Neuroprotective hypothermia - Why keep your head cool during ischemia and reperfusion. Biochim Biophys Acta Gen Subj. 2016;1860:2521-2528. [PMID: 27475000 DOI: 10.1016/j.bbagen.2016.07.024]

Mild and deep hypothermia differentially affect cerebral neuroinflammatory and cold shock response following cardiopulmonary bypass in rat

INTRODUCTION

Targeted temperature management (TTM) is considered to be a neuroprotective strategy during cardiopulmonary bypass (CPB) assisted procedures, possibly through the activation of cold shock proteins. We therefore investigated the effects of mild compared with deep hypothermia on the neuroinflammatory response and cold shock protein expression after CPB in rats.

METHODS

Wistar rats were subjected to 1 hr of mild (33 °C) or deep (18 °C) hypothermia during CPB or sham procedure. PET scan analyses using TSPO ligand [11C]PBR28 were performed on day 1 (short-term) or day 3 and 7 post-procedure (long-term) to assess neuroinflammation. Hippocampal and cortical samples were obtained at day 1 in the short-term group and at day 7 in the long-term group. mRNA expression of M1 and M2 microglia associated cytokines was analysed with RT-PCR. Cold shock protein RNA-binding motive 3 (RBM3) and tyrosine receptor kinase B (TrkB) receptor protein expression were determined with Western Blot and quantified.

RESULTS

In both groups target temperature was reached within an hour. Standard uptake values (SUV) of [11C]PBR28 in CPB rats at 1 day and 3 days were similar to that of sham animals. At 7 days after CPB the SUV was significantly higher in amygdala and hippocampal regions of the CPB 18 °C group as compared to the CPB 33 °C group. No differences were observed in the expression of M1 and M2 microglia-related cytokines between TTM 18 °C and 33 °C. RBM3 protein levels in cortex and hippocampus were significantly higher in CPB 33 °C compared to CPB 18 °C and sham 33 °C, at day 1 and day 7, respectively.

CONCLUSIONS

TTM at 18 °C increased the neuroinflammatory response in amygdala and hippocampus compared to TTM at 33 °C in rats undergoing a CPB procedure. Additionally, TTM at 33 °C induced increased expression of TrkB and RBM3 in cortex and hippocampus of rats on CPB compared to TTM at 18 °C. Together, these data indicate that neuroinflammation is alleviated by TTM at 33 °C, possibly by recruiting protective mechanisms through cold shock protein induction.

Forsythoside B alleviates cerebral ischemia-reperfusion injury via inhibiting NLRP3 inflammasome mediated by SIRT1 activation

BACKGROUND

The inflammatory response is a key factor in the pathogenesis of cerebral ischemia/reperfusion injury (CIRI), and anti-inflammatory interventions may offer a promising therapeutic strategy. Forsythoside B (FB) is a phenylethanoid glycoside isolated from Forsythiae fructus, which has been reported to have anti-inflammatory effects. However, the mechanism of the neuroprotective effect of FB on CIRI remains unclear.

METHODS

Adult male Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion/reperfusion (MCAO/R). FB was administered intraperitoneally for 3 days prior to MCAO/R. Cerebral infarct volume and neurological deficit score were used as indices to evaluate MCAO/R injury. The serum levels of inflammatory factors and antioxidant enzymes were measured. The activation of silent information regulator 2 homolog 1 (Sirt1) and the inhibition of the nucleotide-binding oligomerization domain-like receptor with a pyrin domain 3 (NLRP3) pathway were assessed through western blot and immunohistochemistry analysis. Furthermore, the rats were treated with Sirt1 shRNA 3 days before MCAO/R by stereotactical injection into the ipsilateral hemispheric region to assess the impact of Sirt1 knockdown on the protection of FB during MCAO/R.

RESULTS

FB reduced cerebral infarct volume and neurological deficit score in MCAO/R rats. FB reduced pathological changes and cell apoptosis in the hippocampal CA1 region and cortex on the ischemic side of rats. FB inhibited the serum levels of inflammatory factors and increased the activities of antioxidant enzymes. Further study showed that FB inhibited the activation of the NLRP3 pathway and induced Sirt1 activation.

