Sodium nitrite protects against kidney injury induced by brain death and improves post-transplant function

Complement inhibition alleviates donor brain death-induced liver injury and posttransplant cascade injury by regulating phosphoinositide 3-kinase signaling

Brain death (BD) donors are the primary source of donor organs for liver transplantation. However, the effects of BD on donor livers and outcomes after liver transplantation remain unclear. Here, we explored the role of complement and the therapeutic effect of complement inhibition in BD-induced liver injury and posttransplantation injury in a mouse BD and liver transplantation model. For complement inhibition, we used complement receptor 2 (CR2)-Crry, a murine inhibitor of C3 activation that specifically targets sites of complement activation. In the mouse model, BD resulted in complement activation and liver injury in donor livers and a cascade liver injury posttransplantation, mediated in part through the C3a-C3aR (C3a receptor) signaling pathway, which was ameliorated by treatment with CR2-Crry. Treatment of BD donors with CR2-Crry improved graft survival, which was further improved when recipients received an additional dose of CR2-Crry posttransplantation. Mechanistically, we determined that complement inhibition alleviated BD-induced donor liver injury and posttransplant cascade injury by regulating phosphoinositide 3-kinase (PI3K) signaling pathways. Together, BD induced donor liver injury and cascade injury post-transplantation, which was mediated by complement activation products acting on PI3K signaling pathways. Our study provides an experimental basis for developing strategies to improve the survival of BD donor grafts in liver transplantation.

Supplemental nitrite increases choroidal neovascularization in mice

Low doses of nitrite, close to physiological levels, increase blood flow in normal and ischemic tissues through a nitric oxide (NO) dependent mechanism. Given that nitrite therapy and dietary supplementation with vegetables high in nitrate (e.g. beets) are gaining popularity we decided to determine if low doses of nitrite impact the development of choroidal neovascularization (CNV), a key feature of wet age related macular degeneration (AMD). Sodium nitrite (at 50 mg/L, 150 mg/L, and 300 mg/L), nitrate (1 g/L) or water alone were provided in the drinking water of C57BL/6 J mice aged 2 or 12 months. Mice were allowed to drink ad libitum for 1 week at which time laser-induced choroidal neovascularization (L-CNV) was induced. The mice continued to drink the supplemented water ad libitum for a further 14 days at which point optical coherence tomography (OCT) was performed to determine the volume of the CNV lesion. Blood was drawn to determine nitrite and nitrate levels and eyes taken for histology. CNV volume was 2.86 × 10⁷ μm³ (±0.4 × 10⁷) in young mice on water alone but CNV volume more than doubled to >6.9 × 10⁷ μm³ (±0.8 × 10⁷) in mice receiving 300 mg/L nitrite or 7.34 × 10⁷ μm³ (±1.4 × 10⁷) in 1 g/L nitrate (p < 0.01). A similar trend was observed in older mice. CNV volume was 5.3 × 10⁷ μm³ (±0.5 × 10⁷) in older mice on water alone but CNV volume almost doubled to approximately 9.3 × 10⁷ μm³ (±1.1 × 10⁷) in mice receiving 300 mg/L nitrite or 8.7 × 10⁷ μm³ (±0.9 × 10⁷) 1 g/L nitrate (p < 0.01). Plasma nitrite levels were highest in young mice receiving 150 mg/L in the drinking water with no changes in plasma nitrate observed. In older mice, drinking water nitrite did not significantly change plasma nitrite, but plasma nitrate was increased. Plasma nitrate was elevated in both young and old mice provided with nitrate supplemented drinking water. Our data demonstrate that the CNV lesion is larger in older mice compared to young and that therapeutic levels of oral nitrite increase the volume of CNV lesions in both young and older mice. Therapeutic nitrite or nitrate supplementation should be used with caution in the elderly population prone to CNV.

Minimizing Ischemia Reperfusion Injury in Xenotransplantation

The recent dramatic advances in preventing "initial xenograft dysfunction" in pig-to-non-human primate heart transplantation achieved by minimizing ischemia suggests that ischemia reperfusion injury (IRI) plays an important role in cardiac xenotransplantation. Here we review the molecular, cellular, and immune mechanisms that characterize IRI and associated "primary graft dysfunction" in allotransplantation and consider how they correspond with "xeno-associated" injury mechanisms. Based on this analysis, we describe potential genetic modifications as well as novel technical strategies that may minimize IRI for heart and other organ xenografts and which could facilitate safe and effective clinical xenotransplantation.

