EFFECT OF BRAIN COOLING ON BRAIN ISCHEMIA AND DAMAGE MARKERS AFTER FLUID PERCUSSION BRAIN INJURY IN RATS

Clostridium perfringens epsilon toxin induces permanent neuronal degeneration and behavioral changes

Clostridium perfringens epsilon toxin (ETX), the most potent toxin produced by this bacteria, plays a key role in the pathogenesis of enterotoxaemia in ruminants, causing brain edema and encephalomalacia. Studies of animals suffering from ETX intoxication describe severe neurological disorders that are thought to be the result of vasogenic brain edemas and indirect neuronal toxicity, killing oligodendrocytes but not astrocytes, microglia, or neurons in vitro. In this study, by means of intravenous and intracerebroventricular delivery of sub-lethal concentrations of ETX, the histological and ultrastructural changes of the brain were studied in rats and mice. Histological analysis showed degenerative changes in neurons from the cortex, hippocampus, striatum and hypothalamus. Ultrastructurally, necrotic neurons and apoptotic cells were observed in these same areas, among axons with accumulation of neurofilaments and demyelination as well as synaptic stripping. Lesions observed in the brain after sub-lethal exposure to ETX, result in permanent behavioral changes in animals surviving ETX exposure, as observed individually in several animals and assessed in the Inclined Plane Test and the Wire Hang Test. Pharmacological studies showed that dexamethasone and reserpine but not ketamine or riluzole were able to reduce the brain lesions and the lethality of ETX. Cytotoxicity was not observed upon neuronal primary cultures in vitro. Therefore, we hypothesize that ETX can affect the brain of animals independently of death, producing changes on neurons or glia as the result of complex interactions, independently of ETX-BBB interactions.

Selective Brain Hypothermia Mitigates Brain Damage and Improves Neurological Outcome after Post-Traumatic Decompressive Craniectomy in Mice

Hypothermia and decompressive craniectomy (DC) have been considered as treatment for traumatic brain injury. The present study investigates whether selective brain hypothermia added to craniectomy could improve neurological outcome after brain trauma. Male CD-1 mice were assigned into the following groups: sham; DC; closed head injury (CHI); CHI followed by craniectomy (CHI+DC); and CHI+DC followed by focal hypothermia (CHI+DC+H). At 24 h post-trauma, animals were subjected to Neurological Severity Score (NSS) test and Beam Balance Score test. At the same time point, magnetic resonance imaging using a 9.4 Tesla scanner and subsequent volumetric evaluation of edema and contusion were performed. Thereafter, the animals were sacrificed and subjected to histopathological analysis. According to NSS, there was a significant impairment among all the groups subjected to trauma. Animals with both trauma and craniectomy performed significantly worse than animals with craniectomy alone. This deleterious effect disappeared when additional hypothermia was applied. BBS was significantly worse in the CHI and CHI+DC groups, but not in the CHI+DC+H group, compared to the sham animals. Edema and contusion volumes were significantly increased in CHI+DC animals, but not in the CHI+DC+H group, compared to the DC group. Histopathological analysis showed that neuronal loss and contusional blossoming could be attenuated by application of selective brain hypothermia. Selective brain cooling applied post-trauma and craniectomy improved neurological function and reduced structural damage and may be therefore an alternative to complication-burdened systemic hypothermia. Clinical studies are recommended in order to explore the potential of this treatment.

An experimental study: does the neuroprotective effect increase when hypothermia deepens after traumatic brain injury?

BACKGROUND

Experimental approaches have been promising with the use of therapeutic hypothermia after Traumatic Brain Injury (TBI) whereas clinical data have not supported its efficacy.

OBJECTIVES

This study aimed to investigate whether using selective deeper brain cooling correlates with a more neuroprotective effect on Intracranial Pressure (ICP) increments following TBI in rats.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats (mean weight = 300 g; n = 25) were subjected to brain injury using a modified Marmarou method. Immediately after the onset of TBI, rats were randomized into three groups. Selective brain cooling was applied around the head using ice packages. Intracranial Temperature (ICT) and ICP were continuously measured at 0, 30, 60, 120, and 180 minutes and recorded for all groups. Group 1 (n = 5) was normothermia and was assigned as the control group. Group 2 (n = 10) received moderate hypothermia with a target ICT of between 32°C - 33°C and Group 3 (n = 10) was given a deeper hypothermia with a target ICT of below 32°C.

