Role of mitochondrial-derived oxidants in renal tubular cell cold-storage injury

Cold Storage Followed by Transplantation Induces Immunoproteasome in Rat Kidney Allografts: Inhibition of Immunoproteasome Does Not Improve Function

Key Points

Cold storage (CS) increases the severity of graft dysfunction in a time-dependent manner, and prolonged CS decreases animal survival. CS plus transplant increases iproeasome levels/assembly in renal allografts; IFN-γ is a potential inducer of the iproteasome. Inhibiting iproteasome ex vivo during renal CS did not confer graft protection after transplantation.

Background

It is a major clinical challenge to ensure the long-term function of transplanted kidneys. Specifically, the injury associated with cold storage (CS) of kidneys compromises the long-term function of the grafts after transplantation. Therefore, the molecular mechanisms underlying CS-related kidney injury are attractive therapeutic targets to prevent injury and improve long-term graft function. Previously, we found that constitutive proteasome function was compromised in rat kidneys after CS followed by transplantation. Here, we evaluated the role of the immunoproteasome (i proteasome), a proteasome variant, during CS followed by transplantation.

Methods

Established in vivo rat kidney transplant model with or without CS containing vehicle or iproteasome inhibitor (ONX 0914) was used in this study. The i proteasome function was performed using rat kidney homogenates and fluorescent-based peptide substrate specific to β 5i subunit. Western blotting and quantitative RT-PCR were used to assess the subunit expression/level of the i proteasome (β 5i) subunit.

Results

We demonstrated a decrease in the abundance of the β 5i subunit of the i proteasome in kidneys during CS, but β 5i levels increased in kidneys after CS and transplant. Despite the increase in β 5i levels and its peptidase activity within kidneys, inhibiting β 5i during CS did not improve graft function after transplantation.

Summary

These results suggest that the pharmacologic inhibition of immunoproteasome function during CS does not improve graft function or outcome. In light of these findings, future studies targeting immunoproteasomes during both CS and transplantation may define the role of immunoproteasomes on short-term and long-term kidney transplant outcomes.

Effect of PERLA®, a new cold-storage solution, on oxidative stress injury and early graft function in rat kidney transplantation model

BACKGROUND

The composition of organ preservation solutions is crucial for maintaining graft integrity and early graft function after transplantation. The aim of this study is to compare new organ preservation solution PERLA® with the gold standard preservation solution University of Wisconsin (UW) regarding oxidative stress and early graft injury.

METHODS

In order to assess oxidative stress after cold storage, kidney grafts have been preserved for 18 h at 4° C in either UW solution or PERLA® solution and then assessed for oxidative stress injury (protocol 1). To assess kidney injuries and oxidative stress after reperfusion, rat kidneys were harvested, stored in cold UW or in PERLA® solutions for 18 h at 4 °C and then transplanted heterotopically for 6 h (protocol 2). PERLA® is a high Na+/low K+ solution including PEG-35 (1 g/L), trimetazidine (1 µM), carvedilol (10 µM) and tacrolimus (5 µM).

RESULTS

Our results showed that preservation of kidneys in PERLA® solution significantly attenuates oxidative stress parameters after cold storage and reperfusion. We found a significant decrease in oxidative damage indicators (MDA, CD and CP) and a significant increase in antioxidant indicators (GPx, GSH, CAT, SOD and PSH). Moreover, PERLA® solution decreased kidney injury after reperfusion (creatinine, LDH and uric acid).

CONCLUSION

PERLA® solution was more effective than UW storage solution in preserving rat's kidney grafts.

Cold Storage Followed by Transplantation Induces Interferon-Gamma and STAT-1 in Kidney Grafts

Cold storage (CS)-mediated inflammation, a reality of donor kidney processing and transplantation, can contribute to organ graft failure. However, the mechanisms by which this inflammation is perpetuated during and after CS remain unclear. Here, we examined the immunoregulatory roles of signal transducer and activator of transcription (STAT) family proteins, most notably STAT1 and STAT3, with our in vivo model of renal CS and transplant. Donor rat kidneys were exposed to 4 h or 18 h of CS, which was then followed by transplantation (CS + transplant). STAT total protein level and activity (phosphorylation) were evaluated via Western blot analysis and mRNA expression was tabulated using quantitative RT-PCR after organ harvest on day 1 or day 9 post-surgery. In vivo assays were further corroborated via similar analyses featuring in vitro models, specifically proximal tubular cells (human and rat) as well as macrophage cells (Raw 264.7). Strikingly, gene expression of IFN-γ (a pro-inflammatory cytokine inducer of STAT) and STAT1 were markedly increased after CS + transplant. STAT3 dephosphorylation was additionally observed after CS, a result suggestive of dysregulation of anti-inflammatory signaling as phosphorylated STAT3 acts as a transcription factor in the nucleus to increase the expression of anti-inflammatory signaling molecules. In vitro, IFN-γ gene expression as well as amplification of downstream STAT1 and inducible nitric oxide synthase (iNOS; a hallmark of ischemia reperfusion injury) was remarkably increased after CS + rewarming. Collectively, these results demonstrate that aberrant induction of STAT1 is sustained in vivo post-CS exposure and post-transplant. Thus, Jak/STAT signaling may be a viable therapeutic target during CS to mitigate poor graft outcomes when transplanting kidneys from deceased donors.

