Delayed induction and long-term effects of mild hypothermia in a focal model of transient cerebral ischemia: neurological outcome and infarct size

A pilot protocol and review of triple neuroprotection with targeted hypothermia, controlled induced hypertension, and barbiturate infusion during emergency carotid endarterectomy for acute stroke after failed tPA or beyond 24-hour window of opportunity

An alternative to tissue plasminogen activator (tPA) failure has been a daunting challenge in ischemic stroke management. As tPA is time-dependent, delays can occur in definitive treatment while passively waiting to observe a clinical response to intravenous thrombolysis. Until today, uncertainty exists in the management strategy of wake-up stroke patients or those presenting beyond the therapeutic tPA window. Clinical dilemmas in these situations can prolong the transitional period of inertia, resulting in an adverse neurological outcome. We propose and review an innovative approach called triple neuro-protection (TNP), which encompasses three technical domains-targeted hypothermia, systemic induced hypertension, and barbiturates infusion, to protect the brain during carotid endarterectomy after failed tPA and/or beyond the 24-hour therapeutic mechanical thrombectomy window. This proposal assimilates discussion on the clinical evidence of the individual domains of TNP with our own clinical experience with TNP. Our first TNP was successfully employed in a 55-year-old man in 2015 while performing emergency carotid endarterectomy after he was referred to us 72 hours post tPA failure. The patient had a successful clinical outcome despite being in therapeutic inertia with 90–99% ipsilateral carotid stenosis and contralateral occlusion on presentation. In the last five years, we have safely used TNP in 25 selected cases with favourable clinical outcomes.

Safety of Triple Neuroprotection with Targeted Hypothermia, Controlled Induced Hypertension, and Barbiturate Infusion during Emergency Carotid Endarterectomy for Acute Stroke after Missing the 24 Hours Window Opportunity

BACKGROUND

The aim of this study is to establish the initial safety of triple neuroprotection (TNP) in an acute stroke setting in patients presenting outside the window for systemic tissue plasminogen activator (tPA).

METHODS

Over 12,000 patients were referred to our vascular services with carotid artery disease, of whom 832 had carotid intervention with a stroke rate of 0.72%. Of these, 25 patients presented (3%), between March 2015 and 2019, with acute dense stroke. These patients had either failed tPA or passed the recommended timing for acute stroke intervention. Fifteen (60%) had hemi-neglect with evidence of acute infarct on magnetic resonance imaging of the brain and a Rankin score of 4 or 5. Ninety-six percent had an 80-99% stenosis on the symptomatic side. Mean ABCD3-I score was 11.35. All patients underwent emergency carotid endarterectomy (CEA) with therapeutically induced hypothermia (32-34°C), targeted hypertension (systolic blood pressure 180-200 mm Hg), and brain suppression with barbiturate.

RESULTS

There were no cases of myocardial infarction, death, cranial nerve injury, wound hematoma, or procedural bleeding. Mean hospital stay was 8.4 (±9.5) days. All cases had resolution of neurological symptoms, except 3 who had failed previous thrombolysis. Eighty percent had a postoperative Rankin score of 0 on discharge and 88% of patients were discharged home with 3 requiring rehabilitation.

CONCLUSIONS

Positive neurological outcomes and no serious adverse events were observed using TNP during emergency CEA in patients with acute brain injury. We recommend TNP for patients who are at an increased risk of stroke perioperatively, or who have already suffered from an acute stroke beyond the recommended window of 24 hr. Certainly, the positive outcomes are not likely reproducible outside of high-volume units and patients requiring this surgery should be transferred to experienced surgeons in appropriate tertiary referral centers.

Hypothermia: Impact on plasticity following brain injury

Therapeutic hypothermia (TH) is a potent neuroprotectant against multiple forms of brain injury, but in some cases, prolonged cooling is needed. Such cooling protocols raise the risk that TH will directly or indirectly impact neuroplasticity, such as after global and focal cerebral ischemia or traumatic brain injury. TH, depending on the depth and duration, has the potential to broadly affect brain plasticity, especially given the spatial, temporal, and mechanistic overlap with the injury processes that cooling is used to treat. Here, we review the current experimental and clinical evidence to evaluate whether application of TH has any adverse or positive effects on postinjury plasticity. The limited available data suggest that mild TH does not appear to have any deleterious effect on neuroplasticity; however, we emphasize the need for additional high-quality preclinical and clinical work in this area.

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

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

Emergent Uric Acid Treatment is Synergistic with Mechanical Recanalization in Improving Stroke Outcomes in Male and Female Rats

Preclinical and clinical studies support a promising, albeit not definitive, neuroprotective effect of emergent uric acid (UA) administration in ischemic stroke. We assessed the effects of UA in an ischemic stroke model relevant to the current treatment paradigm of mechanical thrombectomy within the STAIR/RIGOR recommendations. A cohort of male and female Wistar rats was subjected to ischemic stroke with mechanical recanalization under physiological monitoring. The effects of transient middle cerebral artery occlusion (tMCAO) with adjunctive UA (IV, 16 mg/kg) or vehicle treatment were assessed at 24 h and 7 days. Outcomes included neurofunctional impairment, brain infarct (TTC staining, MRI imaging and cresyl violet staining) and edema. At 24 h after tMCAO, neurofunctional scores and brain infarct were significantly reduced in rats subjected to UA treatment compared to vehicle, with a selective effect of UA on cortical infarct. No differential effect of UA between male and female rats was evidenced, as no significant interaction of sex with stroke outcomes was found. Rats achieving higher reperfusion levels after tMCAO showed superior reduction of neurofunctional impairment, cortical infarct and edema by UA. After a 7-day follow-up, male rats subjected to UA treatment still showed reductions in neurofunctional impairment and infarct size, compared to vehicle treatment. In conclusion, UA treatment immediately after transient ischemia results in a sex-independent, maintained reduction of brain damage and neurological impairment, better manifested in hyperperfusion conditions. This synergistic effect of UA with mechanical recanalization supports additional clinical testing of UA as an adjunctive treatment to mechanical thrombectomy.

