Conditions of protection by hypothermia and effects on apoptotic pathways in a rat model of permanent middle cerebral artery occlusion

Mild therapeutic hypothermia protects against inflammatory and proapoptotic processes in the rat model of cochlear implant trauma

OBJECTIVE

Mild therapeutic hypothermia (MTH) has been demonstrated to prevent residual hearing loss from surgical trauma associated with cochlear implant (CI) insertion. Here, we aimed to characterize the mechanisms of MTH-induced hearing preservation in CI in a well-established preclinical rodent model.

APPROACH

Rats were divided into four experimental conditions: MTH-treated and implanted cochleae, cochleae implanted under normothermic conditions, MTH only cochleae and un-operated cochleae (controls). Auditory brainstem responses (ABRs) were recorded at different time points (up to 84 days) to confirm long-term protection and safety of MTH locally applied to the cochlea for 20 min before and after implantation. Transcriptome sequencing profiling was performed on cochleae harvested 24 h post CI and MTH treatment to investigate the potential beneficial effects and underlying active gene expression pathways targeted by the temperature management.

RESULTS

MTH treatment preserved residual hearing up to 3 months following CI when compared to the normothermic CI group. In addition, MTH applied locally to the cochleae using our surgical approach was safe and did not affect hearing in the long-term. Results of RNA sequencing analysis highlight positive modulation of signaling pathways and gene expression associated with an activation of cellular inflammatory and immune responses against the mechanical damage caused by electrode insertion.

SIGNIFICANCE

These data suggest that multiple and possibly independent molecular pathways play a role in the protection of residual hearing provided by MTH against the trauma of cochlear implantation.

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.

Feasibility study of a novel rectal cooling system for hypothermic radical prostatectomy in a swine model

Thermal damage and inflammatory responses of the sphincter and neurovascular bundles (NVBs) are responsible for post-prostatectomy incontinence and erectile dysfunction. Intraoperative hypothermia in the pelvic cavity may reduce the occurrence of these complications. We evaluated the feasibility of a novel rectal cooling system using an animal model. A novel rectal cooling system consisting of a cooling console and a multi-lumen rectal balloon was developed. We conducted animal tests on male pigs to evaluate the efficacy and safety of the system. The primary endpoint was to maintain the temperature of the NVBs at 25℃ (±5℃) during and after the electrocauterization of the bladder neck for 10 seconds. The safety endpoint was device-related complications or significant changes in the core body temperature of the pigs. The NVB temperature was below 30℃ within 3 minutes of activation of the rectal balloon. The temperature of the proximal NVB was consistently maintained below 25℃ in all cases. The temperature 1 cm from the bladder neck did not rise above 38°C and dropped to the initial level within 1 minute after electrocauterization. During cooling, the minimum temperature at the apex of the prostate was reduced to 10.1℃. There were no device-related complications or significant changes in core body temperature throughout the experiment. Animal tests suggest the feasibility and safety of this novel rectal cooling system. A first-in-human trial to assess the safety and efficacy of this system during radical prostatectomy is warranted.

HSP70-mediated neuroprotection by combined treatment of valproic acid with hypothermia in a rat asphyxial cardiac arrest model

It has been reported that valproic acid (VPA) combined with therapeutic hypothermia can improve survival and neurologic outcomes in a rat asphyxial cardiac arrest model. However, neuroprotective mechanisms of such combined treatment of valproic acid with hypothermia remains unclear. We hypothesized that epigenetic regulation of HSP70 by histone acetylation could increase HSP70-mediated neuroprotection suppressed under hypothermia. Male Sprague-Dawley rats that achieved return of spontaneous circulation (ROSC) from asphyxial cardiac arrest were randomized to four groups: normothermia (37°C ± 1°C), hypothermia (33°C ± 1°C), normothermia + VPA (300 mg/kg IV initiated 5 minutes post-ROSC and infused over 20 min), and hypothermia + VPA. Three hours after ROSC, acetyl-histone H3 was highly expressed in VPA-administered groups (normothermia + VPA, hypothermia + VPA). Four hours after ROSC, HSP70 mRNA expression levels were significantly higher in normothermic groups (normothermia, normothermia + VPA) than in hypothermic groups (hypothermia, hypothermia + VPA). The hypothermia + VPA group showed significantly higher HSP70 mRNA expression than the hypothermia group. Similarly, at five hours after ROSC, HSP70 protein levels were significantly higher in normothermic groups than in hypothermic groups. HSP70 levels were significantly higher in the hypothermia + VPA group than in the hypothermia group. Only the hypothermia + VPA group showed significantly attenuated cleaved caspase-9 levels than the normothermia group. Hypothermia can attenuate the expression of HSP70 at transcriptional level. However, VPA administration can induce hyperacetylation of histone H3, leading to epigenetic transcriptional activation of HSP70 even in a hypothermic status. Combining VPA treatment with hypothermia may compensate for reduced activation of HSP70-mediated anti-apoptotic pathway.

