Hypothermic suppression of microglial activation in culture: inhibition of cell proliferation and production of nitric oxide and superoxide

Semi-mechanistic Modeling of Hypoxanthine, Xanthine, and Uric Acid Metabolism in Asphyxiated Neonates

BACKGROUND AND OBJECTIVE

Previously, we developed a pharmacokinetic-pharmacodynamic model of allopurinol, oxypurinol, and biomarkers, hypoxanthine, xanthine, and uric acid, in neonates with hypoxic-ischemic encephalopathy, in which high initial biomarker levels were observed suggesting an impact of hypoxia. However, the full pharmacodynamics could not be elucidated in our previous study. The current study included additional data from the ALBINO study (NCT03162653) placebo group, aiming to characterize the dynamics of hypoxanthine, xanthine, and uric acid in neonates with hypoxic-ischemic encephalopathy.

METHODS

Neonates from the ALBINO study who received allopurinol or placebo mannitol were included. An extended population pharmacokinetic-pharmacodynamic model was developed based on the mechanism of purine metabolism, where synthesis, salvage, and degradation via xanthine oxidoreductase pathways were described. The initial level of the biomarkers was a combination of endogenous turnover and high disease-related amounts. Model development was accomplished by nonlinear mixed-effects modeling (NONMEM^®, version 7.5).

RESULTS

In total, 20 neonates treated with allopurinol and 17 neonates treated with mannitol were included in this analysis. Endogenous synthesis of the biomarkers reduced with 0.43% per hour because of precursor exhaustion. Hypoxanthine was readily salvaged or degraded to xanthine with rate constants of 0.5 1/h (95% confidence interval 0.33-0.77) and 0.2 1/h (95% confidence interval 0.09-0.31), respectively. A greater salvage was found in the allopurinol treatment group consistent with its mechanism of action. High hypoxia-induced initial levels of biomarkers were quantified, and were 1.2-fold to 2.9-fold higher in neonates with moderate-to-severe hypoxic-ischemic encephalopathy compared with those with mild hypoxic-ischemic encephalopathy. Half-maximal xanthine oxidoreductase inhibition was achieved with a combined allopurinol and oxypurinol concentration of 0.68 mg/L (95% confidence interval 0.48-0.92), suggesting full xanthine oxidoreductase inhibition during the period studied.

CONCLUSIONS

This extended pharmacokinetic-pharmacodynamic model provided an adequate description of the complex hypoxanthine, xanthine, and uric acid metabolism in neonates with hypoxic-ischemic encephalopathy, suggesting a positive allopurinol effect on these biomarkers. The impact of hypoxia on their dynamics was characterized, underlining higher hypoxia-related initial exposure with a more severe hypoxic-ischemic encephalopathy status.

Update on mechanisms of the pathophysiology of neonatal encephalopathy

Therapeutic hypothermia is now well established to significantly improve survival without disability after neonatal encephalopathy (NE). To further improve outcomes, we need to better understand the mechanisms of brain injury. The central finding, which offers the potential for neuroprotective and neurorestorative interventions, is that brain damage after perinatal hypoxia-ischemia evolves slowly over time. Although brain cells may die during profound hypoxia-ischemia, even after surprisingly severe insults many cells show transient recovery of oxidative metabolism during a "latent" phase characterized by actively suppressed neural metabolism and activity. Critically, after moderate to severe hypoxia-ischemia, this transient recovery is followed after ~6 h by a phase of secondary deterioration, with delayed seizures, failure of mitochondrial function, cytotoxic edema, and cell death over ~72 h. This is followed by a tertiary phase of remodeling and recovery. This review discusses the mechanisms of injury that occur during the primary, latent, secondary and tertiary phases of injury and potential treatments that target one or more of these phases. By analogy with therapeutic hypothermia, treatment as early as possible in the latent phase is likely to have the greatest potential to prevent injury ("neuroprotection"). In the secondary phase of injury, anticonvulsants can attenuate seizures, but show limited neuroprotection. Encouragingly, there is now increasing preclinical evidence that late, neurorestorative interventions have potential to improve long-term outcomes.

Recombinant erythropoietin does not augment hypothermic white matter protection after global cerebral ischaemia in near-term fetal sheep

Therapeutic hypothermia for hypoxic-ischaemic encephalopathy provides partial white matter protection. Recombinant erythropoietin reduces demyelination after hypoxia-ischaemia, but it is unclear whether adjunct erythropoietin treatment can further improve outcomes after therapeutic hypothermia. Term-equivalent fetal sheep received sham-ischaemia (n = 9) or cerebral ischaemia for 30 min (ischaemia-vehicle, n = 8), followed by intravenous infusion of recombinant erythropoietin (ischaemia-Epo, n = 8; 5000 IU/kg bolus dose, then 833.3 IU/kg/h), cerebral hypothermia (ischaemia-hypothermia, n = 8), or recombinant erythropoietin plus hypothermia (ischaemia-Epo-hypothermia, n = 8), from 3 to 72 h post-ischaemia. Foetal brains were harvested at 7 days after cerebral ischaemia. Ischaemia was associated with marked loss of total Olig2-positive oligodendrocytes with reduced density of myelin and linearity of the white matter tracts (P < 0.01), and microglial induction and increased caspase-3-positive apoptosis. Cerebral hypothermia improved the total number of oligodendrocytes and restored myelin basic protein (P < 0.01), whereas recombinant erythropoietin partially improved myelin basic protein density and tract linearity. Both interventions suppressed microgliosis and caspase-3 (P < 0.05). Co-treatment improved 2′,3′-cyclic-nucleotide 3′-phosphodiesterase-myelin density compared to hypothermia, but had no other additive effect. These findings suggest that although hypothermia and recombinant erythropoietin independently protect white matter after severe hypoxia-ischaemia, they have partially overlapping anti-inflammatory and anti-apoptotic effects, with little additive benefit of combination therapy.

Recent advances in perinatal neuroprotection

Perinatal brain injury is a major cause of neurological disability in both premature and term infants. In this review, we summarize the evidence behind some established neuroprotective practices such as administration of antenatal steroids, intrapartum magnesium for preterm delivery, and therapeutic hypothermia. In addition, we examine emerging practices such as delayed cord clamping, postnatal magnesium administration, recombinant erythropoietin, and non-steroidal anti-inflammatory agents and finally inform the reader about novel interventions, some of which are currently in trials, such as xenon, melatonin, topiramate, allopurinol, creatine, and autologous cord cell therapy.

