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

Clinical Insights and Future Directions in Hypothermia for Severe Traumatic Brain Injury: A Narrative Review

Fever control is essential in patients with severe traumatic brain injury (TBI). The efficacy of therapeutic hypothermia (TH) in severe TBI has been investigated over the last few decades; however, in contrast to experimental studies showing benefits, no evidence of efficacy has been demonstrated in clinical practice. In this review, the mechanisms and history of hypothermia were briefly outlined, while the results of major randomized controlled trials (RCTs) and meta-analyses investigating TH for adult TBI were introduced and discussed. The retrieved meta-analyses showed conflicting results, with a limited number of studies indicating the benefits of TH. Some studies have shown the benefits of long-term TH compared with short-term TH. Although TH is effective at lowering elevated intracranial pressure (ICP), reduced ICP does not lead to favorable outcomes. Low-quality RCTs overestimated the benefits of TH, while high-quality RCTs showed no difference or worse outcomes with TH. RCTs assessing standardized TH quality demonstrated the benefits of TH. As TBI has heterogeneous and complicated pathologies, applying a uniform treatment may not be ideal. A meta-analysis of young patients who underwent early cooling and hematoma removal showed better TH results. TH should not be abandoned, and its optimal usage should be advocated on an individual basis.

Trauma Anesthesiology Perioperative Management Update

Anesthesia for patients with life-threatening injuries is an essential part of post-accident care. Unfortunately, there is variability in trauma anesthesia care and numerous nonstandardized methods of working with patients remain. Uncertainty exists as to when and how best to intubate trauma patients, the use of vasopressors, and the appropriate management of severe traumatic brain injury. Some physicians recommend prehospital rapid sequence intubation, whereas others use bag-mask ventilation at lower pressures with no cricoid pressure and early transport to a trauma center. Overall, the absence of uniformity in trauma anesthesia care underlines the need for continued study and dialogue to define best practices and optimize patient outcomes.

Overview of Hypothermia, Its Role in Neuroprotection, and the Application of Prophylactic Hypothermia in Traumatic Brain Injury

The current standard of practice is to maintain normothermia in traumatic brain injury (TBI) patients despite the theoretical benefits of hypothermia and numerous animal studies with promising results. While targeted temperature management or induced hypothermia to support neurological function is recommended for a select patient population postcardiac arrest, similar guidelines have not been instituted for TBI. In this review, we will examine the pathophysiology of TBI and discuss the benefits and risks of induced hypothermia in this patient population. In addition, we provide an overview of the largest randomized controlled trials testing-induced hypothermia. Our literature review on hypothermia returned a myriad of studies and trials, many of which have inconclusive results. The aim of this review was to recognize the effects of hypothermia, summarize the latest trials, address the inconsistencies, and discuss future directions for the study of hypothermia in TBI.

Overexpressed cold inducible RNA-binding protein improves cell viability and EGF expression in glial cells

BACKGROUND

Cold inducible RNA-binding protein (CIRP) is a key protein in the hypothermic therapy. Highly expressed CIRP exerts a neuroprotective effect on neurons. The aim of this study is to provide the evidence of the protective effects of CIRP on the glial cells and explore the downstream pathway of CIRP.

RESULTS

The results of this study demonstrated that the cell viability of the glial cells with CIRP overexpression was increased significantly compared to the control. With CIRP overexpression, the epidermal growth factor (EGF) mRNA expression was found increasing significantly and the mRNA expressions of derived neurotrophic factor (BDNF), bcl-2, vascular endothelial growth factor (VEGF) and nerve growth factor (NGF) were not upregulated compared to the control. EGF and CIRP co-expression was demonstrated on the glial cells. With CIRP expression, EGF expression on the glial cells was increased statistically compared to the control.

CONCLUSION

CIRP overexpression increases the cell viability of the glial cells, exerting a neuroprotective effect. EGF expression is activated on the glial cells with CIRP overexpression, implying a pathway of CIRP neuroprotection via EGF activation.

Pathogenesis and management of traumatic brain injury (TBI): role of neuroinflammation and anti-inflammatory drugs

Traumatic brain injury (TBI) is an important global health concern that represents a leading cause of death and disability. It occurs due to direct impact or hit on the head caused by factors such as motor vehicles, crushes, and assaults. During the past decade, an abundance of new evidence highlighted the importance of inflammation in the secondary damage response that contributes to neurodegenerative and neurological deficits after TBI. It results in disruption of the blood-brain barrier (BBB) and initiates the release of macrophages, neutrophils, and lymphocytes at the injury site. A growing number of researchers have discovered various signalling pathways associated with the initiation and progression of inflammation. Targeting different signalling pathways (NF-κB, JAK/STAT, MAPKs, PI3K/Akt/mTOR, GSK-3, Nrf2, RhoGTPase, TGF-β1, and NLRP3) helps in the development of novel anti-inflammatory drugs in the management of TBI. Several synthetic and herbal drugs with both anti-inflammatory and neuroprotective potential showed effective results. This review summarizes different signalling pathways, associated pathologies, inflammatory mediators, pharmacological potential, current status, and challenges with anti-inflammatory drugs.

The role of the stress system in recovery after traumatic brain injury: A tribute to Bruce S. McEwen

Traumatic brain injury (TBI) represents a major public health concern. Although the majority of individuals that suffer mild-moderate TBI recover relatively quickly, a substantial subset of individuals experiences prolonged and debilitating symptoms. An exacerbated response to physiological and psychological stressors after TBI may mediate poor functional recovery. Individuals with TBI can suffer from poor stress tolerance, impairments in the ability to evaluate stressors, and poor initiation (and cessation) of neuroendocrine stress responses, all of which can exacerbate TBI-mediated dysfunction. Here, we pay tribute to the pioneering neuroendocrinologist Dr. Bruce McEwen by discussing the ways in which his work on stress physiology and allostatic loading impacts the TBI patient population both before and after their injuries. Specifically, we will discuss the modulatory role of hypothalamic-pituitary-adrenal axis responses immediately after TBI and later in recovery. We will also consider the impact of stressors and stress responses in promoting post-concussive syndrome and post-traumatic stress disorders, two common sequelae of TBI. Finally, we will explore the role of early life stressors, prior to brain injuries, as modulators of injury outcomes.

