Zinc preconditioning protects against renal ischaemia reperfusion injury in a preclinical sheep large animal model

Determination of the median lethal dose of zinc gluconate in mice and safety evaluation

BACKGROUND

Zinc Gluconate (ZG) is a safe and effective supplement for zinc. However, there is limited research on the optimal dosage for intravenous injection and the safety evaluation of animal models for ZG. This study aims to determine the safe dose range of ZG for intravenous injection in C57BL/6J mice.

METHODS

A Dose titration experiment was conducted to determine the LD50 and 95% confidence interval (95%CI) of ZG in mice. Based on the LD50, four sub-lethal doses (SLD) of ZG were evaluated. Following three injections of each SLD and monitoring for seven days, serum zinc levels were measured, and pathological changes in the liver, kidney, and spleen tissues of mice were determined by histological staining.

RESULTS

The dose titration experiment determined the LD50 of ZG in mice to be 39.6 mg/kg, with a 95%CI of 31.8-49.3 mg/kg. There was a statistically significant difference in the overall serum zinc levels (H = 36.912, P < 0.001) following SLD administration. Pairwise comparisons showed that the serum zinc levels of the 1/2 LD50 and 3/4 LD50 groups were significantly higher than those of the control group (P < 0.001); the serum zinc level of the 3/4 LD50 group was significantly higher than those of the 1/8 LD50 and 1/4 LD50 groups (P < 0.05). There was a positive correlation between the different SLDs of ZG and the serum zinc levels in mice (rs = 0.973, P < 0.001). H&E staining showed no significant histological abnormalities or lesions in the liver, kidney, and spleen tissues of mice in all experimental groups.

CONCLUSION

The appropriate dose range of ZG for intravenous injection in C57BL/6J mice was clarified, providing a reference for future experimental research.

Enhancing the expression of a key mitochondrial enzyme at the inception of ischemia-reperfusion injury can boost recovery and halt the progression of acute kidney injury

Hydrodynamic fluid delivery has shown promise in influencing renal function in disease models. This technique provided pre-conditioned protection in acute injury models by upregulating the mitochondrial adaptation, while hydrodynamic injections of saline alone have improved microvascular perfusion. Accordingly, hydrodynamic mitochondrial gene delivery was applied to investigate the ability to halt progressive or persistent renal function impairment following episodes of ischemia-reperfusion injuries known to induce acute kidney injury (AKI). The rate of transgene expression was approximately 33% and 30% in rats with prerenal AKI that received treatments 1 (T_1hr) and 24 (T_24hr) hours after the injury was established, respectively. The resulting mitochondrial adaptation via exogenous IDH2 (isocitrate dehydrogenase 2 (NADP+) and mitochondrial) significantly blunted the effects of injury within 24 h of administration: decreased serum creatinine (≈60%, p < 0.05 at T_1hr; ≈50%, p < 0.05 at T_24hr) and blood urea nitrogen (≈50%, p < 0.05 at T_1hr; ≈35%, p < 0.05 at T_24hr) levels, and increased urine output (≈40%, p < 0.05 at T_1hr; ≈26%, p < 0.05 at T_24hr) and mitochondrial membrane potential, Δψ_m, (≈ by a factor of 13, p < 0.001 at T_1hr; ≈ by a factor of 11, p < 0.001 at T_24hr), despite elevated histology injury score (26%, p < 0.05 at T1_hr; 47%, p < 0.05 at T_24hr). Therefore, this study identifies an approach that can boost recovery and halt the progression of AKI at its inception.

The Sheep as a Large Animal Model for the Investigation and Treatment of Human Disorders

Simple Summary

We review the value of large animal models for improving the translation of biomedical research for human application, focusing primarily on sheep.

