Minimal physiologic temperature variations during renal ischemia alter functional and morphologic outcome

Anaesthesia-Induced Transcriptomic Changes in the Context of Renal Ischemia Uncovered by the Use of a Novel Clamping Device

Ischemia is a common cause of acute kidney injury worldwide, frequently occurring in patients undergoing cardiac surgery or admitted to the intensive care unit (ICU). Thus, ischemia-reperfusion injury (IRI) remains one of the main experimental models for the study of kidney diseases. However, the classical technique, based on non-traumatic surgical clamps, suffers from several limitations. It does not allow the induction of multiple episodes of acute kidney injury (AKI) in the same animal, which would be relevant from a human perspective. It also requires a deep and long sedation, raising the question of potential anaesthesia-related biases. We designed a vascular occluding device that can be activated remotely in conscious mice. We first assessed the intensity and the reproducibility of the acute kidney injury induced by this new device. We finally investigated the role played by the anaesthesia in the IRI models at the histological, functional and transcriptomic levels. We showed that this technique allows the rapid induction of renal ischemia in a repeatable and reproducible manner, breaking several classical limitations. In addition, we used its unique specificities to highlight the renal protective effect conferred by the anaesthesia, related to the mitigation of the IRI transcriptomic program.

Hypothermia and kidney: a focus on ischaemia-reperfusion injury

Cellular damage after reperfusion of ischaemic tissue is defined as ischaemia–reperfusion injury (IRI). Hypothermia is able to decrease oxygen consumption, preventing a rapid loss of mitochondrial activity. However, even though cooling can help to decrease the deleterious effects of ischaemia, the consequences are not exclusively beneficial, such that hypothermic storage is a compromise between benefits and harm. The present review details the relationship between renal IRI and hypothermia, describing the pathophysiology of IRI and hypothermic protection through experimental evidence. Although experimental models of renal IRI are a valuable tool for understanding the pathophysiology of renal ischaemia–reperfusion, the clinical transfer of experimental results has several limitations, particularly because of anatomical and physiological differences. In this review limitations of animal models but also hypothermia as a strategy to protect the kidney from IRI are discussed. We also attempt to describe three clinical scenarios where hypothermia is used in clinical settings of IRI: transplantation, deceased donors and post-cardiac arrest.

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.

Carbamylated erythropoietin-FC fusion protein and recombinant human erythropoietin during porcine kidney ischemia/reperfusion injury

PURPOSE

To test the hypothesis that a carbamylated EPO-FC fusion protein (cEPO-FC) or recombinant human erythropoietin (rhEPO) would protect against kidney ischemia/reperfusion (I/R) injury in pigs with atherosclerosis.

METHODS

Anesthetized and mechanically ventilated animals received cEPO-FC (50 μg kg(-1)), rhEPO (5,000 IU kg(-1)), or vehicle (n = 9 per group) prior to 120 min of aortic occlusion and over 4 h of reperfusion. During aortic occlusion, mean arterial pressure (MAP) was maintained at 80-120 % of baseline values by esmolol, nitroglycerin, and ATP. During reperfusion, noradrenaline was titrated to keep MAP at pre-ischemic levels. Blood creatinine and neutrophil gelatinase-associated lipocalin (NGAL) levels, creatinine clearance, fractional Na(+) excretion, and HE and PAS staining were used to assess kidney function and histological damage. Plasma interleukin-6, tumor necrosis factor-α, nitrate + nitrite and 8-isoprostane levels were measured to assess systemic inflammation, and nitrosative and oxidative stress.

RESULTS

I/R caused acute kidney injury with reduced creatinine clearance, increased fractional Na(+) excretion and NGAL levels, moderate to severe glomerular and tubular damage and apoptosis, systemic inflammation and oxidative and nitrosative stress, but there were no differences between the treatment groups. Pre-ischemia nitrate + nitrite and 8-isoprostanes levels were lower and higher, respectively, than in healthy animals of a previous study, and immune histochemistry showed higher endothelial nitric oxide synthase and lower EPO receptor expression in pre-ischemia kidney biopsies than in biopsies from healthy animals.

CONCLUSIONS

In swine with atherosclerosis, rhEPO and cEPO-FC failed to attenuate prolonged ischemia-induced kidney injury within an 8-h reperfusion period, possibly due to reduced EPO receptor expression resulting from pre-existing oxidative stress and/or reduced NO release.

