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Background

Inflammatory reactions occurring in the brain after ischemia may contribute to secondary damage. In the present study, effects of minocycline, an anti-inflammatory agent, alone or in combination with mild hypothermia on focal embolic cerebral ischemia have been examined.

Methods

Focal ischemic injury was induced by embolizing a preformed clot into the middle cerebral artery (MCA). Infarction volume was measured at 48 h after the injury. Mortality was also recorded.

Results

Delayed administration of minocycline alone or delayed minocycline plus delayed mild hypothermia reduced the infarction volume significantly. However, delayed mild hypothermia alone was not protective and delayed mild hypothermia in combination with minocycline did not show any additive effect.

Conclusions

These results suggest that minocycline is beneficial in focal ischemic brain injury, and the lack of the enhanced neuroprotection may be due to the brief exposure to hypothermia.

Stroke is a dynamic event in the brain involving heterogeneous cells. There is now compelling clinical evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe ischemia can reduce subsequent neuronal death and improve behavioral recovery. The neuroprotective role of hypothermia is also well established in experimental animals. However, the mechanism of hypothermic neuroprotection remains unclear, although, presumably involves the ability of hypothermia to suppress a broad range of injurious factors. In this paper, we addressed this issue by utilizing comprehensive gene and protein expression analyses of ischemic rat brains. To predict precise target molecules, we took advantage of the therapeutic time window and duration of hypothermia necessary to exert neuroprotective effects. We proposed that hypothermia contributes to protect neuroinflammation, and identified candidate molecules such as MIP-3α and Hsp70 that warrant further investigation as targets for therapeutic drugs acting as “hypothermia-like neuroprotectants.”

We recently showed that intraischemic moderate hypothermia (30°C) reduces ischemic damage through the Akt pathway after permanent distal middle cerebral artery occlusion in rats. The only Akt pathway component preserved by hypothermia is phosphorylated phosphatase and tensin homolog deleted on chromosome 10 (p-PTEN), which suggests that p-PTEN may have a central role in neuroprotection. Reactive oxygen species (ROS) are critically involved in mediating ischemic damage after stroke by interacting with signaling molecules, including Akt, PTEN, and δ-protein kinase C (PKC). We investigated the protective mechanisms of moderate hypothermia on these signaling proteins after transient focal ischemia in rats. Early moderate hypothermia (3 h) was administered 15 mins before reperfusion, and delayed moderate hypothermia (3 h) was applied 15 mins after reperfusion. Our results indicate that early hypothermia reduced infarction, whereas delayed hypothermia did not. However, both early and delayed hypothermia maintained levels of Mn-SOD (superoxide dismutase) and phosphorylated Akt and blocked δ-PKC cleavage, suggesting that these factors may not be critical to the protection of hypothermia. Nevertheless, early hypothermia preserved p-PTEN levels after reperfusion, whereas delayed hypothermia did not. Furthermore, ROS inhibition maintained levels of p-PTEN after stroke. Together, these findings suggest that phosphorylation levels of PTEN are closely associated with the protective effect of early hypothermia against stroke.

Background

We and others have reported that rapid ischemic postconditioning, interrupting early reperfusion after stroke, reduces infarction in rats. However, its extremely short therapeutic time windows, from a few seconds to minutes after reperfusion, may hinder its clinical translation. Thus, in this study we explored if delayed postconditioning, which is conducted a few hours after reperfusion, offers protection against stroke.

Methods and Results

Focal ischemia was generated by 30 min occlusion of bilateral common carotid artery (CCA) combined with permanent occlusion of middle cerebral artery (MCA); delayed postconditioning was performed by repetitive, brief occlusion and release of the bilateral CCAs, or of the ipsilateral CCA alone. As a result, delayed postconditioning performed at 3h and 6h after stroke robustly reduced infarct size, with the strongest protection achieved by delayed postconditioning with 6 cycles of 15 min occlusion/15 min release of the ipsilateral CCA executed from 6h. We found that this delayed postconditioning provided long-term protection for up to two months by reducing infarction and improving outcomes of the behavioral tests; it also attenuated reduction in 2-[18F]-fluoro-2-deoxy-D-glucose (FDG)-uptake therefore improving metabolism, and reduced edema and blood brain barrier leakage. Reperfusion in ischemic stroke patients is usually achieved by tissue plasminogen activator (tPA) application, however, t-PA's side effect may worsen ischemic injury. Thus, we tested whether delayed postconditioning counteracts the exacerbating effect of t-PA. The results showed that delayed postconditioning mitigated the worsening effect of t-PA on infarction.

