Effects of intraischemic hypothermia on cerebral damage in a model of reversible focal ischemia

Cold blood perfusion for selective hypothermia in acute ischemic stroke

Hypothermia is the most reliably effective neuroprotectant, and yet systemic complications limit application. A large body of animal data suggests that hypothermia is effective for focal cerebral ischemia, namely acute ischemic stroke. In order to apply hypothermia effectively, a selective approach is required to maximize the effect on the brain while minimizing systemic side effects. Due to poor transferability of promising findings in rodent models to human clinical trials for neuroprotection, the focus of this review is large animal gyrencephalic models. Unlike rodent data which favor mild hypothermia, the majority of large animal studies on selective hypothermia support moderate-to-deep hypothermia (<30°C). Cold blood perfusion produces the rapid rate of temperature reduction and depth of hypothermia required to produce meaningful neuroprotection. Further studies of selective hypothermia in acute ischemic stroke require attention to duration and rate of cooling to optimize the neuroprotection offered by this technique.

Neuroprotective Effects of Nasopharyngeal Perfluorochemical Cooling in a Rat Model of Subarachnoid Hemorrhage

OBJECTIVE

Subarachnoid hemorrhage (SAH) frequently results in severe morbidity, even mortality. Hypothermia is known to have a neuroprotective effect in ischemic injuries. The aim of this study was to determine whether nasopharyngeal (NP) perfluorochemical (PFC) cooling could be used in a rat model of SAH model for neuroprotection.

METHODS

SAH was induced in 16 male Sprague-Dawley rats by cisterna magna injection of 0.3 mL autologous blood. Vital signs, temperatures, cerebral blood flow (CBF), and brain histology were assessed. Brain cooling was performed on the treatment group using the NP-PFC method starting from 20 minutes after SAH.

RESULTS

No SAH-related deaths were observed in either group. SAH caused an immediate decrease in mean arterial pressure (17.0% ± 4.90% below baseline values). SAH induction caused a significant and rapid decrease in CBF from baseline (approximately -65%, ranging from -32% to -85%) in both hemispheres. In the left hemisphere, cooling facilitated the return of CBF to baseline values within 20 minutes of treatment with further increase in CBF that stabilized by the 2 hours after injury time point. Quantitative immunohistochemistry showed that there were significantly more NeuN-positive cells in the cortex and significantly fewer IBA-1-positive microglia and glial fibrillary acidic protein-positive astrocytes cells in both cortex and hippocampus in the animals that received NP-PFC cooling compared with no treatment, reflecting preserved neuronal integrity and reduced inflammation.

CONCLUSIONS

The data from this study indicate that local hypothermia by NP-PFC cooling supports return of CBF and neuronal integrity and suppresses the inflammatory response in SAH, suggestive of a promising neuroprotective approach in management of SAH.

Catheter based selective hypothermia reduces stroke volume during focal cerebral ischemia in swine

BACKGROUND

Total body hypothermia is an established neuroprotectant in global cerebral ischemia. The role of hypothermia in acute ischemic stroke remains uncertain. Selective application of hypothermia to a region of focal ischemia may provide similar protection with more rapid cooling and elimination of systemic side effects. We studied the effect of selective endovascular cooling in a focal stroke model in adult domestic swine.

METHODS

After craniotomy under general anesthesia, a proximal middle cerebral artery branch was occluded for 3 h, followed by 3 h of reperfusion. In half of the animals, selective hypothermia was induced during reperfusion using a dual lumen balloon occlusion catheter placed in the ipsilateral common carotid artery. Following reperfusion, the animals were sacrificed. Brain MRI and histology were evaluated by experts who were blinded to the intervention.

RESULTS

25 animals were available for analysis. Using selective hypothermia, hemicranial temperature was successfully cooled to a mean of 26.5 °C. Average time from start of perfusion to attainment of moderate hypothermia (<30 °C) was 25 min. Mean MRI stroke volumes were significantly reduced by selective cooling (0.050±0.059 control, 0.005±0.011 hypothermia (ratio stroke:hemisphere volume) (p=0.046). Stroke pathology volumes were reduced by 42% compared with controls (p=0.256).

CONCLUSIONS

Selective moderate hypothermia was rapidly induced using endovascular techniques in a clinically realistic swine stroke model. A significant reduction in stroke volume on MRI was observed. Endovascular selective hypothermia can provide neuroprotection within time frames relevant to acute ischemic stroke treatment.

Cooling for cerebral protection during brain surgery

BACKGROUND

Patients undergoing neurosurgery are at risk of cerebral ischaemia with resultant cerebral hypoxia and neuronal cell death. This can increase both the risk of mortality and long term neurological disability. Induced hypothermia has been shown to reduce the risk of cerebral ischaemic damage in both animal studies and in humans who have been resuscitated following cardiac arrest. This had lead to an increasing interest in its neuroprotective potential in neurosurgical patients. This review was originally published in 2011 and did not find any evidence of either effectiveness or harm in these patients. This updated review was designed to capture current evidence to readdress these issues.

OBJECTIVES

To evaluate the effectiveness and safety profile of induced hypothermia versus normothermia for neuroprotection in patients undergoing brain surgery. Effectiveness was to be measured in terms of short and long term mortality and functional neurological outcomes. Safety was to be assessed in terms of the rate of the adverse events infection, myocardial infarction, ischaemic stroke, congestive cardiac failure and any other adverse events reported by the authors of the included studies.

SEARCH METHODS

For the original review, the authors searched the databases Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OvidSP), EMBASE (OvidSP) and LILACS to November 2010. For the updated review all these databases were re-searched from November 2010 to May 2014.For both the original and updated versions, grey literature was sought by searching reference lists of identified studies and relevant review articles, and conference proceedings. No language restrictions were applied.

SELECTION CRITERIA

As in the original review, we included randomized controlled trials (RCTs) of induced hypothermia versus normothermia for neuroprotection in patients of any age and gender undergoing brain surgery, which addressed mortality, neurological morbidity or adverse event outcomes.

DATA COLLECTION AND ANALYSIS

Three review authors independently extracted data and two independently assessed the risk of bias of the included studies. Any discrepancies were resolved by discussion between authors.

MAIN RESULTS

In this updated review, one new ongoing study was found but no new eligible completed studies were identified. This update was therefore conducted using the same four studies included in the original review. These studies included a total of 1219 participants, mean age 40 to 54 years. All included studies were reported as RCTs. Two were multicentred, together including a total of 1114 patients who underwent cerebral aneurysm clipping, and were judged to have an overall low risk of bias. The other two studies were single centred. One included 80 patients who had a craniotomy following severe traumatic brain injury and was judged to have an unclear or low risk of bias. The other study included 25 patients who underwent hemicranicectomy to relieve oedema following cerebral infarction and was judged to have an unclear or high risk of bias. All studies assessed hypothermia versus normothermia. Overall 608 participants received hypothermia with target temperatures ranging from 32.5 °C to 35 °C, and 611 were assigned to normothermia with the actual temperatures recorded in this group ranging form 36.5 °C to 38 °C. For those who were cooled, 556 had cooling commenced immediately after induction of anaesthesia that was continued until the surgical objective of aneurysm clipping was achieved, and 52 had cooling commenced immediately after surgery and continued for 48 to 96 hours.Pooled estimates of effect were calculated for the outcomes mortality during treatment or follow-up (ranging from in-hospital to one year); neurological outcome measured in terms of the Glasgow Outcome Score (GOS) of 3 or less; and adverse events of infections, myocardial infarction, ischaemic stroke and congestive cardiac failure. With regards to mortality, the risk of dying if allocated to hypothermia compared to normothermia was not statistically significantly different (risk ratio (RR) 0.87, 95% confidence interval (CI) 0.59 to 1.27, P = 0.47). There was no indication that the time at which cooling was started affected the risk of dying (RR with intraoperative cooling 0.95, 95% CI 0.60 to 1.51, P = 0.83; RR for cooling postoperatively 0.67, 95% CI 0.34 to 1.35, P = 0.26). For the neurological outcome, the risk of having a poor outcome with a GOS of 3 or less was not statistically different in those who received hypothermia versus normothermia (RR 0.80, 95% CI 0.61 to 1.04, P = 0.09). Again there was no indication that the time at which cooling was started affected this result. Regarding adverse events, there was no statistically significant difference in the incidence in those allocated to hypothermia versus normothermia for risk of surgical infection (RR 1.20, 95% CI 0.73 to 1.97, P = 0.48), myocardial infarction (RR 1.86, 95% CI 0.69 to 4.98, P = 0.22), ischaemic stroke (RR 0.93, 95% CI 0.82 to 1.05, P = 0.24) or congestive heart failure (RR 0.85, 95% CI 0.60 to 1.21, P = 0.38). In contrast to other outcomes, where time of application of cooling did not change the statistical significance of the effect estimates, there was a weak statistically significant increased risk of infection in those who were cooled postoperatively versus those who were not cooled (RR 1.77, 95% CI 1.05 to 2.98, P = 0.03). Overall, as in the original review, no evidence was found that the use of induced hypothermia was either beneficial or harmful in patients undergoing neurosurgery.

