Hypothermic Neuroprotection Research Articles

Deleterious Effect of Crossfostering in Rat Pups on Hypoxic-Ischaemic Injury Tolerance and Hypothermic Neuroprotection

We study the effect of hypothermia (HT) following hypoxic-ischaemic (HI) brain injury in postnatal day 7 (P7) rats. In 2015, new European Union animal transport regulations prompted a change in practice at the breeding facility, which henceforth crossfostered P3 litters to P8 older lactating dams prior to transportation. It is generally assumed that crossfostering does not significantly affect the experimental results. The aim of this study was to examine whether crossfostering affects our model consistency by modifying injury susceptibility and hypothermic neuroprotection. We analysed 219 pups from 11 experiments conducted between 2013 and 2015: 73 non-crossfostered and 146 crossfostered pups. At P7, all pups underwent unilateral common carotid artery ligation followed by 50 min of hypoxia (8% O₂, 36°C). Immediately after this mild insult, the pups were randomized to post-insult normothermia or HT treatment. Pups were culled at P14. Injury was assessed by area loss of the ipsilateral hemisphere and histopathology scoring of the hippocampus, cortex, thalamus, and basal ganglia. Crossfostered pups had double the injury compared to non-crossfostered pups irrespective of the treatment group. Hypothermic neuroprotection was statistically significant, but with a smaller and less consistent effect in crossfostered pups (relative neuroprotection 16% vs. 31% in non-crossfostered). These results demonstrate hypothermic neuroprotection following a mild HI insult. A representative subset of 41 animals was also assessed for evidence of microglial reactivity; however, no detectable difference in microglial reactivity was observed between any of the groups. In conclusion, crossfostering alters outcomes in our established model through reduced insult tolerance and variable neuroprotection. Crossfostering as a common breeding practice is a largely unexplored variable in animal research that may result in invalid research conclusions if inadequately adjusted for by larger group sizes. As a result, crossfostering is likely to be inconsistent with the principles of replacement, reduction, and refinement.

Hybernia post-mechanical thrombectomy – Endovascular cerebral hypothermia trial in acute ischemic stroke (post-mtech trial)

Although significant clinical improvement is achieved with mechanical thrombectomy (MT) in large vessel occlusion (LVO) stroke patients, <1/4 patients have outcomes comparable to their baseline (pre-stroke) conditions. Therapeutic hypothermia is a promising method for acute neuroprotection, with multiple beneficial mechanisms, for which a reduction of brain temperature by several °C is required. Systemic hypothermia has been difficult to implement in stroke patients due to the long delay to reach target temperature, complications related to physiological counter-mechanisms to cold, and adverse events associated with whole body cooling. In contrast, targeted brain cooling may provide effective hypothermic neuroprotection, because 1) of more rapid brain cooling (minutes) and 2) it is safer (avoids systemic cooling).

The evolution of hypothermia for neuroprotection after cardiac arrest: a history in the making.

While much has been observed regarding hypothermia by way of environmental exposure, it is modern day medicine that deployed hypothermia as a therapeutic. From the early 1930s, when Temple Fay deployed "refrigeration" to treat pain, to the work of Wilfred Bigelow and Charles Drew, who utilized hypothermia in open heart surgery-the opportunities seemed endless. However, questions arose surrounding appropriate temperatures to achieve best outcomes and how to minimize adverse events, such as coagulopathy and infection. In the 1980s, hypothermia underwent a resurgence through Peter Safar's critical studies in large animals, which quickly translated into feasibility studies and the landmark trials of 2002 that paved the way for postcardiac arrest care as we currently know it. Through clinical and observational trials, modern-day targeted temperature management continues to adapt, striving to improve patient outcomes. While hypothermia has come a long way from the writings of Hippocrates, the ideal therapy has not yet been defined, and more work is needed. While the history is long, there is more to be written and advances to be achieved as we optimize the neuroprotective effects of hypothermia for comatose survivors of cardiac arrest.

