Combined effect of respirator-induced ventilation and superoxide dismutase in experimental brain injury

Neurodegeneration and Sensorimotor Deficits in the Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) can result in persistent sensorimotor and cognitive deficits, which occur through a cascade of deleterious pathophysiological events over time. In this study, we investigated the hypothesis that neurodegeneration caused by TBI leads to impairments in sensorimotor function. TBI induces the activation of the caspase-3 enzyme, which triggers cell apoptosis in an in vivo model of fluid percussion injury (FPI). We analyzed caspase-3 mediated apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and poly (ADP-ribose) polymerase (PARP) and annexin V western blotting. We correlated the neurodegeneration with sensorimotor deficits by conducting the animal behavioral tests including grid walk, balance beam, the inverted screen test, and the climb test. Our study demonstrated that the excess cell death or neurodegeneration correlated with the neuronal dysfunction and sensorimotor impairments associated with TBI.

Impact of injury location and severity on posttraumatic epilepsy in the rat: role of frontal neocortex

Human posttraumatic epilepsy (PTE) is highly heterogeneous, ranging from mild remitting to progressive disabling forms. PTE results in simple partial, complex partial, and secondarily generalized seizures with a wide spectrum of durations and semiologies. PTE variability is thought to depend on the heterogeneity of head injury and patient's age, gender, and genetic background. To better understand the role of these factors, we investigated the seizures resulting from calibrated fluid percussion injury (FPI) to adolescent male Sprague-Dawley rats with video electrocorticography. We show that PTE incidence and the frequency and severity of chronic seizures depend on the location and severity of FPI. The frontal neocortex was more prone to epileptogenesis than the parietal and occipital, generating earlier, longer, and more frequent partial seizures. A prominent limbic focus developed in most animals, regardless of parameters of injury. Remarkably, even with carefully controlled injury parameters, including type, severity, and location, the duration of posttraumatic apnea and the age and gender of outbred rats, there was great subject-to-subject variability in frequency, duration, and rate of progression of seizures, indicating that other factors, likely the subjects' genetic background and physiological states, have critical roles in determining the characteristics of PTE.

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

The ability of paramedics to predict aspiration in patients undergoing prehospital rapid sequence intubation

One of the purported benefits to invasive prehospital airway management is the prevention of aspiration; however, aspiration events may occur before the arrival of prehospital personnel. We explore the timing of aspiration in patients with severe traumatic brain injury (TBI) undergoing paramedic rapid sequence intubation (RSI). Severely head-injured (Glasgow Coma Scale [GCS] score 3-8) adults were prospectively enrolled into the San Diego Paramedic RSI Trial. As part of the prehospital data collection tool, paramedics prospectively assessed for clinical evidence of aspiration before RSI (pre-intubation), aspiration events occurring during RSI (peri-RSI), and regurgitation of vomitus or blood after intubation (post-intubation). Data were abstracted from work sheets used during the RSI procedure, a telephone debriefing by one of the principal investigators immediately after delivery of the patient, and San Diego County prehospital and trauma databases. The incidence of pre-intubation aspiration, peri-RSI aspiration, and post-intubation regurgitation of vomitus or blood were determined. Patients with and without pre-intubation aspiration were compared with regard to pre- and post-intubation hypoxia and the rate of aspiration pneumonia. Logistic regression was used to explore the association between pre-intubation aspiration and various demographic and clinical factors. The results showed that pre-intubation aspiration was noted by paramedics in 72/269 patients in whom complete data were available. Peri-RSI aspiration was reported in one patient; there were no reported cases of post-intubation regurgitation of vomitus or blood. Patients in the pre-intubation aspiration group required more intubation attempts, had a higher incidence of desaturations and lower pre- and post-intubation SaO(2) values, and were more frequently diagnosed with aspiration pneumonia. Pre-intubation aspiration was associated with severe TBI, GCS score of 3, younger age, and the absence of alcohol intoxication despite controlling for age, gender, GCS, Head AIS (Abbreviated Injury Score), and serum ethanol. It is concluded that paramedics seem to be able to accurately assess for aspiration in patients undergoing prehospital RSI. The vast majority of aspiration events seem to occur before the arrival of prehospital personnel. Alteration in consciousness from TBI may carry a higher risk of aspiration than with other causes, such as alcohol intoxication.

Intracranial pressure response to severe head injury induced apnea and catecholamine surge

BACKGROUND

Apnea and catecholamine surge have been known sequelae in the first few minutes of postexperimentally induced severe head injury for over a century. However, the intracranial pressure (ICP) response to these two pathophysiologic processes is poorly understood.

METHODS

We used the rat fluid percussion head injury model to study apnea and catecholamine surge separately and in combination on measured ICP response

RESULTS

The three experimental groups of apnea, hypertensive surge, and both combined revealed significantly different ICP responses with markedly elevated pressures correlating closely with mean arterial blood pressure.

CONCLUSION

ICP and mean arterial blood pressure correlate closely in the first few minutes after head injury in the absence of space-occupying hematomas, and may initiate pathophysiologic sequelae that can only be treated by earlier medical intervention at the scene.

The neglected prehospital phase of head injury: apnea and catecholamine surge

The prehospital phase of head injury, also called the critical phase, consists of trauma-induced apnea and stress catecholamine release. This immediate period after head injury remains poorly summarized in the literature and essentially ignored with respect to treatment. A MEDLINE search of the literature on apneustic response and catecholamine surge after head injury and a review of literature from my acquired references revealed 116 references (from more than 600) that were pertinent. Apnea induced by head injury produces hypoxia, hypercarbia, and subsequent cardiac failure and hypotension, which, along with substantially elevated catecholamine values, promote secondary mechanisms of organ injury. Treatment for this immediate period after head injury requires a rapid response to the scene of trauma and development of treatment options that can be instituted at the scene of injury.