CONCLUSION

FB demonstrated neuroprotective and anti-inflammatory effects by inhibiting the NLRP3 pathway through Sirt1 activation in CIRI.

Novel insight into the therapeutical potential of flavonoids from traditional Chinese medicine against cerebral ischemia/reperfusion injury

Cerebral ischemia/reperfusion injury (CIRI) is a major contributor to poor prognosis of ischemic stroke. Flavonoids are a broad family of plant polyphenols which are abundant in traditional Chinese medicine (TCM) and have beneficial effects on several diseases including ischemic stroke. Accumulating studies have indicated that flavonoids derived from herbal TCM are effective in alleviating CIRI after ischemic stroke in vitro or in vivo, and exhibit favourable therapeutical potential. Herein, we systematically review the classification, metabolic absorption, neuroprotective efficacy, and mechanisms of TCM flavonoids against CIRI. The literature suggest that flavonoids exert potential medicinal functions including suppressing excitotoxicity, Ca2+ overloading, oxidative stress, inflammation, thrombin's cellular toxicity, different types of programmed cell deaths, and protecting the blood-brain barrier, as well as promoting neurogenesis in the recovery stage following ischemic stroke. Furthermore, we identified certain matters that should be taken into account in future research, as well as proposed difficulties and opportunities in transforming TCM-derived flavonoids into medications or functional foods for the treatment or prevention of CIRI. Overall, in this review we aim to provide novel ideas for the identification of new prospective medication candidates for the therapeutic strategy against ischemic stroke.

Natural product P57 induces hypothermia through targeting pyridoxal kinase

Induction of hypothermia during hibernation/torpor enables certain mammals to survive under extreme environmental conditions. However, pharmacological induction of hypothermia in most mammals remains a huge challenge. Here we show that a natural product P57 promptly induces hypothermia and decreases energy expenditure in mice. Mechanistically, P57 inhibits the kinase activity of pyridoxal kinase (PDXK), a key metabolic enzyme of vitamin B6 catalyzing phosphorylation of pyridoxal (PL), resulting in the accumulation of PL in hypothalamus to cause hypothermia. The hypothermia induced by P57 is significantly blunted in the mice with knockout of PDXK in the preoptic area (POA) of hypothalamus. We further found that P57 and PL have consistent effects on gene expression regulation in hypothalamus, and they may activate medial preoptic area (MPA) neurons in POA to induce hypothermia. Taken together, our findings demonstrate that P57 has a potential application in therapeutic hypothermia through regulation of vitamin B6 metabolism and PDXK serves as a previously unknown target of P57 in thermoregulation. In addition, P57 may serve as a chemical probe for exploring the neuron circuitry related to hypothermia state in mice.

Inhibition of perilipin 2 attenuates cerebral ischemia/reperfusion injury by blocking NLRP3 inflammasome activation both in vivo and in vitro

Cerebral ischemia/reperfusion (CI/R) usually causes neuroinflammation within the central nervous system, further prompting irreversible cerebral dysfunction. Perilipin 2 (Plin2), a lipid droplet protein, has been reported to exacerbate the pathological process in different diseases, including inflammatory responses. However, the role and mechanism of Plin2 in CI/R injury are unclear. In this study, the rat models of transient middle cerebral artery occlusion followed by reperfusion (tMCAO/R) were established to mimic I/R injury, and we found that Plin2 was highly expressed in the ischemic penumbra of tMCAO/R rats. The siRNA-mediated knockdown of Plin2 significantly decreased neurological deficit scores and reduced infarct areas in rats induced by I/R. Detailed investigation showed that Plin2 deficiency alleviated inflammation of tMCAO/R rats as evidenced by reduced secretion of proinflammatory factors and the blockade of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. In vitro experiments showed that Plin2 expression was upregulated in mouse microglia subjected to oxygen-glucose deprivation/reoxygenation (OGD/R). Plin2 knockdown inhibited OGD/R-induced microglia activation and the accumulation of inflammation-related factors. Taken together, this study demonstrates that lipid droplet protein Plin2 contributes to the pathologic process of CI/R damage by impacting inflammatory response and NLRP3 inflammasome activation. Thus, Plin2 may provide a new therapeutic direction for CI/R injury.

