Hydrogen preconditioning during ex vivo lung perfusion improves the quality of lung grafts in rats

Hydrogen in Transplantation: Potential Applications and Therapeutic Implications

Hydrogen gas, renowned for its antioxidant properties, has emerged as a novel therapeutic agent with applications across various medical domains, positioning it as a potential adjunct therapy in transplantation. Beyond its antioxidative properties, hydrogen also exerts anti-inflammatory effects by modulating pro-inflammatory cytokines and signaling pathways. Furthermore, hydrogen's capacity to activate cytoprotective pathways bolsters cellular resilience against stressors. In recent decades, significant advancements have been made in the critical medical procedure of transplantation. However, persistent challenges such as ischemia-reperfusion injury (IRI) and graft rejection continue to hinder transplant success rates. This comprehensive review explores the potential applications and therapeutic implications of hydrogen in transplantation, shedding light on its role in mitigating IRI, improving graft survival, and modulating immune responses. Through a meticulous analysis encompassing both preclinical and clinical studies, we aim to provide valuable insights into the promising utility of hydrogen as a complementary therapy in transplantation.

Primary Graft Dysfunction in Lung Transplantation: A Review of Mechanisms and Future Applications

Lung allograft recipients have worse survival than all other solid organ transplant recipients, largely because of primary graft dysfunction (PGD), a major form of acute lung injury affecting a third of lung recipients within the first 72 h after transplant. PGD is the clinical manifestation of ischemia-reperfusion injury and represents the predominate cause of early morbidity and mortality. Despite PGD's impact on lung transplant outcomes, no targeted therapies are currently available; hence, care remains supportive and largely ineffective. This review focuses on molecular and innate immune mechanisms of ischemia-reperfusion injury leading to PGD. We also discuss novel research aimed at discovering biomarkers that could better predict PGD and potential targeted interventions that may improve outcomes in lung transplantation.

Inflation using hydrogen improves donor lung quality by regulating mitochondrial function during cold ischemia phase

BACKGROUND

Mitochondrial dysfunction results in poor organ quality, negatively affecting the outcomes of lung transplantation. Whether hydrogen benefits mitochondrial function in cold-preserved donors remain unclear. The present study assessed the effect of hydrogen on mitochondrial dysfunction in donor lung injury during cold ischemia phase (CIP) and explored the underlying regulatory mechanism.

METHODS

Left donor lungs were inflated using 40% oxygen + 60% nitrogen (O group), or 3% hydrogen + 40% oxygen + 57% nitrogen (H group). Donor lungs were deflated in the control group and were harvested immediately after perfusion in the sham group (n = 10). Inflammation, oxidative stress, apoptosis, histological changes, mitochondrial energy metabolism, and mitochondrial structure and function were assessed. The expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) were also analyzed.

RESULTS

Compared with the sham group, inflammatory response, oxidative stress, histopathological changes, and mitochondrial damage were severe in the other three groups. However, these injury indexes were remarkably decreased in O and H groups, with increased Nrf2 and HO-1 levels, elevated mitochondrial biosynthesis, inhibition of anaerobic glycolysis and restored mitochondrial structure and function compared with the control group. Moreover, inflation using hydrogen contributed to stronger protection against mitochondrial dysfunction and higher levels of Nrf2 and HO-1 when comparing with O group.

CONCLUSIONS

Lung inflation using hydrogen during CIP may improve donor lung quality by mitigating mitochondrial structural anomalies, enhancing mitochondrial function, and alleviating oxidative stress, inflammation, and apoptosis, which may be achieved through activation of the Nrf2/HO-1 pathway.

L-alanyl-L-glutamine modified perfusate improves human lung cell functions and extend porcine ex vivo lung perfusion

BACKGROUND

The clinical application of normothermic ex vivo lung perfusion (EVLP) has increased donor lung utilization for transplantation through functional assessment. To develop it as a platform for donor lung repair, reconditioning and regeneration, the perfusate should be modified to support the lung during extended EVLP.

METHODS

Human lung epithelial cells and pulmonary microvascular endothelial cells were cultured, and the effects of Steen solution (commonly used EVLP perfusate) on basic cellular function were tested. Steen solution was modified based on screening tests in cell culture, and further tested with an EVLP cell culture model, on apoptosis, GSH, HSP70, and IL-8 expression. Finally, a modified formula was tested on porcine EVLP. Physiological parameters of lung function, histology of lung tissue, and amino acid concentrations in EVLP perfusate were measured.

RESULTS

Steen solution reduced cell confluence, induced apoptosis, and inhibited cell migration, compared to regular cell culture media. Adding L-alanyl-L-glutamine to Steen solution improved cell migration and decreased apoptosis. It also reduced cold preservation and warm perfusion-induced apoptosis, enhanced GSH and HSP70 production, and inhibited IL-8 expression on an EVLP cell culture model. L-alanyl-L-glutamine modified Steen solution supported porcine lungs on EVLP with significantly improved lung function, well-preserved histological structure, and significantly higher levels of multiple amino acids in EVLP perfusate.

CONCLUSIONS

Adding L-alanyl-L-glutamine to perfusate may provide additional energy support, antioxidant, and cytoprotective effects to lung tissue. The pipeline developed herein, with cell culture, cell EVLP, and porcine EVLP models, can be used to further optimize perfusates to improve EVLP outcomes.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

Hydrogen: Potential Applications in Solid Organ Transplantation

Ischemia reperfusion injury (IRI) in organ transplantation has always been an important hotspot in organ protection. Hydrogen, as an antioxidant, has been shown to have anti-inflammatory, antioxidant, and antiapoptotic effects. In this paper, the protective effect of hydrogen against IRI in organ transplantation has been reviewed to provide clues for future clinical studies.

Lung Inflation With Hydrogen During the Cold Ischemia Phase Alleviates Lung Ischemia-Reperfusion Injury by Inhibiting Pyroptosis in Rats

Background: Lung inflation with hydrogen is an effective method to protect donor lungs from lung ischemia-reperfusion injury (IRI). This study aimed to examine the effect of lung inflation with 3% hydrogen during the cold ischemia phase on pyroptosis in lung grafts of rats.

