[Ischemia-reperfusion. Preservation solution and hypothermic machine perfusion]. / Ischémie­reperfusion. Liquides de conservation et machines de perfusion en transplantation rénale.

AIMS: To describe ischemia-reperfusion mechanisms, the impact on kidney graft and strategies developed to minimize ischemia-reperfusion damages. MATERIAL AND METHODS: An exhaustive systematic review of the scientific literature was performed in the Medline database (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) using different associations of the following keywords: ischemia-reperfusion; organ preservation; hypothermic machine perfusion; renal transplantation. Publications obtained were selected based on methodology, language, date of publication and relevance. Prospective and retrospective studies, in English or French, review articles; meta-analysis and guidelines were selected and analyzed. This search found 1293 articles. After reading titles and abstracts, 88 were included in the text, based on their relevance. RESULTS: Ischemia-reperfusion injuries occur when blood supply of an organ is interrupted or drastically reduced. Ischemic damages started immediately after arterial clamping in donor, persist during cold ischemia time, and are increased after reperfusion because of increased oxygen levels, organ warming and recipient cell infiltration. Besides metabolic and biologic impact, IR induced dramatic immunologic impact through immunologic cells activation. CONCLUSIONS: Knowledge of IR mechanisms is crucial to improve organ storage strategies and to decreased impact of IR on long-term graft and patient survival. Hypothermic machine perfusion was associated with prolonged graft survival versus cold storage. Principles and results of hypothermic machine perfusion will be reported.

Mechanistic analysis of nonoxygenated hypothermic machine perfusion's protection on warm ischemic kidney uncovers greater eNOS phosphorylation and vasodilation.

Protection of endothelial cell function may explain the benefits of nonoxygenated hypothermic machine perfusion (MP) for marginal kidney preservation. However, this hypothesis remains to be tested with a preclinical model. We postulated that MP protects the nitric oxide (NO) signaling pathway, altered by static cold storage (CS), and improves renal circulation recovery compared to CS. The endothelium releases the vasodilator NO in response to flow via either increased endothelial NO synthase (eNOS) expression (KLF2-dependent) or activation of eNOS by phosphorylation (via Akt, PKA or AMPK). Using a porcine model of kidney transplantation, including 1 h of warm ischemia and preserved 24 h by CS or MP (n=5), we reported that MP did not alter the cortical levels of KLF2 and eNOS at the end of preservation, but significantly increased eNOS activating phosphorylation compared to CS. eNOS phosphorylation appeared AMPK-dependent and was concomitant to an increased NO-dependent vasodilation of renal arteries measured, ex situ, at the end of preservation. In vivo, laser Doppler showed that cortical microcirculation was improved at reperfusion in MP kidneys. In conclusion, we demonstrate for the first time, in a large-animal model, that MP protects the NO signaling pathway, confirming the value of MP for marginal kidney preservation.

Ischemia-reperfusion: From cell biology to acute kidney injury.

Ischemia reperfusion injury occurs in the kidney when blood supply is interrupted in clinical settings such as kidney transplantation or nephron sparing surgery for renal tumors. These lesions lead to acute kidney injury (AKI) a detrimental situation associated with impaired short-term allograft function (delayed graft function or primary non function) but also long-term transplant survival through the onset of chronic allograft nephropathy. The present review details the cellular and molecular consequences of ischemia reperfusion in a native kidney as well as in a kidney graft after cold ischemia time, giving a comprehensive description of biological pathways involved during the phase of ischemia and during the reperfusion period where the rapid return to normoxia leads to a large burst of reactive oxygen species along with a dramatic reduction in antioxidant defenses. This work also focuses on the distinct susceptibilities of kidney cells to ischemia (endothelial vs epithelial) and the outcome of acute kidney injury.

Does machine perfusion decrease ischemia reperfusion injury?

In 1990's, use of machine perfusion for organ preservation has been abandoned because of improvement of preservation solutions, efficient without perfusion, easy to use and cheaper. Since the last 15 years, a renewed interest for machine perfusion emerged based on studies performed on preclinical model and seems to make consensus in case of expanded criteria donors or deceased after cardiac death donations. We present relevant studies highlighted the efficiency of preservation with hypothermic machine perfusion compared to static cold storage. Machines for organ preservation being in constant evolution, we also summarized recent developments included direct oxygenation of the perfusat. Machine perfusion technology also enables organ reconditioning during the last hours of preservation through a short period of perfusion on hypothermia, subnormothermia or normothermia. We present significant or low advantages for machine perfusion against ischemia reperfusion injuries regarding at least one primary parameter: risk of DFG, organ function or graft survival.