AUTHORS' CONCLUSIONS

We found no evidence that the use of induced hypothermia was associated with a significant reduction in mortality or severe neurological disability, or an increase in harm in patients undergoing neurosurgery.

In cold blood: intraarteral cold infusions for selective brain cooling in stroke

Hypothermia is a promising therapeutic option for stroke patients and an established neuroprotective treatment for global cerebral ischemia after cardiac arrest. While whole body cooling is a feasible approach in intubated and sedated patients, its application in awake stroke patients is limited by severe side effects: Strong shivering rewarms the body and potentially worsens ischemic conditions because of increased O2 consumption. Drugs used for shivering control frequently cause sedation that increases the risk of aspiration and pneumonia. Selective brain cooling by intraarterial cold infusions (IACIs) has been proposed as an alternative strategy for patients suffering from acute ischemic stroke. Preclinical studies and early clinical experience indicate that IACI induce a highly selective brain temperature decrease within minutes and reach targeted hypothermia 10 to 30 times faster than conventional cooling methods. At the same time, body core temperature remains largely unaffected, thus systemic side effects are potentially diminished. This review critically discusses the limitations and side effects of current cooling techniques for neuroprotection from ischemic brain damage and summarizes the available evidence regarding advantages and potential risks of IACI.

Use of hypothermia in the intensive care unit

Used for over 3600 years, hypothermia, or targeted temperature management (TTM), remains an ill defined medical therapy. Currently, the strongest evidence for TTM in adults are for out-of-hospital ventricular tachycardia/ventricular fibrillation cardiac arrest, intracerebral pressure control, and normothermia in the neurocritical care population. Even in these disease processes, a number of questions exist. Data on disease specific therapeutic markers, therapeutic depth and duration, and prognostication are limited. Despite ample experimental data, clinical evidence for stroke, refractory status epilepticus, hepatic encephalopathy, and intensive care unit is only at the safety and proof-of-concept stage. This review explores the deleterious nature of fever, the theoretical role of TTM in the critically ill, and summarizes the clinical evidence for TTM in adults.

Cooling for cerebral protection during brain surgery

BACKGROUND

The brain is at risk of ischaemia during a variety of neurosurgical procedures, and this can lead to devastating results. Induced hypothermia is the controlled lowering of core body temperature for therapeutic purposes. This remains the current practice during neurosurgery for the prevention or minimization of ischaemic brain injury. Brain surgery may lead to severe complications due to factors such as requirement for brain retraction, vessel occlusion, and intraoperative haemorrhage. Many anaesthesiologists believe that induced hypothermia is indicated to protect the central nervous system during surgery. Although hypothermia is often used during brain surgery, clinical efficacy has not yet been established.

OBJECTIVES

To evaluate the effectiveness and safety of induced hypothermia versus normothermia for neuroprotection in patients undergoing brain surgery.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 10), MEDLINE, LILACS, EMBASE and Current Controlled Trials (from inception to November 2010), reference lists of identified trials, and bibliographies of published reviews. We also contacted researchers in the field. There were no language restrictions.

SELECTION CRITERIA

We included randomized controlled trials and quasi-randomized controlled trials of induced hypothermia versus normothermia for neuroprotection in patients undergoing brain surgery.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information.

MAIN RESULTS

We included four trials of cooling for cerebral protection during brain surgery, involving a total of 1219 patients. We did not find any evidence that hypothermia for neuroprotection in patients undergoing brain surgery is either effective or unsafe when compared to normothermia.

AUTHORS' CONCLUSIONS

Although there is some evidence that mild hypothermia is safe, its effectiveness is not clear when compared with normothermia. We need to perform more clinical trials in order to establish the benefit, if any, of hypothermia for cerebral protection during brain surgery before making firm recommendations for the routine use of this intervention.

Protection against focal ischemic injury to the brain by trans-sodium crocetinate. Laboratory investigation

OBJECT

Ischemic injury is a potential complication in a variety of surgical procedures and is a particular impediment to the success of surgeries involving highly vulnerable neural tissue. One approach to limiting this form of injury is to enhance metabolic supply to the affected tissue. Trans-sodium crocetinate (TSC) is a carotenoid compound that has been shown to increase tissue oxygenation by facilitating the diffusivity of small molecules, such as oxygen and glucose. The present study examined the ability of TSC to modify oxygenation in ischemic neural tissue and tested the potential neuroprotective effects of TSC in permanent and temporary models of focal cerebral ischemia.

METHODS

Adult male rats (330–370 g) were subjected to either permanent or temporary focal ischemia by simultaneous occlusion of both common carotid arteries and the left middle cerebral artery (3-vessel occlusion [3-VO]). Using the permanent ischemia paradigm, TSC was administered intravenously beginning 10 minutes after the onset of ischemia at 1 of 8 dosages, ranging from 0.023 to 4.580 mg/kg. Cerebral infarct volume was measured 24 hours after the onset of ischemia. The effect of TSC on infarct volume was also tested after temporary (2-hour) ischemia using a dosage of 0.092 mg/kg. In other animals undergoing temporary ischemia, tissue oxygenation was monitored in the ischemic penumbra using a Licox probe.

RESULTS

Administration of TSC reduced infarct volume in a dose-dependent manner in the permanent ischemia model, achieving statistical significance at dosages ranging from 0.046 to 0.229 mg/kg. The most effective dosage of TSC in the permanent ischemia experiment (0.092 mg/kg) was further tested using a temporary (2-hour) ischemia paradigm. Infarct volume was reduced significantly by TSC in this ischemia-reperfusion model as well. Recordings of oxygen levels in the ischemic penumbra of the temporary ischemia model showed that TSC increased tissue oxygenation during vascular occlusion, but reduced the oxygen overshoot (hyperoxygenation) that occurs upon reperfusion.

CONCLUSIONS

The novel carotenoid compound TSC exerts a neuroprotective influence against permanent and temporary ischemic injury when administered soon after the onset of ischemia. The protective mechanism of TSC remains to be confirmed; however, the permissive effect of TSC on the diffusivity of small molecules is a plausible mechanism based on the observed increase in tissue oxygenation in the ischemic penumbra. This represents a form of protection based on “metabolic reflow” that can occur under conditions of partial vascular perfusion. It is particularly noteworthy that TSC could conceivably limit the progression of a wide variety of cellular injury mechanisms by blunting the ischemic challenge to the brain.

Induced hypothermia in acute ischemic stroke

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS/CONCLUSIONS

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

Neuroprotective effect of mild hypothermia in the temporary brain ischemia in cats

OBJECTIVE

To evaluate the neuroprotective effect of mild hypothermia during temporary focal ischemia in cats.

METHOD

20 cats underwent middle cerebral artery 60 minutes occlusion and 24 hours reperfusion: 10 under normothermia and 10 under mild hypothermia (32 masculine C). Brain coronal sections 2mm thick were stained with 2,3,5-triphenyltetrazolium hydrochloride, photographed and evaluated with software for volume calculation.