Benefits of Hypothermia for Young Patients with Acute Subdural Hematoma: A Computed Tomography Analysis of the Brain Hypothermia Study

Therapeutic hypothermia for severe traumatic brain injury (TBI) has been repeatedly studied, but no past studies have assessed the detailed head computed tomography (CT) findings. We sought to investigate individual CT findings of severe TBI patients treated with targeted temperature management utilizing the head CT database obtained from the Brain Hypothermia study. Enrolled patients underwent either mild therapeutic hypothermia (32.0°C−34.0°C) or fever control (35.5°C−37.0°C). We assessed individual head CT images on arrival and after rewarming and investigated the correlations with outcomes. The initial CT data were available for 125 patients (hypothermia group = 80, fever control group = 45). Baseline characteristics and CT findings, such as hematoma thickness and midline shift, were similar in all aspects between the two groups. The favorable outcomes in the hypothermia and fever control groups were 38 (47.5%) and 24 (53.3%; p = 0.53) for all 125 patients, respectively; 21 (46.7%) vs. 10 (38.5%; p = 0.50) for 71 patients with acute subdural hematoma (SDH), respectively; and 12 (75.0%) vs. 4 (36.4%; p = 0.045) in 27 young adults (≤50 years) with acute SDH, respectively. There was a trend toward favorable outcomes for earlier time to reach 35.5°C (190 vs. 377 min, p = 0.052) and surgery (155 vs. 180 min, p = 0.096) in young patients with acute SDH. The second CT image revealed progression of the brain injury. This study demonstrated the potential benefits of early hypothermia in young patients with acute SDH, despite no difference in CT findings between the two groups. However, the small number of cases involved hindered the drawing of definitive conclusions. Future studies are warranted to validate the results.

Effects of Injury Severity and Brain Temperature on KAT6A Expression after Traumatic Brain Injury in Rats

Background: Traumatic brain injury (TBI) is associated with a range of neural changes. A comprehensive understanding of the injury-induced lysine acetyltransferase 6A (KAT6A) response, particularly the temporal profile of biochemical alterations, is crucial to design effective therapeutic interventions.Methods: Experiments were performed in male Sprague-Dawley rats. The influence of post-traumatic hypothermia (32°C) or hyperthermia (39°C) on the temporal and regional expression profiles of KAT6A was assessed after moderate or severe TBI. qPCR and western blotting were used to determine the expression of KAT6A in different groups.Results: In the ipsilateral and contralateral hemispheres, significantly lower protein and mRNA expression of KAT6A was found after TBI than sham injury. Moreover, two expression minima of KAT6A were observed in the cortex and hippocampus of the ipsilateral hemisphere. A decrease in injury severity was associated with lower levels of KAT6A mRNA at 12 h and protein at 24 h, but KAT6A mRNA at 48 h and protein at 72 h had alterations. Compared with normothermia and hyperthermia, post-traumatic hypothermia intensified the decrease in KAT6A at both the mRNA and protein levels. In contrast, hyperthermia, as compared with normothermia, did not significantly affect the levels of KAT6A mRNA at 12 h and protein at 24 h, but triggered a significant increase in levels of KAT6A mRNA at 24 h and protein at 72 h. Furthermore, an overall upregulation of KAT6A after TBI was associated with greater injury severity in a time-dependent manner.Conclusions: Post-traumatic hypothermia plays a key role in the regulation of KAT6A expression and thus may at least partially explain the phenotype of post-traumatic temperature in secondary injury after TBI.

The benefits of exercise for outcome improvement following traumatic brain injury: Evidence, pitfalls and future perspectives

Traumatic brain injury (TBI), also known as a silent epidemic, is currently a substantial public health problem worldwide. Given the increased energy demands following brain injury, relevant guidelines tend to recommend absolute physical and cognitive rest for patients post-TBI. Nevertheless, recent evidence suggests that strict rest does not provide additional benefits to patients' recovery. By contrast, as a cost-effective non-pharmacological therapy, exercise has shown promise for enhancing functional outcomes after injury. This article summarizes the most recent evidence supporting the beneficial effects of exercise on TBI outcomes, focusing on the efficacy of exercise for cognitive recovery after injury and its potential mechanisms. Available evidence demonstrates the potential of exercise in improving cognitive impairment, mood disorders, and post-concussion syndrome following TBI. However, the clinical application for exercise rehabilitation in TBI remains challenging, particularly due to the inadequacy of the existing clinical evaluation system. Also, a better understanding of the underlying mechanisms whereby exercise promotes its most beneficial effects post-TBI will aid in the development of new clinical strategies to best benefit of these patients.

Efficacy of a Novel Prophylactic Barbiturate Therapy for Severe Traumatic Brain Injuries: Step-down Infusion of a Barbiturate with Normothermia

This study aimed to examine the beneficial effects of a novel prophylactic barbiturate therapy, step-down infusion of barbiturates, using thiamylal with normothermia (NOR+sdB), on the poor outcome in the patients with severe traumatic brain injuries (sTBI), in comparison with mild hypothermia (MD-HYPO). From January 2000 to March 2019, 4133 patients with TBI were admitted to our hospital. The inclusion criteria were: a Glasgow coma scale (GCS) score of ≤8 on admission, age between 20 and 80 years, intracranial hematoma requiring surgical evacuation of the hematoma with craniotomy and/or external decompression, and patients who underwent management of body temperature and assessed their outcome at 6-12 months. Finally, 43 patients were included in the MD-HYPO (n = 29) and NOR+sdB (n = 14) groups. sdB was initiated intraoperatively or immediately after the surgical treatment. There were no significant differences in patient characteristics, including age, sex, past medical history, GCS on admission, type of intracranial hematoma, and length of hospitalization between the two groups. Although NOR+sdB could not improve the patient's poor outcome either at discharge from the intensive care unit (ICU) or at 6-12 months after admission, the treatment inhibited composite death at discharge from the ICU. The mean value of the maximum intracranial pressure (ICP) in the NOR+sdB group was <20 mmHg throughout the first 120 h. NOR+sdB prevented composite death in the ICU in patients with sTBI, and we may obtain novel insights into the beneficial role of prophylactic barbiturate therapy from suppression of the elevated ICP during the first 120 h.

Cardiac arrest caused by accidental severe hypothermia and myocardial infarction during general anesthesia

Therapeutic hypothermia is often used for traumatic brain injury because of its neuroprotective effect and decreased secondary brain injury. However, this procedure lacks clinical evidence supporting its efficacy, and adverse outcomes have been reported during general anesthesia. A 61-year-old man with a history of percutaneous coronary intervention (PCI) was admitted with traumatic brain injury. Immediately after admission, he underwent mild therapeutic hypothermia with a target temperature of 33.0°C for neuroprotection. During general anesthesia for emergency surgery because he developed a mass effect, hypothermic cardiac arrest occurred following an additional decrease in the core body temperature. Moreover, myocardial infarction caused by restenosis of the previous PCI lesion also contributed to the cardiac arrest. Although the patient recovered spontaneous circulation after an hour-long cardiopulmonary resuscitation with rewarming, he eventually died of subsequent repetitive cardiac arrests. When anesthetizing patients undergoing therapeutic hypothermia, caution is required to prevent adverse outcomes that can be caused by unintentional severe hypothermia and exacerbation of underlying heart disease.

Traumatic Brain Injury: Mechanistic Insight on Pathophysiology and Potential Therapeutic Targets

Traumatic brain injury (TBI) causes brain damage, which involves primary and secondary injury mechanisms. Primary injury causes local brain damage, while secondary damage begins with inflammatory activity followed by disruption of the blood-brain barrier (BBB), peripheral blood cells infiltration, brain edema, and the discharge of numerous immune mediators including chemotactic factors and interleukins. TBI alters molecular signaling, cell structures, and functions. Besides tissue damage such as axonal damage, contusions, and hemorrhage, TBI in general interrupts brain physiology including cognition, decision-making, memory, attention, and speech capability. Regardless of the deep understanding of the pathophysiology of TBI, the underlying mechanisms still need to be assessed with a desired therapeutic agent to control the consequences of TBI. The current review gives a brief outline of the pathophysiological mechanism of TBI and various biochemical pathways involved in brain injury, pharmacological treatment approaches, and novel targets for therapy.

