Hydrogen Sulfide Treatment Mitigates Renal Allograft Ischemia-Reperfusion Injury during Cold Storage and Improves Early Transplant Kidney Function and Survival Following Allogeneic Renal Transplantation

Perfusion Techniques in Kidney Allograft Preservation to Reduce Ischemic Reperfusion Injury: A Systematic Review and Meta-Analysis

The limited supply and rising demand for kidney transplantation has led to the use of allografts more susceptible to ischemic reperfusion injury (IRI) and oxidative stress to expand the donor pool. Organ preservation and procurement techniques, such as machine perfusion (MP) and normothermic regional perfusion (NRP), have been developed to preserve allograft function, though their long-term outcomes have been more challenging to investigate. We performed a systematic review and meta-analysis to examine the benefits of MP and NRP compared to traditional preservation techniques. PubMed (MEDLINE), Embase, Cochrane, and Scopus databases were queried, and of 13,794 articles identified, 54 manuscripts were included (n = 41 MP; n = 13 NRP). MP decreased the rates of 12-month graft failure (OR 0.67; 95%CI 0.55, 0.80) and other perioperative outcomes such as delayed graft function (OR 0.65; 95%CI 0.54, 0.79), primary nonfunction (OR 0.63; 95%CI 0.44, 0.90), and hospital length of stay (15.5 days vs. 18.4 days) compared to static cold storage. NRP reduced the rates of acute rejection (OR 0.48; 95%CI 0.35, 0.67) compared to in situ perfusion. Overall, MP and NRP are effective techniques to mitigate IRI and play an important role in safely expanding the donor pool to satisfy the increasing demands of kidney transplantation.

The functions of hydrogen sulfide on the urogenital system of both males and females: from inception to the present

Hydrogen sulfide (H2S) is known as a chemical gas in nature with both enzymatic and non-enzymatic biosynthesis in different human organs. A couple of studies have demonstrated the function of H2S in regulating the homeostasis of the human body. Additionally, they have shown its synthesis, measurement, chemistry, protective effects, and interaction in various aspects of scientific evidence. Furthermore, many researches have demonstrated the beneficial impacts of H2S on genital organs and systems. According to various studies, it is recognized that H2S-producing enzymes and the endogenous production of H2S are expressed in male and female reproductive systems in different mammalian species. The main goal of this comprehensive review is to assess the potential therapeutic impacts of this gasotransmitter in the male and female urogenital system and find underlying mechanisms of this agent. This narrative review investigated the articles that were published from the 1970s to 2022. The review's primary focus is the impacts of H2S on the male and female urogenital system. Medline, CINAHL, PubMed, and Google scholar databases were searched. Keywords used in this review were "Hydrogen sulfide," "H2S," "urogenital system," and "urogenital tract". Numerous studies have demonstrated the therapeutic and protective effects of sodium hydrosulfide (Na-HS) as an H2S donor on male and female infertility disorders. Furthermore, it has been observed that H2S plays a significant role in improving different diseases such as ameliorating sperm parameters. The specific localization of H2S enzymes in the urogenital system provides an excellent opportunity to comprehend its function and role in various disorders related to this system. It is noteworthy that H2S has been demonstrated to be produced in endocrine organs and exhibit diverse activities. Moreover, it is important to recognize that alterations in H2S biosynthesis are closely linked to endocrine disorders. Therefore, hormones can be pivotal in regulating H2S production, and H2S synthesis pathways may aid in establishing novel therapeutic strategies. H2S possesses pharmacological effects on essential disorders, such as anti-inflammation, anti-apoptosis, and anti-oxidant activities, which render it a valuable therapeutic agent for human urogenital disease. Furthermore, this agent shows promise in ameliorating the detrimental effects of various male and female diseases. Despite the limited clinical research, studies have demonstrated that applying H2S as an anti-oxidant source could ameliorate adverse effects of different conditions in the urogenital system. More clinical studies are required to confirm the role of this component in clinical settings.

Evaluating the Effects of Kidney Preservation at 10 °C with Hemopure and Sodium Thiosulfate in a Rat Model of Syngeneic Orthotopic Kidney Transplantation

Kidney transplantation is preferred for end-stage renal disease. The current gold standard for kidney preservation is static cold storage (SCS) at 4 °C. However, SCS contributes to renal graft damage through ischemia-reperfusion injury (IRI). We previously reported renal graft protection after SCS with a hydrogen sulfide donor, sodium thiosulfate (STS), at 4 °C. Therefore, this study aims to investigate whether SCS at 10 °C with STS and Hemopure (blood substitute), will provide similar protection. Using in vitro model of IRI, we subjected rat renal proximal tubular epithelial cells to hypoxia-reoxygenation for 24 h at 10 °C with or without STS and measured cell viability. In vivo, we preserved 36 donor kidneys of Lewis rats for 24 h in a preservation solution at 10 °C supplemented with STS, Hemopure, or both followed by transplantation. Tissue damage and recipient graft function parameters, including serum creatinine, blood urea nitrogen, urine osmolality, and glomerular filtration rate (GFR), were evaluated. STS-treated proximal tubular epithelial cells exhibited enhanced viability at 10 °C compared with untreated control cells (p < 0.05). Also, STS and Hemopure improved renal graft function compared with control grafts (p < 0.05) in the early time period after the transplant, but long-term function did not reach significance. Overall, renal graft preservation at 10 °C with STS and Hemopure supplementation has the potential to enhance graft function and reduce kidney damage, suggesting a novel approach to reducing IRI and post-transplant complications.

Nitric oxide in kidney transplantation

Kidney transplantation is the treatment of choice for patients with kidney failure. Compared to dialysis therapy, it provides better quality of life and confers significant survival advantage at a relatively lower cost. However, the long-term success of this life-saving intervention is severely hampered by an inexorable clinical problem referred to as ischemia-reperfusion injury (IRI), and increases the incidence of post-transplant complications including loss of renal graft function and death of transplant recipients. Burgeoning evidence shows that nitric oxide (NO), a poisonous gas at high concentrations, and with a historic negative public image as an environmental pollutant, has emerged as a potential candidate that holds clinical promise in mitigating IRI and preventing acute and chronic graft rejection when it is added to kidney preservation solutions at low concentrations or when administered to the kidney donor prior to kidney procurement and to the recipient or to the reperfusion circuit at the start and during reperfusion after renal graft preservation. Interestingly, dysregulated or abnormal endogenous production and metabolism of NO is associated with IRI in kidney transplantation. From experimental and clinical perspectives, this review presents endogenous enzymatic production of NO as well as its exogenous sources, and then discusses protective effects of constitutive nitric oxide synthase (NOS)-derived NO against IRI in kidney transplantation via several signaling pathways. The review also highlights a few isolated studies of renal graft protection by NO produced by inducible NOS.

Sodium Hydrosulfide Treatment During Porcine Kidney Ex Vivo Perfusion and Transplantation

Background

In rodents, hydrogen sulfide (H2S) reduces ischemia-reperfusion injury and improves renal graft function after transplantation. Here, we hypothesized that the benefits of H2S are conserved in pigs, a more clinically relevant model.

Methods

Adult porcine kidneys retrieved immediately or after 60 min of warm ischemia (WI) were exposed to 100 µM sodium hydrosulfide (NaHS) (1) during the hypothermic ex vivo perfusion only, (2) during WI only, and (3) during both WI and ex vivo perfusion. Kidney perfusion was evaluated with dynamic contrast-enhanced MRI. MRI spectroscopy was further employed to assess energy metabolites including ATP. Renal biopsies were collected at various time points for histopathological analysis.

Results

Perfusion for 4 h pig kidneys with Belzer MPS UW + NaHS resulted in similar renal perfusion and ATP levels than perfusion with UW alone. Similarly, no difference was observed when NaHS was administered in the renal artery before ischemia. After autotransplantation, no improvement in histologic lesions or cortical/medullary kidney perfusion was observed upon H2S administration. In addition, AMP and ATP levels were identical in both groups.