RESULTS

Cortical ischemia was found in 7 and basal ganglia ischemia in 8 animals of group 1 and in both regions in 5 animals of group 2 (no difference: p=0.6499 for cortical; p=0.3498 for basal ganglia). No ischemia was found in 5 animals of group 2 and in none of group 1 (significant difference, p=0.0325). The infarct volume was greater in group 1 than 2 (p=0.0433).

CONCLUSION

Mild hypothermia did not interfere with location of ischemia, but it was effective for reducing the infarct volume.

The effect of moderate hypothermia in acute ischemic stroke on pericyte migration: an ultrastructural study

Pericytes are essential components of the blood-brain barrier together with endothelial cells and astrocytes. Any disturbance of brain perfusion may result in blood-brain barrier dysfunction due to pericyte migration from the microvascular wall. The neuroprotective influence of hypothermia on ischemic brain injury has been clearly shown in models of both global and focal ischemia. Leakage of plasma proteins contributes to the extension of neuronal injury and hypothermia has a neuroprotective influence during the ischemic insult. This line of thinking impelled us to investigate the possible role of the pericytes in the occurrence of hypothermic protection during cerebral ischemia. In this study, we examined at the ultrastructural level the effect of moderate hypothermia on microvascular pericyte responses using a rat model of permanent middle cerebral artery occlusion. Twenty rats were divided into four groups. Middle cerebral artery occlusion was performed in all rats except the control group (first group), which was used to determine the pericyte morphology under normal conditions. In the second group, pericyte response to irreversible ischemia under normothermic conditions was examined at the end of the first hour. In the third group, pericyte response to hypoxia was examined under normothermic conditions three hours after ischemia. In the fourth group, temporalis muscle temperature was maintained at 27-29 degrees C for 1h after middle cerebral artery occlusion and pericyte response was then examined at the ultrastructural level. In ischemic normothermic conditions at the end of the first hour (Group 2), a separation was observed between pericytes and the basement membrane and this was interpreted as pericyte migration from the microvascular wall. In ischemic normothermic conditions at the end of the third hour (Group 3), basement membrane disorganization and increased space between the basement membranes were seen in addition to the differentiation of second group. In ischemic hypothermic conditions at the end of the first hour (Group 4), pericyte separation or migration from basement membrane were not seen and the blood-brain barrier remained firm. These findings were interpreted by the authors as a possible relationship between pericyte behavior and neural protection during hypothermia. We suggest that hypothermia may delay the pericyte response but not necessarily attenuate it, and should be associated with hypothermic protection.

Focal epidural cooling reduces the infarction volume of permanent middle cerebral artery occlusion in swine

BACKGROUND

The protective effect against ischemic stroke by systemic hypothermia is limited by the cooling rate and it has severe complications. This study was designed to evaluate the effect of SBH induced by epidural cooling on infarction volume in a swine model of PMCAO.

METHODS

Permanent middle cerebral artery occlusion was performed in 12 domestic swine assigned to groups A and B. In group A, the cranial and rectal temperatures were maintained at normal range (37 degrees C-39 degrees C) for 6 hours after PMCAO. In group B, cranial temperature was reduced to moderate (deep brain, <30 degrees C) and deep (brain surface, <20 degrees C) temperature and maintained at that level for 5 hours after 1 hour after PMCAO, by the epidural cooling method. All animals were euthanized 6 hours after MCAO; their brains were sectioned and stained with 2,3,5-triphenyltetrazolium chloride and their infarct volumes were calculated.

RESULTS

The moderate and deep brain temperature (at deep brain and brain surface) can be induced by rapid epidural cooling, whereas the rectal temperature was maintained within normal range. The infarction volume after PMCAO was significantly reduced by epidural cooling compared with controls (13.73% +/- 1.82% vs 5.62% +/- 2.57%, P < .05).

CONCLUSIONS

The present study has demonstrated, with histologic confirmation, that epidural cooling may be a useful strategy for reducing infarct volume after the onset of ischemia.

CEREBROVASCULAR DYSFUNCTION IS AN ATTRACTIVE TARGET FOR THERAPY IN HEAT STROKE¶

1. The aim of the present review is to summarize clinical observations and results of animal models that advance the knowledge of the attenuation of cerebrovascular dysfunction in the setting of heat stroke. It is a narrative review of selected published literature from Medline over the period 1959-2005. 2. All heat-stressed rodents, even under general anaesthesia, have hyperthermia, systemic inflammation, hypercoagulable state, arterial hypotension and tissue ischaemia and injury in multiple organs. These findings demonstrate that rodent heat stroke models can nearly mirror the full spectrum of human heat stroke. Experimental heat stroke fulfills the empirical triad used for the diagnosis of classical human heat stroke, namely hyperthermia, central nervous system alterations and a history of heat stress. 3. These physiological dysfunctions and survival during heat stroke can be improved by whole-body or brain cooling therapy adopted immediately after the onset of heat stroke. 4. However, in the absence of body or brain cooling, these heat stroke reactions can still be reduced by the following measures: (i) fluid replacement with 3% NaCl solution, 10% human albumin or hydroxyethyl starch; (ii) intravenous delivery of anti-inflammatory drugs, free radical scavengers or interleukin-1 receptor antagonists; (iii) hyperbaric oxygen therapy; or (iv) transplantation of human umbilical cord blood cells. 5. In addition, before initiation of heat stress, prior manipulations with one of the following measures was found to be able to protect against heat stroke reactions: (i) systemic delivery of alpha-tocopherol, mannitol, inducible nitric oxide synthase inhibitors, mu-opioid receptor antagonists, endothelin ETA receptor antagonists, serotoninergic nerve depletors or receptor antagonists, or glutamate receptor antagonists; or (ii) heat shock protein 72 preconditioning. 6. There is compelling evidence that cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

Epidural cooling for selective brain hypothermia in porcine model

BACKGROUND

Hypothermia has been shown to be neuroprotective in many animal models and several human trials of brain ischemic and trauma. However systemic hypothermia may result in fatal complications. This study was undertaken to test epidural cooling as a new method of inducing selective brain hypothermia.

METHOD

Six adult swine (mean mass, 33.8+/-3.6 kg) were studied. Anesthesia was maintained with pentobarbital sodium (25 mg kg-1, i.v.) and pancuronium bromide (0.5 mg kg-1 h-1, i.v.). Five probes were placed in the rectum, deep brain, brain surface, epidural space, and room air for temperature monitoring respectively. Epidural cooling was performed using cold-saline (4 degrees C) perfusion into the epidural space through a flexible double-lumen catheter. The dripping speed of cold saline was controlled to maintain the target temperature. The changes of the epidural space pressure, complete blood counts, basic metabolic panels, tests for fibrinolysis and coagulation status were monitored to assess hypothermia-induced changes.

FINDINGS

Following the epidural cooling perfused with cold-saline (4 degrees C) at mean dripping speed of 720 ml per hour, the local brain surface temperature could decrease rapidly to 17.3-21.6 degrees C within one minute, and deep brain temperature decreased to 27.2-29.7 degrees C within 5 minutes. The target temperatures were easily controlled by the dripping speed of cold saline (from mild to deep hypothermia). The rectal temperature was maintained at normal range within 6 perfusion hours. No arrhythmia was observed, and all hematological variables were within the normal range for swine. No increased intracranial pressure was induced by the cooling method.

CONCLUSIONS

The data demonstrate that epidural space cooling was technically feasible and useful for selective brain hypothermia, and the target temperatures are easily controlled. The induction of hypothermia was rapid and maintained for a long period of time, whereas the body temperature was maintained within the normal range and without hemodynamic instability.

