Mild hypothermia attenuates mitochondrial oxidative stress by protecting respiratory enzymes and upregulating MnSOD in a pig model of cardiac arrest

Survival and neurological function in patients treated with extracorporeal membrane oxygenation and therapeutic hypothermia: a protocol for updating a systematic review

INTRODUCTION

The widespread application of extracorporeal membrane oxygenation (ECMO) has enhanced clinical outcomes for patients experiencing cardiac arrest. However, its effectiveness is still limited and falls short of the desired level. Therapeutic hypothermia, which maintains body temperatures between 32°C and 36°C in cardiac arrest patients treated with ECMO, has been proposed as a potential means of neuroprotection and increased survival rates. Nevertheless, it remains controversial, and its impact on patient complications has yet to be fully understood. Thus, this paper aims to update the protocol for a systematic review of patients treated with ECMO and therapeutic hypothermia, in order to explore its effects on survival and neurological function.

METHOD AND ANALYSIS

This protocol has been developed in compliance with the Preferred Reporting Items for Systematic Review and Meta-analysis Protocols 2015. The following databases will be systematically searched: PubMed, Web of Science, Cochrane Library, Embase, Ovid, CNKI, Wanfang and China Biology Medicine Disc. The database search strategy will use a combination of subject terms and free-text keywords. The search will encompass articles from the inception of each database up to 15 June 2023. Inclusion criteria encompass randomised controlled trials, cohort studies, case-control studies and quasi-experimental studies. Two researchers will independently review articles and extract relevant data based on these criteria. Any disagreements will be resolved through discussion. Data analysis will be performed using Review Manager software.

ETHICS AND DISSEMINATION

Since no patient data were collected in this study, ethical approval was not required. Research findings will be released in a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42023435353.

PREDICTIVE VALUE OF NEUTROPHIL EXTRACELLULAR TRAP COMPONENTS FOR 28-DAY ALL-CAUSE MORTALITY IN PATIENTS WITH CARDIAC ARREST: A PILOT OBSERVATIONAL STUDY

ABSTRACT

Background: Ischemia-reperfusion after cardiac arrest (CA) activates peptidyl arginine deiminase and citrullinated histone H3 (CitH3), which leads to the formation of neutrophil extracellular traps (NETs). This study attempted to determine the alterations in NET components in post-CA patients as well as analyze the association of NETs with 28-day all-cause mortality. Methods : In this study, 95 patients with restoration of spontaneous circulation (ROSC) after CA were included. They were categorized into the survivor group (n = 32) and the nonsurvivor group (n = 63) according to their 28-day survival statuses. The control group comprised 20 healthy individuals. The blood samples were collected from the patients on days 1, 3, and 7 after ROSC and from the control subjects at the time of enrollment. The serum cell-free DNA (cfDNA) level was determined using the fluorescent labeling method, and the serum concentrations of NET components, including CitH3, myeloperoxidase, neutrophil elastase, and nucleosomes, were estimated using the enzyme-linked immunosorbent assay. Results : Compared with the control group, the serum NET components were significantly increased in the patients 1 week after ROSC (all P < 0.05). These components were significantly higher in the nonsurvivor group than in the survivor group (all P < 0.05). Spearman correlational analysis revealed that the components were positively correlated with Acute Physiology and Chronic Health Evaluation II scores (both P < 0.05). Binary logistic regression analysis indicated that serum cfDNA, CitH3, and nucleosomes on days 1 and 3 after ROSC were independent predictors of 28-day all-cause mortality. Furthermore, these parameters on day 1 after ROSC had the biggest areas under the receiver operating characteristic curves (0.876, 0.862, and 0.861, respectively). Conclusions: Elevated serum levels of cfDNA, CitH3, myeloperoxidase, neutrophil elastase, and nucleosomes were positively correlated with disease severity after ROSC. However, only serum CitH3, cfDNA, and nucleosomes on day 1 after ROSC showed a good predictive value for 28-day all-cause mortality.

Mild hypothermia attenuates ischaemia/reperfusion injury: insights from serial non-invasive pressure-volume loops

AIMS

Mild hypothermia, 32-35°C, reduces infarct size in experimental studies, potentially mediating reperfusion injuries, but human trials have been ambiguous. To elucidate the cardioprotective mechanisms of mild hypothermia, we analysed cardiac performance in a porcine model of ischaemia/reperfusion, with serial cardiovascular magnetic resonance (CMR) imaging throughout 1 week using non-invasive pressure-volume (PV) loops.

METHODS AND RESULTS

Normothermia and Hypothermia group sessions (n = 7 + 7 pigs, non-random allocation) were imaged with Cardiovascular magnetic resonance (CMR) at baseline and subjected to 40 min of normothermic ischaemia by catheter intervention. Thereafter, the Hypothermia group was rapidly cooled (mean 34.5°C) for 5 min before reperfusion. Additional CMR sessions at 2 h, 24 h, and 7 days acquired ventricular volumes and ischaemic injuries (unblinded analysis). Stroke volume (SV: -24%; P = 0.029; Friedmans test) and ejection fraction (EF: -20%; P = 0.068) were notably reduced at 24 h in the Normothermia group compared with baseline. In contrast, the decreases were ameliorated in the Hypothermia group (SV: -6%; P = 0.77; EF: -6%; P = 0.13). Mean arterial pressure remained stable in Normothermic animals (-3%, P = 0.77) but dropped 2 h post-reperfusion in hypothermic animals (-18%, P = 0.007). Both groups experienced a decrease and partial recovery pattern for PV loop-derived variables over 1 week, but the adverse effects tended to attenuate in the Hypothermia group. Infarct sizes were 10 ± 8% in Hypothermic and 15 ± 8% in Normothermic animals (P = 0.32). Analysis of covariance at 24 h indicated that hypothermia has cardioprotective properties incremental to reducing infarct size, such as higher external power (P = 0.061) and lower arterial elastance (P = 0.015).

CONCLUSION

Using non-invasive PV loops by CMR, we observed that mild hypothermia at reperfusion alleviates the heart's work after ischaemia/reperfusion injuries during the first week and preserves short-term cardiac performance. This hypothesis-generating study suggests hypothermia to have cardioprotective properties, incremental to reducing infarct size. The primary cardioprotective mechanism was likely an afterload reduction acutely unloading the left ventricle.

Effects of temperature control on hyperthermia-related cardiac dysfunction in a porcine model of cardiac arrest

The outcome of cardiac arrest is worse when there is fever after spontaneous circulation is restored (ROSC). The purpose of this study was to investigate the mechanism of post-ROSC cardiac dysfunction after hyperthermia treatment and the effects of temperature control. Twenty-four male Bama minipigs were randomized into 3 groups (8 per group): CPR + controlled normothermia (CN), CPR + hyperthermia (HT), and CPR + therapeutic mild hypothermia (TMH). Defibrillation was given to pigs with ventricular fibrillation after 8 min of untreated fibrillation. Subsequently, these animals received the post-ROSC treatments of hyperthermia (38 °C), controlled normothermia (37 °C) or hypothermia (33 °C) according to the groups. Hemodynamic parameters, left ventricular ejection fraction, blood samples and myocardial tissues were assessed. At 24 h after the post-ROSC treatments, the pigs treated with hyperthermia showed increments in heart rate and plasma cardiac troponin I, and decreases in mean arterial pressure, cardiac index, and left ventricular ejection fraction, compared to those with the controlled normothermia pigs. However, the deterioration of the above parameters can be attenuated by TMH. The pigs in the TMH group also had a reduced percentage of apoptotic cardiomyocytes, an increased anti-apoptotic Bcl-2/Bax ratio and a decreased caspase-3 activity in myocardium, as compared with both controlled normothermia and hyperthermia pigs. In conclusion, hyperthermia is associated with a worse myocardial dysfunction. TMH improves hyperthermia-induced myocardial dysfunction by attenuating apoptosis in a porcine model of cardiac arrest.

Recent developments and controversies in therapeutic hypothermia after cardiopulmonary resuscitation

Therapeutic hypothermia was recommended as the only neuroprotective treatment in comatose patients after return of spontaneous circulation (ROSC). With new evidence suggesting a similar neuroprotective effect of 36 °C and 33 °C, the term "therapeutic hypothermia" was substituted by "targeted temperature management" in 2011, which in turn was replaced by the term "temperature control" in 2022 because of new evidence of the similar effects of target normothermia and 33 °C. However, there is no clear consensus on the efficacy of therapeutic hypothermia. In this article, we provide an overview of the recent evidence from basic and clinical research related to therapeutic hypothermia and re-evaluate its application as a post-ROSC neuroprotective intervention in clinical settings.

