Prolonged but delayed postischemic hypothermia: a long-term outcome study in the rat middle cerebral artery occlusion model

The neurophysiological effect of mild hypothermia in gyrencephalic brains submitted to ischemic stroke and spreading depolarizations

Objective

Characterize the neurophysiological effects of mild hypothermia on stroke and spreading depolarizations (SDs) in gyrencephalic brains.

Methods

Left middle cerebral arteries (MCAs) of six hypothermic and six normothermic pigs were permanently occluded (MCAo). Hypothermia began 1 h after MCAo and continued throughout the experiment. ECoG signals from both frontoparietal cortices were recorded. Five-minute ECoG epochs were collected 5 min before, at 5 min, 4, 8, 12, and 16 h after MCAo, and before, during, and after SDs. Power spectra were decomposed into fast (alpha, beta, and gamma) and slow (delta and theta) frequency bands.

Results

In the vascular insulted hemisphere under normothermia, electrodes near the ischemic core exhibited power decay across all frequency bands at 5 min and the 4th hour after MCAo. The same pattern was registered in the two furthest electrodes at the 12th and 16th hour. When mild hypothermia was applied in the vascular insulted hemispheres, the power decay was generalized and seen even in electrodes with uncompromised blood flow. During SD analysis, hypothermia maintained increased delta and beta power during the three phases of SDs in the furthest electrode from the ischemic core, followed by the second furthest and third electrode in the beta band during preSD and postSD segments. However, in hypothermic conditions, the third electrode showed lower delta, theta, and alpha power.

Conclusion

Mild hypothermia attenuates all frequency bands in the vascularly compromised hemisphere, irrespective of the cortical location. During SD formation, it preserves power spectra more significantly in electrodes further from the ischemic core.

Mild hypothermia reduces spreading depolarizations and infarct size in a swine model

Spreading depolarizations (SDs) have been linked to infarct volume expansion following ischemic stroke. Therapeutic hypothermia provides a neuroprotective effect after ischemic stroke. This study aimed to evaluate the effect of hypothermia on the propagation of SDs and infarct volume in an ischemic swine model. Through left orbital exenteration, middle cerebral arteries were surgically occluded (MCAo) in 16 swine. Extensive craniotomy and durotomy were performed. Six hypothermic and five normothermic animals were included in the analysis. An intracranial temperature probe was placed right frontal subdural. One hour after ischemic onset, mild hypothermia was induced and eighteen hours of electrocorticographic (ECoG) and intrinsic optical signal (IOS) recordings were acquired. Postmortem, 4 mm-thick slices were stained with 2,3,5-triphenyltetrazolium chloride to estimate the infarct volume. Compared to normothermia (36.4 ± 0.4°C), hypothermia (32.3 ± 0.2°C) significantly reduced the frequency and expansion of SDs (ECoG: 3.5 ± 2.1, 73.2 ± 5.2% vs. 1.0 ± 0.7, 41.9 ± 21.8%; IOS 3.9 ± 0.4, 87.6 ± 12.0% vs. 1.4 ± 0.7, 67.7 ± 8.3%, respectively). Further, infarct volume among hypothermic animals (23.2 ± 1.8% vs. 32.4 ± 2.5%) was significantly reduced. Therapeutic hypothermia reduces infarct volume and the frequency and expansion of SDs following cerebral ischemia.

Therapeutic strategies for intracerebral hemorrhage

Stroke is the second highest cause of death globally, with an increasing incidence in developing countries. Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes. ICH is associated with poor neurological outcomes and high mortality due to the combination of primary and secondary injury. Fortunately, experimental therapies are available that may improve functional outcomes in patients with ICH. These therapies targeting secondary brain injury have attracted substantial attention in their translational potential. Here, we summarize recent advances in therapeutic strategies and directions for ICH and discuss the barriers and issues that need to be overcome to improve ICH prognosis.

Unanswered questions regarding therapeutic hypothermia for neonates with neonatal encephalopathy

Therapeutic hypothermia (TH) is now well established to improve intact survival after neonatal encephalopathy (NE). However, many questions could not be addressed by the randomized controlled trials. Should late preterm newborns with NE be cooled? Is cooling beneficial for mild NE? Is the current therapeutic time window optimal, or could it be shortened or prolonged? Will either milder or deeper hypothermia be effective? Does infection/inflammation exposure in the perinatal period in combination with NE offer potentially beneficial preconditioning or might it obviate hypothermic neuroprotection? In the present review, we dissect the evidence, for whom, when and how can TH best be delivered, and highlight areas that need further research.

Therapeutic hypothermia for intracerebral hemorrhage: Systematic review and meta-analysis of the experimental and clinical literature

BACKGROUND

Intracerebral hemorrhage remains the deadliest form of stroke worldwide, inducing neuronal death through a wide variety of pathways. Therapeutic hypothermia is a robust and well-studied neuroprotectant widely used across a variety of specialties.

AIMS

This review summarizes results from preclinical and clinical studies to highlight the overall effectiveness of therapeutic hypothermia to improve long-term intracerebral hemorrhage outcomes while also elucidating optimal protocol regimens to maximize therapeutic effect.

SUMMARY OF REVIEW

A systematic review was conducted across three databases to identify trials investigating the use of therapeutic hypothermia to treat intracerebral hemorrhage. A random-effects meta-analysis was conducted on preclinical studies, looking at neurobehavioral outcomes, blood brain barrier breakdown, cerebral edema, hematoma volume, and tissue loss. Several mixed-methods meta-regression models were also performed to adjust for variance and variations in hypothermia induction procedures. Twwenty-one preclinical studies and five human studies were identified. The meta-analysis of preclinical studies demonstrated a significant benefit in behavioral scores (ES = -0.43, p = 0.02), cerebral edema (ES = 1.32, p = 0.0001), and blood brain barrier (ES = 2.73, p ≤ 0.00001). Therapeutic hypothermia was not found to significantly affect hematoma expansion (ES = -0.24, p = 0.12) or tissue loss (ES = 0.06, p = 0.68). Clinical study outcome reporting was heterogeneous; however, there was recurring evidence of therapeutic hypothermia-induced edema reduction.