Hypothermia augments stress response in mammalian cells

Mild hypothermia (32 °C) is routinely used in medical practice to alleviate hypoxic ischemic damage, however, the mechanisms that underlie its protective effects remain uncertain. Using a systems approach based on genome-wide expression screens, reporter assays and biochemical studies, we find that cellular hypothermia response is associated with the augmentation of major stress-inducible transcription factors Nrf2 and HIF1Α affecting the antioxidant system and hypoxia response pathways, respectively. At the same time, NF-κB, a transcription factor involved in the control of immune and inflammatory responses, was not induced by hypothermia. Furthermore, mild hypothermia did not trigger unfolded protein response. Lower temperatures (27 °C and 22 °C) did not activate Nrf2 and HIF1A pathways as efficiently as mild hypothermia. Current findings are discussed in the context of the thermodynamic hypothesis of therapeutic hypothermia. We argue that the therapeutic effects are likely to stem both from metabolic suppression (inhibitory component) and augmentation of stress tolerance (activating component). We argue that systems coping with cellular stressors are plausible targets of therapeutic hypothermia and deserve more attention in clinical hypothermia research.

Nicotine Alters Estrogen Receptor-Beta-Regulated Inflammasome Activity and Exacerbates Ischemic Brain Damage in Female Rats

Smoking is a preventable risk factor for stroke and smoking-derived nicotine exacerbates post-ischemic damage via inhibition of estrogen receptor beta (ER-β) signaling in the brain of female rats. ER-β regulates inflammasome activation in the brain. Therefore, we hypothesized that chronic nicotine exposure activates the inflammasome in the brain, thus exacerbating ischemic brain damage in female rats. To test this hypothesis, adult female Sprague-Dawley rats (6–7 months old) were exposed to nicotine (4.5 mg/kg/day) or saline for 16 days. Subsequently, brain tissue was collected for immunoblot analysis. In addition, another set of rats underwent transient middle cerebral artery occlusion (tMCAO; 90 min) with or without nicotine exposure. One month after tMCAO, histopathological analysis revealed a significant increase in infarct volume in the nicotine-treated group (64.24 ± 7.3 mm³; mean ± SEM; n = 6) compared to the saline-treated group (37.12 ± 7.37 mm³; n = 7, p < 0.05). Immunoblot analysis indicated that nicotine increased cortical protein levels of caspase-1, apoptosis-associated speck-like protein containing a CARD (ASC) and pro-inflammatory cytokines interleukin (IL)-1β by 88% (p < 0.05), 48% (p < 0.05) and 149% (p < 0.05), respectively, when compared to the saline-treated group. Next, using an in vitro model of ischemia in organotypic slice cultures, we tested the hypothesis that inhibition of nicotine-induced inflammasome activation improves post-ischemic neuronal survival. Accordingly, slices were exposed to nicotine (100 ng/mL; 14–16 days) or saline, followed by treatment with the inflammasome inhibitor isoliquiritigenin (ILG; 24 h) prior to oxygen-glucose deprivation (OGD; 45 min). Quantification of neuronal death demonstrated that inflammasome inhibition significantly decreased nicotine-induced ischemic neuronal death. Overall, this study shows that chronic nicotine exposure exacerbates ischemic brain damage via activation of the inflammasome in the brain of female rats.

Mild hypothermia modulates the expression of nestin and caspase-3 in the sub-granular zone and improves neurological outcomes in rats with ischemic stroke

We assessed neurological outcomes, infarct volume, and the expression of nestin and caspase-3 in the hippocampal dentate gyrus following middle cerebral artery occlusion (MCAO) followed by reperfusion, with mild hypothermia (MH) treatment at the onset of ischemia in a MCAO rat model. Reperfusion began 2 hours after the MCAO model was set-up. MH treatment began at the onset of ischemia and was maintained for 4 hours. We evaluated neurological deficit score, brain infarct volumes, along with the immunohistochemical staining of nestin and caspase-3 in the sub-granular zone of the injured hemisphere on the 1st, 3rd, 7th, and 14th day after the onset of ischemia. Correlations between the number of nestin-positive (nestin⁺) cells, caspase-3-positive (caspase-3⁺) cells with infarct volume, as well as neurological deficit scores, were evaluated by linear regression. MH significantly promoted survival, reduced mortality, improved neurological deficit score, reduced brain infarct volume, increased the number of neural stem/progenitor cells and inhibited neuronal apoptosis in the sub-granular zone of the injured hemisphere. The number of nestin⁺ cells correlated with neurological deficit score in the normothermic group, and with infarct volume in the hypothermia group except for the first day after the onset of ischemia. The number of caspase-3⁺ cells correlated with the neurological deficit score but not infarct volume. The neuroprotective effects of MH may be mediated by modulating neural stem/progenitor cells and neuronal apoptotic cells in the sub-granular zone of the injured hemisphere during cerebral ischemia/reperfusion injury.

