Epsilon PKC may contribute to the protective effect of hypothermia in a rat focal cerebral ischemia model

Ischemic Tolerance—A Way to Reduce the Extent of Ischemia–Reperfusion Damage

Individual tissues have significantly different resistance to ischemia–reperfusion damage. There is still no adequate treatment for the consequences of ischemia–reperfusion damage. By utilizing ischemic tolerance, it is possible to achieve a significant reduction in the extent of the cell damage due to ischemia–reperfusion injury. Since ischemia–reperfusion damage usually occurs unexpectedly, the use of preconditioning is extremely limited. In contrast, postconditioning has wider possibilities for use in practice. In both cases, the activation of ischemic tolerance can also be achieved by the application of sublethal stress on a remote organ. Despite very encouraging and successful results in animal experiments, the clinical results have been disappointing so far. To avoid the factors that prevent the activation of ischemic tolerance, the solution has been to use blood plasma containing tolerance effectors. This plasma is taken from healthy donors in which, after exposure to two sublethal stresses within 48 h, effectors of ischemic tolerance occur in the plasma. Application of this activated plasma to recipient animals after the end of lethal ischemia prevents cell death and significantly reduces the consequences of ischemia–reperfusion damage. Until there is a clear chemical identification of the end products of ischemic tolerance, the simplest way of enhancing ischemic tolerance will be the preparation of activated plasma from young healthy donors with the possibility of its immediate use in recipients during the initial treatment.

Therapeutic hypothermia for stroke: Unique challenges at the bedside

Therapeutic hypothermia has shown promise as a means to improving neurological outcomes at several neurological conditions. At the clinical level, it has been shown to improve outcomes in comatose survivors of cardiac arrest and in neonatal hypoxic ischemic encephalopathy, but has yet to be convincingly demonstrated in stroke. While numerous preclinical studies have shown benefit in stroke models, translating this to the clinical level has proven challenging. Major obstacles include cooling patients with typical stroke who are awake and breathing spontaneously but often have significant comorbidities. Solutions around these problems include selective brain cooling and cooling to lesser depths or avoiding hyperthermia. This review will cover the mechanisms of protection by therapeutic hypothermia, as well as recent progress made in selective brain cooling and the neuroprotective effects of only slightly lowering brain temperature. Therapeutic hypothermia for stroke has been shown to be feasible, but has yet to be definitively proven effective. There is clearly much work to be undertaken in this area.

Advances in intervention methods and brain protection mechanisms of in situ and remote ischemic postconditioning

Ischemic postconditioning (PostC) conventionally refers to a series of brief blood vessel occlusions and reperfusions, which can induce an endogenous neuroprotective effect and reduce cerebral ischemia/reperfusion (I/R) injury. Depending on the site of adaptive ischemic intervention, PostC can be classified as in situ ischemic postconditioning (ISPostC) and remote ischemic postconditioning (RIPostC). Many studies have shown that ISPostC and RIPostC can reduce cerebral IS injury through protective mechanisms that increase cerebral blood flow after reperfusion, decrease antioxidant stress and anti-neuronal apoptosis, reduce brain edema, and regulate autophagy as well as Akt, MAPK, PKC, and KATP channel cell signaling pathways. However, few studies have compared the intervention methods, protective mechanisms, and cell signaling pathways of ISPostC and RIPostC interventions. Thus, in this article, we compare the history, common intervention methods, neuroprotective mechanisms, and cell signaling pathways of ISPostC and RIPostC.

EZH2 inhibitor DZNep modulates microglial activation and protects against ischaemic brain injury after experimental stroke

Enhancer of zeste homolog-2 (EZH2), a histone methyltransferase, has been recognized to play a pivotal role in regulating the immune response in various diseases. However, its role in the inflammatory response induced by ischaemic stroke remains to be further investigated. The aim of this study was to determine the role of EZH2 in microglia-associated inflammation in ischaemic stroke and to further detect the effects of the EZH2 inhibitor, 3-deazaadenosine A (DZNep), in ischaemic brain injury. Here, we found that both in vivo ischemic/reperfusion (I/R) injury and in vitro oxygen-glucose deprivation (OGD) treatment induced a marked upregulation of EZH2 in microglia. The administration of the EZH2 inhibitor DZNep improved behavioural performance and reduced the infarct volume in mice after experimental stroke. Furthermore, we showed that DZNep blocked pro-inflammatory (CD86⁺) microglial activation and triggered anti-inflammatory (CD206⁺) microglial polarization in experimental stroke. Pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and CXCL10 were also significantly downregulated by DZNep. In addition, it was found that DZNep blocked the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in microglia, which was increased by I/R injury and OGD. Collectively, we demonstrated that EZH2 is implicated in regulating microglial activation and exacerbates neurological deficits after ischaemic stroke, probably via activating STAT3, and that the EZH2 inhibitor DZNep can exert neuroprotective effects after ischaemic stroke.

Therapeutic hypothermia to reduce intracranial pressure after traumatic brain injury: the Eurotherm3235 RCT

BACKGROUND

Traumatic brain injury (TBI) is a major cause of disability and death in young adults worldwide. It results in around 1 million hospital admissions annually in the European Union (EU), causes a majority of the 50,000 deaths from road traffic accidents and leaves a further ≈10,000 people severely disabled.

OBJECTIVE

The Eurotherm3235 Trial was a pragmatic trial examining the effectiveness of hypothermia (32-35 °C) to reduce raised intracranial pressure (ICP) following severe TBI and reduce morbidity and mortality 6 months after TBI.

