Delayed onset of prolonged hypothermia improves outcome after intracerebral hemorrhage in rats

Hypothermia protects the integrity of corticospinal tracts and alleviates mitochondria injury after intracerebral hemorrhage in mice

Disruption of corticospinal tracts (CST) is a leading factor for motor impairments following intracerebral hemorrhage (ICH) in the striatum. Previous studies have shown that therapeutic hypothermia (HT) improves outcomes of ICH patients. However, whether HT has a direct protection effect on the CST integrity and the underlying mechanisms remain largely unknown. In this study, we employed a chemogenetics approach to selectively activate bilateral warm-sensitive neurons in the preoptic areas to induce a hypothermia-like state. We then assessed effects of HT treatment on the integrity of CST and motor functional recovery after ICH. Our results showed that HT treatment significantly alleviated axonal degeneration around the hematoma and the CST axons at remote midbrain region, ultimately promoted skilled motor function recovery. Anterograde and retrograde tracing revealed that HT treatment protected the integrity of the CST over an extended period. Mechanistically, HT treatment prevented mitochondrial swelling in degenerated axons around the hematoma, alleviated mitochondrial impairment by reducing mitochondrial ROS accumulation and improving mitochondrial membrane potential in primarily cultured cortical neurons with oxyhemoglobin treatment. Serving as a proof of principle, our study provided novel insights into the application of HT to improve functional recovery after ICH.

An injectable refrigerated hydrogel for inducing local hypothermia and neuroprotection against traumatic brain injury in mice

BACKGROUND

Hypothermia is a promising therapy for traumatic brain injury (TBI) in the clinic. However, the neuroprotective outcomes of hypothermia-treated TBI patients in clinical studies are inconsistent due to several severe side effects. Here, an injectable refrigerated hydrogel was designed to deliver 3-iodothyronamine (T1AM) to achieve a longer period of local hypothermia for TBI treatment. Hydrogel has four advantages: (1) It can be injected into injured sites after TBI, where it forms a hydrogel and avoids the side effects of whole-body cooling. (2) Hydrogels can biodegrade and be used for controlled drug release. (3) Released T1AM can induce hypothermia. (4) This hydrogel has increased medical value given its simple operation and ability to achieve timely treatment.

METHODS

Pol/T hydrogels were prepared by a low-temperature mixing method and characterized. The effect of the Pol/T hydrogel on traumatic brain injury in mice was studied. The degradation of the hydrogel at the body level was observed with a small animal imager. Brain temperature and body temperature were measured by brain thermometer and body thermometer, respectively. The apoptosis of peripheral nerve cells was detected by immunohistochemical staining. The protective effect of the hydrogels on the blood-brain barrier (BBB) after TBI was evaluated by the Evans blue penetration test. The protective effect of hydrogel on brain edema after injury in mice was detected by Magnetic resonance (MR) in small animals. The enzyme linked immunosorbent assay (ELISA) method was used to measure the levels of inflammatory factors. The effects of behavioral tests on the learning ability and exercise ability of mice after injury were evaluated.

RESULTS

This hydrogel was able to cool the brain to hypothermia for 12 h while maintaining body temperature within the normal range after TBI in mice. More importantly, hypothermia induced by this hydrogel leads to the maintenance of BBB integrity, the prevention of cell death, the reduction of the inflammatory response and brain edema, and the promotion of functional recovery after TBI in mice. This cooling method could be developed as a new approach for hypothermia treatment in TBI patients.

CONCLUSION

Our study showed that injectable and biodegradable frozen Pol/T hydrogels to induce local hypothermia in TBI mice can be used for the treatment of traumatic brain injury.

The utility of therapeutic hypothermia on cerebral autoregulation

Cerebral autoregulation (CA) dysfunction is a strong predictor of clinical outcome in patients with acute brain injury (ABI). CA dysfunction is a potential pathologic defect that may lead to secondary injury and worse functional outcomes. Early therapeutic hypothermia (TH) in patients with ABI is controversial. Many factors, including patient selection, timing, treatment depth, duration, and rewarming strategy, impact its clinical efficacy. Therefore, optimizing the benefit of TH is an important issue. This paper reviews the state of current research on the impact of TH on CA function, which may provide the basis and direction for CA-oriented target temperature management.

Consensus recommendations on therapeutic hypothermia after minimally invasive intracerebral hemorrhage evacuation from the hypothermia for intracerebral hemorrhage (HICH) working group

Background and purpose

Therapeutic hypothermia (TH), or targeted temperature management (TTM), is a classic treatment option for reducing inflammation and potentially other destructive processes across a wide range of pathologies, and has been successfully used in numerous disease states. The ability for TH to improve neurological outcomes seems promising for inflammatory injuries but has yet to demonstrate clinical benefit in the intracerebral hemorrhage (ICH) patient population. Minimally invasive ICH evacuation also presents a promising option for ICH treatment with strong preclinical data but has yet to demonstrate functional improvement in large randomized trials. The biochemical mechanisms of action of ICH evacuation and TH appear to be synergistic, and thus combining hematoma evacuation with cooling therapy could provide synergistic benefits. The purpose of this working group was to develop consensus recommendations on optimal clinical trial design and outcomes for the use of therapeutic hypothermia in ICH in conjunction with minimally invasive ICH evacuation.

Methods

An international panel of experts on the intersection of critical-care TH and ICH was convened to analyze available evidence and form a consensus on critical elements of a focal cooling protocol and clinical trial design. Three focused sessions and three full-group meetings were held virtually from December 2020 to February 2021. Each meeting focused on a specific subtopic, allowing for guided, open discussion.

Results

These recommendations detail key elements of a clinical cooling protocol and an outline for the roll-out of clinical trials to test and validate the use of TH in conjunction with hematoma evacuation as well as late-stage protocols to improve the cooling approach. The combined use of systemic normothermia and localized moderate (33.5°C) hypothermia was identified as the most promising treatment strategy.

Conclusions

These recommendations provide a general outline for the use of TH after minimally invasive ICH evacuation. More research is needed to further refine the use and combination of these promising treatment paradigms for this patient population.