Recent antiepileptic and neuroprotective applications of brain cooling

Hypothermia is a widely used clinical practice for neuroprotection and is a well-established method to mitigate the adverse effects of some clinical conditions such as reperfusion injury after cardiac arrest and hypoxic ischemic encephalopathy in newborns. The discovery, that lowering the core temperature has a therapeutic potential dates back to the early 20th century, but the underlying mechanisms are actively researched, even today. Especially, in the area of neural disorders such as epilepsy and traumatic brain injury, cooling has promising prospects. It is well documented in animal models, that the application of focal brain cooling can effectively terminate epileptic discharges. There is, however, limited data regarding human clinical trials. In this review article, we will discuss the main aspects of therapeutic hypothermia focusing on its use in treating epilepsy. The various experimental approaches and device concepts for focal brain cooling are presented and their potential for controlling and suppressing seizure activity are compared.

Comparison of in-hospital and out-of-hospital cardiac arrest patients receiving targeted temperature management: A matched case-control study

BACKGROUND

Evidences that support the use of targeted temperature management (TTM) for in-hospital cardiac arrest (IHCA) are lacking. We aimed to investigate the hypothesis that TTM benefits for patients with IHCA are similar to those with out-of-hospital cardiac arrest (OHCA) and to determine the independent predictors of resuscitation outcomes in patients with cardiac arrest receiving subsequent TTM.

METHODS

This is a retrospective, matched, case-control study (ratio 1:1) including 93 patients with IHCA treated with TTM after the return of spontaneous circulation, who were admitted to Partners HealthCare system in Boston from January 2011 to December 2018. Controls were defined as the same number of patients with OHCA, matched for age, Charlson score, and sex. Survival and neurological outcomes upon discharge were the primary outcome measures.

RESULTS

Patients with IHCA were more likely to have experienced a witnessed arrest and receive bystander cardiopulmonary resuscitation, a larger total dosage of epinephrine, and extracorporeal membrane oxygenation. The time duration for ROSC was shorter in patients with IHCA than in those with OHCA. The IHCA group was more likely associated with mild thrombocytopenia during TTM than the OHCA group. Survival after discharge and favorable neurological outcomes did not differ between the two groups. Among all patients who had cardiac arrest treated with TTM, the initial shockable rhythm, time to ROSC, and medical history of heart failure were independent outcome predictors for survival to hospital discharge. The only factor to predict favorable neurological outcomes at discharge was initial shockable rhythm.

CONCLUSION

The beneficial effects of TTM in eligible patients with IHCA were similar with those with OHCA. Initial shockable rhythm was the only independent predictor of both survival and favorable neurological outcomes at discharge in all cardiac arrest survivors receiving TTM.

Edaravone-Loaded Macrophage-Derived Exosomes Enhance Neuroprotection in the Rat Permanent Middle Cerebral Artery Occlusion Model of Stroke

Edaravone (Edv) can inhibit tissue damage, cause cerebral edema, and delay neuronal death caused by acute cerebral infarction. Exosomes are considered as cargo carriers for intercellular communication and serve as important regulators in many pathological processes. Here, we developed macrophage-derived exosomes (Exo) containing Edv (Exo + Edv) to improve the bioavailability of Edv and enhance the neuroprotective effects in a rat model of permanent middle cerebral artery occlusion (PMCAO). The results showed that Exo + Edv significantly improved the bioavailability of Edv and prolonged half-life (t_1/2). At the same time, Exo + Edv made Edv more easily reach the ischemic side of rats with PMCAO and was localized with neuronal cells and microglia, thus reducing the death of neuronal cells and promoting the polarization of microglia from M1 to M2. Taken together, Exo + Edv may become a potential clinical treatment option for PMCAO.

Midazolam and isoflurane combination reduces late brain damage in the paraoxon-induced status epilepticus rat model

Organophosphates (OPs) are widely used as pesticides and have been employed as warfare agents. OPs inhibit acetylcholinesterase, leading to over-stimulation of cholinergic synapses and can cause status epilepticus (SE). OPs poisoning can result in irreversible brain damage and death. Despite termination of SE, recurrent seizures and abnormal brain activity remain common sequelae often associated with long-term neural damage and cognitive dysfunction. Therefore, early treatment for prevention of seizures is of high interest. Using a rat model of paraoxon poisoning, we tested the efficacy of different neuroprotective and anti-epileptic drugs (AEDs) in suppressing early seizures and preventing brain damage. Electrocorticographic recordings were performed prior, during and after injection of 4.5 LD₅₀ paraoxon, followed by injections of atropine and toxogonin (obidoxime) to prevent death. Thirty minutes later, rats were injected with midazolam alone or in combination with different AEDs (lorazepam, valproic acid, phenytoin) or neuroprotective drugs (losartan, isoflurane). Outcome measures included SE duration, early seizures frequency and epileptiform activity duration in the first 24 -hs after poisoning. To assess delayed brain damage, we performed T2-weighted magnetic resonance imaging one month after poisoning. SE duration and the number of recurrent seizures were not affected by the addition of any of the drugs tested. Delayed brain injury was most prominent in the septum, striatum, amygdala and piriform network. Only isoflurane anesthesia significantly reduced brain damage. We show that acute treatment with isoflurane, but not AEDs, reduces brain damage following SE. This may offer a new therapeutic approach for exposed individuals.

