Current and future role of therapeutic hypothermia

TREATMENT OF COMATOSE SURVIVORS OF IN-HOSPITAL CARDIAC ARREST WITH EXTENDED ENDOVASCULAR COOLING METHOD FOR 72 H: A PROPENSITY SCORE-MATCHED ANALYSIS

ABSTRACT

Aims: Targeted temperature management is recommended for at least 24 h in comatose survivors of in-hospital cardiac arrest (IHCA) after the return of spontaneous circulation; however, whether an extension for 72 h leads to better neurological outcomes is uncertain. Methods: We included data from the Qilu Hospital of Shandong University between July 20, 2019, and June 30, 2022. Unconscious patients who had return of spontaneous circulation lasting >20 consecutive min and received endovascular cooling (72 h) or normothermia treatment were compared in terms of survival-to-discharge and favorable neurological survival. Propensity score matching was used to formulate balanced 1:3 matched patients. Results: In total, 2,084 patients were included. Sixteen patients received extended endovascular cooling and 48 matched controls received normothermia therapy. Compared with the normothermia group, patients who received prolonged endovascular cooling had a higher survival-to-discharge rate. However, good neurological outcomes did not differ significantly. Before matching, Cox regression analysis, using mortality as the event, showed that extended endovascular cooling independently affected the survival of IHCA patients. Conclusions: Among comatose patients who had been resuscitated from IHCA, the use of endovascular cooling for 72 h might confer a benefit on survival-to-discharge.

Administration of selective brain hypothermia using a simple cooling device in neonatal rats

BACKGROUND

The interruption of oxygen and blood supply to the newborn brain around the time of birth is a risk factor for hypoxic-ischemic encephalopathy and may lead to infant mortality or lifelong neurological impairments. Currently, therapeutic hypothermia, the cooling of the infant's head or entire body, is the only treatment to curb the extent of brain damage.

NEW METHOD

In this study, we designed a focal brain cooling device that circulates cooled water at a steady state temperature of 19 ± 1 °C through a coil of tubing fitted onto the neonatal rat's head. We tested its ability to selectively decrease brain temperature and offer neuroprotection in a neonatal rat model of hypoxic-ischemic brain injury.

RESULTS

Our method cooled the brain to 30-33 °C in conscious pups, while keeping the core body temperature approximately 3.2 °C warmer. Furthermore, the application of the cooling device to the neonatal rat model demonstrated a reduction in brain volume loss compared to pups maintained at normothermia and achieved a level of brain tissue protection the same as that of whole-body cooling.

COMPARISON WITH EXISTING METHODS

Prevailing methods of selective brain hypothermia are designed for adult animal models rather than for immature animals such as the rat as a conventional model of developmental brain pathology. Contrary to existing methods, our method of cooling does not require surgical manipulation or anaesthesia.

CONCLUSION

Our simple, economical, and effective method of selective brain cooling is a useful tool for rodent studies in neonatal brain injury and adaptive therapeutic interventions.

POLAR Study Revisited: Therapeutic Hypothermia in Severe Brain Trauma Should Not Be Abandoned

The benefits of therapeutic hypothermia (TH) in severe traumatic brain injury (sTBI) have been long debated. In 2018, the POLAR study, a high-quality international trial, appeared to end the debate by showing that TH did not improve mortality in sTBI. However, the POLAR-based recommendation to abandon TH was challenged by different investigators. In our recent meta-analysis, we introduced the cooling index (COIN) to assess the extent of cooling and showed that TH is beneficial in sTBI, but only when the COIN is sufficiently high. In the present study, we calculated the COIN for the POLAR study and ran a new meta-analysis, which included the POLAR data and accounted for the cooling extent. The POLAR study targeted a high cooling extent (COIN of 276°C × h; calculated for 72 h), but the achieved cooling was much lower (COIN of 193°C × h)-because of deviations from the protocol. When the POLAR data were included in the COIN-based meta-analysis, TH had an overall effect of reducing death (odds rate of 0.686; p = 0.007). Among the subgroups with different COIN levels, the only significantly decreased odds rate (i.e., beneficial effect of TH) was observed in the subgroup with high COIN (0.470; p = 0.013). We conclude that, because of deviations from the targeted cooling protocol, the overall cooling extent was not sufficiently high in the POLAR study, thus masking the beneficial effects of TH. The current analysis shows that TH is beneficial in sTBI, but only when the COIN is high. Abandoning the use of TH in sTBI may be premature.

Artifact Mimicking Ictal Epileptiform Activity in EEG

Although the EEG is designed to record cerebral activity, it also frequently records activity from extracerebral sources, leading to artifact. Differentiating rhythmical artifact from true electrographic ictal activity remains a substantial challenge to even experienced electroencephalographers because the sources of artifact able to mimic ictal activity on EEG have continued to increase with the advent of technology. Knowledge of the characteristics of the polarity and physiologic electrical fields of the brain, as opposed to those generated by the eyes, heart, and muscles, allows the electroencephalographer to intuitively recognize noncerebrally generated waveforms. In this review, we provide practical guidelines for the EEG interpreter to correctly identify physiologic and nonphysiologic artifacts capable of mimicking electrographic seizures. In addition, we further elucidate the common pitfalls in artifact interpretation and the costly impact of epilepsy misdiagnosis due to artifact.