Mild hypothermia reduces polymorphonuclear leukocytes infiltration in induced brain inflammation

Over the last 50 years deep hypothermia (23(0) C) has demonstrated to be an excellent neuroprotective agent in cerebral ischemic injury. Mild hypothermia (31-33(0) C) has proven to have the same neuroprotective properties without the detrimental effects of deep hypothermia. Mechanisms of injury that are exaggerated by moderate hyperthermia and ameliorated by hypothermia include, reduction of oxygen radical production, with peroxidase damage to lipids, proteins and DNA, microglial activation and ischemic depolarization, decrease in cerebral metabolic demand for oxygen and reduction of glycerin and excitatory amino acid (EAA) release. Studies have demonstrated that inflammation potentiates cerebral ischemic injury and that hypothermia can reduce neutrophil infiltration in ischemic regions. To further elucidate the mechanisms by which mild hypothermia produces neuroprotection in ischemia by attenuating the inflammatory response, we provoked inflammatory reaction, in brains of rats, dropping a substance that provokes a heavy inflammatory reaction. Two groups of ten animals underwent the same surgical procedure: the skull bone was partially removed, the duramater was opened and an inflammatory substance (5% carrageenin) was topically dropped. The scalp was sutured and, for the group that underwent neuroprotection, an ice bag was placed covering the entire skull surface, in order to maintain the brain temperature between 29,5-31(0) C during 120 minutes. After three days the animals were sacrificed and their brains were examined. The group protected by hypothermia demonstrated a remarkable reduction of polymorphonuclear leukocytes (PMNL) infiltration, indicating that mild hypothermia can have neuroprotective effects by reducing the inflammatory reaction.

Neurophysiological monitoring, magnetic resonance imaging, and histological assays confirm the beneficial effects of moderate hypothermia after epidural focal mass lesion development in rodents

OBJECTIVE

To assess the effects of moderate intraischemic hypothermia on neurophysiological parameters in an epidural balloon compression model in rats and to correlate the results with magnetic resonance imaging and histological findings.

METHODS

Neurophysiological monitoring included laser Doppler flow, tissue partial oxygen pressure, and intracranial pressure measurements and electroencephalographic assessments during balloon expansion, sustained inflation, and reperfusion. Moderate intraischemic cooling of animals was extended throughout the reperfusion period, and results were compared with those for normothermic animals. Moreover, histological morphometric and magnetic resonance imaging volumetric analyses of the lesions were performed.

RESULTS

Laser Doppler flow decreased slightly during ischemia (P < 0.05) in animals treated with hypothermia, and flow values demonstrated complete reperfusion, compared with incomplete flow restoration in untreated animals (P < 0.05). During ischemia, the tissue partial oxygen pressure was less than 4.3 mm Hg in both groups. After reperfusion, values returned to the normal range in both groups, but the tissue partial oxygen pressure in hypothermic animals was significantly higher (P = 0.042) and demonstrated 19% higher values, compared with normothermic animals, before rewarming. Moderate hypothermia attenuated a secondary increase in intracranial pressure (P < 0.05), and electroencephalographic findings indicated a trend toward faster recovery (P > 0.05) after reperfusion. Lesion size was reduced by 35% in magnetic resonance imaging volumetric evaluations and by 24.5% in histological morphometric analyses.

CONCLUSION

Intraischemic hypothermia improves cerebral microcirculation, attenuates a secondary increase in intracranial pressure, facilitates electroencephalographic recovery, and reduces the lesion size.

Protective effects of brief intra- and delayed postischemic hypothermia in a transient focal ischemia model in the neonatal rat

Hypothermia provides neuroprotection in virtually all animal models of ischemia, including adult stroke models and the neonatal hypoxic-ischemic (HI) model. In these studies, brief periods of hypothermia are examined in a neonatal model employing transient focal ischemia in a 7-day-old rat pup. Pups underwent permanent middle cerebral artery (MCA) occlusion coupled with a temporary (1 h) occlusion of the ipsilateral common carotid artery (CCA). This study included five treatment groups: (1) normothermic (Normo)-brain temperature was maintained at 37 degrees C; (2) intraischemic hypothermia (IntraH)-28 degrees C during the 1-h ischemic period only; (3) postischemic hypothermia (PostH)-28 degrees C for the second hour of reperfusion only; (4) late-onset postischemic hypothermia (LPostH) cooled to 28 degrees C for the fifth and sixth hours of reperfusion only; and (5) Shams. After various times (3 days-6 weeks), the lesion was assessed using 2,3,5-triphenyltetrazolium chloride (TTC) or hematoxylin and eosin (H&E) stains. Intraischemic hypothermia resulted in significant protection in terms of survival, lesion size, and histology. Postischemic hypothermia was not effective in reducing lesion size early after ischemia, but significantly reduced the eventual long-term damage (2-6 weeks). Late-onset postischemic hypothermia did not reduce infarct volume. Therefore, both intraischemic and postischemic hypothermia provided neuroprotection in the neonatal rat, but with different effects on the degenerative time course. While there were no observable differences in simple behaviors or growth, all hypothermic conditions significantly reduced mortality rates. While the protection resulting from intraischemic hypothermia is similar to what is observed in other models, the degree of long-term ischemic protection observed after 1 h of postischemic hypothermia was remarkable and distinct from what has been observed in other adult or neonatal models.

The neuroprotective effect of a free radical scavenger and mild hypothermia following transient focal ischemia in rats

Edaravone, a novel free radical scavenger, has been reported to reduce ischemic damage in rats subjected to transient focal ischemia. The aim of this study is, therefore, to investigate the effect of a combined therapy with edaravone and mild hypothermia of 35 degrees C. Sprague-Dawley rats were subjected to MCA occluding an intraluminal suture technique for 2 hrs. The rats were reperfused for 24 h and decapitated for infarct and edema analysis. Animals were randomly devided into four groups: (I) vehicle + normothermia (control) (II) vehicle + mild hypothermia (III) Edaravone + normothermia (IV) Edaravone + mild hypothermia. Mild hypothermia alone had no reduction of the brain damage. The edaravone alone significantly reduced edema volume. The combined treatment with edaravone and mild hypothermia reduced both infarct and edema volume. In addition, this treatment provided for the best functional outcome. These results demonstrate that free radical scavenger, edaravone attenuates brain edema and that the combined therapy with edaravone and mild hypothermia significantly reduces not only edema but also infarct on transient focal cerebral ischemia in rats. The neuroprotective effects seen in this study may be due to the combined interaction of antiedema activity between edaravone and mild hypothermia, suppressing free radical production.

Hypothermic protection in rat focal ischemia models: strain differences and relevance to "reperfusion injury"

Hypothermic protection was compared in Long-Evans and spontaneously hypertensive rat (SHR) strains using transient focal ischemia, and in Wistar and SHR strains using permanent focal ischemia. Focal ischemia was produced by distal surgical occlusion of the middle cerebral artery and tandem occlusion of the ipsilateral common carotid artery (MCA/CCAO). Moderate hypothermia of 2 hours' duration was produced by systemic cooling to 32 degrees C, with further cooling of the brain achieved by reducing to 30 degrees C the temperature of the saline drip superfusing the exposed occlusion site. Infarct volume was determined from serial hematoxylin and eosin-stained frozen sections obtained routinely at 24 hours, or in some cases after 3 days' survival. In the SHR, moderate hypothermia was only effective when initiated before recirculation after a 90-minute occlusion period. In contrast, the same intervention was strikingly effective in the Long-Evans rat even when initiated after as long as 30-minute reperfusion after a 3-hour occlusion. This magnitude and duration of cooling was not protective in permanent MCA/CCAO in the SHR, but such transient hypothermia did effectively reduce infarct volume after permanent occlusions in Wistar rats. These results show striking differences in the temporal window for hypothermic protection among rat focal ischemia models. As expected, "reperfusion injury" in the Long-Evans strain is particularly responsive to delayed cooling. The finding that the SHR can be protected by hypothermia initiated immediately before recirculation suggests a rapidly evolving component of injury occurs subsequent to reperfusion in this model as well. Hypothermic protection after permanent occlusion in Wistar rats identifies a transient, temperature-sensitive phase of infarct evolution that is not evident in the unreperfused SHR. These observations confirm that distinct mechanisms can underlie the temporal progression of injury in rat stroke models, and emphasize the critical importance of considering model and strain differences in extrapolating results of hypothermic protection studies in animals to the design of interventions in clinical stroke.

