Mild hypothermia protects hippocampal neurons from oxygen-glucose deprivation injury through inhibiting caspase-3 activation

Noninvasive Targeted Temperature Management of the Inner Ear: Numerical Simulations and Experimental Measurements in a Human Cadaver Model

HYPOTHESIS

Mild therapeutic hypothermia (MTH) could be delivered to the human inner ear using a localized, noninvasive approach to achieve protective temperature reductions without systemic side effects.

BACKGROUND

MTH has demonstrated protective effects in the cochlea following injuries such as device implantation, ototoxicity, and noise overexposure. It targets key cellular mechanisms, including proinflammatory pathways, oxidative stress, pyroptosis, and apoptosis. However, systemic and invasive methods for MTH carry risks and are less practical for broader clinical applications. Developing a localized, noninvasive approach could offer a safer, more accessible solution for hearing preservation after cochlear injury.

METHODS

Cadaveric middle and inner ear structures, maintained near physiological conditions, were used to test a custom-designed cooling gel pack (ReBound) placed externally on the temporal bone. Temperature changes were recorded over 60 or 30 minutes. To complement experimental findings, three-dimensional geometrical models were created from imaging data, and finite element heat transfer analysis simulated temperature changes across inner ear structures.

RESULTS

With external gel pack application, inner ear temperatures dropped by 2.9°C within 30 minutes and 4.6°C within 60 minutes. Cooling persisted for 10 minutes post-device removal. Numerical modeling corroborated these findings, indicating average temperature reductions of 2°C to 4°C. Biological sex differences were observed in cooling efficiency and overall temperature drop.

CONCLUSION

This study demonstrates that localized, noninvasive MTH can effectively reduce inner ear temperatures to therapeutically relevant levels. These findings support a promising, clinically translatable approach for protecting cochlear structure and function after injury, with minimal systemic risks.

Mild hypothermia alleviates oxygen−glucose deprivation/reperfusion-induced apoptosis by inhibiting ROS generation, improving mitochondrial dysfunction and regulating DNA damage repair pathway in PC12 cells

The brain ischemia/reperfusion (I/R) injury has a great impact on human life and property safety. As far as we know, mild hypothermia (MH) is an effective measure to reduce neuronal injury after I/R. However, the precise mechanism is not extremely clear. The purpose of this study was to investigate whether mild therapeutic hypothermia can play a protective role in nerve cells dealing with brain I/R injury and explore its specific mechanism in vitro. A flow cytometer, cell counting kit-8 (CCK-8) assay and lactate dehydrogenase (LDH) release assay were performed to detect apoptotic rate of cells, cell viability and cytotoxicity, respectively, reactive oxygen species (ROS) assay kit, JC-1 fluorescent methods, immunofluorescence and western blot were used to explore ROS, mitochondrial transmembrane potential (^Δψm), mitochondrial permeability transition pore (MPTP) and protein expression, respectively. The result indicated that the cell activity was decreased, while the cytotoxicity and apoptosis rate were increased after treating with oxygen-glucose deprivation/reperfusion (OGD/R) in PC12 cells. However, MH could antagonize this phenomenon. Interestingly, treating with OGD/R increased the release of ROS and the transfer of Cytochrome C (Cyt-C) from mitochondria to cytoplasm. In addition, it up-regulated the expression of γH2AX, Bax and Clv-caspase3, down-regulated the expression of PCNA, Rad51 and Bcl-2, and inhibited the function of mitochondria in PC12 cells. Excitingly, the opposite trend was observed after MH treatment. Therefore, our results suggest that MH protects PC12 cells against OGD/R-induced injury with the mechanism of inhibiting cell apoptosis by reducing ROS production, improving mitochondrial function, reducing DNA damage, and enhancing DNA repair.