Conclusions

In conclusion, treatment of porcine kidney grafts using NaHS did not result in a significant reduction of ischemia-reperfusion injury or improvement of kidney metabolism. Future studies will need to define the benefits of H2S in human, possibly using other molecules as H2S donors.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

The Optimization of Renal Graft Preservation Temperature to Mitigate Cold Ischemia-Reperfusion Injury in Kidney Transplantation

Renal transplantation is the preferred treatment for patients with end-stage renal disease. The current gold standard of kidney preservation for transplantation is static cold storage (SCS) at 4 °C. However, SCS contributes to renal ischemia-reperfusion injury (IRI), a pathological process that negatively impacts graft survival and function. Recent efforts to mitigate cold renal IRI involve preserving renal grafts at higher or subnormothermic temperatures. These temperatures may be beneficial in reducing the risk of cold renal IRI, while also maintaining active biological processes such as increasing the expression of mitochondrial protective metabolites. In this review, we discuss different preservation temperatures for renal transplantation and pharmacological supplementation of kidney preservation solutions with hydrogen sulfide to determine an optimal preservation temperature to mitigate cold renal IRI and enhance renal graft function and recipient survival.

Hypothermia-Triggered Mesoporous Silica Particles for Controlled Release of Hydrogen Sulfide to Reduce the I/R Injury of the Myocardium

Despite the fact that heart transplantation (HTx) is a relatively mature procedure, heart ischemic and reperfusion (I/R) injury during HTx remains a challenge. Even after a successful operation, the heart will be at risk of primary graft failure and mortality during the first year. In this study, temperature-sensitive polymer poly(N-n-propylacrylamide-co-N-tert-butyl acrylamide) (PNNTBA) was coated on diallyl trisulfide (DATS)-loaded mesoporous silica nanoparticles (DATS-MSN) to synthesize hypothermia-triggered hydrogen sulfide (H₂S) releasing particles (HT-MSN). Because the PNNTBA shell dissolves in phosphate-buffered saline at 4 °C, the loaded DATS could continuously release H₂S within 6 h when activated by glutathione (GSH). Furthermore, after co-culturing biocompatible HT-MSN with cardiomyocytes, H₂S released from HT-MSN at 4 °C was found to protect cardiomyocytes from ischemic and reperfusion (I/R) injury. In detail, the rate of cell apoptosis and lactate dehydrogenase activity was decreased, as manifested by increased BCL-2 expression and decreased BAX expression. More importantly, in an isolated heart preservation experiment, HT-MSN demonstrated potent protection against cardiac I/R injury and reduced expression of inflammatory factors TNF-α and IL-1β. This study provided a new method for the controlled release of H₂S by the donor and myocardial protection from I/R injury.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Sulfur Amino Acid Supplementation Abrogates Protective Effects of Caloric Restriction for Enhancing Bone Marrow Regrowth Following Ionizing Radiation

Radiation therapy damages and depletes total bone marrow (BM) cellularity, compromising safety and limiting effective dosing. Aging also strains total BM and BM hematopoietic stem and progenitor cell (HSPC) renewal and function, resulting in multi-system defects. Interventions that preserve BM and BM HSPC homeostasis thus have potential clinical significance. Here, we report that 50% calorie restriction (CR) for 7-days or fasting for 3-days prior to irradiation improved mouse BM regrowth in the days and weeks post irradiation. Specifically, one week of 50% CR ameliorated loss of total BM cellularity post irradiation compared to ad libitum-fed controls. CR-mediated BM protection was abrogated by dietary sulfur amino acid (i.e., cysteine, methionine) supplementation or pharmacological inhibition of sulfur amino acid metabolizing and hydrogen sulfide (H₂S) producing enzymes. Up to 2-fold increased proliferative capacity of ex vivo-irradiated BM isolated from food restricted mice relative to control mice indicates cell autonomy of the protective effect. Pretreatment with H₂S in vitro was sufficient to preserve proliferative capacity by over 50% compared to non-treated cells in ex vivo-irradiated BM and BM HSPCs. The exogenous addition of H₂S inhibited Ten eleven translocation 2 (TET2) activity in vitro, thus providing a potential mechanism of action. Short-term CR or fasting therefore offers BM radioprotection and promotes regrowth in part via altered sulfur amino acid metabolism and H₂S generation, with translational implications for radiation treatment and aging.

Supplemental hydrogen sulfide in models of renal transplantation after cardiac death

Background:

The increasing use of kidneys from donations after cardiac death (DCD) for renal transplantation is hindered by negative outcomes owing to organ injury after prolonged warm and cold ischemia–reperfusion. Recently, hydrogen sulfide (H₂S) has shown cytoprotective effects against ischemia–reperfusion injury; however, its effectiveness in the context of DCD renal transplantation is unknown.

Methods:

We tested a novel 30-day in vivo syngeneic murine model of DCD renal transplantation, in which the donor kidney was clamped for 30 minutes and stored for 18 hours in cold University of Wisconsin (UW) solution or UW with 150 μM sodium hydrogen sulfide (UW + NaHS) before transplantation. We also tested a 7-day in vivo porcine model of DCD renal autotransplantation, in which the left kidney was clamped for 60 minutes and preserved for 24 hours using hypothermic perfusion with UW or UW + 150 μM NaHS before autotransplantation. We collected blood and urine samples periodically, and collected kidney samples at the end point for histopathology and quantitative reverse transcription polymerase chain reaction.

Results:

Rats that received H₂S-treated kidneys showed significantly higher survival, faster recovery of graft function and significantly lower acute tubular necrosis than controls. Pig kidneys perfused with UW + NaHS showed significantly higher renal blood flow and lower renal resistance than control kidneys after 24 hours of perfusion. After autotransplantation, pigs that received H₂S-treated kidneys showed significantly lower serum creatinine on days 1 and 7 after transplantation. Rat and pig kidneys treated with H₂S also showed more protective gene expression profiles than controls.

Conclusion:

Our findings support the potential use of H₂S-supplemented UW solution during cold storage as a novel and practical means to improve DCD graft survival and function.

Hydrogen Sulfide and the Kidney: Physiological Roles, Contribution to Pathophysiology, and Therapeutic Potential

Significance: Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has a broad spectrum of biological activities, including antioxidant and cytoprotective actions, as well as vasodilatory, anti-inflammatory and antifibrotic effects. New, significant aspects of H₂S biology in the kidney continue to emerge, underscoring the importance of this signaling molecule in kidney homeostasis, function, and disease. Recent Advances: H₂S signals via three main mechanisms, by maintaining redox balance through its antioxidant actions, by post-translational modifications of cellular proteins (S-sulfhydration), and by binding to protein metal centers. Important renal functions such as glomerular filtration, renin release, or sodium reabsorption have been shown to be regulated by H₂S, using either exogenous donors or by the endogenous-producing systems. Critical Issues: Lower H₂S levels are observed in many renal pathologies, including renal ischemia-reperfusion injury and obstructive, diabetic, or hypertensive nephropathy. Unraveling the molecular targets through which H₂S exerts its beneficial effects would be of great importance not only for understanding basic renal physiology, but also for identifying new pharmacological interventions for renal disease. Future Directions: Additional studies are needed to better understand the role of H₂S in the kidney. Mapping the expression pattern of H₂S-producing and -degrading enzymes in renal cells and generation of cell-specific knockout mice based on this information will be invaluable in the effort to unravel additional roles for H₂S in kidney (patho)physiology. With this knowledge, novel targeted more effective therapeutic strategies for renal disease can be designed. Antioxid. Redox Signal. 36, 220-243.