Inhibition of HDAC3 protects against kidney cold storage/transplantation injury and allograft dysfunction

Cold storage/rewarming is an inevitable process for kidney transplantation from deceased donors, which correlates closely with renal ischemia-reperfusion injury (IRI) and the occurrence of delayed graft function. Histone deacetylases (HDAC) are important epigenetic regulators, but their involvement in cold storage/rewarming injury in kidney transplantation is unclear. In the present study, we showed a dynamic change of HDAC3 in a mouse model of kidney cold storage followed by transplantation. We then demonstrated that the selective HDAC3 inhibitor RGFP966 could reduce acute tubular injury and cell death after prolonged cold storage with transplantation. RGFP966 also improved renal function, kidney repair and tubular integrity when the transplanted kidney became the sole life-supporting graft in the recipient mouse. In vitro, cold storage of proximal tubular cells followed by rewarming induced remarkable cell death, which was suppressed by RGFP966 or knockdown of HDAC3 with shRNA. Inhibition of HDAC3 decreased the mitochondrial pathway of apoptosis and preserved mitochondrial membrane potential. Collectively, HDAC3 plays a pathogenic role in cold storage/rewarming injury in kidney transplantation, and its inhibition may be a therapeutic option.

Female and male mice have differential longterm cardiorenal outcomes following a matched degree of ischemia-reperfusion acute kidney injury

Acute kidney injury (AKI) is common in patients, causes systemic sequelae, and predisposes patients to long-term cardiovascular disease. To date, studies of the effects of AKI on cardiovascular outcomes have only been performed in male mice. We recently demonstrated that male mice developed diastolic dysfunction, hypertension and reduced cardiac ATP levels versus sham 1 year after AKI. The effects of female sex on long-term cardiac outcomes after AKI are unknown. Therefore, we examined the 1-year cardiorenal outcomes following a single episode of bilateral renal ischemia-reperfusion injury in female C57BL/6 mice using a model with similar severity of AKI and performed concomitantly to recently published male cohorts. To match the severity of AKI between male and female mice, females received 34 min of ischemia time compared to 25 min in males. Serial renal function, echocardiograms and blood pressure assessments were performed throughout the 1-year study. Renal histology, and cardiac and plasma metabolomics and mitochondrial function in the heart and kidney were evaluated at 1 year. Measured glomerular filtration rates (GFR) were similar between male and female mice throughout the 1-year study period. One year after AKI, female mice had preserved diastolic function, normal blood pressure, and preserved levels of cardiac ATP. Compared to males, females demonstrated pathway enrichment in arginine metabolism and amino acid related energy production in both the heart and plasma, and glutathione in the plasma. Cardiac mitochondrial respiration in Complex I of the electron transport chain demonstrated improved mitochondrial function in females compared to males, regardless of AKI or sham. This is the first study to examine the long-term cardiac effects of AKI on female mice and indicate that there are important sex-related cardiorenal differences. The role of female sex in cardiovascular outcomes after AKI merits further investigation.

Proximal Tubule p53 in Cold Storage/Transplantation-Associated Kidney Injury and Renal Graft Dysfunction

Kidney injury associated with cold storage/transplantation is a primary factor for delayed graft function and poor outcome of renal transplants. p53 contributes to both ischemic and nephrotoxic kidney injury, but its involvement in kidney cold storage/transplantation is unclear. Here, we report that p53 in kidney proximal tubules plays a critical role in cold storage/transplantation kidney injury and inhibition of p53 can effectively improve the histology and function of transplanted kidneys. In a mouse kidney cold storage/transplantation model, we detected p53 accumulation in proximal tubules in a cold storage time-dependent manner, which correlated with tubular injury and cell death. Pifithrin-α, a pharmacologic p53 inhibitor, could reduce acute tubular injury, apoptosis and inflammation at 24 h after cold storage/transplantation. Similar effects were shown by the ablation of p53 from proximal tubule cells. Notably, pifithrin-α also ameliorated kidney injury and improved the function of transplanted kidneys in 6 days when it became the sole life-supporting kidney in recipient mice. in vitro, cold storage followed by rewarming induced cell death in cultured proximal tubule cells, which was accompanied by p53 activation and suppressed by pifithrin-α and dominant-negative p53. Together, these results support a pathogenic role of p53 in cold storage/transplantation kidney injury and demonstrate the therapeutic potential of p53 inhibitors.

Overexpression of MnSOD Protects against Cold Storage-Induced Mitochondrial Injury but Not against OMA1-Dependent OPA1 Proteolytic Processing in Rat Renal Proximal Tubular Cells

Kidneys from deceased donors undergo cold storage (CS) preservation before transplantation. Although CS is a clinical necessity for extending organ quality preservation, CS causes mitochondrial and renal injury. Specifically, many studies, including our own, have shown that the triggering event of CS-induced renal injury is mitochondrial reactive oxygen species (mROS). Here, we explored the role of OMA1-depedent OPA1 proteolytic processing in rat kidney proximal tubular epithelial (NRK) cells in an in vitro model of renal CS (18 h), followed by rewarming (6 h) (CS + RW). The involvement of mROS was evaluated by stably overexpressing manganese superoxide dismutase (MnSOD), an essential mitochondrial antioxidant enzyme, in NRK cells. Western blots detected rapid OPA1 proteolytic processing and a decrease in ATP-dependent cell viability in NRK cells subjected to CS + RW compared to control cells. Small interfering RNA (siRNA) knockdown of OMA1 reduced proteolytic processing of OPA1, suggesting that OMA1 is responsible for OPA1 proteolytic processing during CS + RW-induced renal injury. Overexpression of MnSOD during CS + RW reduced cell death, mitochondrial respiratory dysfunction, and ATP-dependent cell viability, but it did not prevent OMA1-dependent OPA1 processing. These data show for the first time that OMA1 is responsible for proteolytically cleaving OPA1 in a redox-independent manner during renal cell CS.

