Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia

The BE COOL Treatments (Batroxobin, oxygEn, Conditioning, and cOOLing): Emerging Adjunct Therapies for Ischemic Cerebrovascular Disease

Ischemic cerebrovascular disease (ICD), the most common neurological disease worldwide, can be classified based on the onset time (acute/chronic) and the type of cerebral blood vessel involved (artery or venous sinus). Classifications include acute ischemic stroke (AIS)/transient ischemic attack (TIA), chronic cerebral circulation insufficiency (CCCI), acute cerebral venous sinus thrombosis (CVST), and chronic cerebrospinal venous insufficiency (CCSVI). The pathogenesis of cerebral arterial ischemia may be correlated with cerebral venous ischemia through decreased cerebral perfusion. The core treatment goals for both arterial and venous ICDs include perfusion recovery, reduction of cerebral ischemic injury, and preservation of the neuronal integrity of the involved region as soon as possible; however, therapy based on the current guidelines for either acute ischemic events or chronic cerebral ischemia is not ideal because the recurrence rate of AIS or CVST is still very high. Therefore, this review discusses the neuroprotective effects of four novel potential ICD treatments with high translation rates, known as the BE COOL treatments (Batroxobin, oxygEn, Conditioning, and cOOLing), and subsequently analyzes how BE COOL treatments are used in clinical settings. The combination of batroxobin, oxygen, conditioning, and cooling may be a promising intervention for preserving ischemic tissues.

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.

MicroRNA Cues from Nature: A Roadmap to Decipher and Combat Challenges in Human Health and Disease?

MicroRNAs are small non-coding RNA (18–24 nt long) that fine-tune gene expression at the post-transcriptional level. With the advent of “multi-omics” analysis and sequencing approaches, they have now been implicated in every facet of basic molecular networks, including metabolism, homeostasis, and cell survival to aid cellular machinery in adapting to changing environmental cues. Many animals must endure harsh environmental conditions in nature, including cold/freezing temperatures, oxygen limitation (anoxia/hypoxia), and food or water scarcity, often requiring them to revamp their metabolic organization, frequently on a seasonal or life stage basis. MicroRNAs are important regulatory molecules in such processes, just as they are now well-known to be involved in many human responses to stress or disease. The present review outlines the role of miRNAs in natural animal models of environmental stress and adaptation including torpor/hibernation, anoxia/hypoxia tolerance, and freeze tolerance. We also discuss putative medical applications of advances in miRNA biology including organ preservation for transplant, inflammation, ageing, metabolic disorders (e.g., obesity), mitochondrial dysfunction (mitoMirs) as well as specialized miRNA subgroups respective to low temperature (CryomiRs) and low oxygen (OxymiRs). The review also covers differential regulation of conserved and novel miRNAs involved at cell, tissue, and stress specific levels across multiple species and their roles in survival. Ultimately, the species-specific comparison and conserved miRNA responses seen in evolutionarily disparate animal species can help us to understand the complex miRNA network involved in regulating and reorganizing metabolism to achieve diverse outcomes, not just in nature, but in human health and disease.

Therapeutic hypothermia reduces cortical inflammation associated with utah array implants

OBJECTIVE

Neuroprosthetics hold tremendous promise to restore function through brain-computer interfaced devices. However, clinical applications of implantable microelectrodes remain limited given the challenges of maintaining neuronal signals for extended periods of time and with multiple biological mechanisms negatively affecting electrode performance. Acute and chronic inflammation, oxidative stress, and blood brain barrier disruption contribute to inconsistent electrode performance. We hypothesized that therapeutic hypothermia (TH) applied at the microelectrode insertion site will positively modulate both inflammatory and apoptotic pathways, promoting neuroprotection and improved performance in the long-term.

APPROACH

A custom device and thermoelectric system were designed to deliver controlled TH locally to the cortical implant site at the time of microelectrode array insertion and immediately following surgery. The TH paradigm was derived from in vivo cortical temperature measurements and finite element modeling of temperature distribution profiles in the cortex. Male Sprague-Dawley rats were implanted with non-functional Utah microelectrodes arrays (UMEA) consisting of 4 × 4 grid of 1.5 mm long parylene-coated silicon shanks. In one group, TH was applied to the implant site for two hours following the UMEA implantation, while the other group was implanted under normothermic conditions without treatment. At 48 h, 72 h, 7 d and 14 d post-implantation, mRNA expression levels for genes associated with inflammation and apoptosis were compared between normothermic and hypothermia-treated groups.

MAIN RESULTS

The custom system delivered controlled TH to the cortical implant site and the numerical models confirmed that the temperature decrease was confined locally. Furthermore, a one-time application of TH post UMEA insertion significantly reduced the acute inflammatory response with a reduction in the expression of inflammatory regulating cytokines and chemokines.

SIGNIFICANCE

This work provides evidence that acutely applied hypothermia is effective in significantly reducing acute inflammation post intracortical electrode implantation.

Hypothermic neuroprotection against acute ischemic stroke: The 2019 update

Acute ischemic stroke is a leading cause of death and disability worldwide. Therapeutic hypothermia has long been considered as one of the most robust neuroprotective strategies. Although the neuroprotective effects of hypothermia have only been confirmed in patients with global cerebral ischemia after cardiac arrest and in neonatal hypoxic ischemic encephalopathy, establishing standardized protocols and strictly controlling the key parameters may extend its application in other brain injuries, such as acute ischemic stroke. In this review, we discuss the potential neuroprotective effects of hypothermia, its drawbacks evidenced in previous studies, and its potential clinical application for acute ischemic stroke especially in the era of reperfusion. Based on the different conditions between bench and bedside settings, we demonstrate the importance of vascular recanalization for neuroprotection of hypothermia by analyzing numerous literatures regarding hypothermia in focal cerebral ischemia. Then, we make a thorough analysis of key parameters of hypothermia and introduce novel hypothermic therapies. We advocate in favor of the process of clinical translation of intra-arterial selective cooling infusion in the era of reperfusion and provide insights into the prospects of hypothermia in acute ischemic stroke.

