The Role of Immunosuppressive Drugs in Aggravating Renal Ischemia and Reperfusion Injury

Polyphenols and Novel Insights Into Post-kidney Transplant Complications and Cardiovascular Disease: A Narrative Review

Kidney transplantation is the preferred treatment for end-stage kidney disease. It is, however, not devoid of complications. Delayed graft function related to ischemia-reperfusion injury (IRI), calcineurin inhibitor (CNI) nephrotoxicity, diabetes, and a particularly high-rate cardiovascular disease (CVD) risk, represent important complications following kidney transplantation. Oxidative stress and chronic low-grade inflammation are mechanisms of disease incompletely abrogated in stable kidney transplant recipient (KTR), contributing to the occurrence of these complications. Polyphenols, bioactive compounds with recognized antioxidant and anti-inflammatory properties have been strongly associated with prevention of CVD in the general population and have been shown to decrease IRI and antagonize CNI nephrotoxicity in animal experimental models, therefore they may have a role in prevention of complications in KTR. This narrative review aims to summarize and discuss current evidence on different polyphenols for prevention of complications, particularly prevention of CVD in KTR, pointing toward the need of further studies with potential clinical impact.

Oral Preconditioning of Donors After Brain Death With Calcineurin Inhibitors vs. Inhibitors of Mammalian Target for Rapamycin in Pig Kidney Transplantation

Background: The systemic inflammatory cascade triggered in donors after brain death enhances the ischemia-reperfusion injury after organ transplantation. Intravenous steroids are routinely used in the intensive care units for the donor preconditioning. Immunosuppressive medications could be potentially used for this purpose as well. Data regarding donor preconditioning with calcineurin inhibitors or inhibitors of mammalian target for Rapamycin is limited. The aim of this project is to investigate the effects of (oral) donor preconditioning with a calcineurin inhibitor (Cyclosporine) vs. an inhibitor of mammalian target for Rapamycin (Everolimus) compared to the conventional administration of steroid in the setting of donation after brain death in porcine renal transplantation.

Methods: Six hours after the induction of brain death, German landrace donor pigs (33.2 ± 3.9 kg) were randomly preconditioned with either Cyclosporine (n = 9) or Everolimus (n = 9) administered via nasogastric tube with a repeated dose just before organ procurement. Control donors received intravenous Methylprednisolone (n = 8). Kidneys were procured, cold-stored in Histidine-Tryptophane-Ketoglutarate solution at 4°C and transplanted in nephrectomized recipients after a mean cold ischemia time of 18 h. No post-transplant immunosuppression was given to avoid confounding bias. Blood samples were obtained at 4 h post reperfusion and daily until postoperative day 5 for complete blood count, blood urea nitrogen, creatinine, and electrolytes. Graft protocol biopsies were performed 4 h after reperfusion to assess early histological and immunohistochemical changes.

Results: There was no difference in the hemodynamic parameters, hemoglobin/hematocrit and electrolytes between the groups. Serum blood urea nitrogen and creatinine peaked on postoperative day 1 in all groups and went back to the preoperative levels at the conclusion of the study on postoperative day 5. Histological assessment of the kidney grafts revealed no significant differences between the groups. TNF-α expression was significantly lower in the study groups compared with Methylprednisolone group (p = 0.01) Immunohistochemistry staining for cytochrome c showed no difference between the groups.

Conclusion: Oral preconditioning with Cyclosporine or Everolimus is feasible in donation after brain death pig kidney transplantation and reduces the expression of TNF-α. Future studies are needed to further delineate the role of oral donor preconditioning against ischemia-reperfusion injury.