Post-ischemic hypothermia-induced tissue protection and diminished apoptosis after neonatal cerebral hypoxia–ischemia

Hypothermia is possibly the single most effective method of neuroprotection developed to date. However, the mechanisms are not completely understood. The aim of this study was to investigate the effects of post-ischemic hypothermia on brain injury and apoptotic neuronal cell death as well as related biochemical changes after neonatal hypoxia-ischemia (HI). Seven-day-old rats were subjected to left common carotid artery ligation and hypoxia (7.8%) for 1 h. Systemic hypothermia was induced immediately after hypoxia-ischemia, and body temperature was maintained at 30 degrees C for 10 h. The normothermic group was kept at 36 degrees C. Brain infarct volumes and neuronal loss in the CA1 area of the hippocampus were significantly reduced at 72 h post-HI in the hypothermia group. Cytochrome c release and activation of caspase-3 and -2 at 24 h post-HI were significantly diminished by hypothermia. The numbers of cytochrome c- and TUNEL-positive cells in the cortex and dentate gyrus of the hippocampus were significantly reduced in the hypothermia group compared with the normothermia group at 72 h post-HI. These results indicate that hypothermia may, at least partially, act through inhibition of the intrinsic pathway of caspase activation in the neonatal brain, thereby preventing apoptotic cell death.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Neuroprotection in cardiac surgery

This article reviews past and present neuroprotective efforts and outlines a framework for the future development of techniques for neuroprotection during cardiac surgery.

Evaluation of MCAO stroke models in normotensive rats: standardized neocortical infarction by the 3VO technique

The temporary three-vessel occlusion (3VO) technique with a surgical approach for middle cerebral artery (MCA) produces consistent cerebral infarction in the neocortex in normotensive rats. The intraluminal thread-occlusion technique with an endovascular approach targeting the MCA occlusion (MCAO) is more widely used since it does not require complicated intracranial procedures. The aim of this study was to review the methods/models for MCAO stroke in normotensive rats and to evaluate a 3VO stroke model that provides consistent degrees and variance of cortical stroke injury for additional discussion. First, we analyzed a model with modified temporary 3VO technique requiring less complicated procedures than the temporary 3VO model, i.e., temporary occlusion of the bilateral common carotid arteries (CCAs) superimposed on a permanent occlusion of the MCA, in Sprague-Dawley rats or C57BL/6J mice. In the microvascular tissue (cerebral) perfusion study, significant reductions in regional cerebral perfusion during the 3VO accompanied a rapid return to baseline after release of the CCAs, showing that the technique induces temporary focal ischemia. The average sizes and variances of the neocortical infarction in this model, together with those in the other normotensive rat models caused by the 3VO technique in the literature, indicated a standard size and variance of infarcted lesion in the control groups relative to the specific ischemic period. However, stroke injuries in the neocortex induced by the thread occlusion technique showed greater variability with less consistent lesion sizes. Inclusion/exclusion criteria to avoid inappropriate cases with too mild (no/faint infarction) or too great (huge/fatal infarction) severity in the ischemic injury may differ between laboratories in the thread occlusion model.

Effect of mild hypothermia on focal cerebral ischemia. Review of experimental studies

The purposes of this review are to clarify the effect of hypothermia therapy on focal cerebral ischemia in rats, and to consider the relevancy of its application to human focal cerebral ischemia. Since 1990, 26 reports confirming the brain-protecting effect of hypothermia in rat focal cerebral ischemia models have been published. Seventy-four experimental groups in these 26 reports were classified as having transient middle cerebral arterial occlusion (MCAO) with mild hypothermia (group A; 43 groups), permanent MCAO with mild hypothermia (group B; 14 groups), permanent MCAO with deep hypothermia (group C; 8 groups) and transient or permanent MCAO with mild hyperthermia (group D; 9 groups). The results were evaluated as the % infarct volume change caused by hypothermia or hyperthermia compared with the infarct volume in normothermic animals. The effectiveness was confirmed in 36 (83%) of the 43 groups in group A, 10 (71%) of the 14 in group B, and six (75%) of the eight in group C. The infarct volume of eight of the nine groups in group D was markedly aggravated. The percent infarct volume change was 55.3% +/- 27.1% in group A, 57.6% +/- 24.7% in group B, 60.8% +/- 45.5% in group C, and 189.7% +/- 89.4% in group D. For effective reduction of the infarct volume, hypothermia should be started during ischemia or within 1 h, at latest, after the beginning of reperfusion in the rat transient MCAO model. However, it is not clear whether this neuroprotective effect of hypothermia can also be observed in the chronic stage, such as several months later. Keeping the body temperature normothermic in order to avoid mild hyperthermia seems to be rather important for not aggravating cerebral infarction. Clinical randomized studies on the efficacy of mild hypothermia for focal cerebral ischemia and sophisticated mild hypothermia therapy techniques are mandatory.

Hypothermia attenuates circulatory shock and cerebral ischemia in experimental heatstroke

We tested the hypothesis in a rat model that body cooling suppresses circulatory shock and cerebral ischemia in heatstroke. Animals under urethane anesthesia were exposed to water blanket temperature (Tblanket) of 42 degrees C until mean arterial pressure (MAP) and local cerebral blood flow (CBF) in the hippocampus began to decrease from their peak levels, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 26 degrees C. Extracellular concentrations of glutamate, glycerol, lactate, and lactate/pyruvate in the hippocampus were assessed by microdialysis methods. Cooling was accomplished by decreasing Tblanket from 42 degrees C to 16 degrees C. The values of MAP and CBF after the onset of heat stroke in heatstroke rats received no cooling were all significantly lower than those in control rats. However, the neuronal damage score and extracellular levels of ischemia and damage markers in the hippocampus were greater. Cooling immediately after the onset of heatstroke reduced the heatstroke-induced circulatory shock, cerebral ischemia, neuronal damage, and surge of tissue ischemia and damage markers in the hippocampus, and resulted in prolongation of survival time. Delaying the onset of cooling reduced the therapeutic efficiency. The results suggest that body cooling attenuates circulatory shock and cerebral ischemia insults in heatstroke.

Treatment of space-occupying cerebral infarction

OBJECTIVE

Patients with a hemispheric infarct accompanied by massive edema have a poor prognosis; the case fatality rate may be as high as 80%, and most survivors are left severely disabled. Various treatment strategies have been proposed to limit brain tissue shifts and to reduce intracranial pressure, but their use is controversial. We performed a systematic search of the literature to review the evidence of efficacy of these therapeutic modalities.

DATA SOURCES

Literature searches were carried out on MEDLINE and PubMed.

STUDY SELECTION

Studies were included if they were published in English between 1966 and February 2002 and addressed the effect of osmotherapy, hyperventilation, barbiturates, steroids, hypothermia, or decompressive surgery in supratentorial infarction with edema in animals or humans.

DATA SYNTHESIS

Animal studies of medical treatment strategies in focal cerebral ischemia produced conflicting results. If any, experimental support for these strategies is derived from studies with animal models of moderately severe focal ischemia instead of severe space-occupying infarction. None of the treatment options have improved outcome in randomized clinical trials. Two large nonrandomized studies of decompressive surgery yielded promising results in terms of reduction of mortality and improvement of functional outcome.

CONCLUSIONS

There is no treatment modality of proven efficacy for patients with space-occupying hemispheric infarction. Decompressive surgery might be the most promising therapeutic option. For decisive answers, randomized, controlled clinical trials are needed.