Preventing Brain Damage from Hypoxic-Ischemic Encephalopathy in Neonates: Update on Mesenchymal Stromal Cells and Umbilical Cord Blood Cells

Neonatal hypoxic-ischemic encephalopathy (HIE) causes permanent motor deficit "cerebral palsy (CP)," and may result in significant disability and death. Therapeutic hypothermia (TH) had been established as the first effective therapy for neonates with HIE; however, TH must be initiated within the first 6 hours after birth, and the number needed to treat is from 9 to 11 to prevent brain damage from HIE. Therefore, additional therapies for HIE are highly needed. In this review, we provide an introduction on the mechanisms of HIE cascade and how TH and cell therapies such as umbilical cord blood cells and mesenchymal stromal cells (MSCs), especially umbilical cord-derived MSCs (UC-MSCs), may protect the brain in newborns, and discuss recent progress in regenerative therapies using UC-MSCs for neurological disorders.The brain damage process "HIE cascade" was divided into six stages: (1) energy depletion, (2) impairment of microglia, (3) inflammation, (4) excitotoxity, (5) oxidative stress, and (6) apoptosis in capillary, glia, synapse and/or neuron. The authors showed recent 13 clinical trials using UC-MSCs for neurological disorders.The authors suggest that the next step will include reaching a consensus on cell therapies for HIE and establishment of effective protocols for cell therapy for HIE. KEY POINTS: · This study includes new insights about cell therapy for neonatal HIE and CP in schema.. · This study shows precise mechanism of neonatal HIE cascade.. · The mechanism of cell therapy by comparing umbilical cord blood stem cell with MSC is shown.. · The review of recent clinical trials of UC-MSC is shown..

Prostaglandin E1 attenuates post‑cardiac arrest myocardial dysfunction through inhibition of mitochondria‑mediated cardiomyocyte apoptosis

Post‑cardiac arrest myocardial dysfunction (PAMD) is a leading cause of death in patients undergoing resuscitation patients following cardiac arrest (CA). Although prostaglandin E1 (PGE1) is a clinical drug used to mitigate ischemia injury, its effect on PAMD remains unknown. In the present study, the protective effects of PGE1 on PAMD were evaluated in a rat model of CA and in a hypoxia‑reoxygenation (H/R) in vitro model. Rats were randomly assigned to CA, CA+PGE1 or sham groups. Asphyxia for 8 min followed by cardiopulmonary resuscitation were performed in the CA and CA+PGE1 groups. PGE1 was intravenously administered at the onset of return of spontaneous circulation (ROSC). PGE1 treatment significantly increased the ejection fraction and cardiac output within 4 h following ROSC and improved the survival rate, compared with the CA group. Moreover, PGE1 inactivated GSK3β, prevented mitochondrial permeability transition pore (mPTP) opening, while reducing cytochrome c and cleaved caspase‑3 expression, as well as cardiomyocyte apoptosis in the rat model. To examine the underlying mechanism, H/R H9c2 cells were treated with PGE1 at the start of reoxygenation. The changes in GSK3β activity, mPTP opening, cytochrome c and cleaved caspase‑3 expression, and apoptosis of H9c2 cells were consistent with those noted in vivo. The results indicated that PGE1 attenuated PAMD by inhibiting mitochondria‑mediated cardiomyocyte apoptosis.

The Effects of Targeted Temperature Management on Oxygen-Glucose Deprivation/Reperfusion-Induced Injury and DAMP Release in Murine Primary Cardiomyocytes

