Postischemic hypothermia inhibits the generation of hydroxyl radical following transient forebrain ischemia in rats

Oxidative Stress-Responsive Apoptosis Inducing Protein (ORAIP) Plays a Critical Role in Dextran Sulfate Sodium-Induced Murine Model of Ulcerative Colitis

Oxidative stress is implicated in the pathogenesis of various acute disorders including ischemia/reperfusion injury, ultraviolet/radiation burn, as well as chronic disorders such as dyslipidemia, atherosclerosis, diabetes mellitus, chronic renal disease, and inflammatory bowel disease (IBD). However, the precise mechanism involved remains to be clarified. We formerly identified a novel apoptosis-inducing humoral protein, in a hypoxia/reoxygenation-conditioned medium of cardiac myocytes, which proved to be 69th tyrosine-sulfated eukaryotic translation initiation factor 5A (eIF5A). We named this novel tyrosine-sulfated secreted form of eIF5A Oxidative Stress-Responsive Apoptosis-Inducing Protein (ORAIP). To investigate the role of ORAIP in a dextran sulfate sodium (DSS)-induced murine model of ulcerative colitis (UC), we analyzed the effects of in vivo treatment with anti-ORAIP neutralizing monoclonal antibody (mAb) on the DSS-induced disease exacerbation. The body weight in anti-ORAIP mAb-treated group was significantly heavier than that in a mouse IgG-treated control group on day 8 of DSS-treatment ((85.21 ± 1.03%) vs. (77.38 ± 2.07%); (mean ± SE0, n = 5 each, p < 0.01, t-test). In vivo anti-ORAIP mAb-treatment also significantly suppressed the shortening of colon length as well as Disease Activity Index (DAI) score ((5.00 ± 0.44) vs. (8.20 ± 0.37); (mean ± SE), n = 5 each, p < 0.001, t-test) by suppressing inflammation of the rectal tissue and apoptosis of intestinal mucosal cells. These data reveal the pivotal role of ORAIP in DSS-induced oxidative stress involved in an animal model of UC.

Mild therapeutic hypothermia protects against inflammatory and proapoptotic processes in the rat model of cochlear implant trauma

OBJECTIVE

Mild therapeutic hypothermia (MTH) has been demonstrated to prevent residual hearing loss from surgical trauma associated with cochlear implant (CI) insertion. Here, we aimed to characterize the mechanisms of MTH-induced hearing preservation in CI in a well-established preclinical rodent model.

APPROACH

Rats were divided into four experimental conditions: MTH-treated and implanted cochleae, cochleae implanted under normothermic conditions, MTH only cochleae and un-operated cochleae (controls). Auditory brainstem responses (ABRs) were recorded at different time points (up to 84 days) to confirm long-term protection and safety of MTH locally applied to the cochlea for 20 min before and after implantation. Transcriptome sequencing profiling was performed on cochleae harvested 24 h post CI and MTH treatment to investigate the potential beneficial effects and underlying active gene expression pathways targeted by the temperature management.

RESULTS

MTH treatment preserved residual hearing up to 3 months following CI when compared to the normothermic CI group. In addition, MTH applied locally to the cochleae using our surgical approach was safe and did not affect hearing in the long-term. Results of RNA sequencing analysis highlight positive modulation of signaling pathways and gene expression associated with an activation of cellular inflammatory and immune responses against the mechanical damage caused by electrode insertion.

SIGNIFICANCE

These data suggest that multiple and possibly independent molecular pathways play a role in the protection of residual hearing provided by MTH against the trauma of cochlear implantation.

Oxidative stress-responsive apoptosis inducing protein (ORAIP) plays a critical role in doxorubicin-induced apoptosis in rat cardiac myocytes

BACKGROUND

Oxidative stress is implicated in the pathogenesis of doxorubicin-induced apoptosis in cardiac myocytes. However, the precise mechanism remains uncertain. We identified an apoptosis-inducing humoral factor, in a conditioned medium from cardiac myocytes subjected to hypoxia/reoxygenation, to be 69th tyrosine-sulfated eukaryotic translation initiation factor 5A (eIF5A). We named this novel secreted form of eIF5A, Oxidative stress-Responsive Apoptosis Inducing Protein (ORAIP). We confirmed that ischemia/reperfusion, ultraviolet-irradiation, and ionizing radiation significantly increased plasma levels of ORAIP in vivo, supporting that secretion of ORAIP is specific to the oxidative stress. To investigate the role of ORAIP in doxorubicin-induced apoptosis of cardiac myocytes.

METHODS

We analyzed plasma levels of ORAIP in rats treated with doxorubicin (10 mg/Kg) in vivo, and the effects of neutralizing anti-ORAIP monoclonal antibody (mAb) on doxorubicin-induced apoptosis of cardiac myocytes in vitro.

RESULTS

The (mean ± SE) plasma ORAIP levels before doxorubicin administration were (13.7 ± 2.7) ng/mL, they markedly increased with peak levels ([178.6 ± 6.5] ng/mL, p < 0.00001, vs. before administration) at 20 to 60 min after doxorubicin administration, then gradually decreased to (118.0 ± 4.8) ng/mL at 120 min. Treatment with a neutralizing anti-ORAIP mAb significantly (nearly 50%) suppressed doxorubicin-induced apoptosis of cardiac myocytes.

CONCLUSIONS

These data indicate that doxorubicin induces oxidative stress resulting in the strong expression of ORAIP in cardiac myocytes and marked secretion of ORAIP into peripheral circulation. This strongly suggests that ORAIP can be a novel sensitive biomarker as well as a possible therapeutic target for doxorubicin-induced cell injury in anti-cancer therapy.

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

METHODS

Adult male Sprague Dawley rats were studied in 4 groups: (1) sham; (2) stroke; (3) stroke treated with pharmacological hypothermia before reperfusion (interischemia hypothermia); and (4) stroke treated with pharmacological hypothermia after reperfusion is initiated (inter-reperfusion hypothermia). The combination of chlorpromazine and promethazine with dihydrocapsaicin (DHC) was used to induce hypothermia. To compare the neuroprotective effects of drug-induced hypothermia between the interischemia and inter-reperfusion groups, brain damage was evaluated using infarct volume and neurological deficits at 24 h reperfusion. In addition, mRNA expressions of NADPH oxidase (NOX) subunits (gp91phox, p67phox, p47phox, and p22phox) and glucose transporter subtypes (GLUT1 and GLUT3) were determined by real-time PCR at 6 and 24 h reperfusion. ROS production was measured by flow cytometry assay at the same time points.