Ischaemic preconditioning protects the rat kidney from reperfusion injury

OBJECTIVE

To examine the possible role of ischaemic preconditioning (IPC), an adaptive pathophysiological phenomenon that increases tolerance to ischaemia-reperfusion (I-R) injury, in renal protection when rats are presented with an I-R challenge.

MATERIALS AND METHODS

Female Wistar rats (n=36) were divided randomly into four groups: (A) sham-operated controls; (B) IPC only; (C) renal ischaemia (RI) only; and (D) IPC+RI. The left kidney in groups B and D was preconditioned with four cycles of renal artery occlusion lasting 4 min, each occlusion separated by 11 min of reperfusion. The ischaemic insult, applied in groups C and D, comprised 40 min of sustained left renal artery occlusion. In Group D, the IPC cycle was completed 5 min before the start of the ischaemic insult. Differential left renal function was calculated by 99mTc-labelled dimercaptosuccinic acid scintigraphy at 0, 2 and 9 days after treatment, and expressed as a percentage of the total renal uptake.

RESULTS

The mean (sem) maximum decrease in left renal function, to 14.5 (4.3)% of the total, occurred on day 2 in Group C. The equivalent value in Group D showed relative preservation of function, at 36.0 (3.5)% (P=0.001 compared with Group C). The mean left renal function improved by day 9, to 39.6 (6.7)% (Group C) and 48.6 (1.5)% (Group D). The mean left renal function in Group B (50.5-53.9%) did not differ from that in controls (49.4-51.4%).

CONCLUSION

An IPC regimen applied 5 min before RI in the rat significantly protects it from the functional impairment associated with ischaemia and reperfusion.

Normothermic renal artery perfusion: a comparison of perfusates

Hypothermia and preservative perfusates have been used to decrease ischemic renal injury. This study was performed to identify the preservative function of perfusates independent of the effects of hypothermia. Rats underwent 45 minutes of renal ischemia. Rectal and renal parenchyma temperatures were monitored and maintained within 1 degree C of normal. Perfusates were University of Wisconsin solution (UW), Euro-Collins solution, normal saline solution, and Ringer's lactate solution. A nonperfused ischemic control and a nonischemic control group were also evaluated. Parameters evaluated included serum creatinine and blood urea nitrogen levels, renal ischemic injury grade, renal weight, and gross appearance of the injured kidney. Rats treated with UW solution were found to have a significantly lower creatinine, blood urea nitrogen, and injury grade than the other three perfused groups. The external gross appearance of the UW-treated kidneys was normal, whereas that of the other groups demonstrated moderate to severe injury. Although the mean right/left renal weight difference of the UW-treated group was lower than that of the other three groups, this was not statistically significant. Under normothermic conditions in rats, UW solution affords significant renal protection from ischemia. Euro-Collins, normal saline, and Ringer's lactate solutions display no significant protective effect.

Cardiopulmonary-cerebral resuscitation with 100% oxygen exacerbates neurological dysfunction following nine minutes of normothermic cardiac arrest in dogs

This study investigated the effects of normoxic (FIO2 = 0.21), hyperoxic (FIO2 = 1.0), and hyperoxic (FIO2 = 1.0) plus antioxidant pretreatment (tirilazad mesylate) [corrected] resuscitation on neurologic outcome following 9 min of normothermic (39 +/- 1.0 degrees C) cardiac arrest. Physiologic variables including arterial blood gases and neurologic outcome, which was assessed using a standardized scoring system, were followed over a 24-h period following resuscitation from cardiac arrest. Hyperoxically resuscitated dogs sustained significantly worse neurological deficit at 12 and 24 h (mean scores: 39 +/- 3 and 49 +/- 8, respectively) than did antioxidant pretreated hyperoxically resuscitated dogs (mean scores: 22 +/- 1, P = 0.0007 and 22 +/- 1, P = 0.004, respectively) and normoxically resuscitated dogs (mean scores: 28 +/- 4, P = 0.025 and 33 +/- 8, P = 0.041 respectively). These data suggest that oxidant injury has a major role in central nervous system dysfunction following successful resuscitation from 9 min of cardiac arrest. Also, resuscitation from cardiac arrest with hyperoxic FIO2's may contribute to and further exacerbate neurologic dysfunction.