Effects of cold exposure revealed by global transcriptomic analysis in ferret peripheral blood mononuclear cells

Animal studies, mostly performed in rodents, show the beneficial anti-obesity effects of cold studies. This is due to thermogenic activation of brown adipose tissue (BAT), a tissue also recently discovered in adult humans. Studies in humans, however, are hampered by the accessibility of most tissues. In contrast, peripheral blood mononuclear cells (PBMC) are accessible and share the expression profile of different sets of genes with other tissues, including those that reflect metabolic responses. Ferrets are an animal model physiologically closer to humans than rodents. Here, we investigated the effects on ferrets of one-week acclimation to 4 °C by analysing the PBMC transcriptome. Cold exposure deeply affected PBMC gene expression, producing a widespread down-regulation of genes involved in different biological pathways (cell cycle, gene expression regulation/protein synthesis, immune response, signal transduction, and genes related to extracellular matrix/cytoskeleton), while thermogenic and glycogenolysis-related processes were increased. Results obtained in PBMC reflected those of adipose tissue, but hardly those of the liver. Our study, using ferret as a model, reinforce PBMC usefulness as sentinel biological material for cold-exposure studies in order to deepen our understanding of the general and specific pathways affected by cold acclimation. This is relevant for future development of therapies to be used clinically.

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.

Hypothermia Reduces Mortality, Prevents the Calcium Plateau, and Is Neuroprotective Following Status Epilepticus in Rats

Status Epilepticus (SE) is a major neurological emergency and is considered a leading cause of Acquired Epilepsy (AE). We have shown that SE produces neuronal injury and prolonged alterations in hippocampal calcium levels ([Ca²⁺]_i) that may underlie the development of AE. Interventions preventing the SE-induced Ca²⁺ plateau could therefore prove to be beneficial in lowering the development of AE after SE. Hypothermia is used clinically to prevent neurological complications associated with Traumatic Brain Injury, cardiac arrest, and stroke. Here, we investigated whether hypothermia prevented the development of Ca²⁺ plateau following SE. SE was induced in hippocampal neuronal cultures (HNC) by exposing them to no added MgCl₂ solution for 3 h. To terminate SE, low Mg²⁺ solution was washed off with 31°C (hypothermic) or 37°C (normothermic) physiological recording solution. [Ca²⁺]_i was estimated with ratiometric Fura-2 imaging. HNCs washed with hypothermic solution exhibited [Ca²⁺]_i ratios, which were significantly lower than ratios obtained from HNCs washed with normothermic solution. For in vivo SE, the rat pilocarpine (PILO) model was used. Moderate hypothermia (30–33°C) in rats was induced at 30-min post-SE using chilled ethanol spray in a cold room. Hypothermia following PILO-SE significantly reduced mortality. Hippocampal neurons isolated from hypothermia-treated PILO SE rats exhibited [Ca²⁺]_i ratios which were significantly lower than ratios obtained from PILO SE rats. Hypothermia also provided significant neuroprotection against SE-induced delayed hippocampal injury as characterized by decreased FluoroJade C labeling in hypothermia-treated PILO SE rats. We previously demonstrated that hypothermia reduced Ca²⁺ entry via N-methyl-D-aspartate and ryanodine receptors in HNC. Together, our studies indicate that by targeting these two receptor systems hypothermia could interfere with epileptogenesis and prove to be an effective therapeutic intervention for reducing SE-induced AE.

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.

Hypothermic neuroprotections in the brain of an echolocation bat, Hipposideros terasensis

The present study aimed to investigate how bats protect their brain in a hypothermic situation. Formosan leaf-nosed bats (Hipposideros terasensis) were used in this study and treated under three conditions: room temperature (25±1°C), low temperature (4±1°C), and hibernation. The reactive oxygen species (ROS) levels in the blood and apoptosis-related proteins in the brain tissue were assessed and then compared among those bats under three conditions. Our results showed that the blood ROS levels of bats treated under conditions of low temperature and hibernation were significantly reduced compared with bats treated under the condition of room temperature. Both immunohistochemistry and immunoblotting expressions of hypoxia, inflammation, and apoptosis-related proteins in the brain tissue of bats treated under the condition of hibernation were significantly reduced compared with those bats treated under conditions of room temperature and low temperature. Thus, we suggested that bats can protect the brain in cold environment by reducing blood ROS levels and decreasing expressions of hypoxia, inflammation, and apoptosis-related proteins in the brain. Possible protection mechanisms involved in hypothermic adaptations need to be further clarified.

Anesthesia for Endovascular Approaches to Acute Ischemic Stroke

Involvement of the Anesthesiologist in the early stages of care for acute ischemic stroke patient undergoing endovascular treatment is essential. Anesthetic management includes the anesthetic technique (general anesthesia vs sedation), a matter of much debate and an area in need of well-designed prospective studies. The large numbers of confounding factors make the design of such studies a difficult process. A universally agreed point in the endovascular management of acute ischemic stroke is the importance of decreasing the time to revascularization. Hemodynamic and ventilatory management and implementation of neuroprotective modalities and treatment of acute procedural complications are important components of the anesthetic plan.

