Secondary insults to the injured brain

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Despite extensive research efforts, the majority of trialed monotherapies to date have failed to demonstrate significant benefit. It has been suggested that this is due to the complex pathophysiology of TBI, which may possibly be addressed by a combination of therapeutic interventions. In this article, we have reviewed combinations of different pharmacologic treatments, combinations of non-pharmacologic interventions, and combined pharmacologic and non-pharmacologic interventions for TBI. Both preclinical and clinical studies have been included. While promising results have been found in animal models, clinical trials of combination therapies have not yet shown clear benefit. This may possibly be due to their application without consideration of the evolving pathophysiology of TBI. Improvements of this paradigm may come from novel interventions guided by multimodal neuromonitoring and multimodal imaging techniques, as well as the application of multi-targeted non-pharmacologic and endogenous therapies. There also needs to be a greater representation of female subjects in preclinical and clinical studies.

Improving on Laboratory Traumatic Brain Injury Models to Achieve Better Results

Experimental modeling of traumatic brain injury (TBI) in animals has identified several potential means and interventions that might have beneficial applications for treating traumatic brain injury clinically. Several of these interventions have been applied and tried with humans that are at different phases of testing (completed, prematurely terminated and others in progress). The promising results achieved in the laboratory with animal models have not been replicated with human trails as expected. This review will highlight some insights and significance attained via laboratory animal modeling of TBI as well as factors that require incorporation into the experimental studies that could help in translating results from laboratory to the bedside. Major progress has been made due to laboratory studies; in explaining the mechanisms as well as pathophysiological features of brain damage after TBI. Attempts to intervene in the cascade of events occurring after TBI all rely heavily on the knowledge from basic laboratory investigations. In looking to discover treatment, this review will endeavor to sight and state some central discrepancies between laboratory models and clinical scenarios.

A Coupled Lumped-Parameter and Distributed Network Model for Cerebral Pulse-Wave Hemodynamics

The cerebral circulation is unique in its ability to maintain blood flow to the brain under widely varying physiologic conditions. Incorporating this autoregulatory response is necessary for cerebral blood flow (CBF) modeling, as well as investigations into pathological conditions. We discuss a one-dimensional (1D) nonlinear model of blood flow in the cerebral arteries coupled to autoregulatory lumped-parameter (LP) networks. The LP networks incorporate intracranial pressure (ICP), cerebrospinal fluid (CSF), and cortical collateral blood flow models. The overall model is used to evaluate changes in CBF due to occlusions in the middle cerebral artery (MCA) and common carotid artery (CCA). Velocity waveforms at the CCA and internal carotid artery (ICA) were examined prior and post MCA occlusion. Evident waveform changes due to the occlusion were observed, providing insight into cerebral vasospasm monitoring by morphological changes of the velocity or pressure waveforms. The role of modeling of collateral blood flows through cortical pathways and communicating arteries was also studied. When the MCA was occluded, the cortical collateral flow had an important compensatory role, whereas the communicating arteries in the circle of Willis (CoW) became more important when the CCA was occluded. To validate the model, simulations were conducted to reproduce a clinical test to assess dynamic autoregulatory function, and results demonstrated agreement with published measurements.

Magnesium reduces matrix metalloproteinase-9, but not glial fibrillary acidic protein, in cardiac surgery patients

Magnesium (Mg) is one of the most important ions in the brain. Its supplementation decreases intracellular disorders and improves final outcomes following traumatic brain injury. Aim: The aim of the study was to analyze the effects of magnesium supplementation on arteriovenous differences in plasma magnesium concentration in brain circulation (a–vMg), plasma matrix metalloproteinase-9 (MMP-9) and glial fibrillary acidic protein (GFAP) concentrations in cardiac surgery patients. Methods: A total of 92 adult patients were enrolled. Patients were allocated into three groups: A, receiving 6.66 mg of MgSO4 per min intravenously; B, receiving 10 mg of MgSO4; and C, receiving 13.33 mg of MgSO4. Results: In all groups, GFAP and MMP-9 increased after extracorporeal circulation and immediately after surgery. Sequentially higher concentrations of MMP-9 and a–vMg were noted in groups A, B and C. Plasma GFAP concentrations were similar in all groups. Conclusion: Magnesium supplementation reduces plasma MMP-9 and a-vMg in brain circulation but does not affect plasma GFAP.

