Glutamine donor pretreatment in rat kidney transplants with severe preservation reperfusion injury

Glutamine protection in an experimental model of acetaminophen nephrotoxicity

Acetaminophen (APAP) is a widely prescribed analgesic and antipyretic drug. In the present work, we studied the effects of glutamine (Gln) in an in vivo model of APAP-induced nephrotoxicity in male Wistar rats. Renal function, histological characteristics, and Na+,K+-ATPase cortical abundance and distribution were analyzed. The appearance of HSP70 and actin in urine was also evaluated. Myeloperoxidase (MPO) activity in cortical tissue was measured as an index of the inflammatory response. Gln administration 30 min before APAP protected from the renal functional and histological damage promoted by APAP. Rats that received the dual treatment Gln and APAP (Gln/APAP) showed the same level of Na+,K+-ATPase cortical induction as APAP-treated animals, but the enzyme maintained its normal basolateral localization. HSP70 abundance was increased up to the same level in the Gln, APAP, and Gln/APAP groups. Urinary HSP70 and actin were detected only in the APAP-treated animals, reinforcing the protection of renal tubular integrity afforded by the Gln pretreatment. Gln pretreatment also protected from the increment in MPO activity promoted by APAP. Our results support the idea that Gln pretreatment could be a therapeutic option to prevent APAP-induced renal injury.

The early protective effect of glutamine pretreatment and ischemia preconditioning in renal ischemia-reperfusion injury of rat

BACKGROUND

Heat shock proteins (HSP) play an important role in protecting cells against stress.

METHODS

Using a rat model, we tested the hypothesis that pretreatment with glutamine (Gln) and ischemia preconditioning (IPC) increase the expression of HSP resulting in attenuation of renal ischemia/reperfusion (I/R) injury. Sprague-Dawley rats were randomized into 4 groups [group I, Gln injection (+), IPC (+); group II, Gln injection (+), IPC (-); group III, saline injection (+), IPC (+); group IV, saline injection (+), IPC (-)]. Renal HSP70 expression was determined by Western blotting and kidney function was assessed by blood urea nitrogen and serum creatinine. Renal cross-sections were microscopically examined for tubular necrosis, exfoliation of tubular epithelial cells, cast formation, and monocyte infiltration.

RESULTS

Gln pretreatment increased intrarenal HSP expression (P = .031). In group I, tubulointerstitial abnormalities were clearly slighter compared with the other groups (P < .001).

CONCLUSION

Our experiments suggest that (1) a single dose of Gln could induce HSP expression and (2) IPC could relieve renal I/R injury. In addition, IPC combined with Gln pretreatment had a synergic protective effect against renal I/R injury.

SOD therapeutics: latest insights into their structure-activity relationships and impact on the cellular redox-based signaling pathways

SIGNIFICANCE

Superoxide dismutase (SOD) enzymes are indispensable and ubiquitous antioxidant defenses maintaining the steady-state levels of O2·(-); no wonder, thus, that their mimics are remarkably efficacious in essentially any animal model of oxidative stress injuries thus far explored.

RECENT ADVANCES

Structure-activity relationship (half-wave reduction potential [E1/2] versus log kcat), originally reported for Mn porphyrins (MnPs), is valid for any other class of SOD mimics, as it is dominated by the superoxide reduction and oxidation potential. The biocompatible E1/2 of ∼+300 mV versus normal hydrogen electrode (NHE) allows powerful SOD mimics as mild oxidants and antioxidants (alike O2·(-)) to readily traffic electrons among reactive species and signaling proteins, serving as fine mediators of redox-based signaling pathways. Based on similar thermodynamics, both SOD enzymes and their mimics undergo similar reactions, however, due to vastly different sterics, with different rate constants.