Conclusion

Delayed postconditioning reduced ischemic injury after focal ischemia, which opens a new research avenue for stroke therapy and its underlying protective mechanisms.

Abstract

Hypothermia is robustly protective in pre-clinical models of both global and focal ischemia, as well as in patients after cardiac arrest. Although the mechanism for hypothermic neuroprotection remains unknown, reducing metabolic drive may play a role. Capitalizing on the beneficial effects of hypothermia while avoiding detrimental effects such as infection will be the key to moving this therapy forward as a treatment for stroke. AMPK is a master energy sensor that monitors levels of key energy metabolites. AMPK is activated via phosphorylation (pAMPK) when cellular energy levels are low, such as that seen during ischemia. AMPK activation appears to be detrimental in experimental stroke, likely via exacerbating ischemia-induced metabolic failure. We tested the hypothesis that hypothermia reduces AMPK activation. First, it was found that hypothermia reduced infarct after middle cerebral artery occlusion. Second, induced hypothermia reduced brain pAMPK in both sham control and stroke mice. Third, hypothermic neuroprotection was ameliorated after administration of compound C, an AMPK inhibitor. Finally, deletion of one of the catalytic isoforms of AMPK completely reversed the effect of hypothermia on stroke outcome after both acute and chronic survival. These effects were mediated by a reduction in AMPK activation rather than a reduction in LKB1, an upstream AMPK kinase. In summary, these studies provide evidence that hypothermia exerts its protective effect in part by inhibiting AMPK activation in experimental focal stroke. This suggests that AMPK represents a potentially important biological target for stroke treatment.

We previously showed that hypothermia attenuates inflammation in focal cerebral ischemia (FCI) by suppressing activating kinases of nuclear factor-kappa B (NFκB). Here we characterize the inflammatory response in global cerebral ischemia (GCI), and the influence of mild hypothermia. Rodents were subjected to GCI by bilateral carotid artery occlusion. The inflammatory response was accompanied by microglial activation, but not neutrophil infiltration, or blood brain barrier disruption. Mild hypothermia reduced CA1 damage, decreased microglial activation and decreased nuclear NFκB translocation and activation. Similar anti-inflammatory effects of hypothermia were observed in a model of pure brain inflammation that does not cause brain cell death. Primary microglial cultures subjected to oxygen glucose deprivation (OGD) or stimulated with LPS under hypothermic conditions also experienced less activation and less NFκB translocation. However, NFκB regulatory proteins were not affected by hypothermia. The inflammatory response following GCI and hypothermia’s anti-inflammatory mechanism is different from that observed in FCI.

Mild hypothermia renders potent neuroprotection against acute brain injury. Recent reports show that adenosine 5′-monophosphate (AMP) plays a role in thermoregulation and induces hypothermia in mice. Therefore, this study sought to determine whether AMP induces hypothermia in rats and to study its collective effects on cerebral ischemia induced by 2-h middle cerebral artery occlusion. An intraperitoneal injection of AMP induced hypothermia dose-dependently. At the dose of 4 mmol/kg, AMP induced promising mild hypothermia for 2.5 h. Unexpectedly, the AMP-induced hypothermia failed to reduce infarct volume after brain ischemia; instead, it exaggerated the ischemic damage, indicated by an increased infarct volume, as well as increased incidences of hemorrhagic transformation, seizure, and animal death. Physiologic parameter monitoring revealed that AMP causes profound hypotension, leading to cerebral hypoperfusion. Furthermore, AMP administration resulted in severe hyperglycemia, metabolic acidosis, and hypocalcemia. In addition, western blots showed early dephosphorylation and degradation of AMP-activated kinase in the ischemic cortex in AMP-treated rats. Taken together, our findings suggest that AMP induces hypothermia in rats, probably by limiting cellular access to glucose. However, the potential neuroprotection of AMP-mediated hypothermia against ischemia was overwhelmed by the detrimental effects of hypotension and hyperglycemia, thus making AMP an unlikely agent for inducing hypothermia to protect the brain against ischemic injury.

