass.

Medical gases: a novel strategy for attenuating ischemia-reperfusion injury in organ transplantation?

Ischemia reperfusion injury (IRI) is an inevitable clinical consequence in organ transplantation. It can lead to early graft nonfunction and contribute to acute and chronic graft rejection. Advanced molecular biology has revealed the highly complex nature of this phenomenon and few definitive therapies exist. This paper reviews factors involved in the pathophysiology of IRI and potential ways to attenuate it. In recent years, inhaled nitric oxide, carbon monoxide, and hydrogen sulfide have been increasingly explored as plausible novel medical gases that can attenuate IRI via multiple mechanisms, including microvascular vasorelaxation, reduced inflammation, and mitochondrial modulation. Here, we review recent advances in research utilizing inhaled nitric oxide, carbon monoxide, and hydrogen sulfide in animal and human studies of IRI and postulate on its future applications specific to solid organ transplantation.

How to recondition ex vivo initially rejected donor lungs for clinical transplantation: clinical experience from lund university hospital

A major problem in clinical lung transplantation is the shortage of donor lungs. Only about 20% of donor lungs are accepted for transplantation. We have recently reported the results of the first six double lung transplantations performed with donor lungs reconditioned ex vivo that had been deemed unsuitable for transplantation by the Scandiatransplant, Eurotransplant, and UK Transplant organizations because the arterial oxygen pressure was less than 40 kPa. The three-month survival of patients undergoing transplant with these lungs was 100%. One patient died due to sepsis after 95 days, and one due to rejection after 9 months. Four recipients are still alive and well 24 months after transplantation, with no signs of bronchiolitis obliterans syndrome. The donor lungs were reconditioned ex vivo in an extracorporeal membrane oxygenation circuit using STEEN solution mixed with erythrocytes, to dehydrate edematous lung tissue. Functional evaluation was performed with deoxygenated perfusate at different inspired fractions of oxygen. The arterial oxygen pressure was significantly improved in this model. This ex vivo evaluation model is thus a valuable addition to the armamentarium in increasing the number of acceptable lungs in a donor population with inferior arterial oxygen pressure values, thereby, increasing the lung donor pool for transplantation. In the following paper we present our clinical experience from the first six patients in the world. We also present the technique we used in detail with flowchart.

Primary graft dysfunction

Primary graft dysfunction (PGD) is the most important cause of early morbidity and mortality following lung transplantation. PGD affects up to 25% of all lung transplant procedures and currently has no proven preventive therapy. Lung transplant recipients who recover from PGD may have impaired long-term function and an increased risk of bronchiolitis obliterans syndrome. This article aims to provide a state-of-the-art review of PGD epidemiology, outcomes, and risk factors, and to summarize current efforts at biomarker development and novel strategies for prevention and treatment.

Pathogenetic role of eNOS uncoupling in cardiopulmonary disorders

The homodimeric flavohemeprotein endothelial nitric oxide synthase (eNOS) oxidizes l-arginine to l-citrulline and nitric oxide (NO), which acutely vasodilates blood vessels and inhibits platelet aggregation. Chronically, eNOS has a major role in the regulation of blood pressure and prevention of atherosclerosis by decreasing leukocyte adhesion and smooth muscle proliferation. However, a disturbed vascular redox balance results in eNOS damage and uncoupling of oxygen activation from l-arginine conversion. Uncoupled eNOS monomerizes and generates reactive oxygen species (ROS) rather than NO. Indeed, eNOS uncoupling has been suggested as one of the main pathomechanisms in a broad range of cardiovascular and pulmonary disorders such as atherosclerosis, ventricular remodeling, and pulmonary hypertension. Therefore, modulating uncoupled eNOS, in particular eNOS-dependent ROS generation, is an attractive therapeutic approach to preventing and/or treating cardiopulmonary disorders, including protective effects during cardiothoracic surgery. This review provides a comprehensive overview of the pathogenetic role of uncoupled eNOS in both cardiovascular and pulmonary disorders. In addition, the related therapeutic possibilities such as supplementation with the eNOS substrate l-arginine, volatile NO, and direct NO donors as well as eNOS modulators such as the eNOS cofactor tetrahydrobiopterin and folic acid are discussed in detail.

Pulmonary complications of lung transplantation

Lung transplantation is an effective treatment option for select patients with a variety of end-stage lung diseases. Although transplant can significantly improve the quality of life and prolong survival, a myriad of pulmonary complications may result in significant morbidity and limit long-term survival. The recognition and early treatment of these complications is important for optimizing outcomes. This article provides an overview and update of the pulmonary complications that may be commonly encountered by pulmonologists caring for these patients.

Role of nitric oxide in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) occurs upon restoration of hepatic blood flow after a period of ischemia. Decreased endogenous nitric oxide (NO) production resulting in capillary luminal narrowing is central in the pathogenesis of IRI. Exogenous NO has emerged as a potential therapy for IRI based on its role in decreasing oxidative stress, cytokine release, leukocyte endothelial-adhesion and hepatic apoptosis. This review will highlight the influence of endogenous NO on hepatic IRI, role of inhaled NO in ameliorating IRI, modes of delivery, donor drugs and potential side effects of exogenous NO.

