The therapeutic potential of ischemic conditioning: an update

Protection against renal ischemia-reperfusion injury by ischemic postconditioning

Ischemia-reperfusion injury (IRI) is inevitable during transplantation. Attempts to reduce IRI have mainly focused on ways to improve hypothermic organ preservation and reduce the nephrotoxic effects of calcineurin inhibitors. Recently, it has been shown that short, repeated sequences of intermittent ischemia and reperfusion after a prolonged ischemic episode, so-called ischemic postconditioning (IPoC), reduce myocardial infarct size by approximately 40% in animal models and in humans. The principle of IPoC could be applied to every organ after ischemic injury, including kidney transplants. In fact, IPoC has demonstrated its clinical potential by reducing IRI in different organs in several animal models. In this review, we provide an overview of animal experiments on renal IRI and IPoC, demonstrating benefits with respect to organ damage and kidney function. We propose potential mechanisms by which IPoC protects against IRI. However, thus far, no human trials investigating IPoC in transplantation have been performed. Such clinical studies are needed to establish whether a simple procedure such as IPoC can improve the outcomes of human organ transplantation.

Antiapoptotic activity of argon and xenon

Although chemically non-reactive, inert noble gases may influence multiple physiological and pathological processes via hitherto uncharacterized physical effects. Here we report a cell-based detection system for assessing the effects of pre-defined gas mixtures on the induction of apoptotic cell death. In this setting, the conventional atmosphere for cell culture was substituted with gas combinations, including the same amount of oxygen (20%) and carbon dioxide (5%) but 75% helium, neon, argon, krypton, or xenon instead of nitrogen. The replacement of nitrogen with noble gases per se had no effects on the viability of cultured human osteosarcoma cells in vitro. Conversely, argon and xenon (but not helium, neon, and krypton) significantly limited cell loss induced by the broad-spectrum tyrosine kinase inhibitor staurosporine, the DNA-damaging agent mitoxantrone and several mitochondrial toxins. Such cytoprotective effects were coupled to the maintenance of mitochondrial integrity, as demonstrated by means of a mitochondrial transmembrane potential-sensitive dye and by assessing the release of cytochrome c into the cytosol. In line with this notion, argon and xenon inhibited the apoptotic activation of caspase-3, as determined by immunofluorescence microscopy coupled to automated image analysis. The antiapoptotic activity of argon and xenon may explain their clinically relevant cytoprotective effects.

Protective activity of ischemic preconditioning on rat testicular ischemia: effects of Y-27632 and 5-hydroxydecanoic acid

BACKGROUND/PURPOSE

The aim of this study was to investigate the role of ischemic preconditioning (IPC) on ischemia/reperfusion (I/R)-induced injury of rat testis and determine the effects of 5-hydroxydecanoic acid (5-HD), a selective K(ATP) channel antagonist, and Y-27632, a selective Rho kinase inhibitor, on IPC.

METHODS

I/R injury was induced by 180 min ischemia and 60 min reperfusion of testis. There were 5 groups. Group 1 served as untreated controls. The rats in Group 2 were subjected to I/R only. In Group 3, 3 cycles of IPC (5 min transient ischemia plus 5 min reperfusion) were performed prior to I/R. In groups 4 and 5, the rats were treated as in Group 3 but received intraperitoneal injections of 0.3 mg/kg Y-27632 or 10 mg/kg 5-HD prior to IPC, respectively.

RESULTS

I/R led to severe histopathological lesions in the rat testis and significantly lowered the scoring. I/R resulted in significant elevation in tissue lipid peroxide levels, myeloperoxidase (MPO) activity, and total antioxidative capacity (TAC), total oxidative status, and oxidative stress index levels. Protective effects of IPC on I/R-induced testicular injury of rats were observed with the significant recovery in these biochemical parameters. Y-27632 treatment led to a significant decrease in MPO activity, but there were no significant changes in the remaining parameters. Effects of IPC were blocked by 5-HD except in the TAC levels.

CONCLUSION

Our results showed that IPC protected rat testis against I/R-induced injury via activation of KATP channels. Additionally, Rho kinase inhibition preserved the effects of IPC in testis.