Thymoquinone therapy remediates elevated brain tissue inflammatory mediators induced by chronic administration of food preservatives

Continuous exposure to preservatives such as nitrite salts has deleterious effects on different organs. Meanwhile, Nigella sativa oil can remediate such organ dysfunction. Here, we studied the effect of consumption of thymoquinone (TQ); the main component of Nigella sativa oil on the brain damage induced by sodium nitrite. Forty adult male rats were daily given oral gavage of sodium nitrite (80 mg/kg) with or without thymoquinone (50 mg/kg). Oxidative stress, cytokines of inflammation, fibrotic elements and apoptotic markers in brain tissue were measured. Exposure to sodium nitrite (SN) resulted in increased levels of malondialdehyde, TGF-β, c-reactive protein, NF-κB, TNF-α, IL-1β and caspase-3 associated with reduced levels of glutathione, cytochrome c oxidase, Nrf2 and IL-10. However, exposure of rats’ brain tissues to thymoquinone resulted ameliorated all these effects. In conclusion, thymoquinone remediates sodium nitrite-induced brain impairment through several mechanisms including attenuation of oxidative stress, retrieving the reduced concentration of glutathione, blocks elevated levels of pro-inflammatory cytokines, restores cytochrome c oxidase activity, and reducing the apoptosis markers in the brain tissues of rats.

Preconditioning against renal ischaemia reperfusion injury: the failure to translate to the clinic

Acute kidney injury (AKI) as a result of ischaemia-reperfusion represents a major healthcare burden worldwide. Mortality rates from AKI in hospitalized patients are extremely high and have changed little despite decades of research and medical advances. In 1986, Murry et al. demonstrated for the first time the phenomenon of ischaemic preconditioning to protect against ischaemia-reperfusion injury (IRI). This seminal finding paved the way for a broad body of research, which attempted to understand and ultimately harness this phenomenon for human application. The ability of preconditioning to limit renal IRI has now been demonstrated in multiple different animal models. However, more than 30 years later, a safe and consistent method of protecting human organs, including the kidneys, against IRI is still not available. This review highlights agents which, despite strong preclinical data, have recently failed to reduce AKI in human trials. The multiple reasons which may have contributed to the failure to translate some of the promising findings to clinical therapies are discussed. Agents which hold promise in the clinic because of their recent efficacy in preclinical large animal models are also reviewed.

Delayed graft function and its management in children

Delayed graft function (DGF) is commonly defined as the requirement for dialysis within the first 7 days following renal transplantation. The major underlying mechanism is related to ischaemia/reperfusion injury, which includes microvascular inflammation and cell death and apoptosis, and to the regeneration processes. Several clinical factors related to donor, recipient and organ procurement/transplantation procedures may increase the risk of DGF, including donor cardiovascular instability, older donor age, donor creatinine concentration, long cold ischaemia time and marked body mass index of both the donor and recipient. Some of these parameters have been used in specific predictive formulas created to assess the risk of DGF. A variety of other pre-, intra- and post-transplant clinical factors may also increase the risk of DGF, such as potential drug nephrotoxicity, surgical problems and/or hyperimmunization of the recipient. DGF may decrease the long-term graft function, but data on this effect are inconsistent, partially due to the many different types of organ donation. Relevant management strategies may be classified into the classic clinical approach, which has the aim of minimizing the individual risk factors of DGF, and specific pharmacologic strategies, which are designed to prevent or treat ischaemia/reperfusion injury. Both strategies are currently being evaluated in clinical trials.