CONCLUSIONS

The combined preclinical evidence demonstrates that therapeutic hypothermia reduced multiple cell death mechanisms initiated by intracerebral hemorrhage; yet, there is no definitive evidence in clinical studies. The cooling strategies employed in both preclinical and clinical studies were highly diverse, and focused refinement of cooling protocols should be developed in future preclinical studies. The current data for therapeutic hypothermia in intracerebral hemorrhage remains questionable despite the highly promising indications in preclinical studies. Definitive randomized controlled studies are still required to answer this therapeutic question.

Automation of training and testing motor and related tasks in pre-clinical behavioural and rehabilitative neuroscience

Testing and training animals in motor and related tasks is a cornerstone of pre-clinical behavioural and rehabilitative neuroscience. Yet manually testing and training animals in these tasks is time consuming and analyses are often subjective. Consequently, there have been many recent advances in automating both the administration and analyses of animal behavioural training and testing. This review is an in-depth appraisal of the history of, and recent developments in, the automation of animal behavioural assays used in neuroscience. We describe the use of common locomotor and non-locomotor tasks used for motor training and testing before and after nervous system injury. This includes a discussion of how these tasks help us to understand the underlying mechanisms of neurological repair and the utility of some tasks for the delivery of rehabilitative training to enhance recovery. We propose two general approaches to automation: automating the physical administration of behavioural tasks (i.e., devices used to facilitate task training, rehabilitative training, and motor testing) and leveraging the use of machine learning in behaviour analysis to generate large volumes of unbiased and comprehensive data. The advantages and disadvantages of automating various motor tasks as well as the limitations of machine learning analyses are examined. In closing, we provide a critical appraisal of the current state of automation in animal behavioural neuroscience and a prospective on some of the advances in machine learning we believe will dramatically enhance the usefulness of these approaches for behavioural neuroscientists.

Neuroprotective effect of magnesium supplementation on cerebral ischemic diseases

Ischemic encephalopathy is associated with a high mortality and rate of disability. The most common type of ischemic encephalopathy, ischemic stroke, is the second leading cause of death in the world. At present, the main treatment for ischemic stroke is to reopen blocked blood vessels. However, despite revascularization, many patients are not able to achieve good functional results. At the same time, the strict time window (<4.5 h) of thrombolytic therapy limits clinical application. Therefore, it is important to explore effective neuroprotective drugs for the treatment of ischemic stroke. Magnesium is a natural calcium antagonist, which exerts neuroprotective effects through various mechanisms. However, while most basic studies have shown that magnesium supplementation can help treat cerebral ischemia, intravenous magnesium supplementation in large clinical trials has failed to improve prognosis of ischemic patients. Therefore, we review the basic and clinical studies of magnesium supplementation for cerebral ischemia. According to the route of administration, treatment can be divided into intraperitoneal magnesium supplementation, intravenous magnesium supplementation, arterial magnesium supplementation and intracranial magnesium supplementation. We also summarized the potential influencing factors of magnesium ion intervention in cerebral ischemia injury. Finally, in combination with influencing factors derived from basic research, this article proposes three future research directions, including magnesium supplementation into the circulatory system combined with magnesium supplementation in the lateral ventricle, magnesium supplementation in the lateral ventricle combined with hypothermia therapy, and lateral ventricle magnesium supplementation combined with intracarotid magnesium supplementation combined with selective hypothermia.

Selection of preclinical models to evaluate intranasal brain cooling for acute ischemic stroke

Stroke accounts for a large proportion of global mortality and morbidity. Selective hypothermia, via intranasal cooling devices, is a promising intervention in acute ischemic stroke. However, prior to large clinical trials, preclinical studies in large animal models of ischemic stroke are needed to assess the efficacy, safety, and feasibility of intranasal cooling for selective hypothermia as a neuroprotective strategy. Here, we review the available scientific literature for evidence supporting selective hypothermia and make recommendations of a preclinical, large, animal-based, ischemic stroke model that has the greatest potential for evaluating intranasal cooling for selective hypothermia and neuroprotection. We conclude that among large animal models of focal ischemic stroke including pigs, sheep, dogs, and nonhuman primates (NHPs), cynomolgus macaques have nasal anatomy, nasal vasculature, neuroanatomy, and cerebrovasculature that are most similar to those of humans. Moreover, middle cerebral artery stroke in cynomolgus macaques produces functional and behavioral deficits that are quantifiable to a greater degree of precision and detail than those that can be revealed through available assessments for other large animals. These NHPs are also amenable to extensive neuroimaging studies as a means of monitoring stroke evolution and evaluating infarct size. Hence, we suggest that cynomolgus macaques are best suited to assess the safety and efficacy of intranasal selective hypothermia through an evaluation of hyperacute diffusion-weighted imaging and subsequent investigation of chronic functional recovery, prior to randomized clinical trials in humans.

Therapeutic hypothermia and Type II errors: Do not throw out the baby with the ice water

After initial enthusiasm for mild therapeutic hypothermia (TH) treatment after brain injuries, including global cerebral ischemia after cardiac arrest, subsequent trials suggested similar benefit using only targeted temperature management (TTM), with fewer side effects. Globally, effective treatment of brain ischemia with TH has declined. Recent data suggest, however, that TH to 33°C may be superior to TTM. We review the background and rationale underlying TH and TTM. We present previously published data from our own laboratory that confirms TH to 33°C provides superior brain cytoprotection, compared to 35°C or 37°C, over a range of delays to treatment and several durations of TH. We illustrate that the treatment effect size of either or 35 is superior to 37, but the effect size difference between 33 and 35, although significant, is small. We estimate that to demonstrate the superiority of TTM over TH, a clinical trial would need between 3,000 and 9,000 patients depending on the desired treatment effect size. Our review and our own data suggest that TH to 33°C is superior to TTM to 36°C, but an extremely large clinical trial would be needed to demonstrate the difference.