The BK activator NS11021 partially protects rat kidneys from cold storage and transplantation-induced mitochondrial and renal injury

Kidneys from deceased donors used for transplantation are placed in cold storage (CS) solution during the search for a matched recipient. However, CS induces mitochondrial and cellular injury, which exacerbates renal graft dysfunction, highlighting the need for therapeutic interventions. Using an in vitro model of renal CS, we recently reported that pharmacological activation of the mitochondrial BK channel (mitoBK) during CS protected against CS-induced mitochondrial injury and cell death. Here, we used an in vivo syngeneic rat model of renal CS (18 hr) followed by transplantation (24 hr reperfusion) (CS+Tx) to similarly evaluate whether addition of a mitoBK activator to the CS solution can alleviate CS+Tx-induced renal injury. Western blots detected the pore-forming α subunit of the BK channel in mitochondrial fractions from rat kidneys, and mitoBK protein expression was reduced after CS+Tx compared to sham surgery. The addition of the BK activator NS11021 (3 μM) to the CS solution partially protected against CS+Tx-induced mitochondrial respiratory dysfunction, oxidative protein nitration, and cell death, but not acute renal dysfunction (SCr and BUN). In summary, the current preclinical study shows that pharmacologically targeting mitoBK channels during CS may be a promising therapeutic intervention to prevent CS+Tx-induced mitochondrial and renal injury.

Targeting Mitochondria during Cold Storage to Maintain Proteasome Function and Improve Renal Outcome after Transplantation

Kidney transplantation is the preferred treatment for end-stage kidney disease (ESKD). Compared to maintenance dialysis, kidney transplantation results in improved patient survival and quality of life. Kidneys from living donors perform best; however, many patients with ESKD depend on kidneys from deceased donors. After procurement, donor kidneys are placed in a cold-storage solution until a suitable recipient is located. Sadly, prolonged cold storage times are associated with inferior transplant outcomes; therefore, in most situations when considering donor kidneys, long cold-storage times are avoided. The identification of novel mechanisms of cold-storage-related renal damage will lead to the development of new therapeutic strategies for preserving donor kidneys; to date, these mechanisms remain poorly understood. In this review, we discuss the importance of mitochondrial and proteasome function, protein homeostasis, and renal recovery during stress from cold storage plus transplantation. Additionally, we discuss novel targets for therapeutic intervention to improve renal outcomes.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Sex differences in redox homeostasis in renal disease

Sex differences in redox signaling in the kidney present new challenges and opportunities for understanding the physiology and pathophysiology of the kidney. This review will focus on reactive oxygen species, immune-related signaling pathways and endothelin-1 as potential mediators of sex-differences in redox homeostasis in the kidney. Additionally, this review will highlight male-female differences in redox signaling in several major cardiovascular and renal disorders namely acute kidney injury, diabetic nephropathy, kidney stone disease and salt-sensitive hypertension. Furthermore, we will discuss the contribution of redox signaling in the pathogenesis of postmenopausal hypertension and preeclampsia.

Specific BK Channel Activator NS11021 Protects Rat Renal Proximal Tubular Cells from Cold Storage-Induced Mitochondrial Injury In Vitro

Kidneys from deceased donors used for transplantation are placed in cold storage (CS) solution during the search for a matched recipient. However, CS causes mitochondrial injury, which may exacerbate renal graft dysfunction. Here, we explored whether adding NS11021, an activator of the mitochondrial big-conductance calcium-activated K⁺ (mitoBK) channel, to CS solution can mitigate CS-induced mitochondrial injury. We used normal rat kidney proximal tubular epithelial (NRK) cells as an in vitro model of renal cold storage (18 h) and rewarming (2 h) (CS + RW). Western blots detected the pore-forming α subunit of the BK channel in mitochondrial fractions from NRK cells. The fluorescent K⁺-binding probe, PBFI-AM, revealed that isolated mitochondria from NRK cells exhibited mitoBK-mediated K⁺ uptake, which was impaired ~70% in NRK cells subjected to CS + RW compared to control NRK cells maintained at 37 °C. Importantly, the addition of 1 μM NS11021 to CS solution prevented CS + RW-induced impairment of mitoBK-mediated K⁺ uptake. The NS11021–treated NRK cells also exhibited less cell death and mitochondrial injury after CS + RW, including mitigated mitochondrial respiratory dysfunction, depolarization, and superoxide production. In summary, these new data show for the first time that mitoBK channels may represent a therapeutic target to prevent renal CS-induced injury.

Pancreas Transplantation from Donors after Circulatory Death: an Irrational Reluctance?

PURPOSE OF REVIEW

Beta-cell replacement is the best therapeutic option for patients with type 1 diabetes. Because of donor scarcity, more extended criteria donors are used for transplantation. Donation after circulatory death donors (DCD) are not commonly used for pancreas transplantation, because of the supposed higher risk of complications. This review gives an overview on the pathophysiology, risk factors, and outcome in DCD transplantation and discusses different preservation methods.

RECENT FINDINGS

Studies on outcomes of DCD pancreata show similar results compared with those of donation after brain death (DBD), when accumulation of other risk factors is avoided. Hypothermic machine perfusion is shown to be a safe method to improve graft viability in experimental settings. DCD should not be the sole reason to decline a pancreas for transplantation. Adequate donor selection and improved preservation techniques can lead to enhanced pancreas utilization and outcome.

A Cycle of Altered Proteasome and Reactive Oxygen Species Production in Renal Proximal Tubular Cells

Aims

An intricate relationship exists between the mitochondrial function and proteasome activity. Our recent report showed in a rat model of renal transplantation that mitochondrial dysfunction precedes compromised proteasome function and this results in a vicious cycle of mitochondrial injury and proteasome dysfunction. In this study, we studied whether reactive oxygen species (ROS) has a role in proteasome alteration in renal cells and vice versa.

Methods

We used the genomic and pharmacologic approach on rat normal kidney proximal tubular (NRK) cell lines. First, we knocked down β5 or Rpt6 subunit of the proteasome using small interfering RNA (siRNA) in NRK cells. We also treated NRK cells with Bortezomib, a proteasome inhibitor, and peroxynitrite (a potent ROS).