Abstract

An essential aim of biomedical research is to translate basic science information obtained from preclinical research using small and large animal models into clinical practice for the benefit of humans. Research on rodent models has enhanced our understanding of complex pathophysiology, thus providing potential translational pathways. However, the success of translating drugs from pre-clinical to clinical therapy has been poor, partly due to the choice of experimental model. The sheep model, in particular, is being increasingly applied to the field of biomedical research and is arguably one of the most influential models of human organ systems. It has provided essential tools and insights into cardiovascular disorder, orthopaedic examination, reproduction, gene therapy, and new insights into neurodegenerative research. Unlike the widely adopted rodent model, the use of the sheep model has an advantage over improving neuroscientific translation, in particular due to its large body size, gyrencephalic brain, long lifespan, more extended gestation period, and similarities in neuroanatomical structures to humans. This review aims to summarise the current status of sheep to model various human diseases and enable researchers to make informed decisions when considering sheep as a human biomedical model.

Experimental models of acute kidney injury for translational research

Preclinical models of human disease provide powerful tools for therapeutic discovery but have limitations. This problem is especially apparent in the field of acute kidney injury (AKI), in which clinical trial failures have been attributed to inaccurate modelling performed largely in rodents. Multidisciplinary efforts such as the Kidney Precision Medicine Project are now starting to identify molecular subtypes of human AKI. In addition, over the past decade, there have been developments in human pluripotent stem cell-derived kidney organoids as well as zebrafish, rodent and large animal models of AKI. These organoid and AKI models are being deployed at different stages of preclinical therapeutic development. However, the traditionally siloed, preclinical investigator-driven approaches that have been used to evaluate AKI therapeutics to date rarely account for the limitations of the model systems used and have given rise to false expectations of clinical efficacy in patients with different AKI pathophysiologies. To address this problem, there is a need to develop more flexible and integrated approaches, involving teams of investigators with expertise in a range of different model systems, working closely with clinical investigators, to develop robust preclinical evidence to support more focused interventions in patients with AKI.

Zinc as a Drug for Wilson's Disease, Non-Alcoholic Liver Disease and COVID-19-Related Liver Injury

Zinc is the second most abundant trace element in the human body, and it plays a fundamental role in human physiology, being an integral component of hundreds of enzymes and transcription factors. The discovery that zinc atoms may compete with copper for their absorption in the gastrointestinal tract let to introduce zinc in the therapy of Wilson's disease, a congenital disorder of copper metabolism characterized by a systemic copper storage. Nowadays, zinc salts are considered one of the best therapeutic approach in patients affected by Wilson's disease. On the basis of the similarities, at histological level, between Wilson's disease and non-alcoholic liver disease, zinc has been successfully introduced in the therapy of non-alcoholic liver disease, with positive effects both on insulin resistance and oxidative stress. Recently, zinc deficiency has been indicated as a possible factor responsible for the susceptibility of elderly patients to undergo infection by SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic. Here, we present the data correlating zinc deficiency with the insurgence and progression of Covid-19 with low zinc levels associated with severe disease states. Finally, the relevance of zinc supplementation in aged people at risk for SARS-CoV-2 is underlined, with the aim that the zinc-based drug, classically used in the treatment of copper overload, might be recorded as one of the tools reducing the mortality of COVID-19, particularly in elderly people.

Large animal models for translational research in acute kidney injury

While extensive research using animal models has improved the understanding of acute kidney injury (AKI), this knowledge has not been translated into effective treatments. Many promising interventions for AKI identified in mice and rats have not been validated in subsequent clinical trials. As a result, the mortality rate of AKI patients remains high. Inflammation plays a fundamental role in the pathogenesis of AKI, and one reason for the failure to translate promising therapeutics may lie in the profound difference between the immune systems of rodents and humans. The immune systems of large animals such as swine, nonhuman primates, sheep, dogs and cats, more closely resemble the human immune system. Therefore, in the absence of a basic understanding of the pathophysiology of human AKI, large animals are attractive models to test novel interventions. However, there is a lack of reviews on large animal models for AKI in the literature. In this review, we will first highlight differences in innate and adaptive immunities among rodents, large animals, and humans in relation to AKI. After illustrating the potential merits of large animals in testing therapies for AKI, we will summarize the current state of the evidence in terms of what therapeutics have been tested in large animal models. The aim of this review is not to suggest that murine models are not valid to study AKI. Instead, our objective is to demonstrate that large animal models can serve as valuable and complementary tools in translating potential therapeutics into clinical practice.