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.

Glibenclamide Enhances the Therapeutic Benefits of Early Hypothermia after Severe Stroke in Rats

Glibenclamide (GBC) is an antidiabetic drug that is in a class of medications known as sulfonylureas, which play critical roles in attenuating brain edema and reducing mortality in ischemic stroke patients. Therapeutic hypothermia (TH) is another robust neuroprotectant that prevents brain swelling and improves the neurological outcomes of stroke patients. However, whether the combination of GBC and TH can be used as a reliable neuroprotectant in ischemic stroke remains largely unknown. We used the middle cerebral artery occlusion (MCAO) rat model as well as oxygen and glucose deprivation-reoxygenation (OGD/R) endothelial cells as ischemic stroke models to investigate the efficacy and mechanisms of treating ischemic stroke with the combination of GBC and TH. The serum glucose, mortality rate, neurobehavioral functions, tight junctions, endothelial cells and inflammatory cytokines were evaluated in the stroke models after treatment with GBC, TH or the combination of them. After 5-hour occlusion and subsequent reperfusion, rats exhibited a large volume of hemispheric swelling and a high mortality rate. Stroke rats treated with the combined therapy did not exhibit hypoglycemia. The combination of GBC and TH exhibited synergistic neuroprotective effects in stroke rats that were associated with greater reductions in edema volume, better improvement in neurobehavioral functions, prevention of tight junction loss, and reduction of expression of the inflammatory cytokines COX-2 and iNOS. In OGD/R endothelia cells, the combination reduced endothelial cell death. This study demonstrated that both GBC and TH are neuroprotective after the severe stroke; however, combined therapy with GBC and TH enhanced the efficiency and efficacy of the effects of TH and GBC in the treatment of ischemia. This combined therapy may facilitate the clinical translation of TH management for severe stroke. The combination of GBC and TH seems to be a feasible and promising clinical strategy to alleviate cerebral injury following severe stroke.

The mTOR cell signaling pathway is crucial to the long-term protective effects of ischemic postconditioning against stroke

Ischemic postconditioning (IPostC) protects against stroke, but few have studied the pathophysiological mechanisms of its long-term protective effects. Here, we investigated whether the mTOR pathway is involved in the long-term protective effects of IPostC. Stroke was induced in rats by distal middle cerebral artery occlusion (dMCAo) combined with 30 min of bilateral common carotid artery (CCA) occlusion, and IPostC was induced after the CCA release. Injury size and behavioral tests were measured up to 3 weeks post stroke. We used rapamycin and mTOR shRNA lentiviral vectors to inhibit mTOR activities, while S6K1 viral vectors, a main downstream mTOR gene, were used to promote mTOR activities. We found that rapamycin administration abolished the long-term protective effects of IPostC. In addition, IPostC promoted the presynaptic growth associated protein 43 (GAP-43) and the postsynaptic protein 95 (PSD-95) levels at 1 week post-stroke, which were reduced by rapamycin. Furthermore, rapamycin reduced phosphorylated mTOR (p-mTOR) protein levels measured at 3 weeks after stroke. These results were confirmed by mTOR shRNA transfection. Moreover, we found that injection of S6K1 viral vectors promoted GAP-43 and PSD-95 protein levels. We conclude that mTOR may play a crucial, protective role in brain damage after stroke and contribute to the protective effects of IPostC.

Mild hypothermia protects neurons against oxygen glucose deprivation via poly (ADP-ribose) signaling

OBJECTIVE

Hypothermia is a neuroprotective mechanism that has been validated for use in alleviating neonatal hypoxic-ischemic (HI) brain injury. Nevertheless, it is unclear whether poly (ADP-ribose) (PAR) signaling is involved in hypothermia-induced neuroprotection. In this study, we investigated whether mild hypothermia rescues oxygen glucose deprivation (OGD)-induced cell death by modifying PAR-relative protein expression, such as AIF, PARP-1, and PAR polymer, in primary-cultured hippocampal neurons.

METHODS

We analyzed neuronal morphology and related protein expression of PAR signaling after OGD followed by mild hypothermia in primary-cultured newborn hippocampal neurons.

RESULTS

Hypothermic treatment resulted in improved neuronal viability and alleviated DNA damage. Results from the protein assay showed that hypothermia attenuated nuclear translocation of apoptosis-inducing factor (AIF), inhibited overactivation of poly(ADP-ribose) polymerase-1 (PARP-1), and decreased production of PAR polymer induced by PARP-1 activation after OGD.