Placenta-Derived Cells for Acute Brain Injury

Acute brain injury resulting from ischemic/hemorrhagic or traumatic damage is one of the leading causes of mortality and disability worldwide and is a significant burden to society. Neuroprotective options to counteract brain damage are very limited in stroke and traumatic brain injury (TBI). Given the multifaceted nature of acute brain injury and damage progression, several therapeutic targets may need to be addressed simultaneously to interfere with the evolution of the injury and improve the patient’s outcome. Stem cells are ideal candidates since they act on various mechanisms of protection and repair, improving structural and functional outcomes after experimental stroke or TBI. Stem cells isolated from placenta offer advantages due to their early embryonic origin, ease of procurement, and ethical acceptance. We analyzed the evidence for the beneficial effects of placenta-derived stem cells in acute brain injury, with the focus on experimental studies of TBI and stroke, the engineering strategies pursued to foster cell potential, and characterization of the bioactive molecules secreted by placental cells, known as their secretome, as an alternative cell-free strategy. Results from the clinical application of placenta-derived stem cells for acute brain injury and ongoing clinical trials are summarily discussed.

The duration of hypothermia affects short-term neuroprotection in a mouse model of neonatal hypoxic ischaemic injury

Neonatal hypoxic-ischaemic encephalopathy (HIE) is major cause of neonatal mortality and morbidity. Therapeutic hypothermia is standard clinical care for moderate hypoxic-ischaemic (HI) brain injury, however it reduces the risk of death and disability only by 11% and 40% of the treated infants still develop disabilities. Thus it is necessary to develop supplementary therapies to complement therapeutic hypothermia in the treatment of neonatal HIE. The modified Rice-Vannucci model of HI in the neonatal mouse is well developed and widely applied with different periods of hypothermia used as neuroprotective strategy in combination with other agents. However, different studies use different periods, time of initiation and duration of hypothermia following HI, with subsequent varying degrees of neuroprotection. So far most rodent data is obtained using exposure to 5-6h of therapeutic hypothermia. Our aim was to compare the effect of exposure to three different short periods of hypothermia (1h, 1.5h and 2h) following HI insult in the postnatal day 7 C57/Bl6 mouse, and to determine the shortest period providing neuroprotection. Our data suggests that 1h and 1.5h of hypothermia delayed by 20min following a 60min exposure to 8%O2 do not prove neuroprotective. However, 2h of hypothermia significantly reduced tissue loss, TUNEL+ cell death and microglia and astroglia activation. We also observed improved functional outcome 7 days after HI. We suggest that the minimal period of cooling necessary to provide moderate short term neuroprotection and appropriate for the development and testing of combined treatment is 2h.

Therapeutic hypothermia and targeted temperature management for traumatic brain injury: Experimental and clinical experience

Traumatic brain injury (TBI) is a worldwide medical problem, and currently, there are few therapeutic interventions that can protect the brain and improve functional outcomes in patients. Over the last several decades, experimental studies have investigated the pathophysiology of TBI and tested various pharmacological treatment interventions targeting specific mechanisms of secondary damage. Although many preclinical treatment studies have been encouraging, there remains a lack of successful translation to the clinic and no therapeutic treatments have shown benefit in phase 3 multicenter trials. Therapeutic hypothermia and targeted temperature management protocols over the last several decades have demonstrated successful reduction of secondary injury mechanisms and, in some selective cases, improved outcomes in specific TBI patient populations. However, the benefits of therapeutic hypothermia have not been demonstrated in multicenter randomized trials to significantly improve neurological outcomes. Although the exact reasons underlying the inability to translate therapeutic hypothermia into a larger clinical population are unknown, this failure may reflect the suboptimal use of this potentially powerful therapeutic in potentially treatable severe trauma patients. It is known that multiple factors including patient recruitment, clinical treatment variables, and cooling methodologies are all important in yielding beneficial effects. High-quality multicenter randomized controlled trials that incorporate these factors are required to maximize the benefits of this experimental therapy. This article therefore summarizes several factors that are important in enhancing the beneficial effects of therapeutic hypothermia in TBI. The current failures of hypothermic TBI clinical trials in terms of clinical protocol design, patient section, and other considerations are discussed and future directions are emphasized.

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.

Normothermia in Arthroplasty

BACKGROUND

Since the initial design of surgical theatres, the thermal environment of the operating suite itself has been an area of concern and robust discussion. In the 1950s, correspondence in the British Medical Journal discussed the most suitable design for a surgeon's cap to prevent sweat from dripping onto the surgical field. These deliberations stimulated questions about the effects of sweat-provoking environments on the efficiency of the surgical team, not to mention the effects on the patient. Although these benefits translate to implant-based orthopedic surgery, they remain poorly understood and, at times, ignored.

METHODS

A review and synthesis of the body of literature on the topic of maintenance of normothermia was performed.

RESULTS

Maintenance of normothermia in orthopedic surgery has been proven to have broad implications from bench top to bedside. Normothermia has been shown to impact everything from nitrogen loss and catabolism after hip fracture surgery to infection rates after elective arthroplasty.

CONCLUSION

Given both the physiologic impact this has on patients, as well as a change in the medicolegal environment around this topic, a general understanding of these concepts should be invaluable to all surgeons.