Therapeutic donor hypothermia following brain death to improve the quality of transplanted organs

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

This review aims to examine the benefits and harms of therapeutic donor hypothermia in recipients or organs donated after brain death.

The role of SUMOylation in the neurovascular dysfunction after acquired brain injury

Acquired brain injury (ABI) is the most common disease of the nervous system, involving complex pathological processes, which often leads to a series of nervous system disorders. The structural destruction and dysfunction of the Neurovascular Unit (NVU) are prominent features of ABI. Therefore, understanding the molecular mechanism underlying NVU destruction and its reconstruction is the key to the treatment of ABI. SUMOylation is a protein post-translational modification (PTM), which can degrade and stabilize the substrate dynamically, thus playing an important role in regulating protein expression and biological signal transduction. Understanding the regulatory mechanism of SUMOylation can clarify the molecular mechanism of the occurrence and development of neurovascular dysfunction after ABI and is expected to provide a theoretical basis for the development of potential treatment strategies. This article reviews the role of SUMOylation in vascular events related to ABI, including NVU dysfunction and vascular remodeling, and puts forward therapeutic prospects.

Pharmacological therapy to cerebral ischemia-reperfusion injury: Focus on saponins

Secondary insult from cerebral ischemia-reperfusion injury (CIRI) is a major risk factor for poor prognosis of cerebral ischemia. Saponins are steroid or triterpenoid glycosides with various pharmacological activities that are effective in treating CIRI. By browsing the literature from 2001 to 2021, 55 references involving 24 kinds of saponins were included. Saponins were shown to relieve CIRI by inhibiting oxidation stress, neuroinflammation, and apoptosis, restoring BBB integrity, and promoting neurogenesis and angiogenesis. This review summarizes and classifies several common saponins and their mechanisms in relieving CIRI. Information provided in this review will benefit researchers to design, research and develop new medicines to treat CIRI-related conditions with saponins.

Hypothermia Alleviates Reductive Stress, a Root Cause of Ischemia Reperfusion Injury

Ischemia reperfusion injury is common in transplantation. Previous studies have shown that cooling can protect against hypoxic injury. To date, the protective effects of hypothermia have been largely associated with metabolic suppression. Since kidney transplantation is one of the most common organ transplant surgeries, we used human-derived renal proximal tubular cells (HKC8 cell line) as a model of normal renal cells. We performed a temperature titration curve from 37 °C to 22 °C and evaluated cellular respiration and molecular mechanisms that can counteract the build-up of reducing equivalents in hypoxic conditions. We show that the protective effects of hypothermia are likely to stem both from metabolic suppression (inhibitory component) and augmentation of stress tolerance (activating component), with the highest overlap between activating and suppressing mechanisms emerging in the window of mild hypothermia (32 °C). Hypothermia decreased hypoxia-induced rise in the extracellular lactate:pyruvate ratio, increased ATP/ADP ratio and mitochondrial content, normalized lipid content, and improved the recovery of respiration after anoxia. Importantly, it was observed that in contrast to mild hypothermia, moderate and deep hypothermia interfere with HIF1 (hypoxia inducible factor 1)-dependent HRE (hypoxia response element) induction in hypoxia. This work also demonstrates that hypothermia alleviates reductive stress, a conceptually novel and largely overlooked phenomenon at the root of ischemia reperfusion injury.

On-chip testing of a carbon-based platform for electro-adsorption of glutamate

It is known that excessive concentrations of glutamate in the brain can cause neurotoxicity. A common approach to neutralizing this phenomenon is the use of suppressant drugs. However, excessive dependence on suppressant drugs could potentially lead to adversarial side effects, such as drug addiction. Here, we propose an alternative approach to this problem by controlling excessive amounts of glutamate ions through carbon-based, neural implant–mediated uptake. In this study, we introduce a microfluidic system that enables us to emulate the uptake of glutamate into the carbon matrix. The uptake is controlled using electrical pulses to incorporate glutamate ions into the carbon matrix through electro-adsorption. The effect of electric potential on glutamate ion uptake to control the amount of glutamate released into the microfluidic system was observed. The glutamate concentration was measured using a Ultra Violet-Visible spectrophotometer. The current setup demonstrated that a low pulsatile electric potential (0.5–1.5 V) was able to effectively govern the uptake of glutamate ions. The stimulated carbon matrix was able to decrease glutamate concentration by up to 40%. Furthermore, our study shows that these “entrapped” glutamate molecules can be effectively released upon electrical stimulation, thereby reversing the carbon electrical charge through a process called reverse uptake. A release model was used to study the profile of glutamate release from the carbon matrix at a potential of 0–1.5 V. This study showed that a burst release of glutamate was evident at an applied voltage higher than 0.5 V. Ultimately, the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) test for cytotoxicity indicated a cell viability of more than 80% for the carbon matrix. This test demonstrates that the carbon matrix can support the proliferation of cells and has a nontoxic composition; thus, it could be accepted as a candidate material for use as neural implants.