Results

Studies with RNA interference showed increased mitochondrial ROS following knockdown of β5 or Rpt6 subunit in NRK cells. Similarly, pharmacological inhibition of the proteasome in NRK cells using Bortezomib also showed an increase of mitochondrial ROS in a dose-dependent manner. Next, exposing NRK cells to different concentrations of peroxynitrite provided evidence that the higher levels of peroxynitrite exposure decreased the key subunits (β5 and α3) of the proteasome in NRK cells.

Conclusion

Our results suggest that proteasome inhibition/downregulation increases ROS, which then impairs proteasome subunits in renal proximal tubular cells.

Total Synthesis and Biological Evaluation of Sericetin for Protection against Cisplatin-Induced Acute Kidney Injury

A concise synthesis of sericetin (1) was performed in four steps from readily available 3- O-benzylgalangin (4), featuring electrocyclization to produce the tricyclic core and a sequential aromatic Claisen/Cope rearrangement to incorporate the 8-prenyl group of 1. In addition, the therapeutic potential of sericetin (1), isosericetin (2), and three prenylated tetracyclic synthetic intermediates (11, 12, and 14) against cisplatin-induced nephrotoxicity using renal tubular cells were evaluated. Compound 14 showed therapeutic potential against cisplatin-induced kidney damage.

Renal cold storage followed by transplantation impairs proteasome function and mitochondrial protein homeostasis

Identifying pathways related to renal cold storage (CS) that lead to renal damage after transplantation (Tx) will help us design novel pathway-specific therapies to improve graft outcome. Our recent report showed that mitochondrial function was compromised after CS alone, and this was exacerbated when CS was combined with Tx (CS/Tx). The goal of this study was to determine whether the proteasome exacerbates mitochondrial dysfunction after CS/Tx. We exposed the kidneys of male Lewis rats (in vivo) and rat renal proximal tubular (NRK) cells (in vitro) to CS/Tx or rewarming (CS/RW), respectively. To compare CS-induced effects, in vivo kidney Tx without CS exposure (autotransplantation; ATx) was also used. Our study provides the first evidence that the chymotrypsin-like (ChT-L) peptidase activity of the proteasome declined only after CS/Tx or CS/RW, but not after CS or ATx. Interestingly, key mitochondrial proteins involved with respiration [succinate dehydrogenase complex, subunit A (SDHA), a complex II subunit, and ATP5B, an ATP synthase/complex V subunit] were detected in the detergent-insoluble fraction after CS/Tx or CS/RW, with compromised complex V activity. Pharmacological inhibition of ChT-L activity in NRK cells decreased the activity of mitochondrial complexes I, II, and V and also increased the levels of SDHA and ATP5B in the insoluble fraction. On the other hand, inhibiting mitochondrial respiration in NRK cells with antimycin A compromised ChT-L function and increased the amounts of SDHA and ATP5B in the insoluble fraction. Our results suggest that mitochondrial respiratory dysfunction during CS precedes compromised ChT-L function after CS/Tx and proteasome dysfunction further alters mitochondrial protein homeostasis and decreases respiration in the kidneys after CS/Tx. Therefore, therapeutics that preserve mitochondrial and proteasome function during CS may provide beneficial outcomes following transplantation.

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

SIGNIFICANCE

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

CRITICAL ISSUES

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

FUTURE DIRECTIONS

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

The Crosstalk between ROS and Autophagy in the Field of Transplantation Medicine

Many factors during the transplantation process influence posttransplant graft function and survival, including donor type and age, graft preservation methods (cold storage, machine perfusion), and ischemia-reperfusion injury. Successively, they will lead to cellular and molecular alterations that determine cell and ultimately organ fate. Oxidative stress and autophagy are implicated in posttransplant outcome since they are both affected by the stress responses triggered in each step (donor, preservation, and recipient) of the transplantation process. Furthermore, oxidative stress influences autophagy and vice versa. Interestingly, both processes have positive as well as negative effects on graft outcome, suggesting they are tightly linked during the transplantation process. In this review, we discuss the importance, regulation and crosstalk of oxidative signals, and autophagy in the field of transplantation medicine.

Renal cold storage followed by transplantation impairs expression of key mitochondrial fission and fusion proteins

BACKGROUND

The majority of transplanted kidneys are procured from deceased donors which all require exposure to cold storage (CS) for successful transplantation. Unfortunately, this CS leads to renal and mitochondrial damage but, specific mitochondrial targets affected by CS remain largely unknown. The goal of this study is to determine whether pathways involved with mitochondrial fusion or fission, are disrupted during renal CS.

METHODS

Male Lewis rat kidneys were exposed to cold storage (CS) alone or cold storage combined with transplantation (CS/Tx). To compare effects induced by CS, kidney transplantation without CS exposure (autotransplantation; ATx) was also used. Mitochondrial function was assessed using high resolution respirometry. Expression of mitochondrial fusion and fission proteins were monitored using Western blot analysis.

RESULTS

CS alone (no Tx) reduced respiratory complex I and II activities along with reduced expression of the primary mitochondrial fission protein, dynamin related protein (DRP1), induced loss of the long form of Optic Atrophy Protein (OPA1), and altered the mitochondrial protease, OMA1, which regulates OPA1 processing. CS followed by Tx (CS/Tx) reduced complex I, II, and III activities, and induced a profound loss of the long and short forms of OPA1, mitofusin 1 (MFN1), and mitofusin 2 (MFN2) which all control mitochondrial fusion. In addition, expression of DRP1, along with its primary receptor protein, mitochondrial fission factor (MFF), were also reduced after CS/Tx. Interestingly, CS/Tx lead to aberrant higher molecular weight OMA1 aggregate expression.