A Human Thermoregulation Simulator for Calibrating Water-Perfused Cooling Pad Systems for Therapeutic Hypothermia

The induction of a mild reduction in body core temperature has been demonstrated to provide neuroprotection for patients who have suffered a medical event resulting in ischemia to the brain or vital organs. Temperatures in the range of 32–34 °C provide the required level of protection and can be produced and maintained by diverse means for periods of days. Rewarming from hypothermia must be conducted slowly to avoid serious adverse consequences and usually is performed under control of the thermal therapeutic device based on a closed-loop feedback strategy based on the patient's core temperature. Given the sensitivity and criticality of this process, it is important that the device control system be able to interact with the human thermoregulation system, which itself is highly nonlinear. The therapeutic hypothermia device must be calibrated periodically to ensure that its performance is accurate and safe for the patient. In general, calibration processes are conducted with the hypothermia device operating on a passive thermal mass that behaves much differently than a living human. This project has developed and demonstrated an active human thermoregulation simulator (HTRS) that embodies major governing thermal functions such as central metabolism, tissue conduction, and convective transport between the core and the skin surface via the flow of blood and that replicates primary dimensions of the torso. When operated at physiological values for metabolism and cardiac output, the temperature gradients created across the body layers and the heat exchange with both an air environment and a clinical water-circulating cooling pad system match that which would occur in a living body. Approximately two-thirds of the heat flow between the core and surface is via convection rather than conduction, highlighting the importance of including the contribution of blood circulation to human thermoregulation in a device designed to calibrate the functioning of a therapeutic hypothermia system. The thermoregulation simulator functions as anticipated for a typical living patient during both body cooling and warming processes. This human thermoregulatory surrogate can be used to calibrate the thermal function of water-perfused cooling pads for a hypothermic temperature management system during both static and transient operation.

The role of therapeutic hypothermia in the management of acute spinal cord injury

This review paper investigates the history, efficacy, and administration of systemic and local hypothermia for spinal cord injury (SCI). It summarizes the published experimental and clinical evidence on hypothermia for SCI and analyzes the potential for further research. Early experimental animal research showed that local hypothermia improved recovery and gain of function after acute SCI. However, in the early 1970s, clinical research findings did not coincide with results of these animal trials, which led to a loss of interest in local hypothermia. Since the 1980s, systemic hypothermia has been successfully used to treat SCI in both animals and humans. An abundance of positive evidence suggests that clinical trials are needed to determine the effectiveness of hypothermia for SCI. As a first step, we investigated the published clinical and experimental evidence on the use of hypothermia for SCI patients, who have few available treatment options. We searched PubMed for English-language reports published from 1940 to 2016 containing terms related to SCI treatment using hypothermia. We reviewed all articles on local hypothermia and acute SCI or on systemic hypothermia and acute SCI. Bibliographies of retrieved publications were also screened for additional citations. Ninety-six papers were selected. The clinical use of hypothermia is most successful if applied according to certain optimized parameters (e.g., duration, temperature, time from injury to initiation of cooling, and rewarming time). Preliminary data suggest that modest systemic hypothermia applied for 48h provides the best therapeutic value, but the parameters for use of local hypothermia vary greatly. Experimental evidence and some clinical evidence suggest that both local hypothermia and systemic hypothermia are beneficial for acute SCI. Future research should focus on defining the optimal levels of parameters. Large, multicenter, controlled clinical trials are needed to investigate its therapeutic potential.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

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

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

Hypothermia in Traumatic Brain Injury

For over 50 years, clinicians have used hypothermia to manage traumatic brain injury (TBI). In the last two decades numerous trials have assessed whether hypothermia is of benefit in patients. Mild to moderate hypothermia reduces the intracranial pressure (ICP). Randomized control trials for short-term hypothermia indicate no benefit in outcome after severe TBI, whereas longer-term hypothermia could be of benefit by reducing ICP. This article summarises current evidence and gives recommendations based upon the conclusions.

Temperature Control in Rodent Neuroprotection Studies: Methods and Challenges

Extensive animal research facilitated the clinical translation of therapeutic hypothermia for cardiac arrest in adults and hypoxic-ischemic injury in infants. Similarly, clinical interest in hypothermia for other brain injuries, such as stroke, has been greatly supported by positive findings in preclinical work. The reliability, validity, and utility of animal models, among many research practices (blinding, randomization, etc.), are key to successful clinical translation. Here, we review methods used to induce and maintain hypothermia in animal models. These include physical and pharmacological methods. We emphasize the advantages and limitations of each approach, and the importance of using clinically relevant cooling protocols and appropriate monitoring and reporting approaches. Moreover, we performed a literature survey of ischemic stroke studies published in 2015 to highlight the continuing risk of temperature confounds in neuroprotection studies. For example, many still do not accurately monitor and report temperature during surgery (23.5%), even though almost half of these studies (46.0%) use pharmaceutical agents that likely influence temperature. We hope this review stimulates awareness and discussion of the importance of temperature in neuroprotective studies.