Therapeutic Hypothermia after Cardiac Arrest Attenuates Hindlimb Paralysis and Damage of Spinal Motor Neurons and Astrocytes through Modulating Nrf2/HO-1 Signaling Pathway in Rats

Cardiac arrest (CA) and return of spontaneous circulation (ROSC), a global ischemia and reperfusion event, lead to neuronal damage and/or death in the spinal cord as well as the brain. Hypothermic therapy is reported to protect neurons from damage and improve hindlimb paralysis after resuscitation in a rat model of CA induced by asphyxia. In this study, we investigated roles of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the lumbar spinal cord protected by therapeutic hypothermia in a rat model of asphyxial CA. Male Sprague-Dawley rats were subjected to seven minutes of asphyxial CA (induced by injection of 2 mg/kg vecuronium bromide) and hypothermia (four hours of cooling, 33 ± 0.5 °C). Survival rate, hindlimb motor function, histopathology, western blotting, and immunohistochemistry were examined at 12, 24, and 48 h after CA/ROSC. The rats of the CA/ROSC and hypothermia-treated groups had an increased survival rate and showed an attenuated hindlimb paralysis and a mild damage/death of motor neurons located in the anterior horn of the lumbar spinal cord compared with those of the CA/ROSC and normothermia-treated groups. In the CA/ROSC and hypothermia-treated groups, expressions of cytoplasmic and nuclear Nrf2 and HO-1 were significantly higher in the anterior horn compared with those of the CA/ROSC and normothermia-treated groups, showing that cytoplasmic and nuclear Nrf2 was expressed in both motor neurons and astrocytes. Moreover, in the CA/ROSC and hypothermia-treated group, interleukin-1β (IL-1β, a pro-inflammatory cytokine) expressed in the motor neurons was significantly reduced, and astrocyte damage was apparently attenuated compared with those found in the CA/ROSC and normothermia group. Taken together, our results indicate that hypothermic therapy after CA/ROSC attenuates CA-induced hindlimb paralysis by protecting motor neurons in the lumbar spinal cord via activating the Nrf2/HO-1 signaling pathway and attenuating pro-inflammation and astrocyte damage (reactive astrogliosis).

Hypothermia Prevents Cardiac Dysfunction during Acute Ischemia Reperfusion by Maintaining Mitochondrial Bioenergetics and by Promoting Hexokinase II Binding to Mitochondria

Background

Hypothermia (H), cardioplegia (CP), and both combined (HCP) are known to be protective against myocardial ischemia reperfusion (IR) injury. Mitochondria have molecular signaling mechanisms that are associated with both cell survival and cell death. In this study, we investigated the dynamic changes in proapoptotic and prosurvival signaling pathways mediating H, CP, or HCP-induced protection of mitochondrial function after acute myocardial IR injury.

Methods

Rats were divided into five groups. Each group consists of 3 subgroups based on a specific reperfusion time (5, 20, or 60 min) after a 25-min global ischemia. The time control (TC) groups were not subjected to IR but were perfused with 37 °C Krebs-Ringer's (KR) buffer, containing 4.5 mM K⁺, in a specific perfusion protocol that corresponded with the duration of each IR protocol. The IR group (control) was perfused for 20 min with KR, followed by 25-min global ischemia, and then KR reperfusion for 5, 20, or 60 min. The treatment groups were exposed to 17 °C H, 37 °C CP (16 mM K⁺), or HCP (17 °C + CP) for 5 min before ischemia and for 2 min on reperfusion before switching to 37 °C KR perfusion for the remainder of each of the reperfusion times. Cardiac function and mitochondrial redox state (NADH/FAD) were monitored online in the ex vivo hearts before, during, and after ischemia. Mitochondria were isolated at the end of each specified reperfusion time, and changes in O₂ consumption, membrane potential (ΔΨ_m), and Ca²⁺ retention capacity (CRC) were assessed using complex I and complex II substrates. In another set of hearts, mitochondrial and cytosolic fractions were isolated after a specified reperfusion time to conduct western blot assays to determine hexokinase II (HKII) and Bax binding/translocation to mitochondria, cytosolic pAkt levels, and cytochrome c (Cyto-c) release into the cytosol.

Results

H and HCP were more protective of mitochondrial integrity and, concomitantly, cardiac function than CP alone; H and HCP improved post-ischemic cardiac function by (1) maintaining mitochondrial bioenergetics, (2) maintaining HKII binding to mitochondria with an increase in pAkt levels, (3) increasing CRC, and (4) decreasing Cyto-c release during reperfusion. Bax translocation/binding to mitochondria was unaffected by any treatment, regardless of cardiac functional recovery.

Conclusions

Hypothermia preserved mitochondrial function and cardiac function, in part, by maintaining mitochondrial bioenergetics, by retaining HKII binding to mitochondria via upstream pAkt, and by reducing Cyto-c release independently of Bax binding to mitochondria.

Energy-sparing by 2-methyl-2-thiazoline protects heart from ischaemia/reperfusion injury

AIMS

Cardiac ischaemia/reperfusion (I/R) injury remains a critical issue in the therapeutic management of ischaemic heart failure. Although mild hypothermia has a protective effect on cardiac I/R injury, more rapid and safe methods that can obtain similar results to hypothermia therapy are required. 2-Methyl-2-thiazoline (2MT), an innate fear inducer, causes mild hypothermia resulting in resistance to critical hypoxia in cutaneous or cerebral I/R injury. The aim of this study is to demonstrate the protective effect of systemically administered 2MT on cardiac I/R injury and to elucidate the mechanism underlying this effect.

METHODS AND RESULTS

A single subcutaneous injection of 2MT (50 mg/kg) was given prior to reperfusion of the I/R injured 10 week-old male mouse heart and its efficacy was evaluated 24 h after the ligation of the left anterior descending coronary artery. 2MT preserved left ventricular systolic function following I/R injury (ejection fraction, %: control 37.9 ± 6.7, 2MT 54.1 ± 6.4, P < 0.01). 2MT also decreased infarct size (infarct size/ischaemic area at risk, %: control 48.3 ± 12.1, 2MT 25.6 ± 4.2, P < 0.05) and serum cardiac troponin levels (ng/mL: control 8.9 ± 1.1, 2MT 1.9 ± 0.1, P < 0.01) after I/R. Moreover, 2MT reduced the oxidative stress-exposed area within the heart (%: control 25.3 ± 4.7, 2MT 10.8 ± 1.4, P < 0.01). These results were supported by microarray analysis of the mouse hearts. 2MT induced a transient, mild decrease in core body temperature (°C: -2.4 ± 1.4), which gradually recovered over several hours. Metabolome analysis of the mouse hearts suggested that 2MT minimized energy metabolism towards suppressing oxidative stress. Furthermore, 18F-fluorodeoxyglucose-positron emission tomography/computed tomography imaging revealed that 2MT reduced the activity of brown adipose tissue (standardized uptake value: control 24.3 ± 6.4, 2MT 18.4 ± 5.8, P < 0.05). 2MT also inhibited mitochondrial respiration and glycolysis in rat cardiomyoblasts.

CONCLUSIONS

We identified the cardioprotective effect of systemically administered 2MT on cardiac I/R injury by sparing energy metabolism with reversible hypothermia. Our results highlight the potential of drug-induced hypothermia therapy as an adjunct to coronary intervention in severe ischaemic heart disease.

Therapeutic hypothermia effect on asphyxial cardiac arrest-induced renal ischemia/reperfusion injury via change of Nrf2/HO-1 levels

The present study aimed to investigate the renoprotective effect of therapeutic hypothermia (TH) on renal ischemia-reperfusion injury (RI/RI) induced by asphyxial cardiac arrest (CA) in rats. A total of 48 male rats were randomly divided into five groups: i) Sham (n=6); ii) Normothermia + CA (Normo.) (n=14); iii) Normo. and 2 h of TH after return of spontaneous circulation (ROSC) (n=12); iv) Normo. and 4 h of TH after ROSC (n=9); and v) Normo. and 6 h of TH after ROSC (n=7). All rats except the Sham group underwent asphyxia CA and were sacrificed 1 day after ROSC. The survival rate increased from 42.8% in the Normo. group to 50, 66.6 and 85.7% in the groups with 2, 4 and 6 h of TH after CA, respectively. TH attenuated the histopathological changes of the renal tissues following ROSC and the levels of blood urea nitrogen, serum creatinine and malondialdehyde in renal tissues. On immunohistochemistry, the relative optical density of nuclear erythroid-related factor-2 (Nrf2) and heme oxygenase (HO-1) expression in renal tissues increased in the Normo. group compared with that in the Sham group and exhibited further significant increases at 6 h of TH after ROSC. In conclusion, TH attenuated renal injury and increased the expression of Nrf2 and HO-1 in a TH treatment time-dependent manner.

miR-98-5p protects against cerebral ischemia/reperfusion injury through anti-apoptosis and anti-oxidative stress in mice

Cerebral ischemia/reperfusion (I/R) injury is an obstacle in treating ischemic stroke effectively. miR-98-5p has been reported to have the ability of reducing myocardial I/R injury. To explore the function of miR-98-5p in cerebral I/R, we established mice model of middle cerebral artery occlusion and reperfusion (MCAO/R). The level of miR-98-5p was found to be downregulated in serum of stroke patients and brain tissues of MCAO/R mice. Examination of brain tissues indicated that upregulating miR-98-5p level alleviated the infarction in MCAO/R mice. Moreover, the upregulation of miR-98-5p reduced reactive oxygen species production and enhanced superoxide dismutase activity in brain tissues of MCAO/R mice. These results indicating that miR-98-5p could protect against oxidative stress. Further study showed that miR-98-5p inhibited apoptosis by reducing the levels of death-associated protein kinase 1, B cell lymphoma/leukaemia-2 associated x protein and cleaved caspase-3, as well as increasing the level of B cell lymphoma/leukaemia-2. In addition, miR-98-5p was found to protect against oxidative stress through downregulating the level of BTB domain and CNC homology 1 and upregulating the levels of NAD(P)H: quinone oxidoreductase 1 and heme oxygenase 1. Therefore, miR-98-5p might be a potential target to treat cerebral I/R injury.