Ischemic hypoxic encephalopathy: The role of MRI of neonatal injury and medico-legal implication

Hypoxic ischemic encephalopathy is one of the major causes of neonatal death and neurological disability in the child, and represents the most common birth injury claim. Intrapartum asphyxia often leads to several long-term sequalae, such as cerebral palsy and/or developmental delay, epilepsy. Through the neuroimaging it’s possible to identify and define the different lesioned pictures and provide useful elements to establish the moment in which the damage occurred; indeed, timing of injury is a key element in the legal arena. Magnetic resonance imaging (MRI) is emerging as one of the most important tools in identifying the etiologic of neonatal encephalopathy as well as in predicting long-term outcomes.The aim of this study is to evaluate all MRI tests performed in a group of infants and young patients with possible neonatal encephalopathy, in order to determine the role of MRI in perinatal hypoxic-ischemic damage and the specific patterns that can point towards a diagnosis of the time of the damage’s onset. Another goal is to assess the role of MRI in cases subject to legal-medical ligation. Since the advent of hypothermic neuroprotection, new malpractice allegations have arisen, including the failure to initiate cooling in a timely manner. In all cases, documentation of the status of the baby at birth, including a thorough neurologic exam, can be extremely helpful to the later defence of a malpractice claim, which might occur years later.

An exploratory assessment of serum biomarkers of post-cardiac arrest syndrome in children

AimWe hypothesized that serum biomarkers of inflammation including chemokine, cytokine, pituitary hormones, and growth factors following cardiac arrest in children would independently associate with 6-month neurologic outcome. MethodsIn this prospective observational single center study of children with in-hospital and out-of-hospital cardiac arrest surviving to intensive care unit admission, serum was obtained twice per 24 h period between 0 h and 96 h and once at approximately 196 h post-cardiac arrest. Inflammatory mediators, hormones, and growth factors were analyzed by Luminex Multiplex Bead Immunoassay. We recorded demographics, resuscitation characteristics, and Pediatric Cerebral Performance Category (PCPC) at 6 months. We analyzed the association and area under the curve (AUC) of biomarker levels with favorable (PCPC 1–3) or unfavorable (PCPC 4–6, or >1 increase from baseline) outcome. ResultsForty-two children (50% female; median age of 2.5 [IQR: 0.4–10.2]) were enrolled and 18 (42%) died prior to 6-month follow up. Receiver operator curves for initial levels of ciliary neurotrophic factor (CNTF, AUC 0.84, 95% CI 0.73–0.96, p < 0.001) and interleukin (IL-17, AUC 0.84, 95% CI 0.73–0.97, p < 0.001) best classified favorable versus unfavorable 6-month outcome. In multivariable analysis, initial levels of CNTF and IL-17 remained associated with 6-month PCPC. Peak levels of interferon-γ-inducible protein 10 (IP-10), CNTF, and hepatocyte growth factor (HGF) were also independently associated with outcome. ConclusionIncreased serum concentrations of CNTF and IL-17 associated with unfavorable 6-month neurologic outcome of children surviving cardiac arrest. Further investigation of the prognostic utility and roles of CNTF and IL-17 in the pathophysiology of post-cardiac arrest syndrome are warranted.This project is registered with clinicaltrials.gov (NCT00797680) as “Duration of Hypothermia for Neuroprotection after Pediatric Cardiac Arrest: A Randomized, Controlled Trial”.

Unanswered questions regarding therapeutic hypothermia for neonates with neonatal encephalopathy

Therapeutic hypothermia (TH) is now well established to improve intact survival after neonatal encephalopathy (NE). However, many questions could not be addressed by the randomized controlled trials. Should late preterm newborns with NE be cooled? Is cooling beneficial for mild NE? Is the current therapeutic time window optimal, or could it be shortened or prolonged? Will either milder or deeper hypothermia be effective? Does infection/inflammation exposure in the perinatal period in combination with NE offer potentially beneficial preconditioning or might it obviate hypothermic neuroprotection? In the present review, we dissect the evidence, for whom, when and how can TH best be delivered, and highlight areas that need further research.