Therapeutic Hypothermia for Acute Stroke

Hypothermia is the most potent neuroprotective therapy available. Clinical use of hypothermia is limited by technology and homeostatic mechanisms that maintain core body temperature. Recent advances in intravascular cooling catheters and successful trials of hypothermia for cardiac arrest revivified interest in hypothermia for stroke, resulting in Phase 1 clinical trials and plans for further development. Given the recent spate of neuroprotective therapy failures, we sought to clarify whether clinical trials of therapeutic hypothermia should be mounted in stroke patients. We reviewed the preclinical and early clinical trials of hypothermia for a variety of indications, the putative mechanisms for neuroprotection with hypothermia, and offer several hypotheses that remain to be tested in clinical trials. Therapeutic hypothermia is promising, but further Phase 1 and Phase 2 development efforts are needed to ensure that cooling of stroke patients is safe, before definitive efficacy trials.

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Effects of mild and moderate hypothemia therapy on expression of cerebral neuron apoptosis related proteins and glial fiber acidic protein after rat cardio-pulmonary resuscitation

To explore the effects of different degrees of hypothermia on brain tissue apoptosis after cardio-pulmonary resuscitation (CPR). Cardiac arrest for 5 min induced by asphyxia method was used to create CPR model. 30 SD rats were randomly divided into control group (normothermia), 33 °C hypothermia group and 30 °C hypothermia group with ten rats in each. Rats in control group received routine treatment at 25 °C room temperature after CPR; Rats in mild hypothermia and moderate hypothermia groups were given hypothermia treatment 0.5 h after CPR. Brain tissue in all groups was taken 24 h after CPR, and immunohistochemistry was used to detect the caspase-3 in cerebral cortex and glial fiber acidic protein (GFAP) expression in astrocyte. Western blotting was used to detect Bcl-2 and Bax protein expression, and histopathological change was observed in brain tissue. Compare to the control group, caspase-3 expression in cerebral neurons in hypothermia group was significantly decreased (p<0.01), which was significantly lower in 30 °C group than that in 33 °C group (p > 0.05); GFAP level in hypothermia groups was significantly increased (p < 0.01), which was higher in 30 °C hypothermia group than that in 33 °C hypothermia group (p < 0.05); Bcl-2 expression level in hypothermia group was significantly increased (p < 0.01), which was higher in 30 °C hypothermia group than that in 33 °C hypothermia group (p < 0.05); The level of Bax had no significant difference among the three groups. Hypothermia-regulated GFAP expression by decreasing caspase-3 expression and increasing Bcl-2 expression to promote brain cell signaling transduction, and further inhibited cell apoptosis and reduced brain injury. Moderate hypothermia therapy is more effective than mild hypothermia in preventing brain injure.

Therapeutic hypothermia for stroke: Where to go?

Ischemic stroke is a major cause of death and long-term disability worldwide. Thrombolysis with recombinant tissue plasminogen activator is the only proven and effective treatment for acute ischemic stroke; however, therapeutic hypothermia is increasingly recognized as having a tissue-protective function and positively influencing neurological outcome, especially in cases of ischemia caused by cardiac arrest or hypoxic-ischemic encephalopathy in newborns. Yet, many aspects of hypothermia as a treatment for ischemic stroke remain unknown. Large-scale studies examining the effects of hypothermia on stroke are currently underway. This review discusses the mechanisms underlying the effect of hypothermia, as well as trends in hypothermia induction methods, methods for achieving optimal protection, side effects, and therapeutic strategies combining hypothermia with other neuroprotective treatments. Finally, outstanding issues that must be addressed before hypothermia treatment is implemented at a clinical level are also presented.

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.

Role of induced hypothermia in thoracoabdominal aortic aneurysm surgery

For more than 50 years, hypothermia has been used in aortic surgery as a tool for neuroprotection. Hypothermia has been introduced into thoracoabdominal aortic aneurysm (TAAA) surgery by many cardiovascular centers to protect the body's organs, including the spinal cord. Numerous publications have shown that hypothermia can prevent immediate and delayed motor dysfunction after aortic cross-clamping. Here, we reviewed the historical application of hypothermia in aortic surgery, role of hypothermia in preclinical studies, cellular and molecular mechanisms by which hypothermia confers neuroprotection, and the role of systemic and regional hypothermia in clinical protocols to reduce and/or eliminate the devastating consequences of ischemic spinal cord injury after TAAA repair.

The neuroprotective effect of post ischemic brief mild hypothermic treatment correlates with apoptosis, but not with gliosis in endothelin-1 treated rats

BACKGROUND

Stroke remains one of the most common diseases with a serious impact on quality of life but few effective treatments exist. Mild hypothermia (33°C) is a promising neuroprotective therapy in stroke management. This study investigated whether a delayed short mild hypothermic treatment is still beneficial as neuroprotective strategy in the endothelin-1 (Et-1) rat model for a transient focal cerebral ischemia. Two hours of mild hypothermia (33°C) was induced 20, 60 or 120 minutes after Et-1 infusion. During the experiment the cerebral blood flow (CBF) was measured via Laser Doppler Flowmetry in the striatum, which represents the core of the infarct. Functional outcome and infarct volume were assessed 24 hours after the insult. In this sub-acute phase following stroke induction, the effects of the hypothermic treatment on apoptosis, phagocytosis and astrogliosis were assessed as well. Apoptosis was determined using caspase-3 immunohistochemistry, phagocytic cells were visualized by CD-68 expression and astrogliosis was studied by glial fibrillary acidic protein (GFAP) staining.