Temperature Variability Does Not Attenuate the Beneficial Effects of Therapeutic Hypothermia on Cellular Apoptosis and Endoplasmic Reticulum Stress in the Cerebral Cortex of a Swine Cardiac Arrest Model

BACKGROUND

Endoplasmic reticulum stress (ERS) plays a vital role in mediating apoptosis in the brain following cardiac arrest (CA). Studies have shown that therapeutic hypothermia (TH) provides neuroprotection through anti-apoptosis; however, the effects of temperature variability in TH on the brain remain unclear. In this study, we investigated the different effects of temperature variability through extracorporeal membrane oxygenation on apoptosis and ERS in the brain following CA.

METHODS

Eighteen male domestic pigs underwent 6-min duration of no-flow induced by ventricular fibrillation. Extracorporeal cardiopulmonary resuscitation was then performed, and the return of spontaneous circulation (ROSC) was achieved. The animals were randomly assigned to the following groups: normothermia, non-temperature variability, and temperature variability. TH (core temperature, 33-35 °C) was maintained for 24 h post-ROSC, and the animals were rewarmed for 8 h. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry for Bax and Bcl-2 transcripts and proteins, respectively, were used to investigate apoptosis in the cerebral cortex. Expression levels of the ERS molecules, GRP78 and CHOP, were also detected by qRT-PCR, and cellular morphology was evaluated using transmission electron microscopy.

RESULTS

qRT-PCR and immunohistochemistry results revealed that TH significantly increased the expression levels of Bcl-2 and GRP78 and decreased that of Bax and CHOP than under normothermia conditions. Compared to the non-temperature variability group, temperature variability did not decrease the expression levels of Bcl-2 and GRP78 and not increase the levels of Bax and CHOP. Endoplasmic reticulum ultrastructural changes were significantly improved under TH. No statistical difference was observed between the temperature variability and non-temperature variability groups.

CONCLUSION

TH can reduce neuronal apoptosis by ERS, while temperature variability does not attenuate this beneficial effect.

Targeted Temperature Management Suppresses Hypoxia-Inducible Factor-1α and Vascular Endothelial Growth Factor Expression in a Pig Model of Cardiac Arrest

BACKGROUND

The hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF)/VEGF receptor subtype 2 (VEGFR-2) pathway has been implicated in ischemia/reperfusion injury. The aim of this study was to clarify whether whole-body hypothermic targeted temperature management (HTTM) inhibits the HIF-1α/VEGF/VEGFR-2 pathway in a swine model of cardiac arrest (CA) and cardiopulmonary resuscitation (CPR).

METHODS

Twenty-four domestic male Beijing Landrace pigs were used in this study. CA was electrically induced with ventricular fibrillation and left untreated for 8 min. Return of spontaneous circulation (ROSC) was achieved in 16 pigs, which were randomly assigned either to normothermia at 38 °C or to HTTM at 33 °C (each group: n = 8). HTTM was intravascularly induced immediately after ROSC. The core temperature was reduced to 33 °C and maintained for 12 h after ROSC. The serum levels of HIF-1α, VEGF, VEGFR-2, and neuron-specific enolase (NSE) were measured with enzyme immunoassay kits 0.5, 6, 12, and 24 h after ROSC. The expression of HIF-1α, VEGF, and VEGFR-2 in cerebral cortical tissue was measured by RT-PCR and Western blot analysis 24 h after ROSC. Neurological deficit scores and brain cortical tissue water content were evaluated 24 h after ROSC.

RESULTS

The serum levels of HIF-1α, VEGF, and VEGFR-2 were significantly increased under normothermia within 24 h after ROSC. However, these increases were significantly reduced by HTTM. HTTM also decreased cerebral cortical HIF-1α, VEGF, and VEGFR-2 mRNA and protein expression 24 h after ROSC (all p < 0.05). HTTM pigs had better neurological outcomes and less brain edema than normothermic pigs.

CONCLUSION

The HIF-1α/VEGF/VEGFR-2 system is activated following CA and CPR. HTTM protects against cerebral injury after ROSC, which may be part of the mechanism by which it inhibits the expression of components of the HIF-1α/VEGF/VEGFR-2 signaling pathway.

Healthful aging mediated by inhibition of oxidative stress

The progressive increase in lifespan over the past century carries with it some adversity related to the accompanying burden of debilitating diseases prevalent in the older population. This review focuses on oxidative stress as a major mechanism limiting longevity in general, and healthful aging, in particular. Accordingly, the first goal of this review is to discuss the role of oxidative stress in limiting longevity, and compare healthful aging and its mechanisms in different longevity models. Secondly, we discuss common signaling pathways involved in protection against oxidative stress in aging and in the associated diseases of aging, e.g., neurological, cardiovascular and metabolic diseases, and cancer. Much of the literature has focused on murine models of longevity, which will be discussed first, followed by a comparison with human models of longevity and their relationship to oxidative stress protection. Finally, we discuss the extent to which the different longevity models exhibit the healthful aging features through physiological protective mechanisms related to exercise tolerance and increased β-adrenergic signaling and also protection against diabetes and other metabolic diseases, obesity, cancer, neurological diseases, aging-induced cardiomyopathy, cardiac stress and osteoporosis.

Therapeutic hypothermia reduces inflammation and oxidative stress in the liver after asphyxial cardiac arrest in rats

BACKGROUND

Few studies have evaluated the effects of hypothermia on cardiac arrest (CA)-induced liver damage. This study aimed to investigate the effects of hypothermic therapy on the liver in a rat model of asphyxial cardiac arrest (ACA).

METHODS

Rats were subjected to 5-minute ACA followed by return of spontaneous circulation (RoSC). Body temperature was controlled at 33°C±0.5°C or 37°C±0.5°C for 4 hours after RoSC in the hypothermia group and normothermia group, respectively. Liver tissues in each group were collected at 6 hours, 12 hours, 1 day, and 2 days after RoSC. To examine hepatic inflammation, mast cells were stained with toluidine blue. Superoxide anion radical production was evaluated using dihydroethidium fluorescence straining and expression of endogenous antioxidants (superoxide dismutase 1 [SOD1] and SOD2) was examined using immunohistochemistry.

RESULTS

There were significantly more mast cells in the livers of the normothermia group with ACA than in the hypothermia group with ACA. Gradual increase in superoxide anion radical production was found with time in the normothermia group with ACA, but production was significantly suppressed in the hypothermia group with ACA relative to the normothermia group with ACA. SOD1 and SOD2 levels were higher in the hypothermia group with ACA than in the normothermia group with ACA.

CONCLUSIONS

Experimental hypothermic treatment after ACA significantly inhibited inflammation and superoxide anion radical production in the rat liver, indicating that this treatment enhanced or maintained expression of antioxidants. Our findings suggest that hypothermic therapy after CA can reduce mast cell-mediated inflammation through regulation of oxidative stress and the expression of antioxidants in the liver.

Hypothermia Advocates Functional Mitochondria and Alleviates Oxidative Stress to Combat Acetaminophen-Induced Hepatotoxicity

For years, moderate hypothermia (32 °C) has been proposed as an unorthodox therapy for liver injuries, with proven hepatoprotective potential. Yet, limited mechanistic understanding has largely denied its acceptance over conventional pharmaceuticals for hepatoprotection. Today, facing a high prevalence of acetaminophen-induced liver injury (AILI) which accounts for the highest incidence of acute liver failure, hypothermia was evaluated as a potential therapy to combat AILI. For which, transforming growth factor-α transgenic mouse hepatocytes (TAMH) were subjected to concomitant 5 mM acetaminophen toxicity and moderate hypothermic conditioning for 24 h. Thereafter, its impact on mitophagy, mitochondrial biogenesis, glutathione homeostasis and c-Jun N-terminal kinase (JNK) signaling pathways were investigated. In the presence of AILI, hypothermia displayed simultaneous mitophagy and mitochondrial biogenesis to conserve functional mitochondria. Furthermore, antioxidant response was apparent with higher glutathione recycling and repressed JNK activation. These effects were, however, unremarkable with hypothermia alone without liver injury. This may suggest an adaptive response of hypothermia only to the injured sites, rendering it favorable as a potential targeted therapy. In fact, its cytoprotective effects were displayed in other DILI of similar pathology as acetaminophen i.e., valproate- and diclofenac-induced liver injury and this further corroborates the mechanistic findings of hypothermic actions on AILI.