Methods: Adult male Wistar rats were randomly divided into the sham group, the control group, the oxygen (O₂) group, and the hydrogen (H₂) group. The sham group underwent thoracotomy but no lung transplantation. In the control group, the donor lungs were deflated for 2 h. In the O₂ and H₂ groups, the donor lungs were inflated with 40% O₂ + 60% N₂ and 3% H₂ + 40% O₂ + 57% N₂, respectively, at 10 ml/kg, and the gas was replaced every 20 min during the cold ischemia phase for 2 h. Two hours after orthotopic lung transplantation, the recipients were euthanized.

Results: Compared with the control group, the O₂ and H₂ groups improved oxygenation indices, decreases the inflammatory response and oxidative stress, reduced lung injury, and improved pressure-volume (P-V) curves. H₂ had a better protective effect than O₂. Furthermore, the levels of the pyroptosis-related proteins selective nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), cysteinyl aspartate specific proteinase (caspase)-1 p20, and the N-terminal of gasdermin D (GSDMD-N) were decreased in the H₂ group.

Conclusion: Lung inflation with 3% hydrogen during the cold ischemia phase inhibited the inflammatory response, oxidative stress, and pyroptosis and improved the function of the graft. Inhibiting reactive oxygen species (ROS) production may be the main mechanism of the antipyroptotic effect of hydrogen.

Subnormothermic ex vivo lung perfusion attenuates ischemia reperfusion injury from donation after circulatory death donors

Use of normothermic ex vivo lung perfusion (EVLP) was adopted in clinical practice to assess the quality of marginal donor lungs. Subnormothermic perfusion temperatures are in use among other solid organs to improve biochemical, clinical and immunological parameters. In a rat EVLP model of donation after circulatory death (DCD) lung donors, we tested the effect of four subnormothermic EVLP temperatures that could further improve organ preservation. Warm ischemic time was of 2 hours. EVLP time was of 4 hours. Lung physiological data were recorded and metabolic parameters were assessed. Lung oxygenation at 21°C and 24°C were significantly improved whereas pulmonary vascular resistance and edema formation at 21°C EVLP were significantly worsened when compared to 37°C EVLP. The perfusate concentrations of potassium ions and lactate exiting the lungs with 28°C EVLP were significantly lower whereas sodium and chlorine ions with 32°C EVLP were significantly higher when compared to 37°C EVLP. Also compared to 37°C EVLP, the pro-inflammatory chemokines MIP2, MIP-1α, GRO-α, the cytokine IL-6 were significantly lower with 21°C, 24°C and 28°C EVLP, the IL-18 was significantly lower but only with 21°C EVLP and IL-1β was significantly lower at 21°C and 24°C EVLP. Compared to the 37°C EVLP, the lung tissue ATP content after 21°C, 24°C and 28°C EVLP were significantly higher, the carbonylated protein content after 28°C EVLP was significantly lower and we measured significantly higher myeloperoxidase activities in lung tissues with 21°C, 24°C and 32°C. The 28°C EVLP demonstrated acceptable physiological variables, significantly higher lung tissue ATP content and decreased tissue carbonylated proteins with reduced release of pro-inflammatory cytokines. In conclusion, the 28°C EVLP is a non inferior setting in comparison to the clinically approved 37°C EVLP and significantly improve biochemical, clinical and immunological parameters and may reduce I/R injuries of DCD lung donors.

Ischemia-Reperfusion Injury in Lung Transplantation

Lung transplantation has been established worldwide as the last treatment for end-stage respiratory failure. However, ischemia–reperfusion injury (IRI) inevitably occurs after lung transplantation. The most severe form of IRI leads to primary graft failure, which is an important cause of morbidity and mortality after lung transplantation. IRI may also induce rejection, which is the main cause of mortality in recipients. Despite advances in donor management and graft preservation, most donor grafts are still unsuitable for transplantation. Although the pulmonary endothelium is the primary target site of IRI, the pathophysiology of lung IRI remains incompletely understood. It is essential to understand the mechanism of pulmonary IRI to improve the outcomes of lung transplantation. Therefore, we reviewed the state-of-the-art in the management of pulmonary IRI after lung transplantation. Recently, the ex vivo lung perfusion (EVLP) system has been clinically introduced worldwide. Various promising therapeutic strategies for the protection of the endothelium against IRI, including EVLP, inhalation therapy with therapeutic gases and substances, fibrinolytic treatment, and mesenchymal stromal cell therapy, are awaiting clinical application. We herein review the latest advances in the field of pulmonary IRI in lung transplantation.

Protective effects of molecular hydrogen on lung injury from lung transplantation

Lung grafts may experience multiple injuries during lung transplantation, such as warm ischaemia, cold ischaemia, and reperfusion injury. These injuries all contribute to primary graft dysfunction, which is a major cause of morbidity and mortality after lung transplantation. As a potential selective antioxidant, hydrogen molecule (H₂) protects against post-transplant complications in animal models of multiple organ transplantation. Herein, the authors review the current literature regarding the effects of H₂ on lung injury from lung transplantation. The reviewed studies showed that H₂ improved the outcomes of lung transplantation by decreasing oxidative stress and inflammation at the donor and recipient phases. H₂ is primarily administered via inhalation, drinking hydrogen-rich water, hydrogen-rich saline injection, or a hydrogen-rich water bath. H₂ favorably modulates signal transduction and gene expression, resulting in the suppression of pro-inflammatory cytokines and excess reactive oxygen species production. Although H₂ appears to be a physiological regulatory molecule with antioxidant, anti-inflammatory and anti-apoptotic properties, its exact mechanisms of action remain elusive. Taken together, accumulating experimental evidence indicates that H₂ can significantly alleviate transplantation-related lung injury, mainly via inhibition of inflammatory cytokine secretion and reduction in oxidative stress through several underlying mechanisms. Further animal experiments and preliminary human clinical trials will lay the foundation for the use of H₂ as a treatment in the clinic.