RESULTS

Cooling could be postponed up to 1 hour after the onset of the insult without losing its positive effects on neurological deficit and infarct volume. These results correlated with the caspase-3 staining. In contrast, the increased CD-68 expression post-stroke was reduced in the core of the insult with all treatment protocols. Hypothermia also reduced the increased levels of GFAP staining, even when it was delayed up to 2 hours after the insult. The study confirmed that the induction of the hypothermia treatment in the Et-1 model does not affect the CBF.

CONCLUSIONS

These data indicate that in the Et-1 rat model, a short mild hypothermic treatment delayed for 1 hour is still neuroprotective and correlates with apoptosis. At the same time, hypothermia also establishes a lasting inhibitory effect on the activation of astrogliosis.

Neuroprotection: lessons from hibernators

Mammals that hibernate experience extreme metabolic states and body temperatures as they transition between euthermia, a state resembling typical warm blooded mammals, and prolonged torpor, a state of suspended animation where the brain receives as low as 10% of normal cerebral blood flow. Transitions into and out of torpor are more physiologically challenging than the extreme metabolic suppression and cold body temperatures of torpor per se. Mammals that hibernate show unprecedented capacities to tolerate cerebral ischemia, a decrease in blood flow to the brain caused by stroke, cardiac arrest or brain trauma. While cerebral ischemia often leads to death or disability in humans and most other mammals, hibernating mammals suffer no ill effects when blood flow to the brain is dramatically decreased during torpor or experimentally induced during euthermia. These animals, as adults, also display rapid and pronounced synaptic flexibility where synapses retract during torpor and rapidly re-emerge upon arousal. A variety of coordinated adaptations contribute to tolerance of cerebral ischemia in these animals. In this review we discuss adaptations in heterothermic mammals that may suggest novel therapeutic targets and strategies to protect the human brain against cerebral ischemic damage and neurodegenerative disease.

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.

Hypothermia as a cytoprotective strategy in ischemic tissue injury

Hypothermia is a well established cytoprotectant, with remarkable and consistent effects demonstrated across multiple laboratories. At the clinical level, it has recently been shown to improve neurological outcome following cardiac arrest and neonatal hypoxia-ischemia. It is increasingly being embraced by the medical community, and could be considered an effective neuroprotectant. Conditions such as brain injury, hepatic encephalopathy and cardiopulmonary bypass seem to benefit from this intervention. It's role in direct myocardial protection is also being explored. A review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, cooling needs to begin soon after the insult, and maintained for relatively long period periods of time. In the case of ischemic stroke, cooling should ideally be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, given the technical challenges of rapidly and stably cooling patients. This review will discuss the application of hypothermia especially as it pertains to its effects neurological outcome, cooling methods, and important parameters in optimizing hypothermic protection.

The effects of desflurane on delayed neuronal injury after transient forebrain ischemia in the rat

BACKGROUND

Volatile anesthetics have been shown protective against focal or global cerebral ischemia in animal models. However isoflurane failed to provide persistent protection because of late onset of apoptosis after ischemia. The aim of this study was to elucidate the effects of desflurane on delayed neuronal damage after forebrain ischemia.

METHODS

Rats were divided into 2 groups and anesthetized with desflurane or isoflurane. Forebrain ischemia was produced by both induced hypotension and 10 minutes of common carotid artery clamping. After 2 days and 2 weeks, rats were killed under anesthesia and brains were removed for Western blot analysis of Bcl-2, Bax, and caspase 3 expression and histopathologic study.

RESULTS

The apoptotic cell numbers in hippocampal CA1 area were increased after 2 weeks, and there was no significant difference between groups. There was no significant difference in caspase 3 expression between groups. The Bax/Bcl-2 ratio was increased at 2 weeks after ischemia, and there was no significant difference between group.

CONCLUSIONS

The data indicate that desflurane also delays but does not prevent the neuronal injury caused by ischemia. Desflurane reduced the development of apoptosis early after ischemia but did not prevent it at later stages of post-ischemic recovery.

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.

Modulation of stress proteins and apoptotic regulators in the anoxia tolerant turtle brain

Freshwater turtles survive prolonged anoxia and reoxygenation without overt brain damage by well-described physiological processes, but little work has been done to investigate the molecular changes associated with anoxic survival. We examined stress proteins and apoptotic regulators in the turtle during early (1 h) and long-term anoxia (4, 24 h) and reoxygenation. Western blot analyses showed changes within the first hour of anoxia; multiple stress proteins (Hsp72, Grp94, Hsp60, Hsp27, and HO-1) increased while apoptotic regulators (Bcl-2 and Bax) decreased. Levels of the ER stress protein Grp78 were unchanged. Stress proteins remained elevated in long-term anoxia while the Bcl-2/Bax ratio was unaltered. No changes in cleaved caspase 3 levels were observed during anoxia while apoptosis inducing factor increased significantly. Furthermore, we found no evidence for the anoxic translocation of Bax from the cytosol to mitochondria, nor movement of apoptosis inducing factor between the mitochondria and nucleus. Reoxygenation did not lead to further increases in stress proteins or apoptotic regulators except for HO-1. The apparent protection against cell damage was corroborated with immunohistochemistry, which indicated no overt damage in the turtle brain subjected to anoxia and reoxygenation. The results suggest that molecular adaptations enhance pro-survival mechanisms and suppress apoptotic pathways to confer anoxia tolerance in freshwater turtles.