NAC and Vitamin D Restore CNS Glutathione in Endotoxin-Sensitized Neonatal Hypoxic-Ischemic Rats.

Therapeutic hypothermia does not improve outcomes in neonatal hypoxia ischemia (HI) complicated by perinatal infection, due to well-described, pre-existing oxidative stress and neuroinflammation that shorten the therapeutic window. For effective neuroprotection post-injury, we must first define and then target CNS metabolomic changes immediately after endotoxin-sensitized HI (LPS-HI). We hypothesized that LPS-HI would acutely deplete reduced glutathione (GSH), indicating overwhelming oxidative stress in spite of hypothermia treatment in neonatal rats. Post-natal day 7 rats were randomized to sham ligation, or severe LPS-HI (0.5 mg/kg 4 h before right carotid artery ligation, 90 min 8% O2), followed by hypothermia alone or with N-acetylcysteine (25 mg/kg) and vitamin D (1,25(OH)2D3, 0.05 μg/kg) (NVD). We quantified in vivo CNS metabolites by serial 7T MR Spectroscopy before, immediately after LPS-HI, and after treatment, along with terminal plasma drug concentrations. GSH was significantly decreased in all LPS-HI rats compared with baseline and sham controls. Two hours of hypothermia alone did not improve GSH and allowed glutamate + glutamine (GLX) to increase. Within 1 h of administration, NVD increased GSH close to baseline and suppressed GLX. The combination of NVD with hypothermia rapidly improved cellular redox status after LPS-HI, potentially inhibiting important secondary injury cascades and allowing more time for hypothermic neuroprotection.

Neuroprotective Effects of Early Hypothermia Induced by Phenothiazines and DHC in Ischemic Stroke.

Methods Adult male Sprague Dawley rats were studied in 4 groups: (1) sham; (2) stroke; (3) stroke treated with pharmacological hypothermia before reperfusion (interischemia hypothermia); and (4) stroke treated with pharmacological hypothermia after reperfusion is initiated (inter-reperfusion hypothermia). The combination of chlorpromazine and promethazine with dihydrocapsaicin (DHC) was used to induce hypothermia. To compare the neuroprotective effects of drug-induced hypothermia between the interischemia and inter-reperfusion groups, brain damage was evaluated using infarct volume and neurological deficits at 24 h reperfusion. In addition, mRNA expressions of NADPH oxidase (NOX) subunits (gp91phox, p67phox, p47phox, and p22phox) and glucose transporter subtypes (GLUT1 and GLUT3) were determined by real-time PCR at 6 and 24 h reperfusion. ROS production was measured by flow cytometry assay at the same time points. Results In both hypothermia groups, the cerebral infarct volumes and neurological deficits were reduced in the ischemic rats. At 6 and 24 h reperfusion, ROS production and the expressions of NOX subunits and glucose transporter subtypes were also significantly reduced in both hypothermia groups as compared to the ischemic group. While there were no statistically significant differences between the two hypothermia groups at 6 h reperfusion, brain damage was significantly further decreased by interischemia hypothermia at 24 h. Conclusion Both interischemia and inter-reperfusion pharmacological hypothermia treatments play a role in neuroprotection after stroke. Interischemia hypothermia treatment may be better able to induce stronger neuroprotection after ischemic stroke. This study provides a new avenue and reference for stronger neuroprotective hypothermia before vascular recanalization in stroke patients.