Redox signaling pathways involved in neuronal ischemic preconditioning

There is extensive evidence that the restoration of blood flow following cerebral ischemia contributes greatly to the pathophysiology of ischemia mediated brain injury. The initiating stimulus of reperfusion injury is believed to be the excessive production of reactive oxygen (ROS) and nitrogen (RNS) species by the mitochondria. ROS and RNS generation leads to mitochondrial protein, lipid and DNA oxidation which impedes normal mitochondrial physiology and initiates cellular death pathways. However not all ROS and RNS production is detrimental. It has been demonstrated that low levels of ROS production are protective and may serve as a trigger for activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sublethal ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Numerous proteins and signaling pathways have been implicated in the ischemic preconditioning neuroprotective response. In this review we examine the origin and mechanisms of ROS and RNS production following ischemic/reperfusion and the role of free radicals in modulating proteins associated with ischemic preconditioning neuroprotection.

Enriched environment preconditioning induced brain ischemic tolerance without reducing infarct volume and edema: the possible role of enrichment-related physical activity increase

External stimuli, including environmental enrichment (EE) and physical activity, have been shown to significantly facilitate recovery from brain injury. However, whether EE can be used as a preconditioning method to induce cerebral ischemic tolerance has never been investigated. Furthermore, whether, and to what extent, such environmental stimuli regulate physical activity to promote neuroprotection is largely unclear. To examine the neuroprotective effects of pre-ischemic EE (PIEE) and to investigate the relationship between these effects and EE-induced physical activity, we tested neurobehavioral and morphological recovery of rats following transient focal cerebral ischemia. Our study showed that PIEE improved the recovery of motor function, spatial learning and memory without reduction in brain edema or infarct volume. We also found that PIEE robustly increased the level of physical activity of rats that positively correlated with the extent of neurobehavioral recovery. Our results suggest that PIEE may induce brain ischemic tolerance through, at least partially, increasing physical activity.

Endothelial cell metabolism and tumour angiogenesis: glucose and glutamine as essential fuels and lactate as the driving force

Angiogenic endothelial cells and tumour cells can survive under hypoxic conditions and even proliferate and migrate in a low-oxygen environment. In both cell types, high rates of glycolysis (i.e. conversion of glucose to lactate) and glutaminolysis provide most of the required biosynthetic intermediates and energy to support sprouting and cell division without coupling to oxidative phosphorylation. This metabolic preference is observed under hypoxic conditions, but also in situations in which oxygen is present. In the case of tumour cells, this is known as the Warburg effect and is largely governed by oncogenes. In endothelial cells lining tumour blood vessels, the option of respiration-independent metabolism allows the neovasculature to resist the hostile environment of fluctuating oxygen tension (ranging from severe hypoxia to quasi-normal levels of oxygen). In addition, accumulation in tumours of lactate, the end-product of glycolysis, largely contributes to the angiogenic phenotype through inhibition of prolyl hydroxylase 2 and the activation of HIF1α and NFκB. Activation of the latter in a hypoxia-independent manner leads to the increased production of interleukin-8/CXCL8 which drives the autocrine stimulation of endothelial cell proliferation and maturation of neovessels. In conclusion, the addiction of proliferating endothelial cells for glucose and glutamine as fuels and the driving force of lactate to promote angiogenesis provide novel potential treatment options without the disadvantages of conventional anti-angiogenic drugs.

Remote ischemic postconditioning enhances cell retention in the myocardium after intravenous administration of bone marrow mesenchymal stromal cells

Efficacy of intravenous administration of mesenchymal stromal cells (MSCs) for myocardial infarction (MI) is limited by low cell retention in the damaged myocardium. Previous studies indicated that remote ischemic conditioning could protect against ischemia-reperfusion-induced injury by release of various cytokines including stromal cell derived factor-1 alpha (SDF-1α). However, whether remote ischemic postconditioning (RIPostC) can also enhance the retention of infused cells in the myocardium by activating MSC homing is unclear. In this study, RIPostC was induced with 4cycles of 5min occlusion and reperfusion of the abdominal aorta in female Sprague-Dawley (SD) rats which underwent ligation of the coronary artery 1week previously. Cytokine levels in serum and myocardium were evaluated by enzyme-linked immunosorbent assay (ELISA) at 1, 6, 24 and 48h after RIPostC. Then, a total of 4×10(6) male MSCs were infused intravenously at 24h after RIPostC. The number of survived cells in the myocardium was evaluated by real-time polymerase chain reaction analysis for Y chromosome and the heart function was evaluated by echocardiography at 1month after cell infusion. Furthermore, 10μg/kg rabbit anti-rat CXCR4 polyclonal antibody was injected intraperitoneally to prove the role of SDF-1α for RIPostC. RIPostC induced an increase in SDF-1α in serum at 1h and enhanced SDF-1α transcription and protein synthesis in the myocardium at 24h after the procedure. 1month after cell transplantation, RIPostC significantly increased MSC myocardial retention by 79.1±12.3% and thereby contributed to enhanced cardiac function in comparison with cell transplantation without RIPostC. Furthermore, blockade with a CXCR4-specific antibody after RIPostC markedly attenuated the enhancement of therapeutic efficacy. We conclude that RIPostC activated SDF-1α expression and enhanced retention of the infused MSCs in the injured myocardium. Priming of the heart with RIPostC might be a novel adjunctive approach for intravenous cell delivery.