Subnormothermic Ex Vivo Lung Perfusion Temperature Improves Graft Preservation in Lung Transplantation

Normothermic machine perfusion is clinically used to assess the quality of marginal donor lungs. Although subnormothermic temperatures have proven beneficial for other solid organ transplants, subnormothermia-related benefits of ex vivo lung perfusion (EVLP) still need to be investigated. Material and Methods: In a rat model, we evaluated the effects of 28 °C temperature on 4-h EVLPs with subsequent left lung transplantation. The recipients were observed for 2 h postoperatively. Lung physiology data were recorded and metabolic parameters were assessed. Results: During the 4-h subnormothermic EVLP, the lung oxygenation was significantly higher (p < 0.001), pulmonary vascular resistance (PVR) lower and dynamic compliance (Cdyn) higher when compared to the 37 °C EVLP. During an end-of-EVLP stress test, we recorded significantly higher flow (p < 0.05), lower PVR (p < 0.05) and higher Cdyn (p < 0.01) in the 28 °C group when compared to the 37 °C group. After the left lung transplantation, Cdyn and oxygenation improved in the 28 °C group, which were comparable to the 37 °C group. Chemokines RANTES, MIP-3α, MIP-1α MCP-1 GRO/KC and pro-inflammatory mediators GM-CSF, G-CSF and TNFα were significantly lower after the 28 °C EVLP and remained low in the plasma of the recipient rats after transplantation. The lungs of the 28 °C group showed significantly lowered myeloperoxidase activity and lowered levels of TNFα and IL-1β. Conclusions: Compared to the normothermic perfusion, the 28 °C EVLP improved Cdyn and PVR and reduced both the release of pro-inflammatory cytokines and myeloperoxidase activity in lung tissue. These observations were also observed after the left lung transplantation in the subnormothermic group. The 28 °C EVLP significantly improved biochemical, physiological and inflammatory parameters in lung donors.

Luminal preloading with hydrogen-rich saline ameliorates ischemia-reperfusion injury following intestinal transplantation in rats

Prolonged intestinal cold storage causes considerable mucosal breakdown, which could bolster bacterial translocation and cause life-threatening infection for the transplant recipient. The intestine has an intraluminal compartment, which could be a target for intervention, but has not yet been fully investigated. Hydrogen gas exerts organ protection and has used been recently in several clinical and basic research studies on topics including intestinal transplantation. In this study, we aimed to investigate the cytoprotective efficacy of intraluminally administered hydrogen-rich saline on cold IR injury in intestinal transplantation. Isogeneic intestinal transplantation with 6 hours of cold ischemia was performed on Lewis rats. Hydrogen-rich saline (H₂ concentration at 5 ppm) or normal saline was intraluminally introduced immediately before preservation. Graft intestine was excised 3 hours after reperfusion and analyzed. Histopathological analysis of control grafts revealed blunting of the villi and erosion. These mucosal changes were notably attenuated by intraluminal hydrogen. Intestinal mucosa damage caused by IR injury led to considerable deterioration of gut barrier function 3 h post-reperfusion. However, this decline in permeability was critically prevented by hydrogen treatment. IR-induced upregulation of proinflammatory cytokine mRNAs such as IL-6 was mitigated by hydrogen treatment. Western blot revealed that hydrogen treatment regulated loss of the transmembrane protein ZO-1. Hydrogen-rich saline intraluminally administered in the graft intestine modulated IR injury to transplanted intestine in rats. Successful abrogation of intestinal IR injury with a novel strategy using intraluminal hydrogen may be easily clinically applicable and will compellingly improve patient care after transplantation.

Cyclosporin A Administration During Ex Vivo Lung Perfusion Preserves Lung Grafts in Rat Transplant Model

BACKGROUND

Despite the benefits of ex vivo lung perfusion (EVLP) such as lung reconditioning, preservation, and evaluation before transplantation, deleterious effects, including activation of proinflammatory cascades and alteration of metabolic profiles have been reported. Although patient outcomes have been favorable, further studies addressing optimal conditions are warranted. In this study, we investigated the role of the immunosuppressant drug cyclosporine A (CyA) in preserving mitochondrial function and subsequently preventing proinflammatory changes in lung grafts during EVLP.

METHODS

Using rat heart-lung blocks after 1-hour cold preservation, an acellular normothermic EVLP system was established for 4 hours. CyA was added into perfusate at a final concentration of 1 μM. The evaluation included lung graft function, lung compliance, and pulmonary vascular resistance as well as biochemical marker measurement in the perfusate at multiple time points. After EVLP, single orthotopic lung transplantation was performed, and the grafts were assessed 2 hours after reperfusion.

RESULTS

Lung grafts on EVLP with CyA exhibited significantly better functional and physiological parameters as compared with those without CyA treatment. CyA administration attenuated proinflammatory changes and prohibited glucose consumption during EVLP through mitigating mitochondrial dysfunction in lung grafts. CyA-preconditioned lungs showed better posttransplant lung early graft function and less inflammatory events compared with control.

CONCLUSIONS

During EVLP, CyA administration can have a preconditioning effect through both its anti-inflammatory and mitochondrial protective properties, leading to improved lung graft preservation, which may result in enhanced graft quality after transplantation.

Ex vivo lung perfusion for donor lung assessment and repair: a review of translational interspecies models

For patients with end-stage lung disease, lung transplantation is a lifesaving therapy. Currently however, the number of patients who require a transplant exceeds the number of donor lungs available. One of the contributing factors to this is the conservative mindset of physicians who are concerned about transplanting marginal lungs due to the potential risk of primary graft dysfunction. Ex vivo lung perfusion (EVLP) technology has allowed for the expansion of donor pool of organs by enabling assessment and reconditioning of these marginal grafts before transplant. Ongoing efforts to optimize the therapeutic potential of EVLP are underway. Researchers have adopted the use of different large and small animal models to generate translational preclinical data. This includes the use of rejected human lungs, pig lungs, and rat lungs. In this review, we summarize some of the key current literature studies relevant to each of the major EVLP model platforms and identify the advantages and disadvantages of each platform. The review aims to guide investigators in choosing an appropriate species model to suit their specific goals of study, and ultimately aid in translation of therapy to meet the growing needs of the patient population.