Mild hypothermia reduces ICAM-1 expression, neutrophil infiltration and microglia/monocyte accumulation following experimental stroke

Mild hypothermia is an established neuroprotectant against cerebral ischemic injury. Studies have shown that inflammation potentiates cerebral ischemic injury, particularly in the setting of reperfusion. To further elucidate the mechanism by which mild hypothermia attenuates the inflammatory response, we assessed endothelial intercellular adhesion molecule-1 (ICAM-1) expression, neutrophil and monocyte infiltration, and microglial activation following 2 h of transient focal cerebral ischemia under normothermic and mildly hypothermic conditions. Ischemia was induced using the intraluminal suture method in Sprague-Dawley rats. Immunohistochemistry was used to detect endothelial ICAM-1, infiltrating neutrophils and monocytes, and microglia at 1, 3, and 7 days post-ischemia. Immunopositive cell and vessel densities were measured in the peri-infarct region. Mild hypothermia was associated with decreased neutrophils at 1 and 3 days post-ischemia, decreased ICAM-1-positive vessels at 1, 3, and 7 days, and decreased monocytes/activated microglia at 3 and 7 days, but not at 1 day. These data demonstrate that mild hypothermia significantly reduces endothelial adhesion molecule expression, acute (neutrophil) and subacute (monocyte) leukocyte infiltration, and microglial activation up to 7 days following insult in a rodent model of transient focal cerebral ischemia.

Mild focal cerebral ischemia in the rat. The effect of local temperature on infarct size

We aimed at investigating a new model of mild focal cerebral ischemia in rats with repeated, noninvasive magnetic resonance scanning combined with histology. Magnetic resonance imaging yielded information about infarct development enabling us to test the putative growth of the infarct over time. The effect of local temperature at the occlusion site in this model was furthermore tested. Thirty-three Wistar rats were subjected to 30 min of simultaneous common carotid artery and distal middle cerebral artery occlusion or sham treatment. Animals were magnetic resonance-scanned repeatedly between day one and day 14 after surgery, then sacrificed, and paraffin brain sections stained. All animals scanned 24 h after reperfusion showed an area of edema in the affected cortex, which later was identified as an infarct. Animals with a temperature of 33.9 +/- 1.5 degrees C at the MCA site (hypothermic) showed smaller infarcts (14.4 +/- 10 mm3) than animals with normothermic local temperature (36.7 +/- 0.2 degrees C, 57.7 +/- 26.4 mm3). Infarct size was maximal on day 3 after ischemia but decreased as edema subsided. Infarct volumes from histology and magnetic resonance imaging correlated well. The model reproducibly yielded cortical infarcts, which did not grow after edema had subsided. Local temperature had a considerable effect on final infarct size.

Effects of hypothermia and rewarming on evoked potentials during transient focal cerebral ischemia in cats

We examined the effects of mild to moderate hypothermia and the influence of rewarming on electrophysiological function using somatosensory evoked potentials (SEPs) in transient focal ischemia in the brain. Nineteen cats underwent 60 min of left middle cerebral artery occlusion under normothermic (36 degrees-37 degrees C, n = 6) or hypothermic (30 degrees -31 degrees C, n = 13) conditions followed by 300 min of reperfusion with slow (120 min, n = 6) or rapid (30 min, n = 7) rewarming. Whole-body hypothermia was induced during ischemia and the first 180 min of reperfusion. SEPs and regional cerebral blood flow were measured before and during ischemia and during reperfusion. The specific gravity of gray and white matter was examined as the indicator of edema. During rewarming, SEP amplitudes recovered gradually. After rewarming, SEPs in the normothermic and rapid rewarming groups remained depressed (20%-40% of pre-occlusion values); however, recovery of SEPs was significantly enhanced in the slow rewarming group (p < 0.05). Hypothermia followed by slow rewarming reduced edema in gray and white matter. Rapid rewarming did not reduce edema in the white matter. The recovery of SEPs correlated with the extent of brain edema in transient focal ischemia. Rapid rewarming reduced the protective effect of hypothermia.

Safety and performance of a novel intravascular catheter for induction and reversal of hypothermia in a porcine model

OBJECTIVE

This study was undertaken to assess the acute safety and feasibility of rapidly inducing, maintaining, then reversing hypothermia using a novel heat transfer catheter and a closed-loop automatic feedback temperature control system to overcome limitations imposed by current clinical practices used for perioperative cooling and warming.

METHODS

Six swine (mean mass, 53.8 +/- 3.6 kg) were studied. The heat transfer catheter was placed in the inferior vena cava via the femoral vein. Hypothermia to 32 degrees C was induced, maintained for 6 hours, then reversed to 36 degrees C. The time needed to induce and reverse hypothermia was recorded via continuous temperature monitoring of the lower esophagus, cerebrum, and rectum. Electrocardiography provided continuous monitoring, and blood draws were made at baseline and at 2-hour intervals. Examination of the catheter in situ was performed after the animals were killed.

RESULTS

Cooling from 36.2 to 32.0 degrees C was rapid and uniform (mean, 7.3 +/- 0.7 degrees C/h), with animals reaching the target temperature within 60 minutes. Rewarming was also easily controlled, with animals' temperatures reaching 36 degrees C within 130 minutes. No arrhythmia was observed, and all hematological variables were within the normal range for swine. There was no evidence of hemolysis or platelet changes. Little to no thrombosis was observed.

CONCLUSION

The data presented here suggest that rapid induction and reversal of hypothermia are technically possible using a core intravenous cooling catheter; this method would provide a safe, rapid, and exquisitely reproducible way to induce hypothermia with subsequent restoration of normothermia.

Cooling-induced carotid artery dilatation: an experimental study in isolated vessels

BACKGROUND AND PURPOSE

Clinical and experimental studies seem to indicate that hypothermia may improve outcome in stroke victims and reduce experimental brain injury. The current interpretation is that cooling has a neuroprotective effect by reducing brain metabolism. The objective of our study was to test the hypothesis that hypothermia induces arterial vasodilatation and thereby increases cerebral blood flow.

METHODS

We recorded isometric tension in rabbit carotid artery strips in organ baths during stepwise cooling. The cooling responses were tested at basal tone, in noradrenaline-precontracted vessels, and after electric field stimulation.

RESULTS

Stepwise cooling from 37 degrees C to 4 degrees C induced reproducible graded relaxation, inversely proportional to temperature. The responses could be elicited at basal tone and in precontracted vessels. Cooling decreased the contractile responses to norepinephrine and potassium chloride. Cooling at 20 degrees C decreased the contractile responses to electric field stimulation, while at 10 degrees C these were totally abolished. Cooling-induced vasodilatation is not dependent on an endothelial mechanism.

CONCLUSIONS

Cooling of carotid artery preparations induced a reversible graded vasodilatation and decreased or abolished the effect of vasocontractile neurotransmitters. The effect of local hypothermia could increase cerebral blood flow and may constitute a positive therapeutic modality in stroke patients.

Neuroprotective effect of hypothermia at defined intraischemic time courses in cortical cultures

Many experimental and clinical studies have shown that hypothermia confers cerebroprotective benefits against ischemic insults. Because of the many conflicting reports on hypothermic neuroprotection, we undertook this cellular study to identify the optimal temperature or a range of temperatures for maximal neuroprotection at different times (6-24 hr) during ischemic insults. Cultured Wistar rat cortical neurons were exposed to oxygen deprivation at defined times and temperatures (37 degrees C normothermia, 32 degrees C mild hypothermia, 27 degrees C moderate hypothermia, 22 degrees C deep hypothermia, and 17 degrees C profound hypothermia). The survival rate of neurons was evaluated by assessing viable neurons on photomicrographs. The normothermic group demonstrated a significantly lower survival rate of cultured neurons (6 hr, 80.3% +/- 2.7%; 12 hr, 56.1% +/- 2.1%; 18 hr, 34.2% +/- 1%; 24 hr, 18.1% +/- 2.2%) compared to hypothermic groups (P < 0.001). The survival rate for the profound hypothermic group was significantly reduced (P < 0.01) compared to other hypothermic groups (at 17 degrees C: 12 hr, 85.9% +/- 2.5%, 18 hr, 74.7% +/- 3.7%, 24 hr, 58.7% +/- 2.7%). Almost equal survival rates were observed among mild, moderate, and deep hypothermic groups following <18 hr exposure to hypoxia, but the deep hypothermic group showed a significantly higher survival rate (84.1% +/- 1.6%; P < 0.001) when subjected to hypoxia for 24 hr. In conclusion, hypothermia offers marked neuroprotection against hypoxia, but attenuation of neuronal cell death was less with profound hypothermia compared to mild, moderate, and deep hypothermia. Deep hypothermia affords maximal protection of neurons compared to mild and moderate hypothermia during long-lasting hypoxia (>18 hr).