Cardioprotective proteins upregulated in the liver in response to experimental myocardial ischemia

Myocardial ischemia (MI) activates innate cardioprotective mechanisms, enhancing cardiomyocyte tolerance to ischemia. Here, we report a MI-activated liver-dependent mechanism for myocardial protection. In response to MI in the mouse, hepatocytes exhibited 6- to 19-fold upregulation of genes encoding secretory proteins, including α-1-acid glycoprotein (AGP)2, bone morphogenetic protein-binding endothelial regulator (BMPER), chemokine (C-X-C motif) ligand 13, fibroblast growth factor (FGF)21, neuregulin (NRG)4, proteoglycan 4, and trefoil factor (TFF)3. Five of these proteins, including AGP2, BMPER, FGF21, NRG4, and TFF3, were identified as cardioprotective proteins since administration of each protein significantly reduced the fraction of myocardial infarcts (37 ± 9%, 34 ± 7%, 32 ± 8%, 39 ± 6%, and 31 ± 7%, respectively, vs. 48 ± 7% for PBS at 24 h post-MI). The serum level of the five proteins elevated significantly in association with protein upregulation in hepatocytes post-MI. Suppression of a cardioprotective protein by small interfering (si)RNA-mediated gene silencing resulted in a significant increase in the fraction of myocardial infarcts, and suppression of all five cardioprotective proteins with siRNAs further intensified myocardial infarction. While administration of a single cardioprotective protein mitigated myocardial infarction, administration of all five proteins furthered the beneficial effect, reducing myocardial infarct fractions from PBS control values from 46 ± 6% (5 days), 41 ± 5% (10 days), and 34 ± 4% (30 days) to 35 ± 5%, 28 ± 5%, and 24 ± 4%, respectively. These observations suggest that the liver contributes to cardioprotection in MI by upregulating and releasing protective secretory proteins. These proteins may be used for the development of cardioprotective agents.

Remote ischemic preconditioning regulates HIF-1α levels, apoptosis and inflammation in heart tissue of cardiosurgical patients: a pilot experimental study

Transient episodes of ischemia in a remote organ (remote ischemic preconditioning, RIPC) bears the potential to attenuate myocardial injury, but the underlying mechanisms are only poorly understood. In the pilot experimental study presented we investigated cellular and molecular effects of RIPC in heart tissue of cardiosurgical patients with cardiopulmonary bypass (CPB) and focussed on apoptotic events, local and systemic inflammation as well as the regulation of the hypoxia induced factor-1α (HIF-1α). RIPC was induced by four 5-min cycles of transient upper limb ischemia/reperfusion using a blood-pressure cuff. Right atrial tissue and serum were obtained from patients receiving RIPC (N = 32) and control patients (N = 29) before and after CPB. RIPC patients showed reduced troponin T serum concentrations in the first 48 h after surgery (P < 0.05 vs. control) indicating cardioprotective effects of RIPC. Samples from RIPC patients that were collected before CPB contained significantly increased amounts of HIF-1α and procaspase-3 (HIF-1α: P < 0.05 vs. control, procaspase-3: P < 0.05 vs. control), whereas activities of caspases 3 and 7 were by trend reduced. Samples from RIPC patients that were taken after CPB showed an increased activity of myeloperoxidase (P < 0.05 vs. control; P < 0.05 vs. RIPC before CPB) as well as elevated tissue concentrations of the interleukin (IL)-1β (P < 0.05 vs. RIPC before CPB). Serum levels of IL-8, IL-1β and TNFα were significantly increased in RIPC patients before CPB (P < 0.05 vs. control before CPB). In summary, RIPC regulates HIF-1α levels, apoptosis and inflammation in the myocardium of cardiosurgical patients and leads to increased concentrations of circulating cytokines.