Protective Effects of a Hydrogen-Rich Preservation Solution in a Canine Lung Transplantation Model

BACKGROUND

Molecular hydrogen (H₂) has protective effects against ischemia-reperfusion injury in various organs. Because they are easier to transport and safer to use than inhaled H₂, H₂-rich solutions are suitable for organ preservation. In this study, we examined the protective effects of an H₂-rich solution for lung preservation in a canine left lung transplantation (LTx) model.

METHODS

Ten beagles underwent orthotopic left LTx after 23 hours of cold ischemia followed by reperfusion for 4 hours. Forty-five minutes after reperfusion, the right main pulmonary artery was clamped to evaluate the function of the implanted graft. The beagles were divided into two groups: control group (n = 5), and H₂ group (n = 5). In the control group, the donor lungs were flushed and immersed during cold preservation at 4°C using ET-Kyoto solution, and in the H₂ group, these were flushed and immersed using H₂-rich ET-Kyoto solution. Physiologic assessments were performed during reperfusion. After reperfusion, the wet-to-dry ratios were determined, and histology examinations were performed.

RESULTS

Significantly higher partial pressure of arterial oxygen and significantly lower partial pressure of carbon dioxide were observed in the H₂ group than in the control group (P = .045 and P < .001, respectively). The wet-to-dry ratio was significantly lower in the H₂ group than in the control group (P = .032). Moreover, in histology examination, less lung injury and fewer apoptotic cells were observed in the H₂ group (P < .001 and P < .001, respectively).

CONCLUSIONS

Our results demonstrated that the H₂-rich preservation solution attenuated ischemia-reperfusion injury in a canine left LTx model.

Ex Vivo Lung Perfusion: A Review of Research and Clinical Practices

End-stage lung disease is ultimately treated with lung transplantation. However, there is a paucity of organs with an increasing number of patients being diagnosed with end-stage lung disease. Ex vivo lung perfusion has emerged as a potential tool to assess the quality and to recondition marginal donor lungs prior to transplantation with the goal of increasing the donor pool. This technology has shown promise with similar results compared with the conventional technique of cold static preservation in terms of primary graft dysfunction and overall outcomes. This review provides an update on the results and uses of this technology. The review will also summarize clinical studies and techniques in reconditioning and assessing lungs on ex vivo lung perfusion. Last, we discuss how this technology can be applied to fields outside of transplantation such as thoracic oncology and bioengineering.

Progress of Clinical Application for Ex Vivo Lung Perfusion (EVLP) in Lung Transplantation

In recent years, medical advances make lung transplantation become a standard treatment for terminal lung diseases (such as emphysema, pulmonary fibrosis, pulmonary cystic fibrosis, and pulmonary arterial hypertension) that cannot be cured by drugs or surgery (Lund et al., J Heart Lung Transplant 34:1244, 2015). However, the current number of donor lungs that meet the transplant criteria is no longer sufficient for transplanting, causing some patients to die while waiting for a suitable lung. Current methods for improving the situation of shortage of lung transplant donors include the use of donation after cardiac death (DCD) donors, smoker donors, and Ex Vivo Lung Perfusion (EVLP). Among them, EVLP is a technique for extending lung preservation time and repairing lung injury in the field of lung transplantation. By continuously assessing and improving the function of marginal donor lungs, EVLP increases the number of lungs that meet the transplant criteria and, to some extent, alleviates the current situation of shortage of donor lungs. This chapter reviews the clinical application and research progress of EVLP in the field of lung transplantation.

Organ preservation solution containing dissolved hydrogen gas from a hydrogen-absorbing alloy canister improves function of transplanted ischemic kidneys in miniature pigs

Various methods have been devised to dissolve hydrogen gas in organ preservation solutions, including use of a hydrogen gas cylinder, electrolysis, or a hydrogen-generating agent. However, these methods require considerable time and effort for preparation. We investigated a practical technique for rapidly dissolving hydrogen gas in organ preservation solutions by using a canister containing hydrogen-absorbing alloy. The efficacy of hydrogen-containing organ preservation solution created by this method was tested in a miniature pig model of kidney transplantation from donors with circulatory arrest. The time required for dissolution of hydrogen gas was only 2–3 minutes. When hydrogen gas was infused into a bag containing cold ETK organ preservation solution at a pressure of 0.06 MPa and the bag was subsequently opened to the air, the dissolved hydrogen concentration remained at 1.0 mg/L or more for 4 hours. After warm ischemic injury was induced by circulatory arrest for 30 minutes, donor kidneys were harvested and perfused for 5 minutes with hydrogen-containing cold ETK solution or hydrogen-free cold ETK solution. The perfusion rate was faster from the initial stage with hydrogen-containing cold ETK solution than with hydrogen-free ETK solution. After storage of the kidney in hydrogen-free preservation solution for 1 hour before transplantation, no urine production was observed and blood flow was not detected in the transplanted kidney at sacrifice on postoperative day 6. In contrast, after storage in hydrogen-containing preservation solution for either 1 or 4 hours, urine was detected in the bladder and blood flow was confirmed in the transplanted kidney. This method of dissolving hydrogen gas in organ preservation solution is a practical technique for potentially converting damaged organs to transplantable organs that can be used safely in any clinical setting where organs are removed from donors.

Protective effects of hydrogen inhalation during the warm ischemia phase against lung ischemia-reperfusion injury in rat donors after cardiac death

BACKGROUND

Successful amelioration of long-term warm ischemia lung injury in donors after cardiac death (DCDs) can remarkably improve outcomes. Hydrogen gas provides potent anti-inflammatory and antioxidant effects against ischemia-reperfusion injury (IRI). This study observed the effects of hydrogen inhalation on lung grafts during the warm ischemia phase in cardiac death donors.