RESULTS

All subjects reached the target ICT by the 30th minute of hypothermia induction. The ICT was significantly different in Group 2 compared to Group 1 only at the 120th minute (P = 0.017), while ICP was significantly lower starting from the 30th minute (P = 0.015). The ICT was significantly lower in Group 3 compared to Groups 1 and 2 starting from the 30th minute (P = 0.001 and P = 0.003, respectively). The ICP was significantly lower in Group 3 compared to Group 1 starting from 30th minute (P = 0.001); however, a significant difference in ICP between Group 3 and Group 2 was observed only at the 180th minute (P = 0.047).

CONCLUSIONS

Results of this study indicate that selective brain cooling is an effective method of decreasing ICP in rats; however, the deeper hypothermia caused a greater decrease in ICP three hours after hypothermia induction.

Neurological consequences of cardiac arrest: where do we stand?

With increasing public education in basic life support and with the widespread use of automated defibrillators, post-cardiac arrest comatose patients represent a growing part of ICU admissions. However the prognosis remains very poor and only a very low proportion of these resuscitated patients will recover and will leave the hospital without major neurological impairments. Neurological dysfunction predominantly includes disorders of consciousness, and may also include other manifestations such as seizures, myoclonus status epilepticus and other forms of movement disorders including post-anoxic myoclonus. In the most severe cases, coma may be irreversible or evolve towards a minimally conscious state, a vegetative state or even brain death. These severe conditions represent by far the leading cause of mortality and disability in such patients. Currently, early use of mild therapeutic hypothermia is the only treatment that demonstrated its ability to decrease neurological consequences and to improve the prognosis. Prognostication outcome is still mainly based on a rigorous clinical evaluation coupled with neuro-physiological investigations, but brain functional imaging could become a valuable tool in the near future. Clinical research focusing on survivors should be strongly encouraged in order to assess the mid- and long-terms outcome of survivors and to evaluate the impact of new treatments or strategies.

Attenuating inflammation but stimulating both angiogenesis and neurogenesis using hyperbaric oxygen in rats with traumatic brain injury

BACKGROUND

Inflammation, angiogenesis, neurogenesis, and gliosis are involved in traumatic brain injury (TBI). Several studies provide evidence supporting the neuroprotective effect of hyperbaric oxygen (HBO2) therapy in TBI. The aim of this study was to ascertain whether inflammation, angiogenesis, neurogenesis, and gliosis during TBI are affected by HBO2 therapy.

METHODS

Rats were randomly divided into three groups: TBI + NBA (normobaric air: 21% O2 at 1 absolute atmospheres), TBI + HBO2, and Sham operation + NBA. TBI + HBO2 rats received 100% O2 at 2.0 absolute atmospheres for 1 hr/d for three consecutive days. Behavioral tests and biochemical and histologic evaluations were done 4 days after TBI onset.

RESULTS

TBI + NBA rats displayed: (1) motor and cognitive dysfunction; (2) cerebral infarction and apoptosis; (3) activated inflammation (evidenced by increased brain myeloperoxidase activity and higher serum levels of tumor necrosis factor-α); (4) neuronal loss (evidenced by fewer NeuN-positive cells); and (5) gliosis (evidenced by more glial fibrillary protein-positive cells). In TBI + HBO2 rats, HBO2 therapy significantly reduced TBI-induced motor and cognitive dysfunction, cerebral infarction and apoptosis, activated inflammation, neuronal loss, and gliosis. In addition, HBO2 therapy stimulated angiogenesis (evidenced by more bromodeoxyuridine-positive endothelial and vascular endothelial growth factor-positive cells), neurogenesis (evidenced by more bromodeoxyuridine-NeuN double-positive and glial cells-derived neurotrophic factor-positive cells), and overproduction of interleukin-10 (an anti-inflammatory cytokine).

CONCLUSIONS

Collectively, these results suggest that HBO2 therapy may improve outcomes of TBI in rats by inhibiting activated inflammation and gliosis while stimulating both angiogenesis and neurogenesis in the early stage.