Hypothermia revisited: Impact of ischaemic duration and between experiment variability

To assess the true effect of novel therapies for ischaemic stroke, a positive control that can validate the experimental model and design is vital. Hypothermia may be a good candidate for such a positive control, given the convincing body of evidence from animal models of ischaemic stroke. Taking conditions under which substantial efficacy had been seen in a meta-analysis of hypothermia for focal ischaemia in animal models, we undertook three randomised and blinded studies examining the effect of hypothermia induced immediately following the onset of middle cerebral artery occlusion on infarct volume in rats (n = 15, 23, 264). Hypothermia to a depth of 33℃ and maintained for 130 min significantly reduced infarct volume compared to normothermia treatment (by 27-63%) and depended on ischaemic duration (F(3,244) = 21.242, p < 0.05). However, the protective effect varied across experiments with differences in both the size of the infarct observed in normothermic controls and the time to reach target temperature. Our results highlight the need for sample size and power calculations to take into account variations between individual experiments requiring induction of focal ischaemia.

Therapeutic hypothermia for ischemic stroke; pathophysiology and future promise

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

The cerebral circulation and cerebrovascular disease III: Stroke

In this paper, our review series on cerebrovascular disease anatomy, physiology, and pathology ends with a thorough discussion of the most significant cerebrovascular pathology: stroke. This discussion proceeds through two layers of organization. First, stroke is divided up into its main etiologic categories (ischemic stroke/transient ischemic attack, hemorrhagic stroke, and ischemic to hemorrhagic transformation). Then, the epidemiological, pathophysiological, clinical, and therapeutic (employed currently as well as emerging) aspects of each etiology are explored; emphasis is placed upon the therapeutic aspects. Finally, once we have covered all aspects of each etiologic category, we end our review with a defense of the thesis that there is much hope for the future of stroke treatment to be derived from familiarity with the literature on emerging therapies.

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

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

Assessment of Blood-Brain Barrier Permeability by Dynamic Contrast-Enhanced MRI in Transient Middle Cerebral Artery Occlusion Model after Localized Brain Cooling in Rats

Objective

The purpose of this study was to evaluate the effects of localized brain cooling on blood-brain barrier (BBB) permeability following transient middle cerebral artery occlusion (tMCAO) in rats, by using dynamic contrast-enhanced (DCE)-MRI.

Materials and Methods

Thirty rats were divided into 3 groups of 10 rats each: control group, localized cold-saline (20℃) infusion group, and localized warm-saline (37℃) infusion group. The left middle cerebral artery (MCA) was occluded for 1 hour in anesthetized rats, followed by 3 hours of reperfusion. In the localized saline infusion group, 6 mL of cold or warm saline was infused through the hollow filament for 10 minutes after MCA occlusion. DCE-MRI investigations were performed after 3 hours and 24 hours of reperfusion. Pharmacokinetic parameters of the extended Tofts-Kety model were calculated for each DCE-MRI. In addition, rotarod testing was performed before tMCAO, and on days 1-9 after tMCAO. Myeloperoxidase (MPO) immunohisto-chemistry was performed to identify infiltrating neutrophils associated with the inflammatory response in the rat brain.

Results

Permeability parameters showed no statistical significance between cold and warm saline infusion groups after 3-hour reperfusion 0.09 ± 0.01 min^-1 vs. 0.07 ± 0.02 min^-1, p = 0.661 for K^trans; 0.30 ± 0.05 min^-1 vs. 0.37 ± 0.11 min^-1, p = 0.394 for kep, respectively. Behavioral testing revealed no significant difference among the three groups. However, the percentage of MPO-positive cells in the cold-saline group was significantly lower than those in the control and warm-saline groups (p < 0.05).

Conclusion

Localized brain cooling (20℃) does not confer a benefit to inhibit the increase in BBB permeability that follows transient cerebral ischemia and reperfusion in an animal model, as compared with localized warm-saline (37℃) infusion group.

Therapeutic Hypothermia for Acute Stroke

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

Combining Normobaric Oxygen with Ethanol or Hypothermia Prevents Brain Damage from Thromboembolic Stroke via PKC-Akt-NOX Modulation

In a thromboembolic stroke model after reperfusion by recombinant tissue plasminogen activator (rt-PA), we aimed to determine whether therapeutic hypothermia (TH) and ethanol (EtOH) in combination with low concentration (60 %) of normobaric oxygen (NBO) enhanced neuroprotection, as compared to using each of these agents alone. We further aimed to elucidate a potential role of the NADPH oxidase (NOX), phosphorylated protein kinase B (Akt), and protein kinase C-δ (PKC-δ) pathway in oxidative stress and neuroprotection. In Sprague-Dawley rats, a focal middle cerebral artery (MCA) occlusion was induced by an autologous embolus in the following experimental groups: rt-PA treatment alone, rt-PA + NBO treatment, rt-PA + TH at 33 °C, rt-PA + EtOH, rt-PA + NBO + EtOH, rt-PA + NBO + TH, rt-PA + NOX inhibitor, rt-PA + EtOH + NOX inhibitor, or rt-PA + EtOH + Akt inhibitor. Control groups included sham-operated without stroke or stroke without treatment. Infarct volume and neurological deficit were assessed at 24 h after rt-PA-induced reperfusion with or without treatments. ROS levels, NOX activity, and the protein expression of NOX subunits p22^phox, p47^phox, p67^phox, gp91^phox, as well as PKC-δ and phosphorylated Akt were measured at 3 and 24 h after rt-PA-induced reperfusion. Following rt-PA in thromboembolic stroke rats, NBO combined with TH or EtOH more effectively decreased infarct volume and neurological deficit, as well as reactive oxygen species (ROS) production than with any of the used monotherapies. NOX activity and subunit expressions were downregulated and temporally associated with reduced PKC-δ and increased p-Akt expression. The present study demonstrated that combining NBO with either TH or EtOH conferred similar neuroprotection via modulation of NOX activation. The results suggest a role of Akt in NOX activation and implicate an upstream PKC-δ pathway in the Akt regulation of NOX. It is possible to substitute EtOH for TH, thus circumventing the difficulties in clinical application of TH through the comparatively easier usage of EtOH as a potential stroke management.