Ex-vivo Kidney Machine Perfusion: Therapeutic Potential

Kidney transplantation remains the gold standard treatment for patients suffering from end-stage kidney disease. To meet the constantly growing organ demands grafts donated after circulatory death (DCD) or retrieved from extended criteria donors (ECD) are increasingly utilized. Not surprisingly, usage of those organs is challenging due to their susceptibility to ischemia-reperfusion injury, high immunogenicity, and demanding immune regulation after implantation. Lately, a lot of effort has been put into improvement of kidney preservation strategies. After demonstrating a definite advantage over static cold storage in reduction of delayed graft function rates in randomized-controlled clinical trials, hypothermic machine perfusion has already found its place in clinical practice of kidney transplantation. Nevertheless, an active investigation of perfusion variables, such as temperature (normothermic or subnormothermic), oxygen supply and perfusate composition, is already bringing evidence that ex-vivo machine perfusion has a potential not only to maintain kidney viability, but also serve as a platform for organ conditioning, targeted treatment and even improve its quality. Many different therapies, including pharmacological agents, gene therapy, mesenchymal stromal cells, or nanoparticles (NPs), have been successfully delivered directly to the kidney during ex-vivo machine perfusion in experimental models, making a big step toward achievement of two main goals in transplant surgery: minimization of graft ischemia-reperfusion injury and reduction of immunogenicity (or even reaching tolerance). In this comprehensive review current state of evidence regarding ex-vivo kidney machine perfusion and its capacity in kidney graft treatment is presented. Moreover, challenges in application of these novel techniques in clinical practice are discussed.

Sodium thiosulfate-supplemented UW solution protects renal grafts against prolonged cold ischemia-reperfusion injury in a murine model of syngeneic kidney transplantation

INTRODUCTION

Cold ischemia-reperfusion injury (IRI) is an inevitable event that increases post-transplant complications. We have previously demonstrated that supplementation of University of Wisconsin (UW) solution with non-FDA-approved hydrogen sulfide (H₂S) donor molecules minimizes cold IRI and improves renal graft function after transplantation. The present study investigates whether an FDA-approved H₂S donor molecule, sodium thiosulfate (STS), will have the same or superior effect in a clinically relevant rat model of syngeneic orthotopic kidney transplantation.

METHOD

Thirty Lewis rats underwent bilateral nephrectomy followed by syngeneic orthotopic transplantation of the left kidney after 24-hour preservation in either UW or UW+STS solution at 4 °C. Rats were monitored to post-transplant day 14 and sacrificed to assess renal function (urine output, serum creatinine and blood urea nitrogen). Kidney sections were stained with H&E, TUNEL, CD68, and myeloperoxidase (MPO) to detect acute tubular necrosis (ATN), apoptosis, macrophage infiltration, and neutrophil infiltration.

RESULT

UW+STS grafts showed significantly improved graft function immediately after transplantation, with improved recipient survival compared to UW grafts (p < 0.05). Histopathological examination revealed significantly reduced ATN, apoptosis, macrophage and neutrophil infiltration and downregulation of pro-inflammatory and pro-apoptotic genes in UW+STS grafts compared to UW grafts (p < 0.05).

CONCLUSION

We show for the first time that preservation of renal grafts in STS-supplemented UW solution protects against prolonged cold IRI by suppressing apoptotic and inflammatory pathways, and thereby improving graft function and prolonging recipient survival. This could represent a novel clinically applicable therapeutic strategy to minimize the detrimental clinical outcome of prolonged cold IRI in kidney transplantation.

Gasping for Sulfide: A Critical Appraisal of Hydrogen Sulfide in Lung Disease and Accelerated Aging

Hydrogen sulfide (H₂S) is a gaseous signaling molecule involved in a plethora of physiological and pathological processes. It is primarily synthesized by cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase as a metabolite of the transsulfuration pathway. H₂S has been shown to exert beneficial roles in lung disease acting as an anti-inflammatory and antiviral and to ameliorate cell metabolism and protect from oxidative stress. H₂S interacts with transcription factors, ion channels, and a multitude of proteins via post-translational modifications through S-persulfidation ("sulfhydration"). Perturbation of endogenous H₂S synthesis and/or levels have been implicated in the development of accelerated lung aging and diseases, including asthma, chronic obstructive pulmonary disease, and fibrosis. Furthermore, evidence indicates that persulfidation is decreased with aging. Here, we review the use of H₂S as a biomarker of lung pathologies and discuss the potential of using H₂S-generating molecules and synthesis inhibitors to treat respiratory diseases. Furthermore, we provide a critical appraisal of methods of detection used to quantify H₂S concentration in biological samples and discuss the challenges of characterizing physiological and pathological levels. Considerations and caveats of using H₂S delivery molecules, the choice of generating molecules, and concentrations are also reviewed. Antioxid. Redox Signal. 35, 551-579.

H2S donor molecules against cold ischemia-reperfusion injury in preclinical models of solid organ transplantation

Cold ischemia-reperfusion injury (IRI) is an inevitable and unresolved problem that poses a great challenge in solid organ transplantation (SOT). It represents a major factor that increases acute tubular necrosis, decreases graft survival, and delays graft function. This complicates graft quality, post-transplant patient care and organ transplantation outcomes, and therefore undermines the success of SOT. Herein, we review recent advances in research regarding novel pharmacological strategies involving the use of different donor molecules of hydrogen sulfide (H₂S), the third established member of the gasotransmitter family, against cold IRI in different experimental models of SOT (kidney, heart, lung, liver, pancreas and intestine). Additionally, we discuss the molecular mechanisms underlying the effects of these H₂S donor molecules in SOT, and suggestions for clinical translation. Our reviewed findings showed that storage of donor organs in H₂S-supplemented preservation solution or administration of H₂S to organ donor prior to organ procurement and to recipient at the start and during reperfusion is a novel, simple and cost-effective pharmacological approach to minimize cold IRI, limit post-transplant complications and improve transplantation outcomes. In conclusion, experimental evidence demonstrate that H₂S donors can significantly mitigate cold IRI during SOT through inhibition of a complex cascade of interconnected cellular and molecular events involving microcirculatory disturbance and microvascular dysfunction, mitochondrial injury, inflammatory responses, cell damage and cell death, and other damaging molecular pathways while promoting protective pathways. Translating these promising findings from bench to bedside will lay the foundation for the use of H₂S donor molecules in clinical SOT in the future.

Renal Delivery of Pharmacologic Agents During Machine Perfusion to Prevent Ischaemia-Reperfusion Injury: From Murine Model to Clinical Trials

Donor organ shortage still remains a serious obstacle for the access of wait-list patients to kidney transplantation, the best treatment for End-Stage Kidney Disease (ESKD). To expand the number of transplants, the use of lower quality organs from older ECD or DCD donors has become an established routine but at the price of increased incidence of Primary Non-Function, Delay Graft Function and lower-long term graft survival. In the last years, several improvements have been made in the field of renal transplantation from surgical procedure to preservation strategies. To improve renal outcomes, research has focused on development of innovative and dynamic preservation techniques, in order to assess graft function and promote regeneration by pharmacological intervention before transplantation. This review provides an overview of the current knowledge of these new preservation strategies by machine perfusions and pharmacological interventions at different timing possibilities: in the organ donor, ex-vivo during perfusion machine reconditioning or after implementation in the recipient. We will report therapies as anti-oxidant and anti-inflammatory agents, senolytics agents, complement inhibitors, HDL, siRNA and H2S supplementation. Renal delivery of pharmacologic agents during preservation state provides a window of opportunity to treat the organ in an isolated manner and a crucial route of administration. Even if few studies have been reported of transplantation after ex-vivo drugs administration, targeting the biological pathway associated to kidney failure (i.e. oxidative stress, complement system, fibrosis) might be a promising therapeutic strategy to improve the quality of various donor organs and expand organ availability.