Rapamycin Is Not Protective against Ischemic and Cisplatin-Induced Kidney Injury

Autophagy plays an important role in the pathogenesis of acute kidney injury (AKI). Although autophagy activation was shown to be associated with an increased lifespan and beneficial effects in various pathologies, the impact of autophagy activators, particularly, rapamycin and its analogues on AKI remains obscure. In our study, we explored the effects of rapamycin treatment in in vivo and in vitro models of ischemic and cisplatin-induced AKI. The impact of rapamycin on the kidney function after renal ischemia/reperfusion (I/R) or exposure to the nephrotoxic agent cisplatin was assessed by quantifying blood urea nitrogen and serum creatinine and evaluating the content of neutrophil gelatinase-associated lipocalin, a novel biomarker of AKI. In vitro experiments were performed on the primary culture of renal tubular cells (RTCs) that were subjected to oxygen-glucose deprivation (OGD) or incubated with cisplatin under various rapamycin treatment protocols. Cell viability and proliferation were estimated by the MTT assay and real-time cell analysis using an RTCA iCELLigence system. Although rapamycin inhibited mTOR (mammalian target of rapamycin) signaling, it failed to enhance the autophagy and to ameliorate the severity of AKI caused by ischemia or cisplatin-induced nephrotoxicity. Experiments with RTCs demonstrated that rapamycin exhibited the anti-proliferative effect in primary RTCs cultures but did not protect renal cells exposed to OGD or cisplatin. Our study revealed for the first time that the mTOR inhibitor rapamycin did not prevent AKI caused by renal I/R or cisplatin-induced nephrotoxicity and, therefore, cannot be considered as an ideal mimetic of the autophagy-associated nephroprotective mechanisms (e.g., those induced by caloric restriction), as it had been suggested earlier. The protective action of such approaches like caloric restriction might not be limited to mTOR inhibition and can proceed through more complex mechanisms involving alternative autophagy-related targets. Thus, the use of rapamycin and its analogues for the treatment of various AKI forms requires further studies in order to understand potential protective or adverse effects of these compounds in different contexts.

Autophagy Function and Regulation in Kidney Disease

Autophagy is a dynamic process by which intracellular damaged macromolecules and organelles are degraded and recycled for the synthesis of new cellular components. Basal autophagy in the kidney acts as a quality control system and is vital for cellular metabolic and organelle homeostasis. Under pathological conditions, autophagy facilitates cellular adaptation; however, activation of autophagy in response to renal injury may be insufficient to provide protection, especially under dysregulated conditions. Kidney-specific deletion of Atg genes in mice has consistently demonstrated worsened acute kidney injury (AKI) outcomes supporting the notion of a pro-survival role of autophagy. Recent studies have also begun to unfold the role of autophagy in progressive renal disease and subsequent fibrosis. Autophagy also influences tubular cell death in renal injury. In this review, we reported the current understanding of autophagy regulation and its role in the pathogenesis of renal injury. In particular, the classic mammalian target of rapamycin (mTOR)-dependent signaling pathway and other mTOR-independent alternative signaling pathways of autophagy regulation were described. Finally, we summarized the impact of autophagy activation on different forms of cell death, including apoptosis and regulated necrosis, associated with the pathophysiology of renal injury. Understanding the regulatory mechanisms of autophagy would identify important targets for therapeutic approaches.

Effects of Antirejection Drugs on Innate Immune Cells After Kidney Transplantation

Over the last decades, our understanding of adaptive immune responses to solid organ transplantation increased considerably and allowed development of immunosuppressive drugs targeting key alloreactive T cells mechanism. As a result, rates of acute rejection dropped and short-term graft survival improved significantly. However, long-term outcomes are still disappointing. Recently, increasing evidence supports that innate immune responses plays roles in allograft rejection and represents a valuable target to further improve long-term allograft survival. Innate immune cells are activated by molecules with stereotypical motifs produced during injury (i.e., damage-associated molecular patterns, DAMPS) or infection (i.e., pathogen-associated molecular patterns, PAMPs). Activated innate immune cells can exert direct pro- and anti-inflammatory effects, while also priming adaptive immune responses. These cells are activated after transplantation by multiple stimuli, including ischemia-reperfusion injury, rejection, and infections. Data from animal models of graft rejection, show that inhibition of innate immunity promotes development of tolerance. Therefore, understanding mechanisms of innate immunity is important to improve graft outcomes. This review discusses effects of currently used immunosuppressive agents on innate immune responses in kidney transplantation.

