Acute ischemia/reperfusion injury after isogeneic kidney transplantation is mitigated in a rat model of chronic renal failure

Dissecting recipient from donor contribution in experimental kidney transplantation: focus on endothelial proliferation and inflammation

Kidney transplantation (Tx) is considered the only definite treatment for end-stage kidney disease (ESKD) patients. The increasing prevalence of ESKD has necessitated the introduction of transplantation with kidneys from suboptimal donors. There is, however, still a lack of fundamental and longitudinal research on suboptimal kidney transplants. Specifically, there is a demand for accurate pre-Tx predictors of donor kidney function and injury to predict post-Tx outcome. In the present study, we combine rat models of chronic kidney disease (CKD) and renal Tx to dissect the effects of healthy and CKD renal grafts on healthy and CKD recipients. We show that renal function at 6 weeks post-Tx is exclusively determined by donor graft quality. Using cell tracking within enhanced green fluorescent protein-positive (eGFP⁺) recipients, we furthermore show that most inflammatory cells within the donor kidney originate from the donor. Oxidative and vascular extra-renal damage were, in contrast, determined by the recipient. Post- versus pre-Tx evaluation of grafts showed an increase in glomerular and peritubular capillary rarefaction in healthy but not CKD grafts within a CKD environment. Proliferation of glomerular endothelium was similar in all groups, and influx of eGFP⁺ recipient-derived cells occurred irrespective of graft or recipient status. Glomerular and peritubular capillary rarefaction, severity of inflammation and macrophage subtype data post-Tx were, however, determined by more complicated effects, warranting further study. Our experimental model could help to further distinguish graft from recipient environment effects, leading to new strategies to improve graft survival of suboptimal Tx kidneys.

This article has an associated First Person interview with the first author of the paper.

Summary: Using experimental kidney transplantation, we dissected donor graft from recipient environment effects, focusing on the endothelium and inflammation. These results can direct strategies to improve graft survival after suboptimal transplantation.

High Endogenous Accumulation of ω-3 Polyunsaturated Fatty Acids Protect against Ischemia-Reperfusion Renal Injury through AMPK-Mediated Autophagy in Fat-1 Mice

Regulated autophagy is involved in the repair of renal ischemia-reperfusion injury (IRI). Fat-1 transgenic mice produce ω3-Polyunsaturated fatty acids (ω3-PUFAs) from ω6-Polyunsaturated fatty acids (ω6-PUFAs) without a dietary ω3-PUFAs supplement, leading to a high accumulation of omega-3 in various tissues. ω3-PUFAs show protective effects against various renal injuries and it has recently been reported that ω3-PUFAs regulate autophagy. We assessed whether ω3-PUFAs attenuated IR-induced acute kidney injury (AKI) and evaluated its associated mechanisms. C57Bl/6 background fat-1 mice and wild-type mice (wt) were divided into four groups: wt sham (n = 10), fat-1 sham (n = 10), wt IRI (reperfusion 35 min after clamping both the renal artery and vein; n = 15), and fat-1 IRI (n = 15). Kidneys and blood were harvested 24 h after IRI and renal histological and molecular data were collected. The kidneys of fat-1 mice showed better renal cell survival, renal function, and pathological damage than those of wt mice after IRI. In addition, fat-1 mice showed less oxidative stress and autophagy impairment; greater amounts of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II, Beclin-1, and Atg7; lower amounts of p62; and, higher levels of renal cathepsin D and ATP6E than wt kidneys. They also showed more adenosine monophosphate-activated protein kinase (AMPK) activation, which resulted in the inhibition of phosphorylation of the mammalian target of rapamycin (mTOR). Collectively, ω3-PUFAs in fat-1 mice contributed to AMPK mediated autophagy activation, leading to a renoprotective response.