RESULTS

In both hypothermia groups, the cerebral infarct volumes and neurological deficits were reduced in the ischemic rats. At 6 and 24 h reperfusion, ROS production and the expressions of NOX subunits and glucose transporter subtypes were also significantly reduced in both hypothermia groups as compared to the ischemic group. While there were no statistically significant differences between the two hypothermia groups at 6 h reperfusion, brain damage was significantly further decreased by interischemia hypothermia at 24 h.

CONCLUSION

Both interischemia and inter-reperfusion pharmacological hypothermia treatments play a role in neuroprotection after stroke. Interischemia hypothermia treatment may be better able to induce stronger neuroprotection after ischemic stroke. This study provides a new avenue and reference for stronger neuroprotective hypothermia before vascular recanalization in stroke patients.

Ultrafast Hypothermia Selectively Mitigates the Early Humoral Response After Cardiac Arrest

Background

Total liquid ventilation (TLV) has been shown to prevent neurological damage though ultrafast cooling in animal models of cardiac arrest. We investigated whether its neuroprotective effect could be explained by mitigation of early inflammatory events.

Methods and Results

Rabbits were submitted to 10 minutes of ventricular fibrillation. After resuscitation, they underwent normothermic follow‐up (control) or ultrafast cooling by TLV and hypothermia maintenance for 3 hours (TLV). Immune response, survival, and neurological dysfunction were assessed for 3 days. TLV improved neurological recovery and reduced cerebral lesions and leukocyte infiltration as compared with control (eg, neurological dysfunction score=34±6 versus 66±6% at day 1, respectively). TLV also significantly reduced interleukin‐6 blood levels during the hypothermic episode (298±303 versus 991±471 pg/mL in TLV versus control at 3 hours after resuscitation, respectively), but not after rewarming (752±563 versus 741±219 pg/mL in TLV versus control at 6 hours after resuscitation, respectively). In vitro assays confirmed the high temperature sensitivity of interleukin‐6 secretion. Conversely, TLV did not modify circulating high‐mobility group box 1 levels or immune cell recruitment into the peripheral circulation. The link between interleukin‐6 early transcripts (<8 hours) and neurological outcome in a subpopulation of the previously described Epo‐ACR‐02 (High Dose of Erythropoietin Analogue After Cardiac Arrest) trial confirmed the importance of this cytokine at the early stages as compared with delayed stages (>8 hours).

Conclusions

The neuroprotective effect of hypothermic TLV was associated with a mitigation of humoral interleukin‐6 response. A temperature‐dependent attenuation of immune cell reactivity during the early phase of the post–cardiac arrest syndrome could explain the potent effect of rapid hypothermia.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT00999583.

Recent antiepileptic and neuroprotective applications of brain cooling

Hypothermia is a widely used clinical practice for neuroprotection and is a well-established method to mitigate the adverse effects of some clinical conditions such as reperfusion injury after cardiac arrest and hypoxic ischemic encephalopathy in newborns. The discovery, that lowering the core temperature has a therapeutic potential dates back to the early 20th century, but the underlying mechanisms are actively researched, even today. Especially, in the area of neural disorders such as epilepsy and traumatic brain injury, cooling has promising prospects. It is well documented in animal models, that the application of focal brain cooling can effectively terminate epileptic discharges. There is, however, limited data regarding human clinical trials. In this review article, we will discuss the main aspects of therapeutic hypothermia focusing on its use in treating epilepsy. The various experimental approaches and device concepts for focal brain cooling are presented and their potential for controlling and suppressing seizure activity are compared.

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.

Oxidative stress-responsive apoptosis inducing protein (ORAIP) plays a critical role in cerebral ischemia/reperfusion injury

Oxidative stress is known to play a critical role in the pathogenesis of various disorders, especially in ischemia/reperfusion (I/R) injury. We identified an apoptosis-inducing humoral factor and named this novel post translationally modified secreted form of eukaryotic translation initiation factor 5A (eIF5A) "oxidative stress-responsive apoptosis inducing protein" (ORAIP). The purpose of this study was to investigate the role of ORAIP in the mechanisms of cerebral I/R injury. Hypoxia/reoxygenation induced expression of ORAIP in cultured rat cerebral neurons, resulting in extensive apoptosis of these cells, which was largely suppressed by neutralizing anti-ORAIP monoclonal antibody (mAb) in vitro. Recombinant-ORAIP induced extensive apoptosis of cerebral neurons. Cerebral I/R induced expression of ORAIP in many neurons in a rat tandem occlusion model in vivo. In addition, we analyzed the effects of intracerebroventricular administration of neutralizing anti-ORAIP mAb on the development of cerebral infarction. Cerebral I/R significantly increased ORAIP levels in cerebrospinal fluid. Treatment with intracerebroventricular administration of neutralizing anti-ORAIP mAb reduced infarct volume by 72%, and by 55% even when started after reperfusion. These data strongly suggest that ORAIP plays a pivotal role and will offer a critical therapeutic target for cerebral I/R injury induced by thrombolysis and thrombectomy for acute ischemic stroke.

Free Radical Damage in Ischemia-Reperfusion Injury: An Obstacle in Acute Ischemic Stroke after Revascularization Therapy

Acute ischemic stroke is a common cause of morbidity and mortality worldwide. Thrombolysis with recombinant tissue plasminogen activator and endovascular thrombectomy are the main revascularization therapies for acute ischemic stroke. However, ischemia-reperfusion injury after revascularization therapy can result in worsening outcomes. Among all possible pathological mechanisms of ischemia-reperfusion injury, free radical damage (mainly oxidative/nitrosative stress injury) has been found to play a key role in the process. Free radicals lead to protein dysfunction, DNA damage, and lipid peroxidation, resulting in cell death. Additionally, free radical damage has a strong connection with inducing hemorrhagic transformation and cerebral edema, which are the major complications of revascularization therapy, and mainly influencing neurological outcomes due to the disruption of the blood-brain barrier. In order to get a better clinical prognosis, more and more studies focus on the pharmaceutical and nonpharmaceutical neuroprotective therapies against free radical damage. This review discusses the pathological mechanisms of free radicals in ischemia-reperfusion injury and adjunctive neuroprotective therapies combined with revascularization therapy against free radical damage.