PRMT8 Attenuates Cerebral Ischemia/Reperfusion Injury via Modulating Microglia Activation and Polarization to Suppress Neuroinflammation by Upregulating Lin28a

Activation and polarization of microglia are involved in neuroinflammation and regulate ischemic stroke-associated brain injury. Protein arginine methyltransferase 8 functions as a regulatory component of hypoxic stress-induced neuroinflammation. The protective effect of protein arginine methyltransferase 8 (PRMT8) against ischemic stroke-associated brain injury through regulation of microglia activation and polarization was investigated. First, PRMT8 was downregulated in middle cerebral artery occlusion (MCAO)-induced mice and oxygen-glucose deprivation/reoxygenation (OGD/R)-induced SH-SY5Y. Injection with AAV-PRMT8 reduced infarct volumes in MCAO-induced mice. Moreover, injection with AAV-PRMT8 promoted neuronal survival and ameliorated histopathological changes in the brains of MCAO-induced mice. The neuronal apoptosis and neuroinflammation in MCAO-induced mice were suppressed by AAV-PRMT8 injection. Second, PRMT8 overexpression increased cell viability and suppressed the cell apoptosis and inflammation of OGD/R-induced SH-SY5Y. Third, injection with AAV-PRMT8 reduced almost 50% of CD86 + M1 microglia and enhanced about 20% of CD206 + M2 microglia. Furthermore, PRMT8 overexpression attenuated OGD/R-induced M1 phenotype polarization of BV2. Lastly, PRMT8 upregulated Lin28a and loss of Lin28a attenuated PRMT8 overexpression-induced increase in cell viability and decrease in cell apoptosis and inflammation of OGD/R-induced SH-SY5Y. In conclusion, PRMT8 promoted M2 phenotype polarization of microglia and suppressed neuronal apoptosis to ameliorate cerebral ischemia/reperfusion injury through upregulation of Lin28a.

Pharmacological torpor prolongs rat survival in lethal normobaric hypoxia

Resistance to hypoxia is one of the most prominent features of natural hibernation and is expected to be present in the pharmacological torpor (PT) that simulates hibernation. We studied resistance to lethal hypoxia (3.5% oxygen content) in rats under PT. To initiate PT, we used the previously developed pharmacological composition (PC) which, after a single intravenous injection, can induce a daily decrease in Tb by 7 °C-8 °C at the environmental temperature of 22 °C-23 °C. Half-survival (median) time of rats in lethal hypoxia was found to increase from 5 ± 0.8 min in anesthetized control rats to 150 ± 12 min in rats injected with PC, which is a 30-fold increase. Behavioral tests after PT and hypoxia, including the traveling distance, the number of rearing and grooming episodes, revealed that animal responses are significantly restored within a week. It is assumed that the discovered unprecedented resistance of artificially torpid rats to lethal hypoxia may open up broad prospects for the therapeutic use of PT for preconditioning to various damaging factors, treatment of diseases, and extend the so-called "golden hour" for lifesaving interventions.