Neuroprotective effects of hyperbaric oxygen treatment on traumatic brain injury in the rat

This study was designed to evaluate the potential benefits of hyperbaric oxygen (HBO) in the treatment of traumatic brain injury (TBI). The right cerebral cortex of rats was injured by the impact of a 20-g object dropped from a predetermined height. The rats received HBO treatment at 3 ATA for 60 min after TBI. Neurological behavior score, brain water content, neuronal loss in the hippocampus, and cell apoptosis in brain tissue surrounding the primary injury site were examined to determine brain damage severity. Three and six hours after TBI, HBO-treated rats displayed a significant reduction in brain damage. However, by 12 h after TBI, the efficacy of HBO treatment was considerably attenuated. Furthermore, at 24, 48, and 72 h after TBI, the HBO treatment did not show any notable effects. In contrast, multiple HBO treatments (three or five times in all), even when started 48 h after TBI, remarkably reduced neurology deficit scores and the loss of neuronal numbers in the hippocampus. Although multiple treatments started at 48 h significantly improved neurological behaviors and reduced brain injury, the overall beneficial effects were substantially weaker than those seen after a single treatment at 6 h. These results suggest that: (1) HBO treatment could alleviate brain damage after TBI; (2) a single treatment with HBO has a time limitation of 12 h post-TBI; and (3) multiple HBO treatments have the possibility to extend the post-TBI delivery time window. Therefore, our results clearly suggest the validity of HBO therapy for the treatment of TBI.

Transient receptor potential melastatin 2 expression is increased following experimental traumatic brain injury in rats

Traumatic brain injury (TBI) elicits a sequence of complex biochemical changes including oxidative stress, oedema, inflammation and excitotoxicity. These factors contribute to the high morbidity and mortality following TBI, although their underlying molecular mechanisms remain poorly understood. Transient receptor potential melastatin 2 (TRPM2) is a non-selective cation channel, highly expressed in the brain and immune cells. Recent studies have implicated TRPM2 channels in processes involving oxidative stress, inflammation and cell death. However, no studies have investigated the role of TRPM2 in TBI pathophysiology. In the present study, we have characterised TRPM2 mRNA and protein expression following experimental TBI. Adult male Sprague Dawley rats were injured using the impact-acceleration model of diffuse TBI with survival times between 5 and 5 days. Real-time RT-PCR (including reference gene validation studies) and semi-quantitative immunohistochemistry were used to quantify TRPM2 mRNA and protein levels, respectively, following TBI. Significant increases in TRPM2 mRNA and protein expression were observed in the cerebral cortex and hippocampus of injured animals, suggesting that TRPM2 may contribute to TBI injury processes such as oxidative stress, inflammation and neuronal death. Further characterisation of how TRPM2 may contribute to TBI pathophysiology is warranted.

Hyperbaric oxygen therapy improves spatial learning and memory in a rat model of chronic traumatic brain injury

In the present experiment we use a rat model of traumatic brain injury to evaluate the ability of low-pressure hyperbaric oxygen therapy (HBOT) to improve behavioral and neurobiological outcomes. The study employed an adaptation of the focal cortical contusion model. 64 Male Long-Evans rats received unilateral cortical contusion and were tested in the Morris Water Task (MWT) 31-33 days post injury. Rats were divided into three groups: an untreated control group (N=22), an HBOT treatment group (N=19) and a sham-treated normobaric air group (N=23). The HBOT group received 80 bid, 7 days/week 1.5 ATA/90-min HBOTs and the sham-treated normobaric air group the identical schedule of air treatments using a sham hyperbaric pressurization. All rats were subsequently retested in the MWT. After testing all rats were euthanized. Blood vessel density was measured bilaterally in hippocampus using a diaminobenzadine stain and was correlated with MWT performance. HBOT caused an increase in vascular density in the injured hippocampus (p<0.001) and an associated improvement in spatial learning (p<0.001) compared to the control groups. The increased vascular density and improved MWT in the HBOT group were highly correlated (p<0.001). In conclusion, a 40-day series of 80 low-pressure HBOTs caused an increase in contused hippocampus vascular density and an associated improvement in cognitive function. These findings reaffirm the clinical experience of HBOT-treated patients with chronic traumatic brain injury.

Arterio-Jugular Difference of Oxygen Content and Outcome After Head Injury

This study investigated AJDO2 (arterio-jugular difference of oxygen content) in a large sample of severely head-injured patients to identify its pattern during the first days after injury and to describe the relationship of AJDO2 with acute neurological severity and with outcome 6 mo after trauma. In 229 comatose head-injured patients, we monitored intracranial pressure, cerebral perfusion pressure, and AJDO2. Outcome was defined 6 mo after injury. Jugular hemoglobin oxygen saturation (SjO2) averaged 68%. The mean AJDO2 was 4.24 vol% (SD, 1.3 vol%). There were 80 measurements (4.6%) with SjO2 <55% and 304 (17.6%) with saturation >75%. AJDO2 was higher than 8.7 vol% in 8 measurements (0.4%) and was lower than 3.9 vol% in 718 (42%) measurements. AJDO2 was higher during the first tests and decreased steadily over the next few days. Cases with a favorable outcome had a higher mean AJDO2 (4.3 vol%; SD, 0.3 vol%) than patients with severe disability or vegetative status (3.8 vol%; SD, 1.3 vol%) and patients who died (3.6 vol%; SD, 1 vol%). This difference was significant (P < 0.001). We conclude that low levels of AJDO2 are correlated with a poor prognosis, whereas normal or high levels of AJDO2 are predictive of better results.