Negative feedback loop of autophagy and endoplasmic reticulum stress in rapamycin protection against renal ischemia-reperfusion injury during initial reperfusion phase

Rapamycin, an immunosuppressant, is widely used in patients with kidney transplant. However, the therapeutic effects of rapamycin remain controversial. Additionally, previous studies have revealed deleterious effects of rapamycin predominantly when administered for ≥24 h. Few studies, however, have focused on the short-term effects of rapamycin administered only during the initial reperfusion phase. As such, we designed this study to explore the potential effects and mechanisms of rapamycin under a specific therapeutic regimen in which rapamycin is mixed in the perfusate during the initial reperfusion phase (within 24 h). Interestingly, we found that rapamycin maintained renal function and attenuated ischemia-reperfusion (I/R)-induced apoptosis in vivo and in vitro during the initial reperfusion phase, especially at 8 h after reperfusion. Simultaneously, rapamycin activated autophagy and inhibited endoplasmic reticulum (ER) stress and 3 pathways of unfolding protein response: ATF6, PERK, and IRE1α. Interestingly, we further found that the protective effects of rapamycin were suppressed when autophagy was inhibited by chloroquine and 3-methyladenine or when ER stress was induced by thapsigargin. Moreover, in terms of the regulatory effects of rapamycin, a negative-feedback loop between autophagy and ER stress occurred, with autophagy inhibiting ER stress and increased ER stress promoting autophagy during the initial reperfusion phase of renal I/R injury. Our study provides evidence that immediate reperfusion with rapamycin during the initial reperfusion phase repairs renal function and reduces apoptosis via activating autophagy, which could further inhibit ER stress. These results suggest a novel treatment modality for application during the initial reperfusion phase of renal I/R injury caused by kidney transplantation.-Li, X., Zhu, G., Gou, X., He, W., Yin, H., Yang, X., Li, J. Negative feedback loop of autophagy and endoplasmic reticulum stress in rapamycin protection against renal ischemia-reperfusion injury during initial reperfusion phase.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

Mitochondria-Targeted Antioxidants: Future Perspectives in Kidney Ischemia Reperfusion Injury

Kidney ischemia/reperfusion injury emerges in various clinical settings as a great problem complicating the course and outcome. Ischemia/reperfusion injury is still an unsolved puzzle with a great diversity of investigational approaches, putting the focus on oxidative stress and mitochondria. Mitochondria are both sources and targets of ROS. They participate in initiation and progression of kidney ischemia/reperfusion injury linking oxidative stress, inflammation, and cell death. The dependence of kidney proximal tubule cells on oxidative mitochondrial metabolism makes them particularly prone to harmful effects of mitochondrial damage. The administration of antioxidants has been used as a way to prevent and treat kidney ischemia/reperfusion injury for a long time. Recently a new method based on mitochondria-targeted antioxidants has become the focus of interest. Here we review the current status of results achieved in numerous studies investigating these novel compounds in ischemia/reperfusion injury which specifically target mitochondria such as MitoQ, Szeto-Schiller (SS) peptides (Bendavia), SkQ1 and SkQR1, and superoxide dismutase mimics. Based on the favorable results obtained in the studies that have examined myocardial ischemia/reperfusion injury, ongoing clinical trials investigate the efficacy of some novel therapeutics in preventing myocardial infarct. This also implies future strategies in preventing kidney ischemia/reperfusion injury.

Rapamycin protects kidney against ischemia reperfusion injury through recruitment of NKT cells

Background

NKT cells play a protective role in ischemia reperfusion (IR) injury, of which the trafficking in the body and recruitment in injured organs can be influenced by immunosuppressive therapy. Therefore, we investigated the effects of rapamycin on kidneys exposed to IR injury in early stage and on trafficking of NKT cells in a murine model.

Material and methods

Balb/c mice were subjected to kidney 30 min ischemia followed by 24 h reperfusion. Rapamycin (2.5 ml/kg) was administered by gavage daily, starting 1 day before the operation. Renal function and histological changes were assessed. The proportion of NKT cells in peripheral blood, spleen and kidney was detected by flow cytometry. The chemokines and corresponding receptor involved in NKT cell trafficking were determined by RT-PCR and flow cytometry respectively.