DESIGN

An international, multicentre, randomised controlled trial.

SETTING

Specialist neurological critical care units.

PARTICIPANTS

We included adult participants following TBI. Eligible patients had ICP monitoring in place with an ICP of > 20 mmHg despite first-line treatments. Participants were randomised to receive standard care with the addition of hypothermia (32-35 °C) or standard care alone. Online randomisation and the use of an electronic case report form (CRF) ensured concealment of random treatment allocation. It was not possible to blind local investigators to allocation as it was obvious which participants were receiving hypothermia. We collected information on how well the participant had recovered 6 months after injury. This information was provided either by the participant themself (if they were able) and/or a person close to them by completing the Glasgow Outcome Scale - Extended (GOSE) questionnaire. Telephone follow-up was carried out by a blinded independent clinician.

INTERVENTIONS

The primary intervention to reduce ICP in the hypothermia group after randomisation was induction of hypothermia. Core temperature was initially reduced to 35 °C and decreased incrementally to a lower limit of 32 °C if necessary to maintain ICP at < 20 mmHg. Rewarming began after 48 hours if ICP remained controlled. Participants in the standard-care group received usual care at that centre, but without hypothermia.

MAIN OUTCOME MEASURES

The primary outcome measure was the GOSE [range 1 (dead) to 8 (upper good recovery)] at 6 months after the injury as assessed by an independent collaborator, blind to the intervention. A priori subgroup analysis tested the relationship between minimisation factors including being aged < 45 years, having a post-resuscitation Glasgow Coma Scale (GCS) motor score of < 2 on admission, having a time from injury of < 12 hours and patient outcome.

RESULTS

We enrolled 387 patients from 47 centres in 18 countries. The trial was closed to recruitment following concerns raised by the Data and Safety Monitoring Committee in October 2014. On an intention-to-treat basis, 195 participants were randomised to hypothermia treatment and 192 to standard care. Regarding participant outcome, there was a higher mortality rate and poorer functional recovery at 6 months in the hypothermia group. The adjusted common odds ratio (OR) for the primary statistical analysis of the GOSE was 1.54 [95% confidence interval (CI) 1.03 to 2.31]; when the GOSE was dichotomised the OR was 1.74 (95% CI 1.09 to 2.77). Both results favoured standard care alone. In this pragmatic study, we did not collect data on adverse events. Data on serious adverse events (SAEs) were collected but were subject to reporting bias, with most SAEs being reported in the hypothermia group.

CONCLUSIONS

In participants following TBI and with an ICP of > 20 mmHg, titrated therapeutic hypothermia successfully reduced ICP but led to a higher mortality rate and worse functional outcome.

LIMITATIONS

Inability to blind treatment allocation as it was obvious which participants were randomised to the hypothermia group; there was biased recording of SAEs in the hypothermia group. We now believe that more adequately powered clinical trials of common therapies used to reduce ICP, such as hypertonic therapy, barbiturates and hyperventilation, are required to assess their potential benefits and risks to patients.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN34555414.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 45. See the NIHR Journals Library website for further project information. The European Society of Intensive Care Medicine supported the pilot phase of this trial.

Therapeutic Hypothermia and Neuroprotection in Acute Neurological Disease

Therapeutic hypothermia has consistently been shown to be a robust neuroprotectant in many labs studying different models of neurological disease. Although this therapy has shown great promise, there are still challenges at the clinical level that limit the ability to apply this routinely to each pathological condition. In order to overcome issues involved in hypothermia therapy, understanding of this attractive therapy is needed. We review methodological concerns surrounding therapeutic hypothermia, introduce the current status of therapeutic cooling in various acute brain insults, and review the literature surrounding the many underlying molecular mechanisms of hypothermic neuroprotection. Because recent work has shown that body temperature can be safely lowered using pharmacological approaches, this method may be an especially attractive option for many clinical applications. Since hypothermia can affect multiple aspects of brain pathophysiology, therapeutic hypothermia could also be considered a neuroprotection model in basic research, which would be used to identify potential therapeutic targets. We discuss how research in this area carries the potential to improve outcome from various acute neurological disorders.

Genetic inhibition of PKCε attenuates neurodegeneration after global cerebral ischemia in male mice

Global cerebral ischemia that accompanies cardiac arrest is a major cause of morbidity and mortality. Protein Kinase C epsilon (PKCε) is a member of the novel PKC subfamily and plays a vital role in ischemic preconditioning. Pharmacological activation of PKCε before cerebral ischemia confers neuroprotection. The role of endogenous PKCε after cerebral ischemia remains elusive. Here we used male PKCε-null mice to assess the effects of PKCε deficiency on neurodegeneration after transient global cerebral ischemia (tGCI). We found that the cerebral vasculature, blood flow, and the expression of other PKC isozymes were not altered in the PKCε-null mice. Spatial learning and memory was impaired after tGCI, but the impairment was attenuated in male PKCε-null mice as compared to male wild-type controls. A significant reduction in Fluoro-Jade C labeling and mitochondrial release of cytochrome C in the hippocampus was found in male PKCε-null mice after tGCI. Male PKCε-null mice expressed increased levels of PKCδ in the mitochondria, which may prevent the translocation of PKCδ from the cytosol to the mitochondria after tGCI. Our results demonstrate the neuroprotective effects of PKCε deficiency on neurodegeneration after tGCI, and suggest that reduced mitochondrial translocation of PKCδ may contribute to the neuroprotective action in male PKCε-null mice.