CRITICAL ISSUES

Although log kcat(O2·(-)) is a good measure of therapeutic potential of SOD mimics, discussions of their in vivo mechanisms of actions remain mostly of speculative character. Most recently, the therapeutic and mechanistic relevance of oxidation of ascorbate and glutathionylation and oxidation of protein thiols by MnP-based SOD mimics and subsequent inactivation of nuclear factor κB has been substantiated in rescuing normal and killing cancer cells. Interaction of MnPs with thiols seems to be, at least in part, involved in up-regulation of endogenous antioxidative defenses, leading to the healing of diseased cells.

FUTURE DIRECTIONS

Mechanistic explorations of single and combined therapeutic strategies, along with studies of bioavailability and translational aspects, will comprise future work in optimizing redox-active drugs.

The anti-oxidant effects are not the main mechanism for glutamine's protective effects on acute kidney injury in mice

Acute kidney injury (AKI) is a common problem characterized by an inflammatory response in the kidney and oxidative stress. However, there are no interventions to prevent AKI. Glutamine is an important precursor of glutathione and has also been shown to induce heat shock proteins (HSP). Thus, glutamine may affect both oxidative stress and inflammation. This study was to explore the effects of glutamine pretreatment on nephrotoxic AKI and to investigate the underlying mechanisms. First, the effects of alternate doses of glutamine were compared in CD-1 mice with AKI induced with folic acid intra-peritoneal injection. Then the effects of glutamine quercetin (an HSP inhibitor), and quercetin+glutamine, were compared in the same AKI model. AKI were assessed with plasma creatinine, urine neutrophil gelatinase-associated lipocalin, and renal histology. Inflammatory response was monitored with renal tumor necrosis factor (TNF-α), chemkines (CXCL1 and CCL2) contents, and neutrophil infiltration. Oxidative injury was detected with reduced glutathione, malondialdehyde, and protein thiol. Glutamine provided dose-dependent renal protection. Pretreatment with quercetin, which was showed to inhibit HSP-70 expression, abolished glutamine's renal-protective effects. Quercetin also abrogated glutamine's beneficial effects on renal TNF-α, chemokines, and neutrophil infiltration. However, quercetin did not affect glutamine's anti-oxidative effects. These results suggest that glutamine's renal-protective effects are mainly related to its activation of HSP-70, which mitigates inflammatory response, renal neutrophil infiltration and subsequent AKI. Regulating neutrophil infiltration might be a potential therapeutic target for AKI.

The role of heat shock protein 90 in modulating ischemia-reperfusion injury in the kidney

INTRODUCTION

Kidney transplantation is the gold standard treatment for end-stage renal disease. Ischemia-reperfusion injury (IRI) is an unavoidable consequence of the transplantation procedure and is responsible for delayed graft function and poorer long-term outcomes.

AREAS COVERED

Pharmacological induction of heat shock protein (Hsp) expression is an emerging pre-conditioning strategy aimed at reducing IRI following renal transplantation. Hsp90 inhibition up-regulates protective Hsps (especially Hsp70) and potentially down-regulates NF-κB by disruption of the IκB kinase (IKK) complex. However, the clinical application of Hsp90 inhibitors is currently limited by their toxicity profile and the exact mechanism of protection conferred is unknown. Toll-like receptor 4 (TLR4) is a further regulator of NF-κB and recent studies suggest TLR4 plays a dominant role in mediating kidney damage following IRI. The full interaction of Hsps with TLRs is yet to be delineated and whether TLR4 signalling can be targeted by Hsp90 inhibition in IRI remains uncertain.

EXPERT OPINION

Pharmacological pre-conditioning by Hsp90 inhibition involves direct treatment to the kidney donor and/or organ, which aims to reduce injury prior to the onset of ischemia. The major challenges going forward are to establish the exact mechanism of protection offered by these drugs and the investgiation of less toxic analogues that could be safely translated into human studies.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Effect of glutamine on the total antioxidant system of rats subjected to renal ischemia and reperfusion