Ginkgo biloba extract EGb761 attenuates brain death-induced renal injury by inhibiting pro-inflammatory cytokines and the SAPK and JAK-STAT signalings

This study aimed to investigate the protective effects of EGb761, a Ginkgo Biloba extract, against brain death-induced kidney injury. Sixty male Sprague Dawley rats were randomly divided into six groups: sham, brain-death (BD), BD + EGb b48h (48 hours before BD), BD + EGb 2 h (2 hours after BD), BD + EGb 1 h, and BD + EGb 0.5 h. Six hours after BD, serum sample and kidney tissues were collected for analyses. The levels of blood urea nitrogen (BUN) and serum creatinine significantly elevated in the BD group than in sham group. In all the EGb761-treated BD animals except for the BD + Gb 2 h group, the levels of BUN and serum creatinine significantly reduced (all P < 0.01). EGb761 attenuated tubular injury and lowered the histological score. In addition, the longer duration of drug treatment was, the better protective efficacy could be observed. EGb761 significantly reduced IL-1β, IL-6, TNF-α, MCP-1, IP-10 mRNA expression and macrophage infiltration in the kidney. EGb761 treatment at 48 hour before brain death significantly attenuate the levels of p-JNK-MAPK, p-p38-MAPK, and p-STAT3 proteins (all P < 0.05, compared to BD group). In summary, our data showed that EGb761 treatment protected donor kidney from BD-induced damages by blocking SAPK and JAK-STAT signalings. Early administration of EGb761 can provide better protective efficacy.

Nitrite Confers Preconditioning and Cytoprotection After Ischemia/Reperfusion Injury Through the Modulation of Mitochondrial Function

SIGNIFICANCE

Nitrite is now recognized as an intrinsic signaling molecule that mediates a number of biological processes. One of the most reproducible effects of nitrite is its ability to mediate cytoprotection after ischemia/reperfusion (I/R). This robust phenomenon has been reproduced by a number of investigators in varying animal models focusing on different target organs. Furthermore, nitrite's cytoprotective versatility is highlighted by its ability to mediate delayed preconditioning and remote conditioning in addition to acute protection.

RECENT ADVANCES

In the last 10 years, significant progress has been made in elucidating the mechanisms underlying nitrite-mediated ischemic tolerance.

CRITICAL ISSUES

The mitochondrion, which is essential to both the progression of I/R injury and the protection afforded by preconditioning, has emerged as a major subcellular target for nitrite. This review will outline the role of the mitochondrion in I/R injury and preconditioning, review the accumulated preclinical studies demonstrating nitrite-mediated cytoprotection, and finally focus on the known interactions of nitrite with mitochondria and their role in the mechanism of nitrite-mediated ischemic tolerance.

FUTURE DIRECTIONS

These studies set the stage for current clinical trials testing the efficacy of nitrite to prevent warm and cold I/R injury.

Update on ischemia-reperfusion injury in kidney transplantation: Pathogenesis and treatment

Ischemia/reperfusion injury is an unavoidable relevant consequence after kidney transplantation and influences short term as well as long-term graft outcome. Clinically ischemia/reperfusion injury is associated with delayed graft function, graft rejection, chronic rejection and chronic graft dysfunction. Ischemia/reperfusion affects many regulatory systems at the cellular level as well as in the renal tissue that result in a distinct inflammatory reaction of the kidney graft. Underlying factors of ischemia reperfusion include energy metabolism, cellular changes of the mitochondria and cellular membranes, initiation of different forms of cell death-like apoptosis and necrosis together with a recently discovered mixed form termed necroptosis. Chemokines and cytokines together with other factors promote the inflammatory response leading to activation of the innate immune system as well as the adaptive immune system. If the inflammatory reaction continues within the graft tissue, a progressive interstitial fibrosis develops that impacts long-term graft outcome. It is of particular importance in kidney transplantation to understand the underlying mechanisms and effects of ischemia/reperfusion on the graft as this knowledge also opens strategies to prevent or treat ischemia/reperfusion injury after transplantation in order to improve graft outcome.

Effects of inhalation of low-dose nitrite or carbon monoxide on post-reperfusion mitochondrial function and tissue injury in hemorrhagic shock swine

Introduction

Tissue reperfusion following hemorrhagic shock may paradoxically cause tissue injury and organ dysfunction by mitochondrial free radical expression. Both nitrite and carbon monoxide (CO) may protect from this reperfusion injury by limiting mitochondrial free radial production. We explored the effects of very small doses of inhaled nitrite and CO on tissue injury in a porcine model of hemorrhagic shock.