Adjuvant therapeutic potential of moderate hypothermia for glioblastoma

PURPOSE

Glioblastoma is the most common malignant brain tumor, currently treated by surgery followed by concomitant radiotherapy and temozolomide-based chemotherapy. Despite these treatments, median survival is only 15 months as a result of tumor recurrence in the resection margins. Here, we propose therapeutic hypothermia - known to have neuroprotective effects - as an adjuvant treatment to maintain residual glioblastoma cells in a dormant state, and thus prevent tumor recurrence.

METHODS

In vitro experiments were performed on healthy tissue with primary human astrocytes, and four human glioblastoma cell lines: A172, U251, U87, and T98G. We explored the adjuvant potential of moderate hypothermia (28 °C) by studying the reversibility of its inhibitory effects on cell proliferation and comparing them to currently used temozolomide.

RESULTS

Moderate hypothermia reduced healthy cell growth, but also inhibited glioblastoma cell proliferation even after rewarming. Indeed, hypothermic preconditioning duration strongly enhanced inhibitory effects from 35% after 3 days to 100% after 30 days. In contrast, moderate (28 °C) and severe (23 °C) preconditioning induced similar results. Finally, moderate hypothermia had more uniform inhibitory effects than temozolomide, which reduced proliferation by between 15% and 95%, and also potentiated the effects of the latter.

CONCLUSION

Moderate hypothermia shows promise as an adjuvant therapy for glioblastoma through its inhibition of cell proliferation beyond direct conditioning and potentiation of the effects of chemotherapy. If in vivo preclinical results corroborate our findings, therapeutic hypothermia applied at the resection margins could probably inhibit tumor growth, delay tumor recurrence and reduce inter-patient variability.

Traumatic Brain Injury Update

Traumatic brain injury is a devastating, life-changing event in most cases. After the primary brain insult, it is helpful to use evidence-based monitoring techniques to guide implementation of essential interventions to minimize secondary injury and thereby improve patient outcomes. An update on multimodal neuromonitoring is provided in this narrative review, with discussion of tools and techniques currently used in the treatment of patients with brain injury. Neuroprotective treatments, from the well-studied targeted temperature management to new potential therapeutics under investigation, such as glyburide, also are presented.

Hypothermia Effectively Treats Tumors with Temperature-Sensitive p53 Mutations

The p53 tumor suppressor is frequently inactivated by mutations in cancer. Most p53 mutations are located in the DNA-binding domain, causing local disruption of DNA-binding surface or global misfolding. Rescuing the structural defect of mutant p53 is an attractive therapeutic strategy, but its potential remains unproven due to a lack of drugs capable of efficiently rescuing misfolded p53. Although mutant p53 in tumors is inactive at 37°C, approximately 15% are temperature sensitive (ts) and regain DNA-binding activity at 32°C to 34°C (ts mutants). This temperature is achievable using a therapeutic hypothermia procedure established for resuscitated cardiac arrest patients. To test whether hypothermia can be used to target tumors with ts p53 mutations, the core temperature of tumor-bearing mice was lowered to 32°C using the adenosine A1 receptor agonist N⁶-cyclohexyladenoxine that suppresses brain-regulated thermogenesis. Hypothermia treatment (32 hours at 32°C × 5 cycles) activated endogenous ts mutant p53 in xenograft tumors and inhibited tumor growth in a p53-dependent fashion. Tumor regression and durable remission in a ts p53 lymphoma model was achieved by combining hypothermia with chemotherapy. The results raise the possibility of treating tumors expressing ts p53 mutations with hypothermia. SIGNIFICANCE: Pharmacologic inhibition of brain-regulated thermogenesis and induction of 32°C whole-body hypothermia specifically targets tumors with temperature-sensitive p53 mutations, rescuing p53 transcriptional activity and inducing tumor regression.See related commentary by Hu and Feng, p. 3762.

An Exploratory Report on Electrographic Changes in the Cerebral Cortex Following Mild Traumatic Brain Injury with Hyperthermia in the Rat

Traumatic brain injury (TBI) has the potential to perturb perception by disrupting electrical propagation within and between the thalamus and cerebral cortex. Moderate and severe TBI may result in posttraumatic epilepsy, a condition characterized by convulsive tonic-clonic seizures. Spike/wave discharges (SWDs) of generalized nonconvulsive seizures, also called absence seizures, may also occur as a consequence of brain trauma. As mild hyperthermia has been reported to exacerbate histopathological and behavioral outcomes, we used an unbiased algorithm to detect periodic increases in power across different frequency bands following single or double closed head injury (CHI) under normothermia and hyperthermia conditions. We demonstrated that mild TBI did not significantly alter the occurrence of events containing increases in power between the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta1 (12-20 Hz) frequency bands in the Sprague Dawley rat 12 weeks after injury. However, when hyperthermia (39°C) was induced before and after CHI, electrographic events containing a similar waveform and harmonic frequency to SWDs were observed in a subset of animals. Further experiments utilizing chronic recordings will need to be performed to determine if these trends lead to absence seizures.

Recovery from disorders of consciousness: mechanisms, prognosis and emerging therapies

Substantial progress has been made over the past two decades in detecting, predicting and promoting recovery of consciousness in patients with disorders of consciousness (DoC) caused by severe brain injuries. Advanced neuroimaging and electrophysiological techniques have revealed new insights into the biological mechanisms underlying recovery of consciousness and have enabled the identification of preserved brain networks in patients who seem unresponsive, thus raising hope for more accurate diagnosis and prognosis. Emerging evidence suggests that covert consciousness, or cognitive motor dissociation (CMD), is present in up to 15-20% of patients with DoC and that detection of CMD in the intensive care unit can predict functional recovery at 1 year post injury. Although fundamental questions remain about which patients with DoC have the potential for recovery, novel pharmacological and electrophysiological therapies have shown the potential to reactivate injured neural networks and promote re-emergence of consciousness. In this Review, we focus on mechanisms of recovery from DoC in the acute and subacute-to-chronic stages, and we discuss recent progress in detecting and predicting recovery of consciousness. We also describe the developments in pharmacological and electrophysiological therapies that are creating new opportunities to improve the lives of patients with DoC.