Hypobaric hypoxia preconditioning attenuates acute lung injury during high-altitude exposure in rats via up-regulating heat-shock protein 70

HHP (hypobaric hypoxia preconditioning) induces the overexpression of HSP70 (heat-shock protein 70), as well as tolerance to cerebral ischaemia. In the present study, we hypothesized that HHP would protect against HAE (high-altitude exposure)-induced acute lung injury and oedema via promoting the expression of HSP70 in lungs prior to the onset of HAE. At 2 weeks after the start of HHP, animals were exposed to a simulated HAE of 6000 m in a hypobaric chamber for 24 h. Immediately after being returned to ambient pressure, the non-HHP animals had higher scores of alveolar oedema, neutrophil infiltration and haemorrhage, acute pleurisy (e.g. increased exudate volume, increased numbers of polymorphonuclear cells and increased lung myeloperoxidase activity), increased pro-inflammatory cytokines [e.g. TNF-α (tumour necrosis factor-α), IL (interleukin)-1β and IL-6], and increased cellular ischaemia (i.e. glutamate and lactate/pyruvate ratio) and oxidative damage [glycerol, NOx (combined nitrate+nitrite) and 2,3-dihydroxybenzoic acid] markers in the BALF (bronchoalveolar fluid). HHP, in addition to inducing overexpression of HSP70 in the lungs, significantly attenuated HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage in the lungs. The beneficial effects of HHP in preventing the occurrence of HAE-induced pulmonary oedema, inflammation, and ischaemic and oxidative damage was reduced significantly by pretreatment with a neutralizing anti-HSP70 antibody. In conclusion, HHP may attenuate the occurrence of pulmonary oedema, inflammation, and ischaemic and oxidative damage caused by HAE in part via up-regulating HSP70 in the lungs.

Measuring brain temperature while maintaining brain normothermia in patients with severe traumatic brain injury

The aim of this study was to evaluate the relationship between superficial temporal artery temperature (Tt), rectal temperature (Tr) and intracranial temperature (ICT) when attempting to keep the brain in a normothermic condition in patients with severe traumatic brain injury (TBI). We also compared the incidence of temperature gradient reversal in patients who survived (survivors) and patients who did not (non-survivors) and the difference in temperature gradient reversal between survivors and non-survivors. Tr is normally lower than and ICT and temperature gradient reversal, when Tr exceeds ICT, has been demonstrated to be an early sign of brain death. A total of 28 patients with severe TBI were enrolled retrospectively in our study between November 2008 and February 2010. Each patient's Tt, Tr and ICT was recorded every hour for 4 days. Our results show that the frequency of brain hyperthermia in our participants (ICT>38°C) was 17.7%. Using a paired t-test and Bland-Altman plots, it was shown that a significant temperature difference existed between Tt, Tr and ICT (p<0.001). The use of Spearman's correlation method revealed that Tt, Tr and ICT were positively correlated (p<0.001). Brain death occurred in five patients at a mean of 9.6 hours (range: 8-12 hours) after a temperature gradient reversal between Tt, Tr and ICT. Fisher's exact test showed that there was a significant difference in the incidence of temperature gradient reversal between Tt, Tr and ICT in survivors and non-survivors (p<0.001). We conclude that a significant temperature difference exists between Tt, Tr and ICT when maintaining brain normothermia. The daily practice of non-invasive Tt measurement may cause doctors to underestimate ICT; reversal of the ICT and Tt and/or Tr temperatures could be an early marker of a poor prognosis for patients with severe TBI.

Pharyngeal selective brain cooling is associated with reduced CNS cortical lesion after experimental traumatic brain injury in rats

Therapeutic hypothermia (TH) is still being explored as a therapeutic option after traumatic brain injury (TBI) but clinical data has not supported its efficacy. Experimental approaches were promising, but clinical data did not support its efficacy in the treatment of TBI. A novel approach of pharyngeal selective brain cooling (pSBC), recently introduced by our group, has been accompanied by superior neurofunctional, sensorimotor, and cognitive outcomes. This work is now extended by data on histomorphological and physical outcomes after pSBC in a model of experimental TBI. Male Sprague-Dawley rats were subjected to lateral fluid-percussion (LFP) brain injury, and randomized to the following experimental groups: (1) TBI with pSBC, (2) TBI without pSBC, and (3) sham animals. On day post-injury (DPI) 14, the animals were sacrificed and their brains were harvested for immunohistochemistry using the following antibodies: (1) glial fibrillary acidic protein (GFAP), (2) neurofilament (NF), and (3) synaptophysin (SY). In pSBC animals brain temperature was selectively lowered to 33 ± 0.5°C within 15 min post-injury, and maintained for 180 min after induction, while keeping rectal temperatures at physiological levels. Animals that had undergone pSBC showed a significantly faster recovery of body weight starting on DPI 3, and had gained substantially more weight than TBI-only animals on DPI 14 (p < 0.001), indicating superior physical recovery. Areas of cortical damage were significantly smaller in pSBC animals compared to TBI-only animals (p < 0.01). pSBC was associated with preservation of cortical tissue ipsilateral to the lesion, and superior physical recovery after experimental TBI. These results complement earlier reports in which pSBC was associated with superior neurofunctional and cognitive outcomes using the same experimental model.