Methods

Twenty pigs (mean wt. 30.6 kg, range 27.2 to 36.4 kg) had microdialysis catheters inserted in muscle, peritoneum, and liver to measure lactate, pyruvate, glucose, glycerol, and nitrite. Nineteen of the pigs were bled at a rate of 20 ml/min to a mean arterial pressure of 30 mmHg and kept between 30 and 40 mmHg for 90 minutes and then resuscitated. One pig was instrumented but not bled (sham). Hemorrhaged animals were randomized to inhale nothing (control, n = 7), 11 mg nitrite (nitrite, n = 7) or 250 ppm CO (CO, n = 5) over 30 minutes before fluid resuscitation. Mitochondrial respiratory control ratio was measured in muscle biopsies. Repeated measures from microdialysis catheters were analyzed in a random effects mixed model.

Results

Neither nitrite nor CO had any effects on the measured hemodynamic variables. Following inhalation of nitrite, plasma, but not tissue, nitrite increased. Following reperfusion, plasma nitrite only increased in the control and CO groups. Thereafter, nitrite decreased only in the nitrite group. Inhalation of nitrite was associated with decreases in blood lactate, whereas both nitrite and CO were associated with decreases in glycerol release into peritoneal fluid. Following resuscitation, the muscular mitochondrial respiratory control ratio was reduced in the control group but preserved in the nitrite and CO groups.

Conclusions

We conclude that small doses of nebulized sodium nitrite or inhaled CO may be associated with intestinal protection during resuscitation from severe hemorrhagic shock.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0903-z) contains supplementary material, which is available to authorized users.

Innate and adaptive immune responses subsequent to ischemia-reperfusion injury in the kidney

Understanding innate immune responses and their correlation to alloimmunity after solid organ transplantation is key to optimizing long term graft outcome. While Ischemia/Reperfusion injury (IRI) has been well studied, new insight into central mechanisms of innate immune activation, i.e. chemokine mediated cell trafficking and the role of Toll-like receptors have evolved recently. The mechanistic implications of Neutrophils, Macrophages/Monocytes, NK-cells, Dendritic cells in renal IRI has been proven by selective depletion of these cell types, thereby offering novel therapeutic interventions. At the same time, the multi-faceted role of different T-cell subsets in IRI has gained interest, highlighting the dichotomous effects of differentiated T-cells and suggesting more selective therapeutic approaches. Targeting innate immune cells and their activation and migration pathways, respectively, has been promising in experimental models holding translational potential. This review will summarize the effects of innate immune activation and potential strategies to interfere with the immunological cascade following renal IRI.

Mechanisms of nitrite bioactivation

It is now accepted that the anion nitrite, once considered an inert oxidation product of nitric oxide (NO), contributes to hypoxic vasodilation, physiological blood pressure control, and redox signaling. As such, its application in therapeutics is being actively tested in pre-clinical models and in human phase I-II clinical trials. Major pathways for nitrite bioactivation involve its reduction to NO by members of the hemoglobin or molybdopterin family of proteins, or catalyzed dysproportionation. These conversions occur preferentially under hypoxic and acidic conditions. A number of enzymatic systems reduce nitrite to NO and their activity and importance are defined by oxygen tension, specific organ system and allosteric and redox effectors. In this work, we review different proposed mechanisms of nitrite bioactivation, focusing on analysis of kinetics and experimental evidence for the relevance of each mechanism under different conditions.