Targeted Temperature Management for Subarachnoid Hemorrhage: Excellent Outcome After Severe Vasospasm-A Case Series

Targeted temperature management (TTM) might improve outcome of patients with severe subarachnoid hemorrhage (SAH) in which vasospasm, delayed cerebral ischemia (DCI), and increased intracranial pressure (ICP) are frequent and severe complications. A series of patients (n = 3) with severe aneurysmatic SAH were treated by TTM if they developed ICP crisis and/or severe vasospasm diagnosed by angiography. Once these complications were detected, body core temperature (BCT) was rapidly decreased to 35°C or 33°C, if necessary. BCT induced and maintained by surface cooling remained at the desired level for at least 72 hours. Rewarming was performed by 1°C, only if the target parameters ICP and velocities in the serial Doppler sonography indicating macrovascular vasospasm improved to regular levels. In case of increase of ICP or middle cerebral arteries velocities BCT was decreased again to the last effective level. The patients developed vasospasm between days 6 and 12 after SAH. All aneurysms were treated by coiling. BCT was reduced between days 6 and 12 after SAH. Total duration of BCT <36.5°C was between 5.5 and 8 days. It remained <35°C for 4-6 days, and at 33°C for 3 days on average. ICP could be sufficiently controlled in all patients, because no ICP crisis was observed during TTM and after rewarming. Two patients developed minor DCI. Side effects of prolonged ventilation of 7-18 days included pneumonia for two patients that could be treated sufficiently. Other complications were one case of ventriculitis and two temporary deliriums. Outcome of the patients was good because no focal neurological symptoms could be detected after rehabilitation. TTM represents a promising treatment approach for severe SAH in which standard treatment is often limited and experimental. It deserves further clinical investigation in a larger cohort.

A working model for hypothermic neuroprotection

Therapeutic hypothermia significantly improves survival without disability in near-term and full-term newborns with moderate to severe hypoxic-ischaemic encephalopathy. However, hypothermic neuroprotection is incomplete. The challenge now is to find ways to further improve outcomes. One major limitation to progress is that the specific mechanisms of hypothermia are only partly understood. Evidence supports the concept that therapeutic cooling suppresses multiple extracellular death signals, including intracellular pathways of apoptotic and necrotic cell death and inappropriate microglial activation. Thus, the optimal depth of induced hypothermia is that which effectively suppresses the cell death pathways after hypoxia-ischaemia, but without inhibiting recovery of the cellular environment. Thus mild hypothermia needs to be continued until the cell environment has recovered until it can actively support cell survival. This review highlights that key survival cues likely include the inter-related restoration of neuronal activity and growth factor release. This working model suggests that interventions that target overlapping mechanisms, such as anticonvulsants, are unlikely to materially augment hypothermic neuroprotection. We suggest that further improvements are most likely to be achieved with late interventions that maximise restoration of the normal cell environment after therapeutic hypothermia, such as recombinant human erythropoietin or stem cell therapy.

Prediction of Outcome in Neonates with Hypoxic-Ischemic Encephalopathy II: Role of Amplitude-Integrated Electroencephalography and Cerebral Oxygen Saturation Measured by Near-Infrared Spectroscopy

BACKGROUND

Few data have been published on the combined use of amplitude-integrated electroencephalography (aEEG) and near-infrared spectroscopy (NIRS) for outcome prediction in neonates cooled for hypoxic-ischemic encephalopathy (HIE).

OBJECTIVE

Our aim was to evaluate the predictive values and the most powerful predictive combinations of single aEEG and NIRS parameters and the respective cut-off values with regard to short-term outcomes in HIE II.

METHODS

aEEG and NIRS were prospectively studied at the Medical University of Vienna in the first 102 h of life with regard to magnetic resonance imaging (MRI). Thirty-two neonates diagnosed with HIE II treated with hypothermia were investigated. The measurement period was divided into 6-h epochs. According to MRI, 2 outcome groups were defined and predictive values of aEEG parameters, regional cerebral oxygen saturation (rScO2), and the additional value of both methods combined were studied. Receiver operating curves (ROC) were obtained and area under the curve (AUC) values were calculated. ROC were then used to detect the optimal cut-off points, sensitivity, specificity, positive predictive values, and negative predictive values.

RESULTS

At all time epochs, combined parameter scores were more predictive than single parameter scores. The highest AUC were observed between 18 and 60 h of cooling for the aEEG summation score (0.72-0.84) and for (background pattern + seizures) × rScO2 (0.79-0.85). At 42-60 h sensitivity was similar between those 2 scores (87.5-90.0%), but the addition of NIRS to aEEG led to an increase in specificity (from 52.4-59.1% to 72.7-90.5%).

CONCLUSIONS

In HIE II, aEEG and NIRS are important predictors of short-term outcome. The combination of both methods improves prognostication. The highest predictive abilities were observed between 18 and 60 h of cooling.

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

BACKGROUND

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

SCOPE OF REVIEW

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

MAJOR CONCLUSIONS

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

GENERAL SIGNIFICANCE

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

Hypothermia at 35 °C reduces the time-dependent microglial production of pro-inflammatory and anti-inflammatory factors that mediate neuronal cell death

BACKGROUND

Therapeutic hypothermia protects neurons after severe brain damage. This effect has been mainly achieved at the core temperatures of 32-34 °C; however, the optimum temperature of therapeutic hypothermia is not fully defined. Here we studied whether hypothermic culture at 35 °C had the same effects on the decrease of time-dependent expression of tumor necrosis factor (TNF)-α, interleukin (IL)-10, and nitric oxide (NO) by stimuli-activated microglia as that at 33 °C, as determined in our previous reports, and whether these factors directly induced neuronal cell death.

METHODS

We determined the levels of cytokines and NO produced by microglia cultured with adenosine triphosphate (ATP), a toll-like receptor (TLR)2 agonist (N-palmitoyl-S-(2,3-bis(palmitoyloxy)-(2R,S)-propyl)-(R)-cysteinyl-seryl-(lysyl)3-lysine, Pam(3)CSK(4)), or a TLR4 agonist (lipopolysaccharide) under mild hypothermic (33 °C), minimal hypothermic (35 °C), and normothermic (37 °C) conditions. We also determined the viability of rat neuronal pheochromocytoma PC12 cells treated with recombinant TNF-α or IL-10 or (±)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3, an NO donor).

RESULTS

Production of TNF-α, as well as that of IL-10 and NO were decreased by minimal hypothermia at 1.5-6, and 24-48 h, respectively, compared with normothermia, although some effects were diminished as compared with those by mild hypothermia. Exposure to TNF-α, IL-10, and NOR3 caused the death of PC12 cells in a concentration-dependent manner after 24 h.