Differential effects of hypothermia on neurovascular unit determine protective or toxic results: Toward optimized therapeutic hypothermia

Therapeutic hypothermia (TH) benefits survivors of cardiac arrest and neonatal hypoxic-ischemic injury and may benefit stroke patients. Large TH clinical trials, however, have shown mixed results. Given the substantial pre-clinical literature supporting TH, we explored possible mechanisms for clinical trial variability. Using a standard rodent stroke model (n = 20 per group), we found smaller infarctions after 2 h pre- or post-reperfusion TH compared to 4 h. To explore the mechanism of this discrepancy, we used primary cell cultures of rodent neurons, astrocytes, or endothelial cells subjected to oxygen-glucose deprivation (OGD). Then, cells were randomly assigned to 33℃, 35℃ or 37℃ for varying durations after varying delay times. Both 33 and 35℃ TH effectively preserved all cell types, although 33℃ was superior. Longer cooling durations overcame moderate delays to cooling initiation. In contrast, TH interfered with astrocyte paracrine protection of neurons in a temperature-dependent manner. These findings suggest that longer TH is needed to overcome delays to TH onset, but shorter TH durations may be superior to longer, perhaps due to suppression of astrocytic paracrine support of neurons during injury. We propose a scheme for optimizing TH after cerebral injury to stimulate further studies of cardiac arrest and stroke.

Should therapeutic hypothermia be offered to babies with mild neonatal encephalopathy in the first 6 h after birth?

Infants with moderate to severe neonatal encephalopathy (NE) benefit significantly from therapeutic hypothermia, with reduced risk of death or disability. However, the need for therapeutic hypothermia for infants with milder NE remains unclear. It has been suggested that these infants should not be offered therapeutic hypothermia as they may not be at risk for adverse neurodevelopmental outcome and that the balance of risk against potential benefit is unknown. Several key questions need to be answered including first, whether one can define NE in the first 6 h after birth so as to accurately distinguish infants with brain injury who may be at risk for adverse neurodevelopmental consequences. Second, will treatment of infants with mild NE with therapeutic hypothermia improve or even worsen neurological outcomes? Although alternate treatment protocols for mild NE may be feasible, the use of the current approach combined with rigorous avoidance of hyperthermia and initiation of hypothermia as early as possible after birth may promote optimal outcomes. Animal experimental data support the potential for greater benefit for mild HIE compared with moderate to severe HIE. This review will summarize current knowledge of mild NE and the challenges to a trial in this population.

Therapeutic Hypothermia in Neonatal Hypoxic-Ischemic Encephalopathy

PURPOSE OF REVIEW

Therapeutic hypothermia reduces death or disability in term and near-term infants with moderate-severe hypoxic-ischemic encephalopathy. Nevertheless, many infants still survive with disability, despite hypothermia, supporting further research in to ways to further improve neurologic outcomes.

RECENT FINDINGS

Recent clinical and experimental studies have refined our understanding of the key parameters for hypothermic neuroprotection, including timing of initiation, depth, and duration of hypothermia, and subsequent rewarming rate. However, important knowledge gaps remain. There is encouraging clinical evidence from a small phase II trial that combined treatment of hypothermia with recombinant erythropoietin further reduces risk of disability but definitive studies are still needed. In conclusion, recent studies suggest that current protocols for therapeutic hypothermia are near-optimal, and that the key to better neurodevelopmental outcomes is earlier diagnosis and initiation of hypothermia after birth. Further research is essential to find and evaluate ways to further improve outcomes after hypoxic-ischemic encephalopathy, including add-on therapies for therapeutic hypothermia and preventing pyrexia during labor and delivery.

Neonatal encephalopathy and hypoxic-ischemic encephalopathy

Acute hypoxic-ischemic encephalopathy around the time of birth remains a major cause of death and life-long disability. The key insight that led to the modern revival of studies of neuroprotection was that, after profound asphyxia, many brain cells show initial recovery from the insult during a short "latent" phase, typically lasting approximately 6h, only to die hours to days later after a "secondary" deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration and continued for a sufficient duration to allow the secondary deterioration to resolve is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild to moderate induced hypothermia significantly improves survival and neurodevelopmental outcomes in infancy and mid-childhood.

Luteoloside attenuates neuroinflammation in focal cerebral ischemia in rats via regulation of the PPARγ/Nrf2/NF-κB signaling pathway

Luteoloside, a flavonoid compound, has been reported to have anti-inflammatory, anti-oxidative, antibacterial, antiviral, anticancer, and cardioprotective effects, among others, but its neuroprotective effects have rarely been studied. The purpose of this study was to investigate the protective effect of luteoloside on cerebral ischemia and explore its potential mechanism. Middle cerebral artery occlusion (MCAO) was performed to investigate the effects of luteoloside on cerebral ischemia-reperfusion (I/R). Male Sprague-Dawley rats were randomly divided into six groups: sham, MCAO, luteoloside (20 mg/kg, 40 mg/kg, 80 mg/kg) and nimodipine (4 mg/kg). The results showed that luteoloside alleviated neurologic deficits and cerebral edema as well as improved cerebral infarction and histopathological changes in MCAO rats. Luteoloside significantly inhibited I/R-induced neuroinflammation, as demonstrated by reduced levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in the brain tissues of MCAO rats. Furthermore, our results demonstrated that luteoloside significantly suppressed the activation of nuclear factor-kappa B (NF-κB) signaling, upregulated the protein expression of peroxisome proliferator activated receptor gamma (PPARγ) and increased NF-E2-related factor (Nrf2) nuclear accumulation in MCAO rats. Collectively, our findings suggested that luteoloside played a crucial neuroprotective role by inhibiting NF-κB signaling in focal cerebral ischemia in rats. Furthermore, PPARγ and Nrf2 were also important for the anti-inflammatory effect of luteoloside. In addition, our data suggested that luteoloside might be an effective treatment for cerebral ischemia and other neurological disorders.

Hypothermia in acute ischemic stroke therapy

Therapeutic hypothermia (TH) is a potent neuroprotective therapy in experimental cerebral ischemia, with multiple effects at several stages of the ischemic cascade. In animals, TH is so powerful that all preclinical stroke studies require strict temperature control. In humans, multiple clinical studies documented powerful protection with TH after accidental neonatal hypoxic-ischemic injury and global cerebral ischemia with return of spontaneous circulation after cardiac arrest. National and international guidelines recommend TH for selected survivors of global ischemia, with profound benefits seen. Recently, a study comparing target temperature 33-36°C failed to demonstrate significant effects in cardiac arrest patients. Additionally, clinical trials of TH for head trauma and stroke have so far failed to confirm benefit in humans despite a vast preclinical literature. Therefore, it is now critical to understand the fundamental explanation for the success of TH in some, but famously not all, clinical trials. TH in animals appears to work when used soon after ischemia onset; for a short duration; and at a deep target temperature.