Evaluating the Effects of Subnormothermic Perfusion with AP39 in a Novel Blood-Free Model of Ex Vivo Kidney Preservation and Reperfusion

The use of blood for normothermic and subnormothermic kidney preservation hinders the translation of these approaches and promising therapeutics. This study evaluates whether adding hydrogen sulfide donor AP39 to Hemopure, a blood substitute, during subnormothermic perfusion improves kidney outcomes. After 30 min of renal pedicle clamping, porcine kidneys were treated to 4 h of static cold storage (SCS-4 °C) or subnormothermic perfusion at 21 °C with Hemopure (H-21 °C), Hemopure + 200 nM AP39 (H200nM-21 °C) or Hemopure + 1 µM AP39 (H1µM-21 °C). Then, kidneys were reperfused with Hemopure at 37 °C for 4 h with metabolic support. Perfusate composition, tissue oxygenation, urinalysis and histopathology were analyzed. During preservation, the H200nM-21 °C group exhibited significantly higher urine output than the other groups and significantly higher tissue oxygenation than the H1µM-21 °C group at 1 h and 2h. During reperfusion, the H200nM-21 °C group exhibited significantly higher urine output and lower urine protein than the other groups. Additionally, the H200nM-21 °C group exhibited higher perfusate pO₂ levels than the other groups and significantly lower apoptotic injury than the H-21 °C and the H1µM-21 °C groups. Thus, subnormothermic perfusion at 21 °C with Hemopure + 200 nM AP39 improves renal outcomes. Additionally, our novel blood-free model of ex vivo kidney preservation and reperfusion could be useful for studying other therapeutics.

Hydrogen Sulfide Metabolite, Sodium Thiosulfate: Clinical Applications and Underlying Molecular Mechanisms

Thiosulfate in the form of sodium thiosulfate (STS) is a major oxidation product of hydrogen sulfide (H2S), an endogenous signaling molecule and the third member of the gasotransmitter family. STS is currently used in the clinical treatment of acute cyanide poisoning, cisplatin toxicities in cancer therapy, and calciphylaxis in dialysis patients. Burgeoning evidence show that STS has antioxidant and anti-inflammatory properties, making it a potential therapeutic candidate molecule that can target multiple molecular pathways in various diseases and drug-induced toxicities. This review discusses the biochemical and molecular pathways in the generation of STS from H2S, its clinical usefulness, and potential clinical applications, as well as the molecular mechanisms underlying these clinical applications and a future perspective in kidney transplantation.

Targeting oxidative stress, a crucial challenge in renal transplantation outcome

Disorders characterized by ischemia/reperfusion (I/R) are the most common causes of debilitating diseases and death in stroke, cardiovascular ischemia, acute kidney injury or organ transplantation. In the latter example the I/R step defines both the amplitude of the damages to the graft and the functional recovery outcome. During transplantation the kidney is subjected to blood flow arrest followed by a sudden increase in oxygen supply at the time of reperfusion. This essential clinical protocol causes massive oxidative stress which is at the basis of cell death and tissue damage. The involvement of both reactive oxygen species (ROS) and nitric oxides (NO) has been shown to be a major cause of these cellular damages. In fact, in non-physiological situations, these species escape endogenous antioxidant control and dangerously accumulate in cells. In recent years, the objective has been to find clinical and pharmacological treatments to reduce or prevent the appearance of oxidative stress in ischemic pathologies. This is very relevant because, due to the increasing success of organ transplantation, clinicians are required to use limit organs, the preservation of which against oxidative stress is crucial for a better outcome. This review highlights the key actors in oxidative stress which could represent new pharmacological targets.

Subnormothermic Perfusion with H2S Donor AP39 Improves DCD Porcine Renal Graft Outcomes in an Ex Vivo Model of Kidney Preservation and Reperfusion

Cold preservation is the standard of care for renal grafts. However, research on alternatives like perfusion at higher temperatures and supplementing preservation solutions with hydrogen sulfide (H₂S) has gained momentum. In this study, we investigated whether adding H₂S donor AP39 to porcine blood during subnormothermic perfusion at 21 °C improves renal graft outcomes. Porcine kidneys were nephrectomized after 30 min of clamping the renal pedicles and treated to 4 h of static cold storage (SCS) on ice or ex vivo subnormothermic perfusion at 21 °C with autologous blood alone (SNT) or with AP39 (SNTAP). All kidneys were reperfused ex vivo with autologous blood at 37 °C for 4 h. Urine output, histopathology and RNAseq were used to evaluate the renal graft function, injury and gene expression profiles, respectively. The SNTAP group exhibited significantly higher urine output than other groups during preservation and reperfusion, along with significantly lower apoptotic injury compared to the SCS group. The SNTAP group also exhibited differential pro-survival gene expression patterns compared to the SCS (downregulation of pro-apoptotic genes) and SNT (downregulation of hypoxia response genes) groups. Subnormothermic perfusion at 21 °C with H₂S-supplemented blood improves renal graft outcomes. Further research is needed to facilitate the clinical translation of this approach.

Autophagy Plays a Protective Role in Sodium Hydrosulfide-Induced Acute Lung Injury by Attenuating Oxidative Stress and Inflammation in Rats

Sodium hydrosulfide (NaHS), as an exogenous hydrogen sulfide (H₂S) donor, has been used in various pathological models. NaHS is usually considered to be primarily protective, however, the toxic effect of NaHS has not been well elucidated. The aim of this study was to investigate whether NaHS (1 mg/kg) can induce acute lung injury (ALI is a disease process characterized by diffuse inflammation of the lung parenchyma) and define the mechanism by which NaHS-induced ALI involves autophagy, oxidative stress, and inflammatory response. Wistar rats were randomly divided into three groups (control group, NaHS group, and 3-MA + NaHS group), and samples from each group were collected from 2, 6, 12, and 24 h. We found that intraperitoneal injection of NaHS (1 mg/kg) increased the pulmonary levels of H₂S and oxidative stress-related indicators (reactive oxygen species, myeloperoxidase, and malondialdehyde) in a time-dependent manner. Intraperitoneal injection of NaHS (1 mg/kg) induced histopathological changes of ALI and inhibition of autophagy exacerbated the lung injury. This study demonstrates that administration of NaHS (1 mg/kg) induces ALI in rats and autophagy in response to ROS is protective in NaHS-induced ALI by attenuating oxidative stress and inflammation.

H2S- and NO-releasing gasotransmitter platform: A crosstalk signaling pathway in the treatment of acute kidney injury

Acute kidney injury (AKI) is a syndrome affecting most patients hospitalized due to kidney disease; it accounts for 15 % of patients hospitalized in intensive care units worldwide. AKI is mainly caused by ischemia and reperfusion (IR) injury, which temporarily obstructs the blood flow, increases inflammation processes and induces oxidative stress. AKI treatments available nowadays present notable disadvantages, mostly for patients with other comorbidities. Thus, it is important to investigate different approaches to help minimizing side effects such as the ones observed in patients subjected to the aforementioned treatments. Therefore, the aim of the current review is to highlight the potential of two endogenous gasotransmitters - hydrogen sulfide (H₂S) and nitric oxide (NO) - and their crosstalk in AKI treatment. Both H₂S and NO are endogenous signalling molecules involved in several physiological and pathophysiological processes, such as the ones taking place in the renal system. Overall, these molecules act by decreasing inflammation, controlling reactive oxygen species (ROS) concentrations, activating/inactivating pro-inflammatory cytokines, as well as promoting vasodilation and decreasing apoptosis, hypertrophy and autophagy. Since these gasotransmitters are found in gaseous state at environmental conditions, they can be directly applied by inhalation, or in combination with H₂S and NO donors, which are compounds capable of releasing these molecules at biological conditions, thus enabling higher stability and slow release of NO and H₂S. Moreover, the combination between these donor compounds and nanomaterials has the potential to enable targeted treatments, reduce side effects and increase the potential of H₂S and NO. Finally, it is essential highlighting challenges to, and perspectives in, pharmacological applications of H₂S and NO to treat AKI, mainly in combination with nanoparticulated delivery platforms.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

The history of renal transplantation in Canada: A urologic perspective

While the urologist's involvement in kidney transplantation varies from center to center and country to country, urologists remain integral to many programs across Canada. From the early days of kidney transplant to contemporary times, the leadership, vision, and skillset of Canadian urologists have helped progress the field. In this review of Canadian urologists' role in kidney transplantation, the achievements of this professional group are highlighted and celebrated. Original contributors to the field, as well as notable achievements are highlighted, with a focus on the impact of Canadian urologists.