PURPOSE: To evaluate the protective effects of glutamine administered before renal ischemia-reperfusion on plasma antioxidant protection, and lung and renal tissue injury. METHODS: 33 rats underwent right nephrectomy. On the eighth postoperative day, animals were randomized into three groups (n=11): glutamine, control and sham. Each group of animals received, by gavage, a particular diet for 7 days. On day 14 following nephrectomy, the animals were subjected to left renal ischemia-reperfusion. After this, blood samples were collected and the animals were killed. At necropsy the kidney and lung were removed for histology. RESULTS: The levels of total antioxidant capacity were higher in the glutamine group and control group compared with the sham group. The levels of glutathione peroxidase in both the sham and glutamine groups were higher when compared with the control group (p<0.05). The level of superoxide dismutase in the sham group was clearly higher than that in the glutamine and control groups. Histological examination showed no differences between the three groups. CONCLUSION: Prior intake of glutamine improves total antioxidant capacity and increases glutathione peroxidase levels in rats subjected to renal ischemia-reperfusion.

Preconditioning, postconditioning, and remote conditioning in solid organ transplantation: basic mechanisms and translational applications

Ischemia and reperfusion (I/Rp) injury is inherent to solid organ transplantation and can result in primary nonfunction or delayed function of grafts, which is associated with a significant morbidity and mortality posttransplantation. It is also a major obstacle for the use of marginal grafts to increase the donor pool, as these grafts are prone to a higher degree of I/Rp injury. Pre-, post-, and remote conditioning are protective strategies against I/Rp injury, which can be applied in the transplant setting. These strategies hold the potential to reduce graft injury and to safely expand the donor pool. However, despite convincing experimental data, the protective effects of the "conditioning" protocols remain unclear, and only few have translated to clinical practice. This review summarizes pre-, post-, and remote conditioning strategies in clinical use in solid organ transplantation and discusses an overview of the mechanistic pathways involved in each strategy.

Donor pre-treatment with everolimus or cyclosporine does not reduce ischaemia-reperfusion injury in a rat kidney transplant model

BACKGROUND

Immunosuppressive agents have been investigated in renal ischaemia-reperfusion injury (IRI) and have frequently demonstrated a beneficial effect. Most studies focused on treatment of the recipient at the time of transplantation. Pre-treatment of these organs before injury (pharmacological pre-conditioning) may particularly protect these organs. This study aimed to investigate the possible protective effects of donor pre-treatment with cyclosporine (CsA) or the mTOR inhibitor everolimus or their combination against IRI during renal transplantation in a rat model.

METHODS

Donors received vehicle, CsA (5 mg/kg), everolimus (0.5 mg/kg) or CsA + everolimus. Two oral doses were administered to the donors at 24 h and again at 6 h prior to donor kidney removal. Syngeneic rat kidneys were preserved in UW solution for 24 h prior to transplantation. After 24 h of reperfusion, blood and tissue samples were collected from recipients for further analysis.

RESULTS

Renal functions as determined by creatinine and necrosis scores were not different between the experimental groups. Cleaved caspase-3, heat shock protein 70 (HSP70), tumor-necrosis factor-alpha (TNF-α) and nitrotyrosine protein levels were not statistically different between the four treatment groups at 24 h post-transplantation. Blood NMR analysis on metabolic markers for IRI reveals no beneficial effects of donor pre-treatment on the 24-h outcome in transplantation.

CONCLUSIONS

When given alone or as a combination to donors before organ recovery, cyclosporine or everolimus does not appear to ameliorate IRI.

Innate pathways of immune activation in transplantation

Studies of the immune mechanisms of allograft rejection have predominantly focused on the adaptive immune system that includes T cells and B cells. Recent investigations into the innate immune system, which recognizes foreign antigens through more evolutionarily primitive pathways, have demonstrated a critical role of the innate immune system in the regulation of the adaptive immune system. Innate immunity has been extensively studied in its role as the host's first-line defense against microbial pathogens; however, it is becoming increasingly recognized for its ability to also recognize host-derived molecules that result from tissue damage. The capacity of endogenous damage signals acting through the innate immune system to lower immune thresholds and promote immune recognition and rejection of transplant grafts is only beginning to be appreciated. An improved understanding of these pathways may reveal novel therapeutic targets to decrease graft alloreactivity and increase graft longevity.