Anti-cerebral ischemia reperfusion injury of polysaccharides: A review of the mechanisms

Cerebral ischemia-reperfusion injury can lead to a series of serious brain diseases and cause death or different degrees of disability. Polysaccharide is a kind of biological macromolecule with multiple pharmacological activities and has been proven that it may be used for the treatment of cerebral I/R injury in the future. By sorting out all relevant research from 2000 to 2020, we selected 74 references and identified 22 kinds of polysaccharides. Almost all of these polysaccharides are extracted from traditional Chinese medicine. Research shows that these polysaccharides can improve cerebral ischemia-reperfusion injury through anti-oxidative stress, inhibiting the neuroinflammation, glutamate neurotoxicity and neuronal apoptosis, and exerting neurotrophic effect. The specific mechanisms include clearing ROS and RNS, inhibiting the expression of inflammatory factors, maintaining mitochondrial homeostasis and blocking caspase cascade, regulating NMDA receptor and promoting angiogenesis. We hoped this review is instructive for researchers to design, research and develop polysaccharides.

Targeting Oxidative Stress and Inflammation to Prevent Ischemia-Reperfusion Injury

The cerebral ischemia injury can result in neuronal death and/or functional impairment, which leads to further damage and dysfunction after recovery of blood supply. Cerebral ischemia/reperfusion injury (CIRI) often causes irreversible brain damage and neuronal injury and death, which involves many complex pathological processes including oxidative stress, amino acid toxicity, the release of endogenous substances, inflammation and apoptosis. Oxidative stress and inflammation are interactive and play critical roles in ischemia/reperfusion injury in the brain. Oxidative stress is important in the pathological process of ischemic stroke and is critical for the cascade development of ischemic injury. Oxidative stress is caused by reactive oxygen species (ROS) during cerebral ischemia and is more likely to lead to cell death and ultimately brain death after reperfusion. During reperfusion especially, superoxide anion free radicals, hydroxyl free radicals, and nitric oxide (NO) are produced, which can cause lipid peroxidation, inflammation and cell apoptosis. Inflammation alters the balance between pro-inflammatory and anti-inflammatory factors in cerebral ischemic injury. Inflammatory factors can therefore stimulate or exacerbate inflammation and aggravate ischemic injury. Neuroprotective therapies for various stages of the cerebral ischemia cascade response have received widespread attention. At present, neuroprotective drugs mainly include free radical scavengers, anti-inflammatory agents, and anti-apoptotic agents. However, the molecular mechanisms of the interaction between oxidative stress and inflammation, and their interplay with different types of programmed cell death in ischemia/reperfusion injury are unclear. The development of a suitable method for combination therapy has become a hot topic.

Therapeutic hypothermia promotes cerebral blood flow recovery and brain homeostasis after resuscitation from cardiac arrest in a rat model

Laboratory and clinical studies have demonstrated that therapeutic hypothermia (TH), when applied as soon as possible after resuscitation from cardiac arrest (CA), results in better neurological outcome. This study tested the hypothesis that TH would promote cerebral blood flow (CBF) restoration and its maintenance after return of spontaneous circulation (ROSC) from CA. Twelve Wistar rats resuscitated from 7-min asphyxial CA were randomized into two groups: hypothermia group (7 H, n = 6), treated with mild TH (33-34℃) immediately after ROSC and normothermia group (7 N, n = 6,37.0 ± 0.5℃). Multiple parameters including mean arterial pressure, CBF, electroencephalogram (EEG) were recorded. The neurological outcomes were evaluated using electrophysiological (information quantity, IQ, of EEG) methods and a comprehensive behavior examination (neurological deficit score, NDS). TH consistently promoted better CBF restoration approaching the baseline levels in the 7 H group as compared with the 7 N group. CBF during the first 5-30 min post ROSC of the two groups was 7 H:90.5% ± 3.4% versus 7 N:76.7% ± 3.5% (P < 0.01). Subjects in the 7 H group showed significantly better IQ scores after ROSC and better NDS scores at 4 and 24 h. Early application of TH facilitates restoration of CBF back to baseline levels after CA, which in turn results in the restoration of brain electrical activity and improved neurological outcome.

Clinical potential of pre-reperfusion hypothermia in ischemic injury

The damage caused by ischemic stroke is mostly refractory to medical therapies and amounts to a substantial degree of mortality and morbidity in the world. The core tenet of treatment for acute ischemic stroke (AIS) is to save 'reversible' ischemic tissue (ischemic penumbra) as quickly as possible within a limited therapeutic time window. The neuroprotective effect of hypothermia has been proven previously in a large number of animal experiments and clinical trials. Some of these animal and human studies have shown that pre-reperfusion hypothermia can reduce myocardial infarction and improve clinical outcomes. However, to date, there is little research about hypothermia before reperfusion in the animal model and human study of AIS. This review will explore possible benefits of the application of pre-reperfusion hypothermia in the setting of AIS.