Mild hypothermia is an established neuroprotectant in the laboratory, showing remarkable and consistent effects across multiple laboratories and models of brain injury. At the clinical level, mild hypothermia has shown benefits in patients who have suffered cardiac arrest and in some pediatric populations suffering hypoxic brain insults. However, a review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, brain cooling needs to begin soon after the insult, maintained for relatively long period periods of time, and, in the case of ischemic stroke, should be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, especially rapid cooling and the reestablishment of perfusion. The addition of a second neuroprotectant could potentially (1) enhance overall protection, (2) prolong the temporal therapeutic window for hypothermia, or (3) provide protection where hypothermic treatment is only transient. Combination therapies resulting in recanalization following ischemic stroke would improve the likelihood of a good outcome, as the experimental literature suggests more consistent neuroprotection against ischemia with reperfusion, than ischemia without. Since recombinant tissue plasiminogen activator (rt-PA) is the only FDA approved treatment for acute ischemic stroke, and acts to recanalize occluded vessels, it is an obvious initial strategy to combine with hypothermia. However, the effects of thrombolytics are also temperature dependent, and the risk of hemorrhage is significant. The experimental data nevertheless seem to favor a combinatorial approach. Thus, in order to apply hypothermia to a broader range of patients, combination strategies should be further investigated.

Abstract

Mild hypothermia is an established neuroprotectant in the laboratory, showing remarkable and consistent effects across multiple laboratories and models of brain injury. At the clinical level, mild hypothermia has shown benefits in patients who have suffered cardiac arrest and in some pediatric populations suffering hypoxic brain insults. However, a review of the literature has demonstrated that in order to appreciate the maximum benefits of hypothermia, brain cooling needs to begin soon after the insult, maintained for relatively long period periods of time, and, in the case of ischemic stroke, should be applied in conjunction with the re-establishment of cerebral perfusion. Translating this to the clinical arena can be challenging, especially rapid cooling and the re-establishment of perfusion. The addition of a second neuroprotectant could potentially (1) enhance overall protection, (2) prolong the temporal therapeutic window for hypothermia, or (3) provide protection where hypothermic treatment is only transient. Combination therapies resulting in recanalization following ischemic stroke would improve the likelihood of a good outcome, as the experimental literature suggests more consistent neuroprotection against ischemia with reperfusion, than ischemia without. Since recombinant tissue plasiminogen activator (rt-PA) is the only FDA approved treatment for acute ischemic stroke, and acts to recanalize occluded vessels, it is an obvious initial strategy to combine with hypothermia. However, the effects of thrombolytics are also temperature dependent, and the risk of hemorrhage is significant. The experimental data nevertheless seem to favor a combinatorial approach. Thus, in order to apply hypothermia to a broader range of patients, combination strategies should be further investigated.

Background

Mild therapeutic hypothermia following cardiac arrest is neuroprotective, but its effect on myocardial dysfunction that is a critical issue following resuscitation is not clear. This study sought to examine whether hypothermia and the combination of hypothermia and pharmacological postconditioning are cardioprotective in a model of cardiopulmonary resuscitation following acute myocardial ischemia.