Introduction. Ischemia/Reperfusion (I/R) is a primary cause of myocardial injury after acute myocardial infarction resulting in the release of damage-associated molecular patterns (DAMPs), which can induce a sterile inflammatory response in the myocardial penumbra. Targeted temperature management (TTM) after I/R has been established for neuroprotection, but the cardioprotective effect remains to be elucidated. Therefore, we investigated the effect of TTM on cell viability, immune response, and DAMP release during oxygen-glucose deprivation/reperfusion (OGD/R) in murine primary cardiomyocytes. Methods. Primary cardiomyocytes from P1-3 mice were exposed to 2, 4, or 6 hours OGD (0.2% oxygen in medium without glucose and serum) followed by 6, 12, or 24 hours simulated reperfusion (21% oxygen in complete medium). TTM at 33.5°C was initiated intra-OGD, and a control group was maintained at 37°C normoxia. Necrosis was assessed by lactate dehydrogenase (LDH) release and apoptosis by caspase-3 activation. OGD-induced DAMP secretions were assessed by Western blotting. Inducible nitric oxide synthase (iNOS), cytokines, and antiapoptotic RBM3 and CIRBP gene expressions were measured by quantitative polymerase chain reaction. Results. Increasing duration of OGD resulted in a transition from apoptotic programmed cell death to necrosis, as observed by decreasing caspase-3 cleavage and increasing LDH release. DAMP release and iNOS expression correlated with increasing necrosis and were effectively attenuated by TTM initiated during OGD. Moreover, TTM induced expression of antiapoptotic RBM3 and CIRBP. Conclusion. TTM protects the myocardium by attenuating cardiomyocyte necrosis induced by OGD and caspase-3 activation, possibly via induction of antiapoptotic RBM3 and CIRBP expressions, during reperfusion. OGD induces increased Hsp70 and CIRBP releases, but HMGB-1 is the dominant mediator of inflammation secreted by cardiomyocytes after prolonged exposure. TTM has the potential to attenuate DAMP release.

Proton Magnetic Resonance Spectroscopy Lactate/N-Acetylaspartate Within 48 h Predicts Cell Death Following Varied Neuroprotective Interventions in a Piglet Model of Hypoxia-Ischemia With and Without Inflammation-Sensitization

Despite therapeutic hypothermia, survivors of neonatal encephalopathy have high rates of adverse outcome. Early surrogate outcome measures are needed to speed up the translation of neuroprotection trials. Thalamic lactate (Lac)/N-acetylaspartate (NAA) peak area ratio acquired with proton (1H) magnetic resonance spectroscopy (MRS) accurately predicts 2-year neurodevelopmental outcome. We assessed the relationship between MR biomarkers acquired at 24-48 h following injury with cell death and neuroinflammation in a piglet model following various neuroprotective interventions. Sixty-seven piglets with hypoxia-ischemia, hypoxia alone, or lipopolysaccharide (LPS) sensitization were included, and neuroprotective interventions were therapeutic hypothermia, melatonin, and magnesium. MRS and diffusion-weighted imaging (DWI) were acquired at 24 and 48 h. At 48 h, experiments were terminated, and immunohistochemistry was assessed. There was a correlation between Lac/NAA and overall cell death [terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)] [mean Lac/NAA basal ganglia and thalamus (BGT) voxel r = 0.722, white matter (WM) voxel r = 0.784, p < 0.01] and microglial activation [ionized calcium-binding adapter molecule 1 (Iba1)] (BGT r = -0.786, WM r = -0.632, p < 0.01). Correlation with marker of caspase-dependent apoptosis [cleaved caspase 3 (CC3)] was lower (BGT r = -0.636, WM r = -0.495, p < 0.01). Relation between DWI and TUNEL was less robust (mean diffusivity BGT r = -0.615, fractional anisotropy BGT r = 0.523). Overall, Lac/NAA correlated best with cell death and microglial activation. These data align with clinical studies demonstrating Lac/NAA superiority as an outcome predictor in neonatal encephalopathy (NE) and support its use in preclinical and clinical neuroprotection studies.

Role of the neurovascular unit in the process of cerebral ischemic injury

Cerebral ischemic injury exhibits both high morbidity and mortality worldwide. Traditional research of the pathogenesis of cerebral ischemic injury has focused on separate analyses of the involved cell types. In recent years, the neurovascular unit (NVU) mechanism of cerebral ischemic injury has been proposed in modern medicine. Hence, more effective strategies for the treatment of cerebral ischemic injury may be provided through comprehensive analysis of brain cells and the extracellular matrix. However, recent studies that have investigated the function of the NVU in cerebral ischemic injury have been insufficient. In addition, the metabolism and energy conversion of the NVU depend on interactions among multiple cell types, which make it difficult to identify the unique contribution of each cell type. Therefore, in the present review, we comprehensively summarize the regulatory effects and recovery mechanisms of four major cell types (i.e., astrocytes, microglia, brain-microvascular endothelial cells, and neurons) in the NVU under cerebral ischemic injury, as well as discuss the interactions among these cell types in the NVU. Furthermore, we discuss the common signaling pathways and signaling factors that mediate cerebral ischemic injury in the NVU, which may help to provide a theoretical basis for the comprehensive elucidation of cerebral ischemic injury.