Optical whispering-gallery mode barcodes for high-precision and wide-range temperature measurements

Temperature is one of the most fundamental physical properties to characterize various physical, chemical, and biological processes. Even a slight change in temperature could have an impact on the status or dynamics of a system. Thus, there is a great need for high-precision and large-dynamic-range temperature measurements. Conventional temperature sensors encounter difficulties in high-precision thermal sensing on the submicron scale. Recently, optical whispering-gallery mode (WGM) sensors have shown promise for many sensing applications, such as thermal sensing, magnetic detection, and biosensing. However, despite their superior sensitivity, the conventional sensing method for WGM resonators relies on tracking the changes in a single mode, which limits the dynamic range constrained by the laser source that has to be fine-tuned in a timely manner to follow the selected mode during the measurement. Moreover, we cannot derive the actual temperature from the spectrum directly but rather derive a relative temperature change. Here, we demonstrate an optical WGM barcode technique involving simultaneous monitoring of the patterns of multiple modes that can provide a direct temperature readout from the spectrum. The measurement relies on the patterns of multiple modes in the WGM spectrum instead of the changes of a particular mode. It can provide us with more information than the single-mode spectrum, such as the precise measurement of actual temperatures. Leveraging the high sensitivity of WGMs and eliminating the need to monitor particular modes, this work lays the foundation for developing a high-performance temperature sensor with not only superior sensitivity but also a broad dynamic range.

Selective brain cooling achieves peripheral organs protection in hemorrhagic shock resuscitation via preserving the integrity of the brain-gut axis

Background: Although whole-body cooling has been reported to improve the ischemic/reperfusion injury in hemorrhagic shock (HS) resuscitation, it is limited by its adverse reactions following therapeutic hypothermia. HS affects the experimental and clinical bowel disorders via activation of the brain-gut axis. It is unknown whether selective brain cooling achieves beneficial effects in HS resuscitation via preserving the integrity of the brain-gut axis. Methods: Male Sprague-Dawley rats were bled to hypovolemic HS and resuscitated with blood transfusion followed by retrograde jugular vein flush (RJVF) with 4 °C or 36 °C normal saline. The mean arterial blood pressure, cerebral blood flow, and brain and core temperature were measured. The integrity of intestinal tight junction proteins and permeability, blood pro-inflammatory cytokines, and multiple organs damage score were determined. Results: Following blood transfusion resuscitation, HS rats displayed gut barrier disruption, increased blood levels of pro-inflammatory cytokines, and peripheral vital organ injuries. Intrajugular-based infusion cooled the brain robustly with a minimal effect on body temperature. This brain cooling significantly reduced the HS resuscitation-induced gut disruption, systemic inflammation, and peripheral vital organ injuries in rats. Conclusion: Resuscitation with selective brain cooling achieves peripheral vital organs protection in hemorrhagic shock resuscitation via preserving the integrity of the brain-gut axis.

Targeted Identification of Protein Interactions in Eukaryotic mRNA Translation

To identify protein-protein interactions and phosphorylated amino acid sites in eukaryotic mRNA translation, replicate TAP-MudPIT and control experiments are performed targeting Saccharomyces cerevisiae genes previously implicated in eukaryotic mRNA translation by their genetic and/or functional roles in translation initiation, elongation, termination, or interactions with ribosomal complexes. Replicate tandem affinity purifications of each targeted yeast TAP-tagged mRNA translation protein coupled with multidimensional liquid chromatography and tandem mass spectrometry analysis are used to identify and quantify copurifying proteins. To improve sensitivity and minimize spurious, nonspecific interactions, a novel cross-validation approach is employed to identify the most statistically significant protein-protein interactions. Using experimental and computational strategies discussed herein, the previously described protein composition of the canonical eukaryotic mRNA translation initiation, elongation, and termination complexes is calculated. In addition, statistically significant unpublished protein interactions and phosphorylation sites for S. cerevisiae's mRNA translation proteins and complexes are identified.

Mild Hyperthermia Aggravates Glucose Metabolic Consequences in Repetitive Concussion

Traumatic brain injury (TBI) is one of the leading causes of mortality and disability around the world. Mild TBI (mTBI) makes up approximately 80% of reported cases and often results in transient psychological abnormalities and cognitive disruption. At-risk populations for mTBI include athletes and other active individuals who may sustain repetitive concussive injury during periods of exercise and exertion when core temperatures are elevated. Previous studies have emphasized the impact that increased brain temperature has on adverse neurological outcomes. A lack of diagnostic tools to assess concussive mTBI limits the ability to effectively identify the post-concussive period during which the brain is uniquely susceptible to damage upon sustaining additional injury. Studies have suggested that a temporal window of increased vulnerability that exists corresponds to a period of injury-induced depression of cerebral glucose metabolism. In the current study, we sought to evaluate the relationship between repetitive concussion, local cerebral glucose metabolism, and brain temperature using the Marmarou weight drop model to generate mTBI. Animals were injured three consecutive times over a period of 7 days while exposed to either normothermic or hyperthermic temperatures for 15 min prior to and 1 h post each injury. A ¹⁴C-2-deoxy-d-glucose (2DG) autoradiography was used to measure local cerebral metabolic rate of glucose (lCMR_Glc) in 10 diverse brain regions across nine bregma levels 8 days after the initial insult. We found that repetitive mTBI significantly decreased glucose utilization bilaterally in several cortical areas, such as the cingulate, visual, motor, and retrosplenial cortices, as well as in subcortical areas, including the caudate putamen and striatum, compared to sham control animals. lCMR_Glc was significant in both normothermic and hyperthermic repetitive mTBI animals relative to the sham group, but to a greater degree when exposed to hyperthermic conditions. Taken together, we report significant injury-induced glucose hypometabolism after repetitive concussion in the brain, and additionally highlight the importance of temperature management in the acute period after brain injury.

Hypothermia: Impact on plasticity following brain injury

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

Effects of dexmedetomidine vs sufentanil during percutaneous tracheostomy for traumatic brain injury patients: A prospective randomized controlled trial

BACKGROUND

Percutaneous tracheostomy, almost associated with cough reflex and hemodynamic fluctuations, is a common procedure for traumatic brain injury (TBI) patients, especially those in neurosurgery intensive care units (NICUs). However, there are currently a lack of effective preventive measures to reduce the risk of secondary brain injury. The aim of this study was to compare the effect of dexmedetomidine (DEX) vs sufentanil during percutaneous tracheostomy in TBI patients.

METHODS

The 196 TBI patients who underwent percutaneous tracheostomy were randomized divided into 3 groups: group D1 (n = 62, DEX infusion at 0.5 μg·kg for 10 minutes, then adjusted to 0.2-0.7 μg·kg·hour), group D2 (n = 68, DEX infusion at 1 μg·kg for 10 minutes, then adjusted to 0.2-0.7 μg·kg·hour), and group S (n = 66, sufentanil infusion 0.3 μg·kg for 10 minutes, then adjusted to 0.2-0.4 μg·kg·hour). The bispectral index (BIS) of all patients was maintained at 50 to 70 during surgery. Anesthesia onset time, hemodynamic variables, total cumulative dose of DEX/sufentanil, total doses of rescue propofol and fentanyl, time to first dose of rescue propofol and fentanyl, number of intraoperative patient movements and cough reflexes, adverse events, and surgeon satisfaction score were recorded.