CONCLUSIONS

Our results suggest that CS appears to involve activation of the OMA1, which could be a key player in proteolysis of the fusion and fission protein machinery following transplantation. These findings raise the possibility that impaired mitochondrial fission and fusion may be unrecognized contributors to CS induced mitochondrial injury and compromised renal graft function after transplantation.

Renal Mitochondrial Response to Low Temperature in Non-Hibernating and Hibernating Species

SIGNIFICANCE

Therapeutic hypothermia is commonly applied to limit ischemic injury in organ transplantation, during cardiac and brain surgery and after cardiopulmonary resuscitation. In these procedures, the kidneys are particularly at risk for ischemia/reperfusion injury (IRI), likely due to their high rate of metabolism. Although hypothermia mitigates ischemic kidney injury, it is not a panacea. Residual mitochondrial failure is believed to be a key event triggering loss of cellular homeostasis, and potentially cell death. Subsequent rewarming generates large amounts of reactive oxygen species that aggravate organ injury. Recent Advances: Hibernators are able to withstand periods of profoundly reduced metabolism and body temperature ("torpor"), interspersed by brief periods of rewarming ("arousal") without signs of organ injury. Specific adaptations allow maintenance of mitochondrial homeostasis, limit oxidative stress, and protect against cell death. These adaptations consist of active suppression of mitochondrial function and upregulation of anti-oxidant enzymes and anti-apoptotic pathways.

CRITICAL ISSUES

Unraveling the precise molecular mechanisms that allow hibernators to cycle through torpor and arousal without precipitating organ injury may translate into novel pharmacological approaches to limit IRI in patients.

FUTURE DIRECTIONS

Although the precise signaling routes involved in natural hibernation are not yet fully understood, torpor-like hypothermic states with increased resistance to ischemia/reperfusion can be induced pharmacologically by 5'-adenosine monophosphate (5'-AMP), adenosine, and hydrogen sulfide (H₂S) in non-hibernators. In this review, we compare the molecular effects of hypothermia in non-hibernators with natural and pharmacologically induced torpor, to delineate how safe and reversible metabolic suppression may provide resistance to renal IRI. Antioxid. Redox Signal. 27, 599-617.

Cold Storage Exacerbates Renal and Mitochondrial Dysfunction Following Transplantation

Long-term renal function is compromised in patients receiving deceased donor kidneys which require cold storage exposure prior to transplantation. It is well established that extended cold storage induces renal damage and several labs, including our own, have demonstrated renal mitochondrial damage after cold storage alone. However, to our knowledge, few studies have assessed renal and mitochondrial function after transplantation of rat kidneys exposed to short-term (4 hr) cold storage compared to transplant without cold storage (autotransplantation). Our data reveal that cold storage plus transplantation exacerbated renal and mitochondrial dysfunction when compared to autotransplantation alone.

Stimulation of Dopamine D3 Receptor Attenuates Renal Ischemia-Reperfusion Injury via Increased Linkage With Gα12

BACKGROUND

Renal ischemia-reperfusion (I/R) injury causes renal tubular necrosis, apoptosis, and inflammation leading to acute renal dysfunction. Recent studies have revealed that deletion of Gα12 mitigates the renal damage due to I/R injury. Our previous study showed that activation of dopamine D3 receptor (D3R) increased its linkage with Gα12, and hampered Gα12-mediated stimulation of renal sodium transport. In the present study, we used an in-vivo rat model and an in vitro study of the renal epithelial cell line (NRK52E) to investigate whether or not an increased linkage between D3R and Gα12 contributes to the protective effect of D3R on renal I/R injury.

METHODS

For in vivo studies, I/R injury was induced in a rat renal unilateral clamping model. For in vitro studies, hypoxia/reoxygenation and cold storage/rewarming injuries were performed in NRK52E cells. PD128907, a D3R agonist, or vehicle, was administered 15 minutes before clamping (or hypoxia) in both the in vivo or in vitro studies.

RESULTS

In the rat renal unilateral clamping model, pretreatment with PD128907 (0.2 mg/kg, intravenous) protected against renal I/R injury and increased survival rate during a long-term follow-up after 7 days. A decrease in the generation of reactive oxygen species, apoptosis, and inflammation may be involved in the D3R-mediated protection because pretreatment with PD128907 increased renal glutathione and superoxide dismutase levels and decreased malondialdehyde levels in the I/R group. The increase in cytokines (TNF-α, IL-1β, and IL-10) and myeloperoxidase in I/R injured kidney was also prevented with a simultaneous decrease in the apoptosis of the epithelial cells and expression of apoptosis biomarkers in kidney harvested 1 day after I/R injury. The increase in the coimmunoprecipitation between D3R and Gα12 with D3R stimulation paralleled the observed renal protection from I/R injury. Moreover, in vitro studies showed that transient overexpression of Gα12 in the NRK52E cells attenuated the protective effect of PD128907 on hypoxia/reoxygenation injury. The protective effect of PD128907 might be of significance to renal transplantation because cold storage/rewarming induced injury increased lactate dehydrogenase release and decreased cell viability in NRK52E cells. Conversely, in the presence of PD128907, the increased lactate dehydrogenase release and decreased cell viability were reversed.

CONCLUSIONS

These results suggest that activation of D3R, by decreasing Gα12-induced renal damage, may exert a protective effect from I/R injury.