Effects of Topical Icing on Inflammation, Angiogenesis, Revascularization, and Myofiber Regeneration in Skeletal Muscle Following Contusion Injury

Contusion injuries in skeletal muscle commonly occur in contact sport and vehicular and industrial workplace accidents. Icing has traditionally been used to treat such injuries under the premise that it alleviates pain, reduces tissue metabolism, and modifies vascular responses to decrease swelling. Previous research has examined the effects of icing on inflammation and microcirculatory dynamics following muscle injury. However, whether icing influences angiogenesis, collateral vessel growth, or myofiber regeneration remains unknown. We compared the effects of icing vs. a sham treatment on the presence of neutrophils and macrophages; expression of CD34, von Willebrands factor (vWF), vascular endothelial growth factor (VEGF), and nestin; vessel volume; capillary density; and myofiber regeneration in skeletal after muscle contusion injury in rats. Muscle tissue was collected 1, 3, 7, and 28 d after injury. Compared with uninjured rats, muscles in rats that sustained the contusion injury exhibited major necrosis, inflammation, and increased expression of CD34, vWF, VEGF, and nestin. Compared with the sham treatment, icing attenuated and/or delayed neutrophil and macrophage infiltration; the expression of vWF, VEGF, and nestin; and the change in vessel volume within muscle in the first 7 d after injury (P < 0.05). By contrast, icing did not influence capillary density in muscle 28 d after injury (P = 0.59). The percentage of immature myofibers relative to the total number of fibers was greater in the icing group than in the sham group 28 d after injury (P = 0.026), but myofiber cross-sectional area did not differ between groups after 7 d (P = 0.35) and 28 d (P = 0.30). In conclusion, although icing disrupted inflammation and some aspects of angiogenesis/revascularization, these effects did not result in substantial differences in capillary density or muscle growth.

Protective effects of cyclosporine A and hypothermia on neuronal mitochondria in a rat asphyxial cardiac arrest model

BACKGROUND

Cyclosporine A (CsA) was neuroprotective in the settings of traumatic brain injury and stroke. We sought to investigate the protective effects of CsA and hypothermia on neuronal mitochondria after cardiac arrest.

METHODS AND RESULTS

Five groups were included: sham (S), normothermia (N), CsA (C), hypothermia (H), and CsA plus hypothermia (C+H). Cardiac arrest was induced by 10min of asphyxia. CsA (10mg/kg) was administered immediately after return of spontaneous circulation in the CsA groups. Temperature of the rats was maintained at 33±0.5°C after return of spontaneous circulation in the hypothermia groups. Hippocampal mitochondria were measured after 2h of resuscitation. Mitochondrial transmembrane potential was significantly higher in the C, the H, and the C+H groups than in the N group and was higher in the C+H group than in the C and the H groups. Cytosolic cytochrome c was significantly higher in the N group. Superoxide dismutase activity was significantly lower in the N group than in the other groups and was higher in the C and the C+H groups than in the H group. Malondialdehyde concentration was significantly higher in the N group.

CONCLUSIONS

CsA or hypothermia used immediately after resuscitation enhanced mitochondrial transmembrane potential, kept cytochrome c from releasing out of the mitochondria, increased superoxide dismutase activity, and decreased malondialdehyde concentration in hippocampus. Moreover, the protective effects of CsA were reinforced by hypothermia. One of the mechanisms that hypothermia protected neuronal mitochondria from damage was inhibiting the opening of mitochondrial permeability transition pore.

Combining Normobaric Oxygen with Ethanol or Hypothermia Prevents Brain Damage from Thromboembolic Stroke via PKC-Akt-NOX Modulation

In a thromboembolic stroke model after reperfusion by recombinant tissue plasminogen activator (rt-PA), we aimed to determine whether therapeutic hypothermia (TH) and ethanol (EtOH) in combination with low concentration (60 %) of normobaric oxygen (NBO) enhanced neuroprotection, as compared to using each of these agents alone. We further aimed to elucidate a potential role of the NADPH oxidase (NOX), phosphorylated protein kinase B (Akt), and protein kinase C-δ (PKC-δ) pathway in oxidative stress and neuroprotection. In Sprague-Dawley rats, a focal middle cerebral artery (MCA) occlusion was induced by an autologous embolus in the following experimental groups: rt-PA treatment alone, rt-PA + NBO treatment, rt-PA + TH at 33 °C, rt-PA + EtOH, rt-PA + NBO + EtOH, rt-PA + NBO + TH, rt-PA + NOX inhibitor, rt-PA + EtOH + NOX inhibitor, or rt-PA + EtOH + Akt inhibitor. Control groups included sham-operated without stroke or stroke without treatment. Infarct volume and neurological deficit were assessed at 24 h after rt-PA-induced reperfusion with or without treatments. ROS levels, NOX activity, and the protein expression of NOX subunits p22^phox, p47^phox, p67^phox, gp91^phox, as well as PKC-δ and phosphorylated Akt were measured at 3 and 24 h after rt-PA-induced reperfusion. Following rt-PA in thromboembolic stroke rats, NBO combined with TH or EtOH more effectively decreased infarct volume and neurological deficit, as well as reactive oxygen species (ROS) production than with any of the used monotherapies. NOX activity and subunit expressions were downregulated and temporally associated with reduced PKC-δ and increased p-Akt expression. The present study demonstrated that combining NBO with either TH or EtOH conferred similar neuroprotection via modulation of NOX activation. The results suggest a role of Akt in NOX activation and implicate an upstream PKC-δ pathway in the Akt regulation of NOX. It is possible to substitute EtOH for TH, thus circumventing the difficulties in clinical application of TH through the comparatively easier usage of EtOH as a potential stroke management.

Humidification during laparoscopic surgery: overview of the clinical benefits of using humidified gas during laparoscopic surgery

PURPOSE

The peritoneum is the serous membrane that covers the abdominal cavity and most of the intra-abdominal organs. It is a very delicate layer highly susceptible to damage and it is not designed to cope with variable conditions such as the dry and cold carbon dioxide (CO2) during laparoscopic surgery. The aim of this review was to evaluate the effects caused by insufflating dry and cold gas into the abdominal cavity after laparoscopic surgery.

METHODS

A literature search using the Pubmed was carried out. Articles identified focused on the key issues of laparoscopy, peritoneum, morphology, pneumoperitoneum, humidity, body temperature, pain, recovery time, post-operative adhesions and lens fogging.

RESULTS

Insufflating dry and cold CO2 into the abdomen causes peritoneal damage, post-operative pain, hypothermia and post-operative adhesions. Using humidified and warm gas prevents pain after surgery. With regard to hypothermia due to desiccation, it can be fully prevented using humidified and warm gas. Results relating to the patient recovery are still controversial.

CONCLUSIONS

The use of humidified and warm insufflation gas offers a significant clinical benefit to the patient, creating a more physiologic peritoneal environment and reducing the post-operative pain and hypothermia. In animal models, although humidified and warm gas reduces post-operative adhesions, humidified gas at 32 °C reduced them even more. It is clear that humidified gas should be used during laparoscopic surgery; however, a question remains unanswered: to achieve even greater clinical benefit to the patient, at what temperature should the humidified gas be when insufflated into the abdomen? More clinical trials should be performed to resolve this query.

Therapeutic hypothermia for stroke: Where to go?