RESULTS

Anesthesia onset time was significantly lower in group D2 than in both other groups (14.35 ± 3.23 vs 12.42 ± 2.12 vs 13.88 ± 3.51 minutes in groups D1, D2, and S, respectively; P < .001). Both heart rate and mean arterial pressure during percutaneous tracheostomy were more stable in group D2. Total doses of rescue propofol and fentanyl were significantly lower in group D2 than in group D1 (P < .001). The time to first dose of rescue propofol and fentanyl were significantly longer in group D2 than in both other groups (P < .001). The number of patient movements and cough reflexes during percutaneous tracheostomy were lower in group D2 than in both other groups (P < .001). The overall incidences of tachycardia and hypertension (which required higher doses of esmolol and urapidil, respectively) were also lower in group D2 than in both other groups (P < .05). Three patients in group S had respiratory depression compared to X in the D1 group and X in the D2 group. The surgeon satisfaction score was significantly higher in group D2 than in both other groups (P < .05).

CONCLUSIONS

During percutaneous tracheostomy, compared with sufentanil, DEX (1 μg·kg for 10 minutes, then adjusted to 0.2-0.7 μg·kg·hour) can provide the desired attenuation of the hemodynamic response without increased adverse events. Consequently, DEX could be used safely and effectively during percutaneous tracheostomy in TBI patients.

Role of CB2 Receptor in the Recovery of Mice after Traumatic Brain Injury

Cannabis is one of the most widely used plant drugs in the world today. In spite of the large number of scientific reports on medical marijuana, there still exists much controversy surrounding its use and the potential for abuse due to the undesirable psychotropic effects. However, recent developments in medicinal chemistry of novel non-psychoactive synthetic cannabinoids have indicated that it is possible to separate some of the therapeutic effects from the psychoactivity. We have previously shown that treatment with the endocannabinoid 2-AG, which binds to both CB1 and CB2 receptors 1 h after traumatic brain injury in mice, attenuates neurological deficits, edema formation, infarct volume, blood-brain barrier permeability, neuronal cell loss at the CA3 hippocampal region, and neuroinflammation. Recently, we synthesized a set of camphor-resorcinol derivatives, which represent a novel series of CB2 receptor selective ligands. Most of the novel compounds exhibited potent binding and agonistic properties at the CB2 receptors with very low affinity for the CB1 receptor, and some were highly anti-inflammatory. This selective binding correlated with their intrinsic activities. HU-910 and HU-914 were selected in the present study to evaluate their potential effect in the pathophysiology of traumatic brain injury (TBI). In mice and rats subjected to closed-head injury and treated with these novel compounds, we showed enhanced neurobehavioral recovery, inhibition of tumor necrosis factor α production, increased synaptogenesis, and partial recovery of the cortical spinal tract. We propose these CB2 agonists as potential drugs for development of novel therapeutic modality to TBI.

Therapeutic Hypothermia and Neuroprotection in Acute Neurological Disease

Therapeutic hypothermia has consistently been shown to be a robust neuroprotectant in many labs studying different models of neurological disease. Although this therapy has shown great promise, there are still challenges at the clinical level that limit the ability to apply this routinely to each pathological condition. In order to overcome issues involved in hypothermia therapy, understanding of this attractive therapy is needed. We review methodological concerns surrounding therapeutic hypothermia, introduce the current status of therapeutic cooling in various acute brain insults, and review the literature surrounding the many underlying molecular mechanisms of hypothermic neuroprotection. Because recent work has shown that body temperature can be safely lowered using pharmacological approaches, this method may be an especially attractive option for many clinical applications. Since hypothermia can affect multiple aspects of brain pathophysiology, therapeutic hypothermia could also be considered a neuroprotection model in basic research, which would be used to identify potential therapeutic targets. We discuss how research in this area carries the potential to improve outcome from various acute neurological disorders.

Neuroprotective and neuroregenerative potential of pharmacologically-induced hypothermia with D-alanine D-leucine enkephalin in brain injury

Neurovascular disorders, such as traumatic brain injury and stroke, persist as leading causes of death and disability - thus, the search for novel therapeutic approaches for these disorders continues. Many hurdles have hindered the translation of effective therapies for traumatic brain injury and stroke primarily because of the inherent complexity of neuropathologies and an inability of current treatment approaches to adapt to the unique cell death pathways that accompany the disorder symptoms. Indeed, developing potent treatments for brain injury that incorporate dynamic and multiple disorder-engaging therapeutic targets are likely to produce more effective outcomes than traditional drugs. The therapeutic use of hypothermia presents a promising option which may fit these criteria. While regulated temperature reduction has displayed great promise in preclinical studies of brain injury, clinical trials have been far less consistent and associated with adverse effects, especially when hypothermia is pursued via systemic cooling. Accordingly, devising better methods of inducing hypothermia may facilitate the entry of this treatment modality into the clinic. The use of the delta opioid peptide D-alanine D-leucine enkephalin (DADLE) to pharmacologically induce temperature reduction may offer a potent alternative, as DADLE displays both the ability to cause temperature reduction and to confer a broad profile of other neuroprotective and neuroregenerative processes. This review explores the prospect of DADLE-mediated hypothermia to treat neurovascular brain injuries, emphasizing the translational steps necessary for its clinical translation.

Does the Environment Influence the Frequency of Concussion Incidence in Professional Football?

Background

Sports-related concussion is a major cause of mild traumatic brain injury (mTBI). It is possible that environmental factors, such as temperature, humidity, and stadium's altitude, may influence the overall incidence of concussions during a game.

Purpose

To examine the impact of environmental factors, such as temperature, humidity, barometric pressure, and dew point, on concussion incidence.

Methods

Public Broadcasting Service (PBS) FRONTLINE Concussion Watch was used to collect injury data on 32 NFL teams during regular season games from 2012 to 2015. Weather data points were collected from Weather Underground. Concussion incidence per game, the probability of a concussion during a game, and a difference in mean game-day temperature, humidity, dew point, and barometric pressure between concussion and concussion-free games were calculated. Our analysis included t-tests, analysis of variance (ANOVA), multivariate correlation tests, and logistic and Poisson regression. 

Results

Overall, 564 concussions were reported. There were 411 games with concussions and 549 games without concussions. We observed a significant decrease in concussion incidence with increasing temperature, both when the temperature was divided into 20^oF increments or into quartiles (p = 0.005 and p = 0.002, respectively). We identified a statistically significant lower mean-game day temperature in concussion games compared to concussion-free games (p < 0.0006). We also observed a significant decrease in the incidence of concussion per game with increasing dew point. There was no significant difference in concussion incidence in barometric pressure and humidity. The logistic regression model predicted a decrease in the probability of a concussion in games with higher temperatures and dew points.

Conclusions

National Football League (NFL) players experienced an increased risk of concussion during football games played in colder temperatures and at lower dew points. Further research on environmental effects on concussions may aid in improving player safety in football leagues.