How to Improve the Antioxidant Defense in Asphyxiated Newborns-Lessons from Animal Models

Oxygen free radicals have been implicated in brain damage after neonatal asphyxia. In the early phase of asphyxia/reoxygenation, changes in antioxidant enzyme activity play a pivotal role in switching on and off the cascade of events that can kill the neurons. Hypoxia/ischemia (H/I) forces the brain to activate endogenous mechanisms (e.g., antioxidant enzymes) to compensate for the lost or broken neural circuits. It is important to evaluate therapies to enhance the self-protective capacity of the brain. In animal models, decreased body temperature during neonatal asphyxia has been shown to increase cerebral antioxidant capacity. However, in preterm or severely asphyxiated newborns this therapy, rather than beneficial seems to be harmful. Thus, seeking new therapeutic approaches to prevent anoxia-induced complications is crucial. Pharmacotherapy with deferoxamine (DFO) is commonly recognized as a beneficial regimen for H/I insult. DFO, via iron chelation, reduces oxidative stress. It also assures an optimal antioxidant protection minimizing depletion of the antioxidant enzymes as well as low molecular antioxidants. In the present review, some aspects of recently acquired insight into the therapeutic effects of hypothermia and DFO in promoting neuronal survival after H/I are discussed.

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.

HOE-642 improves the protection of hypothermia on neuronal mitochondria after cardiac arrest in rats

HOE-642 has been shown to provide significant protection in a variety of models of cerebral and myocardial ischemia/reperfusion injury. In this study, we examined the impact of HOE-642, a selective Na⁺/H⁺ exchanger 1 inhibitor, with or without hypothermia on neuronal and neuronal mitochondrial function during resuscitation. Cardiac arrest was induced by 8 min of asphyxia in rats. Five groups were included in this study: sham; normothermia (N); HOE-642 (HOE, 1 mg/kg); hypothermia (Hypo, 33±0.5°C); and HOE-642 plus hypothermia (HOE+Hypo). Survival and neurological deficit scores (NDS) were evaluated after 24 h of resuscitation. ΔΨm, mitochondrial swelling, ROS production, mitochondrial complex I-IV activity, and ultrastructural changes of the hippocampal mitochondria were evaluated. Survival in the HOE+Hypo group (85.7%) was higher than in the N group (42.9%) and HOE group (31.8%), P<0.05. NDS in the Hypo and HOE+Hypo groups were lower than in the N and HOE groups, P<0.05. ΔΨm in the HOE group (2.7±0.9) were higher than in the N (1.3±0.3) and Hypo (1.4±0.4) groups, P<0.05. Mitochondrial swelling in the N group was severe than in the HOE and Hypo groups, P<0.05. The production of ROS in the HOE and HOE+Hypo groups were lower than in the N group, P<0.05. Complex I-IV activity in the HOE+Hypo group was higher than in the other groups. The ultrastructure of mitochondria in the N group was severely damaged. The mitochondria maintained structural integrity in the HOE, Hypo and HOE+Hypo groups. HOE-642 plus hypothermia during resuscitation was beneficial than HOE-642 or hypothermia alone.

Selective brain hypothermia-induced neuroprotection against focal cerebral ischemia/reperfusion injury is associated with Fis1 inhibition

Selective brain hypothermia is considered an effective treatment for neuronal injury after stroke, and avoids the complications of general hypothermia. However, the mechanisms by which selective brain hypothermia affects mitochondrial fission remain unknown. In this study, we investigated the effect of selective brain hypothermia on the expression of fission 1 (Fis1) protein, a key factor in the mitochondrial fission system, during focal cerebral ischemia/reperfusion injury. Sprague-Dawley rats were divided into four groups. In the sham group, the carotid arteries were exposed only. In the other three groups, middle cerebral artery occlusion was performed using the intraluminal filament technique. After 2 hours of occlusion, the filament was slowly removed to allow blood reperfusion in the ischemia/reperfusion group. Saline, at 4°C and 37°C, were perfused through the carotid artery in the hypothermia and normothermia groups, respectively, followed by restoration of blood flow. Neurological function was assessed with the Zea Longa 5-point scoring method. Cerebral infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride staining, and apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. Fis1 and cytosolic cytochrome c levels were assessed by western blot assay. Fis1 mRNA expression was assessed by quantitative reverse transcription-polymerase chain reaction. Mitochondrial ultrastructure was evaluated by transmission electron microscopy. Compared with the sham group, apoptosis, Fis1 protein and mRNA expression and cytosolic cytochrome c levels in the cortical ischemic penumbra and cerebral infarct volume were increased after reperfusion in the other three groups. These changes caused by cerebral ischemia/reperfusion were inhibited in the hypothermia group compared with the normothermia group. These findings show that selective brain hypothermia inhibits Fis1 expression and reduces apoptosis, thereby ameliorating focal cerebral ischemia/reperfusion injury in rats. Experiments were authorized by the Ethics Committee of Qingdao Municipal Hospital of China (approval No. 2019008).

Therapeutic Hypothermia Improves Hind Limb Motor Outcome and Attenuates Oxidative Stress and Neuronal Damage in the Lumbar Spinal Cord Following Cardiac Arrest

Hypothermia enhances outcomes of patients after resuscitation after cardiac arrest (CA). However, the underlying mechanism is not fully understood. In this study, we investigated effects of hypothermic therapy on neuronal damage/death, microglial activation, and changes of endogenous antioxidants in the anterior horn in the lumbar spinal cord in a rat model of asphyxial CA (ACA). A total of 77 adult male Sprague–Dawley rats were randomized into five groups: normal, sham ACA plus (+) normothermia, ACA + normothermia, sham ACA + hypothermia, and ACA + hypothermia. ACA was induced for 5 min by injecting vecuronium bromide. Therapeutic hypothermia was applied after return of spontaneous circulation (ROSC) via rapid cooling with isopropyl alcohol wipes, which was maintained at 33 ± 0.5 °C for 4 h. Normothermia groups were maintained at 37 ± 0.2 °C for 4 h. Neuronal protection, microgliosis, oxidative stress, and changes of endogenous antioxidants were evaluated at 12 h, 1 day, and 2 days after ROSC following ACA. ACA resulted in neuronal damage from 12 h after ROSC and evoked obvious degeneration/loss of spinal neurons in the ventral horn at 1 day after ACA, showing motor deficit of the hind limb. In addition, ACA resulted in a gradual increase in microgliosis with time after ACA. Therapeutic hypothermia significantly reduced neuronal loss and attenuated hind limb dysfunction, showing that hypothermia significantly attenuated microgliosis. Furthermore, hypothermia significantly suppressed ACA-induced increases of superoxide anion production and 8-hydroxyguanine expression, and significantly increased superoxide dismutase 1 (SOD1), SOD2, catalase, and glutathione peroxidase. Taken together, hypothermic therapy was found to have a substantial impact on changes in ACA-induced microglia activation, oxidative stress factors, and antioxidant enzymes in the ventral horn of the lumbar spinal cord, which closely correlate with neuronal protection and neurological performance after ACA.

Genomic Analysis Reveals Specific Patterns of Homozygosity and Heterozygosity in Inbred Pigs

The inbred strain of miniature pig is an ideal model for biomedical research due to its high level of homozygosity. In this study, we investigated genetic diversity, relatedness, homozygosity, and heterozygosity using the Porcine SNP60K BeadChip in both inbred and non-inbred Wuzhishan pigs (WZSPs). Our results from multidimensional scaling, admixture, and phylogenetic analyses indicated that the inbred WZSP, with its unique genetic properties, can be utilized as a novel genetic resource for pig genome studies. Inbreeding depression and run of homozygosity (ROH) analyses revealed an average of 61 and 12 ROH regions in the inbred and non-inbred genomes of WZSPs, respectively. By investigating ROH number, length, and distribution across generations, we further briefly studied the impacts of recombination and demography on ROH in these WZSPs. Finally, we explored the SNPs with higher heterozygosity across generations and their potential functional implications in the inbred WZSP. We detected 56 SNPs showing constant heterozygosity with He = 1 across six generations in inbred pigs, while only one was found in the non-inbred population. Among these SNPs, we observed nine SNPs located in swine RefSeq genes, which were found to be involved in signaling and immune processes. Together, our findings indicate that the inbred-specific pattern of homozygosity and heterozygosity in inbred pigs can offer valuable insights for elucidating the mechanisms of inbreeding in farm animals.