Non-pharmacologic (physiologic) neuroprotection in the treatment of brain ischemia

Clinical trials for ischemic stroke have been characterized by a disappointing series of negative results, using a panoply of pharmacologic agents. This paper emphasizes five physiologic measures that can be taken to mitigate ischemic brain damage. These are (1) hypothermia, (2) insulin, (3) arterial hyperoxemia, (4) blood pressure control and (5) magnesium. Hypothermia is protective in both focal and global ischemia, even postischemically protecting against selective neuronal necrosis and infarction. The total equation for protection includes the (i) postischemic delay, (ii) depth, and (iii) duration of hypothermia. Insulin operates by lowering glucose levels to the normal range in focal ischemia. It is possible that very low glucose levels are detrimental in focal ischemia with paradoxical augmentation of the infarct size, and that spreading depression plays a role in this. Controlled arterial hyperoxemia seems effective experimentally in reducing infarct size, operating mechanistically by either a direct effect of oxygen, or vasoconstriction causing shunting of blood into the infarct, or both. Blood pressure is a critical determinant of infarct size, and raising blood pressure improves collateral blood flow and reduces stroke size. To be used clinically, however, hemorrhage must be ruled out. The most dramatic clinical effects of blood pressure are seen in aneurysm patients with vasospasm, where minor increases in blood pressure reverse temporary hemiparesis by reducing ischemia. Magnesium is likely the safest NMDA antagonist, with a long history of safe administration to pregnant women with eclampsia. There is potential interaction with insulin, in that magnesium causes hyperglycemia, which requires insulin to counteract it. Magnesium and insulin together have been shown effective in experimental brain ischemia. In the absence of safe and effective pharmacologic neuroprotection agents, clinical trials should be designed and launched to test these physiologic measures, singly and in combination, to reduce brain damage after ischemia.

Prolonged mild hypothermia therapy protects the brain against permanent focal ischemia

BACKGROUND AND PURPOSE

The efficacy of hypothermic intervention for permanent focal ischemia has yet to be clarified. This study investigated the effect of a prolonged moderate or mild hypothermia on permanent focal ischemia in rats.

METHODS

Two permanent focal ischemia models in male Sprague-Dawley rats were used. Moderate (30 degrees C, in experiment 1) or mild (33 degrees C, in experiment 2) hypothermia was achieved at the time of the induction of focal ischemia and was maintained for 2 hours under general anesthesia. Thereafter, the hypothermic condition was maintained by means of a cold room for a total of 24 hours. The infarct volume and neurological function were analyzed for a maximum of 21 days and compared with that of the normothermia group. Regional cerebral blood flow was monitored for 6 hours in the ischemic core and penumbra region.

RESULTS

In experiment 1, the total infarct volume in the normothermic group was 368+/-59 mm(3); in contrast, it was significantly smaller in the hypothermia group: 169+/-33 mm(3) at 48 hours (mean+/-SEM, P:<0.05). In experiment 2, the infarct volume was 211+/-19 mm(3) in the normothermia group and 88+/-15 mm(3) in the hypothermia group at 21 days (P:<0.05). There were significant differences in neurological function from days 2 through 21 between the two groups. Mean regional cerebral blood flow in the penumbra region increased to a level >50% of baseline.

CONCLUSIONS

Prolonged mild hypothermia suppressed the development of cerebral infarct and neurological deficit chronically after the induction of permanent focal ischemia.

Intra-ischemic hypothermia attenuates intercellular adhesion molecule-1 (ICAM-1) and migration of neutrophil

Adhesion of neutrophil to the endothelium and subsequent transmigration has been reported to contribute to progression of focal ischemia. Hypothermia has been known to attenuate ischemic insult through various mechanisms of action. The authors evaluated the effect of hypothermia on expression of intercellular adhesion molecule-1 (ICAM-1) protein and on transmigration of neutrophil with immunohistochemical method. Transient focal ischemia model in rats was employed, and animals received 2 h of either normothermic or hypothermic ischemia. To confirm the effectiveness of hypothermia on neuroprotection, cortical infarct area was compared between the two groups. Our results demonstrated that hypothermia reduced both the number of microvessels expressing ICAM-1 and that of neutrophils migrating into ischemic tissue. Comparison of cortical infarct area showed persistent protective effect. This study indicates that reduction of ICAM-1 expression and subsequent reduction of migrating neutrophil in hypothermia can contribute to attenuation of ischemic damage.

Mild hypothermia decreases the incidence of transient ADC reduction detected with diffusion MRI and expression of c-fos and hsp70 mRNA during acute focal ischemia in rats

The effects of mild hypothermia on the apparent diffusion coefficient of water (ADC) and expression of c-fos and hsp70 mRNA were examined during acute focal cerebral ischemia. Young adult rats were subjected to 60-min middle cerebral artery occlusion under either normothermia (37.5 degrees C) or hypothermia (33 degrees C). Diffusion-weighted echo-planar magnetic resonance imaging was used to monitor changes in ADC throughout the ischemic period. Perfusion MRI with dysprosium contrast was used at the end of the ischemic period to verify that the occlusion was successful. C-fos and hsp70 mRNA expression were examined with in situ hybridization at the end of the ischemic period. The results indicate that the size of the region that exhibited reduced ADC was smaller during hypothermia than during normothermia. Hypothermia also decreased the frequency of occurrence of transient ADC reductions, especially in dorsal aspects of cortex. Expression of both c-fos and hsp70 mRNA were markedly reduced by hypothermia. Transient ADC reduction and c-fos expression are associated with spreading depression, which is believed to contribute to lesion expansion during acute focal ischemia. The results suggest that part of the neuroprotective effect of hypothermia may be due to a reduced incidence of spreading depression.

Effects of delayed intraischemic and postischemic hypothermia on a focal model of transient cerebral ischemia in rats

BACKGROUND AND PURPOSE

Intraischemic mild hypothermia has been shown to be neuroprotective in reducing cerebral infarction in transient focal ischemia. As a more clinical relevant issue, we investigated the effect of delayed intraischemic and postischemic hypothermia on cerebral infarction in a rat model of reversible focal ischemia. We also examined the effect of hypothermia on the inflammatory response after ischemia-reperfusion to assess the neuroprotective mechanism of brain hypothermia.

METHODS

Rats were subjected to 2 hours of middle cerebral artery occlusion followed by 22 hours of reperfusion under the following protocols: (1) rats were treated with normothermia (37.0 degrees C, 4 hours) and then housed in room temperature (25 degrees C, 18 hours) and (2) rats were treated with hypothermia (33.0 degrees C, 4 hours, brain temperature modulation was started 30 minutes before the reperfusion) and then housed in cold temperature (5 degrees C, 18 hours). Animals were killed 24 hours after the onset of ischemia. The infarct volume was examined with 2,3,5-triphenyl-tetrazolium chloride staining. The accumulation of polymorphonuclear leukocytes (PMNLs) and the expression of intercellular adhesion molecule-1 mRNA were evaluated in both groups.

RESULTS

A significant reduction (P<0.05) in infarct volume was found in the hypothermia group compared with the normothermia group. Compared with the normothermia group, hypothermic treatment also significantly reduced the accumulation of PMNLs (P<0.01) and inhibited the overexpression of intercellular adhesion molecule-1 mRNA at 22 hours of reperfusion after 2 hours of ischemia.

CONCLUSIONS

Ischemic brain damage can be reduced with delayed intraischemic and prolonged postischemic hypothermia in a focal model of transient cerebral ischemia in rats. The neuroprotective mechanism of hypothermia may be mediated by suppression of PMNL-mediated inflammatory response after ischemia-reperfusion in this model.