Ischemic stroke is a major cause of death and long-term disability worldwide. Thrombolysis with recombinant tissue plasminogen activator is the only proven and effective treatment for acute ischemic stroke; however, therapeutic hypothermia is increasingly recognized as having a tissue-protective function and positively influencing neurological outcome, especially in cases of ischemia caused by cardiac arrest or hypoxic-ischemic encephalopathy in newborns. Yet, many aspects of hypothermia as a treatment for ischemic stroke remain unknown. Large-scale studies examining the effects of hypothermia on stroke are currently underway. This review discusses the mechanisms underlying the effect of hypothermia, as well as trends in hypothermia induction methods, methods for achieving optimal protection, side effects, and therapeutic strategies combining hypothermia with other neuroprotective treatments. Finally, outstanding issues that must be addressed before hypothermia treatment is implemented at a clinical level are also presented.

Molecular and cellular pathways as a target of therapeutic hypothermia: pharmacological aspect

Induced therapeutic hypothermia is the one of the most effective tools against brain injury and inflammation. Even though its beneficial effects are well known, there are a lot of pitfalls to overcome, since the potential adverse effects of systemic hypothermia are still troublesome. Without the knowledge of the precise mechanisms of hypothermia, it will be difficult to tackle the application of hypothermia in clinical fields. Better understanding of the characteristics and modes of hypothermic actions may further extend the usage of hypothermia by developing novel drugs based on the hypothermic mechanisms or by combining hypothermia with other therapeutic modalities such as neuroprotective drugs. In this review, we describe the potential therapeutic targets for the development of new drugs, with a focus on signal pathways, gene expression, and structural changes of cells. Theapeutic hypothermia has been shown to attenuate neuroinflammation by reducing the production of reactive oxygen species and proinflammatory mediators in the central nervous system. Along with the mechanism-based drug targets, applications of therapeutic hypothermia in combination with drug treatment will also be discussed in this review.

Role of induced hypothermia in thoracoabdominal aortic aneurysm surgery

For more than 50 years, hypothermia has been used in aortic surgery as a tool for neuroprotection. Hypothermia has been introduced into thoracoabdominal aortic aneurysm (TAAA) surgery by many cardiovascular centers to protect the body's organs, including the spinal cord. Numerous publications have shown that hypothermia can prevent immediate and delayed motor dysfunction after aortic cross-clamping. Here, we reviewed the historical application of hypothermia in aortic surgery, role of hypothermia in preclinical studies, cellular and molecular mechanisms by which hypothermia confers neuroprotection, and the role of systemic and regional hypothermia in clinical protocols to reduce and/or eliminate the devastating consequences of ischemic spinal cord injury after TAAA repair.

Resuscitation with 100% oxygen increases injury and counteracts the neuroprotective effect of therapeutic hypothermia in the neonatal rat

INTRODUCTION

Mild therapeutic hypothermia (HT) reduces brain injury in survivors after perinatal asphyxia. Recent guidelines suggest that resuscitation of term infants should be started with air, but supplemental oxygen is still in use. It is not known whether supplemental oxygen during resuscitation affects the protection offered by subsequent HT.

RESULTS

Wilcoxon median (95% confidence interval) hippocampal injury scores (range 0.0-4.0; 0 to ≥90% injury) were 21% O(2) normothermia (NT): 2.00 (1.25-2.50), 21% O(2) HT: 1.00 (0.50-1.50), 100% O(2) NT: 2.50 (1.50-3.25), and 100% O(2) HT: 2.00 (1.25-2.50). Although HT significantly reduced hippocampal injury (B = -0.721, SEM = 0.297, P = 0.018), reoxygenation with 100% O(2) increased injury (B = +0.647, SEM = 0.297, P = 0.033). Regression constant B = 1.896, SEM = 0.257 and normally distributed residuals.

DISCUSSION

We confirm an ~50% neuroprotective effect of therapeutic HT in the neonatal rat. Reoxygenation with 100% O(2) increased injury and worsened reflex performance. HT was neuroprotective whether applied after reoxygenation with air or 100% O(2). However, HT after 100% O(2) gave no net neuroprotection.

METHODS

In an established neonatal rat model, hypoxia-ischemia (HI) was followed by 30-min reoxygenation in either 21% O(2) or 100% O(2) before 5 h of NT (37 °C) or HT (32 °C). The effects of HT and 100% O(2) on histopathologic injury in the hippocampus, basal ganglia, and cortex, and on postural reflex performance 7 d after the insult, were estimated by linear regression.

Cerebral reactive oxygen species assessed by electron spin resonance spectroscopy in the initial stage of ischemia-reperfusion are not associated with hypothermic neuroprotection

Using an in vivo L-band electron spin resonance (ESR) system, we determined changes in reactive oxygen species (ROS) levels during the early stage (within 60 minutes) of global cerebral ischemia-reperfusion (IR) under normothermic and hypothermic conditions in rats. To confirm the neuroprotective role of hypothermia in this IR model, we immunohistochemically evaluated the levels of active caspase-3 in the hippocampal CA1 sector. ROS levels increased within the first 15 minutes following IR under both normothermic and hypothermic conditions; however, the ROS levels did not differ significantly between normothermic and hypothermic conditions. In the later periods of IR, there were no significant changes in ROS levels for either normothermic or hypothermic conditions relative to the control. As expected, normothermia increased the number of active caspase-3 immunoreactive nuclei in the IR model. However, this induction was prevented by hypothermia. These results suggest that the neuroprotective role of hypothermia does not correlate with the early ROS-induced oxidative stress following IR as measured by ESR.

Therapeutic hypothermia: critical review of the molecular mechanisms of action

Therapeutic hypothermia (TH) is nowadays one of the most important methods of neuroprotection. The events that occur after an episode of ischemia are multiple and hypothermia can affect the various steps of this cascade. The mechanisms of action of TH are varied and the possible explanation for the benefits of this therapy is probably the multiple mechanisms of action blocking the cascade of ischemia on many levels. TH can affect many metabolic pathways, reactions of inflammation, apoptosis processes, and promote neuronal integrity. To know the mechanisms of action of TH will allow a better understanding about the indications for this therapy and the possibility of searching for other therapies when used in conjunction with hypothermia will provide a therapeutic synergistic effect.