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

BACKGROUND

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

AIMS

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

SUMMARY OF REVIEW

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

CONCLUSIONS

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

Targeting focal ischemic and hemorrhagic stroke neuroprotection: Current prospects for local hypothermia

Therapeutic hypothermia (TH) has applications dating back millennia. In modern history, however, TH saw its importation into medical practice where investigations have demonstrated that TH is efficacious in ischemic insults, notably cardiac arrest and hypoxic-ischemic encephalopathy. As well, studies have been undertaken to investigate whether TH can provide benefit in focal stroke (i.e., focal ischemia and intracerebral hemorrhage). However, clinical studies have encountered various challenges with induction and maintenance of post-stroke TH. Most clinical studies have attempted to use body-wide cooling protocols, commonly hindered by side effects that can worsen post-stroke outcomes. Some of the complications and difficulties with systemic TH can be circumvented by using local hypothermia (LH) methods. Additional advantages include the potential for lower target temperatures to be achieved and faster TH induction rates with LH. This systematic review summarizes the body of clinical and preclinical LH focal stroke studies and raises key points to consider for future LH research. We conclude with an overview of LH neuroprotective mechanisms and a comparison of LH mechanisms with those observed with systemic TH. Overall, whereas many LH studies have been conducted preclinically in the context of focal ischemia, insufficient work has been done in intracerebral hemorrhage. Furthermore, key translational studies have yet to be done in either stroke subtype (e.g., varied models and time-to-treat, studies considering aged animals or animals with co-morbidities). Few clinical LH investigations have been performed and the optimal LH parameters to achieve neuroprotection are unknown.

From systemic to selective brain cooling - Methods in review

Therapeutic hypothermia (TH) remains one of the few proven neuroprotective modalities available in clinical practice today. Although targeting lower temperatures during TH seems to benefit ischemic brain cells, systemic side effects associated with global hypothermia limit its clinical applicability. Therefore, the ability to selectively reduce the temperature of the brain while minimally impacting core temperature allows for maximizing neurological benefit over systemic complications. In that scenario, selective brain cooling (SBC) has emerged as a promising modality of TH. In this report, we reviewed the general concepts of TH, from systemic to selective brain hypothermia, and explored the different cooling strategies and respective evidence, including preclinical and clinical data. SBC has been investigated in different animal models with promising results, wherein organ-specific, rapid, and deep target brain temperature managements stand out as major advantages over systemic TH. Nevertheless, procedure-related complications and adverse events still remain a concern, limiting clinical translation. Different invasive and noninvasive methods for SBC have been clinically investigated with variable results, and although adverse effects were still reported in some studies, therapies rendered overall safe profiles. Further study is needed to define the optimal technique, timing of initiation, rate and length of cooling as well as target temperature and rewarming protocols for different indications.

Poly-arginine-18 peptides do not exacerbate bleeding, or improve functional outcomes following collagenase-induced intracerebral hemorrhage in the rat

Background

Cationic arginine-rich peptides (CARPs) have demonstrated neuroprotective and/or behavioural efficacy in ischemic and hemorrhagic stroke and traumatic brain injury models. Therefore, in this study we investigated the safety and neuroprotective efficacy of the CARPs poly-arginine-18 (R18; 18-mer of arginine) and its D-enantiomer R18D given in the acute bleeding phase in an intracerebral hemorrhage (ICH) model.

Methods

One hundred and fifty-eight male Sprague-Dawley rats received collagenase-induced ICH. Study 1 examined various doses of R18D (30, 100, 300, or 1000 nmol/kg) or R18 (100, 300, 1000 nmol/kg) administered intravenously 30 minutes post-collagenase injection on hemorrhage volume 24 hours after ICH. Study 2 examined R18D (single intravenous dose) or R18 (single intravenous dose, plus 6 daily intraperitoneal doses) at 300 or 1000 nmol/kg commencing 30 minutes post-collagenase injection on behavioural outcomes (Montoya staircase test, and horizontal ladder test) in the chronic post-ICH period. A histological assessment of tissue loss was assessed using a Nissl stain at 28 days after ICH.

Results

When administered during ongoing bleeding, neither R18 or R18D exacerbated hematoma volume or worsened functional deficits. Lesion volume assessment at 28 days post-ICH was not reduced by the peptides; however, animals treated with the lower R18D 300 nmol/kg dose, but not with the higher 1000 nmol/kg dose, demonstrated a statistically increased lesion size compared to saline treated animals.

Conclusion

Overall, both R18 and R18D appeared to be safe when administered during a period of ongoing bleeding following ICH. Neither peptide appears to have any statistically significant effect in reducing lesion volume or improving functional recovery after ICH. Additional studies are required to further assess dose efficacy and safety in pre-clinical ICH studies.

Therapeutic time window and regulation of autophagy by mild hypothermia after intracerebral hemorrhage in rats

Although recent studies have shown that mild hypothermia has neuroprotective effects on intracerebral hemorrhage (ICH), the therapeutic time window of the therapy and the role of autophagy as a potential neuroprotective mechanism remain unclear. This study was aimed to investigate the appropriate time window of mild hypothermia and the regulation of autophagy during the treatment in a rat model of autologous blood-injected ICH injury. The rats were divided into Sham, normothermic (NT) and hypothermic (HT) groups. HT groups received mild hypothermia (33 °C-35 °C) for 48 h starting from 3 h (HT3), 6 h (HT6), and 12 h (HT12) respectively after ICH. The neurological function, brain edema, blood brain barrier (BBB) permeability and volume of tissue loss were tested. The expression of metrix metalloproteinase 9 (MMP-9) and tight junction (TJ) protein including Occludin and Claudin-5 around the hematoma were detected by Western blot. Moreover, autophagy after ICH was detected by the ratio of LC3B-II/I, and the expression of Beclin-1 and p62, while apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dURP nick end labelling (TUNEL) staining and expression of Bcl-2, Bim, cleaved Caspase-3. Compared with NT group, neurological deficit, brain edema and BBB permeability were attenuated in HT6 and HT12 groups, but not in HT3 group, while volume of tissue loss was reduced only in HT12 group. The expression of MMP-9 and the degradation of Occludin and Claudin-5 were suppressed only in HT6 and HT12 groups, especially in the latter one. Moreover, neuronal autophagy and apoptosis induced by ICH were downregulated in HT12 group. The results suggested that mild hypothermia initiated at 6 h or 12 h post-injury was neuroprotective in ICH model of rats, especially at 12 h post-injury, via suppression of autophagy upregulated by ICH.

Multiple mechanisms underlying neuroprotection by secretory phospholipase A2 preconditioning in a surgically induced brain injury rat model

BACKGROUND

Intra-operative bleeding, post-operative brain edema and neuroinflammation are major complications in patients with surgical brain injury (SBI). Phospholipase A2 (PLA2) is the upstream enzyme which initiates the PLA2, 5-lipoxygenase (5-LOX) and leukotriene B4 (LTB4) inflammatory pathway. We hypothesized PLA2preconditioning (PPC) prior to SBI can activate endogenous anti-inflammatory responses to protect against SBI. This study evaluated if PPC can ameliorate neurosurgical complications and elucidated PPC-mediated possible protective mechanisms in a rat SBI model.

METHODS

Total 105 adult male Sprague Dawley rats were used for this study. SBI was induced by partial resection of the right frontal lobe. PLA2 or 0.9% NaCl was injected via rats' tail vein for 3 consecutive days prior to SBI. For mechanism study, a selective PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton were injected intravenously with PPC to elucidate the role of PLA2 and 5-LOX in PPC-mediated anti-inflammatory effects. Brain water content (BWC) and lung water content, neurological tests, ELISA, western blot, immunohistochemistry, white blood cells (WBC) count, and spectrophotometric assay for intra-operative hemorrhage volume were evaluated.