METHODS

After cardiac death, rat donor lungs (n = 8) underwent mechanical ventilation with 40% oxygen plus 60% nitrogen (control group) or 3% hydrogen and 40% oxygen plus 57% nitrogen (hydrogen group) for 2 h during the warm ischemia phase in situ. Then, lung transplantation was performed after 2 h of cold storage and 3 h of recipient reperfusion prior to lung graft assessment. Rats that underwent left thoracotomy without transplantation served as the sham group (n = 8). The results of static compliance and arterial blood gas analysis were assessed in the recipients. The wet-to-dry weight ratio (W/D), inflammation, oxidative stress, cell apoptosis and histologic changes were evaluated after 3 h of reperfusion. Nuclear factor kappa B (NF-κB) protein expression in the graft was analyzed by Western blotting.

RESULTS

Compared with the sham group, lung function, W/D, inflammatory reaction, oxidative stress and histological changes were decreased in both transplant groups (control and hydrogen groups). However, compared with the control group, exposure to 3% hydrogen significantly improved lung graft static compliance and oxygenation and remarkably decreased the wet-to-dry weight ratio, inflammatory reactions, and lipid peroxidation. Furthermore, hydrogen improved the lung graft histological changes, decreased the lung injury score and apoptotic index and reduced NF-κB nuclear accumulation in the lung grafts.

CONCLUSION

Lung inhalation with 3% hydrogen during the warm ischemia phase attenuated lung graft IRI via NF-κB-dependent anti-inflammatory and antioxidative effects in rat donors after cardiac death.

Acute Supplementation with Molecular Hydrogen Benefits Submaximal Exercise Indices. Randomized, Double-Blinded, Placebo-Controlled Crossover Pilot Study

Background

Clinical studies have reported hydrogen-rich water (HRW) to have therapeutic and ergogenic effects. The aim of this study was to determine the effect of acute supplementation with HRW on exercise performance as measured by VO₂, respiratory exchange ratio (RER), heart rate (HR), and respiratory rate (RR).

Methods

Baseline levels of all exercise indices were determined in nineteen (4 female, 23.4 ± 9.1 yr; 15 male, 30.5 ± 6.8 yr) healthy subjects using a graded treadmill exercise test to exhaustion. Each subject was examined two additional times in a randomized double-blinded, placebo-controlled crossover fashion. Subjects received either HRW or placebo, which was consumed the day before and the day of the testing. HRW was delivered using the hydrogen-producing tablets, DrinkHRW (5 mg of H₂). All data was analyzed with SPSS using pairwise comparisons with Bonferroni adjustment.

Results

HRW supplementation did not influence maximal or minimal indices of exercise performance (VO₂, RER, HR and RR) (p < 0.05). However, HRW significantly decreased average exercising RR and HR (p < 0.05). HRW decreased exercising HR during minutes 1–9 of the graded exercise test (121 ± 26 bpm) compared to placebo (126 ± 26 bpm) and baseline (124 ± 27 bpm) (p < 0.001) without substantially influencing VO₂.

Conclusion

Acute supplementation of DrinkHRW tablets may benefit submaximal aerobic exercise performance by lowering exercising HR. Further studies are needed to determine the influence and practical significance of HRW on varying exercise intensities as well as optimal dosing protocols and the effects of chronic use.

Effects of alkaline-electrolyzed and hydrogen-rich water, in a high-fat-diet nonalcoholic fatty liver disease mouse model

AIM

To identify the effect of hydrogen-rich water (HRW) and electrolyzed-alkaline water (EAW) on high-fat-induced non-alcoholic fatty acid disease in mice.

METHODS

Mice were divided into four groups: (1) Regular diet (RD)/regular water (RW); (2) high-fat diet (HFD)/RW; (3) RD/EAW; and (4) HFD/EAW. Weight and body composition were measured. After twelve weeks, animals were sacrificed, and livers were processed for histology and reverse-transcriptase polymerase chain reaction. A similar experiment was performed using HRW to determine the influence and importance of molecular hydrogen (H₂) in EAW. Finally, we compared the response of hepatocytes isolated from mice drinking HRW or RW to palmitate overload.

RESULTS

EAW had several properties important to the study: (1) pH = 11; (2) oxidation-reduction potential of -495 mV; and (3) H₂ = 0.2 mg/L. However, in contrast to other studies, there were no differences between the groups drinking EAW or RW in either the RD or HFD groups. We hypothesized that the null result was due to low H₂ concentrations. Therefore, we evaluated the effects of RW and low and high HRW concentrations (L-HRW = 0.3 mg H₂/L and H-HRW = 0.8 mg H₂/L, respectively) in mice fed an HFD. Compared to RW and L-HRW, H-HRW resulted in a lower increase in fat mass (46% vs 61%), an increase in lean body mass (42% vs 28%), and a decrease in hepatic lipid accumulation (P < 0.01). Lastly, exposure of hepatocytes isolated from mice drinking H-HRW to palmitate overload demonstrated a protective effect from H₂ by reducing hepatocyte lipid accumulation in comparison to mice drinking regular water.

CONCLUSION

H₂ is the therapeutic agent in electrolyzed-alkaline water and attenuates HFD-induced nonalcoholic fatty liver disease in mice.

Hydrogen gas inhalation during ex vivo lung perfusion of donor lungs recovered after cardiac death

BACKGROUND

Ex vivo lung perfusion (EVLP) is a system that circulates normothermic perfusate into procured lungs, allowing for improved lung function and lung assessment. We investigated whether ventilation with hydrogen gas during EVLP improves the donation after cardiac death lung function and whether this effect persists after actual transplantation.

METHODS

Ten pigs were randomly divided into a control group (n = 5) and a hydrogen group (n = 5). No treatment was administered to induce warm ischemic injury for 1 hour after cardiac arrest, and EVLP was applied in procured lungs for 4 hours. During EVLP, the control group was given room air for respiration, and the hydrogen group was given 2% hydrogen gas. After EVLP, the left lung graft was orthotopically transplanted into the recipient and reperfused for 3 hours. During EVLP and reperfusion, the functional parameters and arterial blood gas analysis (ABGA) were measured every hour. Superoxide dismutase, heme oxygenase, interleukin (IL)-6, IL-10, tumor necrosis factor-α, and nucleotide-binding oligomerization domain-like receptor protein 3 were evaluated in lung tissue after reperfusion. Pathologic evaluations were performed, and the degree of apoptosis was evaluated. The wet/dry ratio was measured.