CDK4 and CDK5 Inhibition Have Comparable Mild Hypothermia Effects in Preventing Drp1-Dependent Mitochondrial Fission and Neuron Death Induced by MPP. Mol Neurobiol 2020;57:4090-4105. [PMID: 32666227 DOI: 10.1007/s12035-020-02014-0]

Mild hypothermia has promising effects in the treatment of acute brain insults and also affects cell cycle progression. Mitochondrial dynamics, fusion and fission, are changed along with the cell cycle and disrupted in neurodegenerative diseases, including Parkinson's disease (PD). However, the effects of hypothermia on aberrant mitochondrial dynamics in PD remain unknown. We hypothesized that mild hypothermia protects neurons by regulating cell cycle-dependent protein expression and mitochondrial dynamics in a 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell model of PD. We found that the hypothermia treatment at 32 °C prevented MPP⁺-induced neuron death; however, 32 °C treatment itself also reduced cell viability. This reduction was associated with cell cycle arrest and downregulation of cyclin-dependent kinase 4 (CDK4) in proliferating human SK-N-SH neuroblastoma cells but upregulation in well-differentiated primary rat cortical neurons. In both types of neurons, hypothermia upregulated p27 (an endogenous inhibitor of CDKs) and p35 (CDK5 activator) protein expression. Treatment with hypothermia, or a selective CDK4 inhibitor, or roscovitine (CDK5 inhibitor) prevented MPP⁺-induced mitochondrial fission, upregulation of mitochondrial fission protein dynamin-related protein 1 (Drp1), and neuron death. In addition, overexpression of dominant negative mutant Drp1^K38A improved MPP⁺-induced mitochondrial fission while overexpression of wild-type Drp1 blunted the prevention of mitochondrial fission by hypothermia as well as CDK4 inhibitor and roscovitine. These results elucidate that hypothermia may inhibit CDK4 and CDK5 activation by upregulating p27 and p35 expression to prevent Drp1-dependent mitochondrial fission and neuron loss after MPP⁺ treatment. CDK4 and CDK5 inhibition imitates the neuroprotective functions of hypothermia as a potential therapy for PD.

Hypothermia prevents hippocampal oxidative stress and apoptosis via the GSK-3β/Nrf2/HO-1 signaling pathway in a rat model of cardiac arrest-induced brain damage

OBJECTIVES

The present study was undertaken to investigate the effects and related mechanisms of hypothermia on oxidative stress and apoptosis caused by cardiac arrest (CA)-induced brain damage in rats.

METHODS

The CA/CPR model was initiated by asphyxia. Body temperature in the normothermia and hypothermia groups was maintained at 37°C ± 0.2°C and 34°C ± 0.2°C, respectively, by surface cooling with an ice pack. First, neurological deficit scores (NDSs) were assessed, and then hippocampus samples were collected at 24 and 72 h after return of spontaneous circulation (ROSC).

RESULTS

The NDSs of rats were significantly reduced after CA, and hypothermia ameliorated neurological deficits. Varying degrees of changes in cellular nuclei and mitochondria were observed in the hippocampus following CA; however, morphological changes became less apparent after therapeutic hypothermia. Malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were higher in the hippocampus at 24 h after ROSC. In contrast, hypothermia did not alter MDA content, while SOD activity further increased. Furthermore, hypothermia reversed the caspase-3 enhancement observed in the normothermia group at 24 h after ROSC. CA also inhibited GSK-3β phosphorylation, promoted Nrf2 translocation to the nucleus, and downregulated HO-1 expression. However, hypothermia significantly reversed these CA-induced changes in GSK-3β phosphorylation, Nrf2 translocation, and HO-1 expression.