Pancreatic L-Glutamine Administration Protects Pig Islets From Cold Ischemic Injury and Increases Resistance Toward Inflammatory Mediators

The isolation and transplantation of porcine islets represent a future option for the treatment of type 1 diabetic patients. Stringent product release criteria and limited availability of transgenic and specific pathogen-free pigs will essentially require processing of explanted pig pancreata in specialized, possibly remote isolation facilities, whereby pancreata are exposed to cold ischemia due to prolonged tissue transit time. In the present study we investigated whether pancreas oxygenation can be efficiently combined with an antioxidant strategy utilizing intraductal L-glutamine administration. Pig pancreata were intraductally perfused after retrieval and after cold storage in oxygen-precharged perfluorohexyloctane utilizing University of Wisconsin solution supplemented with (n = 16) or without (n = 14) 5 mmol/L L-glutamine. After isolation purified islets were subjected to extensive quality assessment. Islet recovery postpurification was significantly higher in glutamine-treated pancreata (77.0 ± 3.3% vs. 60.3 ± 6.0%, p < 0.05). Glutamine administration increased intraislet content of reduced glutathione (117.8 ± 16.5 vs. 15.9 ± 2.8 ng/ng protein, p < 0.001) associated with increased islet recovery after culture (65.8 ± 12.1% vs. 40.3 ± 11.7%, p < 0.05), enhanced glucose stimulation index (1.82 ± 0.16 vs. 1.38 ± 0.10, p < 0.05), and improved posttransplant function in diabetic nude mice (p < 0.05). Furthermore, intraductally administered glutamine increased pig islet resistance toward reactive oxygen species, nitric oxide, and high-dose proinflammatory cytokines. The present study demonstrates that quality and function of pig islets exposed to warm and cold ischemia can significantly be improved using intraductal l-glutamine administration. As the efficiency of the intraductal route may be inferior compared to intravascular administration further studies should aim on assessment of l-glutamine as supplement for pancreas perfusion during organ procurement.

Protective activity of Dendropanax morbifera against cisplatin-induced acute kidney injury

BACKGROUND/AIMS

Drug-induced acute kidney injury (AKI) has been a severe threat to hospitalized patients, raising the urgent needs to develop strategies to reduce AKI. We investigated the protective activity of Dendropanax morbifera (DP), a medicinal plant which has been widely used to treat infectious and pain diseases, on acute kidney injury (AKI) using cisplatin-induced nephropathic models.

METHODS

Both in vitro renal tubular cells (NRK-52E) and in vivo rat models were used to demonstrate the nephroprotective effect of DP.

RESULTS

Methanolic extract from DP significantly reduced cisplatin-induced toxicity in renal tubular cells. Through successive liquid extraction, the extract of DP was separated into n-hexane, CHCl3, EtOAc, n-BuOH, and H2O fractions. Among these, the CHCl3 fraction (DPCF) was found to be most potent. The protective activity of DPCF was found to be mediated through anti-oxidant, mitochondrial protective, and anti-apoptotic activities. In in vivo rat models of AKI, treatment with DPCF significantly reversed the cisplatin-induced increase in blood urea nitrogen and serum creatinine and histopathologic damage, recovered the level of anti-oxidant enzymes, and inhibited renal apoptosis.

CONCLUSION

We demonstrated that DP extracts decreased cisplatin-induced renal toxicity, indicating its potential to ameliorate drug-associated acute kidney damage.

Peroxynitrite induced mitochondrial biogenesis following MnSOD knockdown in normal rat kidney (NRK) cells

Superoxide is widely regarded as the primary reactive oxygen species (ROS) which initiates downstream oxidative stress. Increased oxidative stress contributes, in part, to many disease conditions such as cancer, atherosclerosis, ischemia/reperfusion, diabetes, aging, and neurodegeneration. Manganese superoxide dismutase (MnSOD) catalyzes the dismutation of superoxide into hydrogen peroxide which can then be further detoxified by other antioxidant enzymes. MnSOD is critical in maintaining the normal function of mitochondria, thus its inactivation is thought to lead to compromised mitochondria. Previously, our laboratory observed increased mitochondrial biogenesis in a novel kidney-specific MnSOD knockout mouse. The current study used transient siRNA mediated MnSOD knockdown of normal rat kidney (NRK) cells as the in vitro model, and confirmed functional mitochondrial biogenesis evidenced by increased PGC1α expression, mitochondrial DNA copy numbers and integrity, electron transport chain protein CORE II, mitochondrial mass, oxygen consumption rate, and overall ATP production. Further mechanistic studies using mitoquinone (MitoQ), a mitochondria-targeted antioxidant and L-NAME, a nitric oxide synthase (NOS) inhibitor demonstrated that peroxynitrite (at low micromolar levels) induced mitochondrial biogenesis. These findings provide the first evidence that low levels of peroxynitrite can initiate a protective signaling cascade involving mitochondrial biogenesis which may help to restore mitochondrial function following transient MnSOD inactivation.

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MnSOD knockdown in NRK cells results in a transient loss of MnSOD activity, increased nitrotyrosine and mitochondrial superoxide.

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MnSOD knockdown in NRK cells results in a transient induction of mitochondrial biogenesis.

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Nitric oxide synthase inhibition and Mitoquinone blocks mitochondrial biogenesis after MnSOD knockdown.

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Low doses of peroxynitrite induce biogenesis in NRK cells.

Current state of pancreas preservation and implications for DCD pancreas transplantation

One of the main factors limiting potential uptake of pancreas transplantation, particularly in the United Kingdom, is the shortage of grafts. There has therefore been a recent expansion, particularly in the United Kingdom, in the utilization of grafts from donation after cardiac death (DCD) donors. These grafts are subjected to a greater ischemic insult and are arguably at higher risk of poor functional outcome. Although conventional preservation techniques may be adequate for donation after brain death (DBD) and low-risk DCD pancreases, as the number of DCD pancreas transplants increase and the threshold for rejecting organs decreases, the importance of optimal preservation techniques is going to increase. Over recent years, there have been significant advances in preservation techniques for DCD kidneys, improving the outcome of these marginal grafts. However, the use of such techniques for pancreas preservation is extremely limited and mainly historical. This overview describes the background and results of the established method of pancreas preservation for DBD, namely, cold static storage, and describes the use of the two-layer method. It also reviews pulsatile machine perfusion and normothermic perfusion for pancreas preservation techniques, which have shown promise in the preservation of DCD kidney grafts. The use of these techniques in pancreas preservation is predominantly historical but warrants reevaluation as to the feasibility of applying these techniques to DCD pancreas grafts not only for preservation but also for viability assessment. Further areas for development of pancreas preservation are discussed.