CONCLUSION

Hypothermic culture at 35 °C decreased the production of early-phase TNF-α and late-phase IL-10 and NO from ATP- and TLR-activated microglia as observed at 33 °C, albeit with diminished effects. Moreover, these factors caused the death of neuronal cells in a concentration-dependent manner. These results suggest that the attenuation of microglial production of TNF-α, IL-10, and NO by therapeutic hypothermia leads to the inhibition of neuronal cell death. Minimal hypothermia at 35 °C may be sufficient to elicit neuroprotective effect.

Mechanisms of hypothermic neuroprotection

Prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce acute brain injury and improve long-term behavioral recovery in term infants and in adults after cardiac arrest. The specific mechanisms of hypothermic neuroprotection remain unclear, in part because hypothermia suppresses a broad range of potential injurious factors. This article examines proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Knowledge of the mechanisms of hypothermia will help guide the rational development of future combination treatments to augment neuroprotection with hypothermia and identify those most likely to benefit.

The mechanisms and treatment of asphyxial encephalopathy

Acute post-asphyxial encephalopathy occurring around the time of birth remains a major cause of death and disability. The recent seminal insight that allows active neuroprotective treatment is that even after profound asphyxia (the “primary” phase), many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting approximately 6 h, only to die hours to days later after a “secondary” deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Although many of these secondary processes are potentially injurious, they appear to be primarily epiphenomena of the “execution” phase of cell death. Animal and human studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible but before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, has been associated with potent, long-lasting neuroprotection. Recent clinical trials show that while therapeutic hypothermia significantly reduces morbidity and mortality, many babies still die or survive with disabilities. The challenge for the future is to find ways of improving the effectiveness of treatment. In this review, we will dissect the known mechanisms of hypoxic-ischemic brain injury in relation to the known effects of hypothermic neuroprotection.

Hypothermia reduces toll-like receptor 3-activated microglial interferon-β and nitric oxide production

Therapeutic hypothermia protects neurons after injury to the central nervous system (CNS). Microglia express toll-like receptors (TLRs) that play significant roles in the pathogenesis of sterile CNS injury. To elucidate the possible mechanisms involved in the neuroprotective effect of therapeutic hypothermia, we examined the effects of hypothermic culture on TLR3-activated microglial release of interferon (IFN)- β and nitric oxide (NO), which are known to be associated with neuronal cell death. When rat or mouse microglia were cultured under conditions of hypothermia (33°C) and normothermia (37°C) with a TLR3 agonist, polyinosinic-polycytidylic acid, the production of IFN- β and NO in TLR3-activated microglia at 48 h was decreased by hypothermia compared with that by normothermia. In addition, exposure to recombinant IFN- β and sodium nitroprusside, an NO donor, caused death of rat neuronal pheochromocytoma PC12 cells in a concentration-dependent manner after 24 h. Taken together, these results suggest that the attenuation of microglial production of IFN- β and NO by therapeutic hypothermia leads to the inhibition of neuronal cell death.

Temperature-related effects of adenosine triphosphate-activated microglia on pro-inflammatory factors

BACKGROUND

Therapeutic hypothermia protects neurons after severe brain injury. Activated microglia produce several neurotoxic factors, such as pro-inflammatory cytokines and nitric oxide (NO), during neuron destruction. Hence, suppression of microglial release of these factors is thought to contribute partly to the neuroprotective effects of hypothermia. After brain insults, adenosine triphosphate (ATP) is released from injured cells and activates microglia. Here, we examined the acute effects of temperature on ATP-activated microglial production of inflammatory factors, and the possible involvement of p38 mitogen-activated protein kinase (p38) underlying such effects.

METHODS

Microglia were cultured with ATP at 33, 37, and 39°C, or with ATP in the presence of a p38 inhibitor, SB203580, at 37°C. Cytokine and NO levels, and p38 activation were measured.

RESULTS

Compared to 37°C, TNF-α was reduced at 33°C and augmented at 39°C for 1.5 h. IL-6 was reduced at 33°C for 6 h. NO was reduced at 33°C, but augmented at 39°C for 6 h. p38 was reduced at 33°C for 1 min. SB203580 inhibited ATP-induced TNF-α, IL-6, and NO production.

CONCLUSION

Lowering temperature rapidly reduced p38 activation and the subsequent p38-regulated production of pro-inflammatory cytokines and NO in ATP-activated microglia, suggesting that attenuation of early phase inflammatory responses via suppression of p38 in microglia is one possible neuroprotective mechanism of therapeutic hypothermia. Temperature elevation increased TNF-α and NO production in these cells. These temperature-dependent changes imply that monitoring of TNF-α and NO in the cerebrospinal fluid during the early phase might be useful as biomarkers for responses to therapeutic hypothermia and hyperthermia.

Safety and efficacy of topiramate in neonates with hypoxic ischemic encephalopathy treated with hypothermia (NeoNATI)

BACKGROUND

Despite progresses in neonatal care, the mortality and the incidence of neuro-motor disability after perinatal asphyxia have failed to show substantial improvements. In countries with a high level of perinatal care, the incidence of asphyxia responsible for moderate or severe encephalopathy is still 2-3 per 1000 term newborns. Recent trials have demonstrated that moderate hypothermia, started within 6 hours after birth and protracted for 72 hours, can significantly improve survival and reduce neurologic impairment in neonates with hypoxic-ischemic encephalopathy. It is not currently known whether neuroprotective drugs can further improve the beneficial effects of hypothermia. Topiramate has been proven to reduce brain injury in animal models of neonatal hypoxic ischemic encephalopathy. However, the association of mild hypothermia and topiramate treatment has never been studied in human newborns. The objective of this research project is to evaluate, through a multicenter randomized controlled trial, whether the efficacy of moderate hypothermia can be increased by concomitant topiramate treatment.

METHODS/DESIGN

Term newborns (gestational age ≥ 36 weeks and birth weight ≥ 1800 g) with precocious metabolic, clinical and electroencephalographic (EEG) signs of hypoxic-ischemic encephalopathy will be randomized, according to their EEG pattern, to receive topiramate added to standard treatment with moderate hypothermia or standard treatment alone. Topiramate will be administered at 10 mg/kg once a day for the first 3 days of life. Topiramate concentrations will be measured on serial dried blood spots. 64 participants will be recruited in the study. To evaluate the safety of topiramate administration, cardiac and respiratory parameters will be continuously monitored. Blood samplings will be performed to check renal, liver and metabolic balance. To evaluate the efficacy of topiramate, the neurologic outcome of enrolled newborns will be evaluated by serial neurologic and neuroradiologic examinations. Visual function will be evaluated by means of behavioural standardized tests.