Hypothermia-induced ischemic tolerance is associated with Drp1 inhibition in cerebral ischemia-reperfusion injury of mice

Excessive mitochondrial fission activation has been implicated in cerebral ischemia-reperfusion (IR) injury. Hypothermia is effective in preventing cerebral ischemic damage. However, effects of hypothermia on ischemia-induced mitochondrial fission activation is not well known. Therefore, the aim of this study was to investigate whether hypothermia protect the brain by inhibiting mitochondrial fission-related proteins activation following cerebral IR injury. Adult male C57BL/6 mice were subjected to transient forebrain ischemia induced by 15min of bilateral common carotid artery occlusion (BCCAO). Mice were divided into three groups (n=48 each): Hypothermia (HT) group, with mild hypothermia (32-34°C) for 4h; Normothermia (NT) group, similarly as HT group except for cooling; Sham group, with vessels exposed but without occlusion or cooling. Hematoxylin and eosin (HE), Nissl staining, Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining and behavioral testing (n=6 each) demonstrated that hypothermia significantly decreased ischemia-induced neuronal injury. The expressions of Dynamin related protein 1 (Drp1) and Cytochrome C (Cyto C) (n=6 each) in mice hippocampus were measured at 3, 6, 24, and 72h of reperfusion. IR injury significantly increased expressions of total Drp1, phosphorylated Drp1 (P-Drp1 S616) and Cyto C under normothermia. However, mild hypothermia inhibited Drp1 activation and Cyto C cytosolic release, preserved neural cells integrity and reduced neuronal necrosis and apoptosis. These findings indicated that mild hypothermia-induced neuroprotective effects against ischemia-reperfusion injury is associated with suppressing mitochondrial fission-related proteins activation and apoptosis execution.

Subdural hematoma decompression model: A model of traumatic brain injury with ischemic-reperfusional pathophysiology: A review of the literature

The prognosis for patients with traumatic brain injury (TBI) with subdural hematoma (SDH) remains poor. In accordance with an increasing elderly population, the incidence of geriatric TBI with SDH is rising. An important contributor to the neurological injury associated with SDH is the ischemic damage which is caused by raised intracranial pressure (ICP) producing impaired cerebral perfusion. To control intracranial hypertension, the current management consists of hematoma evacuation with or without decompressive craniotomy. This removal of the SDH results in the immediate reversal of global ischemia accompanied by an abrupt reduction of mass lesion and an ensuing reperfusion injury. Experimental models can play a critical role in improving our understanding of the underlying pathophysiology and in exploring potential treatments for patients with SDH. In this review, we describe the epidemiology, pathophysiology and clinical background of SDH.

Microdialysis as Clinical Evaluation of Therapeutic Hypothermia in Rat Subdural Hematoma Model

Cerebral microdialysis (MD) is a fine laboratory technique which has been established for studying physiological, pharmacological, and pathological changes in the experimental studies of traumatic brain injury (TBI). This technique has also been well translated and widely applied to clinical bedside monitoring to provide pathophysiological analysis in severe TBI patients. The MD technique is thus well suited for straightforward translation from basic science to clinical application.In this chapter, we describe our evaluation of MD method in acute subdural hematoma (ASDH) rat model. With 100 kDa cut-off microdialysis membrane, we could measure several biomarkers such as ubiquitin carboxy hydrolase L1 (UCH-L1), a neuronal marker and glial fibrillary acidic protein (GFAP), and a glial marker in extracellular fluid. In this experiment, we could detect that the peak of extracellular UCH-L1 in the early hypothermia group was significantly lower than in the normothermia group. Also, in the late phase of reperfusion (>2.5 h after decompression), extracellular GFAP in the early hypothermia group was lower than in the normothermia. These data thus suggested that early, preoperatively induced hypothermia could mediate the reduction of neuronal and glial damage in the reperfusion phase of ischemia/reperfusion brain injury.Microdialysis allows for the direct measurement of extracellular molecules in an attempt to characterize metabolic derangements before they become clinically relevant. Advancements in technology have allowed for the bedside assay of multiple markers of ischemia and metabolic dysfunction, and the applications for traumatic brain injury have been well established. As clinicians become more comfortable with these tools their widespread use and potential for clinical impact with continue to rise.

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.

Therapeutic hypothermia and targeted temperature management in traumatic brain injury: Clinical challenges for successful translation

The use of therapeutic hypothermia (TH) and targeted temperature management (TTM) for severe traumatic brain injury (TBI) has been tested in a variety of preclinical and clinical situations. Early preclinical studies showed that mild reductions in brain temperature after moderate to severe TBI improved histopathological outcomes and reduced neurological deficits. Investigative studies have also reported that reductions in post-traumatic temperature attenuated multiple secondary injury mechanisms including excitotoxicity, free radical generation, apoptotic cell death, and inflammation. In addition, while elevations in post-traumatic temperature heightened secondary injury mechanisms, the successful implementation of TTM strategies in injured patients to reduce fever burden appear to be beneficial. While TH has been successfully tested in a number of single institutional clinical TBI studies, larger randomized multicenter trials have failed to demonstrate the benefits of therapeutic hypothermia. The use of TH and TTM for treating TBI continues to evolve and a number of factors including patient selection and the timing of the TH appear to be critical in successful trial design. Based on available data, it is apparent that TH and TTM strategies for treating severely injured patients is an important therapeutic consideration that requires more basic and clinical research. Current research involves the evaluation of alternative cooling strategies including pharmacologically-induced hypothermia and the combination of TH or TTM approaches with more selective neuroprotective or reparative treatments. This manuscript summarizes the preclinical and clinical literature emphasizing the importance of brain temperature in modifying secondary injury mechanisms and in improving traumatic outcomes in severely injured patients. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Hypothermia improves disease manifestations in SMA mice via SMN augmentation