Results

Rapamycin significantly improved renal function and ameliorated histological injury. In rapamycin-treated group, the proportion of NKT cells in spleen was significantly decreased but increased in peripheral blood and kidney. In addition, the CXCR3⁺ NKT cell in the kidney increased remarkably in the rapamycin-treated group. The chemokines, CXCL9 and CXCL10, as the ligands of CXCR3, were also increased in the rapamycin-treated kidney.

Conclusions

Rapamycin may recruit NKT cells from spleen to the IR-induced kidney to ameliorate renal IR injury in the early stage.

The effect of mTOR-inhibition on NF-κB activity in kidney ischemia-reperfusion injury in mice

Kidney ischemia-reperfusion injury (IRI) is associated with a robust inflammatory response, which is regulated by nuclear factor-kappaB (NF-κB), mainly its heterodimeric form p65/p50. Considering immunomodulatory properties of mammalian target of rapamycin (mTOR) inhibitors, the effect of everolimus on NF-κB activation in kidney IRI was determined in this study. IRI was induced in C57/BL6 mice by clamping both renal pedicles for 45 minutes. Application of everolimus (0.25 mg/kg bw subcutaneously daily) was started one day before IRI induction. Both everolimus-treated and nontreated mice were sacrificed at several times starting at 30 minutes and finishing on day 7 after IRI induction. The NF-κB activity, proinflammatory cytokines IL-1β, TNF-α, and anti-inflammatory cytokine IL-10 production were determined in kidneys. Compared with nontreated animals, everolimus-treated animals showed significantly increased TNF-α (2741.6 ± 201.72 pg/mg; 1925 ± 185.81 pg/mg, P < .05) and IL-1β (11.47 ± 1.2 pg/mg; 4.3 ± 0.13 pg/mg, P < .01) production on day 2 after IRI induction accompanied by significantly greater NF-κB/DNA binding activity and p65 nuclear expression (P < .01). Two hours after IRI induction, everolimus-treated animals showed significantly increased IL-1β mRNA expression (P < .05) followed by increased IL-1β protein concentrations when compared with nontreated animals measured 6 hours after IRI induction (11.71 ± 1.5 pg/mg; 7.5 ± 1.11 pg/mg, P < .01). Both experimental groups showed increased NF-κB/DNA binding activity at 7 days after IRI induction. Significantly increased nuclear p65 expression was measured in nontreated animals (P < .01), whereas everolimus-treated hosts showed significantly increased nuclear RelB expression (P < .01). These data suggested that everolimus potentiated innate immunity in the early phase of IRI, stimulating the production of NF-κB-driven proinflammatory cytokines such as TNF-α and IL-1β. The NF-κB activity was potentiated under m-TOR inhibition during kidney IRI, implicating a possible beneficial role of alternative NF-κB activation during the repair phase.

Effects of everolimus on oxidative stress in kidney model of ischemia/reperfusion injury

BACKGROUND/AIMS

Reactive oxygen species play an important role in the pathogenesis of kidney ischemia/reperfusion injury (IRI) which may be influenced by immunosuppressive therapy. Pertinent to this, we investigated the effects of the mTOR inhibitor everolimus on redox settings and the activity of the anti-oxidative system in kidneys exposed to IRI.

METHODS

C57BL/6 mice were subjected to IRI by clamping both renal pedicles for 45 min. Everolimus was applied in daily, subcutaneous doses (0.25 mg/kg body weight), starting 1 day before IRI induction. Both everolimus-treated and non-treated mice were sacrificed at several time points, starting 30 min and finishing 7 days after IRI induction. Markers of oxidation such as glutathione and NADPH levels and anti-oxidative enzyme activities were determined in the kidneys.