Dapagliflozin, SGLT2 Inhibitor, Attenuates Renal Ischemia-Reperfusion Injury

Dapagliflozin, a new type of drug used to treat diabetes mellitus (DM), is a sodium/glucose cotransporter 2 (SGLT2) inhibitor. Although some studies showed that SGLT2 inhibition attenuated reactive oxygen generation in diabetic kidney the role of SGLT2 inhibition is unknown. We evaluated whether SLT2 inhibition has renoprotective effects in ischemia-reperfusion (IR) models. We evaluated whether dapagliflozin reduces renal damage in IR mice model. In addition, hypoxic HK2 cells were treated with or without SGLT2 inhibitor to investigate cell survival, the apoptosis signal pathway, and the induction of hypoxia-inducible factor 1 (HIF1) and associated proteins. Dapagliflozin improved renal function. Dapagliflozin reduced renal expression of Bax, renal tubule injury and TUNEL-positive cells and increased renal expression of HIF1 in IR-injured mice. HIF1 inhibition by albendazole negated the renoprotective effects of dapagliflozin treatment in IR-injured mice. In vitro, dapagliflozin increased the expression of HIF1, AMP-activated protein kinase (AMPK), and ERK and increased cell survival of hypoxic HK2 cells in a dose-dependent manner. In conclusion, dapagliflozin attenuates renal IR injury. HIF1 induction by dapagliflozin may play a role in renoprotection against renal IR injury.

Cytoprotective Actions of FTY720 Modulate Severe Preservation Reperfusion Injury in Rat Renal Transplants

BACKGROUND

Fingolimod (FTY720) is a potent agonist of sphingosine 1 phosphate receptors and thereby interferes with lymphocyte trafficking. We previously showed that FTY720 protects from mild preservation reperfusion injury induced by 4 hr of cold ischemia. The purpose of this study was to explore the role of FTY720 in ischemic injury and regeneration using a clinically relevant rat renal transplant model with 24 hr of cold ischemia.

METHODS

Donor kidneys were cold stored in the University of Wisconsin solution for 24 hr before transplantation into bilaterally nephrectomized syngeneic recipients (n=6 per group), which received 0.5 mg/kg/d FTY720 or vehicle through oral gavage. Grafts were harvested 2 or 7 days posttransplantation. Renal tissue was examined histologically, stained for apoptosis, proliferation, inflammatory cell infiltrates, and studied for transforming growth factor-beta, and tumor necrosis factor-alpha expression. Rat proximal tubular cells were incubated with 0.1 to 30 micromol/L of phosphorylated FTY720 to test for in vitro cytopathic effects.

RESULTS

FTY720 induced peripheral lymphopenia and significantly reduced intragraft CD3 and ED1 infiltrates. Acute tubular damage scores and graft function were not influenced by FTY720. Tubular apoptosis was significantly reduced, whereas the number of proliferating cell nuclear antigen-positive tubular cells were markedly increased. FTY720 attenuated renal tumor necrosis factor-alpha and transforming growth factor-beta expression. In vitro, pharmacologic concentrations up to 1 micromol/L of phosphorylated FTY720 did not affect tubular cell viability.

CONCLUSION

FTY720 confers tubular epithelial protection in the presence of severe preservation reperfusion injury. Beneficial effects may in part be due to reduction in cell-mediated immune mechanisms. Furthermore, FTY720 could be helpful in patients with delayed graft function.

Duration of dialysis pretransplantation is an important risk factor for delayed recovery of renal function following deceased donor kidney transplantation

Delayed graft function (DGF) is a common problem in kidney transplantation and is associated with adverse graft outcomes and increased cost of care. The purpose of this study was to determine if the duration of dialysis increases the risk of DGF. All primary deceased donor renal transplants between January 2000 and December 2003 were identified in the Organ Procurement and Transplant Network database. Two separate definitions of DGF were used: dialysis in the first week post-transplant (DPT) and creatinine drop of < 25% in the first 24 h or slow graft function (SGF). The rate of DPT and SGF increased from 5.7% and 34.4%, respectively, for pre-emptively transplanted patients, to 32% and 49.9% for patients who had been on dialysis for 6 or more years. When compared to pre-emptive transplantation, increasing duration of dialysis increased the adjusted risk of both DPT and SGF (OR 6.64 (95% CI 5.49-8.03) and OR 1.76 (95% CI 1.56-2.00) for patients on dialysis for 6 or more years, for DPT and SGF, respectively. A strong association between duration of dialysis and DGF exists, and investigations into the mechanisms by which dialysis influences DGF may lead to useful interventions to limit this complication.