Spinal muscular atrophy (SMA) is a progressive motor neuron disease caused by a deficiency of survival motor neuron (SMN) protein. In this study, we evaluated the efficacy of intermittent transient hypothermia in a mouse model of SMA. SMA mice were exposed to ice for 50 s to achieve transient hypothermia (below 25°C) daily beginning on postnatal day 1. Neonatal SMA mice (Smn(-/-)SMN2(+/-)) who received daily transient hypothermia exhibited reduced motor neuron degeneration and muscle atrophy and preserved the architecture of neuromuscular junction when compared with untreated controls at day 8 post-treatment. Daily hypothermia also prolonged the lifespan, increased body weight and improved motor coordination in SMA mice. Quantitative polymerase chain reaction and western blot analyses showed that transient hypothermia led to an increase in SMN transcript and protein levels in the spinal cord and brain. In in vitro studies using an SMN knockdown motor neuron-like cell-line, transient hypothermia increased intracellular SMN protein expression and length of neurites, confirming the direct effect of hypothermia on motor neurons. These data indicate that the efficacy of intermittent transient hypothermia in improving outcome in an SMA mouse model may be mediated, in part, via an upregulation of SMN levels in the motor neurons.

The regulatory roles of non-coding RNAs in nerve injury and regeneration

Non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have attracted much attention since their regulatory roles in diverse cell processes were recognized. Emerging studies demonstrate that many ncRNAs are differentially expressed after injury to the nervous system, significantly affecting nerve regeneration. In this review, we compile the miRNAs and lncRNAs that have been reported to be dysregulated following a variety of central and peripheral nerve injuries, including acquired brain injury, spinal cord injury, and peripheral nerve injury. We also list investigations on how these miRNAs and lncRNAs exert the regulatory actions in neurodegenerative and neuroregenerative processes through different mechanisms involving their interaction with target coding genes. We believe that comprehension of the expression profiles and the possible functions of ncRNAs during the processes of nerve injury and regeneration will help understand the molecular mechanisms responsible for post-nerve-injury changes, and may contribute to the potential use of ncRNAs as a diagnostic marker and therapeutic target for nerve injury.

Therapeutic hypothermia applicable to cardiac surgery

OBJECTIVE

To review the beneficial and adverse effects of therapeutic hypothermia (TH) applicable to cardiac surgery with cardiopulmonary bypass (CPB) in the contexts of various temperature levels and techniques for achieving TH.

DATABASES USED

Multiple electronic literature searches were performed using PubMed and Google for articles published from June 2012 to December 2014. Relevant terms (e.g. 'hypothermia', 'cardiopulmonary bypass', 'cardiac surgery', 'neuroprotection') were used to search for original articles, letters and reviews without species limitation. Reviews were included despite potential publication bias. References from the studies identified were also searched to find other potentially relevant citations. Abstracts, case reports, conference presentations, editorials and expert opinions were excluded.

CONCLUSIONS

Therapeutic hypothermia is an essential measure of neuroprotection during cardiac surgery that may be achieved most effectively by intravascular cooling using hypothermic CPB. For most cardiac surgical procedures, mild to modest (32-36 °C) TH will be sufficient to assure neuroprotection and will avoid most of the adverse effects of hypothermia that occur at lower body core temperatures.

Intracranial temperature and pressure measurement: in vitro temperature sensing characteristics of the dual sensing element

A pressure sensor has been used to measure temperature concurrently. We have designed, and characterized the measurement of temperature from the same sensor to allow simultaneous monitoring of intracranial temperature and pressure. The temperature measurement has a sensitivity of 85.08 mV/°C across the measurement range 20-45 °C. The time constant of the temperature sensor is 150 ms. We have evaluated the accuracy of the temperature measurement and the long term drift of 13 sensors over 28 days. The mean difference of the temperature measurements from the reference measurements was less than 0.2 °C.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Management of acute traumatic spinal cord injury

OPINION STATEMENT

Spinal cord injury (SCI) causes significant morbidity and mortality. Clinical management in the acute setting needs to occur in the intensive care unit in order to identify, prevent, and treat secondary insults from local ischemia, hypotension, hypoxia, and inflammation. Maintenance of adequate perfusion and oxygenation is quintessential and a mean arterial pressure >85-90 mm Hg should be kept for at least 1 week. A cervical collar and full spinal precautions (log-roll, flat, holding C-spine) should be maintained until the spinal column has been fully evaluated by a spine surgeon. In patients with SCI, there is a high incidence of other bodily injuries, and there should be a low threshold to assess for visceral, pelvic, and long bone injuries. Computed tomography of the spine is superior to plain films, as the former rarely misses fractures, though caution needs to be exerted as occipitocervical dislocation can still be missed. To reliably assess the spinal neural elements, soft tissues, and ligamentous structures, magnetic resonance imaging is indicated and should be obtained within 48-72 h from the time of injury. All patients should be graded daily using the American Spinal Injury Association classification, with the first prognostic score at 72 h postinjury. Patients with high cervical cord (C4 or higher) injury should be intubated immediately, and those with lower cord injuries should be evaluated on a case-by-case basis. However, in the acute setting, respiratory mechanics will be disrupted with any spinal cord lesion above T11. Steroids have become extremely controversial, and the professional societies for neurosurgery in the United States have given a level 1 statement against their use in all patients. We, therefore, do not advocate for them at this time. With every SCI, a spine surgeon must be consulted to discuss operative vs nonoperative management strategies. Indications for surgery include a partial or progressive neurologic deficit, instability of the spine not allowing for mobilization, correction of a deformity, and prevention of potential neurologic compromise. Measures to prevent pulmonary emboli from deep venous thromboembolisms are necessary: IVC filters are recommended in bedbound patients and low-molecular weight heparins are superior to unfractionated heparin. Robust prevention of pressure ulcers as well as nutritional support should be a mainstay of treatment. Lastly, it is important to note that neurologic recovery is a several-year process. The most recovery occurs in the first year following injury, and therefore aggressive rehabilitation is crucial.