Exploration of the optimal dose of HOE-642 for the protection of neuronal mitochondrial function after cardiac arrest in rats

INTRODUCTION

It has been demonstrated HOE-642 ameliorates ischemic contracture, prevents post-resuscitation diastolic dysfunction, and favors the earlier return of contractile function. This study is the first report to explore the optimal dose of HOE-642 in protecting the neuronal mitochondrial function after cardiac arrest.

METHODS

Cardiac arrest was induced by 8 min asphyxia in rats. There were Sham (S), Normothermic (NORM), and Hypothermic (HYPO) groups. The NORM or HYPO groups consist of four subgroups: NORM/HYPO + HOE-642 0, 1, 3, and 5 mg/kg. Survival and NDS were evaluated after 24 h of resuscitation. ΔΨm, mitochondrial swelling, ROS production, and mitochondrial complex IIV activity of the hippocampus were detected.

RESULTS

Survival in the HYPO + 1 mg group was the best and significantly higher than in the NORM + 0 mg and NORM + 1 mg groups. NDS in the HYPO + 0 mg, HYPO + 1 mg, and HYPO + 3 mg groups was significantly lower than in the NORM + 0 mg group. ΔΨm in the NORM + 1 mg (n = 5) group was significantly higher than in the NORM + 0 mg (n = 8), NORM + 3 mg (n = 5), and NORM + 5 mg (n = 5) groups. The ROS production in the NORM + 1 mg and NORM + 3 mg groups were significantly lower than in the NORM + 0 mg and NORM + 5 mg groups. Complex I and III activities in the HYPO + 1 mg (n = 5) group were significantly higher than in the HYPO + 3 mg (n = 5), and HYPO + 5 mg (n = 5) groups. Complex II and IV activities in the NORM + 3 mg and HYPO + 3 mg groups were significantly higher than in the NORM + 0 mg, NORM + 1 mg, and HYPO + 0 mg (n = 4)groups.

CONCLUSIONS

HOE-642 1 or 3 mg/kg showed benefits compared to HOE-642 5 mg/kg used when initiating resuscitation. When combined with hypothermia after cardiac arrest, HOE-642 1 or 3 mg/kg improved survival and neurological function compared with hypothermia or HOE-642 alone, however, HOE-642 5 mg/kg plus hypothermia did not.

Mild Therapeutic Hypothermia Increases Glutathione Levels in Postcardiac Arrest Patients

Ischemia-reperfusion (I/R)-induced oxidative stress is one of the main mechanisms of tissue injury after cardiac arrest (CA). A decrease in antioxidant defenses may contribute to I/R injury. The present study aims to investigate the influence of mild therapeutic hypothermia (MTH) on levels of nonenzymatic antioxidants after CA. We investigated antioxidant levels at 6, 12, 36, and 72 hours after CA in central venous blood samples of patients admitted to intensive care. The sample consisted of 31 patients under controlled normothermia (36°C) and 11 patients treated with 24 hours of MTH (33°C). Erythrocyte glutathione (GSH) levels were elevated by MTH, increasing at 6, 12, 36, and 72 hours after CA in hypothermic patients (mean GSH levels in normothermic patients: 6 hours = 73.89, 12 hours = 56.45, 36 hours = 56.46, 72 hours = 61.80 vs. hypothermic patients: 6 hours = 176.89, 12 hours = 198.78, 36 hours = 186.96, and 72 hours = 173.68 μmol/g of protein). Vitamin C levels decreased significantly at 6 and 12 hours after CA in hypothermic patients (median vitamin C levels in normothermic patients: 6 hours = 7.53, 12 hours = 9.40, 36 hours = 8.56, and 72 hours = 8.51 vs. hypothermic patients: 6 hours = 5.46, 12 hours = 5.44, 36 hours = 6.10, and 72 hours = 5.89 mmol/L), coinciding with the period of therapeutic hypothermia. Vitamin E and nitric oxide levels were not altered by hypothermic treatment. These findings suggest that MTH alters nonenzymatic antioxidants differently, decreasing circulating vitamin C levels during treatment; however, MTH elevates GSH levels, possibly protecting tissues from I/R injury after CA.

Cholecystokinin octapeptide inhibits the inflammatory response and improves neurological outcome in a porcine model of cardiopulmonary resuscitation

Previous studies have demonstrated that cholecystokinin octapeptide (CCK8) induces hypothermia and inhibits the systemic inflammatory response in septic shock in rat and murine models. The present study aimed to ascertain whether CCK8 induced hypothermia and improved the neurological outcomes in a porcine model of cardiopulmonary resuscitation (CPR). Ventricular fibrillation was induced and left untreated for 10 min in 12 male Bama miniature pigs. Defibrillation was attempted after 5 min of CPR. At 5 min following resuscitation, the pigs were randomized and equally assigned into the CCK8 or the control group. CCK8 was continuously infused for 1 h at a dose of 44.4 µg/kg/h and a rate of 20 ml/h in the CCK8 group. Body temperature, hemodynamic measurements and post-resuscitation myocardial function were monitored in the first 4 h following CPR. Neuron specific enzyme (NSE), S100B protein, tumor necrosis factor (TNF)-α and interleukin (IL)-6 were measured at baseline and 4, 12 and 24 h following resuscitation. The neurological deficient score (NDS) was recorded and cerebral samples were collected for terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling assay and integrated optical density (IOD) analysis at 24 h following CPR. The results revealed that hypothermia was not induced by CCK8; however, post-resuscitation NSE, S100B, IL-6 and TNF-α were significantly decreased, and NDS and IOD were significantly improved in the CCK8 group compared with the control group (P<0.05). The present study revealed that in a porcine model of CPR, CCK8 does not induce hypothermia, but inhibits the inflammatory response and significantly improves neurological outcomes.

Role of Perinatal Inflammation in Neonatal Arterial Ischemic Stroke

Based on the review of the literature, perinatal inflammation often induced by infection is the only consistent independent risk factor of neonatal arterial ischemic stroke (NAIS). Preclinical studies show that acute inflammatory processes take place in placenta, cerebral arterial wall of NAIS-susceptible arteries and neonatal brain. A top research priority in NAIS is to further characterize the nature and spatiotemporal features of the inflammatory processes involved in multiple levels of the pathophysiology of NAIS, to adequately design randomized control trials using targeted anti-inflammatory vasculo- and neuroprotective agents.

Therapeutic Whole-body Hypothermia Protects Remote Lung, Liver, and Kidney Injuries after Blast Limb Trauma in Rats

BACKGROUND

Severe blast limb trauma (BLT) induces distant multiple-organ injuries. In the current study, the authors determined whether whole-body hypothermia (WH) and its optimal duration (if any) afford protection to the local limb damage and distant lung, liver, and kidney injuries after BLT in rats.

METHODS

Rats with BLT, created by using chartaceous electricity detonators, were randomly treated with WH for 30 min, 60 min, 3 h, and 6 h (n = 12/group). Rectal temperature and arterial blood pressure were monitored throughout. Blood and lung, liver, and kidney tissue samples were harvested for measuring tumor necrosis factor-α, interleukin-6 and interleukin-10, myeloperoxidase activity, hydrogen sulfide, and biomarkers of oxidative stress at 6 h after BLT. The pathologic lung injury and the water content of the lungs, liver, and kidneys and blast limb tissue were assessed.

RESULTS

Unlike WH for 30 min, WH for 60 min reduced lung water content, lung myeloperoxidase activity, and kidney myeloperoxidase activity by 10, 39, and 28% (all P < 0.05), respectively. WH for 3 h attenuated distant vital organs and local traumatic limb damage and reduced myeloperoxidase activity, hydrogen peroxide and malondialdehyde concentration, and tumor necrosis factor-α and interleukin-6 levels by up to 49% (all P < 0.01). Likewise, WH for 6 h also provided protection to such injured organs but increased blood loss from traumatic limb.

CONCLUSIONS

Results of this study indicated that WH may provide protection for distant organs and local traumatic limb after blast trauma, which warrants further study.