Induction of beta-cell resistance to hypoxia and technologies for oxygen delivery to transplanted pancreatic islets

Hypoxia is believed to be a crucial factor involved in cell adaptation to environmental stress. Islet transplantation, especially with immunoisolated islets, interrupts vascular connections, resulting in the substantially decreased delivery of oxygen and nutrients to islet cells. Insulin-producing pancreatic beta cells are known to be highly susceptible to oxygen deficiency. Such susceptibility to hypoxia is believed to be one of the main causes of beta-cell death in the post-transplantation period. Different strategies have been developed for the protection of beta cells against hypoxic injury and for oxygen delivery to transplanted islets. The enhancement of beta-cell defense properties against hypoxia has been achieved using various techniques such as gene transfection, drug supplementation, co-culturing with stem cells and cell selection. Technologies for oxygen delivery to transplanted islets include local neovascularization of subcutaneous sites, electrochemical and photosynthetic oxygen generation, oxygen refuelling of bio-artificial pancreas and whole body oxygenation by using hyperbaric therapy. Progress in the field of oxygen technologies for islet transplantation requires a multidisciplinary approach to explore and optimize the interaction between components of the biological system and different technological processes. This review article focuses mainly on the recently developed strategies for oxygenation and protection from hypoxic injury - to achieve stable and long-term normoglycaemia in diabetic patients with transplanted pancreatic islets.

The effects of levosimendan on brain metabolism during initial recovery from global transient ischaemia/hypoxia

BACKGROUND

Neuroprotective strategies after cardiopulmonary resuscitation are currently the focus of experimental and clinical research. Levosimendan has been proposed as a promising drug candidate because of its cardioprotective properties, improved haemodynamic effects in vivo and reduced traumatic brain injury in vitro. The effects of levosimendan on brain metabolism during and after ischaemia/hypoxia are unknown.

METHODS

Transient cerebral ischaemia/hypoxia was induced in 30 male Wistar rats by bilateral common carotid artery clamping for 15 min and concomitant ventilation with 6% O2 during general anaesthesia with urethane. After 10 min of global ischaemia/hypoxia, the rats were treated with an i.v. bolus of 24 μg kg-1 levosimendan followed by a continuous infusion of 0.2 μg kg-1 min-1. The changes in the energy-related metabolites lactate, the lactate/pyruvate ratio, glucose and glutamate were monitored by microdialysis. In addition, the effects on global haemodynamics, cerebral perfusion and autoregulation, oedema and expression of proinflammatory genes in the neocortex were assessed.

RESULTS

Levosimendan reduced blood pressure during initial reperfusion (72 ± 14 vs. 109 ± 2 mmHg, p = 0.03) and delayed flow maximum by 5 minutes (p = 0.002). Whereas no effects on time course of lactate, glucose, pyruvate and glutamate concentrations in the dialysate could be observed, the lactate/pyruvate ratio during initial reperfusion (144 ± 31 vs. 77 ± 8, p = 0.017) and the glutamate release during 90 minutes of reperfusion (75 ± 19 vs. 24 ± 28 μmol·L-1) were higher in the levosimendan group. The increased expression of IL-6, IL-1ß TNFα and ICAM-1, extend of cerebral edema and cerebral autoregulation was not influenced by levosimendan.

CONCLUSION

Although levosimendan has neuroprotective actions in vitro and on the spinal cord in vivo and has been shown to cross the blood-brain barrier, the present results showed that levosimendan did not reduce the initial neuronal injury after transient ischaemia/hypoxia.

Activation of Toll-like receptor 3 amplifies mesenchymal stem cell trophic factors and enhances therapeutic potency