Hypothermia and brain inflammation after cardiac arrest

The cessation (ischemia) and restoration (reperfusion) of cerebral blood flow after cardiac arrest (CA) induce inflammatory processes that can result in additional brain injury. Therapeutic hypothermia (TH) has been proven as a brain protective strategy after CA. In this article, the underlying pathophysiology of ischemia-reperfusion brain injury with emphasis on the role of inflammatory mechanisms is reviewed. Potential targets for immunomodulatory treatments and relevant effects of TH are also discussed. Further studies are needed to delineate the complex pathophysiology and interactions among different components of immune response after CA and identify appropriate targets for clinical investigations.

Cerebral ischemia and neuroregeneration

Cerebral ischemia is one of the leading causes of morbidity and mortality worldwide. Although stroke (a form of cerebral ischemia)-related costs are expected to reach 240.67 billion dollars by 2030, options for treatment against cerebral ischemia/stroke are limited. All therapies except anti-thrombolytics (i.e., tissue plasminogen activator) and hypothermia have failed to reduce neuronal injury, neurological deficits, and mortality rates following cerebral ischemia, which suggests that development of novel therapies against stroke/cerebral ischemia are urgently needed. Here, we discuss the possible mechanism(s) underlying cerebral ischemia-induced brain injury, as well as current and future novel therapies (i.e., growth factors, nicotinamide adenine dinucleotide, melatonin, resveratrol, protein kinase C isozymes, pifithrin, hypothermia, fatty acids, sympathoplegic drugs, and stem cells) as it relates to cerebral ischemia.

Potential Therapeutics for Vascular Cognitive Impairment and Dementia

BACKGROUND

As the human lifespan increases, the number of people affected by agerelated dementia is growing at an epidemic pace. Vascular pathology dramatically affects cognitive profiles, resulting in dementia and cognitive impairment. While vascular dementia itself constitutes a medical challenge, hypo-perfusion/vascular risk factors enhance amyloid toxicity and other memory- damaging factors and hasten Alzheimer's disease (AD) and other memory disorders' progression, as well as negatively affect treatment outcome.

METHODS

Research and online content related to vascular cognitive impairment and dementia is reviewed, specifically focusing on the potential treatment of the disorder.

RESULTS

Few therapeutic options are currently available to improve the prognosis of patients with vascular dementia and cognitive impairment, mixed AD dementia with vascular pathology, or other memory disorders. Emerging evidence, however, indicates that, like AD and other memory disorders, synaptic impairment underlies much of the memory impairment in the cognitive decline of vascular cognitive impairment and vascular dementia.

CONCLUSION

Effective rescues of the memory functions might be achieved through synaptic and memory therapeutics, targeting distinct molecular signaling pathways that support the formation of new synapses and maintaining their connections. Potential therapeutic agents include: 1) memory therapeutic agents that rescue synaptic and memory functions after the brain insults; 2) antipathologic therapeutics and an effective management of vascular risk factors; and 3) preventative therapeutic agents that achieve memory therapy through functional enhancement. These therapeutic agents are also likely to benefit patients with AD and/or other types of memory disorders.

Therapeutic hypothermia for ischemic stroke; pathophysiology and future promise

Therapeutic hypothermia, or cooling of the body or brain for the purposes of preserving organ viability, is one of the most robust neuroprotectants at both the preclinical and clinical levels. Although therapeutic hypothermia has been shown to improve outcome from related clinical conditions, the significance in ischemic stroke is still under investigation. Numerous pre-clinical studies of therapeutic hypothermia has suggested optimal cooling conditions, such as depth, duration, and temporal therapeutic window for effective neuroprotection. Several studies have also explored mechanisms underlying the mechanisms of neuroprotection by therapeutic hypothermia. As such, it appears that cooling affects multiple aspects of brain pathophysiology, and regulates almost every pathway involved in the evolution of ischemic stroke. This multifaceted mechanism is thought to contribute to its strong neuroprotective effect. In order to carry out this therapy in optimal clinical settings, methodological and pathophysiological understanding is crucial. However, more investigation is still needed to better understand the underlying mechanisms of this intervention, and to overcome clinical barriers which seem to preclude the routine use therapeutic hypothermia in stroke. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Effects of hypothermia combined with neural stem cell transplantation on recovery of neurological function in rats with spinal cord injury

The microenvironment of the injured spinal cord is hypothesized to be involved in driving the differentiation and survival of engrafted neural stem cells (NSCs). Hypothermia is known to improve the microenvironment of the injured spinal cord in a number of ways. To investigate the effect of NSC transplantation in combination with hypothermia on the recovery of rat spinal cord injury, 60 Sprague-Dawley female rats were used to establish a spinal cord hemisection model. They were divided randomly into three groups: A, spinal cord injury group; B, NSC transplantation group; and C, NSC transplantation + hypothermia group. At 1, 2, 4, 6 and 8 weeks post-injury, the motor function of all animals was evaluated using the Basso, Beattie and Besnaham locomotor scoring system and the inclined plane test. At 4 weeks post-transplantation, histological analysis and immunocytochemistry were performed. At 8 weeks post-transplantation, horseradish peroxidase nerve tracing and transmission electron microscopy were conducted to observe axonal regeneration. The outcome of hind limb motor function recovery in group C significantly surpassed that in group B at 4 weeks post-injury (P<0.05). Recovery was also observed in group A, but to a lesser degree. For the pathological sections no neural axonal were observed in group A. A few axon-like structures were observed in group B and more in group C. Horseradish peroxidase-labeled neurofibers and bromodeoxyuridine-positive cells were observed in the spinal cords of group C. Fewer of these cells were found in group B and fewer still in group A. The differences among the three groups were significant (P<0.05). Using transmission electron microscopy, newly formed nerve fibers and myelinated nerve fibers were observed in the central transverse plane in groups B and C, although these nerve fibers were not evident in group A. In conclusion, NSC transplantation promoted the recovery of hind limb function in rats, and combination treatment with hypothermia produced synergistic effects.