CONCLUSIONS

These results showed that mild hypothermia partially protects immature hippocampal neurons against OGD injury in part by interfering with the PAR signaling pathway.

Hypothermic Cooling Measured by Thermal Magnetic Resonance Imaging; Feasibility and Implications for Virtual Imaging in the Urogenital Pelvis

OBJECTIVE

To study the combination of thermal magnetic resonance imaging (MRI) and novel hypothermic cooling, via an endorectal cooling balloon (ECB), to assess the effective dispersion and temperature drop in pelvic tissue to potentially reduce inflammatory cascade in surgical applications.

METHODS

Three male subjects, before undergoing robot-assisted radical prostatectomy, were cooled via an ECB, rendered MRI compatible for patient safety before ECB hypothermia. MRI studies were performed using a 3T scanner and included T2-weighted anatomic scan for the pelvic structures, followed by a temperature mapping scan. The sequence was performed repeatedly during the cooling experiment, whereas the phase data were collected using an integrated MR-high-intensity focused ultrasound workstation in real time. Pelvic cooling was instituted with a cooling console located outside the MRI magnet room.

RESULTS

The feasibility of pelvic cooling measured a temperature drop of the ECB of 20-25 degrees in real time was achieved after an initial time delay of 10-15 seconds for the ECB to cool. The thermal MRI anatomic images of the prostate and neurovascular bundle demonstrate cooling at this interface to be 10-15 degrees, and also that cooling extends into the prostate itself ~5 degrees, and disperses into the pelvic region as well.

CONCLUSION

An MRI-compatible ECB coupled with thermal MRI is a feasible method to assess effective hypothermic diffusion and saturation to pelvic structures. By inference, hypothermia-induced rectal cooling could potentially reduce inflammation, scarring, and fistula in radical prostatectomy, as well as other urologic tissue procedures of high-intensity focused ultrasound, external beam radiation therapy, radioactive seed implants, transurethral microwave therapy, and transurethral resection of the prostate.

Neuroprotective mechanisms and translational potential of therapeutic hypothermia in the treatment of ischemic stroke

Stroke is a leading cause of disability and death, yet effective treatments for acute stroke has been very limited. Thus far, tissue plasminogen activator has been the only FDA-approved drug for thrombolytic treatment of ischemic stroke patients, yet its application is only applicable to less than 4–5% of stroke patients due to the narrow therapeutic window (< 4.5 hours after the onset of stroke) and the high risk of hemorrhagic transformation. Emerging evidence from basic and clinical studies has shown that therapeutic hypothermia, also known as targeted temperature management, can be a promising therapy for patients with different types of stroke. Moreover, the success in animal models using pharmacologically induced hypothermia (PIH) has gained increasing momentum for clinical translation of hypothermic therapy. This review provides an updated overview of the mechanisms and protective effects of therapeutic hypothermia, as well as the recent development and findings behind PIH treatment. It is expected that a safe and effective hypothermic therapy has a high translational potential for clinical treatment of patients with stroke and other CNS injuries.

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

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

Calcium-sensing receptor (CaSR) as a novel target for ischemic neuroprotection

Object

Ischemic brain injury is the leading cause for death and long-term disability in patients who suffer cardiac arrest and embolic stroke. Excitotoxicity and subsequent Ca²⁺-overload lead to ischemic neuron death. We explore a novel mechanism concerning the role of the excitatory extracellular calcium-sensing receptor (CaSR) in the induction of ischemic brain injury.

Method

Mice were exposed to forebrain ischemia and the actions of CaSR were determined after its genes were ablated specifically in hippocampal neurons or its activities were inhibited pharmacologically. Since the CaSR forms a heteromeric complex with the inhibitory type B γ-aminobutyric acid receptor 1 (GABA_BR1), we compared neuronal responses to ischemia in mice deficient in CaSR, GABA_BR1, or both, and in mice injected locally or systemically with a specific CaSR antagonist (or calcilytic) in the presence or absence of a GABA_BR1 agonist (baclofen).

Results

Both global and focal brain ischemia led to CaSR overexpression and GABA_BR1 downregulation in injured neurons. Genetic ablation of Casr genes or blocking CaSR activities by calcilytics rendered robust neuroprotection and preserved learning and memory functions in ischemic mice, partly by restoring GABA_BR1 expression. Concurrent ablation of Gabbr1 gene blocked the neuroprotection caused by the Casr gene knockout. Coinjection of calcilytics with baclofen synergistically enhanced neuroprotection. This combined therapy remained robust when given 6 h after ischemia.

Interpretation

Our study demonstrates a novel receptor interaction, which contributes to ischemic neuron death through CaSR upregulation and GABA_BR1 downregulation, and feasibility of neuroprotection by concurrently targeting these two receptors.