Clinical trials of bone marrow mesenchymal stem cell (MSC) therapy have thus far demonstrated moderate and inconsistent benefits, indicating an urgent need to improve therapeutic efficacy. Although administration of sufficient cells is necessary to achieve maximal therapeutic benefits, documented MSC clinical trials have largely relied on injections of ∼1 × 10(6) cells/kg, which appears too low to elicit a robust therapeutic response according to published preclinical studies. However, repeated cell passaging necessary for large-scale expansion of MSC causes cellular senescence and reduces stem cell potency. Using the RNA mimetic polyinosinic-polycytidylic acid [poly(I:C)] to engage MSC Toll-like receptor 3 (TLR3), we found that poly(I:C), signaling through multiple mitogen-activated protein kinase pathways, induced therapeutically relevant trophic factors such as interleukin-6-type cytokines, stromal-derived factor 1, hepatocyte growth factor, and vascular endothelial growth factor while slightly inhibiting the proliferation and migration potentials of MSC. At the suboptimal injection dose of 1 × 10(6) cells/kg, poly(I:C)-treated MSC, but not untreated MSC, effectively stimulated regeneration of the failing hamster heart 1 mo after cell administration. The regenerating heart exhibited increased CD34(+)/Ki67(+) and CD34(+)/GATA4(+) progenitor cells in the presence of decreased inflammatory cells and cytokines. Cardiac functional improvement was associated with a ∼50% reduction in fibrosis, a ∼40% reduction in apoptosis, and a ∼55% increase in angiogenesis, culminating in prominent cardiomyogenesis evidenced by abundant distribution of small myocytes and a ∼90% increase in wall thickening. These functional, histological, and molecular characterizations thus establish the utility of TLR3 engagement for enabling the low-dose MSC therapy that may be translated to more efficacious clinical applications.

Ischemic preconditioning of rat livers from non-heart-beating donors decreases parenchymal cell killing and increases graft survival after transplantation

A critical shortage of donors exists for liver transplantation, which non-heart-beating cadaver donors could help ease. This study evaluated ischemic preconditioning to improve graft viability after non-heart-beating liver donation in rats. Ischemic preconditioning was performed by clamping the portal vein and hepatic artery for 10 min followed by unclamping for 5 min. Subsequently, the aorta was cross-clamped for up to 120 min. After 2 h of storage, livers were either transplanted or perfused with warm buffer containing trypan blue. Aortic clamping for 60 and 120 min prior to liver harvest markedly decreased 30-day graft survival from 100% without aortic clamping to 50% and 0%, respectively, which ischemic preconditioning restored to 100 and 50%. After 60 min of aortic clamping, loss of viability of parenchymal and nonparenchymal cells was 22.6 and 5.6%, respectively, which preconditioning decreased to 3.0 and 1.5%. Cold storage after aortic clamping further increased parenchymal and non-parenchymal cell killing to 40.4 and 10.1%, respectively, which ischemic preconditioning decreased to 12.4 and 1.8%. In conclusion, ischemic preconditioning markedly decreased cell killing after subsequent sustained warm ischemia. Most importantly, ischemic preconditioning restored 100% graft survival of livers harvested from non-heart-beating donors after 60 min of aortic clamping.

Small heat shock proteins in redox metabolism: implications for cardiovascular diseases

A timely review series on small heat shock proteins has to appropriately examine their fundamental properties and implications in the cardiovascular system since several members of this chaperone family exhibit robust expression in the myocardium and blood vessels. Due to energetic and metabolic demands, the cardiovascular system maintains a high mitochondrial activity but irreversible oxidative damage might ensue from increased production of reactive oxygen species. How equilibrium between their production and scavenging is achieved becomes paramount for physiological maintenance. For example, heat shock protein B1 (HSPB1) is implicated in maintaining this equilibrium or redox homeostasis by upholding the level of glutathione, a major redox mediator. Studies of gain or loss of function achieved by genetic manipulations have been highly informative for understanding the roles of those proteins. For example, genetic deficiency of several small heat shock proteins such as HSPB5 and HSPB2 is well-tolerated in heart cells whereas a single missense mutation causes human pathology. Such evidence highlights both the profound genetic redundancy observed among the multigene family of small heat shock proteins while underscoring the role proteotoxicity plays in driving disease pathogenesis. We will discuss the available data on small heat shock proteins in the cardiovascular system, redox metabolism and human diseases. From the medical perspective, we envision that such emerging knowledge of the multiple roles small heat shock proteins exert in the cardiovascular system will undoubtedly open new avenues for their identification and possible therapeutic targeting in humans. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Neuroprotective effects of ischemic preconditioning and postconditioning on global brain ischemia in rats through the same effect on inhibition of apoptosis

Transient forebrain or global ischemia induces neuronal death in vulnerable CA1 pyramidal cells with many features. A brief period of ischemia, i.e., ischemic preconditioning, or a modified reperfusion such as ischemic postconditioning, can afford robust protection of CA1 neurons against ischemic challenge. Therefore, we investigated the effect of ischemic preconditioning and postconditioning on neural cell apoptosis in rats. The result showed that both ischemic preconditioning and postconditioning may attenuate the neural cell death and DNA fragment in the hippocampal CA1 region. Further western blot study suggested that ischemic preconditioning and postconditioning down-regulates the protein of cleaved caspase-3, caspase-6, caspase-9 and Bax, but up-regulates the protein Bcl-2. These findings suggest that ischemic preconditioning and postconditioning have a neuroprotective role on global brain ischemia in rats through the same effect on inhibition of apoptosis.