RESULTS

In comparison to both sham and non-treated animals, the treatment with everolimus resulted in an increased level of markers of oxidation, including a lower level of glutathione, increased level of oxidized glutathione and reduced level of NADPH. The activity of superoxide dismutase was reduced in both experimental groups, but the effects were less pronounced in everolimus-treated animals. In the early phase of reperfusion, everolimus-treated animals showed higher activity of glutathione reductase in comparison to non-treated animals, whereas the activities of glutathione peroxidase and catalase were generally similar. The treatment with everolimus significantly reduced heme oxygenase-1 expression and increased iNOS mRNA expression when compared to non-treated animals.

CONCLUSION

Our data imply that everolimus treatment may decrease cytoprotective capacity in kidneys exposed to IRI due to promoted oxidative/nitrosative stress.

Kidney regeneration and repair after transplantation

PURPOSE OF REVIEW

To briefly show which are the mechanisms and cell types involved in kidney regeneration and describe some of the therapies currently under study in regenerative medicine for kidney transplantation.

RECENT FINDINGS

The kidney contains cell progenitors that under specific circumstances have the ability to regenerate specific structures. Apart from the knowledge gained in the self-regenerative properties of the kidney, new concepts in regenerative medicine such as organ engineering and the use of mesenchymal stem cell-based therapies are currently the focus of attention in the field.

SUMMARY

Overall, kidney regeneration is a reality and the knowledge on how to control it will be one of the main scopes in the present and future.

Protective role of p70S6K in intestinal ischemia/reperfusion injury in mice

The mTOR signaling pathway plays a crucial role in the regulation of cell growth, proliferation, survival and in directing immune responses. As the intestinal epithelium displays rapid cell growth and differentiation and is an important immune regulatory organ, we hypothesized that mTOR may play an important role in the protection against intestinal ischemia reperfusion (I/R)-induced injury. To better understand the molecular mechanisms by which the mTOR pathway is altered by intestinal I/R, p70S6K, the major effector of the mTOR pathway, was investigated along with the effects of rapamycin, a specific inhibitor of mTOR and an immunosuppressant agent used clinically in transplant patients. In vitro experiments using an intestinal epithelial cell line and hypoxia/reoxygenation demonstrated that overexpression of p70S6K promoted cell growth and migration, and decreased cell apoptosis. Inhibition of p70S6K by rapamycin reversed these protective effects. In a mouse model of gut I/R, an increase of p70S6K activity was found by 5 min and remained elevated after 6 h of reperfusion. Inhibition of p70S6K by rapamycin worsened gut injury, promoted inflammation, and enhanced intestinal permeability. Importantly, rapamycin treated animals had a significantly increased mortality. These novel results demonstrate a key role of p70S6K in protection against I/R injury in the intestine and suggest a potential danger in using mTOR inhibitors in patients at risk for gut hypoperfusion.

Mammalian target of rapamycin and the kidney. II. Pathophysiology and therapeutic implications

The mTOR pathway plays an important role in a number of common renal diseases, including acute kidney injury (AKI), diabetic nephropathy (DN), and polycystic kidney diseases (PKD). The activity of mTOR complex 1 (mTORC1) is necessary for renal regeneration and repair after AKI, and inhibition of mTORC1 by rapamycin has been shown to delay recovery from ischemic AKI in animal studies, and to prolong delayed graft function in humans who have received a kidney transplant. For this reason, administration of rapamycin should be delayed or discontinued in patients with AKI until full recovery of renal function has occurred. On the other hand, inappropriately high mTORC1 activity contributes to the progression of the metabolic syndrome, the development of type 2 diabetes, and the pathogenesis of DN. In addition, chronic hyperactivity of mTORC1, and possibly also mTORC2, contributes to cyst formation and enlargement in a number of forms of PKD. Inhibition of mTOR, using either rapamycin (which inhibits predominantly mTORC1) or "catalytic" inhibitors (which effectively inhibit both mTORC1 and mTORC2), provide exciting possibilities for novel forms of treatment of DN and PKD. In this second part of the review, we will examine the role of mTOR in the pathophysiology of DN and PKD, as well as the potential utility of currently available and newly developed inhibitors of mTOR to slow the progression of DN and/or PKD.