A review on the role of quinones in renal disorders

Quinones are electron and proton carriers that play a primary role in the aerobic metabolism of virtually every cell in nature. Most physiological quinones are benzoquinones. They undergo highly regulated redox reactions in the mitochondria, Golgi apparatus, plasma membrane and endoplasmic reticulum. Important consequences of these electron transfer reactions are the production of and protection against reactive oxygen species (ROS). Quinones have been extensively studied for both their cytotoxic as well as cellular protective properties and they have been particularly useful in rational drug design. The role of quinones in medicine is explored in this literature review with a particular focus on renal diseases. Due to their high basal metabolism and detoxification role, the kidneys are particularly sensitive to oxidative stress. Regardless of the underlying etiology, ROS plays an important role in both acute kidney injury (AKI) and chronic kidney diseases (CKD). Depending on the oxidative state of the kidney, quinones can be nephrotoxoic or nephro-protective. Many factors play a role in the interaction between quinones and the kidney and the consequences of this are just beginning to be explored.

MitoQ blunts mitochondrial and renal damage during cold preservation of porcine kidneys

Cold preservation has greatly facilitated the use of cadaveric kidneys for transplantation but damage occurs during the preservation episode. It is well established that oxidant production increases during cold renal preservation and mitochondria are a key target for injury. Our laboratory has demonstrated that cold storage of renal cells and rat kidneys leads to increased mitochondrial superoxide levels and mitochondrial electron transport chain damage, and that addition of Mitoquinone (MitoQ) to the preservation solutions blunted this injury. In order to better translate animal studies, the inclusion of large animal models is necessary to develop safe preclinical protocols. Therefore, we tested the hypothesis that addition of MitoQ to cold storage solution preserves mitochondrial function by decreasing oxidative stress, leading to less renal tubular damage during cold preservation of porcine kidneys employing a standard criteria donor model. Results showed that cold storage significantly induced oxidative stress (nitrotyrosine), renal tubular damage, and cell death. Using High Resolution Respirometry and fresh porcine kidney biopsies to assess mitochondrial function we showed that MitoQ significantly improved complex II/III respiration of the electron transport chain following 24 hours of cold storage. In addition, MitoQ blunted oxidative stress, renal tubular damage, and cell death after 48 hours. These results suggested that MitoQ decreased oxidative stress, tubular damage and cell death by improving mitochondrial function during cold storage. Therefore this compound should be considered as an integral part of organ preservation solution prior to transplantation.

Oxygen-charged HTK-F6H8 emulsion reduces ischemia-reperfusion injury in kidneys from brain-dead pigs

BACKGROUND

Prolonged cold ischemia is frequently associated with a greater risk of delayed graft function and enhanced graft failure. We hypothesized that media, combining a high oxygen-dissolving capacity with specific qualities of organ preservation solutions, would be more efficient in reducing immediate ischemia-reperfusion injury from organs stored long term compared with standard preservation media.

METHODS

Kidneys retrieved from brain-dead pigs were flushed using either cold histidine-tryptophan-ketoglutarate (HTK) or oxygen-precharged emulsion composed of 75% HTK and 25% perfluorohexyloctane. After 18 h of cold ischemia the kidneys were transplanted into allogeneic recipients and assessed for adenosine triphosphate content, morphology, and expression of genes related to hypoxia, environmental stress, inflammation, and apoptosis.

RESULTS

Compared with HTK-flushed kidneys, organs preserved using oxygen-precharged HTK-perfluorohexyloctane emulsion had increased elevated adenosine triphosphate content and a significantly lower gene expression of hypoxia inducible factor-1α, vascular endothelial growth factor, interleukin-1α, tumor necrosis factor-α, interferon-α, JNK-1, p38, cytochrome-c, Bax, caspase-8, and caspase-3 at all time points assessed. In contrast, the mRNA expression of Bcl-2 was significantly increased.

CONCLUSIONS

The present study has demonstrated that in brain-dead pigs the perfusion of kidneys with oxygen-precharged HTK-perfluorohexyloctane emulsion results in significantly reduced inflammation, hypoxic injury, and apoptosis and cellular integrity and energy content are well maintained. Histologic examination revealed less tubular, vascular, and glomerular changes in the emulsion-perfused tissue compared with the HTK-perfused counterparts. The concept of perfusing organs with oxygen-precharged emulsion based on organ preservation media represents an efficient alternative for improved organ preservation.

Oxygenated kidney preservation techniques

Improving preservation techniques to minimize injury is of particular importance in organs from marginal donors. Since the introduction of transplantation and routine use of hypothermic temperatures for kidney preservation, there has been much debate on whether it is necessary to add oxygen to support the low level of metabolism under these conditions. Supplementing the kidney with oxygen during hypothermic preservation is not common practice. However, there is evidence to support its application. Oxygen can be added by various techniques such as retrograde persufflation whereby filtered and humidified oxygen is bubbled through the vasculature; under hyperbaric conditions using specialized pressurized chambers; during hypothermic machine perfusion; with the addition of oxygen carriers; and under normothermic conditions. Evidence suggests that oxygenation is particularly beneficial in restoring cellular levels of adenosine triphosphate after kidneys have been subjected to warm or cold ischemic injury. However, under normal conditions, the benefits are less convincing, but the evidence is insufficient to draw any conclusions. This overview explores the ways in which oxygen can be administered during preservation in experimental and clinical models of kidney transplantation.