DISCUSSION

This pilot study will explore the possible therapeutic role of topiramate in combination with moderate hypothermia. Any favourable results of this research might open new perspectives about the reduction of cerebral damage in asphyxiated newborns.

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.

Effect of cerebral hypothermia and asphyxia on the subventricular zone and white matter tracts in preterm fetal sheep

Prolonged, moderate cerebral hypothermia is consistently neuroprotective after experimental hypoxia-ischemia. We have previously shown that hypothermia is also protective after profound asphyxia in the preterm brain. However, there is a concern whether hypothermia could suppress the proliferative response to injury in the white matter or subventricular zone (SVZ). Preterm (0.7 gestation) fetal sheep received complete umbilical cord occlusion for 25 min followed by cerebral hypothermia (extradural temperature reduced from 39.4±0.3 to 29.5±2.6°C) from 90 min to 70h after the end of occlusion or sham cooling. Occlusion-normothermia was associated with no effect on CNPase+ cells, but loss of O4+ oligodendrocytes, induction of cleaved caspase-3, and IB4+ microglia in the gyral and periventricular white matter compared to sham-occlusion (p < 0.05), with a significant increase in KI67+ cells in the periventricular white matter (p < 0.05). Hypothermia was associated with significant protection of O4+ cells, with suppression of IB4+ microglia and KI67+ cells in the periventricular white matter. There was no significant change in astrocytes, microglia, KI67+, or caspase-3+ cells in the SVZ after asphyxia. In conclusion, this study provides strong support for the selective vulnerability of immature oligodendrocytes to a highly relevant insult in the fetal sheep. Although white matter protection with cerebral hypothermia was associated with reduced proliferation in the white matter tracts, it did not impair proliferation in the SVZ.

Temperature- and time-dependent changes in TLR2-activated microglial NF-κB activity and concentrations of inflammatory and anti-inflammatory factors

PURPOSE

Therapeutic hypothermia protects neurons following injury to the central nervous system (CNS). Microglia express toll-like receptors (TLRs) that play significant roles in pathological processes in sterile CNS injury. We have examined the effects of culture temperature on the TLR2-activated microglial production of cytokines and nitric oxide (NO), which are known to be associated with CNS damage, and the possible involvement of nuclear factor-κB (NF-κB) activation underlying such effects.

METHODS

Rat microglia were cultured with a selective TLR2 agonist, Pam(3)CSK(4), under hypothermic, normothermic, and hyperthermic conditions, and with Pam(3)CSK(4) in the presence of a NF-κB activation inhibitor at 37 °C. Cytokine and NO levels and NF-κB p65 activation were measured.

RESULTS

The production of tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), and NO and the activation of NF-κB p65 were reduced by hypothermia, but augmented by hyperthermia at 3-6, 24-48, 48, and 0.5 h, post-treatment initiation, respectively. Pharmacological inhibition of NF-κB activation impaired the Pam(3)CSK(4)-induced TNF-α, IL-10, and NO production.

CONCLUSIONS

In TLR2-activated microglia, hypothermia reduced, while hyperthermia increased, the early activation of NF-κB and the subsequent NF-κB-mediated production of TNF-α, IL-10, and NO in a time-dependent manner, suggesting that attenuation of these factors via suppression of NF-κB in microglia is one possible neuroprotective mechanism of therapeutic hypothermia. Moreover, temperature-dependent changes in microglial TNF-α production during the early phase and IL-10 and NO production during the late phase indicate that these factors might be useful as clinical markers to monitor hypothermia-related neuronal protection and hyperthermia-related neuronal injury.

Pharmacokinetics and pharmacodynamics of medication in asphyxiated newborns during controlled hypothermia. The PharmaCool multicenter study

Background

In the Netherlands, perinatal asphyxia (severe perinatal oxygen shortage) necessitating newborn resuscitation occurs in at least 200 of the 180–185.000 newly born infants per year. International randomized controlled trials have demonstrated an improved neurological outcome with therapeutic hypothermia. During hypothermia neonates receive sedative, analgesic, anti-epileptic and antibiotic drugs. So far little information is available how the pharmacokinetics (PK) and pharmacodynamics (PD) of these drugs are influenced by post resuscitation multi organ failure and the metabolic effects of the cooling treatment itself. As a result, evidence based dosing guidelines are lacking. This multicenter observational cohort study was designed to answer the question how hypothermia influences the distribution, metabolism and elimination of commonly used drugs in neonatal intensive care.

Methods/Design

Multicenter cohort study. All term neonates treated with hypothermia for Hypoxic Ischemic Encephalopathy (HIE) resulting from perinatal asphyxia in all ten Dutch Neonatal Intensive Care Units (NICUs) will be eligible for this study. During hypothermia and rewarming blood samples will be taken from indwelling catheters to investigate blood concentrations of several antibiotics, analgesics, sedatives and anti-epileptic drugs. For each individual drug the population PK will be characterized using Nonlinear Mixed Effects Modelling (NONMEM). It will be investigated how clearance and volume of distribution are influenced by hypothermia also taking maturation of neonate into account. Similarly, integrated PK-PD models will be developed relating the time course of drug concentration to pharmacodynamic parameters such as successful seizure treatment; pain assessment and infection clearance.

Discussion

On basis of the derived population PK-PD models dosing guidelines will be developed for the application of drugs during neonatal hypothermia treatment. The results of this study will lead to an evidence based drug treatment of hypothermic neonatal patients. Results will be published in a national web based evidence based paediatric formulary, peer reviewed journals and international paediatric drug references.

Trial registration

NTR2529.

Mechanisms of hypothermic neuroprotection

There is now compelling clinical evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce subsequent neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. Perhaps surprisingly, the specific mechanisms of hypothermic neuroprotection remain unclear, at least in part because hypothermia suppresses a broad range of potential injurious factors. In the present review we critically examine proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Better knowledge of the mechanisms of hypothermia is critical to help guide the rational development of future combination treatments to augment neuroprotection with hypothermia, and to identify those most likely to benefit from it.

Effects of therapeutic hypothermia on multiorgan dysfunction in asphyxiated newborns: whole-body cooling versus selective head cooling

OBJECTIVE

Multiorgan dysfunction in asphyxiated newborns receiving therapeutic hypothermia achieved by either selective head cooling (SHC) or whole-body cooling (WBC) has not been well characterized. The beneficial effect of SHC in organs other than the brain may potentially be limited because unlike WBC, SHC aims to achieve effective brain cooling with less-systemic hypothermia. However, the relative effects of SHC and WBC with currently available cooling protocols on multiorgan dysfunction are unknown.The aim of this study was to compare the multiorgan dysfunction in infants receiving therapeutic hypothermia induced by either SHC or WBC.