Methodology/Principal Findings

Thirty pigs (28–34 kg) were subjected to cardiac arrest following left anterior descending coronary artery ischemia. After 7 minutes of ventricular fibrillation and 2 minutes of basic life support, advanced cardiac life support was started according to the current AHA guidelines. After successful return of spontaneous circulation (n = 21), coronary perfusion was reestablished after 60 minutes of occlusion, and animals were randomized to either normothermia at 38°C, hypothermia at 33°C or hypothermia at 33°C combined with sevoflurane (each group n = 7) for 24 hours. The effects on cardiac damage especially on inflammation, apoptosis, and remodeling were studied using cellular and molecular approaches. Five animals were sham operated. Animals treated with hypothermia had lower troponin T levels (p<0.01), reduced infarct size (34±7 versus 57±12%; p<0.05) and improved left ventricular function compared to normothermia (p<0.05). Hypothermia was associated with a reduction in: (i) immune cell infiltration, (ii) apoptosis, (iii) IL-1β and IL-6 mRNA up-regulation, and (iv) IL-1β protein expression (p<0.05). Moreover, decreased matrix metalloproteinase-9 activity was detected in the ischemic myocardium after treatment with mild hypothermia. Sevoflurane conferred additional protective effects although statistic significance was not reached.

Conclusions/Significance

Hypothermia reduced myocardial damage and dysfunction after cardiopulmonary resuscitation possible via a reduced rate of apoptosis and pro-inflammatory cytokine expression.

Introduction

Therapeutic hypothermia is being employed, clinically based, on its neuro-protective benefits. Both critical illness and therapeutic hypothermia significantly affect drug disposition, potentially contributing to drug-therapy and drug-disease interaction. Currently, there is limited written information of the known alterations in drug concentration and response during mild hypothermia treatment and there is a limited understanding of the specific mechanisms that underlie alterations in drug concentrations and the potential clinical importance of these changes.

Areas covered

A systemic review of the effect of therapeutic hypothermia on drug metabolism, disposition, and response is provided. Specifically, the clinical and preclinical evidence of the effects of therapeutic hypothermia on blood flow, specific hepatic metabolism pathways, transporter, renal excretion, pharmacodynamics and rewarming effect are reviewed.

Expert Opinion

Available evidence demonstrates that mild hypothermia decreases the clearance of a variety of drugs with apparently little change in drug protein binding. Recent evidence suggests that the magnitude of the change is elimination route specific. Further research is needed to determine the impact of these alterations on both drug concentration and response in order to optimize the hypothermia therapy in this vulnerable patient population.

Protection by mild hypothermia has previously been associated with better mitochondrial preservation and suppression of the intrinsic apoptotic pathway. It is also known that the brain may undergo apoptotic death via extrinsic, or receptor mediated pathways, such as that triggered by Fas/FasL. Male Sprague Dawley rats subjected to 2h middle cerebral artery occlusion with 2h intraischemic mild hypothermia (33C) were assayed for Fas, FasL and caspase-8 expression. Ischemia increased Fas, but decreased FasL by ~50–60% at 6 and 24h post insult. Mild hypothermia significantly reduced expression of Fas and processed caspase-8 both by ~50%, but prevented ischemia-induced FasL decreases. Fractionation revealed that soluble/shed FasL (sFasL) was decreased by hypothermia, while membrane-bound FasL (mFasL) increased. To more directly assess the significance of the Fas/FasL pathway in ischemic stroke, primary neuron cultures were exposed to oxygen glucose deprivation. Since FasL is cleaved by matrix metalloproteinases (MMPs), and mild hypothermia decreases MMP expression, treatment with a pan-MMP inhibitor also decreased sFasL. Thus, mild hypothermia is associated with reduced Fas expression and caspase-8 activation. Hypothermia prevented total FasL decreases, and most of it remained membrane bound. These findings reveal new observations regarding the effect of mild hypothermia on the Fas/FasL and MMP systems.