Inflammation and NFkappaB activation is decreased by hypothermia following global cerebral ischemia

We previously showed that hypothermia attenuates inflammation in focal cerebral ischemia (FCI) by suppressing activating kinases of nuclear factor-kappa B (NFkappaB). Here we characterize the inflammatory response in global cerebral ischemia (GCI), and the influence of mild hypothermia. Rodents were subjected to GCI by bilateral carotid artery occlusion. The inflammatory response was accompanied by microglial activation, but not neutrophil infiltration, or blood brain barrier disruption. Mild hypothermia reduced CA1 damage, decreased microglial activation and decreased nuclear NFkappaB translocation and activation. Similar anti-inflammatory effects of hypothermia were observed in a model of pure brain inflammation that does not cause brain cell death. Primary microglial cultures subjected to oxygen glucose deprivation (OGD) or stimulated with LPS under hypothermic conditions also experienced less activation and less NFkappaB translocation. However, NFkappaB regulatory proteins were not affected by hypothermia. The inflammatory response following GCI and hypothermia's anti-inflammatory mechanism is different from that observed in FCI.

Metabolic downregulation: a key to successful neuroprotection?

BACKGROUND AND PURPOSE

The search for effective neuroprotectants remains frustrating, particularly with regard to specific pharmaceuticals. However, laboratory studies have consistently shown remarkable neuroprotection with 2 nonpharmacological strategies-therapeutic hypothermia and ischemic preconditioning. Recent studies have shown that the mechanism of protection underlying both of these treatments is correlated to downregulation of cellular and tissue metabolism. Thus, understanding the mechanisms underlying such robust protective effects could lead to appropriate translation at the clinical level. In fact, hypothermia is already being used at many centers to improve neurological outcome from cardiac arrest.

METHODS

A systematic review of both topics is presented in terms of underlying pathophysiological mechanisms and application at the clinical level.

RESULTS

Although the mechanisms of protection for both therapeutic strategies are multifold, both share features of downregulating metabolism. Both therapeutic strategies are robust neuroprotectants, but translating them to the clinical arena is challenging, though not impossible, and clinical studies have shown or suggest benefits of both treatments.

CONCLUSIONS

The strategy of metabolic downregulation should be further explored to identify effective neuroprotectants that can be easily applied clinically.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

Differential protein expression following low temperature culture of suspension CHO-K1 cells

Background

To ensure maximal productivity of recombinant proteins (rP) during production culture it is typical to encourage an initial phase of rapid cell proliferation to achieve high biomass followed by a stationary phase where cellular energies are directed towards production of rP. During many such biphasic cultures, the initial phase of rapid cell growth at 37°C is followed by a growth arrest phase induced through reduction of the culture temperature. Low temperature induced growth arrest is associated with many positive phenotypes including increased productivity, sustained viability and an extended production phase, although the mechanisms regulating these phenotypes during mild hypothermia are poorly understood.

Results

In this study differential protein expression in suspension CHO-K1 cells was investigated following a reduction of the culture temperature from 37°C to 31°C in comparison to standard batch culture maintained at 37°C using 2D-DIGE (Fluorescence 2-D Difference Gel Electrophoresis) and mass spectrometry (MS). There is only limited proteomic analysis of suspension-grown CHO cells describing a direct comparison of temperature shifted versus non-temperature shifted cultures using 2D-DIGE. This investigation has enabled the identification of temperature-dependent as well as temperature-independent proteomic changes. 201 proteins were observed as differentially expressed following temperature shift, of which 118 were up regulated. Of the 53 proteins identified by MALDI-ToF MS, 23 were specifically differentially expressed upon reduction of the culture temperature and were found related to a variety of cellular functions such as regulation of growth (HNRPC), cap-independent translation (EIF4A), apoptosis (importin-α), the cytoskeleton (vimentin) and glycoprotein quality control (alpha glucosidase 2).

Conclusion

These results indicate the extent of the temperature response in CHO-K1 cells and suggest a number of key regulatory proteins and pathways that are involved in modulating the response of cells to mild hypothermia. Regulation of these identified proteins and pathways could be useful for future approaches to engineer CHO cells for improved recombinant protein production.

FasL shedding is reduced by hypothermia in experimental stroke

Protection by mild hypothermia has previously been associated with better mitochondrial preservation and suppression of the intrinsic apoptotic pathway. It is also known that the brain may undergo apoptotic death via extrinsic, or receptor-mediated pathways, such as that triggered by Fas/FasL. Male Sprague-Dawley rats subjected to 2 h middle cerebral artery occlusion with 2 h intraischemic mild hypothermia (33 degrees C) were assayed for Fas, FasL and caspase-8 expression. Ischemia increased Fas, but decreased FasL by approximately 50-60% at 6 and 24 h post-insult. Mild hypothermia significantly reduced expression of Fas and processed caspase-8 both by approximately 50%, but prevented ischemia-induced FasL decreases. Fractionation revealed that soluble/shed FasL (sFasL) was decreased by hypothermia, while membrane-bound FasL (mFasL) increased. To more directly assess the significance of the Fas/FasL pathway in ischemic stroke, primary neuron cultures were exposed to oxygen glucose deprivation. Since FasL is cleaved by matrix metalloproteinases (MMPs), and mild hypothermia decreases MMP expression, treatment with a pan-MMP inhibitor also decreased sFasL. Thus, mild hypothermia is associated with reduced Fas expression and caspase-8 activation. Hypothermia prevented total FasL decreases, and most of it remained membrane-bound. These findings reveal new observations regarding the effect of mild hypothermia on the Fas/FasL and MMP systems.