STUDY DESIGN

In 59 asphyxiated newborns who received therapeutic hypothermia by either SHC (n=31) or WBC (n=28), the severity of pulmonary, hepatic and renal dysfunction and coagulopathy and electrolyte disturbances were assessed before the start of cooling (baseline), and at specific time intervals (24, 48 and 72 h) throughout cooling. Enrollment criteria, clinical monitoring and treatment during cooling, whether SHC or WBC, were similar, as reported earlier.

RESULT

The presence of clinical respiratory distress, along with the need for ventilatory support for varying duration during cooling, was similar in both the WBC and SHC groups (100 vs 94%, P=0.49, OR 1.9, 95% CI 1.5-2.5). The use of fresh frozen plasma and platelet transfusion to treat coagulopathy and thrombocytopenia was similar (WBC 48% vs SHC 58%, P=0.59, OR 0.7, 95% CI 0.2-1.9, and WBC 41% vs SHC 32%, P=0.58, OR 1.4, 95% CI 0.5-4.2, respectively), and equivalent numbers of infants from both groups were treated with vasopressors for >24 h (WBC 59% vs SHC 55%, P=0.79, OR 1.2, 95% CI 0.4-3.4). The incidence of oliguria (urine output <0.5 ml kg(-1) h(-1) for >24 h after birth) and rising serum creatinine (with maximum serum creatinine >0.9 mg dl(-1)) was also similar (WBC 18% vs SHC 39%, P=0.15, OR 0.4, 95% CI 0.1-1.3, and WBC 48% vs SHC 58%, P=0.59, OR 0.7, 95% CI 0.2-1.9, respectively). Laboratory parameters to assess the differential effect of WBC versus SHC on multiorgan dysfunction during 72 h of cooling, which include serum transaminases (serum aspartate aminotransferase and alanine aminotransferase), prothrombin time, partial thromboplastin time, INR, platelet counts, serum creatinine, serum sodium, serum potassium and serum calcium, were similar between the groups at the initiation of cooling and did not differ with the method of cooling.

CONCLUSION

Multiorgan system dysfunction in asphyxiated newborns during cooling remains similar for both cooling methods. Concerns regarding a differential effect of WBC versus SHC on multiorgan dysfunction, other than of the brain, should not be a consideration in selecting a method to produce therapeutic hypothermia.

Changes in cerebral hemodynamics and amplitude integrated EEG in an asphyxiated newborn during and after cool cap treatment

Amplitude integrated EEG (aEEG) and Near Infrared Spectroscopy (NIRS) were applied in a newborn with a moderate hypoxic-ischemic encephalopathy before, during and after brain cooling. At 2h of life a selective head cooling with mild systemic hypothermia was started and maintained for 72h. aEEG background pattern improved from severely abnormal to normal during the first 17h of life. NIRS revealed a reduction in cerebral blood volume (CBV) during hypothermia that recovered during the rewarming period, whereas brain oxygenation remained stable. As brain cooling is supposed to reduce delayed hyperemia and help to maintain neuronal metabolism following cerebral insults, aEEG and NIRS monitoring may be useful during hypothermic treatment in order to document changes in CBV and brain oxygenation possibly reflecting the efficacy of hypothermia.

Brain cooling for preterm infants

There is strong evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. This review examines the evidence that mild to moderate hypothermia is protective after hypoxia-ischemia in models of preterm brain injury and evaluates the potential risks. Induced hypothermia likely has potential to significantly reduce disability. Cautious, systematic trials are essential before hypothermia can be used in these vulnerable infants.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

The TOBY Study. Whole body hypothermia for the treatment of perinatal asphyxial encephalopathy: a randomised controlled trial

Background

A hypoxic-ischaemic insult occurring around the time of birth may result in an encephalopathic state characterised by the need for resuscitation at birth, neurological depression, seizures and electroencephalographic abnormalities. There is an increasing risk of death or neurodevelopmental abnormalities with more severe encephalopathy. Current management consists of maintaining physiological parameters within the normal range and treating seizures with anticonvulsants.

Studies in adult and newborn animals have shown that a reduction of body temperature of 3–4°C after cerebral insults is associated with improved histological and behavioural outcome. Pilot studies in infants with encephalopathy of head cooling combined with mild whole body hypothermia and of moderate whole body cooling to 33.5°C have been reported. No complications were noted but the group sizes were too small to evaluate benefit.

Methods/Design

TOBY is a multi-centre, prospective, randomised study of term infants after perinatal asphyxia comparing those allocated to "intensive care plus total body cooling for 72 hours" with those allocated to "intensive care without cooling".

Full-term infants will be randomised within 6 hours of birth to either a control group with the rectal temperature kept at 37 +/- 0.2°C or to whole body cooling, with rectal temperature kept at 33–34°C for 72 hours. Term infants showing signs of moderate or severe encephalopathy +/- seizures have their eligibility confirmed by cerebral function monitoring. Outcomes will be assessed at 18 months of age using neurological and neurodevelopmental testing methods.

Sample size

At least 236 infants would be needed to demonstrate a 30% reduction in the relative risk of mortality or serious disability at 18 months.

Recruitment was ahead of target by seven months and approvals were obtained allowing recruitment to continue to the end of the planned recruitment phase. 325 infants were recruited.

Primary outcome

Combined rate of mortality and severe neurodevelopmental impairment in survivors at 18 months of age. Neurodevelopmental impairment will be defined as any of:

• Bayley mental developmental scale score less than 70

• Gross Motor Function Classification System Levels III – V

• Bilateral cortical visual impairments

Trial Registration

Current Controlled Trials ISRCTN89547571

Changes in laboratory parameters indicating cell necrosis and organ dysfunction in asphyxiated neonates on moderate systemic hypothermia

AIM

Asphyxia is a major cause of morbidity and mortality in term infants. In addition to cerebral injury other organs are also distressed due to hypoxic-ischaemic insult. Systemic hypothermia has a beneficial effect on brain injury. We tested the impact of hypothermia on hypoxic damage of other internal organs.

METHODS

Asphyxiated term neonates (n = 21) were randomised to groups treated with hypothermia (n = 12) and normothermia (n = 9). Hypothermia (33-34 degrees C) was initiated within 6 h of life, and maintained for 72 h. We determined serum transaminase, lactate dehydrogenase, creatine kinase, uric acid, creatinine levels and diuresis during 6, 24, 48 and 72 postnatal hours.

RESULTS

Area under curve values of aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), uric acid and creatinine during the investigated period and alanine aminotransferase (ALAT) value at 72 h were lower in neonates on hypothermia than in those on normothermia. Renal failure and liver impairment affected less hypothermic than normothermic neonates (3/12 vs. 7/9, p = 0.03, 3/12 vs. 6/9 p = 0.08, respectively). Four of the 12 hypothermic and 6 of the 9 normothermic neonates developed multiorgan failure.