A feasible strategy for focal cerebral ischemia-reperfusion injury: remote ischemic postconditioning

It is difficult to control the degree of ischemic postconditioning in the brain and other ischemia-sensitive organs. Remote ischemic postconditioning could protect some ischemia-sensitive organs through measures on terminal organs. In this study, a focal cerebral ischemia-reperfusion injury model was established using three cycles of remote ischemic postconditioning, each cycle consisted of 10-minute occlusion of the femoral artery and 10-minute opening. The results showed that, remote ischemic postconditioning significantly decreased the percentage of the infarct area and attenuated brain edema. In addition, inflammatory nuclear factor-κB expression was significantly lower, while anti-apoptotic Bcl-2 expression was significantly elevated in the cerebral cortex on the ischemic side. Our findings indicate that remote ischemic postconditioning attenuates focal cerebral ischemia/reperfusion injury, and that the neuroprotective mechanism is mediated by an anti-apoptotic effect and reduction of the inflammatory response.

Advances in research of the neuroprotective mechanisms of cerebral ischemic postconditioning

Ischemic postconditioning refers to controlling reperfusion blood flow during reperfusion after ischemia, which can induce an endogenous neuroprotective effect and reduce ischemia-reperfusion injury. Activation of endogenous neuroprotective mechanisms plays a key role in protecting against brain ischemia-reperfusion injury. The mechanisms of cerebral ischemic postconditioning are not completely clear, and the following aspects may be involved: downregulation of oxidative stress, attenuating mitochondrial dysfunction, attenuating endoplasmic reticulum stress, accelerating the elimination of glutamate, increasing rCBF, inhibiting apoptosis, inhibiting autophagy, and regulating signal transduction.

Combination therapy with insulin-like growth factor-1 and hypothermia synergistically improves outcome after transient global brain ischemia in the rat

OBJECTIVES

Hypothermia has a well-established neuroprotective effect and offers a foundation for combination therapy for brain ischemia. The authors evaluated the effect of combination therapy with insulin-like growth factor-1 (IGF-1) and hypothermia on brain structure and function in the setting of global brain ischemia and reperfusion in rats.

METHODS

Male Sprague-Dawley rats were randomly assigned to groups by a registrar. Animals were subjected to 8 minutes of global brain ischemia using bilateral carotid occlusion and systemic hypotension, followed by 7 days (Stage I dose studies) or 28 days (Stage II outcome studies) of reperfusion. Sham controls were subjected to surgery, but not ischemia. Stage II animals were randomized to no treatment, IGF-1 at the dose determined in Stage I, hypothermia (32°C for 4 hours), or a combination of IGF-1 and hypothermia. Stage II animals underwent 21 days of spatial memory testing. At 7 days (Stage I) or 28 days (Stage II), brains were harvested for counting of CA1 neurons. The primary Stage II outcome was a neurologic outcome index computed as the ratio of viable CA1 neurons per 300-μm field to the number of days to reach success criteria on the memory task.

RESULTS

Stage I experiments confirmed the neuroprotective effect of the hypothermia protocol and IGF-1 at a dose of 0.6 U/kg. Stage II studies suggested that early neuroprotection with hypothermia and IGF-1 was not well maintained to 28 days and that combination therapy was more beneficial than either IGF-1 or hypothermia alone. Median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 114 (IQR = 99.5 to 136) for sham, three (IQR = 2 to 4.8) for untreated ischemia, four (IQR = 3 to 70.25) for ischemia treated with IGF-1 alone, 25 (IQR = 3 to 70) for ischemia treated with hypothermia alone, and 78 (IQR 47.3 to 97.5) for ischemia treated with combination therapy. Days to memory success criteria were 13.6 (IQR = 11.5 to 15.5 days) for sham, 23.5 (IQR = 20 to 25.5 days) for untreated ischemia, 17.5 (IQR = 15.5 to 25.5 days) for ischemia treated with IGF-1, 15 (IQR = 14.5 to 21 days) for ischemia treated with hypothermia, and 13.5 (IQR = 12.25 to 18.5 days) for ischemia treated with combination therapy. Neurologic outcome indices were 8.5 (IQR = 7.4 to 9.5) for sham, 0.14 (IQR = 0.08 to 0.2) for untreated ischemia, 0.18 (IQR = 0.17 to 4.6) for ischemia treated with IGF-1, 0.7 (IQR = 0.2 to 4.8) for ischemia treated with hypothermia, and 5.7 (IQR = 3.3 to 6.2) for ischemia treated with combination therapy. Statistically significant differences in neuron counts, days to memory test criteria, and outcome index were found between sham and untreated ischemic animals. Of the three treatment regimens, only combination therapy showed a statistically significant difference from the untreated ischemic group for neuronal salvage (p = 0.02), days to criteria (p = 0.043), and outcome index (p = 0.014).

CONCLUSIONS

Combination therapy with IGF-1 (0.6 U/kg) and therapeutic hypothermia (32°C for 4 hours) at the onset of reperfusion synergistically preserves CA1 structure and function at 28 days after 8 minutes of global brain ischemia in healthy male rats.