Hypothermia has long been known to be a potent neuroprotectant. In this mini review, we highlighted clinical experience that hypothermia protects the brain from cerebral injury. We discussed the clinical practice of hypothermia in ischemic stroke. Multiple factors play a significant role in the mechanisms. Clinical application drew first from two clinical trials with comatose patients after cardiac arrest is attractive. The Australian and European study have led to renewed interest in these patients. More and more evidence bring insight into its effects on cerebral ischemia. The type of cooling technique to be used, the duration of cooling and speed of rewarming appear to be key factors in determining whether hypothermia is effective in preventing or mitigating neurological injury. Although until now, there are no clear therapeutic standards of the parameters in therapeutic hypothermia, it is well accepted that cooling should be initiated as soon as possible. By combining hypothermia with other neuroprotectants, it may be possible to enhance protective effects, reduce side effects and lengthen the maximum time. In addition to its neuroprotective properties hypothermia may extend the therapeutic window for other neuroprotective treatment. Thus, combination therapies with neuroprotective, anti-inflammatory and thrombolytic agents are likely to be investigated in the clinical setting in the future.

Despite many years of research, outcome after cardiac arrest is dismal. Since 2005, the European Resuscitation Council recommends in its guidelines the use of mild therapeutic hypothermia (32-34°) for 12 to 24 hours in patients successfully resuscitated from cardiac arrest. The benefit of resuscitative mild hypothermia (induced after resuscitation) is well established, while the benefit of preservative mild to moderate hypothermia (induced during cardiac arrest) needs further investigation before recommending it for clinical routine. Animal data and limited human data suggest that early and fast cooling might be essential for the beneficial effect of resuscitative mild hypothermia. Out-of-hospital cooling has been shown to be feasible and safe by means of intravenous infusion with cold fluids or non-invasively with cooling pads. A combination of these cooling methods might further improve cooling efficacy. If out-of-hospital cooling will further improve functional outcome as compared with in-hospital cooling needs to be determined in a prospective, randomised, sufficiently powered clinical trial.

Introduction

Hypothermia improves survival and neurological recovery after cardiac arrest. Pro-inflammatory cytokines have been implicated in focal cerebral ischemia/reperfusion injury. It is unknown whether cardiac arrest also triggers the release of cerebral inflammatory molecules, and whether therapeutic hypothermia alters this inflammatory response. This study sought to examine whether hypothermia or the combination of hypothermia with anesthetic post-conditioning with sevoflurane affect cerebral inflammatory response after cardiopulmonary resuscitation.

Methods

Thirty pigs (28 to 34 kg) were subjected to cardiac arrest following temporary coronary artery occlusion. After seven minutes of ventricular fibrillation and two minutes of basic life support, advanced cardiac life support was started according to the current American Heart Association guidelines. Return of spontaneous circulation was achieved in 21 animals who were randomized to either normothermia at 38°C, hypothermia at 33°C or hypothermia at 33°C combined with sevoflurane (each group: n = 7) for 24 hours. The effects of hypothermia and the combination of hypothermia with sevoflurane on cerebral inflammatory response after cardiopulmonary resuscitation were studied using tissue samples from the cerebral cortex of pigs euthanized after 24 hours and employing quantitative RT-PCR and ELISA techniques.

Results

Global cerebral ischemia following resuscitation resulted in significant upregulation of cerebral tissue inflammatory cytokine mRNA expression (mean ± SD; interleukin (IL)-1β 8.7 ± 4.0, IL-6 4.3 ± 2.6, IL-10 2.5 ± 1.6, tumor necrosis factor (TNF)α 2.8 ± 1.8, intercellular adhesion molecule-1 (ICAM-1) 4.0 ± 1.9-fold compared with sham control) and IL-1β protein concentration (1.9 ± 0.6-fold compared with sham control). Hypothermia was associated with a significant (P < 0.05 versus normothermia) reduction in cerebral inflammatory cytokine mRNA expression (IL-1β 1.7 ± 1.0, IL-6 2.2 ± 1.1, IL-10 0.8 ± 0.4, TNFα 1.1 ± 0.6, ICAM-1 1.9 ± 0.7-fold compared with sham control). These results were also confirmed for IL-1β on protein level. Experimental settings employing hypothermia in combination with sevoflurane showed that the volatile anesthetic did not confer additional anti-inflammatory effects compared with hypothermia alone.

Conclusions

Mild therapeutic hypothermia resulted in decreased expression of typical cerebral inflammatory mediators after cardiopulmonary resuscitation. This may confer, at least in part, neuroprotection following global cerebral ischemia and resuscitation.