Brain cooling-stimulated angiogenesis and neurogenesis attenuated traumatic brain injury in rats

BACKGROUND

Although brain cooling has been reported to be effective in improving the outcome after traumatic brain injury (TBI) in rats, the mechanisms of brain cooling-induced neuroprotective actions remain unclear. This study was to test whether angiogenesis and neurogenesis attenuating TBI could be brain cooling stimulated.

METHODS

Anesthetized rats, immediately after the onset of TBI, were divided into two groups and given the brain cooling (infusing 5 mL of 4°C saline via the external jugular vein) or no brain cooling (infusing 5 mL of 37°C saline via the external jugular vein).

RESULTS

Brain cooling without interference with the core temperature in rats significantly attenuated TBI-induced cerebral infarction (90 mm³ vs. 250 mm³) and motor (61 degrees vs. 57 degrees maximal angle) and proprioceptive (14% vs. 42% maximal possible effect) function deficits, significantly reduced TBI-induced neuronal (24 vs. 62 neuronal-specific nuclear [NeuN]-TUNEL double-positive cells) and glial (5 vs. 35 GFAP-TUNEL double-positive cells) apoptosis (increased TUNEL-positive and caspase-3-positive cells), neuronal loss (102 vs. 66 NeuN-positive cells), and gliosis (40 vs. 66 GFAP-positive cells; 66 vs. 89 Iba1-positive cells), and significantly promoted angiogenesis (5-bromodeoxyuridine [BrdU]/endothelial cells vs. 1-BrdU/endothelial cell; 58 vs. 31 vascular endothelial growth factor-positive cells), and neurogenesis (33 vs. 14 BrdU/NeuN positive cells).

CONCLUSIONS

Brain cooling-stimulated angiogenesis and neurogenesis attenuated a fluid percussion TBI in rats.

Attenuation of brain nitrostative and oxidative damage by brain cooling during experimental traumatic brain injury

The aim of the present study was to ascertain whether brain cooling causes attenuation of traumatic brain injury by reducing brain nitrostative and oxidative damage. Brain cooling was accomplished by infusion of 5 mL of 4°C saline over 5 minutes via the external jugular vein. Immediately after the onset of traumatic brain injury, rats were randomized into two groups and given 37°C or 4°C normal saline. Another group of rats were used as sham operated controls. Behavioral and biochemical assessments were conducted on 72 hours after brain injury or sham operation. As compared to those of the sham-operated controls, the 37°C saline-treated brain injured animals displayed motor deficits, higher cerebral contusion volume and incidence, higher oxidative damage (e.g., lower values of cerebral superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, but higher values of cerebral malondialdehyde), and higher nitrostative damage (e.g., higher values of neuronal nitric oxide synthase and 3-nitrotyrosine). All the motor deficits and brain nitrostative and oxidative damage were significantly reduced by retrograde perfusion of 4°C saline via the jugular vein. Our data suggest that brain cooling may improve the outcomes of traumatic brain injury in rats by reducing brain nitrostative and oxidative damage.

Therapeutic evaluation of etanercept in a model of traumatic brain injury

Antagonism of tumor necrosis factor-alpha with etanercept has proved to be effective in the treatment of spinal cord injury and centrally endotoxin-induced brain injury. However, etanercept may offer promise as therapy for traumatic brain injury (TBI). In this study, anesthetized rats, immediately after the onset of TBI, were divided into two major groups and given the vehicle solution (1 mL/kg of body weight) or etanercept (5 mg/kg of body weight) intraperitoneally once per 12 h for consecutive 3 days. Etanercept caused attenuation of TBI-induced cerebral ischemia (e.g., increased cellular levels of glutamate and lactate-to-pyruvate ratio), damage (e.g., increased cellular levels of glycerol) and contusion and motor and cognitive function deficits. TBI-induced neuronal apoptosis (e.g., increased numbers of terminal deoxynucleotidyl transferase αUTP nick-end labeling and neuronal-specific nuclear protein double-positive cells), glial apoptosis (e.g., increased numbers of terminal deoxynucleotidyl transferase αUTP nick-end labeling and glial fibrillary acidic protein double-positive cells), astrocytic (e.g., increased numbers of glial fibrillary acidic protein positive cells) and microglial (e.g., increased numbers of ionized calcium-binding adapter molecule 1-positive cells) activation and activated inflammation (e.g., increased levels of tumor necrosis factor-alpha, interleukin-1β and interleukin-6) were all significantly reduced by etanercept treatment. These findings suggest that etanercept may improve outcomes of TBI by penetrating into the cerebrospinal fluid in rats.