CONCLUSION

Hypothermia attenuated CA-induced neurological deficits and hippocampal morphology changes in rats. The protective effect of hypothermia following CA may have been related to inhibition of oxidative stress and apoptosis, and its underlying mechanisms may have been due, at least in part, to activation of the GSK-3β/Nrf2/HO-1 pathway.

Additive Protective Effects of Delayed Mild Therapeutic Hypothermia and Antioxidants on PC12 Cells Exposed to Oxidative Stress

Mild therapeutic hypothermia is protective against several cellular stresses, but the mechanisms underlying this protection are not completely resolved. In the present study, we used an in vitro model to investigate whether therapeutic hypothermia at 33°C applied following a peroxide-induced oxidative stress would protect PC12 cells. A 1-hour exposure to tert-butyl peroxide increased cell death measured 24 hours later. This cell death was dose-dependent in the range of 100-1000 μM tert-butyl peroxide with ∼50% cell death observed at 24 hours from 500 μM peroxide exposure. Cell survival/death was measured with an alamarBlue viability assay, and propidium iodide/Hoechst imaging for counts of living and dead cells. Therapeutic hypothermia at 33°C applied for 2 hours postperoxide exposure significantly increased cell survival measured 24 hours postperoxide-induced stress. This protection was present even when delayed hypothermia, 15 minutes after the peroxide washout, was applied. Addition of any of the three FDA-approved antioxidants (Tempol, EUK134, Edaravone at 100 μM) in combination with hypothermia improved cell survival. With the therapeutic hypothermia treatment, a significant downregulation of caspases-3 and -8 and tumor necrosis factor-α was observed at 3 and 24 hours poststress. Consistent with this, a cell-permeable pan-caspase inhibitor Z-VAD-FMK applied in combination with hypothermia significantly increased cell survival. Overall, these results suggest that the antioxidants quenching of reactive oxygen species likely works with hypothermia to reduce mitochondrial damage and/or apoptotic mechanisms. Further studies are required to confirm and extend these results to other cell types, including neuronal cells, and other forms of oxidative stress as well as to optimize the critical parameters of hypothermia treatment such as target temperature and duration.

Hypothermic properties of dexmedetomidine provide neuroprotection in rats following cerebral ischemia-reperfusion injury

Dexmedetomidine (Dex) is a sedative and analgesic agent that is widely administered to patients admitted to the intensive care unit, and has been demonstrated to result in hypothermia. Many patients have been revealed to benefit from therapeutic hypothermia, which can mitigate cerebral ischemia/reperfusion (I/R) injury following successful cardiopulmonary resuscitation. However, studies investigating the efficacy of Dex in I/R treatment is lacking. The present study aimed to investigate the efficacy of Dex in mitigating neuronal damage, and to determine the possible mechanism of its effects in a rat model of cardiac arrest (CA). CA was induced in Sprague-Dawley rats by asphyxiation for 5 min. Following successful resuscitation, the surviving rats were randomly divided into two treatment groups; one group was intraperitoneally administered with Dex (D group), whereas the control group was treated with normal saline (N group). Critical parameters, including core temperature and blood pressure were monitored following return of spontaneous circulation (ROSC). Arterial blood samples were collected at 10 min after surgery (baseline) 30 and 120 min post-ROSC; and neurological deficit scores (NDS) of the rats were taken 12 or 24 h after ROSC prior to euthanasia. The hippocampal tissue was then removed for analysis by histology, electron microscopy and western blotting. Rats in the D group exhibited a lower core temperature and higher NDS scores compared with the N group (P<0.05). In addition, Dex injection resulted in reduced expression of apoptotic and autophagy-associated factors in the hippocampus (P<0.05). Dex treatment induced hypothermia and improved neurological function in rats after ROSC following resuscitation from CA by inhibiting neuronal apoptosis and reducing autophagy, which suggested that Dex may be a potential therapy option for patients with CA.