Lung transplantation for pulmonary hypertension in children

Lung and heart-lung transplantation are accepted treatments for children with end-stage pulmonary vascular disease. This is a review of the current literature and our own experience with lung and heart-lung transplantation for children with pulmonary hypertension of a variety of causes. I reviewed the pertinent literature and our lung transplant database to acquire information and data regarding this subject. The patients include those at St. Louis Children's Hospital as well as those reported from other institutions. The major operative complications include those related to the surgical procedure itself (vascular and airway anastomotic stenoses) and those related to graft dysfunction. The 3- and 5-yr survival is approximately 60% and 50%, respectively, for children undergoing lung transplantation for pulmonary hypertension.Although these survival statistics are somewhat poor, transplantation remains the only viable alternative for children with end-stage pulmonary vascular disease failing to respond to medical therapy.

A prospective, randomized, crossover pilot study of inhaled nitric oxide versus inhaled prostacyclin in heart transplant and lung transplant recipients

OBJECTIVE

Inhaled nitric oxide has been shown to reduce pulmonary vascular resistance in patients undergoing cardiothoracic surgery, but it is limited by toxicity, the need for special monitoring, and cost. Inhaled prostacyclin also decreases pulmonary artery pressure, is relatively free of toxicity, requires no specific monitoring, and is less expensive. The objective of this study was to compare nitric oxide and prostacyclin in the treatment of pulmonary hypertension, refractory hypoxemia, and right ventricular dysfunction in thoracic transplant recipients in a prospective, randomized, crossover pilot trial.

METHODS

Heart transplant and lung transplant recipients were randomized to nitric oxide or prostacyclin as initial treatment, followed by a crossover to the other agent after 6 hours. Pulmonary vasodilators were initiated in the operating room for pulmonary hypertension, refractory hypoxemia, or right ventricular dysfunction. Nitric oxide was administered at 20 ppm, and prostacyclin was administered at 20,000 ng/mL. Hemodynamic and oxygenation parameters were recorded before and after initiation of pulmonary vasodilator therapy. At 6 hours, the hemodynamic and oxygenation parameters were recorded again, just before discontinuing the initial agent. Crossover baseline parameters were measured 30 minutes after the initial agent had been stopped. The crossover agent was then started, and the hemodynamic and oxygenation parameters were measured again 30 minutes later.

RESULTS

Heart transplant and lung transplant recipients (n = 25) were randomized by initial treatment (nitric oxide, n = 14; prostacyclin, n = 11). Nitric oxide and prostacyclin both reduced pulmonary artery pressure and central venous pressure, and improved cardiac index and mixed venous oxygen saturation on initiation of therapy. More importantly, at the 6-hour crossover trial, there were no significant differences between nitric oxide and prostacyclin in the reduction of pulmonary artery pressures or central venous pressure, or in improvement in cardiac index or mixed venous oxygen saturation. Nitric oxide and prostacyclin did not affect the oxygenation index or systemic blood pressure. There were no complications associated with nitric oxide or prostacyclin.

CONCLUSION

In heart transplant and lung transplant recipients, nitric oxide and prostacyclin similarly reduce pulmonary artery pressures and central venous pressure, and improve cardiac index and mixed venous oxygen saturation. Inhaled prostacyclin may offer an alternative to nitric oxide in the treatment of pulmonary hypertension in thoracic transplantation.

Clinical translation of nitrite therapy for cardiovascular diseases

The anion nitrite is an oxidative breakdown product of nitric oxide (NO) that has traditionally been viewed as a diagnostic marker of NO formation in biological systems. In this regard, nitrite has long been considered an inert oxidation product of NO metabolism. More recently, this view has changed with the discovery that nitrite represents a physiologically relevant storage reservoir of NO in blood and tissues that can readily be reduced to NO under pathological conditions. This has sparked a renewed interest in the biological role of nitrite and has led to an extensive amount of work investigating its therapeutic potential. As a result, nitrite therapy has now been shown to be cytoprotective in numerous animal models of disease. Given the very robust preclinical data regarding the cytoprotective effects of nitrite therapy it is very logical to consider the clinical translation of nitrite-based therapies. This article will review some of this preclinical data and will discuss the potential use of nitrite therapy as a therapeutic agent for the treatment of cardiovascular diseases including: ischemia-reperfusion injury (i.e. acute myocardial infarction and stroke), hypertension, angiogenesis, and as an adjunctive therapy for transplantation of various organs (i.e. liver and lung).

Post-ischemic infusion of atrial natriuretic peptide attenuates warm ischemia-reperfusion injury in rat lung

BACKGROUND

The serious shortage of organs for transplantation, especially lungs, has drawn increasing attention to donation after cardiac death and protection of organs against warm ischemic injury. Atrial natriuretic peptide (ANP) activates guanylate cyclase receptors and increases cyclic guanosine monophosphate (cGMP) levels, which decrease in the lung during ischemia. In this study we investigated the effect on lung ischemia-reperfusion injury of administering synthetic ANP (carperitide) at the onset of reperfusion after warm ischemia.

METHODS

An isolated rat lung perfusion model was used. The rats were allocated into three groups: the control group; the ANP group; and the sham group. In the control and ANP groups, the heart-lung block was exposed to 60 minutes of ischemia at 37 degrees C, and subsequently reperfused for 60 minutes. At the onset of reperfusion, either saline or ANP was added to the perfusate. In the sham group, lungs were continuously perfused without ischemia and only saline was added to the perfusate.

RESULTS

ANP significantly reduced pulmonary vascular resistance and pulmonary edema, and improved oxygenation. It also significantly increased cGMP levels in reperfused lungs. Histologically, lungs in the ANP group showed significantly fewer signs of injury and fewer cells demonstrated apoptotic changes or single-stranded DNA than lungs in the control group.

CONCLUSIONS

Our results indicate that ANP administered at the onset of reperfusion increases cGMP in lung tissue and attenuates warm ischemia-reperfusion injury in isolated perfused rat lung.