Current concepts on burn wound conversion-A review of recent advances in understanding the secondary progressions of burns

Burn wound conversion describes the process by which superficial partial thickness burns convert into deeper burns necessitating surgical intervention. Fully understanding and thus controlling this phenomenon continues to defy burn surgeons. However, potentially guiding burn wound progression so as to obviate the need for surgery while still bringing about healing with limited scarring is the major unmet challenge. Comprehending the pathophysiologic background contributing to deeper progression of these burns is an essential prerequisite to planning any intervention. In this study, a review of articles examining burn wound progression over the last five years was conducted to analyze trends in recent burn progression research, determine changes in understanding of the pathogenesis of burn conversion, and subsequently examine the direction for future research in developing therapies. The majority of recent research focuses on applying therapies from other disease processes to common underlying pathogenic mechanisms in burn conversion. While ischemia, inflammation, and free oxygen radicals continue to demonstrate a critical role in secondary necrosis, novel mechanisms such as autophagy have also been shown to contribute affect significantly burn progression significantly. Further research will have to determine whether multiple mechanisms should be targeted when developing clinical therapies.

Endovascular Cooling Catheter for Selective Brain Hypothermia: An Animal Feasibility Study of Cooling Performance

BACKGROUND AND PURPOSE

Therapeutic hypothermia represents a promising neuroprotective treatment in acute ischemic stroke. Selective cerebral hypothermia applied early, prior to and during endovascular mechanical recanalization therapy, may be beneficial in the critical phase of reperfusion. We aimed to assess the feasibility of a new intracarotid cooling catheter in an animal model.

MATERIALS AND METHODS

Nine adult sheep were included. Temperature probes were introduced into the frontal and temporal brain cortices bilaterally. The cooling catheter system was introduced into a common carotid artery. Selective blood cooling was applied for 180 minutes. Systemic and local brain temperatures were measured during cooling and rewarming. Common carotid artery diameters and flow were measured angiographically and by Doppler sonography.

RESULTS

The common carotid artery diameter was between 6.7 and 7.3 mm. Common carotid artery blood flow velocities increased moderately during cooling and after catheter removal. Maximum cerebral cooling in the ipsilateral temporal cortex was -4.7°C (95% CI, -5.1 to -4.0°C). Ipsilateral brain temperatures dropped significantly faster and became lower compared with the contralateral cortex with maximum temperature difference of -1.3°C (95% CI, -1.5 to -1.0°C; P < .0001) and compared with systemic temperature (-1.4°C; 95% CI, -1.7 to -1.0°C; P < .0001).

CONCLUSIONS

Sheep proved a feasible animal model for the intracarotid cooling catheter. Fast induction of selective mild hypothermia was achieved within the cooled cerebral hemisphere, with stable temperature gradients in the contralateral brain and systemic blood. Further studies are required to demonstrate any therapeutic benefit of selective cerebral cooling in a stroke model.

Therapeutic hypothermia for stroke: Where to go?

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

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

Early prediction and outcome of septic encephalopathy in acute stroke patients with nosocomial coma

Background

Septic encephalopathy (SE) is the most common acute encephalopathy in ICU; however, little attention has been focused on risk of SE in the course of acute stroke. Our aim is to investigate the early prediction and outcome of SE in stroke patients with nosocomial coma (NC).

Methods

A retrospective cohort study was conducted in an ICU of the tertiary teaching hospital in China from January 2006 to December 2009. Ninety-four acute stroke patients with NC were grouped according to with or without SE. Risk factors for patients with SE were compared with those without SE by univariate and multivariate analysis.

Results

Of 94 stroke patients with NC, 46 (49%) had NC with SE and 48 (51%) had NC without SE. The onset-to-NC time was significant later in stroke patients with SE than those without SE (P < 0.01). There was a significant difference in body temperature, heart rate, respiratory rate, white blood cell (WBC), systolic blood pressure (SBP), diastolic blood pressure (DBP), systemic inflammatory response syndrome (SIRS), acute respiratory failure, septic shock, hypernatremia, and sequential organ failure assessment (SOFA) score between the SE and non-SE group (P < 0.05). On a repeat head imaging, vasogenic edema (P = 0.023) and subcortical white matter lesions (P = 0.011) were significantly higher in patients with SE than those without SE, while hematoma growth (P = 0.000), infarction progress (P = 0.003), and recurrent subarachnoid hemorrhage (SAH) (P = 0.011) were significantly lower in patients with SE than those without SE. Patients with SE had higher adjusted rates of fever ≥ 39 °C (odds ratio (OR): 2.753; 95% confidence interval (CI): 1.116 - 6.794; P = 0.028) and SIRS ≥ 3 items (OR: 6.459; 95% CI: 2.050 - 20.351; P = 0.001). The 30-day mortality in stroke patients with SE was higher than those without SE (76.1% vs. 45.8%, P = 0.003).