Cardioprotection from ischemia/reperfusion injury: basic and translational research

Because ischemic heart diseases (IHDs) are a major cause of mortality and heart failure, novel therapeutic approaches are expected to improve the clinical outcomes of patients with IHDs such as acute myocardial infarction and ischemic heart failure. Brief episodes of nonlethal ischemia and reperfusion before sustained ischemia or at the onset of reperfusion can reduce ischemia-reperfusion injury. These ischemic conditioning phenomena are termed "ischemic preconditioning" and "ischemic postconditioning", respectively. Furthermore, brief episodes of nonlethal ischemia and reperfusion applied to the organ or tissue distal to the heart reduce myocardial infarct size, known as "remote ischemic conditioning". The cardioprotection afforded by these ischemic conditionings can be used to treat patients with acute myocardial infarction or cardiac operations. Extensive research has determined that autacoids (eg, adenosine, bradykinin opioid) and cytokines, their respective receptors, kinase signaling pathways and mitochondrial modulation are involved in ischemic conditioning. Modification of these factors by pharmacological agents mimics the cardioprotection by ischemic conditioning and provides a novel therapeutic intervention for IHDs. Here, the potential mechanisms of ischemic conditioning and its "proof-of-concept" translational studies are reviewed. In the near future, large, multicenter, randomized, placebo-controlled, clinical trials will be required to determine whether pharmacological and ischemic conditioning can improve the clinical outcomes of patients with IHDs.

Cardioprotection during cardiac surgery

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

Ischemic preconditioning in the animal kidney, a systematic review and meta-analysis

Ischemic preconditioning (IPC) is a potent renoprotective strategy which has not yet been translated successfully into clinical practice, in spite of promising results in animal studies. We performed a unique systematic review and meta-analysis of animal studies to identify factors modifying IPC efficacy in renal ischemia/reperfusion injury (IRI), in order to enhance the design of future (clinical) studies. An electronic literature search for animal studies on IPC in renal IRI yielded fifty-eight studies which met our inclusion criteria. We extracted data for serum creatinine, blood urea nitrogen and histological renal damage, as well as study quality indicators. Meta-analysis showed that IPC reduces serum creatinine (SMD 1.54 [95%CI 1.16, 1.93]), blood urea nitrogen (SMD 1.42 [95% CI 0.97, 1.87]) and histological renal damage (SMD 1.12 [95% CI 0.89, 1.35]) after IRI as compared to controls. Factors influencing IPC efficacy were the window of protection (<24 h = early vs. ≥24 h = late) and animal species (rat vs. mouse). No difference in efficacy between local and remote IPC was observed. In conclusion, our findings show that IPC effectively reduces renal damage after IRI, with higher efficacy in the late window of protection. However, there is a large gap in study data concerning the optimal window of protection, and IPC efficacy may differ per animal species. Moreover, current clinical trials on RIPC may not be optimally designed, and our findings identify a need for further standardization of animal experiments.

The diabetic heart: too sweet for its own good?

Diabetes mellitus is a major risk factor for ischemic heart disease (IHD). Patients with diabetes and IHD experience worse clinical outcomes, suggesting that the diabetic heart may be more susceptible to ischemia-reperfusion injury (IRI). In contrast, the animal data suggests that the diabetic heart may be either more, equally, or even less susceptible to IRI. The conflicting animal data may be due to the choice of diabetic and/or IRI animal model. Ischemic conditioning, a phenomenon in which the heart is protected against IRI by one or more brief nonlethal periods of ischemia and reperfusion, may provide a novel cardioprotective strategy for the diabetic heart. Whether the diabetic heart is amenable to ischemic conditioning remains to be determined using relevant animal models of IRI and/or diabetes. In this paper, we review the limitations of the current experimental models used to investigate IRI and cardioprotection in the diabetic heart.