Biochemical Studies in Perfundates and Homogenates of Isolated Porcine Kidneys after Flushing with Zinc or Zinc-Prolactin Modified Preservation Solution Using a Static Cold Storage Technique

Zinc is an effective anti-inflammatory and antioxidant trace element. The aim of this study was to analyse the protective effect of zinc and zinc–prolactin systems as additives of preservation solutions in the prevention of nephron damage caused during ischemia. The study used a model for storing isolated porcine kidneys in Biolasol^®. The solution was modified with the addition of Zn at a dose of 1 µg/L and Zn: 1 µg/L with prolactin (PRL): 0.1 µg/L. After 2 h and 48 h of storage, the levels of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, sodium, potassium, creatinine and total protein were determined. Zinc added to the Biolasol^® composition at a dose of 1 µg/L showed minor effectiveness in the protection of nephrons. In turn, Zn²⁺ added to Biolasol + PRL (PRL: 0.1 µg/L) acted as a prolactin inhibitor. We do not recommend the addition of Zn(II) (1 µg/L) and Zn(II) (1 µg/L) + PRL (0.1 µg/L) to the Biolasol solution.

Zinc supplementation as an adjunct therapy for COVID-19: Challenges and opportunities

An outbreak of a novel coronavirus (COVID‐19 or 2019‐CoV) infection has posed significant threats to international health and the economy. Patients with COVID‐19 are at risk of cytokine storm, acute respiratory distress syndrome (ARDS), reduced blood oxygenation, mechanical ventilation, and a high death rate. Although recent studies have shown remdesivir and dexamethasone as treatment options, there is an urgent need to find a treatment to inhibit virus replication and to control the progression of the disease. Essential biometal zinc has generated a lot of excitement as one of the promising candidates to reduce the severity of COVID‐19 infection. Several published observations outlined in the review are the reasons why there is a global enthusiasm that zinc therapy could be a possible therapeutic option. However, the biggest challenge in realising the therapeutic value of zinc is lack of optimal treatment modalities such as dose, duration of zinc supplementation and the mode of delivery. In this review, we discuss the regulatory mechanism that hinges upon the bioavailability of zinc. Finally, we propose that intravenous zinc could circumvent the confounding factors affecting the bioavailability of zinc and allow zinc to achieve its therapeutic potential. If successful, due to advantages such as lack of toxicity, low cost and ease of availability, intravenous zinc could be rapidly implemented clinically.

A pilot double-blind safety and feasibility randomized controlled trial of high-dose intravenous zinc in hospitalized COVID-19 patients

Zinc inhibits replication of the SARS-CoV virus. We aimed to evaluate the safety, feasibility, and biological effect of administering high-dose intravenous zinc (HDIVZn) to patients with COVID-19. We performed a Phase IIa double-blind, randomized controlled trial to compare HDIVZn to placebo in hospitalized patients with COVID-19. We administered trial treatment per day for a maximum of 7 days until either death or hospital discharge. We measured zinc concentration at baseline and during treatment and observed patients for any significant side effects. For eligible patients, we randomized and administered treatment to 33 adult participants to either HDIVZn (n = 15) or placebo (n = 18). We observed no serious adverse events throughout the study for a total of 94 HDIVZn administrations. However, three participants in the HDIVZn group reported infusion site irritation. Mean serum zinc on Day 1 in the placebo, and the HDIVZn group was 6.9 ± 1.1 and 7.7 ± 1.6 µmol/l, respectively, consistent with zinc deficiency. HDIVZn, but not placebo, increased serum zinc levels above the deficiency cutoff of 10.7 µmol/l (p < .001) on Day 6. Our study did not reach its target enrollment because stringent public health measures markedly reduced patient hospitalizations. Hospitalized COVID-19 patients demonstrated zinc deficiency. This can be corrected with HDIVZn. Such treatment appears safe, feasible, and only associated with minimal peripheral infusion site irritation. This pilot study justifies further investigation of this treatment in COVID-19 patients.