RESULTS

First, PPC reduced brain water content, intra-operative bleeding, and improved neurological function after SBI. Second, PPC decreased 5-LOX expression and brain leukocyte infiltration, while increasing glial fibrillary acidic protein (GFAP) expression in the peri-resection brain tissue after SBI. Third, PPC induced peripheral inflammation represented by mild pulmonary inflammation and increased peripheral blood WBC count and LTB4 level. Lastly, PPC increased blood glucose concentration and glucocorticoid levels after SBI. In addition, PPC mediated above-mentioned changes were partially reversed by administration of PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton.

CONCLUSIONS

PPC conferred neuroprotection against SBI via multi-target involvement induced anti-inflammatory mechanisms.

Examining potential side effects of therapeutic hypothermia in experimental intracerebral hemorrhage

Studies treating intracerebral hemorrhage (ICH) with therapeutic hypothermia (TH) have shown inconsistent benefits. We hypothesized that TH's anti-inflammatory effects may be responsible as inflammatory cells are essential for removing degrading erythrocytes. Here, we subjected rats to a collagenase-induced striatal ICH followed by whole-body TH (∼33℃ for 11-72 h) or normothermia. We used X-ray fluorescence imaging to spatially quantify total and peri-hematoma iron three days post-injury. At three and seven days, we measured non-heme iron levels. Finally, hematoma volume was quantified on one, three, and seven days. In the injured hemisphere, total iron levels were elevated ( p < 0.001) with iron increasing in the peri-hematoma region ( p = 0.007). Non-heme iron increased from three to seven days (p < 0.001). TH had no effect on any measure of iron ( p ≥ 0.479). At one and three days, TH did not affect hematoma volume ( p ≥ 0.264); however, at seven days there was a four-fold increase in hematoma volume in 40% of treated animals ( p = 0.032). Thus, even when TH does not interfere with initial increases in total and non-heme iron or its containment, TH can cause re-bleeding post-treatment. This serious complication could partly account for the intermittent protection previously observed. This also raises serious concerns for clinical usage of TH for ICH.

Targeted temperature management in neurological intensive care unit

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

Selective Brain Hypothermia Mitigates Brain Damage and Improves Neurological Outcome after Post-Traumatic Decompressive Craniectomy in Mice

Hypothermia and decompressive craniectomy (DC) have been considered as treatment for traumatic brain injury. The present study investigates whether selective brain hypothermia added to craniectomy could improve neurological outcome after brain trauma. Male CD-1 mice were assigned into the following groups: sham; DC; closed head injury (CHI); CHI followed by craniectomy (CHI+DC); and CHI+DC followed by focal hypothermia (CHI+DC+H). At 24 h post-trauma, animals were subjected to Neurological Severity Score (NSS) test and Beam Balance Score test. At the same time point, magnetic resonance imaging using a 9.4 Tesla scanner and subsequent volumetric evaluation of edema and contusion were performed. Thereafter, the animals were sacrificed and subjected to histopathological analysis. According to NSS, there was a significant impairment among all the groups subjected to trauma. Animals with both trauma and craniectomy performed significantly worse than animals with craniectomy alone. This deleterious effect disappeared when additional hypothermia was applied. BBS was significantly worse in the CHI and CHI+DC groups, but not in the CHI+DC+H group, compared to the sham animals. Edema and contusion volumes were significantly increased in CHI+DC animals, but not in the CHI+DC+H group, compared to the DC group. Histopathological analysis showed that neuronal loss and contusional blossoming could be attenuated by application of selective brain hypothermia. Selective brain cooling applied post-trauma and craniectomy improved neurological function and reduced structural damage and may be therefore an alternative to complication-burdened systemic hypothermia. Clinical studies are recommended in order to explore the potential of this treatment.

Therapeutic Hypothermia Does Not Mitigate Iron-Induced Injury in Rat

Intracerebral hemorrhage (ICH) is often a devastating stroke, and there are no clinically proven neuroprotective treatments. Considerable research points to iron toxicity as a leading contributor to secondary damage after ICH. Iron, released from degraded erythrocytes, catalyzes free radical production, thereby causing cell death in the ensuing days and weeks. Therapeutic hypothermia (TH) is a potential neuroprotective strategy for ICH, but results from animal studies are inconsistent and generally weaker than that found in ischemia models. Thus, we examined whether TH (∼33°C for 24-72 hours) would specifically mitigate iron toxicity, which we modeled by infusing 3.8 μg of FeCl2 in 30 μL of sterile saline into the striatum of rats. Rats were subjected to whole-body cooling beginning 1 hour after FeCl2 infusion. Use of TH reduced (p = 0.025) the small bleed caused by FeCl2 infusion (∼6 μL). However, TH did not lessen FeCl2-induced edema at 24 and 72 hours postinfusion, nor were behavioral impairments (e.g., walking) or brain injury (at 7 and 28 days) attenuated by TH. These results suggest that TH does not directly protect against iron toxicity, which indicates that this is not a means by which TH improves the outlook after ICH.

Prolonged Localized Mild Hypothermia Does Not Affect Seizure Activity After Intracerebral Hemorrhage in Rats

Intracerebral hemorrhage (ICH) is a devastating stroke with high morbidity and mortality. Post-ICH seizures are a common complication, potentially increasing brain injury and the risk of delayed epilepsy. Mild therapeutic hypothermia (HYPO, ∼33°C) is neuroprotective against several brain insults, such as ischemia, while also mitigating seizure incidence and severity in some instances. Therefore, we tested whether brain-selective HYPO reduced electrographic seizure activity after a collagenase-induced striatal ICH in rats. Animals were injected unilaterally with 0.14 U of bacterial collagenase, implanted with a unilateral brain cooling device, and a probe to bilaterally record electroencephalographic (EEG) activity. Cooling began 6 hours after collagenase infusion and was maintained for 48 hours, followed by rewarming over 6 hours. Our protocol did not affect EEG activity in naïve rats, nor did it increase bleeding after ICH (∼50 μL). Epileptiform activity commonly occurred in untreated ICH rats (∼60% of animals), but HYPO did not affect the incidence, timing, total duration of seizures, or the peaks occurring during epileptiform activity. However, longer average duration was detected on the ipsilateral side to stroke in the HYPO group (p < 0.05). Cooling did not affect neurological deficits (e.g., circling), measured 7 and 14 days after ICH, or lesion volume (∼35 mm(3)). In addition, there was no relationship among endpoints (e.g., seizures and lesion size). In summary, HYPO failed to reduce seizure activity after ICH, which fits with our separate findings that cooling does not mitigate thrombin and iron-mediated secondary injury mechanisms thought to cause seizures after ICH. Additional research is needed to identify better HYPO protocols and the use of cotreatments to maximize the benefit of HYPO to ICH patients.