Serum from patients undergoing remote ischemic preconditioning protects cultured human intestinal cells from hypoxia-induced damage: involvement of matrixmetalloproteinase-2 and -9

Remote ischemic preconditioning (RIPC) can be induced by transient occlusion of blood flow to a limb with a blood pressure cuff and exerts multiorgan protection from ischemia/reperfusion injury. Ischemia/reperfusion injury in the intestinal tract leads to intestinal barrier dysfunction and can result in multiple organ failure. Here we used an intestinal cell line (CaCo-2) to evaluate the effects of RIPC-conditioned patient sera on hypoxia-induced cell damage in vitro and to identify serum factors that mediate RIPC effects. Patient sera (n = 10) derived before RIPC (T0), directly after RIPC (T1) and 1 h after RIPC (T2) were added to the culture medium at the onset of hypoxia until 48 h after hypoxia. Reverse transcription-polymerase chain reaction, lactate dehydrogenase (LDH) assays, caspase-3/7 assays, silver staining, gelatin zymography and Western blotting were performed. Hypoxia led to morphological signs of cell damage and increased the release of LDH in cultures containing sera T0 (P < 0.01) and T1 (P < 0.05), but not sera T2, which reduced the hypoxia-mediated LDH release compared with sera T0 (P < 0.05). Gelatin zymography revealed a significant reduction of activities of the matrixmetalloproteinase (MMP)-2 and MMP-9 in the protective sera T2 compared with the nonprotective sera T0 (MMP-2: P < 0.01; MMP-9: P < 0.05). Addition of human recombinant MMP-2 and MMP-9 to MMP-deficient culture media increased the sensitivity of CaCo-2 cells to hypoxia-induced cell damage (P < 0.05), but did not result in a reduced phosphorylation of prosurvival kinases p42/44 and protein kinase B (Akt) or increased activity of caspase-3/7. Our results suggest MMP-2 and MMP-9 as currently unknown humoral factors that may be involved in RIPC-mediated cytoprotection in the intestine.

Endogenous cardioprotection by ischaemic postconditioning and remote conditioning

Persistent myocardial ischaemia causes cell death if not rescued by early reperfusion. Millions of years in nature's laboratory have evolved protective responses that 'condition' the heart (and other tissues) to adapt to stressors, and these responses are applicable to the relatively new societal stress of myocardial ischaemia and reperfusion injury. Conditioning can be applied before (preconditioning), during (perconditioning), or after (postconditioning) the ischaemic stressor by imposing short periods of non-lethal ischaemia separated by brief periods of reperfusion. This conditioning protects multiple cell types and induces or rebalances a number of physiological and molecular pathways that ultimately attenuate necrosis and apoptosis. The seemingly disparate pathways may converge directly or indirectly on the mitochondria as a final effector, but other pathways not affecting mitochondria broaden the mechanisms of cardioprotection. The potential downsides of imposing even brief ischaemia directly on the heart somewhat tempered the enthusiasm for applying conditioning stimuli to the heart, but this hurdle was surmounted by applying ischaemia to remote organs and tissues in pre-, per-, and postconditioning. Although the clinical translation of remote per- and postconditioning has been rapid compared with classical preconditioning, there are numerous basic questions that require further investigation, and wider adoption awaits large-scale randomized clinical trials. Pharmacological mimetics may provide another important therapeutic approach by which to treat evolving myocardial infarction.

Intestinal microbiota determine severity of myocardial infarction in rats

Signals from the intestinal microbiota are important for normal host physiology; alteration of the microbiota (dysbiosis) is associated with multiple disease states. We determined the effect of antibiotic-induced intestinal dysbiosis on circulating cytokine levels and severity of ischemia/reperfusion injury in the heart. Treatment of Dahl S rats with a minimally absorbed antibiotic vancomycin, in the drinking water, decreased circulating leptin levels by 38%, resulted in smaller myocardial infarcts (27% reduction), and improved recovery of postischemic mechanical function (35%) as compared with untreated controls. Vancomycin altered the abundance of intestinal bacteria and fungi, measured by 16S and 18S ribosomal DNA quantity. Pretreatment with leptin (0.12 μg/kg i.v.) 24 h before ischemia/reperfusion abolished cardioprotection produced by vancomycin treatment. Dahl S rats fed the commercially available probiotic product Goodbelly, which contains the leptin-suppressing bacteria Lactobacillus plantarum 299v, also resulted in decreased circulating leptin levels by 41%, smaller myocardial infarcts (29% reduction), and greater recovery of postischemic mechanical function (23%). Pretreatment with leptin (0.12 μg/kg i.v.) abolished cardioprotection produced by Goodbelly. This proof-of-concept study is the first to identify a mechanistic link between changes in intestinal microbiota and myocardial infarction and demonstrates that a probiotic supplement can reduce myocardial infarct size.