Ischemic pre- and post-conditioning: current clinical applications.

Ischemic conditioning is a phenomenon through which short sequences of ischemia-reperfusion applied to an organ confer some degree of protection towards future ischemic insults. This phenomenon was first observed in the mid-1980s in cardiac surgery, and has been since widely studied in different settings. Different sort of ischemic conditioning exist: local vs remote, direct or pharmacological, and with different timeframes of protection. Ischemic conditioning seems especially suited to applications in transplantation since schedules of both cold and warm ischemia, as well as reperfusion, are carefully and easily controlled, and the benefits of protecting fragile organs against ischemia-reperfusion injuries might help widen the pool of possible grafts and ensure better graft function and survival. The pathways through which ischemic conditioning work are many, offering both preservation of cell energy, protection against oxidative stress, better blood flow to organs and protection against apoptosis. In the field of pharmacological conditioning, which tries to mimic the protective effects of traditional ischemic conditioning without the potential side-effects associated with vessel clamping, many common-use drugs including anesthetics have been shown to be effective. Significant results have been obtained in small animal models, but while ischemic conditioning is successfully used in cardiac surgery, studies in large animal models and human applications in liver and kidney transplantation are still inconclusive.

Contribution of large pig for renal ischemia-reperfusion and transplantation studies: the preclinical model.

Animal experimentation is necessary to characterize human diseases and design adequate therapeutic interventions. In renal transplantation research, the limited number of in vitro models involves a crucial role for in vivo models and particularly for the porcine model. Pig and human kidneys are anatomically similar (characterized by multilobular structure in contrast to rodent and dog kidneys unilobular). The human proximity of porcine physiology and immune systems provides a basic knowledge of graft recovery and inflammatory physiopathology through in vivo studies. In addition, pig large body size allows surgical procedures similar to humans, repeated collections of peripheral blood or renal biopsies making pigs ideal for medical training and for the assessment of preclinical technologies. However, its size is also its main drawback implying expensive housing. Nevertheless, pig models are relevant alternatives to primate models, offering promising perspectives with developments of transgenic modulation and marginal donor models facilitating data extrapolation to human conditions.

Indomethacin improves locomotor deficit and reduces brain concentrations of neuroinhibitory steroids in rats following portacaval anastomosis.

Hepatic encephalopathy (HE) is a neuropsychiatric complication of both acute and chronic liver failure characterized by progressive neuronal inhibition. Some neurosteroids are potent positive allosteric modulators of the gamma-aminobutyric acid (GABA)-A receptor complex, and 'increased GABAergic tone' has been proposed to explain the neuroinhibition characteristics of HE. Brain levels of the neurosteroids pregnenolone, allopregnanolone and tetrahydrodesoxycorticosterone (THDOC) and the functional status of the GABA-A receptor complex were assessed in rats following portacaval anastomosis (PCA). Effects of indomethacin, an inhibitor of the 3alpha-hydroxysteroid dehydrogenase enzyme involved in neurosteroid synthesis, on PCA rat locomotor activity and brain neurosteroid levels were also assessed. Significant increases of the neurosteroid pregnenolone (2.6-fold), allopregnanolone (1.7-fold) and THDOC (4.7-fold) were observed in brains of PCA rats. Brain levels of these neurosteroids were in the nanomolar range, sufficient to exert positive allosteric modulatory effects at the GABA-A receptor. Indomethacin (0.1-5 mg kg(-1)) ameliorated dose-dependently the locomotor deficit of PCA rats and concomitantly normalized brain levels of allopregnanolone and THDOC. Increased brain levels of neurosteroids with positive allosteric modulatory actions at the neuronal GABA-A receptor offer a cogent explanation for the notion of 'increased GABAergic tone' in HE. Pharmacological approaches using agents that either reduce neurosteroid synthesis or modulate the neurosteroid site on GABA-A receptor could offer new therapeutic tools for the management and treatment of HE.

