Deletrious effect of prolonged cold ischemia on renal function

Cold Storage Increases Albumin and Advanced Glycation-End Product-Albumin Levels in Kidney Transplants: A Possible Cause for Exacerbated Renal Damage

Prolonged cold storage (CS) of kidneys is associated with poor renal outcome after transplantation (Tx). We recently showed that in rats (Lewis), proteasome and renal function were severely compromised in kidney transplants subjected to CS (CS/Tx) as compared with those without CS exposure (autotransplanted [ATx]).

Physiological effects of altering oxygenation during kidney normothermic machine perfusion

Kidney normothermic machine perfusion (NMP) has historically used a 95% O₂-5% CO₂ gas mixture. Using a porcine model of organ retrieval, NMP, and reperfusion, we tested the hypothesis that reducing perfusate oxygenation ( PpO2 ) would be detrimental to renal function and cause injury. In the minimal ischemic injury experiment, kidneys sustained 10 min of warm ischemia and 2 h of static cold storage before 1 h of NMP with either 95%, 25%, or 12% O₂ with 5% CO₂ and N₂ balance. In the clinical injury experiment, kidneys with 10-min warm ischemia and 17-h static cold storage underwent 1-h NMP with the above gas combinations or 18-h static cold storage as a control. They were then reperfused with whole blood and 95% O₂ for 3 h. Overall, reducing PpO2 did not significantly influence renal function in either experiment. Furthermore, there were no differences in the injury markers urinary neutrophil gelatinase-associated lipocalin or tissue high-motility group box protein 1. In the minimal ischemic injury experiment, a PpO2 of 25% significantly reduced renal blood flow and increased vascular resistance. Oxygen delivery, consumption, and extraction (oxygen extraction ratio) were significantly greater at 95% PpO2 . In the clinical injury experiment, renal blood flow was significantly increased at 25% PpO2 and Na⁺ excretion decreased. At 95% PpO2 , the oxygen content and oxygen extraction ratio were significantly increased. During reperfusion, renal blood flow was significantly increased in the 25% group. The control group pH was significantly decreased compared with the 25% group. Our data suggest that reducing PpO2 during NMP does not have detrimental effects on renal function or markers of injury.

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.

Unilateral Renal Ischemia-Reperfusion as a Robust Model for Acute to Chronic Kidney Injury in Mice

Acute kidney injury (AKI) is an underestimated, yet important risk factor for development of chronic kidney disease (CKD). Even after initial total recovery of renal function, some patients develop progressive and persistent deterioration of renal function and these patients are more likely to progress to end-stage renal disease (ESRD). Animal models are indispensable for unravelling the mechanisms underlying this progression towards CKD and ESRD and for the development of new therapeutic strategies in its prevention or treatment. Ischemia (i.e. hypoperfusion after surgery, bleeding, dehydration, shock, or sepsis) is a major aetiology in human AKI, yet unilateral ischemia-reperfusion is a rarely used animal model for research on CKD and fibrosis. Here, we demonstrate in C57Bl/6J mice, by both histology and gene expression, that unilateral ischemia-reperfusion without contralateral nephrectomy is a very robust model to study the progression from acute renal injury to long-term tubulo-interstitial fibrosis, i.e. the histopathological hallmark of CKD. Furthermore, we report that the extent of renal fibrosis, in terms of Col I, TGFβ, CCN2 and CCN3 expression and collagen I immunostaining, increases with increasing body temperature during ischemia and ischemia-time. Thus, varying these two main determinants of ischemic injury allows tuning the extent of the long-term fibrotic outcome in this model. Finally, in order to cover the whole practical finesse of ischemia-reperfusion and allow model and data transfer, we provide a referenced overview on crucial technical issues (incl. anaesthesia, analgesia, and pre- and post-operative care) with the specific aim of putting starters in the right direction of implementing ischemia in their research and stimulate them, as well as the community, to have a critical view on ischemic literature data.

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.

Transgenic overexpression of CD39 protects against renal ischemia-reperfusion and transplant vascular injury

The vascular ectonucleotidases CD39[ENTPD1 (ectonucleoside triphosphate diphosphohydrolase-1), EC 3.6.1.5] and CD73[EC 3.1.3.5] generate adenosine from extracellular nucleotides. CD39 activity is critical in determining the response to ischemia-reperfusion injury (IRI), and CD39 null mice exhibit heightened sensitivity to renal IRI. Adenosine has multiple mechanisms of action in the vasculature including direct endothelial protection, antiinflammatory and antithrombotic effects and is protective in several models of IRI. Mice transgenic for human CD39 (hCD39) have increased capacity to generate adenosine. We therefore hypothesized that hCD39 transgenic mice would be protected from renal IRI. The overexpression of hCD39 conferred protection in a model of warm renal IRI, with reduced histological injury, less apoptosis and preserved serum creatinine and urea levels. Benefit was abrogated by pretreatment with an adenosine A2A receptor antagonist. Adoptive transfer experiments showed that expression of hCD39 on either the vasculature or circulating cells mitigated IRI. Furthermore, hCD39 transgenic kidneys transplanted into syngeneic recipients after prolonged cold storage performed significantly better and exhibited less histological injury than wild-type control grafts. Thus, systemic or local strategies to promote adenosine generation and signaling may have beneficial effects on warm and cold renal IRI, with implications for therapeutic application in clinical renal transplantation.