Hurdles to clear before clinical translation of ischemic postconditioning against stroke

Ischemic postconditioning has been established for its protective effects against stroke in animal models. It is performed after post-stroke reperfusion and refers to a series of induced ischemia or a single brief one. This review article addresses major hurdles in clinical translation of ischemic postconditioning to stroke patients, including potential hazards, the lack of well-defined protective paradigms, and the paucity of deeply-understood protective mechanisms. A hormetic model, often used in toxicology to describe a dose-dependent response to a toxic agent, is suggested to study both beneficial and detrimental effects of ischemic postconditioning. Experimental strategies are discussed, including how to define the hazards of ischemic (homologous) postconditioning and the possibility of employing non-ischemic (heterologous) postconditioning to facilitate clinical translation. This review concludes that a more detailed assessment of ischemic postconditioning and studies of a broad range of heterologous postconditioning models are warranted for future clinical translation.

From rapid to delayed and remote postconditioning: the evolving concept of ischemic postconditioning in brain ischemia

Ischemic postconditioning is a concept originally defined to contrast with that of ischemic preconditioning. While both preconditioning and postconditioning confer a neuroprotective effect on brain ischemia, preconditioning is a sublethal insult performed in advance of brain ischemia, and postconditioning, which conventionally refers to a series of brief occlusions and reperfusions of the blood vessels, is conducted after ischemia/reperfusion. In this article, we first briefly review the history of preconditioning, including the experimentation that initially uncovered its neuroprotective effects and later revealed its underlying mechanisms-of-action. We then discuss how preconditioning research evolved into that of postconditioning--a concept that now represents a broad range of stimuli or triggers, including delayed postconditioning, pharmacological postconditioning, remote postconditioning--and its underlying protective mechanisms involving the Akt, MAPK, PKC and K(ATP) channel cell-signaling pathways. Because the concept of postconditioning is so closely associated with that of preconditioning, and both share some common protective mechanisms, we also discuss whether a combination of preconditioning and postconditioning offers greater protection than preconditioning or postconditioning alone.

Sevoflurane postconditioning involves an up-regulation of HIF-1α and HO-1 expression via PI3K/Akt pathway in a rat model of focal cerebral ischemia

Administration of sevoflurane at the onset of reperfusion has been confirmed to provide a cerebral protection. However, little is known about the mechanism. In this study, we tested the hypothesis that sevoflurane postconditioning induces neuroprotection through the up-regulation hypoxia inducible factor-1α (HIF-1α) and heme oxygenase-1 (HO-1) involving phosphatidylinositol-3-kinase (PI3K)/Akt pathway. In the first experiment, male Sprague-Dawley rats were subjected to focal cerebral ischemia. Postconditioning was performed by exposure to 2.5% sevoflurane immediately at the onset of reperfusion. The mRNA and protein expression of HIF-1α and its target gene, HO-1, intact neurons and the activity of caspase-3 was evaluated at 6, 24 and 72h after reperfusion. In the second experiment, we investigated the relationship between PI3K/Akt pathway and the expression of HIF-1α and HO-1 in the neuroprotection induced by sevoflurane. Cerebral infarct volume, apoptotic neuron and the expression of HIF-1α, HO-1 and p-Akt were evaluated at 24h after reperfusion. Compared with the control group, sevoflurane postconditiong significantly ameliorated neuronal injury, up-regulated mRNA and protein levels of HIF-1α and HO-1, inhibited the activity of caspase-3, and decreased the number of TUNEL-positive cells and infarct sizes. However, the selective PI3K inhibitor, wortmannin not only partly eliminated the neuroprotection of sevoflurane as shown by reducing infarct size and apoptotic neuronal cells, but also reversed the elevation of HIF-1α, HO-1 and p-Akt expression in the ischemic penumbra induced by sevoflurane. Therefore, our data demonstrate that the cerebral protection from sevoflurane postconditioning is partly mediated by PI3K/Akt pathway via the up-regulation of HIF-1α and HO-1.

The "Refrige-a-RAT-or": an accurate, inexpensive, and clinically relevant small animal model of therapeutic hypothermia

BACKGROUND

Physical and molecular mechanisms for the neuroprotective effect of therapeutic hypothermia are not completely understood, and new therapeutic applications incorporating hypothermia remain to be developed and tested. Clinically relevant animal models of therapeutic hypothermia are not well established or consistent.

OBJECTIVES

The objective was to develop and test an inexpensive small animal therapeutic hypothermia system that models those in widespread clinical use and verify that such a system confers neuroprotection in a rat model of global brain ischemia.

METHODS

A water-cooled extracorporeal system and attendant anesthesia/sedation protocol were developed and tested. In Stage 1, animals were instrumented for brain, temporalis, and rectal temperature monitoring, and the system was tested for its effect on temperature and hemodynamics. In Stage 2, animals were instrumented for rectal temperature only, subjected to global brain ischemia by two-vessel occlusion and hypotension for 8 minutes, and given either sham therapy (37°C) or hypothermia (32°C) for 4 hours. Viable CA1 neurons were counted at 7 days.

RESULTS

The system was well tolerated, provided exquisite control of animal core and brain temperatures, and conferred robust neuroprotection at 7 days. The median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 130 (IQR = 128 to 135) for sham control, 19 (IQR = 15 to 30) for untreated ischemic animals, and 101 (IQR = 94 to 113) for ischemic animals treated with hypothermia (p < 0.05 for comparison between all groups).

CONCLUSIONS

Like human protocols, this model incorporates sedation and analgesia, results in robust neuroprotection, is well tolerated, and offers exquisite temperature control. The system is noninvasive and inexpensive and offers a model that is similar to methods used in clinical practice. This system will be of interest to investigators using small animal models to examine neuroprotective mechanisms of hypothermia and translational strategies that combine hypothermia with targeted pharmacotherapy.