Conclusion

High fever and severe SIRS are two early predictors of stroke patients with SE, and survival rates were worse in stroke patients with SE than those without SE.

Pharmacologically induced hypothermia attenuates traumatic brain injury in neonatal rats

Neonatal brain trauma is linked to higher risks of mortality and neurological disability. The use of mild to moderate hypothermia has shown promising potential against brain injuries induced by stroke and traumatic brain injury (TBI) in various experimental models and in clinical trials. Conventional methods of physical cooling, however, are difficult to use in acute treatments and in induction of regulated hypothermia. In addition, general anesthesia is usually required to mitigate the negative effects of shivering during physical cooling. Our recent investigations demonstrate the potential therapeutic benefits of pharmacologically induced hypothermia (PIH) using the neurotensin receptor (NTR) agonist HPI201 (formerly known as ABS201) in stroke and TBI models of adult rodents. The present investigation explored the brain protective effects of HPI201 in a P14 rat pediatric model of TBI induced by controlled cortical impact. When administered via intraperitoneal (i.p.) injection, HPI201 induced dose-dependent reduction of body and brain temperature. A 6-h hypothermic treatment, providing an overall 2-3°C reduction of brain and body temperature, showed significant effect of attenuating the contusion volume versus TBI controls. Attenuation occurs whether hypothermia is initiated 15min or 2h after TBI. No shivering response was seen in HPI201-treated animals. HPI201 treatment also reduced TUNEL-positive and TUNEL/NeuN-colabeled cells in the contusion area and peri-injury regions. TBI-induced blood-brain barrier damage was attenuated by HPI201 treatment, evaluated using the Evans Blue assay. HPI201 significantly decreased MMP-9 levels and caspase-3 activation, both of which are pro-apototic, while it increased anti-apoptotic Bcl-2 gene expression in the peri-contusion region. In addition, HPI201 prevented the up-regulation of pro-inflammatory tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6. In sensorimotor activity assessments, rats in the HPI201 treated group exhibited improved functional recovery after TBI versus controls. These data support that PIH therapy using our NTR agonist is effective in reducing neuronal and BBB damage, attenuating inflammatory response and detrimental cellular signaling, and promoting functional recovery after TBI in the developing brain, supporting its potential for further evaluation towards clinical development.

Incomplete Assessment of Experimental Cytoprotectants in Rodent Ischemia Studies

Background:

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

Methods:

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

Results:

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

Conclusion:

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

Effects of selective hypothermia on blood-brain barrier integrity and tight junction protein expression levels after intracerebral hemorrhage in rats

Hypothermia has neuroprotective effects on global cerebral ischemic injuries. However, its efficacy after intracerebral hemorrhage (ICH) is inconclusive. In this study, bacterial collagenase was used to induce ICH stroke in male Wistar rats. We assessed the effects of normothermia and 4 h of local hypothermia (~33.2°C) initiated 1, 6, or 12 h after collagenase infusion on hemorrhage volume and neurological outcomes. Following early cooling initiated after 1 h, blood-brain barrier (BBB) disruption and brain water content were tested. Furthermore, the expression levels of tight junction (TJ) proteins (claudin 5 and occludin) and the proinflammatory cytokines interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) were determined using Western blotting, real-time quantitative PCR, and immunohistochemical staining at 1 and 3 d after ICH. Early local hypothermia tends to reduce hemorrhagic volume and neurological deficits, but the difference is not statistically significant compared with other groups. However, early hypothermia significantly reduces BBB disruption, edema formation, the expression levels of IL-1β and TNF-α, and the loss of TJ proteins. Together, these data suggest that local hypothermia is an effective treatment for edema formation and BBB disruption via the upregulation of TJ proteins and the suppression of TNF-α and IL-1β.

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

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

Rapid induction of brain hypothermia by endovascular intra-arterial perfusion

OBJECTIVES

Achieving rapid, brain cooling has potentially important clinical implications. To investigate potential practicalities, we induced brain hypothermia in canines by perfusing cooled crystalloid solution into the carotid artery using an extracorporeal cooling-filtration system.

METHODS

Ringer's solution cooled to approximately 6.5 degrees C was infused at a rate of 3 ml/kg/min for 30 minutes into the right common carotid artery through an angiographic catheter via the right femoral artery in six adult canines (13.81 +/- 0.60 kg). Excessive fluid was ultrafiltrated through a venovenous extracorporeal circuit via the right femoral vein. Temperature was monitored in the cerebral hemispheres, the rectum and the vena cava. The extracellular lactate concentrations were measured by microdialysis in the frontal lobes.

RESULTS

Right brain temperature decreased to 33.6 +/- 2.0 degrees C from 37.7 +/- 1.1 degrees C 30 minutes after initiation of perfusion, while left brain and rectal temperatures were 34.3 +/- 1.7 and 34.1 +/- 1.3 degrees C, respectively. The cooling rate of the right cerebral hemisphere was 4.2 +/- 1.1 degrees C/ 30 minutes and advanced compared with the rectum (p<0.01), the left cerebral hemisphere and the vena cava (both p<0.05). There was no significant increase in the extracellular lactate concentrations in the cerebral hemispheres. Hemoglobin, hematocrit and cardiac function significantly changed during perfusion (p<0.05).

CONCLUSIONS

Brain hypothermia was rapidly and safely induced using an intra-arterial crystalloid infusion and an extracorporeal cooing-filtration system. With refinement and further assessment of metabolic and physiologic parameters, the method holds a potential for clinical utility.