Inorganic nitrite supplementation for healthy arterial aging

Aging is the major risk factor for cardiovascular diseases (CVD). This is attributable primarily to adverse changes in arteries, notably, increases in large elastic artery stiffness and endothelial dysfunction mediated by inadequate concentrations of the vascular-protective molecule, nitric oxide (NO), and higher levels of oxidative stress and inflammation. Inorganic nitrite is a promising precursor molecule for augmenting circulating and tissue NO bioavailability because it requires only a one-step reduction to NO. Nitrite also acts as an independent signaling molecule, exerting many of the effects previously attributed to NO. Results of recent studies indicate that nitrite may be effective in the treatment of vascular aging. In old mice, short-term oral sodium nitrite supplementation reduces aortic pulse wave velocity, the gold-standard measure of large elastic artery stiffness, and ameliorates endothelial dysfunction, as indicated by normalization of NO-mediated endothelium-dependent dilation. These improvements in age-related vascular dysfunction with nitrite are mediated by reductions in oxidative stress and inflammation, and may be linked to increases in mitochondrial biogenesis and health. Increasing nitrite levels via dietary intake of nitrate appears to have similarly beneficial effects in many of the same physiological and clinical settings. Several clinical trials are being performed to determine the broad therapeutic potential of increasing nitrite bioavailability on human health and disease, including studies related to vascular aging. In summary, inorganic nitrite, as well as dietary nitrate supplementation, represents a promising therapy for treatment of arterial aging and prevention of age-associated CVD in humans.

Redox therapeutics in hepatic ischemia reperfusion injury

Ischemia-reperfusion plays a major role in the injury experienced by the liver during transplantation. Much work has been done recently investigating the role of redox species in hepatic ischemia-reperfusion. As animal models are better characterized and developed, and more insights are gained into the pathophysiology of hepatic ischemia reperfusion injury in humans the questions into exactly how oxidants participate in this injury are becoming more refined. These questions include effects of cellular location, timing of injury, and ability of therapeutics to access this site are increasing our appreciation of the complexity of ischemia reperfusion and improving attempts to ameliorate its effects. In this review, we aim to discuss the various methods to alter redox chemistry during ischemia reperfusion injury and future prospects for preventing organ injury during hepatic ischemia reperfusion.

Emerging role of gasotransmitters in renal transplantation

Once patients with kidney disease progress to end-stage renal failure, transplantation is the preferred option of treatment resulting in improved quality of life and reduced mortality compared to dialysis. Although 1-year survival has improved considerably, graft and patient survival in the long term have not been concurrent, and therefore new tools to improve long-term graft and patient survival are warranted. Over the past decades, the gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) have emerged as potent cytoprotective mediators in various diseases. All three gasotransmitters are endogenously produced messenger molecules that possess vasodilatory, anti-apoptotic, anti-inflammatory and anti-oxidant properties by influencing an array of intracellular signaling processes. Although many regulatory functions of gasotransmitters have overlapping actions, differences have also been reported. In addition, crosstalk between NO, CO and H2S results in synergistic regulatory effects. Endogenous and exogenous manipulation of gasotransmitter levels modulates several processes involved in renal transplantation. This review focuses on mechanisms of gas-mediated cytoprotection and complex interactions between gasotransmitters in renal transplantation.

Safety and pharmacokinetics of sodium nitrite in patients with subarachnoid hemorrhage: a Phase IIA study

Object

Intravenous sodium nitrite has been shown to prevent and reverse cerebral vasospasm in a primate model of subarachnoid hemorrhage (SAH). The present Phase IIA dose-escalation study of sodium nitrite was conducted to determine the compound's safety in humans with aneurysmal SAH and to establish its pharmacokinetics during a 14-day infusion.

Methods

In 18 patients (3 cohorts of 6 patients each) with SAH from a ruptured cerebral aneurysm, nitrite (3 patients) or saline (3 patients) was infused. Sodium nitrite and saline were delivered intravenously for 14 days, and a dose-escalation scheme was used for the nitrite, with a maximum dose of 64 nmol/kg/min. Sodium nitrite blood levels were frequently sampled and measured using mass spectroscopy, and blood methemoglobin levels were continuously monitored using a pulse oximeter.

Results

In the 14-day infusions in critically ill patients with SAH, there was no toxicity or systemic hypotension, and blood methemoglobin levels remained at 3.3% or less in all patients. Nitrite levels increased rapidly during intravenous infusion and reached steady-state levels by 12 hours after the start of infusion on Day 1. The nitrite plasma half-life was less than 1 hour across all dose levels evaluated after stopping nitrite infusions on Day 14.

Conclusions

Previous preclinical investigations of sodium nitrite for the prevention and reversal of vasospasm in a primate model of SAH were effective using doses similar to the highest dose examined in the current study (64 nmol/kg/min). Results of the current study suggest that safe and potentially therapeutic levels of nitrite can be achieved and sustained in critically ill patients after SAH from a ruptured cerebral aneurysm. Clinical trial registration no.: NCT00873015 (ClinicalTrials.gov).