Cellular and Molecular Mechanisms Underlying Non-Pharmaceutical Ischemic Stroke Therapy in Aged Subjects

The incidence of ischemic stroke in humans increases exponentially above 70 years both in men and women. Comorbidities like diabetes, arterial hypertension or co-morbidity factors such as hypercholesterolemia, obesity and body fat distribution as well as fat-rich diet and physical inactivity are common in elderly persons and are associated with higher risk of stroke, increased mortality and disability. Obesity could represent a state of chronic inflammation that can be prevented to some extent by non-pharmaceutical interventions such as calorie restriction and hypothermia. Indeed, recent results suggest that H₂S-induced hypothermia in aged, overweight rats could have a higher probability of success in treating stroke as compared to other monotherapies, by reducing post-stroke brain inflammation. Likewise, it was recently reported that weight reduction prior to stroke, in aged, overweight rats induced by caloric restriction, led to an early re-gain of weight and a significant improvement in recovery of complex sensorimotor skills, cutaneous sensitivity, or spatial memory.

CONCLUSION

animal models of stroke done in young animals ignore age-associated comorbidities and may explain, at least in part, the unsuccessful bench-to-bedside translation of neuroprotective strategies for ischemic stroke in aged subjects.

Assessment of behavioural deficits following ischaemic stroke in the marmoset

Stroke is a common and devastating disease worldwide. Over the last two decades, many therapeutic approaches to ameliorate ischaemic stroke have been promising in animal studies but failed when transferred to the clinical situation. One of the possible explanations for these failures is the widespread use of animal models of cerebral ischemia that do not mimic the pathology encountered in the clinic. Accordingly, many expert committees recommended the integration of higher order species such as non-human primates in pre-clinical stroke studies. The common marmoset (Callithrix jacchus), a small New World monkey, start to stand out in the neuroscience field as a good compromise between larger primates and rodents. In this review, we discuss the relevance of the use of the marmoset in stroke studies. We will focus on behavioural tests developed in this species to assess sensorimotor deficits and their recovery during acute and chronic stages of brain ischaemia. The aim of this appraisal is to provide a comprehensive overview of the existing approaches to induce stroke in the marmoset as well as the paradigms for behavioural testing in this species. The data summarized in this review should contribute to the improvement of future stoke studies in the marmoset and accordingly improve the translation of the results from bench to bed.

Impact of Stroke Therapy Academic Industry Roundtable (STAIR) Guidelines on Peri-Anesthesia Care for Rat Models of Stroke: A Meta-Analysis Comparing the Years 2005 and 2015

Numerous studies using rats in stroke models have failed to translate into successful clinical trials in humans. The Stroke Therapy Academic Industry Roundtable (STAIR) has produced guidelines on the rodent stroke model for preclinical trials in order to promote the successful translation of animal to human studies. These guidelines also underline the importance of anaesthetic and monitoring techniques. The aim of this literature review is to document whether anaesthesia protocols (i.e., choice of agents, mode of ventilation, physiological support and monitoring) have been amended since the publication of the STAIR guidelines in 2009. A number of articles describing the use of a stroke model in adult rats from the years 2005 and 2015 were randomly selected from the PubMed database and analysed for the following parameters: country where the study was performed, strain of rats used, technique of stroke induction, anaesthetic agent for induction and maintenance, mode of intubation and ventilation, monitoring techniques, control of body temperature, vascular accesses, and administration of intravenous fluids and analgesics. For each parameter (stroke, induction, maintenance, monitoring), exact chi-square tests were used to determine whether or not proportions were significantly different across year and p values were corrected for multiple comparisons. An exact p-test was used for each parameter to compare the frequency distribution of each value followed by a Bonferroni test. The level of significant set at < 0.05. Results show that there were very few differences in the anaesthetic and monitoring techniques used between 2005 and 2015. In 2015, significantly more studies were performed in China and significantly fewer studies used isoflurane and nitrous oxide. The most striking finding is that the vast majority of all the studies from both 2005 and 2015 did not report the use of ventilation; measurement of blood gases, end-tidal carbon dioxide concentration, or blood pressure; or administration of intravenous fluids or analgesics. The review of articles published in 2015 showed that the STAIR guidelines appear to have had no effect on the anaesthetic and monitoring techniques in rats undergoing experimental stroke induction, despite the publication of said guidelines in 2009.

Therapeutic hypothermia translates from ancient history in to practice

Acute postasphyxial encephalopathy around the time of birth remains a major cause of death and disability. The possibility that hypothermia may be able to prevent or lessen asphyxial brain injury is a "dream revisited". In this review, a historical perspective is provided from the first reported use of therapeutic hypothermia for brain injuries in antiquity, to the present day. The first uncontrolled trials of cooling for resuscitation were reported more than 50 y ago. The seminal insight that led to the modern revival of studies of neuroprotection was that after profound asphyxia, many brain cells show initial recovery from the insult during a short "latent" phase, typically lasting ~6 h, only to die hours to days later during a "secondary" deterioration phase characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this conceptual framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild induced hypothermia significantly improves intact survival and neurodevelopmental outcomes to midchildhood.

Regulation of therapeutic hypothermia on inflammatory cytokines, microglia polarization, migration and functional recovery after ischemic stroke in mice

Stroke is a leading threat to human life and health in the US and around the globe, while very few effective treatments are available for stroke patients. Preclinical and clinical studies have shown that therapeutic hypothermia (TH) is a potential treatment for stroke. Using novel neurotensin receptor 1 (NTR1) agonists, we have demonstrated pharmacologically induced hypothermia and protective effects against brain damages after ischemic stroke, hemorrhage stroke, and traumatic brain injury (TBI) in rodent models. To further characterize the mechanism of TH-induced brain protection, we examined the effect of TH (at ±33°C for 6h) induced by the NTR1 agonist HPI-201 or physical (ice/cold air) cooling on inflammatory responses after ischemic stroke in mice and oxygen glucose deprivation (OGD) in cortical neuronal cultures. Seven days after focal cortical ischemia, microglia activation in the penumbra reached a peak level, which was significantly attenuated by TH treatments commenced 30min after stroke. The TH treatment decreased the expression of M1 type reactive factors including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-12, IL-23, and inducible nitric oxide synthase (iNOS) measured by RT-PCR and Western blot analyses. Meanwhile, TH treatments increased the expression of M2 type reactive factors including IL-10, Fizz1, Ym1, and arginase-1. In the ischemic brain and in cortical neuronal/BV2 microglia cultures subjected to OGD, TH attenuated the expression of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1α (MIP-1α), two key chemokines in the regulation of microglia activation and infiltration. Consistently, physical cooling during OGD significantly decreased microglia migration 16h after OGD. Finally, TH improved functional recovery at 1, 3, and 7days after stroke. This study reveals the first evidence for hypothermia mediated regulation on inflammatory factor expression, microglia polarization, migration and indicates that the anti-inflammatory effect is an important mechanism underlying the brain protective effects of a TH therapy.