Effects of mild induced hypothermia on hippocampal connexin 43 and glutamate transporter 1 expression following traumatic brain injury in rats

Traumatic brain injury (TBI) is a common cause of worldwide disability and mortality. Currently, the incidence and prevalence of TBI is markedly increasing and an effective therapy is lacking. Therapeutic hypothermia (32‑35˚C) has been reported to reduce intracranial pressure and induce putative neuroprotective effects. However, the underlying molecular mechanisms remain to be elucidated. The aim of the present study was to investigate the effects of mild induced hypothermia (MIH) on the expression of connexin 43 (Cx43) and glutamate transporter 1 (GLT‑1) in the hippocampus following TBI in rats. A rat model of TBI was created using a modified weight‑drop device, followed by 4 h of hypothermia (33˚C) or normothermia (37˚C). A wet‑dry weight method was used to assess brain edema and spatial learning ability was evaluated using a Morris water maze. The levels of Cx43 and GLT‑1 were detected by immunohistochemical and western blot analysis, respectively. The results demonstrated that MIH treatment improved TBI‑induced brain edema and neurological function deficits. In addition, therapeutic MIH significantly downregulated Cx43 expression and upregulated the levels of GLT‑1 in the hippocampus post‑TBI. These findings suggested that treatment with MIH may provide a novel neuroprotective therapeutic strategy for TBI through reversing the increase in Cx43 protein and the decrease in GLT‑1.

Rationale, methodology, and implementation of a nationwide multicenter randomized controlled trial of long-term mild hypothermia for severe traumatic brain injury (the LTH-1 trial)

BACKGROUND

Traumatic brain injury (TBI) is a major public health problem recently, however, no intervention showing convincing efficacy. Therapeutic hypothermia with a relatively long duration (more than 48 h), as a promising treatment measure, might improve the patient outcome following severe TBI.

METHODS/DESIGN

The LTH-1 trial is a prospective, nationwide multicenter, randomized, controlled clinical trial to examine the efficacy and safety of long-term mild hypothermia in adult patients after severe traumatic brain injury. A total of 300 consecutive patients will be recruited from 15 large neurosurgical centers in China. The eligible patient will be randomized to receive either long-term mild hypothermia (34-35 °C) for 5 days, or normothermia (36-37 °C). Additionally, a standardized management protocol will be used in all patients. The primary end point is the neurological outcome 6 months post-injury on the Glasgow Outcome Scale. The secondary outcomes include GOS score at one month post-injury, mortality during six months after injury, length of ICU and hospital stay, intracranial pressure control and Glasgow Coma Scale score during the hospital stay and frequency of complications during the six-month follow-up period.

DISCUSSION

Long-term hypothermia is recommended by most recent studies and its efficacy urgently needs to be established in randomized controlled settings. The LTH-1 trial, together with other ongoing studies, will present more evidence for optimal use of hypothermia in severe TBI patients.

Revisiting therapeutic hypothermia for severe traumatic brain injury... again

Improved understanding of the molecular mechanisms of secondary brain injury has informed the optimum depth and duration of cooling and led to increased clinical interest in the therapeutic moderate hypothermia for severe traumatic brain injury over the past two decades. Although several large multi-center clinical trials have not found a treatment effect, multiple single-center trials have, and a recent meta-analysis by Crossley and colleagues now finds that the cumulative findings of those single-center trials dilute the multi-center trial results and show an overall reduction in mortality and poor outcomes associated with cooling. The need for consistent support of key physiologic parameters during cooling is emphasized by this finding.

Therapeutic hypothermia for adult community-acquired bacterial meningitis-historical control study

OBJECTIVE

Despite advances in antibiotic therapy and critical care, community-acquired bacterial meningitis (CABM) continues to have poor outcome in a significant portion of patients. This study was designed to assess the efficacy of therapeutic hypothermia (TH) in the treatment of CABM.

MATERIAL AND METHODS

In a period from January 2009 to January 2013, 41 enrolled patients with CABM were treated with TH. Their outcome was compared to 90 patients in the historical control group that were recruited from the existing database and included patients in a period between 1994 and 2008 with Glasgow coma scale score (GCS) ≤9 and respiratory failure. TH was indicated in patients with GCS ≤9, respiratory failure, and breath holding index ≤0.835 (measured with transcranial Doppler). If the acoustic window was absent, GCS ≤9 plus optic nerve sheath diameter of ≥6mm plus respiratory failure were indications for TH.

RESULTS

Outcome variables were mortality and neurologic recovery measured with the Glasgow outcome scale (GOS). The incidence of hospital mortality (19.5% vs 48.9%, p=0.002) and adverse neurological outcome (GOS 1-3) (43.9% vs 65.6%, p=0.023) were significantly lower in patients treated with TH. Multivariate analysis confirmed the positive effect of TH on hospital mortality (OR=0.059, 95% CI 0.017-0.211) and risk of adverse neurological outcome (OR=0.209, 95% CI 0.082-0.534) after an adjustment for other risk factors of unfavorable patients' outcome.

CONCLUSIONS

The new therapeutic concept based on hypothermia significantly improves the outcome in adult patients with severe CABM.