Dephosphorylated and activated glycogen synthase kinase (GSK) 3β hyperphophorylates β-catenin, leading to its ubiquitin-proteosome-mediated degradation. β-catenin-knockdown increases while β-catenin overexpression prevents neuronal death in vitro; in addition, protein levels of β-catenin are reduced in the brain of Alzheimer’s patients. However, whether β-catenin degradation is involved in stroke-induced brain injury is unknown. Here we studied activities of GSK3 β and β-catenin, and the protective effect of moderate hypothermia (30 °C) on these activities after focal ischemia in rats. The results of Western blot showed that GSK3 β was dephosphorylated at 5 and 24 hours after stroke in the normothermic (37 °C) brain; hypothermia augmented GSK3β dephosphorylation. Because hypothermia reduces infarction, these results contradict with previous studies showing that GSK3β dephosphorylation worsens neuronal death. Nevertheless, hypothermia blocked degradation of total GSK3β protein. Corresponding to GSK3β activity in normothermic rats, β-catenin phosphorylation transiently increased at 5 hours in both the ischemic penumbra and core, and the total protein level of β-catenin degraded after normothermic stroke. Hypothermia did not inhibit β-catenin phosphorylation, but it blocked β-catenin degradation in the ischemic penumbra. In conclusion, moderate hypothermia can stabilize β-catenin, which may contribute to the protective effect of moderate hypothermia.

Background

In experimentally induced myocardial infarction, mild hypothermia (33–35°C) is beneficial if applied prior to ischemia or reperfusion. Hypothermia, when applied after reperfusion seems to confer little or no benefit. The mechanism by which hypothermia exerts its cell-protective effect during cardiac ischemia remains unclear. It has been hypothesized that hypothermia reduces the reperfusion damage; the additional damage incurred upon the myocardium during reperfusion. Reperfusion results in a massive increase in blood flow, reactive hyperemia, which may contribute to reperfusion damage. We postulated that hypothermia could attenuate the post-ischemic reactive hyperemia.

Methods

Sixteen 25–30 kg pigs, in a closed chest model, were anesthetized and temperature was established in all pigs at 37°C using an intravascular cooling catheter. The 16 pigs were then randomized to hypothermia (34°C) or control (37°C). The left main coronary artery was then catheterized with a PCI guiding catheter. A Doppler flow wire was placed in the mid part of the LAD and a PCI balloon was then positioned proximal to the Doppler wire but distal to the first diagonal branch. The LAD was then occluded for ten minutes in all pigs. Coronary blood flow was measured before, during and after ischemia/reperfusion.

Results

The peak flow seen during post-ischemic reactive hyperemia (during the first minutes of reperfusion) was significantly reduced by 43 % (p < 0.01) in hypothermic pigs compared to controls.

Conclusion

Mild hypothermia significantly reduces post-ischemic hyperemia in a closed chest pig model. The reduction of reactive hyperemia during reperfusion may have an impact on cardiac reperfusion injury.

Background

Whole-body hypothermia reduced the frequency of death or moderate/severe disabilities in neonates with hypoxic-ischemic encephalopathy in a randomized, controlled multicenter trial.

Objective

Our goal was to evaluate outcomes of safety and effectiveness of hypothermia in infants up to 18 to 22 months of age.

Design/Methods

A priori outcomes were evaluated between hypothermia (n = 102) and control (n = 106) groups.