HMG-CoA Reductase Inhibitors Relieve Endoplasmic Reticulum Stress by Autophagy Inhibition in Rats With Permanent Brain Ischemia

Exploring and expanding the indications of common clinical drugs, such as statins, is important to improve the prognosis of patients with permanent cerebral infarction. It has been suggested that reversing the defects in cellular autophagy and ER stress with statin therapy may be a potential treatment option for reducing ischemic damage. Male Sprague-Dawley rats underwent permanent middle cerebral artery occlusion (PMCAO) by electrocoagulation surgery. Atorvastatin (ATV, 10 mg/kg/day) or vehicle was administered intraperitoneally. Rats were divided into the vehicle-treated (SHAM), ATV pretreatment for MCAO (AMCAO), and 3-methyladenine (3MA) combined with ATV pretreatment (3MAMCAO) groups. Magnetic resonance imaging, as well as immunohistochemical and Western blot assessments, were performed 24 h after MCAO. Each ATV-treated group demonstrated significant reductions in infarct volume compared with that in the vehicle-treated group at 24 h after MCAO, which was associated with autophagy reduction and ER stress attenuation in neurons and neovascularization. Next, Western blotting was used to detect the levels of the autophagy-related proteins LC3B and P62 and of ER stress pathway proteins. However, 3MA significantly partially inhibited the ER stress pathway via limiting the autophagic flux in the AMCAO group. In conclusion, our results imply that the neuroprotective function of ATV depends on autophagic activity to diminish ER stress-related cell apoptosis in rats with PMCAO and suggest that compounds that inhibit autophagic activity might reduce the neuroprotective effect of ATV after brain ischemia.

Combination of mild therapeutic hypothermia and adipose-derived stem cells for ischemic brain injury

Mild therapeutic hypothermia has been shown to mitigate cerebral ischemia, reduce cerebral edema, and improve the prognosis of patients with cerebral ischemia. Adipose-derived stem cell-based therapy can decrease neuronal death and infiltration of inflammatory cells, exerting a neuroprotective effect. We hypothesized that the combination of mild therapeutic hypothermia and adipose-derived stem cells would be neuroprotective for treatment of stroke. A rat model of transient middle cerebral artery occlusion was established using the nylon monofilament method. Mild therapeutic hypothermia (33°C) was induced after 2 hours of ischemia. Adipose-derived stem cells were administered through the femoral vein during reperfusion. The severity of neurological dysfunction was measured by a modified Neurological Severity Score Scaling System. The area of the infarct lesion was determined by 2,3,5-triphenyltetrazolium chloride staining. Apoptotic neurons were detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. The regeneration of microvessels and changes in the glial scar were detected by immunofluorescence staining. The inflammatory responses after ischemic brain injury were evaluated by in situ staining using markers of inflammatory cells. The expression of inflammatory cytokines was measured by reverse transcription-polymerase chain reaction. Compared with mild therapeutic hypothermia or adipose-derived stem cell treatment alone, their combination substantially improved neurological deficits and decreased infarct size. They synergistically reduced the number of TUNEL-positive cells and glial fibrillary acidic protein expression, increased vascular endothelial growth factor levels, effectively reduced inflammatory cell infiltration and down-regulated the mRNA expression of the proinflammatory cytokines interleukin-1β, tumor necrosis factor-α and interleukin-6. Our findings indicate that combined treatment is a better approach for treating stroke compared with mild therapeutic hypothermia or adipose-derived stem cells alone.

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.