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.

Moderate hypothermia prevents neural cell apoptosis following spinal cord ischemia in rabbits

Paraplegia is a disastrous complication after operations of descending and thoracoabdominal aortic aneurysm. Regional hypothermia protects against spinal cord ischemia although the protective mechanism is not well know. The objective of this study is to examine whether hypothermia protects the spinal cord by preventing apoptosis of nerve cell and also investigate a possible mechanism involved in hypothermia neuroprotection. Cell apoptosis with necrosis was evident in the spinal cord 24 h after 30 min of ischemia. Moderate hypothermia decreased the incidence of apoptotic nerve cells. Both cell apoptosis and necrosis were attenuated by hypothermia. p53 expression increased and bcl-2 expression declined after ischemia, while hypothermia mitigated these changes. This study suggests that apoptosis contributes to cell death after spinal cord ischemia, and that moderate hypothermia can prevent nerve cell apoptosis by a mechanism associated with bcl-2 and p53 genes.

Hypothermia

Experimental studies show that, following hypoxic ischaemic injury, mild induced hypothermia-a reduction of body temperature by about 3 degrees C -- preserves cerebral energy metabolism, reduces cerebral tissue injury and improves neurological function. Randomized trials in full-term and near-full-term newborns suggest that treatment with mild hypothermia is safe and improves survival without disabilities up to 18 months of age. Although the optimal time of initiation, the depth and duration, and the method of cooling are uncertain, in the absence of specific treatments many clinicians will wish to consider treating asphyxiated infants with hypothermia. Guidance now needs to be provided to promote uniform practice, to avoid inappropriate treatment and to foster continuing collaboration in future studies of neuroprotection following asphyxia. If the promising results of the current trials are confirmed by the findings from other on-going studies, with longer follow-up, the impact of such a treatment on the babies, their families and health resources in the shorter and longer terms will be considerable.

Hypothermia treatment potentiates ERK1/2 activation after traumatic brain injury

Traumatic brain injury (TBI) results in significant hippocampal pathology and hippocampal-dependent memory loss, both of which are alleviated by hypothermia treatment. To elucidate the molecular mechanisms regulated by hypothermia after TBI, rats underwent moderate parasagittal fluid-percussion brain injury. Brain temperature was maintained at normothermic or hypothermic temperatures for 30 min prior and up to 4 h after TBI. The ipsilateral hippocampus was assayed with Western blotting. We found that hypothermia potentiated extracellular signal-regulated kinase 1/2 (ERK1/2) activation and its downstream effectors, p90 ribosomal S6 kinase (p90RSK) and the transcription factor cAMP response element-binding protein. Phosphorylation of another p90RSK substrate, Bad, also increased with hypothermia after TBI. ERK1/2 regulates mRNA translation through phosphorylation of mitogen-activated protein kinase-interacting kinase 1 (Mnk1) and the translation factor eukaryotic initiation factor 4E (eIF4E). Hypothermia also potentiated the phosphorylation of both Mnk1 and eIF4E. Augmentation of ERK1/2 activation and its downstream signalling components may be one molecular mechanism that hypothermia treatment elicits to improve functional outcome after TBI.

Neuronal apoptosis following cerebral ischaemia: pathophysiology and possible therapeutic implications

PURPOSE OF REVIEW

Neuronal apoptosis following cerebral ischaemia has become an issue of extraordinary scientific interest in the past decade. Besides necrosis, this highly relevant pathomechanism has been shown to be markedly involved in the pathogenesis of delayed postischaemic neuronal damage. As a result, a variety of possible neuroprotective strategies and therapeutic options subsequent to cerebral ischaemia have emerged. This article provides an overview of the pathophysiologic mechanisms underlying delayed neuronal apoptotic degeneration after cerebral ischaemia. Based on these facts, selected therapeutic implications are discussed in detail.

RECENT FINDINGS

Recent findings from experimental studies have demonstrated a new therapeutic neuroprotective potential of pharmaceutical blockade of death-inducing ligands (e.g. Fas/CD95 ligand), enhancement of survival signal transduction with endogenous ligands (e.g. erythropoietin) and therapeutically modulating the balance between intracellular anti- and proapoptotic Bcl proteins with intriguing molecular techniques after cerebral ischaemia.

SUMMARY

Neuronal apoptosis is highly relevant in the pathophysiology of neurodegenerative disorders, neurotrauma and cerebral ischaemia/reperfusion. Within the past few years, a variety of therapeutic strategies have emerged based on our increasing knowledge of the pathophysiology of apoptosis. Whereas inhibition of single factors in apoptotic cascades (e.g. proteases) has produced rather unsatisfying results, new opportunities have emerged at the molecular level due to advances in molecular medicine. These approaches offer promising opportunities for neuroprotective therapeutic strategies subsequent to cerebral ischaemia. It is tempting to speculate that a combination ('cocktail') of these antiapoptotic interventions might even increase their neuroprotective potential.