Expression regulation of cold-inducible protein RBM3 by FAK/Src signaling for neuroprotection against rotenone under mild hypothermia

Mild hypothermia is a well-established technique for alleviating neurological injuries in clinical surgery. RNA-binding protein motif 3 (RBM3) has been identified as a crucial factor in mediating hypothermic neuroprotection, providing its induction as a promising strategy for mimicking therapeutic hypothermia. However, little is known about molecular control of RBM3 and signaling pathways affected by hypothermia. In the present study, human SH-SY5Y neuroblastoma cells were used as a neural cell model. Screening of signaling pathways showed that cold exposure led to inactivation of ERK and AMPK pathways, and activation of FAK and PLCγ pathways, with activities of p38, JNK and AKT pathways moderately changed. Next, various small molecule inhibitors specific to these signaling pathways were applied. Interestingly, only FAK-specific inhibitor exhibited a significant inhibitory effect on hypothermia-induced RBM3 gene transcription and protein expression. Likewise, FAK silencing using siRNA technique significantly abrogated the induction of RBM3 by hypothermia. Moreover, FAK inhibition accounted for an inactivation of Src, a known kinase downstream of FAK. Next, either the silencing of Src by siRNA or its inactivation by a chemical inhibitor, strongly blocked the induction of RBM3 by cooling. Notably, in HEK293 and PC12 cells, FAK/Src activation was also shown to be indispensable for hypothermia-stimulated RBM3 expression. Lastly, the CCK8 and Western blot assays showed that both FAK/Src inacitivation and their knockdown substantially abrogate the neuroprotective effects of mild hypothermia against rotenone in SH-SY5Y cells. These data suggest that FAK/Src signaling axis regulates the transcription of Rbm3 gene and mediates neuroprotective effects of mild hypothermia.

Combination treatments with therapeutic hypothermia for hypoxic‐ischemic neuroprotection

Therapeutic hypothermia is now proven to reduce death or disability in term and near-term born infants with moderate to severe hypoxic-ischemic encephalopathy. Nevertheless, many infants still survive with disability, despite treatment with hypothermia. Recent preclinical and clinical studies suggest that current protocols for therapeutic hypothermia are near-optimal. The obvious strategy, in addition to improving early initiation of therapeutic hypothermia after birth, is to combine hypothermia with other neuroprotective agents. We review evidence that the mechanisms of action of many promising agents overlap with the anti-excitotoxic, anti-apoptotic, and anti-inflammatory mechanisms of hypothermia, leading to a lack of benefit from combination treatment. Moreover, even apparently beneficial combinations have failed to translate in clinical trials. These considerations highlight the need for preclinical studies to test clinically realistic protocols of timing and duration of treatment, before committing to large randomized controlled trials.

Variability and sex-dependence of hypothermic neuroprotection in a rat model of neonatal hypoxic\u2013ischaemic brain injury: a single laboratory meta-analysis

Therapeutic hypothermia (HT) is standard care for term infants with hypoxic–ischaemic (HI) encephalopathy. However, the efficacy of HT in preclinical models, such as the Vannucci model of unilateral HI in the newborn rat, is often greater than that reported from clinical trials. Here, we report a meta-analysis of data from every experiment in a single laboratory, including pilot data, examining the effect of HT in the Vannucci model.Across 21 experiments using 106 litters, median (95% CI) hemispheric area loss was 50.1% (46.0–51.9%; n = 305) in the normothermia group, and 41.3% (35.1–44.9%; n = 317) in the HT group, with a bimodal injury distribution. Median neuroprotection by HT was 17.6% (6.8–28.3%), including in severe injury, but was highly-variable across experiments. Neuroprotection was significant in females (p < 0.001), with a non-significant benefit in males (p = 0.07). Animals representing the median injury in each group within each litter (n = 277, 44.5%) were also analysed using formal neuropathology, which showed neuroprotection by HT throughout the brain, particularly in females. Our results suggest an inherent variability and sex-dependence of the neuroprotective response to HT, with the majority of studies in the Vannucci model vastly underpowered to detect true treatment effects due to the distribution of injury.