Dual response of animals with chronic cyclosporine nephrotoxicity to an acute ischemic injury

Normal kidneys regenerate after acute injury with little development of chronic fibrosis. However, the long-term effects of an acute injury in kidneys with established chronic toxicity induced by cyclosporine (CsA) are not entirely clear. To study the consequences of an ischemia and reperfusion (IR) injury in long-term CsA-treated rats, male Wistar rats (250-300 g) were treated daily with CsA (10 mg/kg) or vehicle (olive oil 1 mL/kg) for 28 days. On day 21, ischemia was performed by clamping the renal vessel for 1 hour. Blood samples were collected on days 0 and 21 (before IR) as well as days 22 and 28. On day 28, the kidneys were collected to examine the mRNA expression of MCP-1 by real-time PCR. For renal function, serum creatinine levels were measured. Twenty-four hours after reperfusion, long-term CsA-treated animals showed better renal function compared with the control group, as demonstrated by serum creatinine levels: 2.2 +/- 0.13 mg/dL vs 2.9 +/- 0.18 mg/dL, respectively (P < .05). However, 1 week after IR, the renal function was worse among the long-term CsA-treated group than the controls: 1.16 +/- 0.08 mg/dL vs 0.8 +/- 0.09 mg/dL, respectively (P < .05). Interestingly, CsA treatment was associated with lower MCP-1 mRNA expression than that in the control group: mean MCP-1 mRNA expression 0.58 +/- 0.13 vs 1.02 +/- 0.12, respectively (P < .05). In conclusion, animals with chronic CsA nephrotoxicity were protected from an acute renal injury, possibly through decreased chemokine production, although at later time points, renal function was clearly impaired, probably by the acceleration of vasculopathy caused by nephrotoxicity.

Effect of mycophenolate mofetil on rat kidney grafts with prolonged cold preservation

The impact of mycophenolate mofetil (MMF) on initial renal transplant function is not well characterized. We tested how MMF may modulate graft function and survival in a syngeneic rat kidney transplantation model after prolonged cold preservation. Donor kidneys were preserved in University of Wisconsin for either 24 or 39 h prior to transplantation into nephrectomized rats. Recipients received MMF (20 mg/kg/day) or vehicle. Mycophenolic acid (MPA) blood concentrations were measured by high-performance liquid chromatography. The inflammatory response, tubular epithelial proliferation, and histologic damage 3 days post-transplantation were assessed microscopically. In the 24 h cold storage (c.s.) group serum-creatinine was measured. In the 39 h c.s. group 1-week recipient survival was determined. After 24 h of c.s., recipient survival was 100%. The number of T-cell infiltrates was low and not influenced by MMF, whereas renal ED1+ cell infiltration was significantly suppressed by MMF. Tubular cell proliferation was enhanced by MMF. Serum-creatinine levels and renal histology were comparable between MMF and vehicle-treated animals. In the 39 h c.s. group, recipient survival was 20% in MMF-treated vs 90% in vehicle-treated animals (P=0.001). MMF effectively suppressed inflammatory cell infiltration and inhibited tubular cell proliferation. MMF-induced structural damage was most striking in the renal papilla. In rat kidney grafts with moderate preservation injury (24 h c.s.), MMF, given at an immunosuppressive dose, showed predominantly antiinflammatory effects without compromising graft function. In grafts with severe preservation injury (39 h c.s.), MMF caused irreversible structural damage and inhibited tubular cell regeneration resulting in renal failure.