CONCLUSIONS

These results suggest that systemic hypothermia may protect against cell necrosis and tissue dysfunction of internal organs after neonatal asphyxia.

The effect of cerebral hypothermia on white and grey matter injury induced by severe hypoxia in preterm fetal sheep

Prolonged, moderate cerebral hypothermia is consistently neuroprotective after experimental hypoxia-ischaemia; however, it has not been tested in the preterm brain. Preterm (0.7 gestation) fetal sheep received complete umbilical cord occlusion for 25 min followed by cerebral hypothermia (fetal extradural temperature reduced from 39.4 +/- 0.3 to 29.5 +/- 2.6 degrees C) from 90 min to 70 h after the end of occlusion or sham cooling. Occlusion led to severe acidosis and profound hypotension, which recovered rapidly after release of occlusion. After 3 days recovery the EEG spectral frequency, but not total intensity, was increased in the hypothermia-occlusion group compared with normothermia-occlusion. Hypothermia was associated with a significant overall reduction in loss of immature oligodendrocytes in the periventricular white matter (P < 0.001), and neuronal loss in the hippocampus and basal ganglia (P < 0.001), with suppression of activated caspase-3 and microglia (isolectin-B4 positive). Proliferation was significantly reduced in periventricular white matter after occlusion (P < 0.05), but not improved after hypothermia. In conclusion, delayed, prolonged head cooling after a profound hypoxic insult in the preterm fetus was associated with a significant reduction in loss of neurons and immature oligodendroglia, with evidence of EEG and haemodynamic improvement after 3 days recovery, but also with a persisting reduction in proliferation of cells in the periventricular region. Further studies are required to evaluate the long-term impact of cooling on brain growth and maturation.

Intracarotid injection of granulocyte-macrophage colony-stimulating factor induces neuroprotection in a rat transient middle cerebral artery occlusion model

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was found to promote collateral flow in patients with coronary artery disease and also to induce arteriogenesis in a rat hypoperfusion brain model. Activated macrophages have been shown to induce vascular proliferation and play an important role in ischemic stroke. In this study, we examined the therapeutic effect of GM-CSF on the ischemic brain by activating microglia/macrophages. Rats were subjected to 1-h intraluminal middle cerebral artery occlusion (MCAO) and received an intracarotid injection of GM-CSF (5 ng) or saline immediately after reperfusion. Infarct volume, neurological function and histological findings were assessed 48 h later. An intracarotid injection of GM-CSF reduced the infarct volume and improved neurological function at 48 h after reperfusion. Histological analysis revealed that the number of activated microglia/macrophages to be increased and the number of apoptotic cells to be decreased in the area of the penumbra. These results suggest that intracarotid injection of GM-CSF may have a therapeutic effect on brain ischemia via activation of microglia/macrophages.

Hypothermic neuroprotection

The possibility that hypothermia during or after resuscitation from asphyxia at birth, or cardiac arrest in adults, might reduce evolving damage has tantalized clinicians for a very long time. It is now known that severe hypoxia-ischemia may not necessarily cause immediate cell death, but can precipitate a complex biochemical cascade leading to the delayed neuronal loss. Clinically and experimentally, the key phases of injury include a latent phase after reperfusion, with initial recovery of cerebral energy metabolism but EEG suppression, followed by a secondary phase characterized by accumulation of cytotoxins, seizures, cytotoxic edema, and failure of cerebral oxidative metabolism starting 6 to 15 h post insult. Although many of the secondary processes can be injurious, they appear to be primarily epiphenomena of the 'execution' phase of cell death. Studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration in relation to the severity of the cerebral injury, has been associated with potent, long-lasting neuroprotection in both adult and perinatal species. Two large controlled trials, one of head cooling with mild hypothermia, and one of moderate whole body cooling have demonstrated that post resuscitation cooling is generally safe in intensive care, and reduces death or disability at 18 months of age after neonatal encephalopathy. These studies, however, show that only a subset of babies seemed to benefit. The challenge for the future is to find ways of improving the effectiveness of treatment.

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.

Microglia induce neural cell death via a proximity-dependent mechanism involving nitric oxide

Microglial cells play a major role in the pathogenesis of many neurological diseases by exacerbating neuronal and non-neuronal cell death, but the mechanisms involved are unclear. To investigate the microglial-neuronal interactions, we used the murine BV-2 microglial cell line and the human neuronal-like SK-N-SH neuroblastoma cell line in a co-culture system that enabled proximity-dependent interaction and communication, a trans-well system that allowed proximity-independent communication through diffusible molecules only, and a conditioned media system through which no proximity-dependent interactions or cell-to-cell communication is possible. Activation of BV-2 cells with lipopolysaccharide and interferon-gamma (LPS/IFN-gamma) decreased viability of the BV-2 cells alone and in co-cultures with SK-N-SH cells, but not SK-N-SH cells grown alone. In contrast, activation of BV-2 cells in the trans-well and conditioned media system did not have any effect on the viability of SK-N-SH cells, suggesting that microglia must be in close proximity to the neural cells to elicit cytotoxicity. To determine the molecules involved in proximity-dependent cell death, inhibitors of microglial activation were investigated. Only the specific inducible nitric oxide synthase (iNOS) inhibitor S-methylisothiourea, and hypothermia, which is known to suppress microglial iNOS expression, prevented cell death after LPS/IFN-gamma activation. These results suggest that activated microglia release nitric oxide that is, at least partially, responsible for proximity-dependent microglial-mediated neural toxicity.

Keeping cool in acute liver failure: rationale for the use of mild hypothermia

Encephalopathy, brain edema and intracranial hypertension are neurological complications responsible for substantial morbidity/mortality in patients with acute liver failure (ALF), where, aside from liver transplantation, there is currently a paucity of effective therapies. Mirroring its cerebro-protective effects in other clinical conditions, the induction of mild hypothermia may provide a potential therapeutic approach to the management of ALF. A solid mechanistic rationale for the use of mild hypothermia is provided by clinical and experimental studies showing its beneficial effects in relation to many of the key factors that determine the development of brain edema and intracranial hypertension in ALF, namely the delivery of ammonia to the brain, the disturbances of brain organic osmolytes and brain extracellular amino acids, cerebro-vascular haemodynamics, brain glucose metabolism, inflammation, subclinical seizure activity and alterations of gene expression. Initial uncontrolled clinical studies of mild hypothermia in patients with ALF suggest that it is an effective, feasible and safe approach. Randomized controlled clinical trials are now needed to adequately assess its efficacy, safety, clinical impact on global outcomes and to provide the guidelines for its use in ALF.