Cerebral ischemia-reperfusion injury: a novel therapeutic approach with TAK-218

The goal of the present study was to evaluate the potential neuroprotective effect of TAK-218 in an in vivo rat focal cerebral ischemia/reperfusion model. TAK-218 is a novel compound with multiple antiischemic properties, including suppression of aberrant dopamine release, modulation of sodium channels, and inhibition of lipid peroxidation. The study was a blinded, randomized, placebo-controlled study of TAK-218 in a three-vessel focal ischemic rat model. A total of 22 rats were randomly assigned to the treatment or placebo group. Animals were injected intrapertoneally with either a 2 mg/kg dose of drug or saline at 2 hours after reperfusion. Infarction volume was measured with use of 2,3,5-triphenyltetrazolium chloride. Total adjusted infarction volume in treated animals decreased by 10%. With use of a statistical analysis requiring 80% power with a 20% reduction desired effect, there was no statistically significant difference in the end-point of infarction volume between drug and placebo treatment groups. In light of the proven efficacy of thrombolytic therapy for acute stroke, it is now desirable to test neuroprotective agents during the 3-hour therapeutic window after ischemia. Further research is necessary to discern if a therapeutic agent with multiple antiischemic properties may provide a more robust neuroprotective effect than an agent with a single neuroprotective action.

Comparative neuroprotective efficacy of prolonged moderate intraischemic and postischemic hypothermia in focal cerebral ischemia

OBJECT

The purpose of this study was to compare the effects of prolonged hypothermia on ischemic injury in a highly reproducible model of middle cerebral artery (MCA) occlusion in rats.

METHODS

Male Sprague-Dawley rats were anesthetized with halothane and subjected to 120 minutes of temporary MCA occlusion by retrograde insertion of an intraluminal nylon suture coated with poly-L-lysine through the external carotid artery into the internal carotid artery and the MCA. Two levels of prolonged postischemic cranial hypothermia (32 degrees C and 27 degrees C) and one level of intraischemic cranial hypothermia (32 degrees C) were compared with the ischemic normothermia (37 degrees C) condition. Target cranial temperatures were maintained for 3 hours and then gradually restored to 35 degrees C over an additional 2-hour period. The animals were evaluated using a quantitative neurobehavioral battery of tests before inducing MCA occlusion, during occlusion (at 60 minutes postonset in all rats except those in the intraischemic hypothermia group), and at 24, 48, and 72 hours after reperfusion. The rat brains were perfusion fixed at 72 hours after ischemia, and infarct volumes and brain edema were determined. Both intraischemic and postischemic cooling to 32 degrees C led to similar significant reductions in cortical infarct volume (by 89% and 88%, respectively) and total infarct volume (by 54% and 69%, respectively), whereas postischemic cooling to 27 degrees C produced lesser reductions (64% and 49%, respectively), which were not statistically significant. All three hypothermic regimens significantly lessened hemispheric swelling and improved the neurological score at 24 hours. The authors' data confirm that a high degree of histological neuroprotection is conferred by postischemic cooling to 32 degrees C, which is virtually equivalent to that observed with intraischemic cooling to the same level.

CONCLUSIONS

These results may be relevant to the design of future clinical trials of therapeutic hypothermia for acute ischemic stroke.

Combination of intraischemic and postischemic hypothermia provides potent and persistent neuroprotection against temporary focal ischemia in rats

BACKGROUND AND PURPOSE

It is not known whether a combination of intraischemic and postischemic mild hypothermia provides extra neuroprotection and if so, whether the neuroprotection is persistent.

METHODS

Sixty-eight Sprague-Dawley rats were used. In group 1, ischemia and reperfusion were performed under normothermic (N) conditions (control, N-N). In group 2, ischemia was induced and maintained under hypothermic conditions (33 degrees C for 2 hours) and reperfusion was performed under normothermic conditions, H-N. In group 3, both ischemia and reperfusion were performed under hypothermic conditions for an additional 21 hours after the surgery, H-22H. In group 4, ischemia was induced and maintained under hypothermic conditions and reperfusion was performed under hypothermic conditions only for the initial 3 hours (H-3H). In group 5, ischemia was induced and maintained under normothermic conditions and reperfusion was performed under hypothermic conditions (33 degrees C) (N-22H). All rats were perfused 48 hours after the induction of ischemia. In addition, the normothermic or hypothermic therapy used for groups 1, 3, and 4 was performed again, and these rats were killed 30 days after the induction of ischemia. Furthermore, neurological deficits were monitored in groups N-N and H-22H for 4 weeks.

RESULTS

In the H-3H and H-22H groups, the total infarct volume was significantly reduced by 41% or 66%, respectively, assessed 48 hours after ischemia. The significant reduction in group H-22H was again confirmed 30 days after ischemia, ie, 50% reduction was observed. In contrast, the reduction in group H-3H (31%) was not significant. The neurological deficits were significantly more severe in the N-N group than in the H-22H group during week 4.

CONCLUSIONS

The neuroprotective effects against temporary focal ischemia evaluated by infarct volume and neurological functions by the combination therapy with intraischemic and prolonged postischemic mild hypothermia were persistent in rats. Appropriate design of mild hypothermia therapy extending into the late reperfusion period is important to maximize the neuroprotective effects of hypothermia.

Reproducibility of cerebral cortical infarction in the wistar rat after middle cerebral artery occlusion

Although middle cerebral artery (MCA) occlusion in the rat is often used to study focal cerebral ischemia, the model of ischemia affects the size and reproducibility of infarction. The purpose of this experiment was to methodically examine different preparations to determine the optimum focal cerebral ischemia model to produce a reproducible severe ischemic injury. Eighty-two Wistar rats underwent either 1 hour, 3 hour, or permanent MCA occlusion combined with no, unilateral, or bilateral common carotid artery artery (CCA) occlusion. Three days after ischemia, the animals were prepared for tetrazolium chloride assessment of infarction size. One-hour MCA occlusion produced a coefficient of variation (CV) of 200% with an infarction volume of 20.3+/-10.5 mm(3). Adding unilateral or bilateral CCA occlusion resulted in a CV of 134% and 101%, respectively. Three-hour MCA occlusion combined with bilateral CCA occlusion decreased the CV to 58% with a cortical infarction volume of 82.6+/-12.1 mm(3), P<05, compared with 1-hour MCA occlusion with or without CCA occlusion. Permanent MCA occlusion combined with 3 hours of bilateral CCA occlusion resulted in a CV of 47% with a cortical infarction volume of 89.6+/-16.0 mm(3). These results indicate that 3-hour MCA occlusion combined with bilateral CCA occlusion provide consistently a large infarction volume after temporary focal cerebral ischemia.

Effects of moderate hypothermia on leukocyte- endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion

Background and Purpose--It has been demonstrated that moderate hypothermia attenuates brain damage, but the mechanism whereby this is achieved has not been clearly shown. Recently, the role of leukocytes as mediators of secondary brain damage after brain ischemia has been discussed. The aim of this study is to examine the effects of moderate hypothermia on leukocyte-endothelium interaction in the rat pial microvasculature after transient middle cerebral artery occlusion (MCAO). Methods--Rhodamine 6G-labeled leukocytes in brain surface were visualized with intravital fluorescence videomicroscopy through a closed cranial window. We analyzed the number of leukocytes adhering to the venular and arteriolar endothelium before ischemic insult and up to 3 hours after reperfusion. Rats were divided into 4 experimental groups. Group I (n=6) consisted of sham-operated animals. Groups II (n=6) and III (n=6) received left MCAO for 1 hour under normothermia (36 degrees C to 37 degrees C, group II) and under moderate hypothermia (30 degrees C to 32 degrees C, group III). Group IV (n=4) received left common carotid artery occlusion for 1 hour under normothermia. Results--The number of adhering leukocytes in venules in groups II and IV increased significantly (P<0.001) after reperfusion compared with the group I, but that in group III did not increase significantly (P>0.05). The number of adhering leukocytes in arterioles in group II increased significantly (P<0.01) compared with the other groups, although the adhering leukocytes were not as numerous as those seen in venules. Conclusions--It is demonstrated that hypothermia attenuates adhering leukocytes in venules and arterioles after reperfusion of MCAO. The inhibition of the leukocyte function may be an important factor in the neuroprotective effect of hypothermia.