Carbon monoxide-releasing molecule-3: Amelioration of renal ischemia reperfusion injury in a rat model

Purpose

Despite the role of carbon monoxide in ameliorating ischemia-reperfusion injury (IRI), its use in the clinical setting is restricted owing to its toxicity. Herein, we investigated the in vivo effects of carbon monoxide–releasing molecule-3 (CORM-3) on IRI.

Materials and Methods

Fifteen rats were equally and randomly divided into three groups: sham (right nephrectomy), control (right nephrectomy and left renal ischemia), and CORM-3 (right nephrectomy and CORM-3 injection before left renal ischemia). Kidney tissues and blood samples collected from sacrificed rats were evaluated to determine the renoprotective effect and mechanism of CORM-3.

Results

Concentrations of serum creatinine and kidney injury molecule-1 in the CORM-3 group were significantly lower than in the control group after 75 minutes of IRI (1.2 vs. 2.4 mg/dL, p=0.01, and 292 vs. 550 pg/mL, p<0.001, respectively). Furthermore, the CORM-3 group exhibited a higher portion of normal tubules and glomeruli. TUNEL staining revealed fewer apoptotic renal tubular cells in the CORM-3 group than in the control group. The expression of 960 genes in the CORM-3 group was also altered. Pretreatment with CORM-3 before renal IRI produced a significant renoprotective effect. Fifteen of the altered genes were found to be involved in the peroxisome proliferator-activated receptors signaling pathway, and the difference in the expression of these genes between the CORM-3 and control groups was statistically significant (p<0.001).

Conclusions

CORM-3 ameliorates IRI by decreasing apoptosis and may be a novel strategy for protection against renal warm IRI.

Urinary sulfate excretion and risk of late graft failure in renal transplant recipients - a prospective cohort study

Hydrogen sulfide (H₂S), produced from metabolism of dietary sulfur‐containing amino acids, is allegedly a renoprotective compound. Twenty‐four‐hour urinary sulfate excretion (USE) may reflect H₂S bioavailability. We aimed to investigate the association of USE with graft failure in a large prospective cohort of renal transplant recipients (RTR). We included 704 stable RTR, recruited at least 1 year after transplantation. We applied log‐rank testing and Cox regression analyses to study association of USE, measured from baseline 24 h urine samples, with graft failure. Median age was 55 [45–63] years (57% male, eGFR was 45 ± 19 ml/min/1.73 m²). Median USE was 17.1 [13.1–21.1] mmol/24 h. Over median follow‐up of 5.3 [4.5–6.0] years, 84 RTR experienced graft failure. RTR in the lowest sex‐specific tertile of USE experienced a higher rate of graft failure during follow‐up than RTR in the middle and highest sex‐specific tertiles (18%, 13%, and 5%, respectively, log‐rank P < 0.001). In Cox regression analyses, USE was inversely associated with graft failure [HR per 10 mmol/24 h: 0.37 (0.24–0.55), P < 0.001]. The association remained independent of adjustment for potential confounders, including age, sex, eGFR, proteinuria, time between transplantation and baseline, BMI, smoking, and high sensitivity C‐reactive protein [HR per 10 mmol/24 h: 0.51 (0.31–0.82), P = 0.01]. In conclusion, this study demonstrates a significant inverse association of USE with graft failure in RTR, suggesting high H₂S bioavailability as a novel, potentially modifiable factor for prevention of graft failure in RTR.

Renal Procurement: Techniques for Optimizing the Quality of the Graft in the Cadaveric Setting

PURPOSE OF REVIEW

Kidney transplantation is the best treatment for end-stage renal disease. However, due to organ shortage, suboptimal grafts are increasingly being used.

RECENT FINDINGS

We carried out a review on the methods and techniques of organ optimization in the cadaveric setting. Donor care is the first link in a chain of care. Right after brain death, there is a set of changes, of which hormonal and hemodynamic changes are the most relevant. Several studies have been conducted to determine which drugs to administer, although in most cases, the results are not definitive. The main goal seems rather achieve a set of biochemical and hemodynamic objectives. The ischemia-reperfusion injury is a critical factor for kidney damage in transplantation. One of the ways found to deal with this type of injury is preconditioning. Local and remote ischemic preconditioning has been studied for various organs, but studies on the kidney are scarce. A new promising area is pharmacological preconditioning, which is taking its first steps. Main surgical techniques were established in the late twentieth century. Some minor new features have been introduced to deal with anatomical variations or the emergence of donation after circulatory death. Finally, after harvesting, it is necessary to ensure the best conditions for the kidneys until the time of transplantation. Much has evolved since static cold preservation, but the best preservation conditions are yet to be determined. Conservation in the cold has come to be questioned, and great results have appeared at temperatures closer to physiological.

Erythropoietin Derived Peptide Improved Endoplasmic Reticulum Stress and Ischemia-Reperfusion Related Cellular and Renal Injury

Ischemia-reperfusion (IR) injury often affects transplant and native kidneys alike. IR injury is one of the main causes of acute kidney injury (AKI) and further associated with the progression of chronic kidney disease. Our previous study revealed the renoprotection of erythropoietin derived cyclic helix-B surface peptide (CHBP) against IR injury. However, the precise role and underlying mechanism of endoplasmic reticulum stress (ERS) in the injury and the renoprotection induced by IR or CHBP, respectively, have not been fully defined. This study using mouse kidney epithelial cells (TCMK-1) revealed that the level of CHOP (a key marker of ERS), PERK, and JNK (regulators of CHOP) was gradually increased by the prolonged time of hydrogen peroxide (H₂O₂) stimulation. In addition, CHOP mRNA and protein were significantly reduced by small interfering RNA (siRNA) target CHOP, as were apoptotic and inflammatory mediator caspase-3 and HMGB-1, and early apoptosis. Furthermore, CHOP mRNA was correlated positively with PERK protein, active caspase-3, HMGB-1 and apoptosis, but negatively with cell viability in vitro, while CHOP protein was also correlated positively with the level of tubulointerstitial damage and active caspase-3 protein in vivo. Finally, CHBP improved the viability of TCMK-1 cells subjected to H₂O₂ stimulation time-dependently, with reduced level of CHOP mRNA. CHBP also inhibited the increase of CHOP protein, not only in TCMK-1 cells, but also in the IR injury kidneys at 2 weeks. Moreover, CHBP reduced the expression of PERK mRNA and protein, JNK and HMGB-1 protein, as well as early and later apoptosis. In addition, raised CHOP at 12 h post IR injury might be an early time window for intervention. In conclusion, the differential role of ERS and CHBP in IR-related injury was proved in mouse TCMK-1 cells and kidneys, in which the mechanistic signaling pathway was associated with CHOP/PERK/JNK, HMGB-1/caspase-3, and apoptosis. CHOP might be a potential biomarker and CHBP might be therapeutic drug for IR-induced AKI.