Control and regulation of the cellular responses to cold shock: the responses in yeast and mammalian systems

Although the cold-shock response has now been studied in a number of different organisms for several decades, it is only in the last few years that we have begun to understand the molecular mechanisms that govern adaptation to cold stress. Notably, all organisms from prokaryotes to plants and higher eukaryotes respond to cold shock in a comparatively similar manner. The general response of cells to cold stress is the elite and rapid overexpression of a small group of proteins, the so-called CSPs (cold-shock proteins). The most well characterized CSP is CspA, the major CSP expressed in Escherichia coli upon temperature downshift. More recently, a number of reports have shown that exposing yeast or mammalian cells to sub-physiological temperatures (<30 or <37 degrees C respectively) invokes a co-ordinated cellular response involving modulation of transcription, translation, metabolism, the cell cycle and the cell cytoskeleton. In the present review, we summarize the regulation and role of cold-shock genes and proteins in the adaptive response upon decreased temperature with particular reference to yeast and in vitro cultured mammalian cells. Finally, we present an integrated model for the co-ordinated responses required to maintain the viability and integrity of mammalian cells upon mild hypothermic cold shock.

Neuroprotective role of Z-ligustilide against forebrain ischemic injury in ICR mice

Radix Angelica sinensis, known as Danggui in Chinese, has been used to treat cardiovascular and cerebrovascular diseases in Traditional Chinese Medicine for a long time. Modern phytochemical studies showed that Z-ligustilide (LIG) is the main lipophilic component of Danggui. In this study, we examined whether LIG could protect ischemia/reperfusion-induced brain injury by minimizing oxidative stress and anti-apoptosis. Transient forebrain cerebral ischemia (FCI) was induced by the bilateral common carotid arteries occlusion for 30 min. LIG was intraperitoneally injected to ICR mice at the beginning of reperfusion. As determined via 2,3,5-triphenyl tetrazolium chloride (TTC) staining at 24 h following ischemia, the infarction volume in the FCI mice treated without LIG (22.1 +/- 2.6%) was significantly higher than that in the FCI mice treated with 5 mg/kg (11.8 +/- 5.2%) and 20 mg/kg (2.60 +/- 1.5%) LIG (P < 0.05 or P < 0.01). LIG treatment significantly decreased the level of malondialdehyde (MDA) and increased the activities of the antioxidant enzyme glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) in the ischemic brain tissues (P < 0.05 or P < 0.01 vs. FCI group). In addition, LIG provided a great increase in Bcl-2 expression as well as a significant decrease in Bax and caspase-3 immunoreactivities in the ischemic cortex. The findings demonstrated that LIG could significantly protect the brain from damage induced by transient forebrain cerebral ischemia. The antioxidant and anti-apoptotic properties of LIG may contribute to the neuroprotective potential of LIG in cerebral ischemic damage.

The cold-shock response in cultured mammalian cells: harnessing the response for the improvement of recombinant protein production

There are a growing number of reports on the sub-physiological temperature culturing (<37 degrees C) of mammalian cells for increased recombinant protein yield, although the effect is variable between cell lines, expression systems, and the product of interest. What is becoming clear is that exposing mammalian cells to sub-physiological temperatures invokes a coordinated cellular response involving modulation of the cell cycle, metabolism, transcription, translation, and the cell cytoskeleton. Opportunities currently exist for further enhancement of the cold-shock effect on recombinant protein production in mammalian cells through advancements in our understanding of the mechanisms involved in the cold-shock response.

99mTc-HYNIC-annexin V SPECT imaging of acute stroke and its response to neuroprotective therapy with anti-Fas ligand antibody

PURPOSE

The first aim of the study was to determine whether (99m)Tc-HYNIC-annexin V, a marker of cellular stress and apoptosis, can detect ischemic injury in patients with acute stroke. Secondly, we wished to test radiolabeled annexin's ability to monitor therapy in a rodent model of focal ischemic injury.

METHODS

SPECT imaging of patients was performed between 1 and 2 h after intravenous injection of 30 mCi (1,110 MBq) of tracer. Eight MFL4 (anti-FasL) antibody-treated (400 microg i.p. days 0 and 3) and 21 control adult male Sprague-Dawley rats underwent small animal SPECT imaging with 5-10 mCi (185-370 MBq) of tracer, 1 and 6 days after a 2-h intraluminal thread occlusion of the left middle cerebral artery.

RESULTS

Two patients with acute stroke had regions of multifocal annexin uptake that correlated with sites of restricted diffusion on MRI. Anti-FasL antibody treatment significantly reduced annexin uptake by 92% with a 60% decrease in the number of caspase-8 staining (apoptotic) neurons on day 1. On day 6, treated animals had an 80% reduction in tracer uptake with a 75% decrease in infarct size as compared with controls. Annexin uptake in controls and treated animals (day 6) linearly correlated with infarct size (r (2)=0.603, p=0.0036) and the number of TUNEL-positive (apoptotic) nuclei (r (2)=0.728, p=0.00084).

CONCLUSION

Annexin imaging shows foci of increased uptake at sites of ischemic injury in patients with acute stroke. Annexin imaging can assess the effects of therapy for ischemic cerebral injury in rats, suggesting its potential as a non-invasive indicator of drug efficacy in future clinical trials.

Intraischemic mild hypothermia prevents neuronal cell death and tissue loss after neonatal cerebral hypoxia-ischemia

The effectiveness of hypothermia in preventing ischemic brain damage depends on when it is started. The purpose of this study was to investigate the effects of temperature reduction during a hypoxic-ischemic (HI) insult on brain injury and signalling pathways of neuronal cell death and survival. Seven-day-old mice were subjected to left common carotid artery ligation and hypoxia (10% oxygen) at different temperatures (37, 36 or 34 degrees C) for 50 min. Brain injury at 7 days post-HI was significantly reduced from 67.4% at 37 degrees C to 31.6% at 36 degrees C and 10% at 34 degrees C, with no observable injury in the cortex of the 34 degrees C group. Cytochrome c release, caspase-3 activation and apoptosis-inducing factor translocation from mitochondria to nuclei were all significantly inhibited after intraischemic temperature reduction. Concurrently, the cell survival signalling pathway involving Akt was significantly sustained (the phosphorylated form of Akt was maintained) when the hypoxia temperature was decreased. These results indicate that intraischemic hypothermia diminished apoptosis through inhibition of both caspase-dependent and caspase-independent neuronal cell death pathways and promoted cell survival by inhibition of phosphorylated Akt dephosphorylation in the neonatal brain, thereby preventing neuronal cell death.