Diminished apoptosis in hypoxic porcine retina explant cultures through hypothermia

Simulation of hypoxic processes in vitro can be achieved through cobalt chloride (CoCl2), which induces strong neurodegeneration. Hypoxia plays an important role in the progression of several retinal diseases. Thus, we investigated whether hypoxia can be reduced by hypothermia. Porcine retinal explants were cultivated for four and eight days and hypoxia was mimicked by adding 300 µM CoCl2 from day one to day three. Hypothermia treatment (30 °C) was applied simultaneously. Retinal ganglion, bipolar and amacrine cells, as well as microglia were evaluated via immunohistological and western blot analysis. Furthermore, quantitative real-time PCR was performed to analyze cellular stress and apoptosis. In addition, the expression of specific marker for the previously described cell types were investigated. A reduction of ROS and stress markers HSP70, iNOS, HIF-1α was achieved via hypothermia. In accordance, an inhibition of apoptotic proteins (caspase 3, caspase 8) and the cell cycle arrest gene p21 was found in hypothermia treated retinae. Furthermore, neurons of the inner retina were protected by hypothermia. In this study, we demonstrate that hypothermia lowers hypoxic processes and cellular stress. Additionally, hypothermia inhibits apoptosis and protects neurons. Hence, this seems to be a promising treatment for retinal neurodegeneration.

Moderate brain hypothermia started before resuscitation improves survival and neurobehavioral outcomes after CA/CPR in mice

AIM OF THE STUDY

No definitive experimental or clinical evidence exists whether brain hypothermia before, rather than during or after, resuscitation can reduce hypoxic-ischemic brain injury following cardiac arrest/cardiopulmonary resuscitation (CA/CPR) and improve outcomes. We examined the effects of moderate brain hypothermia before resuscitation on survival and histopathological and neurobehavioral outcomes in a mouse model.

METHODS

Adult C57BL/6 male mice (age: 8-12 weeks) were subjected to 8-min CA followed by CPR. The animals were randomly divided into sham, normothermia (NT; brain temperature 37.5 °C), and extracranial hypothermia (HT; brain temperature 28-32 °C) groups. The hippocampal CA1 was assessed 7 day after resuscitation by histochemical staining. Neurobehavioral outcomes were evaluated by the Barnes maze (BMT), openfield (OFT), rotarod, and light/dark (LDT) tests. Cleaved caspase-3 and heat shock protein 60 (HSP70) levels were investigated by western blotting.

RESULTS

The HT group exhibited higher survival and lower CA1 neuronal injury than did the NT group. HT mice showed improved spatial memory in the BMT compared with NT mice. NT mice travelled a shorter distance in the OFT and tended to spend more time in the light compartment in the LDT than did sham and HT mice. The levels of cleaved caspase-3 and HSP70 were non-significantly higher in the NT than in the sham and HT groups.

CONCLUSIONS

Moderate brain hypothermia before resuscitation improved survival and reduced histological neuronal injury, spatial memory impairment, and anxiety-like behaviours after CA/CPR in mice.

Neuroprotective Role of Hypothermia in Hypoxic-ischemic Brain Injury: Combined Therapies using Estrogen

Hypoxic-ischemic brain injury is a complex network of factors, which is mainly characterized by a decrease in levels of oxygen concentration and blood flow, which lead to an inefficient supply of nutrients to the brain. Hypoxic-ischemic brain injury can be found in perinatal asphyxia and ischemic-stroke, which represent one of the main causes of mortality and morbidity in children and adults worldwide. Therefore, knowledge of underlying mechanisms triggering these insults may help establish neuroprotective treatments. Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators exert several neuroprotective effects, including a decrease of reactive oxygen species, maintenance of cell viability, mitochondrial survival, among others. However, these strategies represent a traditional approach of targeting a single factor of pathology without satisfactory results. Hence, combined therapies, such as the administration of therapeutic hypothermia with a complementary neuroprotective agent, constitute a promising alternative. In this sense, the present review summarizes the underlying mechanisms of hypoxic-ischemic brain injury and compiles several neuroprotective strategies, including Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators, which represent putative agents for combined therapies with therapeutic hypothermia.