Reduced expression of DNA glycosylases in post-hypoxic newborn pigs undergoing therapeutic hypothermia

Supplementary oxygen during resuscitation of the asphyxiated newborn is associated with increased generation of reactive oxygen species and oxidative stress. It is suspected that hyperoxic reoxygenation may cause increased damage to DNA, resulting in replication errors, and cell death or potential fixation of mutations if unrepaired. Therapeutic hypothermia may attenuate the development of brain damage after asphyxia, but it is not known how post-hypoxic hyperoxia and hypothermia affect accumulation of DNA-damage and DNA repair. Anaesthetised newborn pigs were randomised to control (n=6) or severe global hypoxia (n=46). After 20min of reoxygenation with either room air or 100% O(2), followed by 6.5h of normothermia (deep rectal temperature 39°C) or total body cooling (35°C), oxidative DNA damage (8-hydroxy-2'-deoxyguanosine) in brain, liver and urine, and transcription of DNA repair glycosylases (NEIL1, NEIL3, and OGG1) in brain and liver were measured. Hypoxic pigs displayed increased urinary 8-oxodG levels: mean (SD) 8-oxodG/creatinine was 3.55 (1.46) vs. control 2.02 (0.53), p<0.05, but levels were not affected by hyperoxia or hypothermia. Accumulation of 8-oxodG in the brain and liver did not differ across groups. Post-hypoxic transcription of DNA glycosylases was down-regulated by hypothermia: OGG1 in hippocampus and liver (p<0.01); NEIL1 in hippocampus (p<0.01), cortex and striatum (p<0.05) and liver (p<0.001); and NEIL3 in hippocampus (p<0.01) and cerebellum (p<0.001). Hyperoxia did not affect transcription of glycosylases in the brain. We confirm increased oxidative stress after hypoxia. DNA repair glycosylases were down-regulated by hypothermia but with no effect on accumulation of oxidative damage in genomic DNA.

Early protective effect of hypothermia in newborn pigs after hyperoxic, but not after normoxic, reoxygenation

Abstract Mild hypothermia can attenuate the development of brain damage after asphyxia. Supplemental oxygen during resuscitation increases generation of reactive oxygen species, compared to room air. It is unknown if supplemental oxygen affects hypothermic neuroprotection. We studied the early effects of hyperoxic reoxygenation and subsequent hypothermia on tissue oxygenation, microcirculation, inflammation and brain damage after global hypoxia. Anesthetized newborn pigs were randomized to control (n=6), or severe global hypoxia (n=46). Three pigs died during hypoxia or reoxygenation. After 20-min reoxygenation with room air (n=22) or 100% oxygen (n=21), pigs were randomized to normothermia (deep rectal temperature 39 degrees C, n=22) or total body cooling (35 degrees C, n=21) for 6.5 h before the experiment was terminated. We demonstrated a differential effect of post-hypoxic hypothermia between animals reoxygenated with 100% oxygen and with room air, with reduced damage only in hypothermic animals reoxygenated with 100% oxygen (P=0.001). Hyperoxic reoxygenation resulted in a significant overshoot in striatal oxygen tension, without affecting microcirculation. Inflammatory response after the insult did not differ between groups. The results indicate an early protective effect of hypothermia which may vary with oxygen level used during reoxygenation.

Hyperbaric oxygenation alleviates MCAO-induced brain injury and reduces hydroxyl radical formation and glutamate release

The present study examined the effect of hyperbaric oxygen (HBO) on the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the products of salicylate trapping of hydroxyl free radicals, and glutamate release in the striatum during acute ischemia and reperfusion. Non-HBO rats (n = 8) were subjected to 1-h ischemia. Study rats (n = 8) were treated with HBO at 2.8 ATA for 1 h during ischemia. Artificial CSF solution containing 5 mM sodium salicylate was perfused at 1 microl/min. Samples were continuously collected at 15 min intervals and the levels of 2,3-DHBA, 2,5-DHBA, and glutamate were analyzed. The lesion volume was determined by TTC stain. Occlusion of the middle cerebral artery induced a significant increase in the levels of 2,3-DHBA and 2,5-DHBA. A peak of approximately two and fourfold of baseline levels was reached at 45 min and was maintained at elevated levels during reperfusion. The level of glutamate increased approximately two times at 30 min during ischemia, continued to increase, and reached approximately three times baseline level during reperfusion. HBO significantly alleviated brain injury associated with decreased levels of 2,3-DHBA, 2,5-DHBA and glutamate. This study suggests that the decreased glutamate release and the reduced formation of hydroxyl free radicals might contribute to the neuroprotective effect of HBO.

Intraoperative hypothermia during vascular neurosurgical procedures

Increasing evidence in animal models and clinical trials for stroke, hypoxic encephalopathy for children, and traumatic brain injury have shown that mild hypothermia may attenuate ischemic damage and improve neurological outcome. However, it is less clear if mild intraoperative hypothermia during vascular neurosurgical procedures results in improved outcomes for patients. This review examines the scientific evidence behind hypothermia as a treatment and discusses factors that may be important for the use of this adjuvant technique, including cooling temperature, duration of hypothermia, and rate of rewarming.

[Therapeutic hypothermia]

The use of therapeutic hypothermia has been shown to improve survival and neurological outcome following cardiac arrest. Patients with traumatic brain injury or ischemic stroke also responded positively to therapeutic hypothermia, which may be induced by various procedures including surface cooling, endovascular cooling catheter and cold infusion. Possible side effects include infection and hemorrhage, as well as changes in water and electrolyte levels. It is the aim of this article to provide an overview of studies to date, as well as practical guidance for the application of therapeutic hypothermia.

Induced hypothermia in acute ischemic stroke

BACKGROUND

Induced hypothermia is a promising neuroprotective treatment for acute ischemic stroke. Data from both global and focal ischemia animal models have been encouraging. However, only a few small clinical studies have investigated its use in humans.

OBJECTIVE

To review the background, possible mechanisms of action, and the preclinical and clinical data supporting the neuroprotective role of induced hypothermia following acute ischemic stroke.

METHODS

A literature search was performed using the PubMed database. Only papers in English were reviewed.

RESULTS/CONCLUSIONS

Induced hypothermia is effective as a neuroprotectant in animal models of acute ischemic stroke. Its multimodal mechanism of action makes it a very attractive method of neuroprotection. Although human studies suggest it is safe and feasible, larger randomized controlled trials are necessary to address clinical efficacy and to refine the methods and parameters of induced hypothermia protocols.