Activation of volume regulated chloride channels protects myocardium from ischemia/reperfusion damage in second-window ischemic preconditioning

Activation of volume regulated chloride channels (VRCCs) has been shown to be cardioprotective in ischemic preconditioning (IPC) of isolated hearts but the underlying molecular mechanisms remain unclear. Recent independent studies support that ClC-3, a ClC voltage-gated chloride channel, may function as a key component of the VRCCs. Thus, ClC-3 knockout (Clcn3(-/-)) mice and their age-matched heterozygous (Clcn3(+/-)) and wild-type (Clcn3(+/+)) littermates were used to test whether activation of VRCCs contributes to cardioprotection in early and/or second-window IPC. Targeted disruption of ClC-3 gene caused a decrease in the body weight but no changes in heart/body weight ratio. Telemetry ECG and echocardiography revealed no differences in ECG and cardiac function under resting conditions among all groups. Under treadmill stress (10 m/min for 10 min), the Clcn3(-/-) mice had significant slower heart rate (648±12 bpm) than Clcn3(+/+) littermates (737±19 bpm, n=6, P<0.05). Ex vivo IPC in the isolated working-heart preparations protected cardiac function during reperfusion and significantly decreased apoptosis and infarct size in all groups. In vivo early IPC significantly reduced infarct size in all groups including Clcn3(-/-) mice (22.7±3.7% vs control 40.1±4.3%, n=22, P=0.004). Second-window IPC significantly reduced apoptosis and infarction in Clcn3(+/+) (22.9±3.2% vs 45.7±5.4%, n=22, P<0.001) and Clcn3(+/-) mice (27.5±4.1% vs 42.2±5.7%, n=15, P<0.05) but not in Clcn3(-/-) littermates (39.8±4.9% vs 41.5±8.2%, n=13, P>0.05). Impaired cell volume regulation of the Clcn3(-/-) myocytes may contribute to the failure of cardioprotection by second-window IPC. These results strongly support that activation of VRCCs may play an important cardioprotective role in second-window IPC.

Physiology of potassium channels in the inner membrane of mitochondria

The inner membrane of the ATP-producing organelles of endosymbiotic origin, mitochondria, has long been considered to be poorly permeable to cations and anions, since the strict control of inner mitochondrial membrane permeability is crucial for efficient ATP synthesis. Over the past 30 years, however, it has become clear that various ion channels--along with antiporters and uniporters--are present in the mitochondrial inner membrane, although at rather low abundance. These channels are important for energy supply, and some are a decisive factor in determining whether a cell lives or dies. Their electrophysiological and pharmacological characterisations have contributed importantly to the ongoing elucidation of their pathophysiological roles. This review gives an overview of recent advances in our understanding of the functions of the mitochondrial potassium channels identified so far. Open issues concerning the possible molecular entities giving rise to the observed activities and channel protein targeting to mitochondria are also discussed.

Labdane diterpenes protect against anoxia/reperfusion injury in cardiomyocytes: involvement of AKT activation

Several labdane diterpenes exert anti-inflammatory and cytoprotective actions; therefore, we have investigated whether these molecules protect cardiomyocytes in an anoxia/reperfusion (A/R) model, establishing the molecular mechanisms involved in the process. The cardioprotective activity of three diterpenes (T1, T2 and T3) was studied in the H9c2 cell line and in isolated rat cardiomyocyte subjected to A/R injury. In both cases, treatment with diterpenes T1 and T2 protected from A/R-induced apoptosis, as deduced by a decrease in the percentage of apoptotic and caspase-3 active positive cells, a decrease in the Bcl-2/Bax ratio and an increase in the expression of antiapoptotic proteins. Analysis of cell survival signaling pathways showed that diterpenes T1 and T2 added after A/R increased phospho-AKT and phospho-ERK 1/2 levels. These cardioprotective effects were lost when AKT activity was pharmacologically inhibited. Moreover, the labdane-induced cardioprotection involves activation of AMPK, suggesting a role for energy homeostasis in their mechanism of action. Labdane diterpenes (T1 and T2) also exerted cardioprotective effects against A/R-induced injury in isolated cardiomyocytes and the mechanisms involved activation of specific survival signals (PI3K/AKT pathways, ERK1/2 and AMPK) and inhibition of apoptosis.