Therapeutic Hypothermia Reduces Oxidative Damage and Alters Antioxidant Defenses after Cardiac Arrest

After cardiac arrest, organ damage consequent to ischemia-reperfusion has been attributed to oxidative stress. Mild therapeutic hypothermia has been applied to reduce this damage, and it may reduce oxidative damage as well. This study aimed to compare oxidative damage and antioxidant defenses in patients treated with controlled normothermia versus mild therapeutic hypothermia during postcardiac arrest syndrome. The sample consisted of 31 patients under controlled normothermia (36°C) and 11 patients treated with 24 h mild therapeutic hypothermia (33°C), victims of in- or out-of-hospital cardiac arrest. Parameters were assessed at 6, 12, 36, and 72 h after cardiac arrest in the central venous blood samples. Hypothermic and normothermic patients had similar S100B levels, a biomarker of brain injury. Xanthine oxidase activity is similar between hypothermic and normothermic patients; however, it decreases posthypothermia treatment. Xanthine oxidase activity is positively correlated with lactate and S100B and inversely correlated with pH, calcium, and sodium levels. Hypothermia reduces malondialdehyde and protein carbonyl levels, markers of oxidative damage. Concomitantly, hypothermia increases the activity of erythrocyte antioxidant enzymes superoxide dismutase, glutathione peroxidase, and glutathione S-transferase while decreasing the activity of serum paraoxonase-1. These findings suggest that mild therapeutic hypothermia reduces oxidative damage and alters antioxidant defenses in postcardiac arrest patients.

Induced hypothermia is associated with reduced circulating subunits of mitochondrial DNA in cardiac arrest patients

Induced hypothermia may protect from ischemia reperfusion injury. The mechanism of protection is not fully understood and may include an effect on mitochondria. Here we describe the effect of hypothermia on circulating mitochondrial (mt) DNA in a substudy of a multicenter randomized trial (the Target Temperature Management trial). Circulating levels of mtDNA were elevated in patients with cardiac arrest at all-time points compared to healthy controls. After 24 h of temperature management, patients kept at 33 °C had significantly lower levels of COX3, NADH1 and NADH2 compared to baseline, in contrast to those kept at 36 °C. After regain of temperature, cytochrome - B was significantly reduced in patients kept at 33 °C with cardiac arrest. Cardiac arrest results in circulating mtDNA levels, which reduced during a temperature management protocol in patients with a target temperature of 33 °C.

Mild hypothermia alleviates brain oedema and blood-brain barrier disruption by attenuating tight junction and adherens junction breakdown in a swine model of cardiopulmonary resuscitation

Mild hypothermia improves survival and neurological recovery after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). However, the mechanism underlying this phenomenon is not fully elucidated. The aim of this study was to determine whether mild hypothermia alleviates early blood-brain barrier (BBB) disruption. We investigated the effects of mild hypothermia on neurologic outcome, survival rate, brain water content, BBB permeability and changes in tight junctions (TJs) and adherens junctions (AJs) after CA and CPR. Pigs were subjected to 8 min of untreated ventricular fibrillation followed by CPR. Mild hypothermia (33°C) was intravascularly induced and maintained at this temperature for 12 h, followed by active rewarming. Mild hypothermia significantly reduced cortical water content, decreased BBB permeability and attenuated TJ ultrastructural and basement membrane breakdown in brain cortical microvessels. Mild hypothermia also attenuated the CPR-induced decreases in TJ (occludin, claudin-5, ZO-1) and AJ (VE-cadherin) protein and mRNA expression. Furthermore, mild hypothermia decreased the CA- and CPR-induced increases in matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) expression and increased angiogenin-1 (Ang-1) expression. Our findings suggest that mild hypothermia attenuates the CA- and resuscitation-induced early brain oedema and BBB disruption, and this improvement might be at least partially associated with attenuation of the breakdown of TJ and AJ, suppression of MMP-9 and VEGF expression, and upregulation of Ang-1 expression.

Neuroprotective effects of hypothermia in inflammatory-sensitized hypoxic-ischemic encephalopathy

BACKGROUND

Despite the recent introduction of hypothermia as a mandatory standard of care, the incidence of neonatal encephalopathy in full-term newborns and its devastating neuro-behavioral outcomes continues to be a major individual, familial and social issue. Neonatal encephalopathy is mainly due to the compounding and interacting effects of hypoxia-ischemia and inflammation resulting from placental and other perinatal infections. It is unclear why hypothermia is effective in alleviating neonatal encephalopathy in some, but not all, full-term newborns. However, newborns exposed to inflammatory-sensitized hypoxia-ischemia seem to have less therapeutic benefit from hypothermia than those exposed to hypoxia-ischemia alone.

OBJECTIVES

To clarify this uncertainty, we tested the efficacy of hypothermia in a double-hit model of neonatal encephalopathy induced by inflammatory-sensitized hypoxia-ischemia.

METHODS

Using a rat preclinical model of endotoxin plus hypoxia-ischemia-induced neonatal encephalopathy of term newborns, we assessed the following in pups exposed (or not) to hypothermia: the extent of brain injuries and the expressions of molecules implicated in neural cell death, namely: pro-inflammatory cytokines, matrix metalloproteinase-9, antioxidant enzymes, as well as receptor-interacting protein-3.

RESULTS

Hypothermia was neuroprotective on inflammatory-sensitized hypoxia-ischemia-induced penumbra, but not core, brain injuries. This beneficial effect was associated with a hypothermia-induced increase of antioxidant enzymes (superoxide dismutase-1, glutathione peroxidase-1), but was not associated with any variations of the other inflammatory mediators tested, namely: interleukin-1β, interleukin-1 receptor antagonist, tumor necrosis factor-α and matrix metalloproteinase-9.

CONCLUSION

Hypothermia is neuroprotective against inflammatory-sensitized hypoxia-ischemia possibly through a hypothermia-induced increase of antioxidant enzymes. This neuroprotective effect seems to be independent of the interleukin-1 system.

Neuroprotective hypothermia - Why keep your head cool during ischemia and reperfusion

BACKGROUND

Targeted temperature management (TTM) is the induced cooling of the entire body or specific organs to help prevent ischemia and reperfusion (I/R) injury, as may occur during major surgery, cardiac resuscitation, traumatic brain injury and stroke. Ischemia and reperfusion induce neuronal damage by mitochondrial dysfunction and oxidative injury, ER stress, neuronal excitotoxicity, and a neuroinflammatory response, which may lead to activation of apoptosis pathways.

SCOPE OF REVIEW

The aim of the current review is to discuss TTM targets that convey neuroprotection and to identify potential novel pharmacological intervention strategies for the prevention of cerebral ischemia and reperfusion injury.

MAJOR CONCLUSIONS

TTM precludes I/R injury by reducing glutamate release and oxidative stress and inhibiting release of pro-inflammatory factors and thereby counteracts mitochondrial induced apoptosis, neuronal excitotoxicity, and neuroinflammation. Moreover, TTM promotes regulation of the unfolded protein response and induces SUMOylation and the production of cold shock proteins. These advantageous effects of TTM seem to depend on the clinical setting, as well as type and extent of the injury. Therefore, future aims should be to refine hypothermia management in order to optimize TTM utilization and to search for pharmacological agents mimicking the cellular effects of TTM.

GENERAL SIGNIFICANCE

Bundling knowledge about TTM in the experimental, translational and clinical setting may result in better approaches for diminishing I/R damage. While application of TTM in the clinical setting has some disadvantages, targeting its putative protective pathways may be useful to prevent I/R injury and reduce neurological complications.

Carbon Monoxide Improves Neurologic Outcomes by Mitochondrial Biogenesis after Global Cerebral Ischemia Induced by Cardiac Arrest in Rats

Mitochondrial dysfunction contributes to brain injury following global cerebral ischemia after cardiac arrest. Carbon monoxide treatment has shown potent cytoprotective effects in ischemia/reperfusion injury. This study aimed to investigate the effects of carbon monoxide-releasing molecules on brain mitochondrial dysfunction and brain injury following resuscitation after cardiac arrest in rats. A rat model of cardiac arrest was established by asphyxia. The animals were randomly divided into the following 3 groups: cardiac arrest and resuscitation group, cardiac arrest and resuscitation plus carbon monoxide intervention group, and sham control group (no cardiac arrest). After the return of spontaneous circulation, neurologic deficit scores (NDS) and S-100B levels were significantly decreased at 24, 48, and 72 h, but carbon monoxide treatment improved the NDS and S-100B levels at 24 h and the 3-day survival rates of the rats. This treatment also decreased the number of damaged neurons in the hippocampus CA1 area and increased the brain mitochondrial activity. In addition, it increased mitochondrial biogenesis by increasing the expression of biogenesis factors including peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor-1, nuclear respiratory factor-2 and mitochondrial transcription factor A. Thus, this study showed that carbon monoxide treatment alleviated brain injury after cardiac arrest in rats by increased brain mitochondrial biogenesis.

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

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

Assessment of oxidative stress after out-of-hospital cardiac arrest

INTRODUCTION

Pathophysiology of cardiac arrest corresponds to a whole body ischemia-reperfusion. This phenomenon is usually associated with an oxidative stress in various settings, but few data are available on cardiac arrest in human. The aim of the present study was to evaluate different oxidative stress markers in out-of-hospital cardiac arrest (OHCA) patients treated with therapeutic hypothermia.