H2S alleviates renal injury and fibrosis in response to unilateral ureteral obstruction by regulating macrophage infiltration via inhibition of NLRP3 signaling

Renal fibrosis is a key pathological feature in chronic kidney diseases (CKDs). Dysregulation of hydrogen sulfide (H₂S) homeostasis is implicated in the pathogenesis of CKDs. Here, C57/BL6 mice were allocated to Sham and unilateral ureteral obstruction (UUO) groups, which were treated with NaHS or NLRP3 inflammasome inhibitor 16673-34-0 for 3-14 days. UUO mice displayed downregulation of H₂S production and increased macrophage infiltration in obstructed kidneys. H₂S donor NaHS treatment attenuated renal damage and fibrosis and inhibited M1 and M2 macrophage infiltration. NLPR3 inflammasome was activated and levels of phosphorylated nuclear factor κB (NF-κB) p65 subunit, phosphorylated signal transducer and activator of transcription 6 (STAT6) and interleukin (IL)-4 protein were increased in the kidneys after UUO. NLRP3 inhibitor inactivated NF-κB and IL-4/STAT6 signaling, suppressed M1 and M2 macrophage infiltration and attenuated renal damage and fibrosis in UUO mice. NaHS treatment also suppressed NLRP3, NF-κB and IL-4/STAT6 activation in the obstructed kidneys. In conclusion, the therapeutic effects of H₂S on UUO-induced renal injury and fibrosis are at least in part by inhibition of M1 and M2 macrophage infiltration. H₂S suppresses NLRP3 activation and subsequently inactivates NF-κB and IL-4/STAT6 signaling, which may contribute to the anti-inflammatory and anti-fibrotic effects of H₂S.

Involvement of hydrogen sulfide in the progression of renal fibrosis

OBJECTIVE

Renal fibrosis is the most common manifestation of chronic kidney disease (CKD). Noting that existing treatments of renal fibrosis only slow disease progression but do not cure it, there is an urgent need to identify novel therapies. Hydrogen sulfide (H2S) is a newly discovered endogenous small gas signaling molecule exerting a wide range of biologic actions in our body. This review illustrates recent experimental findings on the mechanisms underlying the therapeutic effects of H2S against renal fibrosis and highlights its potential in future clinical application.

DATA SOURCES

Literature was collected from PubMed until February 2019, using the search terms including "Hydrogen sulfide," "Chronic kidney disease," "Renal interstitial fibrosis," "Kidney disease," "Inflammation factor," "Oxidative stress," "Epithelial-to-mesenchymal transition," "H2S donor," "Hypertensive kidney dysfunction," "Myofibroblasts," "Vascular remodeling," "transforming growth factor (TGF)-beta/Smads signaling," and "Sulfate potassium channels."

STUDY SELECTION

Literature was mainly derived from English articles or articles that could be obtained with English abstracts. Article type was not limited. References were also identified from the bibliographies of identified articles and the authors' files.

RESULTS

The experimental data confirmed that H2S is widely involved in various renal pathologies by suppressing inflammation and oxidative stress, inhibiting the activation of fibrosis-related cells and their cytokine expression, ameliorating vascular remodeling and high blood pressure, stimulating tubular cell regeneration, as well as reducing apoptosis, autophagy, and hypertrophy. Therefore, H2S represents an alternative or additional therapeutic approach for renal fibrosis.

CONCLUSIONS

We postulate that H2S may delay the occurrence and progress of renal fibrosis, thus protecting renal function. Further experiments are required to explore the precise role of H2S in renal fibrosis and its application in clinical treatment.

Hydrogen Sulfide: Emerging Role in Bladder, Kidney, and Prostate Malignancies

Hydrogen sulfide (H₂S) is the latest member of the gasotransmitter family and known to play essential roles in cancer pathophysiology. H₂S is produced endogenously and can be administered exogenously. Recent studies showed that H₂S in cancers has both pro- and antitumor roles. Understanding the difference in the expression and localization of tissue-specific H₂S-producing enzymes in healthy and cancer tissues allows us to develop tools for cancer diagnosis and treatment. Urological malignancies are some of the most common cancers in both men and women, and their early detection is vital since advanced cancers are recurrent, metastatic, and often resistant to treatment. This review summarizes the roles of H₂S in cancer and looks at current studies investigating H₂S activity and expression of H₂S-producing enzymes in urinary cancers. We specifically focused on urothelial carcinoma, renal cell carcinoma, and prostate cancer, as they form the majority of newly diagnosed urinary cancers. Recent studies show that besides the physiological activity of H₂S in cancer cells, there are patterns between the development and prognosis of urinary cancers and the expression of H₂S-producing enzymes and indirectly the H₂S levels. Though controversial and not completely understood, studying the expression of H₂S-producing enzymes in cancer tissue may represent an avenue for novel diagnostic and therapeutic strategies for addressing urological malignancies.

Preservation Solutions for Kidney Transplantation: History, Advances and Mechanisms

Solid organ transplantation was one of the greatest medical advances during the past few decades. Organ preservation solutions have been applied to diminish ischemic/hypoxic injury during cold storage and improve graft survival. In this article, we provide a general review of the history and advances of preservation solutions for kidney transplantation. Key components of commonly used solutions are listed, and effective supplementations for current available preservation solutions are discussed. At cellular and molecular levels, further insights were provided into the pathophysiological mechanisms of effective ingredients against ischemic/hypoxic renal injury during cold storage. We pay special attention to the cellular and molecular events during transplantation, including ATP depletion, acidosis, mitochondrial dysfunction, oxidative stress, inflammation, and other intracellular mechanisms.

Gasotransmitters in health and disease: a mitochondria-centered view

Gasotransmitters fulfill important roles in cellular homeostasis having been linked to various pathologies, including inflammation and cardiovascular diseases. In addition to the known pathways mediating the actions of gasotransmitters, their effects in regulating mitochondrial function are emerging. Given that mitochondria are key organelles in energy production, formation of reactive oxygen species and apoptosis, they are important mediators in preserving health and disease. Preserving or restoring mitochondrial function by gasotransmitters may be beneficial, and mitigate pathogenetic processes. In this review we discuss the actions of gasotransmitters with focus on their role in mitochondrial function and their therapeutic potential.

Organ preservation solutions: linking pharmacology to survival for the donor organ pathway

PURPOSE OF REVIEW

To provide an understanding of the scientific principles, which underpinned the development of organ preservation solutions, and to bring into context new strategies and challenges for solution development against the background of changing preservation technologies and expanded criteria donor access.

RECENT FINDINGS

Improvements in organ preservation solutions continue to be made with new pharmacological approaches. New solutions have been developed for dynamic perfusion preservation and are now in clinical application. Principles defining organ preservation solution pharmacology are being applied for cold chain logistics in tissue engineering and regenerative medicine.

SUMMARY

Organ preservation solutions support the donor organ pathway. The solution compositions allow additives and pharmacological agents to be delivered direct to the target organ to mitigate preservation injury. Changing preservation strategies provide further challenges and opportunities to improve organ preservation solutions.

Machine preservation of donor kidneys in transplantation

With increasing demands for 'less than ideal' kidneys for transplantation, machine perfusion of kidneys has been utilized to improve the preservation of kidneys during storage. Hypothermic machine perfusion (HMP) of renal allografts has been shown to reduce delayed graft function rates in both expanded criteria and donation after cardiac death renal allografts. However, the beneficial impact upon long-term graft function is unclear. There has been emerging evidence that both subnormothermic (room temperature) and normothermic machine perfusion (NMP) of allografts have beneficial effects with regards to early graft function, survival and injury in pre-clinical and early clinical studies. Additionally, machine perfusion allows functional assessment of the organ prior to transplantation. Ultimately, the greatest benefit of machine perfusion may be the ability to treat the organ with agents to protect the graft against ischemia reperfusion injury, while awaiting transplantation.