Functional recovery not correlated with axon regeneration through olfactory ensheathing cell-seeded scaffolds in a model of acute spinal cord injury

The implantation of bioengineered scaffolds into lesion-induced gaps of the spinal cord is a promising strategy for promoting functional tissue repair because it can be combined with other intervention strategies. Our previous investigations showed that functional improvement following the implantation of a longitudinally microstructured collagen scaffold into unilateral mid-cervical spinal cord resection injuries of adult Lewis rats was associated with only poor axon regeneration within the scaffold. In an attempt to improve graft-host integration as well as functional recovery, scaffolds were seeded with highly enriched populations of syngeneic, olfactory bulb-derived ensheathing cells (OECs) prior to implantation into the same lesion model. Regenerating neurofilament-positive axons closely followed the trajectory of the donor OECs, as well as that of the migrating host cells within the scaffold. However, there was only a trend for increased numbers of regenerating axons above that supported by non-seeded scaffolds or in the untreated lesions. Nonetheless, significant functional recovery in skilled forelimb motor function was observed following the implantation of both seeded and non-seeded scaffolds which could not be correlated to the extent of axon regeneration within the scaffold. Mechanisms other than simple bridging of axon regeneration across the lesion must be responsible for the improved motor function.

Hypothermia inhibits the propagation of acute ischemic injury by inhibiting HMGB1

Acute ischemic stroke causes significant chronic disability worldwide. We designed this study to clarify the mechanism by which hypothermia helps alleviate acute ischemic stroke. In a middle cerebral artery occlusion model (4 h ischemia without reperfusion), hypothermia effectively reduces mean infarct volume. Hypothermia also prevents neurons in the infarct area from releasing high mobility group box 1 (HMGB1), the most well-studied damage-associated molecular pattern protein. By preventing its release, hypothermia also prevents the typical middle cerebral artery occlusion-induced increase in serum HMGB1. We also found that both glycyrrhizin-mediated inhibition of HMGB1 and intracerebroventricular neutralizing antibody treatments before middle cerebral artery occlusion onset diminish infarct volume. This suggests a clear neuroprotective effect of HMGB1 inhibition by hypothermia in the brain. We next used real-time polymerase chain reaction to measure the levels of pro-inflammatory cytokines in peri-infarct regions. Although middle cerebral artery occlusion increases the expression of interleukin-1β and tissue necrosis factor-α, this elevation is suppressed by both hypothermia and glycyrrhizin treatment. We show that hypothermia reduces the production of inflammatory cytokines and helps salvage peri-infarct regions from the propagation of ischemic injury via HMGB1 blockade. In addition to suggesting a potential mechanism for hypothermia’s therapeutic effects, our results suggest HMGB1 modulation may lengthen the therapeutic window for stroke treatments.

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.

Novel method for inducing rapid, controllable therapeutic hypothermia in rats using a perivascular implanted closed-loop cooling circuit

BACKGROUND

Hypothermia is the most potent protective therapy available for cerebral ischemia. In experimental models, cooling the brain even a single degree Celsius alters outcome after global and focal ischemia. Difficulties translating therapeutic hypothermia to patients with stroke or after cardiac arrest include: uncertainty as to the optimal treatment duration; best target-depth temperature; and longest time delay after which therapeutic hypothermia won't benefit. Recent results from human clinical trials suggest that cooling with surface methods provides insufficient cooling speed or control over target temperature.

COMPARISON WITH EXISTING METHODS

Available animal models incorporate surface cooling methods that are slow, and do not allow for precise control of the target temperature.

NEW METHOD

To address this need, we developed a rapid, simple, inexpensive model for inducing hypothermia using a perivascular implanted closed-loop cooling circuit. The method allows precise control of the target temperature.

RESULTS

Using this method, target temperature for therapeutic hypothermia was reached within 13±1.07min (Mean±SE). Once at target, the temperature was maintained within 0.09°C for 4h.

CONCLUSIONS

This method will allow future experiments to determine under what conditions therapeutic hypothermia is effective, determine the optimal relationship among delay, duration, and depth, and provide the research community with a new model for conducting further research into mechanistic questions underlying the efficacy of therapeutic hypothermia.

Twenty-four hours hypothermia has temporary efficacy in reducing brain infarction and inflammation in aged rats

Stroke is a major cause of disability for which no neuroprotective measures are available. Age is the principal nonmodifiable risk factor for this disease. Previously, we reported that exposure to hydrogen sulfide for 48 hours after stroke lowers whole body temperature and confers neuroprotection in aged animals. Because the duration of hypothermia in most clinical trials is between 24 and 48 hours, we questioned whether 24 hours exposure to gaseous hypothermia confers the same neuroprotective efficacy as 48 hours exposure. We found that a shorter exposure to hypothermia transiently reduced both inflammation and infarct size. However, after 1 week, the infarct size became even larger than in controls and after 2 weeks there was no beneficial effect on regenerative processes such as neurogenesis. Behaviorally, hypothermia also had a limited beneficial effect. Finally, after hydrogen sulfide-induced hypothermia, the poststroke aged rats experienced a persistent sleep impairment during their active nocturnal period. Our data suggest that cellular events that are delayed by hypothermia in aged rats may, in the long term, rebound, and diminish the beneficial effects.

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.

Incomplete Assessment of Experimental Cytoprotectants in Rodent Ischemia Studies

Background:

Inadequate preclinical testing (e.g., rodent studies) has been partly blamed for the failure of many cytoprotectants to effectively treat stroke in humans. For example, some drugs went to clinical trial without rigorous functional and histological assessment over long survival times. In this study, we characterized recent experimental practices in rodent cytoprotection experiments to determine whether the limitations of early studies have been rectified.