Mild hypothermia alleviates excessive autophagy and mitophagy in a rat model of asphyxial cardiac arrest

Mild hypothermia is an effective therapeutic strategy to improve poor neurological outcomes in patients following cardiac arrest (CA). However, the underlying mechanism remains unclear. The aim of the study was to evaluate the effect of mild hypothermia on intracellular autophagy and mitophagy in hippocampal neurons in a rat model of CA. CA was induced in Sprague-Dawley (SD) rats by asphyxia for 5 min. After successful resuscitation, the surviving rats were randomly divided into two groups, the normothermia (NT) group and the hypothermia (HT) group. Mild hypothermia (32 °C) was induced following CA for 4 h, and animals were rewarmed at a rate of 0.5 °C/h. Neurologic deficit scores (NDS) were used to determine the status of neurological function. Cytoplasmic and mitochondrial protein from the hippocampus was extracted, and the expression of LC3B-II/I and Parkin were measured as markers of intracellular autophagy and mitophagy, respectively. Of the 60 rats that underwent CA, 44 were successfully resuscitated (73 %), and 33 survived until the end of the experiment (55 %). Mild hypothermia maintained eumorphism of nuclear and mitochondrial structures and significantly improved NDS (p < 0.05). Expression of LC3B-II/I and Parkin in hippocampal nerve cells were significantly increased (p < 0.05) in the NT group relative to the control. Meanwhile, mild hypothermia reduced the level of LC3B-II/I and Parkin (p < 0.05) relative to the NT group. Mild hypothermia protected mitochondria and improved neurological function following CA and resuscitation after ischemia/reperfusion (I/R) injury, likely by reducing excessive autophagy and mitophagy in neurons.

Systematic review and meta-analysis of therapeutic hypothermia in animal models of spinal cord injury

Background

Therapeutic hypothermia is a clinically useful neuroprotective therapy for cardiac arrest and neonatal hypoxic ischemic encephalopathy and may potentially be useful for the treatment of other neurological conditions including traumatic spinal cord injury (SCI). The pre-clinical studies evaluating the effectiveness of hypothermia in acute SCI broadly utilise either systemic hypothermia or cooling regional to the site of injury. The literature has not been uniformly positive with conflicting studies of varying quality, some performed decades previously.

Methods

In this study, we systematically review and meta-analyse the literature to determine the efficacy of systemic and regional hypothermia in traumatic SCI, the experimental conditions influencing this efficacy, and the influence of study quality on outcome. Three databases were utilised; PubMed, ISI Web of Science and Embase. Our inclusion criteria consisted of the (i) reporting of efficacy of hypothermia on functional outcome (ii) number of animals and (iii) mean outcome and variance in each group.

Results

Systemic hypothermia improved behavioural outcomes by 24.5% (95% CI 10.2 to 38.8) and a similar magnitude of improvement was seen across a number of high quality studies. The overall behavioural improvement with regional hypothermia was 26.2%, but the variance was wide (95% CI −3.77 to 56.2). This result may reflect a preponderance of positive low quality data, although a preferential effect of hypothermia in ischaemic models of injury may explain some of the disparate data. Sufficient heterogeneity was present between studies of regional hypothermia to reveal a number of factors potentially influencing efficacy, including depth and duration of hypothermia, animal species, and neurobehavioural assessment. However, these factors could reflect the influence of earlier lower quality literature.

Conclusion

Systemic hypothermia appears to be a promising potential method of treating acute SCI on the basis of meta-analysis of the pre-clinical literature and the results of high quality animal studies.

Hypothermia-induced neuroprotection is associated with reduced mitochondrial membrane permeability in a swine model of cardiac arrest

Increasing evidence has shown that mild hypothermia is neuroprotective for comatose patients resuscitated from cardiac arrest, but the mechanism of this protection is not fully understood. The aim of this study was to determine whether prolonged whole-body mild hypothermia inhibits mitochondrial membrane permeability (MMP) in the cerebral cortex after return of spontaneous circulation (ROSC). Thirty-seven inbred Chinese Wuzhishan minipigs were successfully resuscitated after 8 minutes of untreated ventricular fibrillation (VF) and underwent recovery under normothermic (NT) or prolonged whole-body mild hypothermic (HT; 33°C) conditions for 24 or 72 hours. Cerebral samples from the frontal cortex were collected at 24 and 72 hours after ROSC. Mitochondria were isolated by differential centrifugation. At 24 hours, relative to NT, HT was associated with reductions in opening of the mitochondrial permeability transition pore, release of pro-apoptotic substances from mitochondria, caspase 3 cleavage, apoptosis, and neurologic deficit scores, as well as increases in mitochondrial membrane potential and mitochondrial respiration. Together, these findings suggest that mild hypothermia inhibits ischemia-induced increases in MMP, which may provide neuroprotection against cerebral injury after cardiac arrest.

The emerging roles of microRNAs in CNS injuries

The consequences of injuries to the CNS are profound and persistent, resulting in substantial burden to both the individual patient and society. Existing treatments for CNS injuries such as stroke, traumatic brain injury and spinal cord injury have proved inadequate, partly owing to an incomplete understanding of post-injury cellular and molecular changes. MicroRNAs (miRNAs) are RNA molecules composed of 20-24 nucleotides that function to inhibit mRNA translation and have key roles in normal CNS development and function, as well as in disease. However, a role for miRNAs as effectors of CNS injury has recently emerged. Use of bioinformatics to assess the mRNA targets of miRNAs enables high-order analysis of interconnected networks, and can reveal affected pathways that may not be identifiable with the use of traditional techniques such as gene knock-in or knockout approaches, or mRNA microarrays. In this Review, we discuss the findings of miRNA microarray studies of spinal cord injury, traumatic brain injury and stroke, as well as the use of gene ontological algorithms to discern global patterns of molecular and cellular changes following such injuries. Furthermore, we examine the current state of miRNA-based therapies and their potential to improve functional outcomes in patients with CNS injuries.