Effect of Hypothermia by JZL-184 on Muscle Strength and Sensory-Motor Dysfunction in Permanent Middle Cerebral Artery Ischemia Model in Male Mice

Introduction: Currently, there is no effective and comprehensive treatment for ischemic stroke. There is strong clinical evidence for the benefits of hypothermia in neuroprotection. Therefore, the present study aimed to determine the effect of mild non-invasive hypothermia by JZL-184 on behavioral improvement in stroke rats. Methods: This study was performed on 5 groups of male mice weighing 25-30 g. The groups were as follows: 1- Healthy group 2- Control group (Stroke) 3- Stroke + DMSO solvent 4- Stroke + Aspirin (40mg /kg) 5- Stroke + JZL-184 (16mg / kg) (n = 8 per group). The drugs were injected intraperitoneally immediately after the stroke. At the times before (time zero) and at 5, 24 and 48 h after stroke induction, body temperature, behavioral testing, including muscle strength and sensory-motor dysfunction were measured. Data were analyzed by SPSS version 18 software and Two-way ANOVA test (P ≤ 0.05). Results: JZL-184 decreased body temperature at 5, 24 and 48 hours compared to intact and control groups (p &lt;0.001). Injection JZL-184 and Aspirin improved muscle strength and sensory-motor function (p &lt;0.001) compared to the control group. Aspirin also improved behavioral tests compared to the control group (p &lt;0.01), but did not show any effect on the body temperature compared to the intact group at time 48. Only in JZL-184 group, the behavioral tests score was similar to the intact group at the 48 h after stroke. Conclusion: JZL-184 may have been able to improve neuronal function by hypothermia induced by the agonist effects of cannabinoid receptor 1 (CB1), thereby improving muscle strength and sensory-motor function after cerebral ischemia.

Cooling and immunomodulation for treating hypoxic-ischemic brain injury.

Therapeutic hypothermia is now well established to partially reduce disability in term and near-term infants with moderate-severe hypoxic-ischemic encephalopathy. Preclinical and clinical studies have confirmed that current protocols for therapeutic hypothermia are near optimal. The challenge is now to identify complementary therapies that can further improve outcomes, in combination with therapeutic hypothermia. Overall, anti-excitatory and anti-apoptotic agents have shown variable or even no benefit in combination with hypothermia, suggesting overlapping mechanisms of neuroprotection. Inflammation appears to play a critical role in the pathogenesis of injury in the neonatal brain, and thus, there is potential for drugs with immunomodulatory properties that target inflammation to be used as a therapy in neonates. In this review, we examine the evidence for neuroprotection with immunomodulation after hypoxia-ischemia. For example, stemcell therapy can reduce inflammation, increase cell survival, and promote cell maturation and repair. There are also encouraging preclinical data from small animals suggesting that stemcell therapy can augment hypothermic neuroprotection. However, there is conflicting evidence, and rigorous testing in translational animal models is now needed.

Insightful Backbone Modifications Preventing Proteolytic Degradation of Neurotensin Analogs Improve NTS1-Induced Protective Hypothermia.

Therapeutic hypothermia represents a brain-protective strategy for multiple emergency situations, such as stroke or traumatic injury. Neurotensin (NT), which exerts its effects through activation of two G protein-coupled receptors, namely NTS1 and NTS2, induces a strong and long-lasting decrease in core body temperature after its central administration. Growing evidence demonstrates that NTS1 is the receptor subtype mediating the hypothermic action of NT. As such, potent NTS1 agonists designed on the basis of the minimal C-terminal NT(8-13) bioactive fragment have been shown to produce mild hypothermia and exert neuroprotective effects under various clinically relevant conditions. The high susceptibility of NT(8-13) to protease degradation (half-life <2 min) represents, however, a serious limitation for its use in pharmacological therapy. In light of this, we report here a structure-activity relationship study in which pairs of NT(8-13) analogs have been developed, based on the incorporation of a reduced Lys8-Lys9 bond. To further stabilize the peptide bonds, a panel of backbone modifications was also inserted along the peptide sequence, including Sip10, D-Trp11, Dmt11, Tle12, and TMSAla13. Our results revealed that the combination of appropriate chemical modifications leads to compounds exhibiting improved resistance to proteolytic cleavages (>24 h; 16). Among them, the NT(8-13) analogs harboring the reduced amine bond combined with the unnatural amino acids TMSAla13 (4) and Sip10 (6) or the di-substitution Lys11 - TMSAla13 (12), D-Trp11-TMSAla13 (14), and Dmt11-Tle12 (16) produced sustained hypothermic effects (−3°C for at least 1 h). Importantly, we observed that hypothermia was mainly driven by the increased stability of the NT(8-13) derivatives, instead of the high binding-affinity at NTS1. Altogether, these results reveal the importance of the reduced amine bond in optimizing the metabolic properties of the NT(8-13) peptide and support the development of stable NTS1 agonists as first drug candidate in neuroprotective hypothermia.