Mild hypothermia as a treatment for central nervous system injuries: Positive or negative effects

Besides local neuronal damage caused by the primary insult, central nervous system injuries may secondarily cause a progressive cascade of related events including brain edema, ischemia, oxida-tive stress, excitotoxicity, and dysregulation of calcium homeostasis. Hypothermia is a beneficial strategy in a variety of acute central nervous system injuries. Mild hypothermia can treat high intra-cranial pressure following traumatic brain injuries in adults. It is a new treatment that increases sur-vival and quality of life for patients suffering from ischemic insults such as cardiac arrest, stroke, and neurogenic fever following brain trauma. Therapeutic hypothermia decreases free radical produc-tion, inflammation, excitotoxicity and intracranial pressure, and improves cerebral metabolism after traumatic brain injury and cerebral ischemia, thus protecting against central nervous system dam-age. Although a series of pathological and physiological changes as well as potential side effects are observed during hypothermia treatment, it remains a potential therapeutic strategy for central nervous system injuries and deserves further study.

Inhibition of hydrogen sulfide production by gene silencing attenuates inflammatory activity by downregulation of NF-κB and MAP kinase activity in LPS-activated RAW 264.7 cells

Hydrogen sulfide is an endogenous inflammatory mediator produced by the activity of cystathionine γ-lyase (CSE) in macrophages. The objective of this study was to explore the mechanism by which hydrogen sulfide acts as an inflammatory mediator in lipopolysaccharide- (LPS-) induced macrophages. In this study, we used small interfering RNA (siRNA) to inhibit CSE expression in macrophages. We found that CSE silencing siRNA could reduce the LPS-induced activation of transcription factor nuclear factor-κB (NF-κB) significantly. Phosphorylation and activation of extra cellular signal-regulated kinase 1/2 (ERK1/2) increased in LPS-induced macrophages. We showed that phosphorylation of ERK in LPS-induced RAW 264.7 cells reached a peak 30 min after activation. Our findings show that silencing CSE gene by siRNA reduces phosphorylation and activation of ERK1/2 in LPS-induced RAW 264.7 cells. These findings suggest that siRNA reduces the inflammatory effects of hydrogen sulfide through the ERK-NF-κB signalling pathway and hydrogen sulfide plays its inflammatory role through ERK-NF-κB pathway in these cells.

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.

Fundamental research progress of mild hypothermia in cerebral protection

Through the years, the clinical application of mild hypothermia has been carried out worldwide and is built from the exploration and cognition of neuroprotection mechanisms by hypothermia. However, within the last decade, extensive and fundamental researches in this area have been conducted. In addition to aspects of the previous findings, scholars have discovered several new contents and uncertain results. This article reviews and summarizes this decade’s progression of mild hypothermia in lowering the cerebral oxygen metabolism, protecting the blood–brain-barrier, regulating the inflammatory response, regulating the excessive release of neurotransmitters, inhibiting calcium overload, and reducing neuronal apoptosis. In many aspects, particularly in regulating inflammatory reverse reaction, various results have been reported and therefore guide scholars to conduct more detailed analysis and investigation in order to discover the inherent theories surrounding the effect of mild hypothermia, and for better clinical services.

Hypothermia for acute ischaemic stroke

Ischaemic stroke is one of the leading causes of death and disability worldwide, and intravenous alteplase is the only proven effective treatment in the acute setting. Hypothermia has been shown to improve neurological outcomes after global ischaemia-hypoxia in comatose patients who have had cardiac arrest, and is one of the most extensively studied and powerful therapeutic strategies in acute ischaemic stroke. The protective mechanisms of therapeutic hypothermia affect the ischaemic cascade across several parallel pathways and, when coupled with reperfusion strategies, might yield synergistic benefits for patients who have had a stroke. Technological advances have allowed hypothermia to be induced rapidly, and the treatment has been used safely in acute stroke patients. Conclusive efficacy trials assessing therapeutic hypothermia combined with reperfusion therapies in acute ischaemic stroke are ongoing.

The protective effects of T cell deficiency against brain injury are ischemic model-dependent in rats

Previous studies have reported that T cell deficiency reduced infarct sizes after transient middle cerebral artery (MCA) suture occlusion in mice. However, how reperfusion and different models affect the detrimental effects of T cells have not been studied. We investigated the effects of T cell deficiency in nude rats using two stroke models and compared their infarct sizes with those in WT rats. In the distal MCA occlusion (MCAo) model, the distal MCA was permanently occluded and the bilateral common carotid arteries (CCAs) were transiently occluded for 60 min. In the suture MCAo model, the MCA was transiently occluded for 100 min by the insertion of a monofilament suture. Our results showed that T cell deficiency resulted in about a 50% reduction in infarct size in the suture MCAo model, whereas it had no effect in the distal MCAo model, suggesting the protective effects of T cell deficiency are dependent on the ischemic model used. We further found more total T cells, CD4 T cells and CD8 T cells in the ischemic brains of WT rats in the suture MCAo model than in the distal MCAo model. In addition, we detected more CD68-expressing macrophages in the ischemic brains of WT rats than in nude rats in the suture MCAo but not the distal MCAo model. Lymphocyte reconstitution in nude rats resulted in larger infarct sizes in the suture MCAo, but not in the distal MCAo stroke model. The results of regional CBF measurement indicated a total reperfusion in the MCAo model but only a partial reperfusion in the distal MCAo model. In conclusion, the protective effects of T cell deficiency on brain injury are dependent on the ischemic model used; likely associated with different degrees of reperfusion.