Bioenergetics of cerebral ischemia: a cellular perspective

In cerebral ischemia survival of neurons, astrocytes, oligodendrocytes and endothelial cells is threatened during energy deprivation and/or following re-supply of oxygen and glucose. After a brief summary of characteristics of different cells types, emphasizing the dependence of all on oxidative metabolism, the bioenergetics of focal and global ischemia is discussed, distinguishing between events during energy deprivation and subsequent recovery attempt after re-circulation. Gray and white matter ischemia are described separately, and distinctions are made between mature and immature brains. Next comes a description of bioenergetics in individual cell types in culture during oxygen/glucose deprivation or exposure to metabolic inhibitors and following re-establishment of normal aerated conditions. Due to their expression of NMDA and non-NMDA receptors neurons and oligodendrocytes are exquisitely sensitive to excitotoxicity by glutamate, which reaches high extracellular concentrations in ischemic brain for several reasons, including failing astrocytic uptake. Excitotoxicity kills brain cells by energetic exhaustion (due to Na(+) extrusion after channel-mediated entry) combined with mitochondrial Ca(2+)-mediated injury and formation of reactive oxygen species. Many (but not all) astrocytes survive energy deprivation for extended periods, but after return to aerated conditions they are vulnerable to mitochondrial damage by cytoplasmic/mitochondrial Ca(2+) overload and to NAD(+) deficiency. Ca(2+) overload is established by reversal of Na(+)/Ca(2+) exchangers following Na(+) accumulation during Na(+)-K(+)-Cl(-) cotransporter stimulation or pH regulation, compensating for excessive acid production. NAD(+) deficiency inhibits glycolysis and eventually oxidative metabolism, secondary to poly(ADP-ribose)polymerase (PARP) activity following DNA damage. Hyperglycemia can be beneficial for neurons but increases astrocytic death due to enhanced acidosis.

General versus specific actions of mild-moderate hypothermia in attenuating cerebral ischemic damage

Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.

Hypothermia affects translocation of numerous cytoplasmic proteins following global cerebral ischemia

Using a decapitation ischemia model, we studied translocation of proteins to and from the cytosol in normothermic (NT) and hypothermic (HT) rat brains. 2D gel analysis identified 74 proteins whose cytosolic level changed significantly after 15 min of ischemia. HT preserved the cytosolic levels of several glycolytic enzymes, as well as many plasticity related proteins, otherwise decreased following NT ischemia. The levels of redox-related proteins was lower in HT than in NT. Our results indicate that translocation of proteins to and from the cytosol is an important issue during ischemia.

BRAIN COOLING CAUSES ATTENUATION OF CEREBRAL OXIDATIVE STRESS, SYSTEMIC INFLAMMATION, ACTIVATED COAGULATION, AND TISSUE ISCHEMIA/INJURY DURING HEATSTROKE

The purpose of the present study was to assess the therapeutic effect of hypothermic retrograde jugular vein flush (HRJVF) on heatstroke. HRJVF was accomplished by infusion of 4 degrees C isotonic sodium chloride solution via the external jugular vein (1.7 mL/100 g of body weight over 5 min). Immediately after the onset of heatstroke, anesthetized rats were divided into 2 major groups and given the following: 36 degrees C or 4 degrees C isotonic sodium chloride solution, i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. When the 36 degrees C saline-treated rats underwent heat exposure, their survival time values were found to be 23 to 28 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline significantly improved survival during heatstroke (208-252 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time, and d-dimer, and decreased platelet count and protein C. Biochemical markers evidenced cellular ischemia and injury/dysfunction: plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; and striatal levels of glycerol, glutamate, and lactate/pyruvate; dihydroxy benzoic acid, lipid peroxidation, oxidized-form glutathione reduced-form glutathione, dopamine, and serotonin were all elevated during heatstroke. Core and brain temperatures and intracranial pressure were also increased during heatstroke. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and striatal levels of local blood flow, partial pressure of oxygen, superoxide dismutase, catalase, glutathione peroxidase, and glutathions reductase activities were all significantly lower during heatstroke. The circulatory dysfunction, systemic inflammation, hypercoagulable state, and cerebral oxidative stress, ischemia, and damage during heatstroke were all significantly suppressed by HRJVF. These findings demonstrate that brain cooling caused by HRJVF therapy may resuscitate persons who had a stroke by attenuating cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke.

Effect of desiccation and temperature during laparoscopy on adhesion formation in mice

OBJECTIVE

To investigate the effects of desiccation (without cooling) and of oversaturation of the pneumoperitoneum on adhesion formation.

DESIGN

Prospective randomized trial.

SETTING

Academic research center.

ANIMAL(S)

BALB/c and NMRI female mice.

INTERVENTION(S)

The effect of desiccation using nonhumidified CO(2) on adhesion formation was evaluated in a laparoscopic mouse model. Body temperature (BT) was maintained at 37 degrees C using a homeothermic blanket. In addition to controls without desiccation, the effect of both hypothermia and desiccation on adhesion formation was evaluated. Subsequently the effect of oversaturating the pneumoperitoneum using a high energy gas to avoid any desiccation was studied.

MAIN OUTCOME MEASURE(S)

During surgery BT, pneumoperitoneum temperature, and relative humidity were monitored. Adhesions were scored after 7 days.

RESULT(S)

Adhesions increased with increasing levels of desiccation when BT was kept at 37 degrees C. This was prevented with humidified gas. If BT decreased, adhesions were fewer. Oversaturating the pneumoperitoneum increased adhesions due to high energy gas causing an increase in both BT and pneumoperitoneum temperature.

CONCLUSION(S)

Adhesions increase with desiccation and decrease when BT is reduced. Adhesions are minimized when humidified gas is used. Since desiccation is associated with cooling, its effect is generally underestimated because of the counterbalance with cooling. The concept of combining controlled intraperitoneal cooling with a rigorous prevention of desiccation might be important for clinical adhesion prevention.

[Therapeutic hypothermia]

The benefit of therapeutic hypothermia after severe head injury is highly controversial. However, hypothermia is still used and studied in this context for multiple reasons. Efficacy of hypothermia is demonstrated after cerebral ischemia in numerous animal studies and after cardiac arrest in human studies. Hyperthermia is a major independent factor of outcome after cerebral ischemic or traumatic brain injury. Moreover, ICP is related to core temperature, and hypothermia may be used to decrease intracranial hypertension. However, many questions are still unresolved and can explain discrepancies between clinical studies: direct measurement of cerebral temperature, relationship between ICP, temperature and PaCO(2), level and duration of hypothermia and precise methods for cooling and particularly for rewarming.

GABA-mediated effects of some taurine derivatives injected i.c.v. on rabbit rectal temperature and gross motor behavior

Some synthetic taurine analogues, namely ethanolamine-O-sulphate (EOS), N,N-dimethyltaurine (DMT), N,N,N-trimethyltaurine (TMT) and 2-aminoethylphosphonic acid (AEP) were shown to interact with rabbit brain GABA(A)- or GABA(B)-receptors, while (+/-)piperidine-3-sulfonic acid (PSA) inhibited the activity of rabbit brain 4-aminobutyrate transaminase. This suggests that they behave like direct/indirect GABA agonists or GABA antagonists and affect thermoregulation and gross motor behaviour (GMB) which are under GABA control. In the present study micromole (1.2-48) amounts of these compounds were i.c.v. injected in conscious, restrained rabbits while monitoring rectal temperature (RT), ear skin temperature (EST) and GMB. AEP, EOS, DMT and TMT induced a dose-related hyperthermia, ear vasoconstriction and excitation of GMB, while PSA induced a dose-related hypothermia, ear vasodilation and inhibition of GMB. EOS antagonized in a dose-related fashion hypothermia induced by 60 nmol THIP, a GABA(A) agonist, while AEP, DMT and TMT counteracted that induced by 8 nmol R(-)Baclofen, a GABA(B) agonist. In conclusion, EOS and AEP, DMT, TMT seem to act as GABA(A) and GABA(B) antagonists, respectively, while PSA behaves like an indirect GABA agonist, all affecting the central mechanisms which drive rabbit thermoregulation.