Methods:

We identified 138 rodent cytoprotection studies published in several leading journals (Journal of Neuroscience, Stroke, Journal of Cerebral Blood Flow and Metabolism and Experimental Neurology) for 2000 - 2002 and compared these to those published in 1990. From each study we determined the ischemia model, age and sex of the animal, the histological and functional endpoints used, and the methodology used to assess intra- and postischemic temperature.

Results:

Ninety-eight percent of recent studies used young adult rodents and most used males. Most studies (60%) did not assess functional outcome and survival times were often ≤ 48 hr (66%) for focal ischemia and ≤ 7 days (80%) for global ischemia. Over 60% of the experiments relied solely upon rectal temperature during ischemia and only 32.6% of ischemia studies measured temperature after surgery. The 1990 data were similar.

Conclusion:

Many investigators ignore the need to assess long-term functional and histological outcome and do not accurately represent clinical conditions of ischemia (e.g., use of aged animals). In addition, intra- and postischemic temperature measurement and control is frequently neglected or inadequately performed. Further clinical failures are likely.

Mild hypothermia combined with neural stem cell transplantation for hypoxic-ischemic encephalopathy: neuroprotective effects of combined therapy

Neural stem cell transplantation is a useful treatment for ischemic stroke, but apoptosis often occurs in the hypoxic-ischemic environment of the brain after cell transplantation. In this study, we determined if mild hypothermia (27-28°C) can increase the survival rate of neural stem cells (1.0 × 10(5)/μL) transplanted into neonatal mice with hypoxic-ischemic encephalopathy. Long-term effects on neurological functioning of the mice were also examined. After mild hypothermia combined with neural stem cell transplantation, we observed decreased expression levels of inflammatory factor nuclear factor-kappa B and apoptotic factor caspase-3, reduced cerebral infarct volumes, increased survival rate of transplanted cells, and marked improvements in neurological function. Thus, the neuroprotective effects of mild hypothermia combined with neural stem cell transplantation are superior to those of monotherapy. Moreover, our findings suggest that the neuroprotective effects of mild hypothermia combined with neural stem cell transplantation on hypoxic-ischemic encephalopathy are achieved by anti-inflammatory and anti-apoptotic mechanisms.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Mechanisms of hypothermic neuroprotection

Prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce acute brain injury and improve long-term behavioral recovery in term infants and in adults after cardiac arrest. The specific mechanisms of hypothermic neuroprotection remain unclear, in part because hypothermia suppresses a broad range of potential injurious factors. This article examines proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Knowledge of the mechanisms of hypothermia will help guide the rational development of future combination treatments to augment neuroprotection with hypothermia and identify those most likely to benefit.

The mechanisms and treatment of asphyxial encephalopathy

Acute post-asphyxial encephalopathy occurring around the time of birth remains a major cause of death and disability. The recent seminal insight that allows active neuroprotective treatment is that even after profound asphyxia (the “primary” phase), many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting approximately 6 h, only to die hours to days later after a “secondary” deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Although many of these secondary processes are potentially injurious, they appear to be primarily epiphenomena of the “execution” phase of cell death. Animal and human studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible but before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, has been associated with potent, long-lasting neuroprotection. Recent clinical trials show that while therapeutic hypothermia significantly reduces morbidity and mortality, many babies still die or survive with disabilities. The challenge for the future is to find ways of improving the effectiveness of treatment. In this review, we will dissect the known mechanisms of hypoxic-ischemic brain injury in relation to the known effects of hypothermic neuroprotection.

New avenues for treatment of intracranial hemorrhage

OPINION STATEMENT

The mortality and morbidity from intracerebral hemorrhage (ICH) remain high despite advances in medical, neurologic, and surgical care during the past decade. The lessons learned from previous therapeutic trials in ICH, improved understanding of the pathophysiology of neuronal injury after ICH, and advances in imaging and pre-hospital assessment technologies provide optimism that more effective therapies for ICH are likely to emerge in the coming years. The potential new avenues for the treatment of ICH include a combination of increased utilization of minimally invasive surgical techniques with or without thrombolytic usage to evacuate or reduce the size of the hematoma; utilization of advanced imaging to improve selection of patients who are likely to benefit from reversal of coagulopathy or hemostatic therapy; ultra-early diagnosis and initiation of therapy in the ambulance; and the use of novel drugs to target the secondary injury mechanisms, including the inflammatory cascade, perihematomal edema reduction, and hemoglobin degradation products-mediated toxicity.

Emerging experimental therapies for intracerebral hemorrhage: targeting mechanisms of secondary brain injury

Intracerebral hemorrhage (ICH) is associated with a higher degree of morbidity and mortality than other stroke subtypes. Despite this burden, currently approved treatments have demonstrated limited efficacy. To date, therapeutic strategies have principally targeted hematoma expansion and resultant mass effect. However, secondary mechanisms of brain injury are believed to be critical effectors of cell death and neurological outcome following ICH. This article reviews the pathophysiology of secondary brain injury relevant to ICH, examines pertinent experimental models, and highlights emerging therapeutic strategies. Treatment paradigms discussed include thrombin inhibitors, deferoxamine, minocycline, statins, granulocyte-colony stimulating factors, and therapeutic hypothermia. Despite promising experimental and preliminary human data, further studies are warranted prior to effective clinical translation.

Pharmacologically induced hypothermia via TRPV1 channel agonism provides neuroprotection following ischemic stroke when initiated 90 min after reperfusion

Traditional methods of therapeutic hypothermia show promise for neuroprotection against cerebral ischemia-reperfusion (I/R), however, with limitations. We examined effectiveness and specificity of pharmacological hypothermia (PH) by transient receptor potential vanilloid 1 (TRPV1) channel agonism in the treatment of focal cerebral I/R. Core temperature (T(core)) was measured after subcutaneous infusion of TRPV1 agonist dihydrocapsaicin (DHC) in conscious C57BL/6 WT and TRPV1 knockout (KO) mice. Acute measurements of heart rate (HR), mean arterial pressure (MAP), and cerebral perfusion were measured before and after DHC treatment. Focal cerebral I/R (1 h ischemia + 24 h reperfusion) was induced by distal middle cerebral artery occlusion. Hypothermia (>8 h) was initiated 90 min after start of reperfusion by DHC infusion (osmotic pump). Neurofunction (behavioral testing) and infarct volume (TTC staining) were measured at 24 h. DHC (1.25 mg/kg) produced a stable drop in T(core) (33°C) in naive and I/R mouse models but not in TRPV1 KO mice. DHC (1.25 mg/kg) had no measurable effect on HR and cerebral perfusion but produced a slight transient drop in MAP (<6 mmHg). In stroke mice, DHC infusion produced hypothermia, decreased infarct volume by 87%, and improved neurofunctional score. The hypothermic and neuroprotective effects of DHC were absent in TRPV1 KO mice or mice maintained normothermic with heat support. PH via TRPV1 agonist appears to be a well-tolerated and effective method for promoting mild hypothermia in the conscious mouse. Furthermore, TRPV1 agonism produces effective hypothermia in I/R mice and significantly improves outcome when initiated 90 min after start of reperfusion.