High-Dose Melatonin and Ethanol Excipient Combined with Therapeutic Hypothermia in a Newborn Piglet Asphyxia Model

With the current practice of therapeutic hypothermia for neonatal encephalopathy, disability rates and the severity spectrum of cerebral palsy are reduced. Nevertheless, safe and effective adjunct therapies are needed to optimize outcomes. This study’s objective was to assess if 18 mg/kg melatonin given rapidly over 2 h at 1 h after hypoxia-ischemia with cooling from 1–13 h was safe, achieved therapeutic levels within 3 h and augmented hypothermic neuroprotection. Following hypoxia-ischemia, 20 newborn piglets were randomized to: (i) Cooling 1–13 h (HT; n = 6); (ii) HT+ 2.5% ethanol vehicle (HT+V; n = 7); (iii) HT + Melatonin (HT+M; n = 7). Intensive care was maintained for 48 h; aEEG was acquired throughout, brain MRS acquired at 24 and 48 h and cell death (TUNEL) evaluated at 48 h. There were no differences for insult severity. Core temperature was higher in HT group for first hour after HI. Comparing HT+M to HT, aEEG scores recovered more quickly by 19 h (p < 0.05); comparing HT+V to HT, aEEG recovered from 31 h (p < 0.05). Brain phosphocreatine/inorganic phosphate and NTP/exchangeable phosphate were higher at 48 h in HT+M versus HT (p = 0.036, p = 0.049 respectively). Including both 24 h and 48 h measurements, the rise in Lactate/N-acetyl aspartate was reduced in white (p = 0.030) and grey matter (p = 0.038) after HI. Reduced overall TUNEL positive cells were observed in HT+M (47.1 cells/mm2) compared to HT (123.8 cells/mm2) (p = 0.0003) and HT+V (97.5 cells/mm2) compared to HT (p = 0.012). Localized protection was seen in white matter for HT+M versus HT (p = 0.036) and internal capsule for HT+M compared to HT (p = 0.001) and HT+V versus HT (p = 0.006). Therapeutic melatonin levels (15–30mg/l) were achieved at 2 h and were neuroprotective following HI, but ethanol vehicle was partially protective.

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.

Cold-inducible protein RBM3 mediates hypothermic neuroprotection against neurotoxin rotenone via inhibition on MAPK signalling.

Mild hypothermia and its key product, cold‐inducible protein RBM3, possess robust neuroprotective effects against various neurotoxins. However, we previously showed that mild hypothermia fails to attenuate the neurotoxicity from MPP+, one of typical neurotoxins related to the increasing risk of Parkinson disease (PD). To better understand the role of mild hypothermia and RBM3 in PD progression, another known PD‐related neurotoxin, rotenone (ROT) was utilized in this study. Using immunoblotting, cell viability assays and TUNEL staining, we revealed that mild hypothermia (32°C) significantly reduced the apoptosis induced by ROT in human neuroblastoma SH‐SY5Y cells, when compared to normothermia (37°C). Meanwhile, the overexpression of RBM3 in SH‐SY5Y cells mimicked the neuroprotective effects of mild hypothermia on ROT‐induced cytotoxicity. Upon ROT stimulation, MAPK signalling like p38, JNK and ERK, and AMPK and GSK‐3β signalling were activated. When RBM3 was overexpressed, only the activation of p38, JNK and ERK signalling was inhibited, leaving AMPK and GSK‐3β signalling unaffected. Similarly, mild hypothermia also inhibited the activation of MAPKs induced by ROT. Lastly, it was demonstrated that the MAPK (especially p38 and ERK) inhibition by their individual inhibitors significantly decreased the neurotoxicity of ROT in SH‐SY5Y cells. In conclusion, these data demonstrate that RBM3 mediates mild hypothermia‐related neuroprotection against ROT by inhibiting the MAPK signalling of p38, JNK and ERK.