Delayed localized hypothermia reduces intracranial pressure following collagenase-induced intracerebral hemorrhage in rat

Brain injury, such as from intracerebral hemorrhage (ICH), causes edema and raises intracranial pressure (ICP)--a potentially life-threatening complication. Clinical studies suggest that therapeutic hypothermia (TH) reduces edema and ICP after ICH. Similarly, animal studies show that TH can sometimes reduce edema, but whether ICP would be attenuated is not known. Here we tested whether 24-h delayed TH reduces edema and ICP in rats with severe striatal ICH (collagenase model). First, we showed that ICH increased epidural ICP (mean of 18 vs. 6.5mm Hg in controls), measured via telemetry. Second, we confirmed that delayed TH did not affect hematoma size at 7d ay (~65 vs. ~61 µL in controls). A cranial cooling device lowered striatal temperature to ~33 °C from 24 to 72 h after ICH. Third, we compared normothermic rats to those with TH that were rewarmed immediately or over 6h. Both TH protocols significantly reduced average and peak ICP by the second treatment day, and benefits persisted after rewarming. However, TH with slow rewarming failed to mitigate edema at 96 h (83.2% vs. 83.6% in controls) whereas rapid rewarming worsened edema (85.7%). Finally, we compared normothermic and TH rats without rewarming and found no impact on edema at 72 h (~81%). In summary, it appears that 24-h delayed local TH lowers ICP by a mechanism other than edema. Rapid rewarming worsens edema after local cooling, but this did not markedly impact ICP. Thus, TH should reduce ICP in patients with severe ICH, but not necessarily through mitigating edema.

Therapeutic hypothermia for acute brain injuries

Therapeutic hypothermia, recently termed target temperature management (TTM), is the cornerstone of neuroprotective strategy. Dating to the pioneer works of Fay, nearly 75 years of basic and clinical evidence support its therapeutic value. Although hypothermia decreases the metabolic rate to restore the supply and demand of O₂, it has other tissue-specific effects, such as decreasing excitotoxicity, limiting inflammation, preventing ATP depletion, reducing free radical production and also intracellular calcium overload to avoid apoptosis. Currently, mild hypothermia (33°C) has become a standard in post-resuscitative care and perinatal asphyxia. However, evidence indicates that hypothermia could be useful in neurologic injuries, such as stroke, subarachnoid hemorrhage and traumatic brain injury. In this review, we discuss the basic and clinical evidence supporting the use of TTM in critical care for acute brain injury that extends beyond care after cardiac arrest, such as for ischemic and hemorrhagic strokes, subarachnoid hemorrhage, and traumatic brain injury. We review the historical perspectives of TTM, provide an overview of the techniques and protocols and the pathophysiologic consequences of hypothermia. In addition, we include our experience of managing patients with acute brain injuries treated using endovascular hypothermia.

Intracerebral hemorrhage in mouse models: therapeutic interventions and functional recovery

There has been strong pre-clinical research on mechanisms of initial cell death and tissue injury in intracerebral hemorrhage (ICH). This data has led to the evaluation of several therapeutics for neuroprotection or the mitigation of early tissue damage. Most of these studies have been done in the rat. Also, there has been little study of the mechanisms of tissue repair and recovery. This review examines the testing of candidate therapeutics in mouse models of ICH for their effect on tissue protection and repair. This review will help the readers compare it to the extensively researched rat model of ICH and thus enhance work that are pending in mouse model.

Localized hypothermia aggravates bleeding in the collagenase model of intracerebral hemorrhage

Animal studies testing whether therapeutic hypothermia is neuroprotective after intracerebral hemorrhage (ICH) have been inconclusive. In rodents, ICH is often produced in the striatum by infusing collagenase, which causes prolonged hemorrhaging from multiple vessels. Our previous data shows that this bleeding (hematoma) is worsened by systemic hypothermia given soon after collagenase infusion. In this study we hypothesized that localized brain hypothermia would also aggravate bleeding in this model (0.2 U of collagenase in 1.2 μL of saline). We also evaluated cooling after intrastriatal thrombin infusion (1 U in 30 μL of saline)-a simplified model of ICH thought to cause bleeding. Focal hypothermia was achieved by flushing cold water through an implanted cooling device attached to the skull underneath the temporalis muscle of adult rats. Previous work and data at this time shows this method cools the striatum to ∼33°C, whereas the body remains normothermic. In comparison to normothermic groups, cooling significantly worsened bleeding when instituted at 6 hours (∼94 vs. 42 μL, p=0.018) and 12 hours (79 vs. 61 μL, p=0.042) post-ICH (24-hour survival), but not after a 24-hour delay (36-hour survival). Rats were cooled until euthanasia when hematoma size was determined by a hemoglobin-based spectrophotometry assay. Cooling did not influence cerebral blood volume after just saline or thrombin infusion. The latter is explained by the fact that thrombin did not cause bleeding beyond that caused by saline infusion. In summary, local hypothermia significantly aggravates bleeding many hours after collagenase infusion suggesting that bleeding may have confounded earlier studies with hypothermia. Furthermore, these findings serve as a cautionary note on using cooling even many hours after cerebral bleeding.

A mathematical model of cellular metabolism during ischemic stroke and hypothermia

Stroke is a major cause of death and disability worldwide. Therapeutic hypothermia is a potentially useful neuroprotective treatment. A mathematical model of brain metabolism during stroke is extended here to simulate the effect of hypothermia on cell survival. Temperature decreases were set to reduce chemical reaction rates and slow diffusion through ion channels according to the Q10 rule. Heat delivery to tissues was set to depend on metabolic heat generation rate and perfusion. Two cooling methods, scalp and vascular, were simulated to approximate temperature variation in the brain during treatment. Cell death was assumed to occur at continued cell membrane depolarization. Simulations showed that hypothermia to 34.5 °C induced within 1-1.5 h of stroke onset could extend cell survival time by at least 5 h in tissue with perfusion reduced by 80% of normal. There was good agreement between simulated metabolite dynamics and those reported in rat model studies.

Vagus nerve stimulation during rehabilitative training improves functional recovery after intracerebral hemorrhage

BACKGROUND AND PURPOSE

Vagus nerve stimulation (VNS) delivered during rehabilitative training enhances neuroplasticity and improves recovery in models of cortical ischemic stroke. However, VNS therapy has not been applied in a model of subcortical intracerebral hemorrhage (ICH). We hypothesized that VNS paired with rehabilitative training after ICH would enhance recovery of forelimb motor function beyond rehabilitative training alone.

METHODS

Rats were trained to perform an automated, quantitative measure of forelimb function. Once proficient, rats received an intrastriatal injection of bacterial collagenase to induce ICH. Rats then underwent VNS paired with rehabilitative training (VNS+Rehab; n=14) or rehabilitative training without VNS (Rehab; n=12). Rehabilitative training began ≥9 days after ICH and continued for 6 weeks.