Effects of hypothermia on oligodendrocyte precursor cell proliferation, differentiation and maturation following hypoxia ischemia in vivo and in vitro

Hypoxic-ischemia (HI) not only causes gray matter injury but also white matter injury, leading to severe neurological deficits and mortality, and only limited therapies exist. The white matter of animal models and human patients with HI-induced brain injury contains increased oligodendrocyte precursor cells (OPCs). However, little OPC can survive and mature to repair the injured white matter. Here, we test the effects of mild hypothermia on OPC proliferation, differentiation and maturation. Animals suffered to left carotid artery ligation followed by 8% oxygen for 2h in 7-day-old rats. They were divided into a hypothermic group (rectal temperature 32-33 °C for 48 h) and a normothermic group (36-37 °C for 48 h), then animals were sacrificed at 3, 7, 14 and 42 days after HI surgery. Our results showed that hypothermia successfully enhanced early OL progenitors (NG2(+)) and its proliferation in the corpus callosum (CC) after HI. Late OL progenitor (O4(+)) accumulation decreased accompanied with increased OL maturation which is detected by myelin basic protein (MBP) and proteolipid protein. (PLP) immunostaining and immunoblotting in hypothermia compared to normothermia. Additionally, using an in vitro hypoxic-ischemia model-oxygen glucose deprivation (OGD), we demonstrated that hypothermia decreased preOL accumulation and promoted OPC differentiation and maturation. Further data indicated that OPC death was significantly suppressed by hypothermia in vitro. The myelinated axons and animal behavior both markedly increased in hypothermic- compared to normothermic-animals after HI. In summary, these data suggest that hypothermia has the effects to protect OPC and to promote OL maturation and myelin repair in hypoxic-ischemic events in the neonatal rat brain. This study proposed new aspects that may contribute to elucidate the mechanism of hypothermic neuroprotection for white matter injury in neonatal rat brain injury.

Hypothermia for acute spinal cord injury--a review

OBJECTIVE

Spinal cord injury (SCI) is a catastrophic neurological event with no proven treatments that protect against its consequences. Potential benefits of hypothermia in preventing/limiting central nervous system injury are now well known. There has been an interest in its potential use after SCI. This article reviews the current experimental and clinical evidence on the use of therapeutic hypothermia in patients with SCI.

METHODS

Review of literature.

RESULTS

There are various mechanisms by which hypothermia is known to protect the central nervous system. Modest hypothermia (32°C-34°C) can deliver the potential benefits of hypothermia without incurring the complications associated with deep hypothermia. Several recent experimental studies have repeatedly shown that the use of hypothermia provides the benefit of neuroprotection after SCI. Although older clinical studies were often focused on local cooling strategies and demonstrated mixed results, more recent data from systemic hypothermia use demonstrate its safety and its benefits. Endovascular cooling is a safe and reliable method of inducing hypothermia.

CONCLUSIONS

There is robust experimental and some clinical evidence that hypothermia is beneficial in acute SCI. Larger, multicenter trials should be initiated to further study the usefulness of systemic hypothermia in SCI.

Neuroprotective effects of hypothermia after spinal cord injury in rats: comparative study between epidural hypothermia and systemic hypothermia

STUDY DESIGN

An experimental comparative study on moderate epidural hypothermia (MEH) versus moderate systemic hypothermia (MSH) after spinal cord injury (SCI).

OBJECTIVE

To compare neuroprotective effects of hypothermia between MEH and MSH after SCI in rats.

SUMMARY OF BACKGROUND DATA

Experimental MEH or MSH has been attempted for neuroprotection after ischemic or traumatic SCI. However, there is no comparative study on neuroprotective effect of MEH and MSH after SCI. If hypothermia is to be considered as 1 modality for treating SCI, further studies on the advantages and disadvantages of hypothermia will be mandatory.

METHODS

A spinal cord contusion was produced in all 32 rats, and these rats were randomly divided into 4 groups-8 rats in each group: (1) the control group (spinal cord contusion only), (2) the methylprednisolone group, (3) the MEH group (28°C for 48 hr), and (4) the MSH group (32°C for 48 hr). The functional recovery was assessed using Basso, Beattie, Bresnahan scale and antiapoptotic and anti-inflammatory effects were assessed.

RESULTS

The Basso, Beattie, Bresnahan scale scores in both the hypothermia groups were significantly higher than that in the control group at 6 weeks. The numbers of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells and OX-42 positive cells were significantly lower in both the MEH and MSH groups than that in the control group. The p38 mitogen-activated protein kinases expression of the treated groups was significantly lower than that of the control group. The expression of caspase-8 and caspase-9 significantly decreased in the treated groups compared with that of the control group. However, in terms of caspase-3, only the MSH group has shown to be significantly lower than that of the control group.

CONCLUSION

This study presented that both systemic and epidural hypothermia demonstrated neuroprotective effects after SCI. Systemic hypothermia showed more neuroprotective effect by antiapoptotic and anti-inflammatory effects.