Oxidative metabolites are involved in polyamine-induced microglial cell death

Pathological activation of microglia, which reside quiescently in physiological CNS, is associated with various neurodegenerative diseases. Endogenous polyamines, spermidine and spermine, are known to be activators of cell proliferation and differentiation. We previously reported that both spermidine and spermine induce dose-dependent cell death in cultured rat brain microglia at a submicromolar concentration range via apoptotic process, whereas cultured astrocytes were less sensitive to these polyamines [Neuroscience 120 (2003) 961]. These polyamine effects were observed only in the presence of fetal bovine serum. In the present study we examined further the mechanism of polyamine-induced microglial cell death. Amine oxidase in fetal bovine serum produces hydrogen peroxide and an aminoaldehyde from spermine, and the latter generates acrolein spontaneously. Acrolein was found to be much more toxic to microglia than to astrocytes and the effective concentration of acrolein was similar to that of spermine, whereas hydrogen peroxide was marginally toxic. Aminoguanidine, an inhibitor of amine oxidase, blocked the toxic effects of spermine on microglia. Spermine cytotoxicity was also prevented by antioxidant reagents; glutathione (reduced form), cysteine, and N-acetylcysteine. These results suggest that polyamine-induced apoptotic cell death of microglia is triggered by an oxidative stress with acrolein, which is produced by amine oxidase from polyamine. The different toxicities of polyamine between two glial cells may regulate the balance of glial activation in some pathological conditions of CNS.

Postischemic mild hypothermia reduces neurotransmitter release and astroglial cell proliferation during reperfusion after asphyxial cardiac arrest in rats

The present study investigated whether postischemic mild hypothermia attenuates the ischemia-induced striatal glutamate (GLU) and dopamine (DA) release, as well as astroglial cell proliferation in the brain. Anesthetized rats were exposed to 8 min of asphyxiation, including 5 min of cardiac arrest. The cardiac arrest was reversed to restoration of spontaneous circulation (ROSC), by brief external heart massage and ventilation within a period of 2 min. After the insult and during reperfusion, the extracellular glutamate and dopamine overflow increased to, respectively, 3000% and 5000% compared with the baseline values in the normothermic group and resulted in brain damage, ischemic neurons and gliosis. However, when hypothermia was induced for a period of 60 min after the insult and restoration of spontaneous circulation, the glutamate and dopamine overflows were not significantly different from that in the sham group. Histological analysis of the brain showed that postischemic mild hypothermia reduced brain damage, ischemic neurons, as well as astroglial cell proliferation. Thus, postischemic mild hypothermia reduces the excitotoxic process, brain damage, as well as astroglial cell proliferation during reperfusion. Moreover, these results emphasize the trigger effect of dopamine on the excitotoxic pathway.

Window of opportunity of cerebral hypothermia for postischemic white matter injury in the near-term fetal sheep

Postresuscitation cerebral hypothermia is consistently neuroprotective in experimental preparations; however, its effects on white matter injury are poorly understood. Using a model of reversible cerebral ischemia in unanesthetized near-term fetal sheep, we examined the effects of cerebral hypothermia (fetal extradural temperature reduced from 39.4 +/- 0.1 degrees C to between 30 and 33 degrees C), induced at different times after reperfusion and continued for 72 hours after ischemia, on injury in the parasagittal white matter 5 days after ischemia. Cooling started within 90 minutes of reperfusion was associated with a significant increase in bioactive oligodendrocytes in the intragyral white matter compared with sham cooling (41 +/- 20 vs 18 +/- 11 per field, P < 0.05), increased myelin basic protein density and reduced expression of activated caspase-3 (14 +/- 12 vs 91 +/- 51, P < 0.05). Reactive microglia were profoundly suppressed compared with sham cooling (4 +/- 6 vs 38 +/- 18 per field, P < 0.05) with no effect on numbers of astrocytes. When cooling was delayed until 5.5 hours after reperfusion there was no significant effect on loss of oligodendrocytes (24 +/- 12 per field). In conclusion, hypothermia can effectively protect white matter after ischemia, but only if initiated early after the insult. Protection was closely associated with reduced expression of both activated caspase-3 and of reactive microglia.

Hypothermia inhibits cytokine release of alveolar macrophage and activation of nuclear factor kappaB in endotoxemic lung

OBJECTIVE

We have previously reported that endotoxin-induced neutrophil infiltration of the lung is lower during hypothermia than during normothermia. Because neutrophil infiltration of the lung is considered a downstream phenomenon following an activation of tissue macrophages, we examined the effects of induced hypothermia on the proximal aspects of acute lung injury, which involves alveolar macrophages and nuclear transcription of cytokine genes.

DESIGN AND SETTING

Animal study in an institutional animal laboratory.

SUBJECTS

Thirty-six Sprague-Dawley rats.

INTERVENTIONS

Rats were assigned to the following groups: normothermia (37 degrees C) with saline; hypothermia (27 degrees C) with saline; normothermia with lipopolysaccharide; hypothermia with lipopolysaccharide. After 1 h of stable temperature rats were intraperitoneally given lipopolysaccharide or an equivalent volume of normal saline. The temperature of rats was maintained within +/-1 degrees C of the target temperature for the subsequent 2 h, after which rats were subjected to lung lavage.

MEASUREMENTS AND RESULTS

Neutrophil count, TNF-alpha, and IL-1beta in lavage fluid were all higher with normothermia-LPS than in normothermia-saline. Neutrophil count, TNF-alpha, and IL-1beta levels of lavage fluid were lower with hypothermia-LPS than with normothermia-LPS. TNF-alpha release from cultured alveolar macrophages and NF-kappaB activity in lung tissue were both lower with hypothermia-LPS than with normothermia-LPS. I-kappaBalpha level in lung tissue was lower with normothermia-LPS than with the normothermia-saline, whereas I-kappaBalpha level in lung tissue did not differ between normothermia-saline and hypothermia-LPS.

CONCLUSIONS

Induced hypothermia suppressed the release of inflammatory cytokine from alveolar macrophages and NF-kappaB activation in endotoxemic lung.