Preconditioning donor with a combination of tacrolimus and rapamacyn to decrease ischaemia-reperfusion injury in a rat syngenic kidney transplantation model

Reperfusion injury remains one of the major problems in transplantation. Repair from ischaemic acute renal failure (ARF) involves stimulation of tubular epithelial cell proliferation. The aim of this exploratory study was to evaluate the effects of preconditioning donor animals with rapamycin and tacrolimus to prevent ischaemia-reperfusion (I/R) injury. Twelve hours before nephrectomy, the donor animals received immunosuppressive drugs. The animals were divided into four groups, as follows: group 1 control: no treatment; group 2: rapamycin (2 mg/kg); group 3 FK506 (0, 3 mg/kg); and group 4: FK506 (0, 3 mg/kg) plus rapamycin (2 mg/kg). The left kidney was removed and after 3 h of cold ischaemia, the graft was transplanted. Twenty-four hours after transplant, the kidney was recovered for histological analysis and cytokine expression. Preconditioning treatment with rapamycin or tacrolimus significantly reduced blood urea nitrogen and creatinine compared with control [blood urea nitrogen (BUN): P < 0·001 versus control and creatinine: P < 0·001 versus control]. A further decrease was observed when rapamycin was combined with tacrolimus. Acute tubular necrosis was decreased significantly in donors treated with immunosuppressants compared with the control group (P < 0·001 versus control). Moreover, the number of apoptotic nuclei in the control group was higher compared with the treated groups (P < 0·001 versus control). Surprisingly, only rapamycin preconditioning treatment increased anti-apoptotic Bcl2 levels (P < 0·001). Finally, inflammatory cytokines, such as tumour necrosis factor (TNF)-α and interleukin (IL)-6, showed lower levels in the graft of those animals that had been pretreated with rapamycin or tacrolimus. This exploratory study demonstrates that preconditioning donor animals with rapamycin or tacrolimus improves clinical outcomes and reduce necrosis and apoptosis in kidney I/R injury.

Rapamycin promotes autophagy and reduces neural tissue damage and locomotor impairment after spinal cord injury in mice

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that negatively regulates autophagy. Rapamycin, an inhibitor of mTOR signaling, can promote autophagy and exert neuroprotective effects in several diseases of the central nervous system (CNS). In the present study, we examined whether rapamycin treatment promotes autophagy and reduces neural tissue damage and locomotor impairment after spinal cord injury (SCI) in mice. Our results demonstrated that the administration of rapamycin significantly decreased the phosphorylation of the p70S6K protein and led to higher expression levels of LC3 and Beclin 1 in the injured spinal cord. In addition, neuronal loss and cell death in the injured spinal cord were significantly reduced in the rapamycin-treated mice compared to the vehicle-treated mice. Furthermore, the rapamycin-treated mice showed significantly higher locomotor function in Basso Mouse Scale (BMS) scores than did the vehicle-treated mice. These results indicate that rapamycin promoted autophagy by inhibiting the mTOR signaling pathway, and reduced neural tissue damage and locomotor impairment after SCI. The administration of rapamycin produced a neuroprotective function at the lesion site following SCI. Rapamycin treatment may represent a novel therapeutic strategy after SCI.

Mitochondria-targeted peptide accelerates ATP recovery and reduces ischemic kidney injury

The burst of reactive oxygen species (ROS) during reperfusion of ischemic tissues can trigger the opening of the mitochondrial permeability transition (MPT) pore, resulting in mitochondrial depolarization, decreased ATP synthesis, and increased ROS production. Rapid recovery of ATP upon reperfusion is essential for survival of tubular cells, and inhibition of oxidative damage can limit inflammation. SS-31 is a mitochondria-targeted tetrapeptide that can scavenge mitochondrial ROS and inhibit MPT, suggesting that it may protect against ischemic renal injury. Here, in a rat model of ischemia-reperfusion (IR) injury, treatment with SS-31 protected mitochondrial structure and respiration during early reperfusion, accelerated recovery of ATP, reduced apoptosis and necrosis of tubular cells, and abrogated tubular dysfunction. In addition, SS-31 reduced medullary vascular congestion, decreased IR-mediated oxidative stress and the inflammatory response, and accelerated the proliferation of surviving tubular cells as early as 1 day after reperfusion. In summary, these results support MPT as an upstream target for pharmacologic intervention in IR injury and support early protection of mitochondrial function as a therapeutic maneuver to prevent tubular apoptosis and necrosis, reduce oxidative stress, and reduce inflammation. SS-31 holds promise for the prevention and treatment of acute kidney injury.