RESULTS

VNS paired with rehabilitative training significantly improved recovery of forelimb function when compared with rehabilitative training without VNS. The VNS+Rehab group displayed a 77% recovery of function, whereas the Rehab group only exhibited 29% recovery. Recovery was sustained after cessation of stimulation. Both groups performed similar amounts of trials during rehabilitative, and lesion size was not different between groups.

CONCLUSIONS

VNS paired with rehabilitative training confers significantly improved forelimb recovery after ICH compared to rehabilitative training without VNS.

Mild hypothermia reduces tissue plasminogen activator-related hemorrhage and blood brain barrier disruption after experimental stroke

Therapeutic hypothermia has shown neuroprotective promise, but whether it can be used to improve outcome in stroke has yet to be determined in patients. Recombinant tissue plasminogen activator (rt-PA) is only given to a minority of patients with acute ischemic stroke, and is not without risk, namely significant brain hemorrhage.We explored whether mild hypothermia, in combination with rt-PA, influences the safety of rt-PA. Mice were subjected to middle cerebral artery occlusion (MCAO) using a filament model, followed by 24 hours reperfusion.Two paradigms were studied. In the first paradigm, cooling and rt-PA treatment began at the same time upon reperfusion, whereas in the second paradigm, cooling began soon after ischemia onset, and rt-PA began after rewarming and upon reperfusion. Experimental groups included: tPA treatment at normothermia (37°C), rt-PA treatment at hypothermia (33°C), no rt-PA at normothermia, and no rt-PA treatment at hypothermia. Infarct size, neurological deficit scores, blood brain barrier (BBB) permeability, brain hemorrhage, and expression of endogenous tissue plasminogen activator (tPA) and its inhibitor, plasminogen activator inhibitor (PAI-1) were assessed. For both paradigms, hypothermia reduced infarct size and neurological deficits compared to normothermia, regardless of whether rt-PA was given. rt-PA treatment increased brain hemorrhage and BBB disruption compared to normothermia, and this was prevented by cooling. However, mortality was higher when rt-PA and cooling were administered at the same time, beginning 1–2 hours post MCAO. Endogenous tPA expression was reduced in hypothermic mice, whereas PAI-1 levels were unchanged by cooling. In the setting of rt-PA treatment, hypothermia reduces brain hemorrhage, and BBB disruption, suggesting that combination therapy with mild hypothermia and rt-PA appears safe.

The role of hemorrhage following spinal-cord injury

Spinal-cord injury is characterized by primary damage as a direct consequence of mechanical insult, and secondary damage that is partly due to the acute inflammatory response. The extent of any hemorrhage within the injured cord is also known to be associated with the formation of intraparenchymal cavities and has been anecdotally linked to secondary damage. This study was designed to examine the contribution of blood components to the outcome of spinal-cord injury. We stereotaxically microinjected collagenase, which causes localized bleeding, into the spinal cord to model the hemorrhage associated with spinal cord injury in the absence of significant mechanical trauma. Tissue damage was observed at the collagenase injection site over time, and was associated with localized disruption of the blood-spinal-cord barrier, neuronal cell death, and the recruitment of leukocytes. The magnitude of the bleed was related to neutrophil mobilization. Interestingly, the collagenase-induced injury also provoked extended axonal damage. With this model, the down-stream effects of hemorrhage are easily discernible, and the impact of treatment strategies for spinal-cord injury on hemorrhage-related injury can be evaluated.

Targeted temperature management after intracerebral hemorrhage (TTM-ICH): methodology of a prospective randomized clinical trial

RATIONALE

Intracerebral hemorrhage causes 15% of strokes annually in the United States, and there is currently no effective therapy.

AIMS AND HYPOTHESIS

This is a clinical trial designed to study the safety, feasibility, and efficacy of a protocol of targeted temperature management to moderate hypothermia in intracerebral hemorrhage patients.

METHODS

The targeted temperature management after intracerebral hemorrhage trial is a prospective, single-center, interventional, randomized, parallel, two-arm (1:1) phase-II clinical trial with blinded end-point ascertainment. Intracerebral hemorrhage patients will be randomized within 18 h of symptom onset to either 72 h of targeted temperature management to moderate hypothermia (32-34°C) followed by a controlled rewarming at of 0·05-0·1°C per hour or 72 h of targeted temperature management to normothermia (36-37°C) using endovascular or surface cooling.

OUTCOMES

The primary outcome is the development of serious adverse events possibly and probably related to treatment. Secondary outcomes include in-hospital neurological deterioration between day 0-7, in-hospital mortality, functional outcome measured by the modified Rankin scale at discharge and 90 days, and effect of treatment allocation on cerebral edema and hematoma volume.

DISCUSSION

Intracerebral hemorrhage remains the most severe form of stroke with limited options to improve survival. As the early resuscitation phase in the intensive care unit represents the greatest opportunity for impact on clinical outcome, it also appears to be the most promising window of opportunity to demonstrate a benefit when investigating aggressive treatments.

CONCLUSION

More research of novel therapies to improve outcomes after intracerebral hemorrhage is desperately needed. The results of the targeted temperature management after intracerebral hemorrhage clinical trial may provide additional information on the applicability of targeted temperature management after intracerebral hemorrhage.

New avenues for treatment of intracranial hemorrhage

OPINION STATEMENT

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

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

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

Relationship between temperature, hematoma growth, and functional outcome after intracerebral hemorrhage

BACKGROUND

Fever and hematoma growth are known to be independent predictors of poor outcome after intracerebral hemorrhage (ICH). We sought to assess the distribution of temperature at different stages in relation to hematoma growth and functional outcome at 90 days in a cohort of ICH patients.

METHODS

Data of patients registered in the Virtual International Stroke Trials Archive--ICH were analyzed. Temperatures at baseline, 24, 48, 72, and 168 h were assessed in relation to the hematoma growth and functional outcome at 90 days. We calculated the daily linear variation of each subject's temperature by subtracting 37 °C from the maximal daily recorded temperature (delta-temperature). We used logistic regression and mixed-effects models to identify factors associated with hematoma growth, poor outcome, and temperature elevation after ICH.

RESULTS

303 patients were included in the analysis. The average age was 66 ± 12 years, 200 (66 %) were males, median admission NIHSS was 13 [Interquartile range (IQR), 9-18), median GCS was 15 (IQR, 14-15). Hematoma growth occurred in 22 % and poor functional outcome at 90-days occurred in 41 % of the patients. Cumulative delta-temperature at 72 h was associated with hematoma growth; age, ICH score, hematoma growth, and cumulative delta-temperature at 168 h were associated with poor outcome at 90 days. Factors associated with fever in mixed-models were day after onset of ICH, hypertension, base hematoma volume, intraventricular-hemorrhage, pneumonia, and hematoma growth.