Magnetic Resonance Spectroscopy Thermometry at 3 Tesla: Importance of Calibration Measurements

To demonstrate the importance of calibration measurements in 3 Tesla proton magnetic resonance (MR) spectroscopy (¹H-MRS) thermometry for human brain temperature estimation for routine clinical applications. In vitro proton MR spectroscopy to obtain calibration constants of the water-chemical shift was conducted at 3 Tesla with a temperature-controlled phantom, containing a pH-buffered aqueous solution of N-acetyl aspartate (NAA), creatine (Cr), methylene protons of Cr (Cr2), dimethyl silapentane sulfonic acid (DSS), and sodium formate (NaFor). Estimations of absolute human brain temperature were performed utilizing the correlation of temperature to the water-chemical shift for the resonances of NAA, Cr, and Cr2. Data for calibration of the metabolites' chemical shift differences and in vivo temperature estimations were acquired with single-voxel point-resolved spectroscopy (PRESS) sequences (repetition time/echo time = 2000/30 ms; voxel size 2 × 2 × 2 cm³). Spectroscopy data were quantified in the time-domain, and a Pearson correlation analysis was performed to estimate the correlation between the chemical shift of metabolites and measured temperatures. The correlation coefficients (r) of our calibration measurements were NAA 0.9975 (±0.0609), Cr -0.9979 (±0.0621), Cr2 - 0.9973 (±0.0577), DSS -0.9976 (±0.0615), and NaFor -0.8132 (±2.348). The mean calculated brain temperature was 37.78 ± 1.447°C, and the mean tympanic temperature was 36.83 ± 0.2456°C. Calculated temperatures derived from Cr and Cr2 provided significant (p = 0.0241 and p = 0.0210, respectively) correlations with measured temperatures (r = 0.4108 and r = -0.4194, respectively). Calibration measurements are vital for ¹H-MRS thermometry. Small numeric differences in measured signal and data preprocessing without any calibration measurements reduce accuracy of temperature calculations, which indicates that calculated temperatures should be interpreted with caution. Application of this method for clinical purposes warrants further investigation and a more practical approach.

Targeted Temperature Management in Pediatric Neurocritical Care

Targeted temperature management encompasses a range of clinical interventions to regulate systemic temperature, and includes both induction of varying degrees of hypothermia and fever prevention ("targeted normothermia"). Targeted temperature management plays a key role in the contemporary management of critically ill neonates and children with acute brain injury. Yet, many unanswered questions remain regarding optimal temperature management in pediatric neurocritical care. The introduction highlights experimental studies that have evaluated the neuroprotective efficacy of therapeutic hypothermia and explored possible mechanisms of action in several brain injury models. The next section focuses on three major clinical conditions in which therapeutic hypothermia has been evaluated in randomized controlled trials in pediatric populations: neonatal hypoxic-ischemic encephalopathy, postcardiac arrest encephalopathy, and traumatic brain injury. Clinical implications of targeted temperature management in pediatric neurocritical care are also discussed. The final section examines some of the factors that may underlie the limited neuroprotective efficacy of hypothermia that has been observed in several major pediatric clinical trials, and outlines important directions for future research.

Selective Brain Cooling Reduces Motor Deficits Induced by Combined Traumatic Brain Injury, Hypoxemia and Hemorrhagic Shock

Selective brain cooling (SBC) can potentially maximize the neuroprotective benefits of hypothermia for traumatic brain injury (TBI) patients without the complications of whole body cooling. We have previously developed a method that involved extraluminal cooling of common carotid arteries, and demonstrated the feasibility, safety and efficacy for treating isolated TBI in rats. The present study evaluated the neuroprotective effects of 4-h SBC in a rat model of penetrating ballistic-like brain injury (PBBI) combined with hypoxemic and hypotensive insults (polytrauma). Rats were randomly assigned into two groups: PBBI+polytrauma without SBC (PHH) and PBBI+polytrauma with SBC treatment (PHH+SBC). All animals received unilateral PBBI, followed by 30-min hypoxemia (fraction of inspired oxygen = 0.1) and then 30-min hemorrhagic hypotension (mean arterial pressure = 40 mmHg). Fluid resuscitation was given immediately following hypotension. SBC was initiated 15 min after fluid resuscitation and brain temperature was maintained at 32-33°C (core temperature at ~36.5°C) for 4 h under isoflurane anesthesia. The PHH group received the same procedures minus the cooling. At 7, 10, and 21 days post-injury, motor function was assessed using the rotarod task. Cognitive function was assessed using the Morris water maze at 13-17 days post-injury. At 21 days post-injury, blood samples were collected and the animals were transcardially perfused for subsequent histological analyses. SBC transiently augmented cardiovascular function, as indicated by the increase in mean arterial pressure and heart rate during cooling. Significant improvement in motor functions were detected in SBC-treated polytrauma animals at 7, 10, and 21 days post-injury compared to the control group (p < 0.05). However, no significant beneficial effects were detected on cognitive measures following SBC treatment in the polytrauma animals. In addition, the blood serum and plasma levels of cytokines interleukin-1 and -10 were comparable between the two groups. Histological results also did not reveal any between-group differences in subacute neurodegeneration and astrocyte/ microglial activation. In summary, 4-h SBC delivered through extraluminal cooling of the common carotid arteries effectively ameliorated motor deficits induced by PBBI and polytrauma. Improving cognitive function or mitigating subacute neurodegeneration and neuroinflammation might require a different cooling regimen such as extended cooling, a slow rewarming period and a lower temperature.

Is there still a role for hypothermia in neurocritical care?

PURPOSE OF REVIEW

Therapeutic hypothermia (i.e. induced body core temperature ≈ 33-35°C) in neurological patients with cerebrovascular disease and traumatic brain injury is a controversially discussed issue in the literature. In this review, we have included the most recently published research covering the use of therapeutic hypothermia and targeted temperature management in neurologic diseases and translated the results into a clinical decision support for the professional healthcare community.

RECENT FINDINGS

Recent findings from large multicenter studies investigating therapeutic hypothermia in patients with various acute neurologic diseases have revealed that although short-term and long-term temperature modulation on different temperature levels is feasible with the latest device technology, the effect on outcome is controversial.

SUMMARY

There is overwhelming evidence that fever is an independent predictor of morbidity and mortality in patients with acute severe neurologic diseases. Although therapeutic hypothermia has been proven to be a potent neuroprotective measure acting on various levels in animal models, many questions such as optimal depth of target temperature, speed of rewarming, duration of cooling and management of side-effects accompanying therapeutic hypothermia are unresolved in human. Therefore, the application of therapeutic hypothermia outside of strictly supervised clinical trials must be carefully considered.

Dexmedetomidine attenuated early brain injury in rats with subarachnoid haemorrhage by suppressing the inflammatory response: The TLR4/NF-κB pathway and the NLRP3 inflammasome may be involved in the mechanism

Early brain injury (EBI) plays a pivotal role in the prognosis of patients with subarachnoid haemorrhage (SAH). Dexmedetomidine (DEX), a highly selective α₂ receptor agonist, is reported to exert multiple protective effects in many neurological diseases. This study was designed to investigate whether DEX had neuroprotective functions in EBI after SAH, and to explore the possible mechanisms. The SAH model was established by an endovascular perforation in adult male Sprague-Dawley (SD) rats. DEX (25 µg/kg) or vehicle was administered intraperitoneally 2 h after SAH. Neurological deficits, brain oedema, inflammation, BBB damage, and cell apoptosis at 24 h after SAH were evaluated. Additionally, the expression of components of the Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway, and the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome were also assessed. We demonstrated that DEX treatment improved neurological scores, alleviated brain oedema, reduced the permeability of the blood-brain barrier (BBB), and up-regulated the expression of tight junction proteins. DEX treatment could reduce the neutrophil infiltration, microglial activation, and pro-inflammatory factor release. In addition, DEX alleviated cell apoptosis at 24 h after SAH. Notably, DEX could also suppress the activation of the TLR4/NF-κB pathway and the NLRP3 inflammasome. These findings suggested that treatment with DEX after SAH attenuated SAH-induced EBI, partially through the suppression of the TLR4/NF-κB pathway and the NLRP3 inflammasome.