Triggering Receptor Expressed on Myeloid Cells-2 Correlates to Hypothermic Neuroprotection in Ischemic Stroke

Hypothermia is neuroprotective against many acute neurological insults, including ischemic stroke. We and others have previously shown that protection by hypothermia is partially associated with an anti-inflammatory effect. Phagocytes are thought to play an important role in the clearance of necrotic debris, paving the way for endogenous repair mechanisms to commence, but the effect of cooling and phagocytosis has not been extensively studied. Triggering receptor expressed on myeloid cells-2 (TREM2) is a newly identified surface receptor shown to be involved in phagocytosis. In this study, we examined the effect of therapeutic hypothermia on TREM2 expression. Mice underwent permanent middle cerebral artery occlusion (MCAO) and were treated with one of the two cooling paradigms: one where cooling (30°C) began at the onset of MCAO (early hypothermia [eHT]) and another where cooling began 1 hour later (delayed hypothermia [dHT]). In both groups, cooling was maintained for 2 hours. A third group was maintained at normothermia (NT) as a control (37°C). Mice from the NT and dHT groups had similar ischemic lesion sizes and neurological performance, but the eHT group showed marked protection as evidenced by a smaller lesion size and less neurological deficits up to 30 days after the insult. Microglia and macrophages increased after MCAO as early as 3 days, peaked at 7 days, and decreased by 14 days. Both hypothermia paradigms were associated with decreased numbers of microglia and macrophages at 3 and 7 days, with greater decreases in the early paradigm. However, the proportion of the TREM2-positive microglia/macrophages was actually increased among the eHT group at day 7. eHT showed a long-term neurological benefit, but neuroprotection did not correlate to immune suppression. However, hypothermic neuroprotection was associated with a relative increase in TREM2 expression, and suggests that TREM2 may serve a beneficial role in brain ischemia.

Limitations of Mild, Moderate, and Profound Hypothermia in Protecting Developing Hippocampal Neurons After Simulated Ischemia

Mild hypothermia (33°C-34°C) after cerebral ischemia in intact animals or ischemia-like conditions in vitro reduces neuron death. However, it is now clear that more profound hypothermia or delayed hypothermia may not provide significant protection. To further define the limitations of hypothermia after cerebral ischemia, we used hippocampal slice cultures to examine the effects of various degrees, durations, and delays of hypothermia on neuron death after an ischemia-like insult. Organotypic cultures of the hippocampus from 7- to 8 day-old rat pups were cooled to 32°C, 23°C, 17°C, or 4°C immediately or after a 2-4 hour delay from an injurious insult of oxygen and glucose deprivation (OGD). Cell death in CA1, CA3 and dentate regions of the cultures was assessed 24 hours later with SYTOX® or propidium iodide, both of which are fluorescent markers labeling damaged cells. OGD caused extensive cell death in CA1, CA3, and dentate regions of the hippocampal cultures. Hypothermia (32°C, 23°C and 17°C) for 4-6 hours immediately after OGD was protective at 24 hours, but when hypothermia was applied for longer periods or delayed after OGD, no protection or increased death was seen. Ultra-profound hypothermia (4°C) increased cell death in all cell areas of the hippocampus even when after a milder insult of only hypoxia. In an in vitro model of recovery after an ischemia-like insult, mild to profound hypothermia is protective only when applied without delay and for limited periods of time (6-8 hours). Longer durations of hypothermia, or delayed application of the hypothermia can increase neuron death. These findings may have implications for clinical uses of therapeutic hypothermia after hypoxic or ischemic insults, and suggest that further work is needed to elucidate the limitations of hypothermia as a protective treatment after ischemic stress.

Acute and delayed protective effects of pharmacologically induced hypothermia in an intracerebral hemorrhage stroke model of mice

Hemorrhagic stroke, including intracerebral hemorrhage (ICH), is a devastating subtype of stroke; yet, effective clinical treatment is very limited. Accumulating evidence has shown that mild to moderate hypothermia is a promising intervention for ischemic stroke and ICH. Current physical cooling methods, however, are less efficient and often impractical for acute ICH patients. The present investigation tested pharmacologically induced hypothermia (PIH) using the second-generation neurotensin receptor (NTR) agonist HPI-201 (formerly known as ABS-201) in an adult mouse model with ICH. Acute or delayed administrations of HPI-201 (2mg/kg bolus injection followed by 2 injections of 1mg/kg, i.p.) were initiated at 1 or 24h after ICH. HPI-201 induced mild hypothermia within 30 min and body and brain temperatures were maintained at 32.7 ± 0.4°C for at least 6h without causing observable shivering. With the 1-h delayed treatment, HPI-201-induced PIH significantly reduced ICH-induced cell death and brain edema compared to saline-treated ICH animals. When HPI-201-induced hypothermia was initiated 24h after the onset of ICH, it still significantly attenuated brain edema, cell death and blood-brain barrier breakdown. HPI-201 significantly decreased the expression of matrix metallopeptidase-9 (MMP-9), reduced caspase-3 activation, and increased Bcl-2 expression in the ICH brain. Moreover, ICH mice received 1-h delayed HPI-201 treatment performed significantly better in the neurological behavior test 48 h after ICH. All together, these data suggest that systemic injection of HPI-201 is an effective hypothermic strategy that protects the brain from ICH injury with a wide therapeutic window. The protective effect of this PIH therapy is partially mediated through the alleviation of apoptosis and neurovascular damage. We suggest that pharmacological hypothermia using the newly developed neurotensin analogs is a promising therapeutic treatment for ICH.