Hydrogen sulfide: a gaseous signaling molecule modulates tissue homeostasis: implications in ophthalmic diseases

Hydrogen sulfide (H2S) serves as a gasotransmitter in the regulation of organ development and maintenance of homeostasis in tissues. Its abnormal levels are associated with multiple human diseases, such as neurodegenerative disease, myocardial injury, and ophthalmic diseases. Excessive exposure to H2S could lead to cellular toxicity, orchestrate pathological process, and increase the risk of various diseases. Interestingly, under physiological status, H2S plays a critical role in maintaining cellular physiology and limiting damages to tissues. In mammalian species, the generation of H2S is catalyzed by cystathionine beta-synthase (CBS), cystathionine gamma-lyase (CSE), 3-mercapto-methylthio pyruvate aminotransferase (3MST) and cysteine aminotransferase (CAT). These enzymes are found inside the mammalian eyeballs at different locations. Their aberrant expression and the accumulation of substrates and intermediates can change the level of H2S by orders of magnitude, causing abnormal structures or functions in the eyes. Detailed investigations have demonstrated that H2S donors' administration could regulate intraocular pressure, protect retinal cells, inhibit oxidative stress and alleviate inflammation by modulating the function of intra or extracellular proteins in ocular tissues. Thus, several slow-releasing H2S donors have been shown to be promising drugs for treating multiple diseases. In this review, we discuss the biological function of H2S metabolism and its application in ophthalmic diseases.

Effects of hydrogen sulfide on acetaminophen-induced acute renal toxicity in rats

INTRODUCTION AND AIM

Hydrogen sulfide (H₂S) is an endogenously produced gas-structure mediator. It is proposed to have antioxidant, anti-inflammatory and antiapoptotic effects. Acetaminophen (N-acetyl-P-aminophenol; APAP) is an antipyretic and analgesic medication known as paracetamol. When taken at therapeutic doses there are few side-effects, but at high doses APAP can cause clear liver and kidney damage in humans and experimental animals. In this study, the effects of the H₂S donor of sodium hydrosulfide (NaHS) on acute renal toxicity induced by APAP in rats were researched in comparison with N-acetyl cysteine (NAC).

METHOD

Rats were divided into six groups (n = 7) as control. APAP, APAP + NAC, APAP + NaHS 25 µmol/kg, NaHS 50 µmol/kg and NaHS 100 µmol/kg. After oral dose of 2 g/kg APAP, NAC and NaHS were administered via the i.p. route for 7 days. In renal homogenates, KIM-1 (Kidney Injury Molecule-1), NGAL (neutrophil gelatinase-associated lipocalin), TNF-α and TGFβ levels were measured with the ELISA method for tissue injury and inflammation. In renal tissue, oxidative stress levels were identified by spectrophotometric measurement of TAS and TOS. Histopathologic investigation of renal tissue used caspase 3 staining for apoptotic changes, Masson trichrome and H&E staining for variations occurring in glomerular and tubular systems.

RESULTS

NaHS lowered KIM-1, NGAL, TNF-α, TGF-β and TOS levels elevated in renal tissue linked to APAP and increased TAS values. NaHS prevented apoptosis in the kidney and was identified to ensure histologic amelioration in glomerular and tubular structures. NaHS at 50 µmol/kg dose was more effective, with the effect reduced with 100 µmol/kg dose.

CONCLUSION

H₂S shows protective effect against acute renal injury linked to APAP. This protective effect reduces with high doses of H₂S. The anti-inflammatory and antioxidant activity of H₂S may play a role in the renoprotective effect.

Complement Inhibitor CRIg/FH Ameliorates Renal Ischemia Reperfusion Injury via Activation of PI3K/AKT Signaling

Complement activation is involved in the pathogenesis of ischemia reperfusion injury (IRI), which is an inevitable process during kidney transplantation. Therefore, complement-targeted therapeutics hold great potential in protecting the allografts from IRI. We observed universal deposition of C3d and membrane attack complex in human renal allografts with delayed graft function or biopsy-proved rejection, which confirmed the involvement of complement in IRI. Using FB-, C3-, C4-, C5-, C5aR1-, C5aR2-, and C6-deficient mice, we found that all components, except C5aR2 deficiency, significantly alleviated renal IRI to varying degrees. These gene deficiencies reduced local (deposition of C3d and membrane attack complex) and systemic (serum levels of C3a and C5a) complement activation, attenuated pathological damage, suppressed apoptosis, and restored the levels of multiple local cytokines (e.g., reduced IL-1β, IL-9, and IL-12p40 and increased IL-4, IL-5, IL-10, and IL-13) in various gene-deficient mice, which resulted in the eventual recovery of renal function. In addition, we demonstrated that CRIg/FH, which is a targeted complement inhibitor for the classical and primarily alternative pathways, exerted a robust renoprotective effect that was comparable to gene deficiency using similar mechanisms. Further, we revealed that PI3K/AKT activation, predominantly in glomeruli that was remarkably inhibited by IRI, played an essential role in the CRIg/FH renoprotective effect. The specific PI3K antagonist duvelisib almost completely abrogated AKT phosphorylation, thus abolishing the renoprotective role of CRIg/FH. Our findings suggested that complement activation at multiple stages induced renal IRI, and CRIg/FH and/or PI3K/AKT agonists may hold the potential in ameliorating renal IRI.

The role of nitric oxide signaling in renoprotective effects of hydrogen sulfide against chronic kidney disease in rats: Involvement of oxidative stress, autophagy and apoptosis

The interplay between H₂ S and nitric oxide (NO) is thought to contribute to renal functions. The current study was designed to assess the role of NO in mediating the renoprotective effects of hydrogen sulfide in the 5/6 nephrectomy (5/6 Nx) animal model. Forty rats were randomly assigned to 5 experimental groups: (a) Sham; (b) 5/6 Nx; (c) 5/6Nx+sodium hydrosulfide-a donor of H ₂ S, (5/6Nx+sodium hydrosulfide [NaHS]); (d) 5/6Nx+NaHS+ L-NAME (a nonspecific nitric oxide synthase [NOS] inhibitor); (e) 5/6Nx+NaHS+aminoguanidine (a selective inhibitor of inducible NOS [iNOS]). Twelve weeks after 5/6 Nx, we assessed the expressions of iNOS and endothelial NOS (eNOS), oxidative/antioxidant status, renal fibrosis, urine N-acetyl-b-glucosaminidase (NAG) activity as the markers of kidney injury and various markers of apoptosis, inflammation, remodeling, and autophagy. NaHS treatment protected the animals against chronic kidney injury as depicted by improved oxidative/antioxidant status, reduced apoptosis, and autophagy and attenuated messenger RNA (mRNA) expression of genes associated with inflammation, remodeling, and NAG activity. Eight weeks Nω-nitro-l-arginine methyl ester ( L-NAME) administration reduced the protective effects of hydrogen sulfide. In contrast, aminoguanidine augmented the beneficial effects of hydrogen sulfide. Our finding revealed some fascinating interactions between NO and H ₂ S in the kidney. Moreover, the study suggests that NO, in an isoform-dependent manner, can exert renoprotective effects in 5/6 Nx model of CKD.

Hydrogen Sulfide: A Potential Novel Therapy for the Treatment of Ischemia

Hydrogen sulfide (H2S) is a novel signaling molecule most recently found to be of fundamental importance in cellular function as a regulator of apoptosis, inflammation, and perfusion. Mechanisms of endogenous H2S signaling are poorly understood; however, signal transmission is thought to occur via persulfidation at reactive cysteine residues on proteins. Although much has been discovered about how H2S is synthesized in the body, less is known about how it is metabolized. Recent studies have discovered a multitude of different targets for H2S therapy, including those related to protein modification, intracellular signaling, and ion channel depolarization. The most difficult part of studying hydrogen sulfide has been finding a way to accurately and reproducibly measure it. The purpose of this review is to: elaborate on the biosynthesis and catabolism of H2S in the human body, review current knowledge of the mechanisms of action of this gas in relation to ischemic injury, define strategies for physiological measurement of H2S in biological systems, and review potential novel therapies that use H2S for treatment.