Randomised controlled trial for high-dose intravenous zinc as adjunctive therapy in SARS-CoV-2 (COVID-19) positive critically ill patients: trial protocol

INTRODUCTION

SARS-CoV-2 (COVID-19) has caused an international pandemic of respiratory illness, resulting in significant healthcare and economic turmoil. To date, no robust vaccine or treatment has been identified. Elemental zinc has previously been demonstrated to have beneficial effects on coronaviruses and other viral respiratory infections due to its effect on RNA polymerase. Additionally, zinc has well-demonstrated protective effects against hypoxic injury-a clear mechanism of end-organ injury in respiratory distress syndrome. We aimed to assess the effect of high-dose intravenous zinc (HDIVZn) on SARS-CoV-2 infection. The end of study analyses will evaluate the reduction of impact of oxygen saturations or requirement of oxygen supplementation.

METHODS AND ANALYSIS

We designed a double-blind randomised controlled trial of daily HDIVZn (0.5 mg/kg) versus placebo. Primary outcome measures are lowest oxygen saturation (or greatest level of supplemental oxygenation) for non-ventilated patients and worst PaO2/FiO2 for ventilated patients. Following power calculations, 60 hospitalised patients and 100 ventilated patients will be recruited to demonstrate a 20% difference. The duration of follow-up is up to the point of discharge.

ETHICS AND DISSEMINATION

Ethical approval was obtained through the independent Human Research Ethics Committee. Participant recruitment will commence in May 2020. Results will be published in peer-reviewed medical journals.

TRIAL REGISTRATION NUMBER

ACTRN126200000454976.

Role of Zinc Supplementation on Ischemia/Reperfusion Injury in Various Organs

Ischemia-reperfusion (I/R) injury is a serious condition which is associated with myocardial infarction, stroke, acute kidney injury, trauma, circulatory arrest, sickle cell disease, and sleep apnea and can lead to high morbidity and mortality. Salts of zinc (Zn) are commonly used by humans and have protective effects against gastric, renal, hepatic, muscle, myocardial, or neuronal ischemic injury. The present review evaluates molecular mechanisms underlying the protective effects of Zn supplement against I/R injury. Data of this review have been collected from the scientific articles published in databases such as Science Direct, Scopus, PubMed, and Scientific Information Database from 1991 to 2019. Zn supplementation increased the decreased parameters including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), metallothionein (MT), protein sulfhydryl (P-SH), and nuclear factor-erythroid 2-related factor-2 (Nrf2) expression and decreased the increased elements such as endoplasmic reticulum (ER) stress, mitochondrial permeability transition pore (mPTP) opening, malondialdehyde (MDA), serum level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and microRNAs-(122 and 34a), apoptotic factors, and histopathological changes. Zn also increases phosphatidylinositol 3-kinase (PI3K)/Akt and glycogen synthase kinase-3β (GSK-3β) phosphorylation and preserves protein kinase C isoforms. It is suggested that Zn can be administered before elective surgeries for prevention of side effects of I/R injury.

Recent advances in acute kidney injury and its consequences and impact on chronic kidney disease

PURPOSE OF REVIEW

Acute kidney injury (AKI) remains a major unmet medical need and associates with high morbidity, mortality, and healthcare costs. Among survivors, long-term outcomes of AKI can include development of chronic kidney disease (CKD) or progression of preexisting CKD. In this review, we focus on ongoing efforts by the AKI community to understand the human AKI to CKD continuum, with an emphasis on the cellular stress responses that underlie AKI and the maladaptive responses that persist in the acute-to-chronic phase. The emphasis is on work that has been published in the past year in this rapidly expanding field.