Neuroprotective efficacy of selective brain hypothermia induced by a novel external cooling device on permanent cerebral ischemia in rats

OBJECTIVES

This study was aimed at examining whether hypothermia is neuroprotective against permanent cerebral ischemia in rats.

METHODS

A total of 32 male Sprague--Dawley rats were subjected to a middle cerebral artery occlusion. In the hypothermic group, rats (n=10) underwent selective brain hypothermia for 5 hours with the use of a novel surface coil with coolant circulating inside. In the control (n=13) and sham groups (n=9), the rats were maintained at normothermia. After a period of 168 hours ischemia, animals were killed to measure the infarction volume of the brain stained with hematoxylin-eosin.

RESULTS

There were no significant differences in physiological parameters except for the temperature. The present style of hypothermia significantly reduced infarction volume in the cortex and caudoputamen.

DISCUSSION

The present results endorse the neuroprotective effect of our method of hypothermia in permanent focal cerebral ischemia at an endpoint of 1 week under the following two conditions: (1) reduction of muscle and caudoputamen temperature to 29 and 31 degrees C, respectively; (2) maintenance of the mean arterial blood pressure above 90 mmHg during hypothermia.

Hypothermia-induced neuroprotection is associated with reduced mitochondrial membrane permeability in a swine model of cardiac arrest

Increasing evidence has shown that mild hypothermia is neuroprotective for comatose patients resuscitated from cardiac arrest, but the mechanism of this protection is not fully understood. The aim of this study was to determine whether prolonged whole-body mild hypothermia inhibits mitochondrial membrane permeability (MMP) in the cerebral cortex after return of spontaneous circulation (ROSC). Thirty-seven inbred Chinese Wuzhishan minipigs were successfully resuscitated after 8 minutes of untreated ventricular fibrillation (VF) and underwent recovery under normothermic (NT) or prolonged whole-body mild hypothermic (HT; 33°C) conditions for 24 or 72 hours. Cerebral samples from the frontal cortex were collected at 24 and 72 hours after ROSC. Mitochondria were isolated by differential centrifugation. At 24 hours, relative to NT, HT was associated with reductions in opening of the mitochondrial permeability transition pore, release of pro-apoptotic substances from mitochondria, caspase 3 cleavage, apoptosis, and neurologic deficit scores, as well as increases in mitochondrial membrane potential and mitochondrial respiration. Together, these findings suggest that mild hypothermia inhibits ischemia-induced increases in MMP, which may provide neuroprotection against cerebral injury after cardiac arrest.

Hypothermia enhances induction of protective protein metallothionein under ischemia

BACKGROUND

Hypothermic protection against ischemic stroke has been reported by many studies. Hypothermia is supposed to mitigate the effects of deleterious genes and proteins and promote the activity of protective genes and proteins in the ischemic brain. Metallothionein (MT)-1/2 is thought to be a crucial factor for metal homeostasis, immune function, and apoptosis. This protein was found to exert protective effects in models of brain injury as well. In the present study, we investigated the effect of hypothermia on MT expression and the underlying mechanisms.

METHODS

Cultured bEnd.3 brain endothelial cells were exposed to oxygen glucose deprivation and reperfusion (OGD+R). Reverse transcription PCR and western blot analyses were performed to measure the expression of MT, transcription factors, and methylation regulating factors. Transcription factor binding assays were also performed. Methylation profiles of the promoter area were obtained with pyrosequencing.

RESULTS

Hypothermia protected bEnd.3 cells from OGD+R. When the cells were exposed to OGD+R, MT expression was induced. Hypothermia augmented MT levels. While OGD+R-induced MT expression was mainly associated with metal regulatory transcription factor 1 (MTF-1), MT expression promoted by hypothermia was primarily mediated by the signal transducer and activator of transcription 3 (STAT3). Significantly increased STAT3 phosphorylation at Ser727 was observed with hypothermia, and JSI-124, a STAT-3 inhibitor, suppressed MT expression. The DNA demethylating drug 5-aza-2'-deoxycytidine (5-Aza) enhanced MT expression. Some of the CpG sites in the promoter MT=> it should be "the CpG sites in the MT promoter" showed different methylation profiles and some methylation regulating factors had different expressional profiles in the presence of OGD+R and hypothermia.

CONCLUSIONS

We demonstrated that hypothermia is a potent inducer of MT gene transcription in brain endothelial cells, and enhanced MT expression might contribute to protection against ischemia. MT gene expression is induced by hypothermia mainly through the STAT3 pathway. DNA methylation may contribute to MT gene regulation under ischemic or hypothermic conditions.

Efficacy of mild hypothermia (35°C) and moderate hypothermia (33°C) with and without magnesium when administered 30min post-reperfusion after 90min of middle cerebral artery occlusion in Spontaneously Hypertensive rats

In this study we compared the efficacy of mild (35°C) and moderate (33°C) hypothermia alone and when combined with magnesium in a transient focal cerebral ischaemia rat model. Spontaneously Hypertensive rats were subjected to 90min of transient intraluminal thread middle cerebral artery occlusion (MCAO). Thirty minutes after reperfusion animals were treated with mild (35°C/24h) or moderate (33°C/24h) hypothermia combined with either magnesium (intravenous MgSO4 infusion: 360μmol/kg, then 120μmol/kg/h for 24h) or a similar volume of saline. Control animals were maintained normothermic (37°C/24h) and received vehicle infusion (saline for 24h). Infarct volumes and functional assessment (bi-symmetrical adhesive tape removal) were measured 48h after MCAO induction. After transient MCAO, only moderate hypothermia and mild hypothermia combined with magnesium treatment significantly reduced infarct volumes by 32.9% (P=0.01) and by 24.8% (P=0.046), respectively. Mild hypothermia alone reduced infarct volume by 23.8%, but did not reach statistical significance (P=0.054), while moderate hypothermia combined with magnesium reduced infarct volume by 17.3% (P=0.17). No treatment improved adhesive tape removal time. In summary, moderate hypothermia and mild hypothermia with or without magnesium can reduce infarct volume, however magnesium may reduce the efficacy of moderate hypothermia. Given the potential advantages of mild hypothermia over moderate hypothermia in terms of side-effects and induction, and the potential beneficial effects of magnesium, these findings have important implications for the use of hypothermia for stroke.