Administration of nitrite after chlorine gas exposure prevents lung injury: effect of administration modality

Cl(2) gas toxicity is complex and occurs during and after exposure, leading to acute lung injury (ALI) and reactive airway syndrome (RAS). Moreover, Cl(2) exposure can occur in diverse situations encompassing mass casualty scenarios, highlighting the need for postexposure therapies that are efficacious and amenable to rapid and easy administration. In this study, we assessed the efficacy of a single dose of nitrite (1 mg/kg) to decrease ALI when administered to rats via intraperitoneal (ip) or intramuscular (im) injection 30 min after Cl(2) exposure. Exposure of rats to Cl(2) gas (400 ppm, 30 min) significantly increased ALI and caused RAS 6-24h postexposure as indexed by BAL sampling of lung surface protein and polymorphonucleocytes (PMNs) and increased airway resistance and elastance before and after methacholine challenge. Intraperitoneal nitrite decreased Cl(2)-dependent increases in BAL protein but not PMNs. In contrast im nitrite decreased BAL PMN levels without decreasing BAL protein in a xanthine oxidoreductase-dependent manner. Histological evaluation of airways 6h postexposure showed significant bronchial epithelium exfoliation and inflammatory injury in Cl(2)-exposed rats. Both ip and im nitrite improved airway histology compared to Cl(2) gas alone, but more coverage of the airway by cuboidal or columnar epithelium was observed with im compared to ip nitrite. Airways were rendered more sensitive to methacholine-induced resistance and elastance after Cl(2) gas exposure. Interestingly, im nitrite, but not ip nitrite, significantly decreased airway sensitivity to methacholine challenge. Further evaluation and comparison of im and ip therapy showed a twofold increase in circulating nitrite levels with the former, which was associated with reversal of post-Cl(2) exposure-dependent increases in circulating leukocytes. Halving the im nitrite dose resulted in no effect in PMN accumulation but significant reduction of BAL protein levels, indicating a distinct nitrite dose dependence for inhibition of Cl(2)-dependent lung permeability and inflammation. These data highlight the potential for nitrite as a postexposure therapeutic for Cl(2) gas-induced lung injury and also suggest that administration modality is a key consideration in nitrite therapeutics.

Overexpression of endothelial nitric oxide synthase prevents diet-induced obesity and regulates adipocyte phenotype

RATIONALE

Endothelial dysfunction is a characteristic feature of diabetes and obesity in animal models and humans. Deficits in nitric oxide production by endothelial nitric oxide synthase (eNOS) are associated with insulin resistance, which is exacerbated by high-fat diet. Nevertheless, the metabolic effects of increasing eNOS levels have not been studied.

OBJECTIVE

The current study was designed to test whether overexpression of eNOS would prevent diet-induced obesity and insulin resistance.

METHODS AND RESULTS

In db/db mice and in high-fat diet-fed wild-type C57BL/6J mice, the abundance of eNOS protein in adipose tissue was decreased without significant changes in eNOS levels in skeletal muscle or aorta. Mice overexpressing eNOS (eNOS transgenic mice) were resistant to diet-induced obesity and hyperinsulinemia, although systemic glucose intolerance remained largely unaffected. In comparison with wild-type mice, high-fat diet-fed eNOS transgenic mice displayed a higher metabolic rate and attenuated hypertrophy of white adipocytes. Overexpression of eNOS did not affect food consumption or diet-induced changes in plasma cholesterol or leptin levels, yet plasma triglycerides and fatty acids were decreased. Metabolomic analysis of adipose tissue indicated that eNOS overexpression primarily affected amino acid and lipid metabolism; subpathway analysis suggested changes in fatty acid oxidation. In agreement with these findings, adipose tissue from eNOS transgenic mice showed higher levels of PPAR-α and PPAR-γ gene expression, elevated abundance of mitochondrial proteins, and a higher rate of oxygen consumption.

CONCLUSIONS

These findings demonstrate that increased eNOS activity prevents the obesogenic effects of high-fat diet without affecting systemic insulin resistance, in part, by stimulating metabolic activity in adipose tissue.