Limited Therapeutic Time Windows of Mild-to-Moderate Hypothermia in a Focal Ischemia Model in Rat

Although many studies have shown the great potential of induced hypothermia in stroke treatment, we recognize that there are limitations to the protective effects of hypothermia even in the laboratory. Here, we review our experiments on the protective effects of mild-to-moderate hypothermia in rats. Focal ischemia was induced by bilateral common carotid artery (CCA) occlusion for 1 to 2 hours combined with permanent or transient middle cerebral artery (MCA) occlusion. We compared the effects of mild (33°C) and moderate (30°C) hypothermia, evaluated therapeutic time windows, and studied the underlying mechanisms. On review, our findings revealed that the protective effects of induced mild hypothermia (33°C) were limited, and the therapeutic time window of even moderate hypothermia (30°C) was very short in our specific models, although this limitation might be due to the relatively brief periods of hypothermia used. In addition, we found that hypothermia reduced brain injury by preserving Akt activity, PTEN phosphorylation and εPKC activity, while inhibiting ROS production, and δPKC activity.

Kainate postconditioning restores LTP in ischemic hippocampal CA1: onset-dependent second pathophysiological stress

Postconditioning can be induced by a broad range of stimuli within minutes to days after an ischemic cerebral insult. A special form is elicited by pharmacological intervention called second pathophysiological stress. The present study aimed to evaluate the effects of low-dose (5 mg/kg) kainate postconditioning with onsets 0, 24 and 48 h after the ischemic insult on the hippocampal synaptic plasticity in a 2-vessel occlusion model in rat. The hippocampal function was tested by LTP measurements of Schaffer collateral-CA1 pyramidal cell synapses in acute slices and the changes in density of Golgi-Cox-stained apical dendritic spines. Postconditioning 0 and 24 h after ischemia was not protective, whereas 48-h-onset postconditioning resulted in the reappearance of a normal spine density (>100,000 spines) 3 days after ischemia, in parallel with the long-term restoration of the damaged LTP function. Similar, but somewhat less effects were observed after 10 days. Our data clearly demonstrate the onset dependence of postconditioning elicited by a subconvulsant dose of kainate treatment in global ischemia, with restoration of the structural plasticity and hippocampal function.

Therapeutic hypothermia: critical review of the molecular mechanisms of action

Therapeutic hypothermia (TH) is nowadays one of the most important methods of neuroprotection. The events that occur after an episode of ischemia are multiple and hypothermia can affect the various steps of this cascade. The mechanisms of action of TH are varied and the possible explanation for the benefits of this therapy is probably the multiple mechanisms of action blocking the cascade of ischemia on many levels. TH can affect many metabolic pathways, reactions of inflammation, apoptosis processes, and promote neuronal integrity. To know the mechanisms of action of TH will allow a better understanding about the indications for this therapy and the possibility of searching for other therapies when used in conjunction with hypothermia will provide a therapeutic synergistic effect.

Therapeutic hypothermia and traumatic brain injury

PURPOSE OF REVIEW

Therapeutic hypothermia after traumatic brain injury (TBI)? For the last 10 years, no topic has been more popular and more controversial among neurointensivists. This article reviews the most current findings (experimental, clinical, adult and pediatric TBI), as well as the clinical management of therapeutic hypothermia.

RECENT FINDINGS

Despite ample experimental evidence, the clinical utility of therapeutic hypothermia has still to be conclusively demonstrated in terms of reduced mortality or improved functional recovery after TBI (even in pediatric TBI). Current findings support that hypothermia should be initiated as soon as possible, for at least 48 h duration, and that outcome is worse when barbiturates are part of ICU management. Currently, available cooling techniques, including prehospital cooling protocols, expand and improve clinical management of therapeutic hypothermia.

SUMMARY

Taking into consideration all results from clinical hypothermia TBI studies discussion has to be focused around the possibility that a better outcome could be achieved if protocols for therapeutic hypothermia are reviewed. It is possible that the negative effects of the cooling and the rewarming procedure currently overshadow the neuroprotective effects.

Ischemic postconditioning may not influence early brain injury induced by focal cerebral ischemia/reperfusion in rats

Background

Experimental studies have shown that ischemic postconditioning can reduce neuronal injury in the setting of cerebral ischemia, but the mechanisms are not yet clearly elucidated. This study was conducted to determine whether ischemic postconditioning can alter expression of heat shock protein 70 and reduce acute phase neuronal injury in rats subjected to transient focal cerebral ischemia/reperfusion.

Methods

Focal cerebral ischemia was induced by intraluminal middle cerebral artery occlusion for 60 min in twenty male Sprague-Dawley rats (250-300 g). Rats were randomized into control group and an ischemic postconditioning group (10 rats per group). The animals of control group had no intervention either before or after MCA occlusion. Ischemic postconditioning was elicited by 3 cycles of 30 s reperfusion interspersed by 10 s ischemia immediately after onset of reperfusion. The infarct ratios, brain edema ratios and motor behavior deficits were analyzed 24 hrs after ischemic insult. Caspase-3 reactive cells and cells showing heat shock protein 70 activity were counted in the caudoputamen and frontoparietal cortex.

Results

Ischemic postconditiong did not reduce infarct size and brain edema ratios compared to control group. Neurologic scores were not significantly different between groups. The number of caspase-3 reactive cells in the ischemic postconditioning group was not significantly different than the value of the control group in the caudoputamen and frontoparietal cortex. The number of cells showing heat shock protein 70 activity was not significantly different than the control group, as well.