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.

Drp1 dephosphorylation in ATP depletion-induced mitochondrial injury and tubular cell apoptosis

Recent studies revealed a striking morphological change of mitochondria during apoptosis. Mitochondria become fragmented and notably, the fragmentation contributes to mitochondrial outer membrane permeabilization and consequent release of apoptotic factors. In renal tubular cells, mitochondrial fragmentation involves the activation of Drp1, a key mitochondrial fission protein. However, it is unclear how Drp1 is regulated during tubular cell apoptosis. In this study, we examined Drp1 regulation during tubular cell apoptosis following ATP depletion. Rat kidney proximal tubular cells (RPTC) were subjected to azide treatment or severe hypoxia in glucose-free medium to induce ATP depletion. During ATP depletion, Drp1 was shown to be dephosphorylated at serine-637. Drp1 dephosphorylation could be suppressed by cyclosporine A and FK506, two calcineurin inhibitors. Importantly, cyclosporine A and FK506 could also prevent mitochondrial fragmentation, Bax accumulation, cytochrome c release, and apoptosis following ATP depletion in RPTC. The results suggest that calcineurin-mediated serine-637 dephosphorylation is involved in Drp1 activation during ATP depletion in renal tubular cells. Upon activation, Drp1 contributes to mitochondrial fragmentation and outer membrane permeabilization, resulting in the release of apoptogenic factors and apoptosis.

Prospects for mTOR inhibitor use in patients with polycystic kidney disease and hamartomatous diseases

Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.

The role of the mammalian target of rapamycin (mTOR) in renal disease

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a pivotal role in mediating cell size and mass, proliferation, and survival. mTOR has also emerged as an important modulator of several forms of renal disease. mTOR is activated after acute kidney injury and contributes to renal regeneration and repair. Inhibition of mTOR with rapamycin delays recovery of renal function after acute kidney injury. Activation of mTOR within the kidney also occurs in animal models of diabetic nephropathy and other causes of progressive kidney disease. Rapamycin ameliorates several key mechanisms believed to mediate changes associated with the progressive loss of GFR in chronic kidney disease. These include glomerular hypertrophy, intrarenal inflammation, and interstitial fibrosis. mTOR also plays an important role in mediating cyst formation and enlargement in autosomal dominant polycystic kidney disease. Inhibition of mTOR by rapamycin or one of its analogues represents a potentially novel treatment for autosomal dominant polycystic kidney disease. Finally, inhibitors of mTOR improve survival in patients with metastatic renal cell carcinoma.

Emerging therapy-related kidney disease

CONTEXT

Many new therapies have emerged within the last 5 to 10 years to treat a variety of conditions. Several of these have direct or indirect renal toxicities that may go undiagnosed without careful attention of the pathologist to a patient's clinical history, particularly the addition of new medications or treatments.

OBJECTIVE

To discuss patterns of renal injury resulting from medications or therapeutic regimens that have been introduced within the last 10 years. Recognition of these patterns may allow the pathologist to alert the attending clinician to a possible drug-induced renal injury and prevent further deterioration of renal function and possible chronic kidney disease.

DATA SOURCES

A review of recent literature and unpublished observations of case-derived material.

CONCLUSIONS

A number of newer therapies have emerged as agents of renal toxicity, producing a variety of pathologic changes in the kidney. The outcome can be acute or chronic glomerular, tubular, interstitial, and/or vascular injury. Some drugs will result in irreversible changes and end-stage renal disease, whereas many of the alterations can be reversed with removal of the offending agent, avoiding potential long-term kidney injury.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.