CONCLUSIONS

There is a temporal and independent association between fever and hematoma growth. Fever after ICH is associated with poor outcome at 90 days. Future research is needed to study the mechanisms of this phenomenon and if early protocols of temperature modulation would be associated with improved outcomes after ICH.

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.

Combination therapy with insulin-like growth factor-1 and hypothermia synergistically improves outcome after transient global brain ischemia in the rat

OBJECTIVES

Hypothermia has a well-established neuroprotective effect and offers a foundation for combination therapy for brain ischemia. The authors evaluated the effect of combination therapy with insulin-like growth factor-1 (IGF-1) and hypothermia on brain structure and function in the setting of global brain ischemia and reperfusion in rats.

METHODS

Male Sprague-Dawley rats were randomly assigned to groups by a registrar. Animals were subjected to 8 minutes of global brain ischemia using bilateral carotid occlusion and systemic hypotension, followed by 7 days (Stage I dose studies) or 28 days (Stage II outcome studies) of reperfusion. Sham controls were subjected to surgery, but not ischemia. Stage II animals were randomized to no treatment, IGF-1 at the dose determined in Stage I, hypothermia (32°C for 4 hours), or a combination of IGF-1 and hypothermia. Stage II animals underwent 21 days of spatial memory testing. At 7 days (Stage I) or 28 days (Stage II), brains were harvested for counting of CA1 neurons. The primary Stage II outcome was a neurologic outcome index computed as the ratio of viable CA1 neurons per 300-μm field to the number of days to reach success criteria on the memory task.

RESULTS

Stage I experiments confirmed the neuroprotective effect of the hypothermia protocol and IGF-1 at a dose of 0.6 U/kg. Stage II studies suggested that early neuroprotection with hypothermia and IGF-1 was not well maintained to 28 days and that combination therapy was more beneficial than either IGF-1 or hypothermia alone. Median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 114 (IQR = 99.5 to 136) for sham, three (IQR = 2 to 4.8) for untreated ischemia, four (IQR = 3 to 70.25) for ischemia treated with IGF-1 alone, 25 (IQR = 3 to 70) for ischemia treated with hypothermia alone, and 78 (IQR 47.3 to 97.5) for ischemia treated with combination therapy. Days to memory success criteria were 13.6 (IQR = 11.5 to 15.5 days) for sham, 23.5 (IQR = 20 to 25.5 days) for untreated ischemia, 17.5 (IQR = 15.5 to 25.5 days) for ischemia treated with IGF-1, 15 (IQR = 14.5 to 21 days) for ischemia treated with hypothermia, and 13.5 (IQR = 12.25 to 18.5 days) for ischemia treated with combination therapy. Neurologic outcome indices were 8.5 (IQR = 7.4 to 9.5) for sham, 0.14 (IQR = 0.08 to 0.2) for untreated ischemia, 0.18 (IQR = 0.17 to 4.6) for ischemia treated with IGF-1, 0.7 (IQR = 0.2 to 4.8) for ischemia treated with hypothermia, and 5.7 (IQR = 3.3 to 6.2) for ischemia treated with combination therapy. Statistically significant differences in neuron counts, days to memory test criteria, and outcome index were found between sham and untreated ischemic animals. Of the three treatment regimens, only combination therapy showed a statistically significant difference from the untreated ischemic group for neuronal salvage (p = 0.02), days to criteria (p = 0.043), and outcome index (p = 0.014).

CONCLUSIONS

Combination therapy with IGF-1 (0.6 U/kg) and therapeutic hypothermia (32°C for 4 hours) at the onset of reperfusion synergistically preserves CA1 structure and function at 28 days after 8 minutes of global brain ischemia in healthy male rats.

The bradykinesia assessment task: an automated method to measure forelimb speed in rodents

Bradykinesia in upper extremities is associated with a wide variety of motor disorders; however, there are few tasks that assay forelimb movement speed in rodent models. This study describes the bradykinesia assessment task, a novel method to quantitatively measure forelimb speed in rats. Rats were trained to reach out through a narrow slot in the cage and rapidly press a lever twice within a predefined time window to receive a food reward. The task provides measurement of multiple parameters of forelimb function, including inter-press interval, number of presses per trial, and success rate. The bradykinesia assessment task represents a significant advancement in evaluating bradykinesia in rat models because it directly measures forelimb speed. The task is fully automated, so a single experimenter can test multiple animals simultaneously with typically in excess of 300 trials each per day, resulting in high statistical power. Several parameters of the task can be modified to adjust difficulty, which permits application to a broad spectrum of motor dysfunction models. Here we show that two distinct models of brain damage, ischemic lesions of primary motor cortex and hemorrhagic lesions of the dorsolateral striatum, cause impairment in all facets of performance measured by the task. The bradykinesia assessment task provides insight into bradykinesia and motor dysfunction in multiple disease models and may be useful in assessing therapies that aim to improve forelimb function following brain damage.

Challenges and controversies in the medical management of primary and antithrombotic-related intracerebral hemorrhage

Intracerebral hemorrhage (ICH) represents 10-15% of all cerebrovascular events, and is associated with substantial morbidity and mortality. In contrast to ischemic cerebrovascular disease in which acute therapies have proven beneficial, ICH remains a more elusive condition to treat, and no surgical procedure has proven to be beneficial. Aspects pertinent to medical ICH management include cessation or minimization of hematoma enlargement, prevention of intraventricular extension, and treatment of edema and mass effect. Therapies focusing on these aspects include prothrombotic (hemostatic) agents, antihypertensive strategies, and antiedema therapies. Therapies directed towards the reversal of antithrombosis caused by antiplatelet and anticoagulant agents are frequently based on limited data, allowing for diverse opinions and practice styles. Several newer anticoagulants that act by direct thrombin or factor Xa inhibition have no natural antidote, and are being increasingly used for various prophylactic and therapeutic indications. As such, these new anticoagulants will inevitably pose major challenges in the treatment of patients with ICH. Ongoing issues in the management of patients with ICH include the need for effective treatments that not only limit hematoma expansion but also result in improved clinical outcomes, the identification of patients at greatest risk for continued hemorrhage who may most benefit from treatment, and the initiation of therapies during the hyperacute period of most active hemorrhage. Defining hematoma volume increases at various anatomical locations that translate into clinically meaningful outcomes will also aid in directing future trials for this disease. The focus of this review is to underline and discuss the various controversies and challenges involved in the medical management of patients with primary and antithrombotic-related ICH.