Results

Encephalopathy attributable to causes other than hypoxia-ischemia at birth was not noted. Inotropic support (hypothermia, 59% of infants; control, 56% of infants) was similar during the 72-hour study intervention period in both groups. Need for blood transfusions (hypothermia, 24%; control, 24%), platelet transfusions (hypothermia, 20%; control, 12%), and volume expanders (hypothermia, 54%; control, 49%) was similar in the 2 groups. Among infants with persistent pulmonary hypertension (hypothermia, 25%; control, 22%), nitric-oxide use (hypothermia, 68%; control, 57%) and placement on extracorporeal membrane oxygenation (hypothermia, 4%; control, 9%) was similar between the 2 groups. Non–central nervous system organ dysfunctions occurred with similar frequency in the hypothermia (74%) and control (73%) groups. Rehospitalization occurred among 27% of the infants in the hypothermia group and 42% of infants in the control group. At 18 months, the hypothermia group had 24 deaths, 19 severe disabilities, and 2 moderate disabilities, whereas the control group had 38 deaths, 25 severe disabilities, and 1 moderate disability. Growth parameters were similar between survivors. No adverse outcomes were noted among infants receiving hypothermia with transient reduction of temperature below a target of 33.5°C at initiation of cooling. There was a trend in reduction of frequency of all outcomes in the hypothermia group compared with the control group in both moderate and severe encephalopathy categories.

Conclusions

Although not powered to test these secondary outcomes, whole-body hypothermia in infants with encephalopathy was safe and was associated with a consistent trend for decreasing frequency of each of the components of disability.

Numerous multiple trauma and surgical patients suffer from accidental hypothermia. While induced hypothermia is commonly used in elective cardiac surgery due to its protective effects, accidental hypothermia is associated with increased posttraumatic complications and even mortality in severely injured patients. This paper focuses on protective molecular mechanisms of hypothermia on apoptosis and the posttraumatic immune response. Although information regarding severe trauma is limited, there is evidence that induced hypothermia may have beneficial effects on the posttraumatic immune response as well as apoptosis in animal studies and certain clinical situations. However, more profound knowledge of mechanisms is necessary before randomized clinical trials in trauma patients can be initiated.

Background

Hypothermia is neuroprotective in experimental stroke and may extend the so far limited therapeutic time window for thrombolysis. Therefore, hypothermia of 34°C and its effects on delayed thrombolysis including reperfusion-associated injury were investigated in a model of thromboembolic stroke (TE).

Methods

Male Wistar rats (n = 48) were subjected to TE. The following treatment groups were investigated: control group - normothermia (37°C); thrombolysis group - rt-PA 90 min after TE; hypothermia by 34°C applied 1.5 to 5 hours after TE; combination therapy- hypothermia and rt-PA. After 24 hours infarct size, brain edema and neuroscore were assessed. Protein markers for inflammation and adhesion, gelatinase activity, and blood brain barrier (BBB) disruption were determined. MRI-measurements investigated infarct evolution and blood flow parameters.

Results

The infarct volume and brain swelling were smaller in the hypothermia group compared to the other groups (p < 0.05 to p < 0.01). Thrombolysis resulted in larger infarct and brain swelling than all others. Hypothermia in combination with thrombolysis reduced these parameters compared to thrombolysis (p < 0.05). Moreover, the neuroscore improved in the hypothermia group compared to control and thrombolysis. Animals of the combination therapy performed better than after thrombolysis alone (p < 0.05). Lower serum concentration of sICAM-1, and TIMP-1 were shown for hypothermia and combination therapy. Gelatinase activity was decreased by hypothermia in both groups.

Conclusions

Therapeutic hypothermia reduced side-effects of rt-PA associated treatment and reperfusion in our model of TE.

The purpose of this article is to review published experimental and clinical evidence for the benefits of modest hypothermia in the treatment of traumatic brain injury (TBI). Therapeutic hypothermia has been reported to improve outcome in several animal models of CNS injury and has been successfully translated to specific patient populations. A Pub Med search for hypothermia and TBI was conducted and important papers reviewed on the subject. Summarized research was conducted at major academic institutions throughout the world. Experimental studies have emphasized that hypothermia can affect multiple pathophysiological mechanisms felt to participate in the detrimental consequences of TBI. Published data from several relevant clinical trials on the use of hypothermia in severely injured TBI patients is also included. The consequences of mild to moderate levels of hypothermia introduced by different strategies to the head injured patient for variable periods of time are discussed. Both experimental and clinical data support the beneficial effects of modest hypothermia following TBI in specific patient populations. In addition to single institution studies, positive findings from multicenter TBI trials are now required before this experimental treatment is considered standard of care.