Hypothermia and ERK activation after cardiac arrest

Mild hypothermia improves survival and neurological outcome after cardiac arrest, as well as increasing activation of the extracellular-signal-regulated kinase (ERK) in hippocampus. ERK signaling is involved in neuronal growth and survival. We tested the hypothesis that the beneficial effects of hypothermia required ERK activation. ERK activation was measured by immunoblotting with phosphorylation-specific antibodies. Rats (n = 8 per group) underwent 8 min of asphyxial cardiac arrest and were resuscitated with chest compressions, ventilation, epinephrine and bicarbonate. At 30 min after resuscitation, vehicle (50% saline:50% DMSO) or the ERK kinase inhibitor U0126 (100 microg) was infused into the lateral ventricle. Cranial temperature was kept at either 33 degrees C (hypothermia) or 37 degrees C (normothermia) between 1 and 24 h. Neurological function was assessed daily for 14 days. Surviving neurons were counted in the hippocampus. A dose of 100 mug U0126 inhibited ERK bilaterally for 12 to 24 h and decreased phosphorylation of the ERK substrates ATF-2 and CREB. As in previous studies, hypothermia improved survival, neurological and histological outcome after cardiac arrest. However, survival, neurological score and histology did not differ between U0126 and vehicle-treated rats after cardiac arrest. Therefore, a dose of U0126 sufficient to inhibit biochemical markers of ERK signaling in hippocampus does not alter the beneficial effects of hypothermia induced after resuscitation in rats and did not affect recovery of normothermia-treated rats. These results suggest that hypothermia-induced improvement in outcomes does not require ERK activation.

Biphasic cytochrome c release after transient global ischemia and its inhibition by hypothermia

Hypothermia is effective in preventing ischemic damage. A caspase-dependent apoptotic pathway is involved in ischemic damage, but how hypothermia inhibits this pathway after global cerebral ischemia has not been well explored. It was determined whether hypothermia protects the brain by altering cytochrome c release and caspase activity. Cerebral ischemia was produced by two-vessel occlusion plus hypotension for 10 mins. Body temperature in hypothermic animals was reduced to 33 degrees C before ischemia onset and maintained for 3 h after reperfusion. Western blots of subcellular fractions revealed biphasic cytosolic cytochrome c release, with an initial peak at about 5 h after ischemia, which decreased at 12 to 24 h, and a second, larger peak at 48 h. Caspase-3 and -9 activity increased at 12 and 24 h. A caspase inhibitor, Z-DEVD-FMK, administered 5 and 24 h after ischemia onset, protected hippocampal CA1 neurons from injury and blocked the second cytochrome c peak, suggesting that caspases mediate this second phase. Hypothermia (33 degrees C), which prevented CA1 injury, did not inhibit cytochrome c release at 5 h, but reduced cytochrome c release at 48 h. Caspase-3 and -9 activity was markedly attenuated by hypothermia at 12 and 24 h. Thus, biphasic cytochrome c release occurs after transient global ischemia and mild hypothermia protects against ischemic damage by blocking the second phase of cytochrome c release, possibly by blocking caspase activity.

Long-term effects of hypothermia on neuronal cell death and the concentration of apoptotic proteins after incomplete cerebral ischemia and reperfusion in rats

BACKGROUND

The present study investigates the long-term effects of postischemic hypothermia on neuronal cell damage and concentration changes of apoptotic proteins after cerebral ischemia.

METHODS

Sixty-four Sprague-Dawley rats were anesthetized, intubated and ventilated with 2.0 Vol% isoflurane and 70% N2O/O2. After preparation the animals were randomly assigned to the following groups: group 1 (n = 32, fentanyl-N2O/normothermia 37.5 degrees C), and group 2 (n = 32, fentanyl-N2O/hypothermia 34.0 degrees C. Ischemia (45 min) was induced by common carotid artery occlusion plus hemorrhagic hypotension (MAP = 40 mmHg). Arterial blood gases and pH were maintained constant. After 1, 3, 7, or 28 days (each n = 8) the brains were removed, frozen and cut. Neuronal damage was assessed by analyzing Bax, Bcl-2, p53, and Mdm-2 proteins, activated caspases-3-positive and eosinophilic cells. A third group (n = 8) of untreated animals served as naive controls.

RESULTS

In hypothermic animals, Bax concentration was decreased by 50-70% over time compared to normothermia. On days 1 and 3, Bcl-2 was increased by 50% with hypothermia. The amount of activated caspase-3-positive cells in the ischemic hemisphere was 0.5% in the hypothermic and 1-2% in the normothermic animals. Of the hippocampal cells, 10-25% were eosinophilic in both groups over time.

CONCLUSION

The present data show that hypothermia prevents an ischemia-induced increase of the pro-apoptotic protein Bax for as long as 28 days and increases the concentration of the antiapoptotic protein Bcl-2 up to 3 days compared to normothermic animals. Therefore, after cerebral ischemia, hypothermia has the sustained neuroprotective potential to shift apoptosis-related proteins towards neuronal cell survival.