Intracerebral hemorrhage: clinical overview and pathophysiologic concepts

Intracerebral hemorrhage is by far the most destructive form of stroke. Apart from the management in a specialized stroke or neurological intensive care unit (NICU), no specific therapies have been shown to consistently improve outcomes after ICH. Current guidelines endorse early aggressive optimization of physiologic derangements with ventilatory support when indicated, blood pressure control, reversal of any preexisting coagulopathy, intracranial pressure monitoring for certain cases, osmotherapy, temperature modulation, seizure prophylaxis, treatment of hyerglycemia, and nutritional support in the stroke unit or NICU. Ventriculostomy is the cornerstone of therapy for control of intracranial pressure patients with intraventricular hemorrhage. Surgical hematoma evacuation does not improve outcome for more patients, but is a reasonable option for patients with early worsening due to mass effect due to large cerebellar or lobar hemorrhages. Promising experimental treatments currently include ultra-early hemostatic therapy, intraventricular clot lysis with thrombolytics, pioglitazone, temperature modulation, and deferoxamine to reduce iron-mediated perihematomal inflammation and tissue injury.

Prolonged hypothermia in rat: a safety study using brain-selective and systemic treatments

Hypothermia is an effective neuroprotectant for cardiac arrest and perinatal ischemic injury. Hypothermia also improves outcome after traumatic brain injury and stroke. Although the ideal treatment parameters (duration, delay, and depth) are not fully delineated, prolonged cooling is usually more effective than shorter periods. There is the concern that extended cooling may be hazardous to brain plasticity and cause damage. In order to evaluate this possibility, we assessed the effects of 3 days of systemic hypothermia (32°C) in rats subjected to a sham stroke surgery. There were no detrimental behavioral effects or signs of brain damage. As even longer cooling may be needed in some patients, we cooled (∼32°C) the right hemisphere of rats for 3 or 21 days. Physiological variables, functional outcome, and measures of cell injury were examined. Focal brain cooling for 21 days modestly decreased heart rate, blood pressure, and core temperature. However, focal hypothermia did not affect subsequent behavior (e.g., spontaneous limb usage), cell morphology (e.g., dendritic arborization, ultrastructure), or cause cell death. In conclusion, prolonged mild hypothermia did not harm the brain of normal animals. Further research is now needed to evaluate whether such treatments affect plasticity after brain injury.

The "Refrige-a-RAT-or": an accurate, inexpensive, and clinically relevant small animal model of therapeutic hypothermia

BACKGROUND

Physical and molecular mechanisms for the neuroprotective effect of therapeutic hypothermia are not completely understood, and new therapeutic applications incorporating hypothermia remain to be developed and tested. Clinically relevant animal models of therapeutic hypothermia are not well established or consistent.

OBJECTIVES

The objective was to develop and test an inexpensive small animal therapeutic hypothermia system that models those in widespread clinical use and verify that such a system confers neuroprotection in a rat model of global brain ischemia.

METHODS

A water-cooled extracorporeal system and attendant anesthesia/sedation protocol were developed and tested. In Stage 1, animals were instrumented for brain, temporalis, and rectal temperature monitoring, and the system was tested for its effect on temperature and hemodynamics. In Stage 2, animals were instrumented for rectal temperature only, subjected to global brain ischemia by two-vessel occlusion and hypotension for 8 minutes, and given either sham therapy (37°C) or hypothermia (32°C) for 4 hours. Viable CA1 neurons were counted at 7 days.

RESULTS

The system was well tolerated, provided exquisite control of animal core and brain temperatures, and conferred robust neuroprotection at 7 days. The median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 130 (IQR = 128 to 135) for sham control, 19 (IQR = 15 to 30) for untreated ischemic animals, and 101 (IQR = 94 to 113) for ischemic animals treated with hypothermia (p < 0.05 for comparison between all groups).

CONCLUSIONS

Like human protocols, this model incorporates sedation and analgesia, results in robust neuroprotection, is well tolerated, and offers exquisite temperature control. The system is noninvasive and inexpensive and offers a model that is similar to methods used in clinical practice. This system will be of interest to investigators using small animal models to examine neuroprotective mechanisms of hypothermia and translational strategies that combine hypothermia with targeted pharmacotherapy.

A critical appraisal of experimental intracerebral hemorrhage research

The likelihood of translating therapeutic interventions for stroke rests on the quality of preclinical science. Given the limited success of putative treatments for ischemic stroke and the reasons put forth to explain it, we sought to determine whether such problems hamper progress for intracerebral hemorrhage (ICH). Approximately 10% to 20% of strokes result from an ICH, which results in considerable disability and high mortality. Several animal models reproduce ICH and its underlying pathophysiology, and these models have been widely used to evaluate treatments. As yet, however, none has successfully translated. In this review, we focus on rodent models of ICH, highlighting differences among them (e.g., pathophysiology), issues with experimental design and analysis, and choice of end points. A Pub Med search for experimental ICH (years: 2007 to 31 July 2011) found 121 papers. Of these, 84% tested neuroprotectants, 11% tested stem cell therapies, and 5% tested rehabilitation therapies. We reviewed these to examine study quality (e.g., use of blinding procedures) and choice of end points (e.g., behavioral testing). Not surprisingly, the problems that have plagued the ischemia field are also prevalent in ICH literature. Based on these data, several recommendations are put forth to facilitate progress in identifying effective treatments for ICH.

Elevated blood pressure aggravates intracerebral hemorrhage-induced brain injury

Elevated blood pressure (BP) is commonly seen in patients with intracerebral hemorrhage (ICH), and is independently associated with poor functional outcomes. Little is known about how elevated BP influences ICH-related brain injury. In the present study, we investigated the physiological and brain histological changes, as well as functional recovery following ICH in renovascular hypertensive rats. Renovascular hypertension (RVHT) was achieved by applying a silver clip onto the left renal artery of adult Sprague-Dawley rats. ICH was induced by an intrastriatal injection of bacterial collagenase IV about 5-6 weeks after left renal artery clipping or the sham operation. Following induction of ICH, both the normotensive and RVHT rats demonstrated an ultra-acute elevation in BP. Elevated BP increased hematoma volume, brain swelling, and apoptosis in the perihematomal areas. Brain degeneration, including local atrophy and lateral ventricle enlargement, was greater in the RVHT rats. In addition, many proliferating cells were seen over the ipsilateral striatum in the RVHT rats after ICH. The modified limb placing tests were done weekly for 3 weeks. In line with the histological damage, elevated BP worsened neurological deficits. These results suggest that ICH in the hypertensive rats mimics the clinical scenario of hypertensive ICH and may provide a platform to study the mechanisms of ICH-induced brain injury and potential therapies for ICH.