Hypothermic neuroprotection during reperfusion following exposure to aglycemia in central white matter is mediated by acidification.

Hypoglycemia is a common iatrogenic consequence of type 1 diabetes therapy that can lead to central nervous system injury and even death if untreated. In the absence of clinically effective neuroprotective drugs we sought to quantify the putative neuroprotective effects of imposing hypothermia during the reperfusion phase following aglycemic exposure to central white matter. Mouse optic nerves (MONs), central white matter tracts, were superfused with oxygenated artificial cerebrospinal fluid (aCSF) containing 10 mmol/L glucose at 37°C. The supramaximal compound action potential (CAP) was evoked and axon conduction was assessed as the CAP area. Extracellular lactate was measured using an enzyme biosensor. Exposure to aglycemia, simulated by omitting glucose from the aCSF, resulted in axon injury, quantified by electrophysiological recordings, electron microscopic analysis confirming axon damage, the extent of which was determined by the duration of aglycemia exposure. Hypothermia attenuated injury. Exposing MONs to hypothermia during reperfusion resulted in improved CAP recovery compared with control recovery measured at 37°C, an effect attenuated in alkaline aCSF. Hypothermia decreases pH implying that the hypothermic neuroprotection derives from interstitial acidification. These results have important clinical implications demonstrating that hypothermic intervention during reperfusion can improve recovery in central white matter following aglycemia.

The Therapeutic Hypothermia in Treatment of Hyperammonemic Encephalopathy due to Urea Cycle Disorders and Organic Acidemias.

Hyperammonemic encephalopathy in newborns with urea cycle disorders and certain organic acidurias can cause severe brain injury, coma and death. Standard therapy includes protein restriction, nitrogen-scavenging drugs, prevention of catabolism and hemodialysis. Neuroprotective hypothermia as part of the treatment has been reported only 3 times. It has been suggested that mild systemic hypothermia can contribute to better neurological outcomes in hyperammonemic encephalopathy. However, the limited experience precludes accurate conclusions on safety and efficacy. Whole body therapeutic hypothermia was included in the standard treatment of hyperammonemic encephalopathy in 4 neonates with urea cycle disorder or organic aciduria. Two patients survived the initial crisis. One patient has a developmental quotient of 0.8, while the other shows severe developmental delay. The cooling protocol had to be discontinued in 3 patients due to the otherwise untreatable complications (hypotension and hemorrhage). The efficacy and safety of therapeutic hypothermia in the treatment of neonatal hyperammonemic encephalopathy depend on various factors, requiring further evaluation.

Therapeutic Hypothermia in Neonatal Hypoxic-Ischemic Encephalopathy.

Therapeutic hypothermia reduces death or disability in term and near-term infants with moderate-severe hypoxic-ischemic encephalopathy. Nevertheless, many infants still survive with disability, despite hypothermia, supporting further research in to ways to further improve neurologic outcomes. Recent clinical and experimental studies have refined our understanding of the key parameters for hypothermic neuroprotection, including timing of initiation, depth, and duration of hypothermia, and subsequent rewarming rate. However, important knowledge gaps remain. There is encouraging clinical evidence from a small phase II trial that combined treatment of hypothermia with recombinant erythropoietin further reduces risk of disability but definitive studies are still needed. In conclusion, recent studies suggest that current protocols for therapeutic hypothermia are near-optimal, and that the key to better neurodevelopmental outcomes is earlier diagnosis and initiation of hypothermia after birth. Further research is essential to find and evaluate ways to further improve outcomes after hypoxic-ischemic encephalopathy, including add-on therapies for therapeutic hypothermia and preventing pyrexia during labor and delivery.