Effects of erythropoietin on ischaemia/reperfusion injury in a controlled nonheart beating donor kidney model

Erythropoietin (EPO) has been shown to have an anti-apoptotic action and has the potential to protect against ischaemia/reperfusion injury. This study investigated the effect of high dose EPO (5000 U), administered as a bolus at the onset of reperfusion and at the onset of cold storage in a model of controlled nonheart beating donors kidneys. Porcine kidneys(n = 6) were subjected to 10min warm ischaemia and preserved as follows: Group 1:16 h Cold storage +2 h Normothermic perfusion (16 h CS + 2 h NP) Group 2:16 h CS + 2 h NP + EPO given at the onset of reperfusion Group 3:18 h CS (static hypothermic storage) Group 4:18 h CS + EPO given at the onset of cold storage Haemodynamic and functional parameters were assessed during 3-h reperfusion using autologous blood. Renal blood flow improved in Groups 1 and 2 vs. Groups 3 and 4 though no difference was noted between Groups 3 and 4 (563 +/- 119 vs. 491 +/- 95 vs. 325 +/- 70 vs. 418 +/- 112, respectively; P = 0.012). Total urine output showed no difference between Groups (271 +/- 172 vs. 359 +/- 184 vs. 302 +/- 21 vs. 421 +/- 88; P = 0.576). Percentage serum creatinine fall at 3 h was significantly better in Groups 1 and 2 vs. Group 3 (64 +/- 17 vs. 60 +/- 11 vs. 44 +/- 13 vs. 52 +/- 8; P = 0.04). Fractional-excretion of sodium was significantly lower for Groups 1 and 2 vs. Group 3 and 4 (17 +/- 14 vs. 18 +/- 9 vs. 49 +/- 21 vs. 45 +/- 16 respectively; P = 0.002). There was significant improvement in oxygen consumption in Groups 2 vs. Groups 3 and 4 (P = 0.037) (39 +/- 10 vs. 46 +/- 10 vs. 24 +/- 12 vs. 24 +/- 7 respectively). EPO added at the time of reperfusion improved oxygen consumption when added to NP in comparison to static hypothermic storage but did not exert any other major benefits.

Effects of arterial pressure in an experimental isolated haemoperfused porcine kidney preservation system

Background

Normothermic preservation provides metabolic support to an ischaemically damaged organ before use as a kidney transplant. Optimal conditions for ex vivo preservation have not yet been established. This study examined the effects of arterial pressure on renal preservation using isolated haemoperfused kidneys.

Methods

An isolated organ preservation system, developed using cardiopulmonary bypass technology, was used to perfuse porcine kidneys with normothermic oxygenated blood. Groups of kidneys (n = 6) were perfused at a mean arterial pressure of 95, 75 or 55 mmHg.

Results

Kidneys perfused at the higher mean arterial pressures of 95 and 75 mmHg demonstrated improved renal function: mean(s.d.) area under the curve (AUC) for creatinine clearance 71(19) and 55(30) respectively versus 14(12) in the 55-mmHg group, P = 0·002; AUC for serum creatinine 938(140) and 1290(394) versus 2404(595), P = 0·003. The higher perfusion pressures were also associated with better acid–base homeostasis and improved renal haemodynamics.

Conclusion

Mean arterial pressures of either 95 or 75 mmHg were capable of sustaining physiological renal function, but kidneys in the 95-mmHg group demonstrated superior renal function overall.

An audit over 2 years’ practice of open and laparoscopic live-donor nephrectomy at renal transplant centres in the UK and Ireland

OBJECTIVE

To collate information on the practice of live-donor nephrectomy and compare this with the published British Transplantation Society (BTS) guidelines for best practice, using two questionnaires sent to all renal transplant centres in the UK and Ireland to cover practice for the years 2000 and 2002.

METHODS

A postal questionnaire was sent to all surgical kidney transplant consultants in the UK and Ireland, including questions on the practice of live-donor nephrectomy in the year 2000 (the questionnaire was sent in 2001) and 2002 (questionnaire sent in 2003).

RESULTS

All 28 centres responded fully for both years; 27 centres used live kidney donation in 2000, decreasing to 24 in 2002. Consultants reported 356 operations in 2000, representing 19% of all kidney transplants, and 403 in 2002, representing 23% of all kidney transplants. Three centres offered laparoscopic donor nephrectomy in 2000, and five did so in 2002. Most centres organize donor and recipient operations synchronously, and most have a consultant anaesthetist present for the donor procedure. There were variations in the use of analgesia and thromboprophylaxis, and in donor follow-up.

CONCLUSIONS

There is widespread application of live-donor nephrectomy in the UK but BTS guidelines are not closely followed. Minimal access donor nephrectomy is offered at a few centres but many have plans to introduce this into their practice.