Long-term neuroprotection induced by regional brain cooling with saline infusion into ischemic territory in rats: a behavioral analysis

The neuroprotective effect of hypothermia has long been recognized. Our recent studies have demonstrated the significant therapeutic value of local brain cooling in the ischemic territory prior to reperfusion in stroke, with reduced infarction and inflammatory responses up to 48 hours of reperfusion. The goal of this study was to determine if local brain cooling, produced by infusion of cold saline, could induce long-term functional improvement after stroke. A hollow filament was used to block the middle cerebral artery (MCA) for 3 hours, and then to locally infuse the ischemic territory with 6 ml cold saline (20 degrees C) for 10 minutes prior to reperfusion. This brain cooling infusion induced a significant (p < 0.01) decrease in neurologic deficits and significantly (p < 0.01) improved motor behavior in ischemic rats after 14 days of reperfusion, compared with ischemic rats without local cold saline infusion. This improvement continued for up to 28 days after reperfusion. No significant difference in motor performance was observed between the brain cooling infusion and normal control groups. Significant (p < 0.01) reductions in infarct volume were also evident. In conclusion, a local cerebral hypothermia induced by local saline infusion prior to reperfusion produced a long-term functional recovery after ischemic stroke. A therapeutic procedure, which combines prereperfusion infusion into an ischemic region with coincident cerebral hypothermia and perhaps subsequent recanalization of an occluded intracranial vessel, may improve the outcome for stroke patients.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

DISCUSSION

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

Hypothermia as a neuroprotective strategy in subarachnoid hemorrhage: a pathophysiological review focusing on the acute phase

Aneurysmal subarachnoid hemorrhage (SAH) remains a very prevalent challenge in neurosurgery associated with a high morbidity and mortality due to the lack of specific treatment modalities. The prognosis of SAH patients depends primarily on three factors: (i) the severity of the initial bleed, (ii) the endovascular or neurosurgical procedure to occlude the aneurysm and (iii) the occurrence of late sequelae, namely delayed ischemic neurological deficits due to cerebral vasospasm. While neurosurgeons and interventionalists have put significant efforts in minimizing periprocedural complications and a multitude of investigators have been devoted to the research on chronic vasospasm, the acute phase of SAH has not been studied in comparable detail. In various experimental studies during the past decade, hypothermia has been shown to reduce neuronal damage after ischemia, traumatic brain injury and other cerebrovascular diseases. Clinically, only some of these encouraging results could be reproduced. This review analyses results of studies on the effects of hypothermia on SAH with special respect to the acute phase in an experimental setting. Based on the available data, some considerations for the application of mild to moderate hypothermia in patients with subarachnoid hemorrhage are given.

Feasibility of endovascular and surface cooling strategies in acute stroke

BACKGROUND

Therapeutic hypothermia (TH) is a promising treatment of stroke, but limited data are available regarding the safety and effectiveness of cooling methodology. We investigated the safety of TH and compared the cooling capacity of two widely used cooling strategies - endovascular and surface cooling.

METHODS

COOLAID Oresund is a bicentre randomized trial in Copenhagen (Denmark) and Malmö (Sweden). Patients were randomized to either TH (33°C for 24 h) in a general intensive care unit (ICU) or standardized stroke unit care (control). Cooling was induced by a surface or endovascular-based strategy.

RESULTS

Thirty-one patients were randomized. Seven were cooled using endovascular and 10 using surface-based cooling methods and 14 patients received standard care (controls). 14 (45%) patients received thrombolysis. Pneumonia was recorded in 6 (35%) TH patients and in 1 (7%) control. 4 TH patients and 1 control developed massive infarction. 1 TH patient and 2 control suffered asymptomatic haemorrhagic transformation. Mortality was comparable with 2 (12%) in the TH group and 1 (7%) among controls. Mean (SD) duration of hospital stay was 25.0 days (24, 9) in TH and 22.5 days (20.6) in control patients (P = 0.767). Mean (SD) induction period (cooling onset to target temperature) was 126.3 min (80.6) with endovascular cooling and 196.3 min (76.3) with surface cooling (P = 0.025).

CONCLUSIONS

Therapeutic hypothermia with general anaesthesia is feasible in stroke patients. We noticed increased rates of pneumonia, while the length of hospital stay remained comparable. The endovascular cooling strategy provides a faster induction period than surface cooling.

Pre, intra and post-ischemic hypothermic neuroprotection in temporary focal cerebral ischemia in rats: morphometric analysis

OBJECTIVE

To evaluate the neuroprotection of mild hypothermia, applied in different moments, in temporary focal cerebral ischemia in rats.

METHODS

Rats was divided into Control (C), Sham (S), Ischemic-control(IC), Pre-ischemic Hypothermia (IH1), Intra-ischemic Hypothermia (IH2), and Post-ischemic Hypothermia (IH3) groups. Morphometry was performed using the KS400 software (Carl Zeiss®) in coronal sections stained by Luxol Fast Blue. Ischemic areas and volumes were obtained.

RESULTS

Statistically, blue areas showed difference for C vs. IC, IC vs. IH1 and IC vs. IH2 (p=0.0001; p=0.01; p=0.03), and no difference between C vs. S, IC vs. IH3 and IH vs. IH2 (p=0.39; p=0.85; p=0.63). Red areas showed difference between C vs. IC, IC vs. IH1 and IC vs. IH2 (p=0.0001; p=0.009; p=0.03), and no difference between C vs. S, IC vs. IH3 and IH1 vs. IH2 (p=0.48; p=0.27; p=0.68). Average ischemic areas and ischemic volumes showed difference between IC vs. IH1 and IC vs. IH2 (p=0.0001 and p=0.0011), and no difference between IC vs. IH3 and IH1 vs. IH2 (p=0.57; p=0.79).