Conclusions

These results suggest that ischemic postconditioning may not influence the early brain damage induced by focal cerebral ischemia in rats.

Bench-to-bedside review: Hypothermia in traumatic brain injury

Traumatic brain injury remains a major cause of death and severe disability throughout the world. Traumatic brain injury leads to 1,000,000 hospital admissions per annum throughout the European Union. It causes the majority of the 50,000 deaths from road traffic accidents and leaves 10,000 patients severely handicapped: three quarters of these victims are young people. Therapeutic hypothermia has been shown to improve outcome after cardiac arrest, and consequently the European Resuscitation Council and American Heart Association guidelines recommend the use of hypothermia in these patients. Hypothermia is also thought to improve neurological outcome after neonatal birth asphyxia. Cardiac arrest and neonatal asphyxia patient populations present to health care services rapidly and without posing a diagnostic dilemma; therefore, therapeutic systemic hypothermia may be implemented relatively quickly. As a result, hypothermia in these two populations is similar to the laboratory models wherein systemic therapeutic hypothermia is commenced very soon after the injury and has shown so much promise. The need for resuscitation and computerised tomography imaging to confirm the diagnosis in patients with traumatic brain injury is a factor that delays intervention with temperature reduction strategies. Treatments in traumatic brain injury have traditionally focussed on restoring and maintaining adequate brain perfusion, surgically evacuating large haematomas where necessary, and preventing or promptly treating oedema. Brain swelling can be monitored by measuring intracranial pressure (ICP), and in most centres ICP is used to guide treatments and to monitor their success. There is an absence of evidence for the five commonly used treatments for raised ICP and all are potential 'double-edged swords' with significant disadvantages. The use of hypothermia in patients with traumatic brain injury may have beneficial effects in both ICP reduction and possible neuro-protection. This review will focus on the bench-to-bedside evidence that has supported the development of the Eurotherm3235Trial protocol.

Intraoperative hypothermia during vascular neurosurgical procedures

Increasing evidence in animal models and clinical trials for stroke, hypoxic encephalopathy for children, and traumatic brain injury have shown that mild hypothermia may attenuate ischemic damage and improve neurological outcome. However, it is less clear if mild intraoperative hypothermia during vascular neurosurgical procedures results in improved outcomes for patients. This review examines the scientific evidence behind hypothermia as a treatment and discusses factors that may be important for the use of this adjuvant technique, including cooling temperature, duration of hypothermia, and rate of rewarming.

Protection in animal models of brain and spinal cord injury with mild to moderate hypothermia

For the past 20 years, various laboratories throughout the world have shown that mild to moderate levels of hypothermia lead to neuroprotection and improved functional outcome in various models of brain and spinal cord injury (SCI). Although the potential neuroprotective effects of profound hypothermia during and following central nervous system (CNS) injury have long been recognized, more recent studies have described clinically feasible strategies for protecting the brain and spinal cord using hypothermia following a variety of CNS insults. In some cases, only a one or two degree decrease in brain or core temperature can be effective in protecting the CNS from injury. Alternatively, raising brain temperature only a couple of degrees above normothermia levels worsens outcome in a variety of injury models. Based on these data, resurgence has occurred in the potential use of therapeutic hypothermia in experimental and clinical settings. The study of therapeutic hypothermia is now an international area of investigation with scientists and clinicians from every part of the world contributing to this important, promising therapeutic intervention. This paper reviews the experimental data obtained in animal models of brain and SCI demonstrating the benefits of mild to moderate hypothermia. These studies have provided critical data for the translation of this therapy to the clinical arena. The mechanisms underlying the beneficial effects of mild hypothermia are also summarized.

Ischemic postconditioning as a novel avenue to protect against brain injury after stroke

Ischemic postconditioning initially referred to a stuttering reperfusion performed immediately after reperfusion, for preventing ischemia/reperfusion injury in both myocardial and cerebral infarction. It has evolved into a concept that can be induced by a broad range of stimuli or triggers, and may even be performed as late as 6 h after focal ischemia and 2 days after transient global ischemia. The concept is thought to be derived from ischemic preconditioning or partial/gradual reperfusion, but in fact the first experiment for postconditioning was carried out much earlier than that of preconditioning or partial/gradual reperfusion, in the research on myocardial ischemia. This review first examines the protective effects and parameters of postconditioning in various cerebral ischemic models. Thereafter, it provides insights into the protective mechanisms of postconditioning associated with reperfusion injury and the Akt, mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and ATP-sensitive K+ (K(ATP)) channel cell signaling pathways. Finally, some open issues and future challenges regarding clinical translation of postconditioning are discussed.

epsilonPKC confers acute tolerance to cerebral ischemic reperfusion injury

In response to mild ischemic stress, the brain elicits endogenous survival mechanisms to protect cells against a subsequent lethal ischemic stress, referred to as ischemic tolerance. The molecular signals that mediate this protection are thought to involve the expression and activation of multiple kinases, including protein kinase C (PKC). Here we demonstrate that epsilonPKC mediates cerebral ischemic tolerance in vivo. Systemic delivery of psiepsilonRACK, an epsilonPKC-selective peptide activator, confers neuroprotection against a subsequent cerebral ischemic event when delivered immediately prior to stroke. In addition, activation of epsilonPKC by psiepsilonRACK treatment decreases vascular tone in vivo, as demonstrated by a reduction in microvascular cerebral blood flow. Here we demonstrate the role of acute and transient epsilonPKC in early cerebral tolerance in vivo and suggest that extra-parenchymal mechanisms, such as vasoconstriction, may contribute to the conferred protection.