MATERIALS AND METHODS

We conducted a prospective study assessing oxidative stress markers (thiobarbituric acid reactive species, carbonyls, thiols, glutathione, and glutathione peroxidase) in OHCA patients treated with therapeutic hypothermia. Measurements were performed during the 4 days after admission and compared between good and poor outcome patients according to Cerebral Performance Category.

RESULTS

Thirty-four patients were included, 10 good and 24 poor outcomes at 6 months. Thiobarbituric acid reactive species were higher in the poor outcome group on admission and when therapeutic hypothermia was reached. The other markers were not different between groups. No markers seemed modified by the use of therapeutic hypothermia in each group.

CONCLUSIONS

After OHCA, good outcome patients exhibit lower oxidative stress markers than poor outcome patients. Thiobarbituric acid reactive species appears to be an early prognostic parameter. Oxidative stress markers seem not mitigated by therapeutic hypothermia.

Treatment temperature and insult severity influence the neuroprotective effects of therapeutic hypothermia

Therapeutic hypothermia (HT) is standard care for moderate and severe neonatal hypoxic-ischaemic encephalopathy (HIE), the leading cause of permanent brain injury in term newborns. However, the optimal temperature for HT is still unknown, and few preclinical studies have compared multiple HT treatment temperatures. Additionally, HT may not benefit infants with severe encephalopathy. In a neonatal rat model of unilateral hypoxia-ischaemia (HI), the effect of five different HT temperatures was investigated after either moderate or severe injury. At postnatal-day seven, rat pups underwent moderate or severe HI followed by 5 h at normothermia (37 °C), or one of five HT temperatures: 33.5 °C, 32 °C, 30 °C, 26 °C, and 18 °C. One week after treatment, neuropathological analysis of hemispheric and hippocampal area loss, and CA1 hippocampal pyramidal neuron count, was performed. After moderate injury, a significant reduction in hemispheric and hippocampal loss on the injured side, and preservation of CA1 pyramidal neurons, was seen in the 33.5 °C, 32 °C, and 30 °C groups. Cooling below 33.5 °C did not provide additional neuroprotection. Regardless of treatment temperature, HT was not neuroprotective in the severe HI model. Based on these findings, and previous experience translating preclinical studies into clinical application, we propose that milder cooling should be considered for future clinical trials.

Mild hypothermia inhibits systemic and cerebral complement activation in a swine model of cardiac arrest

Complement activation has been implicated in ischemia/reperfusion injury. This study aimed to determine whether mild hypothermia (HT) inhibits systemic and cerebral complement activation after resuscitation from cardiac arrest. Sixteen minipigs resuscitated from 8 minutes of untreated ventricular fibrillation were randomized into two groups: HT group (n=8), treated with HT (33°C) for 12 hours; and normothermia group (n=8), treated similarly as HT group except for cooling. Blood samples were collected at baseline and 0.5, 6, 12, and 24 hours after return of spontaneous circulation (ROSC). The brain cortex was harvested 24 hours after ROSC. Complement and pro-inflammatory markers were detected using enzyme-linked immunosorbent assay. Neurologic deficit scores were evaluated 24 hours after ROSC. C1q, Bb, mannose-binding lectin (MBL), C3b, C3a, C5a, interleukin-6, and tumor necrosis factor-α levels were significantly increased under normothermia within 24 hours after ROSC. However, these increases were significantly reduced by HT. Hypothermia decreased brain C1q, MBL, C3b, and C5a contents 24 hours after ROSC. Hypothermic pigs had a better neurologic outcome than normothermic pigs. In conclusion, complement is activated through classic, alternative, and MBL pathways after ROSC. Hypothermia inhibits systemic and cerebral complement activation, which may provide an additional mechanism of cerebral protection.

Moderate hypothermia ameliorates enterocyte mitochondrial dysfunction in severe shock and reperfusion

BACKGROUND

Hypothermia can ameliorate ischemia-reperfusion-induced intestinal injury; however, whether the therapeutic mechanism of hypothermia on hemorrhagic shock, a severe condition of ischemia-reperfusion, is associated with mitochondrial protection in enterocytes is rarely reported. We aimed to evaluate the effects of hypothermia on mitochondria after shock-induced intestinal injury.

MATERIALS AND METHODS

A severe hemorrhagic shock model was constructed in Sprague-Dawley rats at induced hypothermic (32°C or 34°C) or normothermic temperatures (37°C), followed by resuscitation with whole shed blood and Ringer lactate (15 mg/kg body weight). After 2 h, 24 rats were killed and their intestinal tissue was collected; the remaining animals were returned to the normothermic environment to observe the survival time.

RESULTS

There was severe mitochondrial dysfunction in the normothermia group, as well as increased oxidative stress and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling apoptotic index. As expected, hypothermia treatment decreased mitochondrial permeability transition pore opening and restored the mitochondrial membrane potential and intracellular adenosine triphosphate content. Furthermore, hypothermia elevated mitochondrial-reduced glutathione and decreased mitochondrial malondialdehyde; consistent with the restored mitochondrial function, intestinal cell apoptosis and intestinal histopathologic injury were attenuated, the systemic inflammatory response was mitigated, and survival time was significantly prolonged. Additionally, moderate-induced hypothermia (32°C) had better therapeutic effects than mild hypothermia (34°C).

CONCLUSIONS

The results suggest that moderate hypothermia resuscitation is an effective treatment for shock-induced intestinal injury, and its therapeutic mechanism may be related to mitochondrial protection.

Inhibition of the mitochondrial fission protein dynamin-related protein 1 improves survival in a murine cardiac arrest model

OBJECTIVES

Survival following sudden cardiac arrest is poor despite advances in cardiopulmonary resuscitation and the use of therapeutic hypothermia. Dynamin-related protein 1, a regulator of mitochondrial fission, is an important determinant of reactive oxygen species generation, myocardial necrosis, and left ventricular function following ischemia/reperfusion injury, but its role in cardiac arrest is unknown. We hypothesized that dynamin-related protein 1 inhibition would improve survival, cardiac hemodynamics, and mitochondrial function in an in vivo model of cardiac arrest.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

INTERVENTIONS

Anesthetized and ventilated adult female C57BL/6 wild-type mice underwent an 8-minute KCl-induced cardiac arrest followed by 90 seconds of cardiopulmonary resuscitation. Mice were then blindly randomized to a single IV injection of Mdivi-1 (0.24 mg/kg), a small molecule dynamin-related protein 1 inhibitor or vehicle (dimethyl sulfoxide).

MEASUREMENTS AND MAIN RESULTS

Following resuscitation from cardiac arrest, mitochondrial fission was evidenced by dynamin-related protein 1 translocation to the mitochondrial membrane and a decrease in mitochondrial size. Mitochondrial fission was associated with increased lactate and evidence of oxidative damage. Mdivi-1 administration during cardiopulmonary resuscitation inhibited dynamin-related protein 1 activation, preserved mitochondrial morphology, and decreased oxidative damage. Mdivi-1 also reduced the time to return of spontaneous circulation (116 ± 4 vs 143 ± 7 s; p < 0.001) during cardiopulmonary resuscitation and enhanced myocardial performance post-return of spontaneous circulation. These improvements were associated with significant increases in survival (65% vs 33%) and improved neurological scores up to 72 hours post cardiac arrest.

CONCLUSIONS

Post-cardiac arrest inhibition of dynamin-related protein 1 improves time to return of spontaneous circulation and myocardial hemodynamics, resulting in improved survival and neurological outcomes in a murine model of cardiac arrest. Pharmacological targeting of mitochondrial fission may be a promising therapy for cardiac arrest.

Protective effect of shen-fu injection on neuronal mitochondrial function in a porcine model of prolonged cardiac arrest

Background. Shen-Fu injection (SFI) following cardiac arrest exhibits neurological effects, but its effect on neurological dysfunction is unclear. This study sought to investigate the protective effect of SFI on nerve cells in a porcine model of cardiac arrest. Methods. After eight minutes of untreated ventricular fibrillation (VF) and 2 minutes of basic life support, 24 pigs were randomized and divided into three cardiopulmonary resuscitation groups, which received central venous injection of either Shen-Fu (SFI group; 1.0 ml/kg), epinephrine (EP group; 0.02 mg/kg), or saline (SA group). Surviving pigs were sacrificed at 24 h after ROSC and brains were removed for analysis for morphologic changes of mitochondria by electron microscopy, for mitochondrial transmembrane potential (MTP) by flow cytometry, and for opening of the mitochondrial permeability transition pore (MPTP) by mitochondrial light scattering. Results. Compared with the EP and SA groups, SFI treatment reduced opening of MPTP, showing higher MMP. In addition, animals treated with SFI showed slight cerebral ultrastructure damage under the electron microscopy. Conclusion. Shen-Fu injection alleviated brain injury, improved neurological ultrastructure, stabilized membrane potential, and inhibited opening of MPTP. Therefore, SFI could significantly attenuate postresuscitation cerebral ischemia and reperfusion injury by modulating mitochondrial dysfunction of nerve cells.