RESULTS

During EVLP and reperfusion, functional parameters and ABGA results were better in the hydrogen group. The expressions of superoxide dismutase (p = 0.022) and heme oxygenase-1 (p = 0.047) were significantly higher in the hydrogen group. The expressions of IL-6 (p = 0.024) and nucleotide-binding oligomerization domain-like receptor protein 3 (p = 0.042) were higher in the control group, but IL-10 (p = 0.037) was higher in the hydrogen group. The lung injury severity score and the number of apoptotic cells were higher and the degree of pulmonary edema was more severe in the control group than in the hydrogen group.

CONCLUSIONS

Hydrogen gas inhalation during EVLP improved donation after cardiac death lung function via reduction of inflammation and apoptosis, and this effect persisted after LTx.

Organ preservation: from the past to the future

Organ transplantation is the most effective therapy for patients with end-stage disease. Preservation solutions and techniques are crucial for donor organ quality, which is directly related to morbidity and survival after transplantation. Currently, static cold storage (SCS) is the standard method for organ preservation. However, preservation time with SCS is limited as prolonged cold storage increases the risk of early graft dysfunction that contributes to chronic complications. Furthermore, the growing demand for the use of marginal donor organs requires methods for organ assessment and repair. Machine perfusion has resurfaced and dominates current research on organ preservation. It is credited to its dynamic nature and physiological-like environment. The development of more sophisticated machine perfusion techniques and better perfusates may lead to organ repair/reconditioning. This review describes the history of organ preservation, summarizes the progresses that has been made to date, and discusses future directions for organ preservation.

Hypoxic conditioning in blood vessels and smooth muscle tissues: effects on function, mechanisms, and unknowns

Hypoxic preconditioning, the protective effect of brief, intermittent hypoxic or ischemic episodes on subsequent more severe hypoxic episodes, has been known for 30 yr from studies on cardiac muscle. The concept of hypoxic preconditioning has expanded; excitingly, organs beyond the heart, including the brain, liver, and kidney, also benefit. Preconditioning of vascular and visceral smooth muscles has received less attention despite their obvious importance to health. In addition, there has been no attempt to synthesize the literature in this field. Therefore, in addition to overviewing the current understanding of hypoxic conditioning, in the present review, we consider the role of blood vessels in conditioning and explore evidence for conditioning in other smooth muscles. Where possible, we have distinguished effects on myocytes from other cell types in the visceral organs. We found evidence of a pivotal role for blood vessels in conditioning and for conditioning in other smooth muscle, including the bladder, vascular myocytes, and gastrointestinal tract, and a novel response in the uterus of a hypoxic-induced force increase, which helps maintain contractions during labor. To date, however, there are insufficient data to provide a comprehensive or unifying mechanism for smooth muscles or visceral organs and the effects of conditioning on their function. This also means that no firm conclusions can be drawn as to how differences between smooth muscles in metabolic and contractile activity may contribute to conditioning. Therefore, we have suggested what may be general mechanisms of conditioning occurring in all smooth muscles and tabulated tissue-specific mechanistic findings and suggested ideas for further progress.

Current state of ex-vivo lung perfusion

PURPOSE OF REVIEW

The purpose of the current report is to review the ex-vivo peer-reviewed literature published in the last 5 years and to summarize the findings.

RECENT FINDINGS

Encouraging data have been published by several centers utilizing ex-vivo lung perfusion (EVLP) as a means to identify viable grafts from the high-risk donor pool. The outcomes of transplanted lungs that were initially declined because of poor quality, but reevaluated with ex-vivo perfusion, are equivalent to standard criteria donor lungs. Further, research reports have emphasized the role of ex-vivo perfusion as a platform to improve graft quality and reduce the injurious effects of ischemia-reperfusion.

SUMMARY

Over the last 10 years, EVLP has proved its value as a reassessment tool to increase donor utilization. As short- and long-term data demonstrate the safety of EVLP, its use as a therapeutic platform is emerging, along with the promise of a new era in lung transplantation.

Immersing lungs in hydrogen-rich saline attenuates lung ischaemia-reperfusion injury

Objectives

Anti-oxidant effects of hydrogen have been reported in studies examining ischaemia-reperfusion injury (IRI). In this study, we evaluated the therapeutic efficacy of immersing lungs in hydrogen-rich saline on lung IRI.

Methods

Lewis rats were divided into three groups: (i) sham, (ii) normal saline and (iii) hydrogen-rich saline. In the first experiment, the left thoracic cavity was filled with either normal saline or hydrogen-rich saline for 1 h. Then, we measured the hydrogen concentration in the left lung using a sensor gas chromatograph ( N = 3 per group). In the second experiment, lung IRI was induced by occlusion of the left pulmonary hilum for 1 h, followed by reperfusion for 3 h. During the ischaemic period, the left thoracic cavity was filled with either normal saline or hydrogen-rich saline. After reperfusion, we assessed lung function, histological changes and cytokine production ( N = 5-7 per group).

Results

Immersing lungs in hydrogen-rich saline resulted in an elevated hydrogen concentration in the lung (6.9 ± 2.9 μmol/1 g lung). After IRI, pulmonary function (pulmonary compliance and oxygenation levels) was significantly higher in the hydrogen-rich saline group than in the normal saline group ( P  < 0.05). Similarly, pro-inflammatory cytokine levels (interleukin-1β and interleukin-6) in the left lung were significantly lower in the hydrogen-rich saline group than in the normal saline group ( P  < 0.05).

Conclusions

Immersing lungs in hydrogen-rich saline delivered hydrogen into the lung and consequently attenuated lung IRI. Hydrogen-rich solution appears to be a promising approach to managing lung IRI.