Whole-body moderate hypothermia confers protection from wood smoke-induced acute lung injury in rats: The therapeutic window*

OBJECTIVE

Toxic smoke inhalation causes acute lung injury. We studied the efficacy and therapeutic window of whole-body hypothermia in rats with wood smoke-induced acute lung injury.

DESIGN

Randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Anesthetized, paralyzed, and artificially ventilated rats (n = 100) were used.

INTERVENTIONS

Air or wood smoke (30 breaths) was delivered into the lung using a respirator. Immediately after challenge, the rat's colonic temperature was kept a) 37 degrees C (normothermia, NT) for 1 (NT-1-Air and NT-1-Smoke), 2.5 (NT-2.5-Air and NT-2.5-Smoke), or 5 hrs (NT-5-Air and NT-5-Smoke) in six groups; b) 30 degrees C (hypothermia, HT) for 2.5 (HT-2.5-Smoke) or 5 hrs (HT-5-Air and HT-5-Smoke) in three groups; c) 30 degrees C for the first 2.5 hrs followed by 37 degrees C for another 2.5 hrs (HT-NT-5-Smoke) in one group; or d) 37 degrees C for the first 2.5 hrs followed by 30 degrees C for another 2.5 hrs (NT-HT-5-Smoke) in on group.

MEASUREMENTS AND MAIN RESULTS

Various acute lung injury indexes were assessed at 1, 2.5, or 5 hrs after challenge. In the air group, whole-body hypothermia did not affect the level of lung lipid peroxidation and the amount of proteins, total and differential cell counts, and concentrations of tumor necrosis factor-alpha and interleukin-1beta in bronchoalveolar lavage fluid. In the smoke groups, these acute lung injury indexes were increased showing that NT-5-Smoke > NT-2.5-Smoke > NT-1-Smoke. Whole-body hypothermia prevented increases in these acute lung injury indexes in the HT-2.5-Smoke and HT-5-Smoke groups. The efficacy of whole-body hypothermia in the HT-NT-5-Smoke group was superior to that in the NT-HT-5-Smoke group and similar to that in the HT-5-Smoke group. Whole-body hypothermia also alleviated smoke-induced poor gas exchange, pulmonary edema, and pathohistologic injurious signs.

CONCLUSIONS

Whole-body hypothermia confers protection from wood smoke-induced acute lung injury in rats by suppressing oxidant bronchoalveolar damage and pulmonary inflammation. Early and short-period (2 hrs) application of whole-body hypothermia provides favorable therapeutic effects.

Post-ischaemic mild hypothermia inhibits apoptosis in the penumbral region by reducing neuronal nitric oxide synthase activity and thereby preventing endothelin-1-induced hydroxyl radical formation

Previously, we showed that treatment with resuscitative, post-ischaemic mild hypothermia (34 degrees C for 2 h) reduced apoptosis in the penumbra (cortex), but not in the core (striatum) of an endothelin-1 (Et-1)-induced focal cerebral infarct in the anaesthetized rat. Therefore, the purpose of this study was to investigate by which pathways resuscitative mild hypothermia exerts its neuroprotective effect in this model. The amino acids glutamate, serine, glutamine, alanine, taurine, arginine and the NO-related compound citrulline were sampled from the striatum and cortex of the ischaemic hemisphere using in vivo microdialysis. The in vivo salicylate trapping method was applied for monitoring hydroxyl radical formation via 2,3 dihydroxybenzoic acid (2,3 DHBA) detection. Caspase-3, neuronal nitric oxide synthase (nNOS) immunoreactivity and the volume of ischaemic damage were determined 24 h after the insult. In both the striatum and the cortex, Et-1-induced increases in glutamate, taurine and alanine were refractory to mild hypothermia. However, mild hypothermia significantly attenuated the ischaemia-induced 2,3 DHBA levels and the nNOS immunoreactivity in the cortex, but not in the striatum. These observations were associated with a decreased caspase-3 immunoreactivity. These results suggest that mild hypothermia exerts its neuroprotective effect in the penumbra partially by reducing nNOS activity and thereby preventing oxidative stress. Furthermore, we confirm our previous findings that the neuroprotective effect of resuscitative hypothermia is not mediated by changes in ischaemia-induced amino acid release as they could not be associated with the ischaemia-induced damage in the Et-1 rat model.

Astrocytic contributions to bioenergetics of cerebral ischemia

Astrocytes are multifunctional cells that interact with neurons and other astrocytes in signaling and metabolic functions, and their resistance to pathophysiological conditions can help restrict loss of tissue after an ischemic event provided adequate nutrients are supplied to support their requirements. Astrocytes have substantial oxidative capacity and mechanisms to upregulate glycolytic capability when respiration is impaired. An astrocytic enzyme that synthesizes a powerful activator of glycolysis is not present in neurons, endowing astrocytes with the ability to sustain ATP production under restrictive conditions. The monocarboxylic acid transporter (MCT) isoforms predominating in astrocytes are optimized to facilitate very large increases in lactate flux as lactate concentration increases within (1-3 mM) and above (>3 mM) the normal range. In sharp contrast, the major neuronal MCT serves as a barrier to increased transmembrane transport as lactate rises above 1 mM, restricting both entry and efflux. Lactate can serve as fuel during recovery from ischemia but direct evidence that lactate is oxidized by neurons (vs. astrocytes) to maintain synaptic function is lacking. Astrocytes have critical roles in regulation of ionic homeostasis and control of extracellular glutamate levels, and spreading depression associated with ischemia places high demands on energy supplies in astrocytes and contributes to metabolic exhaustion and demise. Disruption of Ca2+ homeostasis, generation of oxygen free radicals and nitric oxide, and mitochondrial depolarization contribute to astrocyte death during and after a metabolic insult. Novel pharmaceutical agents targeted to astrocytes and hyperoxic therapy that restores penumbral oxygen level during energy failure might improve postischemic outcome.

Effects of hypothermia for a short period on histologic outcome and extracellular glutamate concentration during and after cardiac arrest in rats*

OBJECTIVE

To evaluate the therapeutic effects of hypothermia for a short period (20 mins, 31 degrees C) using a cardiac arrest model (5 mins) in rats.

DESIGN

Prospective animal study.

SETTING

Experimental laboratory in a university hospital.