Treating childhood traumatic brain injury with autologous stem cell therapy

INTRODUCTION

Neonatal traumatic brain injury (TBI) is a significant cause of developmental disorders. Autologous stem cell therapy may enhance neonatal brain plasticity towards repair of the injured neonatal brain.

AREAS COVERED

The endogenous neonatal anti-inflammatory response can be enhanced through the delivery of anti-inflammatory agents. Stem cell therapy stands as a robust approach for sequestering the inflammation-induced cell death in the injured brain. Here, we discuss the use of umbilical cord blood cells and bone marrow stromal cells for acute and chronic treatment of experimental neonatal TBI. Autologous stem cell transplantation may dampen neuroinflammation. Clinical translation of this stem cell therapy will require identifying the therapeutic window post-injury and harvesting ample supply of transplantable autologous stem cells. Stem cell banking of cryopreserved cells may allow readily available transplantable cells and circumvent the unpredictable nature of neonatal TBI. Harnessing the anti-inflammatory properties of stem cells is key in combating the progressive neurodegeneration after the initial injury.

EXPERT OPINION

Combination treatments, such as with hypothermia, may enhance the therapeutic effects of stem cells. Stem cell therapy has immense potential as a stand-alone or adjunctive therapy for treating neuroinflammation associated with neonatal TBI acutely and for preventing further progression of the injury.

Neuroprotective assessment of prolonged local hypothermia post contusive spinal cord injury in rodent model

BACKGROUND CONTEXT

Although general hypothermia is recognized as a clinically applicable neuroprotective intervention, acute moderate local hypothermia post contusive spinal cord injury (SCI) is being considered a more effective approach. Previously, we have investigated the feasibility and safety of inducing prolonged local hypothermia in the central nervous system of a rodent model.

PURPOSE

Here, we aimed to verify the efficacy and neuroprotective effects of 5 and 8 hours of local moderate hypothermia (30±0.5°C) induced 2 hours after moderate thoracic contusive SCI in rats.

STUDY DESIGN

Rats were induced with moderate SCI (12.5 mm) at its T8 section. Local hypothermia (30±0.5°C) was induced 2 hours after injury induction with an M-shaped copper tube with flow of cold water (12°C), from the T6 to the T10 region. Experiment groups were divided into 5-hour and 8-hour hypothermia treatment groups, respectively, whereas the normothermia control group underwent no hypothermia treatment.

METHODS

The neuroprotective effects were assessed through objective weekly somatosensory evoked potential (SSEP) and motor behavior (basso, beattie and bresnahan Basso, Beattie and Bresnahan (BBB) scoring) monitoring. Histology on spinal cord was performed until at the end of day 56. All authors declared no conflict of interest. This work was supported by the Singapore Institute for Neurotechnology Seed Fund (R-175-000-121-733), National University of Singapore, Ministry of Education, Tier 1 (R-172-000-414-112.).

RESULTS

Our results show significant SSEP amplitudes recovery in local hypothermia groups starting from day 14 post-injury onward for the 8-hour treatment group, which persisted up to days 28 and 42, whereas the 5-hour group showed significant improvement only at day 42. The functional improvement plateaued after day 42 as compared with control group of SCI with normothermia. This was supported by both 5-hour and 8-hour improvement in locomotion as measured by BBB scores. Local hypothermia also observed insignificant changes in its SSEP latency, as compared with the control. In addition, 5- and 8-hour hypothermia rats' spinal cord showed higher percentage of parenchyma preservation.

CONCLUSIONS

Early local moderate hypothermia can be induced for extended periods of time post SCI in the rodent model. Such intervention improves functional electrophysiological outcome and motor behavior recovery for a long time, lasting until 8 weeks.

Hyperthermia and Mild Traumatic Brain Injury: Effects on Inflammation and the Cerebral Vasculature

Mild traumatic brain injury (mTBI) or concussion represents the majority of brain trauma in the United States. The pathophysiology of mTBI is complex and may include both focal and diffuse injury patterns. In addition to altered circuit dysfunction and traumatic axonal injury (TAI), chronic neuroinflammation has also been implicated in the pathophysiology of mTBI. Recently, our laboratory has reported the detrimental effects of mild hyperthermic mTBI in terms of worsening histopathological and behavioral outcomes. To clarify the role of temperature-sensitive neuroinflammatory processes on these consequences, we evaluated the effects of elevated brain temperature (39°C) on altered microglia/macrophage phenotype patterns after mTBI, changes in leukocyte recruitment, and TAI. Sprague-Dawley male rats underwent mild parasagittal fluid-percussion injury under normothermic (37°C) or hyperthermic (39°C) conditions. Cortical and hippocampal regions were analyzed using several cellular and molecular outcome measures. At 24 h, the ratio of iNOS-positive (M1 type phenotype) to arginase-positive (M2 type phenotype) cells after hyperthermic mTBI showed an increase compared with normothermia by flow cytometry. Inflammatory response gene arrays also demonstrated a significant increase in several classes of pro-inflammatory genes with hyperthermia treatment over normothermia. The injury-induced expression of chemokine ligand 2 (Ccl2) and alpha-2-macroglobulin were also increased with hyperthermic mTBI. With western blot analysis, an increase in CD18 and intercellular cell adhesion molecule-1 (ICAM-1) with hyperthermia and a significant increase in Iba1 reactive microglia are reported in the cerebral cortex. Together, these results demonstrate significant differences in the cellular and molecular consequences of raised brain temperature at the time of mTBI. The observed polarization toward a M1-phenotype with mild hyperthermia would be expected to augment chronic inflammatory cascades, sustained functional deficits, and increased vulnerability to secondary insults. Mild elevations in brain temperature may contribute to the more severe and longer lasting consequences of mTBI or concussion reported in some patients.

Traumatic brain injury: classification, models, and markers

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality worldwide. Due to its high incidence rate and often long-term sequelae, TBI contributes significantly to increasing costs of health care expenditures annually. Unfortunately, advances in the field have been stifled by patient and injury heterogeneity that pose a major challenge in TBI prevention, diagnosis, and treatment. In this review, we briefly discuss the causes of TBI, followed by its prevalence, classification, and pathophysiology. The current imaging detection methods and animal models used to study brain injury are examined. We discuss the potential use of molecular markers in detecting and monitoring the progression of TBI, with particular emphasis on microRNAs as a novel class of molecular modulators of injury and its repair in the neural tissue.