RECENT FINDINGS

Recent studies in preclinical models highlight the importance of mitochondrial dysfunction, cell death, and inflammation on the underlying pathogenesis of AKI. These pathogenic mechanisms can resolve with adaptive kidney repair but persist in maladaptive repair that leads to progressive chronic disease. The complexity and interconnections of these pathways involve cross-talk between the tubular epithelium, endothelium, and interstitial compartments.

SUMMARY

Approaches which lessen or counteract these cellular responses represent novel strategies to prevent AKI and stop or slow down the progression to CKD.

The Protective Effect of Zinc Against Liver Ischaemia Reperfusion Injury in a Rat Model of Global Ischaemia

BACKGROUND

Ischaemia-reperfusion injury (IRI) is a major obstacle during liver transplantation and resection surgeries for cancer, with a need for effective and safe drugs to reduce IRI. Zinc preconditioning has been shown to protect against liver IRI in a partial (70%) ischaemia model. However, its efficacy against a clinically relevant Pringle manoeuvre that results in global liver ischaemia (100%) is unknown.

AIMS

The aim of this study was to test the efficacy of zinc preconditioning in a rat model of global liver ischaemia.

METHODS

Rats were preconditioned via subcutaneous injection of 10 mg/kg of ZnCl₂, 24 h and 4 h before ischaemia. Total liver ischaemia (100%) was induced by placing a clamp across the portal triad for 30 min. Liver injury was assessed by serum alanine transaminase (ALT) and aspartate transaminase (AST) levels in blood taken before ischaemia (baseline) and at 1, 2, 4, 24, 48, 72, 96 and 120 hours after ischaemia. Animals were culled after 7 days, and the harvested livers were histologically analysed.

RESULTS

On a two-way repeated-measures analysis of variance, there was a statistically significant (p = 0.025) difference in the mean ALT levels between saline- and ZnCl₂-treated groups. Specifically at 24 h after ischaemia, the ALT (341 ± 99 U/L) and AST (606 ± 78 U/L) in the zinc-treated group were significantly less than the ALT (2863 ± 828 U/L) and AST (3591 ± 948 U/L) values in the saline-treated group. Zinc significantly reduced neutrophil infiltration and necrosis compared with the saline control.

CONCLUSION

Zinc preconditioning reduces the overall hepatocellular damage from IRI. These results lay the foundation to assess the benefit of zinc preconditioning for clinical applications.

Why is it worth testing the ability of zinc to protect against ischaemia reperfusion injury for human application

Ischaemia (interruption in the blood/oxygen supply) and subsequent damage induced by reperfusion (restoration of blood/oxygen supply) ultimately leads to cell death, tissue injury and permanent organ dysfunction. The impact of ischaemia reperfusion injury (IRI) is not limited to heart attack and stroke but can be extended to patients undergoing surgeries such as partial nephrectomy for renal cancer, liver resection for colorectal cancer liver metastasis, cardiopulmonary bypass, and organ transplantation. Unfortunately, there are no drugs that can protect organs against the inevitable peril of IRI. Recent data show that a protocol incorporating specific Zn formulation, dosage, number of dosages, time of injection, and mode of Zn delivery (intravenous) and testing of efficacy in a large preclinical sheep model of IRI strongly supports human trials of Zn preconditioning. No doubt, scepticism still exists among funding bodies and research fraternity on whether Zn, a naturally occurring metal, will work where everything else has failed. Therefore, in this article, we review the conflicting evidence on the promoter and protector role of Zn in the case of IRI and highlight factors that may help explain the contradictory evidence. Finally, we review the literature related to the knowledge of Zn's mechanism of action on ROS generation, apoptosis, HIF activation, inflammation, and signal transduction pathways, which highlight Zn's likelihood of success compared to various other interventions targeting IRI.

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.