Comparison of two strategies for ex vivo lung perfusion

BACKGROUND

Two clinically used strategies for ex vivo lung perfusion (EVLP) were compared in a porcine model with respect to lung function, metabolism, inflammatory response, oxidative stress, and cell viability.

METHODS

Porcine lungs (n = 20) were preserved, harvested, and kept cooled for 2 hours. After randomization, EVLP was performed using a cellular perfusate and open left atrium (COA group) or an acellular perfusate and a closed left atrium (ACA group). Oxygenation (partial pressure of arterial oxygen/fraction of inspired oxygen), compliance, dead space, weight, and perfusate oncotic pressure were registered before and after a 4-hour period of reconditioning. Lung tissue samples were collected before and after EVLP for quantitative polymerase chain reaction analysis of gene expression for inflammatory markers, measurement of tissue hypoxia (hypoxia inducible factor-1α) and oxidative stress (ascorbyl radical), and viability (trypan blue staining) and lung histopathology.

RESULTS

In 3 of 10 lungs undergoing EVLP in the ACA group, EVLP was terminated prematurely because of severe lung edema and inability to perfuse the lungs. There were no significant differences in changes of lung oxygenation or pulmonary vascular resistance between groups. Compliance decreased and lung weights increased in both groups, but more in the ACA group (p = 0.083 and p = 0.065, respectively). There was no obvious difference in gene expression for hypoxia inducible factor-1α, inflammatory markers, free radicals, or lung injury between groups.

CONCLUSIONS

Lung edema formation and decreased lung compliance occurs with both EVLP techniques but were more pronounced in the ACA group. Otherwise, there were no differences in lung function, inflammatory response, ischemia/reperfusion injury, or histopathologic changes between the EVLP techniques.

Models of Lung Transplant Research: a consensus statement from the National Heart, Lung, and Blood Institute workshop

Lung transplantation, a cure for a number of end-stage lung diseases, continues to have the worst long-term outcomes when compared with other solid organ transplants. Preclinical modeling of the most common and serious lung transplantation complications are essential to better understand and mitigate the pathophysiological processes that lead to these complications. Various animal and in vitro models of lung transplant complications now exist and each of these models has unique strengths. However, significant issues, such as the required technical expertise as well as the robustness and clinical usefulness of these models, remain to be overcome or clarified. The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop in March 2016 to review the state of preclinical science addressing the three most important complications of lung transplantation: primary graft dysfunction (PGD), acute rejection (AR), and chronic lung allograft dysfunction (CLAD). In addition, the participants of the workshop were tasked to make consensus recommendations on the best use of these complimentary models to close our knowledge gaps in PGD, AR, and CLAD. Their reviews and recommendations are summarized in this report. Furthermore, the participants outlined opportunities to collaborate and directions to accelerate research using these preclinical models.

Hydrogen, a potential safeguard for graft-versus-host disease and graft ischemia-reperfusion injury?

Post-transplant complications such as graft-versus-host disease and graft ischemia-reperfusion injury are crucial challenges in transplantation. Hydrogen can act as a potential antioxidant, playing a preventive role against post-transplant complications in animal models of multiple organ transplantation. Herein, the authors review the current literature regarding the effects of hydrogen on graft ischemia-reperfusion injury and graft-versus-host disease. Existing data on the effects of hydrogen on ischemia-reperfusion injury related to organ transplantation are specifically reviewed and coupled with further suggestions for future work. The reviewed studies showed that hydrogen (inhaled or dissolved in saline) improved the outcomes of organ transplantation by decreasing oxidative stress and inflammation at both the transplanted organ and the systemic levels. In conclusion, a substantial body of experimental evidence suggests that hydrogen can significantly alleviate transplantation-related ischemia-reperfusion injury and have a therapeutic effect on graft-versus-host disease, mainly via inhibition of inflammatory cytokine secretion and reduction of oxidative stress through several underlying mechanisms. Further animal experiments and preliminary human clinical trials will lay the foundation for hydrogen use as a drug in the clinic.

Ascorbic acid prolongs the viability and stability of isolated perfused lungs: A mechanistic study using 31P and hyperpolarized 13C nuclear magnetic resonance

Ex vivo lung perfusion (EVLP) has recently shown promise as a means of more accurately gauging the health of lung grafts and improving graft performance post-transplant. However, reperfusion of ischemic lung promotes the depletion of high-energy compounds and a progressive loss of normal mitochondrial function, and it remains unclear how and to what extent the EVLP approach contributes to this metabolic decline. Although ascorbate has been used to mitigate the effects of ischemia-reperfusion injury, the nature of its effects during EVLP are also not clear. To address these uncertainties, this study monitored the energy status of lungs during EVLP and after the administration of ascorbate using (31)P and hyperpolarized (13)C NMR (nuclear magnetic resonance). Our experiments demonstrated that the oxidative phosphorylation capacity and pyruvate dehydrogenase flux of lungs decline during ex vivo perfusion. The addition of ascorbate to the perfusate prolonged lung viability by 80% and increased the hyperpolarized (13)C bicarbonate signal by a factor of 2.7. The effect of ascorbate is apparently due not to its antioxidant quality but rather to its ability to energize cellular respiration given that it increased the lung's energy charge significantly, whereas other antioxidants (glutathione and α-lipoic acid) did not alter energy metabolism. During ascorbate administration, inhibition of mitochondrial complex I with rotenone depressed energy charge and shifted the metabolic state of the lung toward glycolysis; reenergizing the electron transport chain with TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) recovered metabolic activity. This indicates that ascorbate slows the decline of the ex vivo perfused lung's mitochondrial activity through an independent interaction with the electron transport chain complexes.