Nutritional control of growth and development in yeast

Availability of key nutrients, such as sugars, amino acids, and nitrogen compounds, dictates the developmental programs and the growth rates of yeast cells. A number of overlapping signaling networks--those centered on Ras/protein kinase A, AMP-activated kinase, and target of rapamycin complex I, for instance--inform cells on nutrient availability and influence the cells' transcriptional, translational, posttranslational, and metabolic profiles as well as their developmental decisions. Here I review our current understanding of the structures of the networks responsible for assessing the quantity and quality of carbon and nitrogen sources. I review how these signaling pathways impinge on transcriptional, metabolic, and developmental programs to optimize survival of cells under different environmental conditions. I highlight the profound knowledge we have gained on the structure of these signaling networks but also emphasize the limits of our current understanding of the dynamics of these signaling networks. Moreover, the conservation of these pathways has allowed us to extrapolate our finding with yeast to address issues of lifespan, cancer metabolism, and growth control in more complex organisms.

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.

The beneficial effect of mild therapeutic hypothermia depends on the time of complete circulatory standstill in patients with cardiac arrest

AIM

Mild therapeutic hypothermia has shown to improve long-time survival as well as favorable functional outcome after cardiac arrest. Animal models suggest that ischemic durations beyond 8 min results in progressively worse neurologic deficits. Based on these considerations, it would be obvious that cardiac arrest survivors would benefit most from mild therapeutic hypothermia if they have reached a complete circulatory standstill of more than 8 min.

METHODS

In this retrospective cohort study we included cardiac arrest survivors of 18 years of age or older suffering a witnessed out-of-hospital cardiac arrest, which remain comatose after restoration of spontaneous circulation. Data were collected from 1992 to 2010. We investigated the interaction of 'no-flow' time on the association between post arrest mild therapeutic hypothermia and good neurological outcome. 'No-flow' time was categorized into time quartiles (0, 1-2, 3-8, >8 min).

RESULTS

One thousand-two-hundred patients were analyzed. Hypothermia was induced in 598 patients. In spite of showing a statistically significant improvement in favorable neurologic outcome in all patients treated with mild therapeutic hypothermia (odds ratio [OR]: 1.49; 95% confidence interval [CI]: 1.14-1.93) this effect varies with 'no-flow' time. The effect is significant in patients with 'no-flow' times of more than 2 min (OR: 2.72; CI: 1.35-5.48) with the maximum benefit in those with 'no-flow' times beyond 8 min (OR: 6.15; CI: 2.23-16.99).

CONCLUSION

The beneficial effect of mild therapeutic hypothermia increases with cumulative time of complete circulatory standstill in patients with witnessed out-of-hospital cardiac arrest.

Therapeutic applications of hypothermia in cerebral ischaemia

There is considerable experimental evidence that hypothermia is neuroprotective and can reduce the severity of brain damage after global or focal cerebral ischaemia. However, despite successful clinical trials for cardiac arrest and perinatal hypoxia-ischaemia and a number of trials demonstrating the safety of moderate and mild hypothermia in stroke, there are still no established guidelines for its use clinically. Based upon a review of the experimental studies we discuss the clinical implications for the use of hypothermia as an adjunctive therapy in global cerebral ischaemia and stroke and make some suggestions for its use in these situations.

Surface cooling for induction of mild hypothermia in conscious healthy volunteers - a feasibility trial

Introduction

Animal and human studies suggest beneficial outcome effects of mild hypothermia for stroke, for acute myocardial infarction, and for cardiogenic shock. The aim of this study was to investigate the feasibility and safety of non-invasive surface cooling for induction and maintenance of mild hypothermia (32 to 34°C) in healthy, conscious volunteers.

Methods

The trial was set at a clinical research ward in a tertiary care center, and included 16 healthy male volunteers 18 to 70 years old. Surface cooling was established by a novel non-invasive cooling pad with an esophageal target temperature of 32 to 34°C and maintenance for six hours. Shivering-control was achieved with meperidine and buspirone and additional administration of magnesium in eight subjects.

Results

The primary endpoint to reach a target temperature of 32 to 34°C was only reached in 6 of the 16 participating subjects. Temperatures below 35°C were reached after a median cooling time of 53 minutes (38 to 102 minutes). Cooling rate was 1.1°C/h (0.7 to 1.8°C). Additional administration of magnesium had no influence on cooling rate. At no time during the cooling procedure did the participants report uncomfortable conditions for which termination of cooling had to be considered. No severe skin damage was reported.