Mild hypothermia protects hippocampal neurons from oxygen-glucose deprivation injury through inhibiting caspase-3 activation

Mild hypothermia (MH) is thought to be one of the most effective therapeutic methods to treat hypoxic-ischemic encephalopathy (HIE) after cardiac arrest (CA). However, its precise mechanisms remain unclear. In this research, hippocampal neurons were cultured and treated with mild hypothermia and Ac-DEVD-CHO after oxygen-glucose deprivation (OGD). The activity of caspase-3 was detected, in order to find the precise concentration of Ac-DEVD-CHO with the same protective role in OGD injury as MH treatment. Western blot and immunofluorescence staining were conducted to analyze the effects of MH and Ac-DEVD-CHO on the expressions of caspase-3, caspase-8, and PARP. The neuronal morphology was observed with an optical microscope. The lactic acid dehydrogenase (LDH) release rate, neuronal viability, and apoptotic rate were also detected. We found that MH (32 °C) and Ac-DEVD-CHO (5.96 μMol/L) had equal effects on blocking the activation of caspase-3 and the OGD-induced cleavage of PARP, but neither had any effect on the activation of caspase-8, which goes on to activate caspase-3 in the apoptotic pathway. Meanwhile, both MH and Ac-DEVD-CHO had similar effects in protecting cell morphology, reducing LDH release, and inhibiting OGD-induced apoptosis in neurons. They also similarly improved neuronal viability after OGD. In conclusion, caspase-3 serves as a key intervention point of the key modulation site or regulatory region in MH treatment that protects neuronal apoptosis against OGD injury. Inhibiting the expression of caspase-3 had a protective effect against OGD injury in MH treatment, and caspase-3 activation could be applied to evaluate the neuroprotective effectiveness of MH on HIE.

Targeted temperature management in neurological intensive care unit

Targeted temperature management (TTM) shows the most promising neuroprotective therapy against hypoxic/ischemic encephalopathy (HIE). In addition, TTM is also useful for treatment of elevated intracranial pressure (ICP). HIE and elevated ICP are common catastrophic conditions in patients admitted in Neurologic intensive care unit (ICU). The most common cause of HIE is cardiac arrest. Randomized control trials demonstrate clinical benefits of TTM in patients with post-cardiac arrest. Although clinical benefit of ICP control by TTM in some specific critical condition, for an example in traumatic brain injury, is still controversial, efficacy of ICP control by TTM is confirmed by both in vivo and in vitro studies. Several methods of TTM have been reported in the literature. TTM can apply to various clinical conditions associated with hypoxic/ischemic brain injury and elevated ICP in Neurologic ICU.

Necrostatin-1 protects hippocampal neurons against ischemia/reperfusion injury via the RIP3/DAXX signaling pathway in rats

Global cerebral ischemia/reperfusion (I/R) induces selective neuronal injury in CA1 region of hippocampus, leading to severe impairment in behavior, learning and memory functions. However, the molecular mechanism underlying the processes was not elucidated clearly. RIP3 is a key molecular switch connecting apoptosis, necrosis and necroptosis. DAXX, as a novel substrate of RIP3, plays a vital role in ischemia-induced neuronal death. The aim of this study is to investigate the role and mechanism of RIP3/DAXX signaling pathway on neurons in CA1 region of the rat hippocampus after cerebral I/R. Global cerebral ischemia was induced by the method of four-vessel occlusion. RIP1 specific inhibitor Necrostatin-1 was administered by intracerebroventricular injection 1h before ischemia. Open-field, closed-field, and Morris water maze tests were performed respectively to examine the anxiety and cognitive behavior in each group. Hematoxylin and eosinstaining was used to examine the survival of hippocampal CA1 pyramidal neurons. Western blot or immunoprecipitation were carried to detect protein expression, phosphorylation, and interaction. We found that pre-treatment with Nec-1 protected locomotive ability, relieved anxiety behavior, and improved cognitive ability in the rats subjected to cerebral I/R. In addition Moreover, Nec-1 decreased significantly the dead rate of neurons in hippocampal CA1 region after cerebral I/R through suppressing RIP1-RIP3 interaction and RIP3 activation along with RIP3-DAXX interaction, and then blocked DAXX translocation from nucleaus to cytoplasm, which resulted in the inactiviation of DAXX. We concluded that pre-treatment with Nec-1 can protect neurons in the hippocampal CA1 region against ischemic damage through the RIP3-DAXX signaling pathway.