Superoxide dismutase 3 limits collagen-induced arthritis in the absence of phagocyte oxidative burst

Extracellular superoxide dismutase (SOD3), an enzyme mediating dismutation of superoxide into hydrogen peroxide, has been shown to reduce inflammation by inhibiting macrophage migration into injured tissues. In inflamed tissues, superoxide is produced by the phagocytic NOX2 complex, which consists of the catalytic subunit NOX2 and several regulatory subunits (e.g., NCF1). To analyze whether SOD3 can regulate inflammation in the absence of functional NOX2 complex, we injected an adenoviral vector overexpressing SOD3 directly into the arthritic paws of Ncf1^∗/∗ mice with collagen-induced arthritis. SOD3 reduced arthritis severity in both oxidative burst-deficient Ncf1^∗/∗ mice and also in wild-type mice. The NOX2 complex independent anti-inflammatory effect of SOD3 was further characterized in peritonitis, and SOD3 was found to reduce macrophage infiltration independently of NOX2 complex functionality. We conclude that the SOD3-mediated anti-inflammatory effect on arthritis and peritonitis operates independently of NOX2 complex derived oxidative burst.

Role of mitochondrial oxidants in an in vitro model of sepsis-induced renal injury

Oxidative stress has been implicated to play a major role in multiorgan dysfunction during sepsis. To study the mechanism of oxidant generation in acute kidney injury (AKI) during sepsis, we developed an in vitro model of sepsis using primary cultures of mouse cortical tubular epithelial cells exposed to serum (2.5-10%) collected from mice at 4 h after induction of sepsis by cecal ligation and puncture (CLP) or Sham (no sepsis). CLP serum produced a concentration-dependent increase in nitric oxide (NO) (nitrate + nitrite) release at 6 h and cytotoxicity (lactate dehydrogenase release) at 18 h compared with Sham serum treatment. Before cytotoxicity there was a decrease in mitochondrial membrane potential, which was followed by increased superoxide and peroxynitrite levels compared with Sham serum. The role of oxidants was evaluated by using the superoxide dismutase mimetic and peroxynitrite scavenger manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin tetratosylate hydroxide (MnTmPyP). MnTmPyP (10-100 μM) produced a concentration-dependent preservation of ATP and protection against cytotoxicity. MnTmPyP blocked mitochondrial superoxide and peroxynitrite generation produced by CLP serum but had no effect on NO levels. Although MnTmPyP did not block the initial CLP serum-induced fall in mitochondrial membrane potential, it allowed mitochondrial membrane potential to recover. Data from this in vitro model suggest a time-dependent generation of mitochondrial oxidants, mitochondrial dysfunction, and renal tubular epithelial cell injury and support the therapeutic potential of manganese porphyrin compounds in preventing sepsis-induced AKI.

Generation and characterization of a novel kidney-specific manganese superoxide dismutase knockout mouse

Inactivation of manganese superoxide dismutase (MnSOD), a mitochondrial antioxidant, has been associated with renal disorders and often results in detrimental downstream events that are mechanistically not clear. Development of an animal model that exhibits kidney-specific deficiency of MnSOD would be extremely beneficial in exploring the downstream events that occur following MnSOD inactivation. Using Cre-Lox recombination technology, kidney-specific MnSOD deficient mice (both 100% and 50%) were generated that exhibited low expression of MnSOD in discrete renal cell types and reduced enzymatic activity within the kidney. These kidney-specific 100% KO mice possessed a normal life-span, although it was interesting that the mice were smaller. Consistent with the important role in scavenging superoxide radicals, the kidney-specific KO mice showed a significant increase in oxidative stress (tyrosine nitration) in a gene-dose dependent manner. In addition, loss of MnSOD resulted in mild renal damage (tubular dilation and cell swelling). Hence, this novel mouse model will aid in determining the specific role (local and/or systemic) governed by MnSOD within certain kidney cells. Moreover, these mice will serve as a powerful tool to explore molecular mechanisms that occur downstream of MnSOD inactivation in renal disorders or possibly in other pathologies that rely on normal renal function.

The mitochondria-targeted antioxidant mitoquinone protects against cold storage injury of renal tubular cells and rat kidneys

The majority of kidneys used for transplantation are obtained from deceased donors. These kidneys must undergo cold preservation/storage before transplantation to preserve tissue quality and allow time for recipient selection and transport. However, cold storage (CS) can result in tissue injury, kidney discardment, or long-term renal dysfunction after transplantation. We have previously determined mitochondrial superoxide and other downstream oxidants to be important signaling molecules that contribute to CS plus rewarming (RW) injury of rat renal proximal tubular cells. Thus, this study's purpose was to determine whether adding mitoquinone (MitoQ), a mitochondria-targeted antioxidant, to University of Wisconsin (UW) preservation solution could offer protection against CS injury. CS was initiated by placing renal cells or isolated rat kidneys in UW solution alone (4 h at 4°C) or UW solution containing MitoQ or its control compound, decyltriphenylphosphonium bromide (DecylTPP) (1 μM in vitro; 100 μM ex vivo). Oxidant production, mitochondrial function, cell viability, and alterations in renal morphology were assessed after CS exposure. CS induced a 2- to 3-fold increase in mitochondrial superoxide generation and tyrosine nitration, partial inactivation of mitochondrial complexes, and a significant increase in cell death and/or renal damage. MitoQ treatment decreased oxidant production ~2-fold, completely prevented mitochondrial dysfunction, and significantly improved cell viability and/or renal morphology, whereas DecylTPP treatment did not offer any protection. These findings implicate that MitoQ could potentially be of therapeutic use for reducing organ preservation damage and kidney discardment and/or possibly improving renal function after transplantation.