Beneficial biological effects and the underlying mechanisms of molecular hydrogen - comprehensive review of 321 original articles

Therapeutic effects of molecular hydrogen for a wide range of disease models and human diseases have been investigated since 2007. A total of 321 original articles have been published from 2007 to June 2015. Most studies have been conducted in Japan, China, and the USA. About three-quarters of the articles show the effects in mice and rats. The number of clinical trials is increasing every year. In most diseases, the effect of hydrogen has been reported with hydrogen water or hydrogen gas, which was followed by confirmation of the effect with hydrogen-rich saline. Hydrogen water is mostly given ad libitum. Hydrogen gas of less than 4 % is given by inhalation. The effects have been reported in essentially all organs covering 31 disease categories that can be subdivided into 166 disease models, human diseases, treatment-associated pathologies, and pathophysiological conditions of plants with a predominance of oxidative stress-mediated diseases and inflammatory diseases. Specific extinctions of hydroxyl radical and peroxynitrite were initially presented, but the radical-scavenging effect of hydrogen cannot be held solely accountable for its drastic effects. We and others have shown that the effects can be mediated by modulating activities and expressions of various molecules such as Lyn, ERK, p38, JNK, ASK1, Akt, GTP-Rac1, iNOS, Nox1, NF-κB p65, IκBα, STAT3, NFATc1, c-Fos, and ghrelin. Master regulator(s) that drive these modifications, however, remain to be elucidated and are currently being extensively investigated.

Argon and xenon ventilation during prolonged ex vivo lung perfusion

BACKGROUND

Evidence supports the use of ex vivo lung perfusion (EVLP) as a platform for active reconditioning before transplantation to increase the potential donor pool and to reduce the incidence of primary graft dysfunction. A promising reconditioning strategy is the administration of inhaled noble gases based on their organoprotective effects. Our aim was to validate a porcine warm ischemic lung injury model and investigate postconditioning with argon (Ar) or xenon (Xe) during prolonged EVLP.

METHODS

Domestic pigs were divided in four groups (n = 5 per group). In the negative control group, lungs were flushed immediately. In the positive control (PC) and treatment (Ar, Xe) groups, lungs were flushed after a warm ischemic interval of 2-h in situ. All grafts were evaluated and treated during normothermic EVLP for 6 h. In the control groups, lungs were ventilated with 70% N2/30% O2 and in the treatment groups with 70% Ar/30% O2 or 70% Xe/30% O2, respectively. Outcome parameters were physiological variables (pulmonary vascular resistance, peak airway pressures, and PaO2/FiO2), histology, wet-to-dry weight ratio, bronchoalveolar lavage, and computed tomography scan.

RESULTS

A significant difference between negative control and PC for pulmonary vascular resistance, peak airway pressures, PaO2/FiO2, wet-to-dry weight ratio, histology, and computed tomography-imaging was observed. No significant differences between the injury group (PC) and the treatment groups (Ar, Xe) were found.

CONCLUSIONS

We validated a reproducible prolonged 6-h EVLP model with 2 h of warm ischemia and described the physiological changes over time. In this model, ventilation during EVLP with Ar or Xe administered postinjury did not improve graft function.

Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences.

Biliary tract external drainage increases the expression levels of heme oxygenase-1 in rat livers

Background

Heme oxygenase-1 (HO-1) protects cells by anti-oxidation, maintaining normal microcirculation and anti-inflammatory under stress. This study investigated the effects of biliary tract external drainage (BTED) on the expression levels of HO-1 in rat livers.

Methods

Biliary tract external drainage was performed by inserting a cannula into the bile duct. Sixty Sprague–Dawley rats were randomized to the following groups: sham 1 h group; BTED 1 h group; bile duct ligation (BDL) 1 h group; sham 6 h group and BTED 6 h group. The expression levels of HO-1 mRNA were analyzed using real-time RT-PCR. The expression levels of HO-1 were analyzed using immunohistochemistry.

Results

The expression levels of HO-1 mRNA in the liver of the BTED group increased significantly compared with the sham group 1 and 6 h after surgery (p < 0.05).The expression levels of HO-1 in the BTED group increased significantly compared with the sham group 1 and 6 h after surgery. The expression levels of HO-1 mRNA in the liver in the BDL group decreased significantly compared with the sham group 1 h after surgery (p < 0.05).The expression levels of HO-1 in the BDL group decreased significantly compared with the sham group at this time.

Conclusion

Biliary tract external drainages increase the expression levels of HO-1 in the liver.

The effects of hydrogen gas inhalation during ex vivo lung perfusion on donor lungs obtained after cardiac death

OBJECTIVES

Lung transplantation is a well-established treatment of end-stage lung disease; however, it is limited by a shortage of donor lungs. To overcome this problem, donation after cardiac death (DCD) and ex vivo lung perfusion (EVLP) are being widely investigated. In this study, the effect of hydrogen gas, a known antioxidant, was investigated on a DCD lung model during EVLP.

METHODS

Ten pigs were randomized into either a control (n = 5) or a hydrogen group (n = 5). After fibrillation by electric shock, no further treatment was administered in order to induce warm ischaemic injury for 1 h. The lungs were then procured, followed by 4 h of EVLP. During EVLP, the lungs were ventilated with room air in the control group, and with 2% hydrogen gas in the hydrogen group. Oxygen capacity (OC), pulmonary vascular resistance (PVR) and peak airway pressure (PAP) were measured every hour, and the expressions of interleukin-1 beta (IL-1β), IL-6 (IL-6), IL-8 (IL-8) and tumour necrosis factor-alpha (TNF-α) were evaluated in lung tissue after EVLP. Pathological evaluations were performed using lung injury severity (LIS) scores and the wet/dry ratio was also measured.

RESULTS

The OC in the hydrogen group was higher than in the control group, but the difference was not statistically significant (P = 0.0862). PVR (P = 0.0111) and PAP (P = 0.0189) were statistically significantly lower in the hydrogen group. Compared with the control group, the hydrogen group had a statistically significantly lower expression of IL-1β (P = 0.0317), IL-6 (P = 0.0159), IL-8 (P = 0.0195) and TNF-α (P = 0.0159). The LIS scores (P = 0.0358) and wet/dry ratios (P = 0.040) were also significantly lower in the hydrogen group.

CONCLUSIONS

Hydrogen gas inhalation during EVLP improved the function of DCD lungs, which may increase the utilization of DCD lungs.