Dexmedetomidine attenuates traumatic brain injury: action pathway and mechanisms

Traumatic brain injury induces potent inflammatory responses that can exacerbate secondary blood-brain barrier (BBB) disruption, neuronal injury, and neurological dysfunction. Dexmedetomidine is a novel α2-adrenergic receptor agonist that exert protective effects in various central nervous system diseases. The present study was designed to investigate the neuroprotective action of dexmedetomidine in a mouse traumatic brain injury model, and to explore the possible mechanisms. Adult male C57BL/6J mice were subjected to controlled cortical impact. After injury, animals received 3 days of consecutive dexmedetomidine therapy (25 µg/kg per day). The modified neurological severity score was used to assess neurological deficits. The rotarod test was used to evaluate accurate motor coordination and balance. Immunofluorescence was used to determine expression of ionized calcium binding adapter molecule-1, myeloperoxidase, and zonula occluden-1 at the injury site. An enzyme linked immunosorbent assay was used to measure the concentration of interleukin-1β (IL-1β), tumor necrosis factor α, and IL-6. The dry-wet weight method was used to measure brain water content. The Evans blue dye extravasation assay was used to measure BBB disruption. Western blot assay was used to measure protein expression of nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3), caspase-1 p20, IL-1β, nuclear factor kappa B (NF-κB) p65, occluding, and zonula occluden-1. Flow cytometry was used to measure cellular apoptosis. Results showed that dexmedetomidine treatment attenuated early neurological dysfunction and brain edema. Further, dexmedetomidine attenuated post-traumatic inflammation, up-regulated tight junction protein expression, and reduced secondary BBB damage and apoptosis. These protective effects were accompanied by down-regulation of the NF-κB and NLRP3 inflammasome pathways. These findings suggest that dexmedetomidine exhibits neuroprotective effects against acute (3 days) post-traumatic inflammatory responses, potentially via suppression of NF-κB and NLRP3 inflammasome activation.

Pathophysiological Bases of Comorbidity: Traumatic Brain Injury and Post-Traumatic Stress Disorder

The high rates of traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) diagnoses encountered in recent years by the United States Veterans Affairs Healthcare System have increased public awareness and research investigation into these conditions. In this review, we analyze the neural mechanisms underlying the TBI/PTSD comorbidity. TBI and PTSD present with common neuropsychiatric symptoms including anxiety, irritability, insomnia, personality changes, and memory problems, and this overlap complicates diagnostic differentiation. Interestingly, both TBI and PTSD can be produced by overlapping pathophysiological changes that disrupt neural connections termed the "connectome." The neural disruptions shared by PTSD and TBI and the comorbid condition include asymmetrical white matter tract abnormalities and gray matter changes in the basolateral amygdala, hippocampus, and prefrontal cortex. These neural circuitry dysfunctions result in behavioral changes that include executive function and memory impairments, fear retention, fear extinction deficiencies, and other disturbances. Pathophysiological etiologies can be identified using experimental models of TBI, such as fluid percussion or blast injuries, and for PTSD, using models of fear conditioning, retention, and extinction. In both TBI and PTSD, there are discernible signs of neuroinflammation, excitotoxicity, and oxidative damage. These disturbances produce neuronal death and degeneration, axonal injury, and dendritic spine dysregulation and changes in neuronal morphology. In laboratory studies, various forms of pharmacological or psychological treatments are capable of reversing these detrimental processes and promoting axonal repair, dendritic remodeling, and neurocircuitry reorganization, resulting in behavioral and cognitive functional enhancements. Based on these mechanisms, novel neurorestorative therapeutics using anti-inflammatory, antioxidant, and anticonvulsant agents may promote better outcomes for comorbid TBI and PTSD.

Brain metabolism and severe pediatric traumatic brain injury

Age-dependent changes in brain metabolism may influence the response to and tolerance of secondary insults, potentially affecting outcomes. More complete characterization of brain metabolism across the clinical trajectory of severe pediatric TBI is needed to improve our ability to measure and better mitigate the impact of secondary insults. Better management of secondary insults will impact clinical care and the probability of success of future neuroprotective clinical trials. Improved bedside monitoring and imaging technologies will be required to achieve these goals. Effective and sustained integration of brain metabolism information into the pediatric critical care setting will be equally challenging and important.

Posttraumatic therapeutic hypothermia alters microglial and macrophage polarization toward a beneficial phenotype

Posttraumatic inflammatory processes contribute to pathological and reparative processes observed after traumatic brain injury (TBI). Recent findings have emphasized that these divergent effects result from subsets of proinflammatory (M1) or anti-inflammatory (M2) microglia and macrophages. Therapeutic hypothermia has been tested in preclinical and clinical models of TBI to limit secondary injury mechanisms including proinflammatory processes. This study evaluated the effects of posttraumatic hypothermia (PTH) on phenotype patterns of microglia/macrophages. Sprague-Dawley rats underwent moderate fluid percussion brain injury with normothermia (37℃) or hypothermia (33℃). Cortical and hippocampal regions were analyzed using flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR) at several periods after injury. Compared to normothermia, PTH attenuated infiltrating cortical macrophages positive for CD11b⁺ and CD45^high. At 24 h, the ratio of iNOS⁺ (M1) to arginase⁺ (M2) cells after hypothermia showed a decrease compared to normothermia. RT-PCR of M1-associated genes including iNOS and IL-1β was significantly reduced with hypothermia while M2-associated genes including arginase and CD163 were significantly increased compared to normothermic conditions. The injury-induced increased expression of the chemokine Ccl2 was also reduced with PTH. These studies provide a link between temperature-sensitive alterations in macrophage/microglia activation and polarization toward a M2 phenotype that could be permissive for cell survival and repair.

Traumatic Brain Injury: Current Treatment Strategies and Future Endeavors

Traumatic brain injury (TBI) presents in various forms ranging from mild alterations of consciousness to an unrelenting comatose state and death. In the most severe form of TBI, the entirety of the brain is affected by a diffuse type of injury and swelling. Treatment modalities vary extensively based on the severity of the injury and range from daily cognitive therapy sessions to radical surgery such as bilateral decompressive craniectomies. Guidelines have been set forth regarding the optimal management of TBI, but they must be taken in context of the situation and cannot be used in every individual circumstance. In this review article, we have summarized the current status of treatment for TBI in both clinical practice and basic research. We have put forth a brief overview of the various subtypes of traumatic injuries, optimal medical management, and both the noninvasive and invasive monitoring modalities, in addition to the surgical interventions necessary in particular instances. We have overviewed the main achievements in searching for therapeutic strategies of TBI in basic science. We have also discussed the future direction for developing TBI treatment from an experimental perspective.

Traumatic Brain Injury Advances

There have been many recent advances in the management of traumatic brain injury (TBI). Research regarding established and novel therapies is ongoing. Future research must not only focus on development of new strategies but determine the long-term benefits or disadvantages of current strategies. In addition, the impact of these advances on varying severities of brain injury must not be ignored. It is hoped that future research strategies in TBI will prioritize large-scale trials using common data elements to develop large registries and databases, and leverage international collaborations.