SUBJECTS

Male Wistar rats (n = 42).

INTERVENTION

Direct current (DC) potential and extracellular glutamate concentrations (microdialysis) were monitored in the hippocampal region. Histologic observation was performed 7 days later.

MEASUREMENTS AND MAIN RESULTS

No animal died or showed severe complications as a result of hypothermia for a short period. In nontreated animals (group F), extracellular glutamate concentration simultaneously increased with the onset of membrane depolarization and continued to increase during the reperfusion period (maximum, 212% +/- 40% of the pre-ischemia level) until the onset of DC recovery. In animals in which hypothermia was initiated before the onset of ischemia (group A), extracellular glutamate concentration did not increase during the ischemia period. When hypothermia was initiated at the onset of resuscitation (group B), the glutamate concentration immediately decreased. In animals in which hypothermia was initiated at 4.9 +/- 1.3 mins (immediately after DC recovery, group C), 10 mins (group D), and 20 mins (group E) after the onset of resuscitation, changes in extracellular glutamate concentration were the same as those in nontreated animals. The percentage of injured neurons was significantly attenuated (compared with group F, 82% +/- 10%) when hypothermia was initiated before DC recovery (group A, 5% +/- 3%; group B, 29% +/- 22%) or immediately after DC recovery (group C, 58% +/- 18%, 9.9 +/- 1.3 mins after the onset of ischemia).

CONCLUSIONS

Hypothermia for a short period decreased glutamate concentration when it was initiated before DC recovery and attenuated neuronal damage when it was initiated before or immediately after DC recovery. The therapeutic time window for hypothermia for a short period is about 10 mins after the onset of ischemia.

Evidence that free radical generation occurs during scorpion envenomation

Although it is well established that symptomatology, morbidity and death following scorpion envenomation are due to increases in neurotransmitter release secondary to toxins binding to voltage-sensitive sodium channels, the mechanism by which venom action is involved in damaging heart, liver, lungs and kidneys remains unclear. We hypothesized that scorpion toxins could induce the generation of high levels of free radicals responsible for membrane damage in organs targeted by venom action. We have investigated lipid peroxidation in different organs, through the evaluation of thiobarbituric acid reactive substances (TBARS), after experimental envenomation of rats by toxic fractions of Androctonus australis Hector venom. We have shown that scorpion toxins cause considerable lipid peroxidation in most vital organs. We also evaluated the protective effects of antioxidants in mice injected with lethal doses of toxins. Among the drugs tested, N-acetylcysteine (NAC) was effective in protecting the mice when injected prior to toxin application. However, the free radical scavenging properties of NAC seem less implicated in these protective effects than its ability to increase the fluidity of bronchial secretions. We therefore conclude that free radical generation only plays a minor role in the toxicity of scorpion venom.

Regional changes in glial cell line-derived neurotrophic factor after cardiac arrest and hypothermia in rats

Hypothermia after resuscitation from cardiac arrest reduces functional and histological brain injury. Stimulation of neurotrophic factors may contribute to the beneficial effects of hypothermia. This study examined the effects of cardiac arrest and induced hypothermia on regional levels of glial cell line-derived neurotrophic factor (GDNF) over the first 24 h after rat cardiac arrest. Hypothermia increased GDNF in hippocampus at 6 h, but did not prevent a subsequent decline in hippocampal GDNF. In contrast, hypothermia prevented early increases in cortical levels of GDNF at 3 and 6 h. Cerebellar GDNF increased slightly over 24 h in hypothermia-treated rats, but brainstem levels of GDNF did not change in response to cardiac arrest or hypothermia. These results suggest that temperature after resuscitation produces regionally specific changes of GNDF levels in brain.

Effect of temperature upon adhesion formation in a laparoscopic mouse model

BACKGROUND

Pneumoperitoneum can be a cofactor in adhesion formation. Pneumoperitoneum with non-humidified gas causes desiccation in the peritoneal cavity which decreases temperature. The effect of desiccation upon adhesion formation is widely accepted. The specific effect of the associated cooling upon adhesion formation remains unexplored, and was addressed specifically in our laparoscopic mouse model.

METHODS

Adhesions were induced during laparoscopy and scored after 7 days during laparotomy. Pneumoperitoneum was performed using CO2 or CO2 with oxygen with or without humidification. Animals were placed at different environmental temperatures to modulate body and intraperitoneal temperature.

RESULTS

Anaesthesia, environment with a lower temperature and pneumoperitoneum all independently decrease body temperature. A decrease in body temperature decreases adhesion formation (P=0.004). Therefore, at 37 degrees C, pneumoperitoneum-enhanced adhesion formation is more important than at room temperature (P=0.04). As was observed at room temperature, adhesion formation at 37 degrees C increases with the duration (P=0.01) of pneumoperitoneum and decreases with the addition of 3% of oxygen (P=0.03).

CONCLUSIONS

Hypothermia reduces pneumoperitoneum-enhanced adhesion formation, which supports hypoxia as a driving mechanism, since hypothermia decreases the toxic effects of hypoxia and of the ischaemia-reperfusion process. These data could open up new possibilities for adhesion prevention in laparoscopic surgery.

Motor enrichment and the induction of plasticity before or after brain injury

Voluntary exercise, treadmill activity, skills training, and forced limb use have been utilized in animal studies to promote brain plasticity and functional change. Motor enrichment may prime the brain to respond more adaptively to injury, in part by upregulating trophic factors such as GDNF, FGF-2, or BDNF. Discontinuation of exercise in advance of brain injury may cause levels of trophic factor expression to plummet below baseline, which may leave the brain more vulnerable to degeneration. Underfeeding and motor enrichment induce remarkably similar molecular and cellular changes that could underlie their beneficial effects in the aged or injured brain. Exercise begun before focal ischemic injury increases BDNF and other defenses against cell death and can maintain or expand motor representations defined by cortical microstimulation. Interfering with BDNF synthesis causes the motor representations to recede or disappear. Injury to the brain, even in sedentary rats, causes a small, gradual increase in astrocytic expression of neurotrophic factors in both local and remote brain regions. The neurotrophic factors may inoculate those areas against further damage and enable brain repair and use-dependent synaptogenesis associated with recovery of function or compensatory motor learning. Plasticity mechanisms are particularly active during time-windows early after focal cortical damage or exposure to dopamine neurotoxins. Motor and cognitive impairments may contribute to self-imposed behavioral impoverishment, leading to a reduced plasticity. For slow degenerative models, early forced forelimb use or exercise has been shown to halt cell loss, whereas delayed rehabilitation training is ineffective and disuse is prodegenerative. However, it is possible that, in the chronic stages after brain injury, a regimen of exercise would reactivate mechanisms of plasticity and thus enhance rehabilitation targeting residual functional deficits.