Mild hypothermia protects against oxygen glucose deprivation/reoxygenation-induced apoptosis via the Wnt/β-catenin signaling pathway in hippocampal neurons

Mild hypothermia is thought to be one of the most effective therapies for cerebral ischemia/reperfusion injuries. Our previous research revealed that mild hypothermia inhibits the activation of caspase-3 and protects against oxygen glucose deprivation/reoxygenation (OGD/R)-induced injury in hippocampal neurons. However, the mechanisms behind the activation of caspase-3 remain unclear. The aims of this study were to determine whether the protective effects of mild hypothermia were exerted through the Wnt/β-catenin signaling pathway. We found that, under OGD/R conditions, the pathway was down regulated, but mild hypothermia induced the reactivation of the Wnt/β-catenin signaling pathway, which had been suppressed by OGD/R injury. Mild hypothermia also caused the down regulation of the expression of apoptosis promoting proteins (Bax cleaved caspase-3), up-regulated the expression of apoptosis inhibiting proteins (Bcl-2), and ameliorated OGD/R injury-induced apoptosis. The protective effects of mild hypothermia were blocked by DKK1 (an antagonist of the canonical Wnt signaling pathway). Taken together, these results indicate that the Wnt/β-catenin signaling pathway mediates the protective effects of mild hypothermia against OGD/R-induced apoptosis. Our study provides evidence that mild hypothermia reactivates the Wnt/β-catenin signaling pathway, which is suppressed by OGD/R injury, in hippocampal neurons and protects neurons from OGD/R-induced apoptosis via the reactivation of the Wnt/β-catenin signaling pathway, ultimately suggesting that mild hypothermia could have therapeutic effects on OGD/R-induced apoptosis.

Rosmarinic acid protects rat hippocampal neurons from cerebral ischemia/reperfusion injury via the Akt/JNK3/caspase-3 signaling pathway

Cerebral ischemia/reperfusion injury can result in neuronal death, which further results in brain damage and can even lead to death. Although recent studies showed that rosmarinic acid (RA) exerts neuroprotective effects and attenuates ischemia-induced brain injury and neuronal cell death, little is known about the precise mechanisms that occur during cerebral ischemia/reperfusion (I/R). Therefore, the aim of this study was to examine the underlying mechanism of the neuroprotective effects of RA against ischemic brain injury induced by cerebral I/R. Transient global brain ischemia was induced by 4-vessel occlusion in adult male Sprague-Dawley rats. We randomly divided rats into five groups: sham, I/R, I/R+RA, I/R+Vehicle and I/R+RA+LY. Open-field, closed-field and Morris water maze tests were carried our separately to examine the anxiety and cognitive behavior of each group. Cresyl violet staining was used to examine the survival of hippocampal CA1 pyramidal neurons. The levels of p-Akt, p-JNK3 and cleaved caspase-3 in the hippocampus were also examined by Western blotting. Our results showed that administration of RA protected locomotive ability, relieved anxiety behavior and protected cognitive ability in cerebral I/R-injured rats. Additionally, RA significantly protected neurons in the hippocampal CA1 region against cerebral I/R-induced damage. Furthermore, RA increased the phosphorylation of Akt1, downregulated the phosphorylation of JNK3 and reduced the expression of cleaved caspase-3. Finally, the Akt inhibitor LY294002 reversed all the protective effects of RA, indicating that RA protects neurons in the hippocampal CA1 region from ischemic damage through the Akt/JNK3/caspase-3 signaling pathway.

Potential role of the gut microbiota in synthetic torpor and therapeutic hypothermia

Therapeutic hypothermia is today used in several clinical settings, among them the gut related diseases that are influenced by ischemia/reperfusion injury. This perspective paved the way to the study of hibernation physiology, in natural hibernators, highlighting an unexpected importance of the gut microbial ecosystem in hibernation and torpor. In natural hibernators, intestinal microbes adaptively reorganize their structural configuration during torpor, and maintain a mutualistic configuration regardless of long periods of fasting and cold temperatures. This allows the gut microbiome to provide the host with metabolites, which are essential to keep the host immunological and metabolic homeostasis during hibernation. The emerging role of the gut microbiota in the hibernation process suggests the importance of maintaining a mutualistic gut microbiota configuration in the application of therapeutic hypothermia as well as in the development of new strategy such as the use of synthetic torpor in humans. The possible utilization of tailored probiotics to mold the gut ecosystem during therapeutic hypothermia can also be taken into consideration as new therapeutic strategy.