Active cooling in traumatic brain-injured patients: a questionable therapy?

Hypothermia is shown to be beneficial for the outcome after a transient global brain ischaemia through its neuroprotective effect. Whether this is also the case after focal ischaemia, such as following a severe traumatic brain injury (TBI), has been investigated in numerous studies, some of which have shown a tendency towards an improved outcome, whereas others have not been able to demonstrate any beneficial effect. A Cochrane report concluded that the majority of the trials that have already been published have been of low quality, with unclear allocation concealment. If only high-quality trials are considered, TBI patients treated with active cooling were more likely to die, a conclusion supported by a recent high-quality Canadian trial on children. Still, there is a belief that a modified protocol with a shorter time from the accident to the start of active cooling, longer cooling and rewarming time and better control of blood pressure and intracranial pressure would be beneficial for TBI patients. This belief has led to the instigation of new trials in adults and in children, including these types of protocol adjustments. The present review provides a short summary of our present knowledge of the use of active cooling in TBI patients, and presents some tentative explanations as to why active cooling has not been shown to be effective for outcome after TBI. We focus particularly on the compromised circulation of the penumbra zone, which may be further reduced by the stress caused by the difference in thermostat and body temperature and by the hypothermia-induced more frequent use of vasoconstrictors, and by the increased risk of contusional bleedings under hypothermia. We suggest that high fever should be reduced pharmacologically.

Defeating normal thermoregulatory defenses: induction of therapeutic hypothermia

Therapeutic hypothermia may be useful in various circumstances including stroke. However, core body temperature is normally tightly regulated. Even mild hypothermia in conscious subjects thus provokes vigorous thermoregulatory defenses which are potentially harmful in fragile patients. Furthermore, thermoregulatory responses are effective, which reduces the rate at which hypothermia can be induced. Drugs are thus often given to blunt normal thermoregulatory defenses. General anesthetics profoundly impair thermoregulatory control, but prolonged general anesthesia is rarely practical or appropriate. A variety of other drugs have therefore been evaluated. Most opioids only slightly impair thermoregulatory defenses, but meperidine is considerably more effective than equipotent doses of other opioids. The central alpha-2 agonists clonidine and dexmedetomidine are also useful. However, the best overall approach to inducing thermal tolerance appears to be a combination of buspirone and meperidine, which reduces the core temperature triggering shivering to about 33.5 degrees C in doses that maintain adequate ventilation.

Resuscitation from experimental traumatic brain injury by agmatine therapy

Both nitric oxide and glutamate contribute to ischaemic brain injury. Agmatine inhibits all isoforms of nitric oxide synthase and blocks N-methyl-d-aspartate receptors. In this study, we gave agmatine intraperitoneally and assessed its effect on fluid percussion brain injury in rats. Anaesthetised rats, immediately after the onset of fluid percussion traumatic brain injury (TBI), were divided into two major groups and given the vehicle solution (1mL/kg) or agmatine (50mg/kg) intraperitoneally. Mean arterial pressure, intracranial pressure, cerebral perfusion pressure, and levels of glutamate, nitric oxide, lactate/pyruvate ratio, and glycerol in hippocampus were monitored continuously within 120min after TBI. The weight loss was determined by the difference between the first and third day of body weight after TBI. The maximal grip angle in an inclined plane was measured to determine motor performance whereas the percent of maximal possible effect was used to measure blockade of proprioception. The triphenyltetrazolium chloride staining procedures were used for cerebral infarction assay. Compared to those of the sham-operated controls, the animals with TBI had higher values of extracellular levels of glutamate, nitric oxide, lactate-to-pyruvate ratio, and glycerol in hippocampus and intracranial pressure, but lower values of cerebral perfusion pressure. Agmatine administered immediately after TBI significantly attenuated the TBI-induced increased hippocampal levels of glutamate, nitric oxide, lactate-to-pyruvate ratio, and glycerol, intracranial hypertension, and cerebral hypoperfusion. In addition, the TBI-induced cerebral infarction, motor and proprioception deficits, and body weight loss evaluated 3 days after TBI were significantly attenuated by agmatine therapy. The present data indicate that agmatine may attenuate TBI by reducing the excessive accumulation of both glutamate and nitric oxide in the brain.