Mild hypothermia enhances the neuroprotective effects of FK506 and expands its therapeutic window following transient focal ischemia in rats

FK506 (tacrolimus), an immunosuppressant, reportedly reduces ischemic brain injury following transient middle cerebral artery occlusion (MCAO) in rats. The authors previously reported that the therapeutic window of FK506 in this model is more than 1 h, but less than 2 h. The aim of the present study is to determine whether mild hypothermia (35 degrees C) enhances the neuroprotective effects of FK506 and expands its therapeutic window. Sprague-Dawley rats were subjected to 2 h MCAO followed by 24 h reperfusion. Animals were randomly divided into four groups: (I) vehicle-treated normothermic group; (II) FK506-treated normothermic group; (III) vehicle-treated hypothermic group; (IV) FK506-treated hypothermic group. Animals received a single injection of FK506 (0.3 mg/kg) or vehicle intravenously at 2 h after ischemic induction. During ischemia, temporal muscle and rectal temperatures were maintained at 37 degrees C in the normothermic animals and at 35 degrees C in the hypothermic animals. Infarct volumes and neurological performance were evaluated at 24 h after reperfusion. The combination of FK506 and mild hypothermia significantly reduced infarct volume (cortex, -61%; striatum, -31%) and edema volume (cortex, -57%; striatum, -41%), while mild hypothermia or FK506 alone failed to improve ischemic brain damage. Furthermore, this combination also provided for the best functional outcome. These results demonstrate that the combination of FK506 and mild hypothermia significantly reduces ischemic brain damage following transient MCAO in rats, and expands the therapeutic window for FK506. This therapy may be a new approach for treatment of acute stroke.

The neuroprotective effect of a free radical scavenger and mild hypothermia following transient focal ischemia in rats

Edaravone, a novel free radical scavenger, has been reported to reduce ischemic damage in rats subjected to transient focal ischemia. The aim of this study is, therefore, to investigate the effect of a combined therapy with edaravone and mild hypothermia of 35 degrees C. Sprague-Dawley rats were subjected to MCA occluding an intraluminal suture technique for 2 hrs. The rats were reperfused for 24 h and decapitated for infarct and edema analysis. Animals were randomly devided into four groups: (I) vehicle + normothermia (control) (II) vehicle + mild hypothermia (III) Edaravone + normothermia (IV) Edaravone + mild hypothermia. Mild hypothermia alone had no reduction of the brain damage. The edaravone alone significantly reduced edema volume. The combined treatment with edaravone and mild hypothermia reduced both infarct and edema volume. In addition, this treatment provided for the best functional outcome. These results demonstrate that free radical scavenger, edaravone attenuates brain edema and that the combined therapy with edaravone and mild hypothermia significantly reduces not only edema but also infarct on transient focal cerebral ischemia in rats. The neuroprotective effects seen in this study may be due to the combined interaction of antiedema activity between edaravone and mild hypothermia, suppressing free radical production.

(?)-Epigallocatechin gallate inhibits lipopolysaccharide-induced microglial activation and protects against inflammation-mediated dopaminergic neuronal injury

Microglial activation is believed to play a pivotal role in the selective neuronal injury associated with several neurodegenerative disorders, including Parkinson's disease (PD) and Alzheimer's disease. We provide evidence that (-)-epigallocatechin gallate (EGCG), a major monomer of green tea polyphenols, potently inhibits lipopolysaccharide (LPS)-activated microglial secretion of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) through the down-regulation of inducible NO synthase and TNF-alpha expression. In addition, EGCG exerted significant protection against microglial activation-induced neuronal injury both in the human dopaminergic cell line SH-SY5Y and in primary rat mesencephalic cultures. Our study demonstrates that EGCG is a potent inhibitor of microglial activation and thus is a useful candidate for a therapeutic approach to alleviating microglia-mediated dopaminergic neuronal injury in PD.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Microglial cell death induced by a low concentration of polyamines

Pathological activation of microglia, which reside quiescently in physiological CNS, contributes various neurodegenerative diseases. Endogenous polyamines, spermidine (SPD) and spermine (SPM) are known to be activators of cell proliferation and differentiation. We examined the effect of polyamines on microglial activation in culture. Cultured microglia prepared from the whole brains of newborn rats produced nitric oxide (NO) by the stimulation with lipopolysaccharide (LPS). LPS-induced NO production was markedly inhibited by SPD and SPM; half effective concentrations (EC(50)) of SPD and SPM were about 3 and 1 microM, respectively. Cell viability assessed by total mitochondrial activity decreased by the incubation with SPD and SPM for 24 h at similar concentration ranges. After the treatment with SPM for 24 h, the cells changed into small round morphology, and were strongly stained with propidium iodide. By the staining with bis-benzimide trihydrochloride, condensation and fragmentation of the nucleus were often observed. Semiquantitative analysis of fragmented DNA with enzyme-linked immunosorbent assay technique revealed that a large amount of fragmented DNA appeared in cytosol prior to disruption of the cell membrane. Fragmented DNA in the cytosol increased dose dependently with SPM; EC(50) was less than 10 microM. Furthermore, most of the cells after 24 h incubation with 10 microM SPD and SPM were positive for terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick end labeling. These results suggest that microglial cell death is induced by a low concentration of polyamines via an apoptotic process rather than necrotic one.

Mild hypothermia inhibits inflammation after experimental stroke and brain inflammation

BACKGROUND AND PURPOSE

We previously showed that mild hypothermia protects against experimental stroke, even when cooling was delayed by 2 hours. Protection may be due in part to inhibiting inflammation. To clarify, we examined leukocyte infiltration, microglial activation, and adhesion molecule expression in models of stroke and pure brain inflammation.

METHODS

Rats underwent 2-hour middle cerebral artery occlusion (MCAO; n=36) or intravenous injection with 5 mg/kg lipopolysaccharide (LPS; n=22). Temperature was lowered to 33 degrees C for 2 hours or kept at 37 degrees C. In MCAO, cooling was applied intraischemically or on reperfusion (delayed). In the LPS model, cooling began after injection. One and 3 days later, brains were assessed for neutrophils, monocytes/microglia, major histocompatibility complex class II antigen, and intercellular adhesion molecule-1 (ICAM-1).

RESULTS

One day after MCAO, both intraischemic and delayed hypothermia decreased ICAM-1 (51% and 60%, respectively, versus normothermia; P<0.001), monocytes (63% and 57%; P<0.01), and microglia (55% and 53%; P<0.001). Similar decreases were seen at 3 days for ICAM-1 (91% and 93%; P<0.001), monocytes (62% and 54%; P<0.01), and microglia (55% and 53%; P<0.001). In the LPS model, ED-1-positive cells were not observed in the brain, but hypothermia decreased ICAM-1 (26%; P<0.05), OX6 (56%; P<0.01), and microglia (47%; P<0.01) at 1 day.

CONCLUSIONS

Mild hypothermia decreases inflammatory responses in both brain inflammation and stroke, implicating a direct anti-inflammatory effect of cooling. This suggests that hypothermia can attenuate factors contributing to delayed ischemic injury.