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.

Objective:

Therapeutic hypothermia instituted within 6 h of birth has been shown to improve neurodevelopmental outcomes in term newborns with moderate–to–severe hypoxic–ischemic encephalopathy (HIE). The majority of infants who would benefit from cooling are born at centers that do not offer the therapy, and adding the time for transport will result in delays in therapy, that may lead to suboptimal or no neuroprotection for some patients. Our objective was to evaluate the effect of our center's experience with therapeutic hypothermia on neonatal transport.

Study Design:

Retrospective review of all cases of therapeutic hypothermia at a single neonatal intensive care unit from 2005 to 2009.

Result:

Of 50 infants with HIE treated with hypothermia, 40 were outborn and 35 were cooled on transport. The majority of patients were passively cooled by the referring clinicians, then actively cooled by our transport team. Overcooling to <32 °C occurred in 34% of patients, but there were no significant differences in admission vital signs or laboratory values between overcooled and appropriately cooled infants. The average time after birth of initiation of passive cooling was 1.4 h and active cooling was 2.7 h compared with the time of admission to our unit of 5.9 h.

Conclusion:

We discuss the important aspects of our program, including the education of referring and receiving clinicians and avoidance of overcooling.

Mild hypothermia is the only effective treatment confirmed clinically to improve neurological outcomes for comatose patients with cardiac arrest. However, the underlying mechanism is not fully elucidated. In this study, our aim was to determine the effect of mild hypothermia on mitochondrial oxidative stress in the cerebral cortex. We intravascularly induced mild hypothermia (33°C), maintained this temperature for 12 h, and actively rewarmed in the inbred Chinese Wuzhishan minipigs successfully resuscitated after 8 min of untreated ventricular fibrillation. Cerebral samples were collected at 24 and 72 h following return of spontaneous circulation (ROSC). We found that mitochondrial malondialdehyde and protein carbonyl levels were significantly increased in the cerebral cortex in normothermic pigs even at 24 h after ROSC, whereas mild hypothermia attenuated this increase. Moreover, mild hypothermia attenuated the decrease in Complex I and Complex III (i.e., major sites of reactive oxygen species production) activities of the mitochondrial respiratory chain and increased antioxidant enzyme manganese superoxide dismutase (MnSOD) activity. This increase in MnSOD activity was consistent with the upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and protein expressions, and with the increase of Nrf2 nuclear translocation in normothermic pigs at 24 and 72 h following ROSC, whereas mild hypothermia enhanced these tendencies. Thus, our findings indicate that mild hypothermia attenuates mitochondrial oxidative stress in the cerebral cortex, which may be associated with reduced impairment of mitochondrial respiratory chain enzymes, and enhancement of MnSOD activity and expression via Nrf2 activation.

Although the protective mechanisms of delayed ischemic preconditioning have received extensive studies, few have addressed the mechanisms associated with rapid ischemic postconditioning. We investigated whether ischemic tolerance induced by rapid preconditioning is regulated by the Akt survival signaling pathway. Stroke was generated by permanent occlusion of the left distal middle cerebral artery (MCA) plus 30 min or 1 h occlusion of the bilateral common carotid artery (CCA) in male rats. Rapid preconditioning performed 1h before stroke onset reduced infarct size by 69% in rats with 30 min CCA occlusion, but by only 19% with 1 h occlusion. After control ischemia with 30 min CCA occlusion, Western Blot showed that P-Akt was transiently increased while Akt kinase assay showed that Akt activity was decreased. Although preconditioning did not change P-Akt levels at 1h and 5h compared with control ischemia, it attenuated reduction in Akt activity at 5h in the penumbra. However, preconditioning did not change the levels of P-PDK1, P-PTEN, and P-GSK3β in the Akt pathway, all of which were decreased after stroke. At last, the PI3K kinase inhibitor, LY294002, completely reversed the protection from ischemic preconditioning. In conclusion, Akt contributes to the protection of rapid preconditionin against stroke.