CONCLUSION

Pre-ischemic and intra-ischemic hypothermia were shown to be similarly neuroprotective, but this was not true for post-ischemic hypothermia.

Brain temperature: physiology and pathophysiology after brain injury

The regulation of brain temperature is largely dependent on the metabolic activity of brain tissue and remains complex. In intensive care clinical practice, the continuous monitoring of core temperature in patients with brain injury is currently highly recommended. After major brain injury, brain temperature is often higher than and can vary independently of systemic temperature. It has been shown that in cases of brain injury, the brain is extremely sensitive and vulnerable to small variations in temperature. The prevention of fever has been proposed as a therapeutic tool to limit neuronal injury. However, temperature control after traumatic brain injury, subarachnoid hemorrhage, or stroke can be challenging. Furthermore, fever may also have beneficial effects, especially in cases involving infections. While therapeutic hypothermia has shown beneficial effects in animal models, its use is still debated in clinical practice. This paper aims to describe the physiology and pathophysiology of changes in brain temperature after brain injury and to study the effects of controlling brain temperature after such injury.

A magnetic resonance (MR) compatible selective brain temperature manipulation system for preclinical study

There is overwhelming evidence that hypothermia can improve the outcome of an ischemic stroke. However, the most widely used systemic cooling method could lead to multiple side effects, while the incompatibility with magnetic resonance imaging of the present selective cooling methods highly limit their application in preclinical studies. In this study, we developed a magnetic resonance compatible selective brain temperature manipulation system for small animals, which can regulate brain temperature quickly and accurately for a desired period of time, while maintaining the normal body physiological conditions. This device was utilized to examine the relationship between T1 relaxation, cerebral blood flow, and temperature in brain tissue during magnetic resonance imaging of ischemic stroke. The results showed that this device can be an efficient brain temperature manipulation tool for preclinical studies needing local hypothermic or hyperthermic conditions.

Moderate systemic hypothermia decreases burn depth progression

BACKGROUND

Therapeutic hypothermia has been proposed to be beneficial in an array of human pathologies including cardiac arrest, stroke, traumatic brain and spinal cord injury, and hemorrhagic shock. Burn depth progression is multifactorial but inflammation plays a large role. Because hypothermia is known to reduce inflammation, we hypothesized that moderate hypothermia will decrease burn depth progression.

METHODS

We used a second-degree 15% total body surface area thermal injury model in rats. Burn depth was assessed by histology of biopsy sections. Moderate hypothermia in the range of 31-33°C was applied for 4h immediately after burn and in a delayed fashion, starting 2h after burn. In order to gain insight into the beneficial effects of hypothermia, we analyzed global gene expression in the burned skin.

RESULTS

Immediate hypothermia decreased burn depth progression at 6h post injury, and this protective effect was sustained for at least 24h. Burn depth was 18% lower in rats subjected to immediate hypothermia compared to control rats at both 6 and 24h post injury. Rats in the delayed hypothermia group did not show any significant decrease in burn depth at 6h, but had 23% lower burn depth than controls at 24h. Increased expression of several skin-protective genes such as CCL4, CCL6 and CXCL13 and decreased expression of tissue remodeling genes such as matrix metalloprotease-9 were discovered in the skin biopsy samples of rats subjected to immediate hypothermia.

CONCLUSIONS

Systemic hypothermia decreases burn depth progression in a rodent model and up-regulation of skin-protective genes and down-regulation of detrimental tissue remodeling genes by hypothermia may contribute to its beneficial effects.

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.

Blood glutamate scavenging: insight into neuroprotection

Brain insults are characterized by a multitude of complex processes, of which glutamate release plays a major role. Deleterious excess of glutamate in the brain's extracellular fluids stimulates glutamate receptors, which in turn lead to cell swelling, apoptosis, and neuronal death. These exacerbate neurological outcome. Approaches aimed at antagonizing the astrocytic and glial glutamate receptors have failed to demonstrate clinical benefit. Alternatively, eliminating excess glutamate from brain interstitial fluids by making use of the naturally occurring brain-to-blood glutamate efflux has been shown to be effective in various animal studies. This is facilitated by gradient driven transport across brain capillary endothelial glutamate transporters. Blood glutamate scavengers enhance this naturally occurring mechanism by reducing the blood glutamate concentration, thus increasing the rate at which excess glutamate is cleared. Blood glutamate scavenging is achieved by several mechanisms including: catalyzation of the enzymatic process involved in glutamate metabolism, redistribution of glutamate into tissue, and acute stress response. Regardless of the mechanism involved, decreased blood glutamate concentration is associated with improved neurological outcome. This review focuses on the physiological, mechanistic and clinical roles of blood glutamate scavenging, particularly in the context of acute and chronic CNS injury. We discuss the details of brain-to-blood glutamate efflux, auto-regulation mechanisms of blood glutamate, natural and exogenous blood glutamate scavenging systems, and redistribution of glutamate. We then propose different applied methodologies to reduce blood and brain glutamate concentrations and discuss the neuroprotective role of blood glutamate scavenging.