Effect of β-sodium aescinate on hypoxia-inducible factor-1α expression in rat brain cortex after cardiopulmonary resuscitation

BACKGROUND

This study was undertaken to investigate the expression of hypoxia-inducible factor-1α (HIF-1α) in rat cerebral cortex and the effects of β-sodium aescinate (SA) administration after return of spontaneous circulation (ROSC).

METHODS

SIXTY RATS WERE DIVIDED INTO THREE GROUPS: SA group, injected intraperitoneally with SA instantly after ROSC; control group, injected intraperitoneally with normal saline; and sham-operated group, without cardiac arrest or SA. The cardiac arrest model was established using asphyxiation and intravenous potassium chloride. Blood was sampled 1, 6, 12, and 24 hours after ROSC. Protein and mRNA levels of HIF-1α, VEGF and EPO were detected in the cerebral cortex by immunohistochemistry and real-time RT-PCR; serum levels of NSE and S100β were determined by enzyme-linked immunosorbent assays.

RESULTS

Serum S100β and NSE were significantly increased in the control group versus the sham-operated group 1, 6, 12 and 24 hours after ROSC (P<0.05). Protein and mRNA levels of HIF-1α, VEGF and EPO were significantly increased in the control rats (P<0.05). Serum NSE and S100β were significantly decreased in the SA group versus the control group 1, 6, 12 and 24 hours after ROSC (P<0.05). Protein and mRNA levels of HIF-1α, VEGF and EPO were significantly increased in the SA group (P<0.05).

CONCLUSIONS

The expression of HIF-1α is increased in rat cerebral cortex after ROSC, and SA up-regulates the expression of HIF-1α. The up-regulation of HIF-1α improves the resistance of the cortex to ischemia and hypoxia and contributes to neuroprotection, possibly because of up-regulation of EPO and VEGF expression.

Neuronal injury from cardiac arrest: aging years in minutes

Cardiac arrest is a leading cause of death and permanent disability. Most victims succumb to the oxidative and inflammatory damage sustained during cardiac arrest/resuscitation, but even survivors typically battle long-term neurocognitive impairment. Although extensive research has delineated the complex mechanisms that culminate in neuronal damage and death, no effective treatments have been developed to interrupt these mechanisms. Of importance, many of these injury cascades are also active in the aging brain, where neurons and other cells are under persistent oxidative and inflammatory stress which eventually damages or kills the cells. In light of these similarities, it is reasonable to propose that the brain essentially ages the equivalent of several years within the few minutes taken to resuscitate a patient from cardiac arrest. Accordingly, cardiac arrest-resuscitation models may afford an opportunity to study the deleterious mechanisms underlying the aging process, on an accelerated time course. The aging and resuscitation fields both stand to gain pivotal insights from one another regarding the mechanisms of injury sustained during resuscitation from cardiac arrest and during aging. This synergism between the two fields could be harnessed to foster development of treatments to not only save lives but also to enhance the quality of life for the elderly.

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

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

Prolonged therapeutic hypothermia is more effective in attenuating brain apoptosis in a Swine cardiac arrest model

OBJECTIVES

To investigate whether 48 hours of therapeutic hypothermia is more effective to attenuate brain apoptosis than 24 hours and to determine whether the antiapoptotic effects of therapeutic hypothermia are associated with the suppressions of the cleavage of protein kinase C-δ, the cytosolic release of cytochrome c, and the cleavage of caspase 3 in a swine cardiac arrest model.

DESIGN

Prospective laboratory study.

SETTING

University laboratory.

SUBJECTS

Male domestic pigs (n = 24).

INTERVENTIONS

After 6 minutes of no-flow time that was induced by ventricular fibrillation, cardiopulmonary resuscitation was provided, and the return of spontaneous circulation was achieved. The animals were randomly assigned to the following groups: sham, normothermia, 24 hours of therapeutic hypothermia, or 48 hours of therapeutic hypothermia. Therapeutic hypothermia (core temperature, 32-34°C) was maintained for 24 or 48 hours post return of spontaneous circulation, and the animals were rewarmed for 8 hours. At 60 hours post return of spontaneous circulation, the animals were killed, and brain tissues were harvested.

MEASUREMENTS AND MAIN RESULTS

We examined cellular apoptosis and neuronal damage in the brain hippocampal cornu ammonis 1 region. We also measured the cleavage of protein kinase C-δ, the cytosolic release of cytochrome c, and the cleavage of caspase 3 in the hippocampus. The 48 hours of therapeutic hypothermia attenuated cellular apoptosis and neuronal damage when compared with normothermia. There was also a decrease in the cleavage of protein kinase C-δ, the cytosolic release of cytochrome c, and the cleavage of caspase 3. However, 24 hours of therapeutic hypothermia did not significantly attenuate cellular apoptosis or neuronal damage.

CONCLUSIONS

We found that 48 hours of therapeutic hypothermia was more effective in attenuating brain apoptosis than 24 hours of therapeutic hypothermia. We also found that the antiapoptotic effects of therapeutic hypothermia were associated with the suppressions of the cleavage of protein kinase C-δ, the cytosolic release of cytochrome c, and the cleavage of caspase 3.

Transient regional hypothermia applied to a traumatic limb attenuates distant lung injury following blast limb trauma

OBJECTIVES

Explosive traumatic injury to an extremity may lead to both local and distant organ injury. Regional traumatic tissue hypothermia has been reported to offer systemic protection; here we investigated the protective effects of regional limb hypothermia on local tissue trauma and the lungs. Furthermore, the optimal duration of regional traumatic limb hypothermic treatment was also evaluated.

DESIGN

Prospective, controlled, animal study.

SETTING

University research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Anesthetized rats were randomized to sham, blast limb trauma, sham and regional hypothermia for 30 minutes, and blast limb trauma and regional hypothermia for 30 minutes, 60 minutes, and 6 hours. Blast limb trauma was created using chartaceous electricity detonators.

MEASUREMENTS AND MAIN RESULTS

Distant lung and local tissue injury following blast limb trauma were attenuated by regional traumatic limb hypothermic treatment for 30 minutes, 60 minutes, and 6 hours reflected by reduced lung histopathological changes and water content. Regional traumatic limb hypothermic treatment for 60 minutes and 6 hours failed to further attenuate distant lung and local tissue injury compared with regional traumatic limb hypothermic treatment for 30 minutes. Inhibition of cystathionine gamma-lyase/hydrogen sulfide was reduced by regional traumatic limb hypothermic treatment for 30 minutes in blast limb trauma rats. A surrogate of neutrophil accumulation, myeloperoxidase activity, and release of tumor necrosis factor-α and interleukin-6 were also attenuated by regional traumatic limb hypothermic treatment for 30 minutes in blast limb trauma rats. Oxidative stress was alleviated by regional traumatic limb hypothermic treatment for 30 minutes evidenced by reduction of hydrogen peroxide and malondialdehyde and an increase of superoxide dismutase and glutathione in blast limb trauma rats.

CONCLUSIONS

Our data indicate that regional traumatic limb hypothermic treatment for 30 minutes offers both local protection for traumatic tissue and systemic protection for the lungs, which is likely associated with restoration of the cystathionine gamma-lyase/hydrogen sulfide pathway and inhibition of the inflammatory response and oxidative stress.

Evidence for the therapeutic efficacy of either mild hypothermia or oxygen radical scavengers after repetitive mild traumatic brain injury

Repetitive brain injury, particularly that occurring with sporting-related injuries, has recently garnered increased attention in both the clinical and public settings. In the laboratory, we have demonstrated the adverse axonal and vascular consequences of repetitive brain injury and have demonstrated that moderate hypothermia and/or FK506 exerted protective effects after repetitive mild traumatic brain injury (mTBI) when administered within a specific time frame, suggesting a range of therapeutic modalities to prevent a dramatic exacerbation. In this communication, we revisit the utility of targeted therapeutic intervention to seek the minimal level of hypothermia needed to achieve protection while probing the role of oxygen radicals and their therapeutic targeting. Male Sprague-Dawley rats were subjected to repetitive mTBI by impact acceleration injury. Mild hypothermia (35 °C, group 2), superoxide dismutase (group 3), and Tempol (group 4) were employed as therapeutic interventions administered 1  h after the repetitive mTBI. To assess vascular function, cerebral vascular reactivity to acetylcholine was evaluated 3 and 4 h after the repetitive mTBI, whereas to detect the burden of axonal damage, amyloid precursor protein (APP) density in the medullospinal junction was measured. Whereas complete impairment of vascular reactivity was observed in group 1 (without intervention), significant preservation of vascular reactivity was found in the other groups. Similarly, whereas remarkable increase in the APP-positive axon was observed in group 1, there were no significant increases in the other groups. Collectively, these findings indicate that even mild hypothermia or the blunting free radical damage, even when performed in a delayed period, is protective in repetitive mTBI.