A Hibernation-Like State for Transplantable Organs: Is Hydrogen Sulfide Therapy the Future of Organ Preservation?

SIGNIFICANCE

Renal transplantation is the treatment of choice for end-stage renal disease, during which renal grafts from deceased donors are routinely cold stored to suppress metabolic demand and thereby limit ischemic injury. However, prolonged cold storage, followed by reperfusion, induces extensive tissue damage termed cold ischemia/reperfusion injury (IRI) and puts the graft at risk of both early and late rejection. Recent Advances: Deep hibernators constitute a natural model of coping with cold IRI as they regularly alternate between 4°C and 37°C. Recently, endogenous hydrogen sulfide (H₂S), a gas with a characteristic rotten egg smell, has been implicated in organ protection in hibernation.

CRITICAL ISSUES

In renal transplantation, H₂S also seems to confer cytoprotection by lowering metabolism, thereby creating a hibernation-like environment, and increasing preservation time while allowing cellular processes of preservation of homeostasis and tissue remodeling to take place, thus increasing renal graft survival.

FUTURE DIRECTIONS

Although the underlying cellular and molecular mechanisms of organ protection during hibernation have not been fully explored, mammalian hibernation may offer a great clinical promise to safely cold store and reperfuse donor organs. In this review, we first discuss mammalian hibernation as a natural model of cold organ preservation with reference to the kidney and highlight the involvement of H₂S during hibernation. Next, we present recent developments on the protective effects and mechanisms of exogenous and endogenous H₂S in preclinical models of transplant IRI and evaluate the potential of H₂S therapy in organ preservation as great promise for renal transplant recipients in the future. Antioxid. Redox Signal. 28, 1503-1515.

Daily therapy with a slow-releasing H2S donor GYY4137 enables early functional recovery and ameliorates renal injury associated with urinary obstruction

OBJECTIVES

To assess the effects of slow-releasing H₂S donor GYY4137 on post-obstructive renal function and injury following unilateral ureteral obstruction (UUO) by using the UUO and reimplantation (UUO-R) model in rats and to elucidate potential mechanisms by using an in vitro model of epithelial-mesenchymal transition (EMT).

METHODS

Male Lewis rats underwent UUO at the left ureterovesical junction. From post-operative day (POD) 1-13, rats received daily intraperitoneal (IP) injection of phosphate buffered saline (PBS, 1 mL) or GYY4137 (200 μmol/kg/day in 1 mL PBS, IP). On POD 14, the ureter was reimplanted back into the bladder, followed by a right nephrectomy. Urine and serum samples were collected to monitor renal function. On POD 30, the left kidney was removed and tissue sections were stained with H&E, TUNEL, CD68, CD206, myeloperoxidase, and Masson's trichrome to determine cortical thickness, apoptosis, inflammation, and fibrosis. In our in vitro model of EMT, NRK52E cells were treated with 10 ng/mL TGF-β1, 10 μM GYY4137 and/or 50 μM GYY4137. Western blot analysis was performed to determine the expression of E-cadherin, vimentin, Smad7 and TGF-β1 receptor II (TβRII).

RESULTS

GYY4137 led to a moderate decrease in post-obstructive serum creatinine, cystatin C and FENa. We also observed a trend towards a decrease in post-obstructive proteinuria following GYY4137 treatment. Histologically, we observed a significant decrease in apoptosis, inflammation, and fibrosis. Furthermore, our in vitro studies demonstrate that in the presence of TGF-β1, GYY4137 significantly decreases vimentin and TβRII and significantly increases E-cadherin and Smad7.

CONCLUSIONS

H₂S may help to accelerate the recovery of renal function post-obstruction and attenuates renal injury associated with UUO. It is possible that H₂S mitigates fibrosis by regulating the TGF-β1-mediated EMT pathway. Taken together, our data suggest that H₂S may be a potential novel therapy for improving renal function and limiting renal injury associated with obstructive uropathy.

The smell of renal protection against chronic kidney disease: Hydrogen sulfide offers a potential stinky remedy

Chronic kidney disease (CKD) is a common global health challenge characterized by irreversible pathological processes that reduce kidney function and culminates in development of end-stage renal disease. It is associated with increased morbidity and mortality in addition to increased caregiver burden and higher financial cost. A central player in CKD pathogenesis and progression is renal hypoxia. Renal hypoxia stimulates induction of oxidative and endoplasmic reticulum stress, inflammation and tubulointerstitial fibrosis, which in turn, promote cellular susceptibility and further aggravate hypoxia, thus forming a pathological vicious cycle in CKD progression. Although the importance of CKD is widely appreciated, including improvements in the quality of existing therapies such as dialysis and transplantation, new therapeutic options are limited, as there is still increased morbidity, mortality and poor quality of life among CKD patients. Growing evidence indicates that hydrogen sulfide (H₂S), a small gaseous signaling molecule with an obnoxious smell, accumulates in the renal medulla under hypoxic conditions, and functions as an oxygen sensor that restores oxygen balance and increases medullary flow. Moreover, plasma H₂S level has been recently reported to be markedly reduced in CKD patients and animal models. Also, H₂S has been established to possess potent antioxidant, anti-inflammatory, and anti-fibrotic properties in several experimental models of kidney diseases, suggesting that its supplementation could protect against CKD and retard its progression. The purpose of this review is to discuss current clinical and experimental developments regarding CKD, its pathophysiology, and potential cellular and molecular mechanisms of protection by H₂S in experimental models of CKD.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

Over the last decade, hydrogen sulfide (H2S) has emerged as an important endogenous gasotransmitter in mammalian cells and tissues. Similar to the previously characterized gasotransmitters nitric oxide and carbon monoxide, H2S is produced by various enzymatic reactions and regulates a host of physiologic and pathophysiological processes in various cells and tissues. H2S levels are decreased in a number of conditions (e.g., diabetes mellitus, ischemia, and aging) and are increased in other states (e.g., inflammation, critical illness, and cancer). Over the last decades, multiple approaches have been identified for the therapeutic exploitation of H2S, either based on H2S donation or inhibition of H2S biosynthesis. H2S donation can be achieved through the inhalation of H2S gas and/or the parenteral or enteral administration of so-called fast-releasing H2S donors (salts of H2S such as NaHS and Na2S) or slow-releasing H2S donors (GYY4137 being the prototypical compound used in hundreds of studies in vitro and in vivo). Recent work also identifies various donors with regulated H2S release profiles, including oxidant-triggered donors, pH-dependent donors, esterase-activated donors, and organelle-targeted (e.g., mitochondrial) compounds. There are also approaches where existing, clinically approved drugs of various classes (e.g., nonsteroidal anti-inflammatories) are coupled with H2S-donating groups (the most advanced compound in clinical trials is ATB-346, an H2S-donating derivative of the non-steroidal anti-inflammatory compound naproxen). For pharmacological inhibition of H2S synthesis, there are now several small molecule compounds targeting each of the three H2S-producing enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Although many of these compounds have their limitations (potency, selectivity), these molecules, especially in combination with genetic approaches, can be instrumental for the delineation of the biologic processes involving endogenous H2S production. Moreover, some of these compounds (e.g., cell-permeable prodrugs of the CBS inhibitor aminooxyacetate, or benserazide, a potentially repurposable CBS inhibitor) may serve as starting points for future clinical translation. The present article overviews the currently known H2S donors and H2S biosynthesis inhibitors, delineates their mode of action, and offers examples for their biologic effects and potential therapeutic utility.