Insulin, PKC signaling pathways and synaptic remodeling during memory storage and neuronal repair

Protein kinase C (PKC) is involved in synaptic remodeling, induction of protein synthesis, and many other processes important in learning and memory. Activation of neuronal protein kinase C correlates with, and may be essential for, all phases of learning, including acquisition, consolidation, and reconsolidation. Protein kinase C activation is closely tied to hydrolysis of membrane lipids. Phospholipases C and A2 produce 1,2-diacylglycerol and arachidonic acid, which are direct activators of protein kinase C. Phospholipase C also produces inositol triphosphate, which releases calcium from internal stores. Protein kinase C interacts with many of the same pathways as insulin; therefore, it should not be surprising that insulin signaling and protein kinase C activation can both have powerful effects on memory storage and synaptic remodeling. However, investigating the possible roles of insulin in memory storage can be challenging, due to the powerful peripheral effects of insulin on glucose and the low concentration of insulin in the brain. Although peripheral for insulin, synthesized in the beta-cells of the pancreas, is primarily involved in regulating glucose, small amounts of insulin are also present in the brain. The functions of this brain insulin are inadequately understood. Protein kinase C may also contribute to insulin resistance by phosphorylating the insulin receptor substrates required for insulin signaling. Insulin is also responsible insulin-long term depression, a type of synaptic plasticity that is also dependent on protein kinase C. However, insulin can also activate PKC signaling pathways via PLC gamma, Erk 1/2 MAP kinase, and src stimulation. Taken together, the available evidence suggests that the major impact of protein kinase C and its interaction with insulin in the mature, fully differentiated nervous system appears to be to induce synaptogenesis, enhance memory, reduce Alzheimer's pathophysiology, and stimulate neurorepair.

The Akt signaling pathway contributes to postconditioning's protection against stroke; the protection is associated with the MAPK and PKC pathways

We previously reported that ischemic postconditioning with a series of mechanical interruptions of reperfusion reduced infarct volume 2 days after focal ischemia in rats. Here, we extend this data by examining long-term protection and exploring underlying mechanisms involving the Akt, mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) signaling pathways. Post-conditioning reduced infarct and improved behavioral function assessed 30 days after stroke. Additionally, postconditioning increased levels of phosphorylated Akt (Ser473) as measured by western blot and Akt activity as measured by an in vitro kinase assay. Inhibiting Akt activity by a phosphoinositide 3-kinase inhibitor, LY294002, enlarged infarct in postconditioned rats. Postconditioning did not affect protein levels of phosphorylated-phosphatase and tensin homologue deleted on chromosome 10 or -phosphoinositide-dependent protein kinase-1 (molecules upstream of Akt) but did inhibit an increase in phosphorylated-glycogen synthase kinase 3beta, an Akt effector. In addition, postconditioning blocked beta-catenin phosphorylation subsequent to glycogen synthase kinase, but had no effect on total or non-phosphorylated active beta-catenin protein levels. Furthermore, postconditioning inhibited increases in the amount of phosphorylated-c-Jun N-terminal kinase and extracellular signal-regulated kinase 1/2 in the MAPK pathway. Finally, postconditioning blocked death-promoting deltaPKC cleavage and attenuated reduction in phosphorylation of survival-promoting epsilonPKC. In conclusion, our data suggest that postconditioning provides long-term protection against stroke in rats. Additionally, we found that Akt activity contributes to postconditioning's protection; furthermore, increases in epsilonPKC activity, a survival-promoting pathway, and reductions in MAPK and deltaPKC activity; two putative death-promoting pathways correlate with postconditioning's protection.

General versus specific actions of mild-moderate hypothermia in attenuating cerebral ischemic damage

Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.

Protein kinase C as a stress sensor

While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information.

PKCɛ upregulates voltage-dependent calcium channels in cultured astrocytes

Astrocytes express voltage-gated calcium channels (VGCCs) that are upregulated in the context of the reactive astrogliosis occurring in several CNS pathologies. Moreover, the ability of selective calcium channel blockers to inhibit reactive astrogliosis has been revealed in a variety of experimental models. However, the functions and regulation of VGCC in astrocytes are still poorly understood. Interestingly, protein kinase C epsilon (PKCepsilon), one of the known regulators of VGCC in several cell types, induces in astrocytes a stellated morphology similar to that associated to gliosis. Thereby, here we explored the possible regulation of VGCC by adenovirally expressed PKCepsilon in astrocytes. We found that PKCepsilon potently increases the mRNA levels of two different calcium channel alpha(1) subunits, Ca(V)1.2 (L-type channel) and Ca(V)2.1 (P/Q-type channel). The mRNA upregulation was followed by a robust increase in the corresponding peptides. Moreover, the new calcium channels formed as a consequence of PKCepsilon activation are functional, since overexpression of constitutively-active PKCepsilon increased significantly the calcium current density in astrocytes. PKCepsilon raised currents carried by both L- and P/Q-type channels. However, the effect on the P/Q-type channel was more prominent since an increase of the relative contribution of this channel to the whole cell calcium current was observed. Finally, we found that PKCepsilon-induced stellation was significantly reduced by the specific L-type channel blocker nifedipine, indicating that calcium influx through VGCC mediates the change in astrocyte morphology induced by PKCepsilon. Therefore, here we describe a novel regulatory pathway involving VGCC that participates in PKCepsilon-dependent astrocyte activation.