Conclusions

Cooling to body temperature below 35°C by the use of non-invasive surface cooling is feasible and safe in conscious healthy volunteers. Further studies are needed to investigate an altered cooling protocol to achieve temperatures below 35°C.

Trial Registration

ISRCTN: ISRCTN50530495

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.

Therapeutic hypothermia: critical review of the molecular mechanisms of action

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

Mild hypothermia reduces ischemic neuron death via altering the expression of p53 and bcl-2

OBJECTIVE

Studies exploring roles of p53 and bcl-2 in neuroprotection by hypothermia in focal cerebral ischemia have not provided consistent results. In the present study, we determined whether p53 and bcl-2 are involved in the hypothermia-induced neuroprotection.

METHODS

Male Sprague-Dawley rats were divided into four groups: normothermic (37-38 degrees C) ischemia, hypothermic (31-32 degrees C) ischemia, hyperthermic (41-42 degrees C) ischemia and sham-operated group. Global cerebral ischemia was established for 20 minutes using the Pulsinelli four-vessel occlusion model and the brain temperature was maintained at defined levels for 60 minutes following the 20 min ischemia. The mortality in rats was evaluated at 72 hour and 168 hour reperfusion. The expression of p53 and bcl-2 proteins was detected at 24, 48 and 72 hours after reperfusion. At the same intervals, neuron necrosis and apoptosis in brain regions was also detected using hematoxylin and eosin (HE) staining and terminal deoxynucleotldyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL).

RESULTS

The mortalities of rats in normothemia, hypothermia and hyperthermia groups was 33.3, 16.7 and 50% at 72 hour reperfusion. At 168 hours of reperfusion, the mortality in the three groups was 58.3, 25 and 100%, respectively. In light microscopy studies, necrotic neurons and apoptotic neurons were found in the hippocampus after global cerebral ischemia. Surviving neurons in hippocampus was increased in mild hypothermic ischemia group (p<0.05) and decreased in hyperthermia ischemia group (p<0.01) at 24, 48 and 72 hour reperfusion. TUNEL-positive neurons in hippocampus decreased in hypothermic ischemia group (p<0.05 or p<0.01) and increased in hyperthermic ischemia group (p<0.01) at 24, 48 and 72 hour reperfusion. The expression of p53 and bcl-2 proteins was found in the neurons of cerebral cortex after global cerebral ischemia. P53 decreased and bcl-2 increased in hypothermia group.

CONCLUSION

Hypothermia reduces ischemic neuronal necrosis and apoptosis by reducing p53 and increasing bcl-2 expression. Hyperthermia accelerated ischemic neuronal injury by increasing p53 and reducing bcl-2 expression.

Therapeutic hypothermia and traumatic brain injury

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

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 protective effect of early hypothermia on PTEN phosphorylation correlates with free radical inhibition in rat stroke

We recently showed that intraischemic moderate hypothermia (30 degrees C) reduces ischemic damage through the Akt pathway after permanent distal middle cerebral artery occlusion in rats. The only Akt pathway component preserved by hypothermia is phosphorylated phosphatase and tensin homolog deleted on chromosome 10 (p-PTEN), which suggests that p-PTEN may have a central role in neuroprotection. Reactive oxygen species (ROS) are critically involved in mediating ischemic damage after stroke by interacting with signaling molecules, including Akt, PTEN, and delta-protein kinase C (PKC). We investigated the protective mechanisms of moderate hypothermia on these signaling proteins after transient focal ischemia in rats. Early moderate hypothermia (3 h) was administered 15 mins before reperfusion, and delayed moderate hypothermia (3 h) was applied 15 mins after reperfusion. Our results indicate that early hypothermia reduced infarction, whereas delayed hypothermia did not. However, both early and delayed hypothermia maintained levels of Mn-SOD (superoxide dismutase) and phosphorylated Akt and blocked delta-PKC cleavage, suggesting that these factors may not be critical to the protection of hypothermia. Nevertheless, early hypothermia preserved p-PTEN levels after reperfusion, whereas delayed hypothermia did not. Furthermore, ROS inhibition maintained levels of p-PTEN after stroke. Together, these findings suggest that phosphorylation levels of PTEN are closely associated with the protective effect of early hypothermia against stroke.

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.

Hypothermic inhibition of apoptotic pathways for combined neurotoxicity of iron and ascorbic acid in differentiated PC12 cells: reduction of oxidative stress and maintenance of the glutathione redox state