Unilateral brain hypothermia as a method to examine efficacy and mechanisms of neuroprotection against global ischemia

Hypothermia, especially applied during ischemia, is the gold-standard neuroprotectant. When delayed, cooling must often be maintained for a day or more to achieve robust, permanent protection. Most animal and clinical studies use whole-body cooling-an arduous technique that can cause systemic complications. Brain-selective cooling may avoid such problems. Thus, in this rat study, we used a method that cools one hemisphere without affecting the contralateral side or the body. Localized brain hypothermia was achieved by flushing cold water through a metal tube attached to the rats' skull. First, in anesthetized rats we measured temperature in the cooled and contralateral hemisphere to demonstrate selective unilateral cooling. Subsequent telemetry recordings in awake rats confirmed that brain cooling did not cause systemic hypothermia during prolonged treatment. Additionally, we subjected rats to transient global ischemia and after recovering from anesthesia they remained at normothermia or had their right hemisphere cooled for 2 days (∼32°C-33°C). Hypothermia significantly lessened CA1 injury and microglia activation on the right side at 1 and 4 week survival times. Near-complete injury and a strong microglia response occurred in the left (normothermic) hippocampus as occurred in both hippocampi of the untreated group. Thus, this focal cooling method is suitable for evaluating the efficacy and mechanisms of hypothermic neuroprotection in global ischemia models. This method also has advantages over many current systemic cooling protocols in rodents, namely: (1) lower cost, (2) simplicity, (3) safety and suitability for long-term cooling, and (4) an internal control-the normothermic hemisphere.

Treatment of intracerebral hemorrhage in animal models: meta-analysis

OBJECTIVE

Interventions that improve functional outcome after acute intracerebral hemorrhage (ICH) in animals might benefit humans. Therefore, we systematically reviewed the literature to find studies of nonsurgical treatments tested in animal models of ICH.

METHODS

In July 2009 we searched Ovid Medline (from 1950), Embase (from 1980), and ISI Web of Knowledge (from 1969) for controlled animal studies of nonsurgical interventions given after the induction of ICH that reported neurobehavioral outcome. We assessed study quality and performed meta-analysis using a weighted mean difference random effects model.

RESULTS

Of 13,343 publications, 88 controlled studies described the effects of 64 different medical interventions (given a median of 2 hours after ICH induction) on 38 different neurobehavioral scales in 2,616 treated or control animals (median 14 rodents per study). Twenty-seven (31%) studies randomized treatment allocation, and 7 (8%) reported allocation concealment; these studies had significantly smaller effect sizes than those without these attributes (p < 0.001). Of 64 interventions stem cells, calcium channel blockers, anti-inflammatory drugs, iron chelators, and estrogens improved both structural outcomes and neurobehavioral scores in >1 study. Meta-regression revealed that together, structural outcome and the intervention used accounted for 65% of the observed heterogeneity in neurobehavioral score (p < 0.001, adjusted r(2) = 0.65).

INTERPRETATION

Further animal studies of the interventions that we found to improve both functional and structural outcomes in animals, using better experimental designs, could target efforts to translate effective treatments for ICH in animals into randomized controlled trials in humans.

Rodent models of intracerebral hemorrhage

The collagenase and whole blood intracerebral hemorrhage (ICH) models are widely used to identify mechanisms of injury and to evaluate treatments. Despite preclinical successes, to date, no treatment tested in phase III clinical trials has benefited ICH patients. These failures call into question the predictive value of current ICH models. By highlighting differences between these common rodent models of ICH, we sought to help investigators choose the more appropriate model for their study and to encourage the use of both whenever possible. For instance, we previously reported substantial differences in the bleeding profile, progression of cell death, and functional outcome between these models. These and other differences influence the efficacy and mechanisms of action of various treatment modalities. Thus, in this review, we also summarize neuroprotective and rehabilitation findings in each model. We conclude that differences between ICH models along with our current inability to identify the more clinically predictive model necessitate that preclinical assessments should normally be done in both. Such an approach, coupled with better assessment practices, will likely improve chances of future clinical success.

Therapeutic hypothermia for acute ischemic stroke: ready to start large randomized trials?

Therapeutic hypothermia is a means of neuroprotection well established in the management of acute ischemic brain injuries such as anoxic encephalopathy after cardiac arrest and perinatal asphyxia. As such, it is the only neuroprotective strategy for which there is robust evidence for efficacy. Although there is overwhelming evidence from animal studies that cooling also improves outcome after focal cerebral ischemia, this has not been adequately tested in patients with acute ischemic stroke. There are still some uncertainties about crucial factors relating to the delivery of hypothermia, and the resolution of these would allow improvements in the design of phase III studies in these patients and improvements in the prospects for successful translation. In this study, we discuss critical issues relating first to the targets for therapy including the optimal depth and duration of cooling, second to practical issues including the methods of cooling and the management of shivering, and finally, of factors relating to the design of clinical trials. Consideration of these factors should inform the development of strategies to establish beyond doubt the place of hypothermia in the management of acute ischemic stroke.

Hypothermia as a cytoprotective strategy in ischemic tissue injury

Hypothermia is a well established cytoprotectant, with remarkable and consistent effects demonstrated across multiple laboratories. At the clinical level, it has recently been shown to improve neurological outcome following cardiac arrest and neonatal hypoxia-ischemia. It is increasingly being embraced by the medical community, and could be considered an effective neuroprotectant. Conditions such as brain injury, hepatic encephalopathy and cardiopulmonary bypass seem to benefit from this intervention. It's role in direct myocardial protection is also being explored. A review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, cooling needs to begin soon after the insult, and maintained for relatively long period periods of time. In the case of ischemic stroke, cooling should ideally be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, given the technical challenges of rapidly and stably cooling patients. This review will discuss the application of hypothermia especially as it pertains to its effects neurological outcome, cooling methods, and important parameters in optimizing hypothermic protection.

Failure of deferoxamine, an iron chelator, to improve outcome after collagenase-induced intracerebral hemorrhage in rats

Intracerebral hemorrhage (ICH) is a devastating stroke with no clinically proven treatment. Deferoxamine (DFX), an iron chelator, is a promising therapy that lessens edema, mitigates peri-hematoma cell death, and improves behavioral recovery after whole-blood-induced ICH in rodents. In this model, blood is directly injected into the brain, usually into the striatum. This mimics many but not all clinical features of ICH (e.g., there is no spontaneous bleed). Thus, we tested whether DFX improves outcome after collagenase-induced striatal ICH in rats. In the first experiment, 3- and 7-day DFX regimens (100 mg/kg twice per day starting 6 h after ICH), similar to those shown effective in the whole-blood model, were compared to saline treatment. Functional recovery was evaluated from 3 to 28 days with several behavioral tests. Except for one instance, DFX failed to lessen ICH-induced behavioral impairments and it did not lessen brain injury, which averaged 43.5 mm(3) at a 28-day survival. In the second experiment, 3 days of DFX treatment were given starting 0 or 6 h after collagenase infusion. Striatal edema occurred, but it was not affected by either DFX treatment (vs. saline treatment). Therefore, in contrast to studies using the whole-blood model, DFX treatment did not improve outcome in the collagenase model. Our findings, when compared to others, suggest that there are critical differences between these ICH models. Perhaps, the current clinical work with DFX will help identify the more clinically predictive model for future neuroprotection studies.