Mild hypothermia prevents cerebral edema and CSF lactate accumulation in acute liver failure.

Evidence from both clinical and experimental studies demonstrates that mild hypothermia prevents encephalopathy and brain edema in acute liver failure (ALF). As part of a series of studies to elucidate the mechanism(s) involved in this protective effect, groups of rats with ALF resulting from hepatic devascularization were maintained at either 37 degrees C (normothermic) or 35 C (hypothermic), and neurological status was monitored in relation to cerebrospinal fluid (CSF) concentrations of ammonia and lactate. CSF was removed via implanted cisterna magna catheters. Mild hypothermia resulted in a delay in onset of encephalopathy and prevention of brain edema, CSF concentrations of ammonia and lactate were concomitantly decreased. Blood ammonia concentrations, on the other hand, were not affected by hypothermia in ALF rats. These findings suggest that brain edema and encephalopathy in ALF are the consequence of ammonia-induced impairment of brain energy metabolism and open the way for magnetic resonance spectroscopic monitoring of cerebral function in ALF. Mild hypothermia could be beneficial in the prevention of severe encephalopathy and brain edema in patients with ALF awaiting liver transplantation.

Evidence for a serotonin transporter deficit in experimental acute liver failure.

It has been suggested that alterations of serotonin transport may be implicated in the pathogenesis of the neuropsychiatric symptoms encountered in acute liver failure. In order to address this issue, microdialysate concentrations of serotonin, its precursor L-tryptophan and metabolite 5-hydroxyindoleacetic acid (5-HIAA) as well as brain regional distribution of serotonin transporter ([3H]-citalopram) sites were measured in rats with acute liver failure resulting from hepatic devascularization. A significant loss of [3H]-citalopram sites was observed in dorsal Raphe nucleus, in frontal and frontoparietal cortices as well as in substantia nigra of rats with severe encephalopathy resulting from acute liver failure. In frontal cortex, this loss of transporter binding sites was accompanied by significant increases of L-tryptophan, serotonin and 5-HIAA concentrations in extracellular fluid. Pharmacological manipulation of the brain serotonin system could afford a novel therapeutic approach to the prevention of the neuropsychiatric symptoms characteristic of acute liver failure in humans.

Mild hypothermia delays the onset of coma and prevents brain edema and extracellular brain glutamate accumulation in rats with acute liver failure.

Mild hypothermia is effective in the prevention of brain edema associated with cerebral ischemia and traumatic brain injury. Brain edema is also a serious complication of acute liver failure (ALF). To assess the effectiveness of hypothermia in ALF, groups of rats were subjected to hepatic devascularization (portacaval anastomosis, followed 48 hours later by hepatic artery ligation), and body temperatures were maintained at either 35 degrees C (hypothermic) or 37 degrees C (normothermic). Mild hypothermia resulted in a significant delay in the onset of severe encephalopathy and in reduction of brain water content compared with normothermic ALF rats (control [n = 8] 80.22%; ALF-37 degrees C [n = 8] 81.74%; ALF-35 degrees C [n = 8] 80.48% [P <.01 compared with ALF-37 degrees C]). This protective effect was accompanied by a significant reduction of cerebrospinal fluid (CSF) (but not plasma) ammonia concentrations (CSF ammonia: control: 0.05 mg/dL; ALF-37 degrees C: 1.01 mg/dL; ALF-35 degrees C: 0.07 mg/dL, P <.01 compared with ALF-37 degrees C). In vivo cerebral microdialysis studies revealed that mild hypothermia resulted in a significant reduction of extracellular glutamate concentrations in the brains of rats with ALF (control: 1. 06 micromol/L; ALF-37 degrees C: 2.74 micromol/L; ALF-35 degrees C: 1.49 micromol/L [P <.01 compared with ALF-37 degrees C]). These findings suggest that: 1) mild hypothermia is an effective approach to the prevention of the central nervous system consequences of experimental ALF; and that 2) the beneficial effect of hypothermia is mediated via mechanisms involving reduced blood-brain transfer of ammonia and/or reduction of extracellular brain glutamate concentrations. Mild hypothermia may be an effective approach to delay the onset of brain edema in patients with ALF awaiting liver transplantation.