Time-dependent effects of hypothermia on microglial activation and migration

Background

Therapeutic hypothermia is one of the neuroprotective strategies that improve neurological outcomes after brain damage in ischemic stroke and traumatic brain injury. Microglial cells become activated following brain injury and play an important role in neuroinflammation and subsequent brain damage. The aim of this study was to determine the time-dependent effects of hypothermia on microglial cell activation and migration, which are accompanied by neuroinflammation.

Methods

Microglial cells in culture were subjected to mild (33 °C) or moderate (29 °C) hypothermic conditions before, during, or after lipopolysaccharide (LPS) or hypoxic stimulation, and the production of nitric oxide (NO), proinflammatory cytokines, reactive oxygen species, and neurotoxicity was evaluated. Effects of hypothermia on microglial migration were also determined in in vitro as well as in vivo settings.

Results

Early-, co-, and delayed-hypothermic treatments inhibited microglial production of inflammatory mediators to varying degrees: early treatment was the most efficient, and delayed treatment showed time-dependent effects. Delayed hypothermia also suppressed the mRNA levels of proinflammatory cytokines and iNOS, and attenuated microglial neurotoxicity in microglia-neuron co-cultures. Furthermore, delayed hypothermia reduced microglial migration in the Boyden chamber assay and wound healing assay. In a stab injury model, delayed local hypothermia reduced migration of microglia toward the injury site in the rat brain.

Conclusion

Taken together, our results indicate that delayed hypothermia is sufficient to attenuate microglial activation and migration, and provide the basis of determining the optimal time window for therapeutic hypothermia. Delayed hypothermia may be neuroprotective by inhibiting microglia-mediated neuroinflammation, indicating the therapeutic potential of post-injury hypothermia for patients with brain damages exhibiting some of the inflammatory components.

Long-term and spatial memory effects of selective β1-antagonists after transient focal ischaemia in rats

BACKGROUND

Although various reports have shown that β-antagonists provide neuroprotective effects after cerebral ischaemia, their effect on spatial memory after transient focal ischaemia is not known. We investigated the treatment of β1-antagonists on neurological outcome spatial memory for 1 month after focal cerebral ischaemia in rats.

METHODS

Male rats randomly received an i.v. infusion of saline 0.5 ml h(-1), esmolol 200 μg kg(-1) min(-1), or landiolol 50 μg kg(-1) min(-1). Infusion was initiated 30 min before middle cerebral artery occlusion and continued for 24 h. The infarct areas in the hippocampus and striatum were measured after the final retention trial and neurological examinations.

RESULTS

Neurological deficit scores in the landiolol- and esmolol-treated rats were significantly lower than in the control rats at 1, 4, 7, and 11 days after ischaemia (P<0.05). Using the Morris water maze to assess spatial memory, we found that escape latency and swimming path length to the platform were significantly shorter in the landiolol-treated rats, compared with the saline-treated rats at 4 and 11 days after ischaemia (P<0.05). The mean (SD) infarct area was 19.1 (8.0)% in the striatum and 18.6 (10.0)% in the hippocampus of the landiolol-treated rats, and 16.8 (14.0)% and 16.8 (15.0)% in the striatum and hippocampus, respectively, of esmolol-treated rats. This was significantly less than in control rats [striatum 31.7 (14.0)% and hippocampus 29.8 (13.0)%, P<0.05].

CONCLUSIONS

The current study indicates that although esmolol and landiolol provided long-term neuroprotection in terms of histological outcome, they had no effect on neurological outcome and spatial memory retention.

Hypothermia for acute brain injury--mechanisms and practical aspects

Hypothermia is widely accepted as the gold-standard method by which the body can protect the brain. Therapeutic cooling--or targeted temperature management (TTM)--is increasingly being used to prevent secondary brain injury in patients admitted to the emergency department and intensive care unit. Rapid cooling to 33 °C for 24 h is considered the standard of care for minimizing neurological injury after cardiac arrest, mild-to-moderate hypothermia (33-35 °C) can be used as an effective component of multimodal therapy for patients with elevated intracranial pressure, and advanced cooling technology can control fever in patients who have experienced trauma, haemorrhagic stroke, or other forms of severe brain injury. However, the practical application of therapeutic hypothermia is not trivial, and the treatment carries risks. Development of clinical management protocols that focus on detection and control of shivering and minimize the risk of other potential complications of TTM will be essential to maximize the benefits of this emerging therapeutic modality. This Review provides an overview of the potential neuroprotective mechanisms of hypothermia, practical considerations for the application of TTM, and disease-specific evidence for the use of this therapy in patients with acute brain injuries.

C5a receptor (CD88) inhibition improves hypothermia-induced neuroprotection in an in vitro ischemic model

The concept of 'salvageble penumbra' has prompted both scientists and physicians to explore various neuroprotective approaches that could be beneficial during stroke therapy. Unfortunately, most of them have proved ineffective in targeting multiple cellular death cascades incited within the ischemic penumbra. Hypothermia has been shown to be capable of addressing this problem to some extent. Although many studies have shown that hypothermia targets several cellular processes, its effects on innate immune receptor-mediated apoptotic death still remain unclear. Moreover, whether inhibiting the signaling of innate immune receptors like complement anaphylatoxin C5a receptor (CD88) plays a role in this hypothermic neuroprotection still need to be deciphered. Using various types of ischemic insults in different neuronal cells, we confirm that hypothermia does indeed attenuate apoptotic neuronal cell death in vitro and this effect can be further enhanced by pharmacologically blocking or knocking out CD88. Thus, our study raises a promising therapeutic possibility of adding CD88 antagonists along with hypothermia to improve stroke outcomes.