Continuous measurements of cerebral tissue oxygen pressure during hyperbaric oxygenation—HBO effects on brain edema and necrosis after severe brain trauma in rabbits

INTRODUCTION

Severe brain injury is one of the most frequent causes of severe disability in the young. In acute management of brain trauma, new approaches based on experimental animal investigations should be sought.

METHODS

Twenty male, juvenile Chinchilla-Bastard rabbits received standardized cold-injury-induced-brain-trauma (CIBT). A metal probe (temperature -196 degrees C) was applied epidurally over 10 s. The hyperbaric oxygenation (HBO) group (n=10) underwent 90-min HBO sessions with 100% oxygen at 2.5 atmospheres absolute (1 h, 24+/-2 h, 48+/-2 h after CIBT). Cerebral tissue pO2-measurements were performed 60 min after CIBT, during the three HBO sessions and on day 4. The control group (n=10) underwent no treatment. Animals were sacrificed on day 4, and brains were analyzed histologically.

RESULTS

In the HBO group, pO2 measurements showed a significant increase in pO2 between day 1 and day 4, whereas no significant changes were observed in the control group. During the first HBO session, mean pO2 was 169 mm Hg, during the second 305 mm Hg and during the third 420 mm Hg. The mean area of necrosis was 16.2 mm2 in the HBO group, in the control group 19.9 mm2. The areas of brain edema were significantly smaller in the HBO group. Mortality in the HBO group was 0%, in the control group 20%.

CONCLUSION

HBO appears to be beneficial as an adjunct treatment of severe head trauma. To find optimal treatment protocols, further clinical studies must be developed.

Monitoring of serum ionized magnesium in neurosurgical intensive care unit: preliminary results

BACKGROUND

Our purpose was to determine the values for serum ionized magnesium (Mg) concentrations in traumatic brain injury and its effect on the prognostic scores of patients.

METHODS

We prospectively measured serum ionized magnesium concentrations in 30 patients that were classified into three groups (severe, moderate, mild) by Glasgow Coma Scale Score. Serum ionized magnesium concentrations were measured during posttraumatic 5 days. Thirty patients with head trauma were followed in a neurosurgical intensive care unit with monitoring serum ionized magnesium concentrations. All patients were treated conservatively.

RESULTS

We found significant difference of serum ionized magnesium concentrations when we compared all groups with each other (p<0.001).

CONCLUSIONS

Based on this clinical preliminary study, traumatic brain injury is associated with graded deficit in serum ionized magnesium concentrations. Thus, measurement of serum ionized magnesium concentrations can be used as a clinical marker in traumatic brain injury.

Interaction between anesthesia, gender, and functional outcome task following diffuse traumatic brain injury in rats

A number of experimental and clinical studies have demonstrated that functional outcome following traumatic brain injury differs between males and females. Some studies report that females have a better outcome than males following trauma while others report the opposite. In experimental studies, some of the contradictory results may be due to the different experimental conditions, including type of anesthesia and the outcome measures employed. In the present study we have used three different anesthetic protocols and four different outcome measures to determine how these parameters interact and affect functional outcome following traumatic brain injury in male and female rats. Diffuse traumatic brain injury was induced in adult male and female animals using the impact-acceleration brain injury model. Mortality in female animals was no different than males when using halothane anesthesia, slightly better than males when using isoflurane anesthesia, but significantly worse than males under pentobarbital anesthesia. Female animals always performed better than males on rotarod tests of motor outcome, with this effect being unrelated to anesthetic effects. Conversely, in cognitive tests using the Barnes Maze, only isoflurane-anesthetized females performed better than their male counterparts. Similarly, in an open field activity task, females always performed better than males after trauma, with isoflurane-anesthetized females also performing significantly better than the halothane-anesthetized female group after injury. Our results suggest that female animals do better than males after diffuse traumatic brain injury, although this observation is dependent upon the type of anesthesia and the functional task employed. Isoflurane is particularly protective in females, pentobarbital is deleterious to female outcome, while halothane anesthesia has the least influence on gender-related outcome.