Recent clinical trials have demonstrated the efficacy and safety of therapeutic hypothermia for neonatal hypoxic ischemic encephalopathy (HIE). We previously reported that the levels of non-protein-bound iron and ascorbic acid (AA) are increased in the CSF of infants with HIE. In this study, we investigated the effect of hypothermia on the combined cytotoxicity of Fe and AA for differentiated PC12 cells. The optimal settings for hypothermic treatment were a temperature of 30-32 degrees C, rescue time window of less than 6 h, and minimum duration of at least 24 h. Hypothermia effectively prevented the loss of the mitochondrial transmembrane potential from 6 h to 72 h (end of the study period) and attenuated the release of apoptotic proteins (cytochrome c and apoptosis-inducing factor) at 6 h of exposure to Fe-AA. Activation of caspase-3 was also delayed until 24 h. Akt was transiently activated, although no influence of temperature was observed. Elevation of oxidative stress markers, including ortho-, meta-, and di-tyrosine (markers of protein oxidation) and 4-hydroxynonenal (lipid peroxidation) was significantly attenuated when the temperature was reduced by 5 degrees C. The half-cell reduction potential (Ehc) of GSSG/2GSH redox couple ranged from -220 to -180 mV in unstressed differentiated PC12 cells, and apoptosis was triggered when Ehc exceeded -180 mV. Hypothermia prevented Ehc from rising above -180 mV within 24 h of exposure to Fe-AA. In conclusion, hypothermia prevented cell death due to Fe-AA toxicity by inhibiting apoptotic pathways through maintenance of a reduced cellular environment, as well as by alleviating oxidative stress.

Combination therapy with hypothermia for treatment of cerebral ischemia

Mild hypothermia is an established neuroprotectant in the laboratory, showing remarkable and consistent effects across multiple laboratories and models of brain injury. At the clinical level, mild hypothermia has shown benefits in patients who have suffered cardiac arrest and in some pediatric populations suffering hypoxic brain insults. However, a review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, brain cooling needs to begin soon after the insult, maintained for relatively long period periods of time, and, in the case of ischemic stroke, should be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, especially rapid cooling and the re-establishment of perfusion. The addition of a second neuroprotectant could potentially (1) enhance overall protection, (2) prolong the temporal therapeutic window for hypothermia, or (3) provide protection where hypothermic treatment is only transient. Combination therapies resulting in recanalization following ischemic stroke would improve the likelihood of a good outcome, as the experimental literature suggests more consistent neuroprotection against ischemia with reperfusion, than ischemia without. Since recombinant tissue plasiminogen activator (rt-PA) is the only FDA approved treatment for acute ischemic stroke, and acts to recanalize occluded vessels, it is an obvious initial strategy to combine with hypothermia. However, the effects of thrombolytics are also temperature dependent, and the risk of hemorrhage is significant. The experimental data nevertheless seem to favor a combinatorial approach. Thus, in order to apply hypothermia to a broader range of patients, combination strategies should be further investigated.

Induced hypothermia in acute ischemic stroke

BACKGROUND

Induced hypothermia is a promising neuroprotective treatment for acute ischemic stroke. Data from both global and focal ischemia animal models have been encouraging. However, only a few small clinical studies have investigated its use in humans.

OBJECTIVE

To review the background, possible mechanisms of action, and the preclinical and clinical data supporting the neuroprotective role of induced hypothermia following acute ischemic stroke.

METHODS

A literature search was performed using the PubMed database. Only papers in English were reviewed.

RESULTS/CONCLUSIONS

Induced hypothermia is effective as a neuroprotectant in animal models of acute ischemic stroke. Its multimodal mechanism of action makes it a very attractive method of neuroprotection. Although human studies suggest it is safe and feasible, larger randomized controlled trials are necessary to address clinical efficacy and to refine the methods and parameters of induced hypothermia protocols.

Comparison of 12, 24 and 48 h of systemic hypothermia on outcome after permanent focal ischemia in rat

Mild hypothermia reduces injury in models of global and focal cerebral ischemia even when initiated after the insult. Neuroprotection depends critically upon the duration of hypothermia with longer treatments often being more efficacious. However, the ideal treatment duration is not known for most insults and this knowledge would facilitate clinical studies. Thus, we compared 12, 24 and 48 h of systemic hypothermia (33 degrees C vs. normothermia) initiated 1 h after permanent middle cerebral artery occlusion (pMCAO), which was produced by permanent occlusion of the carotid arteries and cauterization of the distal MCA in rat. Behavioral recovery and lesion volume were determined 7 days after pMCAO. All three treatments significantly and equally attenuated neurological deficits (e.g., forelimb placing response). Conversely, stepping error rate in the horizontal ladder test was significantly reduced only by the 24-h (18.7%) and 48-h treatments (11.7%) compared to normothermic rats (34.4%), and the 48-h treatment was significantly better than the 12-h treatment (28.8%). Similarly, brain injury was significantly reduced by 24-h (78.8 mm(3) lesion volume) and 48-h (66.8 mm(3)) treatments compared to normothermia (142.6 mm(3)), and the 48-h treatment was significantly better than the 12-h duration (114.6 mm(3)). In separate experiments cerebral edema was measured via wet-dry weight measurements and significantly reduced by hypothermia (e.g., from 83.7% water in the injured cortex of normothermic rats to 81.4% in rats cooled for one day), but for this there were no significant duration effects. In summary, prolonged hypothermia treatment provides superior protection overall, but this is not explained by reductions in edema.