Role of nitric oxide in traumatic brain injury in the rat

OBJECT

Although nitric oxide (NO) has been shown to play an important role in the pathophysiological process of cerebral ischemia, its contribution to the pathogenesis of traumatic brain injury (TBI) remains to be clarified. The authors investigated alterations in constitutive nitric oxide synthase (NOS) activity after TBI and the histopathological response to pharmacological manipulations of NO.

METHODS

Male Sprague-Dawley rats underwent moderate (1.7-2.2 atm) parasagittal fluid-percussion brain injury. Constitutive NOS activity significantly increased within the ipsilateral parietal cerebral cortex, which is the site of histopathological vulnerability, 5 minutes after TBI occurred (234.5+/-60.2% of contralateral value [mean+/-standard error of the mean ¿SEM¿], p < 0.05), returned to control values by 30 minutes (114.1+/-17.4%), and was reduced at 1 day after TBI (50.5+/-13.1%, p < 0.01). The reduction in constitutive NOS activity remained for up to 7 days after TBI (31.8+/-6.0% at 3 days, p < 0.05; 20.1+/-12.7% at 7 days, p < 0.01). Pretreatment with 3-bromo-7-nitroindazole (7-NI) (25 mg/kg), a relatively specific inhibitor of neuronal NOS, significantly decreased contusion volume (1.27+/-0.17 mm3 [mean+/-SEM], p < 0.05) compared with that of control (2.52+/-0.35 mm3). However, posttreatment with 7-NI or pre- or posttreatment with nitro-L-arginine-methyl ester (L-NAME) (15 mg/kg), a nonspecific inhibitor of NOS, did not affect the contusion volume compared with that of control animals (1.87+/-0.46 mm3, 2.13+/-0.43 mm3, and 2.18+/-0.53 mm3, respectively). Posttreatment with L-arginine (1.1+/-0.3 mm3, p < 0.05), but not 3-morpholino-sydnonimine (SIN-1) (2.48+/-0.37 mm3), significantly reduced the contusion volume compared with that of control animals.

CONCLUSIONS

These data indicate that constitutive NOS activity is affected after moderate parasagittal fluid percussion brain injury in a time-dependent manner. Inhibition of activated neuronal NOS and/or enhanced endothelial NOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Postischemic infusion of Cu/Zn superoxide dismutase or SOD:Tet451 reduces cerebral infarction following focal ischemia/reperfusion in rats

Oxygen-free radicals play a major role in neuronal cell injury following cerebral ischemia/reperfusion. The free-radical scavenging enzyme, Cu/Zn superoxide dismutase (SOD-1), ameliorates various types of brain injury resulting from temporary CNS ischemia. We have compared the cerebroprotective properties of human SOD-1 (hSOD-1) with a novel recombinant SOD-1 hybrid protein, SOD:Tet451, composed of hSOD-1 linked to the neuronal binding fragment of tetanus toxin (TTxC). Following 2 h of temporary middle cerebral artery occlusion, rats infused with equivalent activities of either hSOD-1 or SOD:Tet451 for the initial 3 h of reperfusion showed reductions in cerebral infarct volume of 43 and 57%, respectively, compared to saline-treated controls (P < 0.01). Serum hSOD-1 concentrations in rats receiving SOD:Tet451 were seven-fold higher than those in rats receiving the native enzyme. Animals treated with SOD:Tet451 also demonstrated an extended persistence of hSOD-1 in the bloodstream during drug washout as compared to animals given free enzyme. Immunohistochemical examination of brain sections from an SOD:Tet451-treated ischemic rat showed positive immunoreactivity in the ipsilateral cerebral cortex using either anti-TTxC or anti-human SOD-1 antibodies. Our results document that both hSOD-1 and SOD:Tet451 significantly reduce brain infarct volume in a model of transient focal ischemia/reperfusion in rats. Additionally, our findings suggest that the cerebroprotective effects of SOD-1 may be enhanced by neuronal targeting as seen with the hybrid protein SOD:Tet451.

Control of vasogenic edema in a brain tumor model: comparison between dexamethasone and superoxide dismutase

OBJECTIVE

The production of prostaglandin (PG) within brain tumors probably generates excessive amounts of oxygen free radicals that may disrupt microvessel permeability within the tumor and in the adjacent brain. We evaluated the effect of systemic therapy with recombinant human manganese-superoxide dismutase (r-hMnSOD) and with dexamethasone on the vascular permeability (VP) of a brain tumor and the adjacent brain. Treatment effect was also evaluated in control animals subjected to mild penetration injury.

METHODS

Fischer rats were injected stereotactically with either 10(5) cells of malignant sarcoma or with vehicle into the right parietal hemisphere. Nine days later, the animals were treated with r-hMnSOD (50 mg/kg of body weight every 12 h [one intravenous, then two intraperitoneal injections]; serum levels, 1100-1800 micrograms/ml), dexamethasone (2 mg/kg every 12 h [one intravenous, then two intraperitoneal injections]), or vehicle and were killed after 30 hours for evaluation of VP and PG production.

RESULTS

The VP was markedly increased within the tumor (P < 0.001), in the brain adjacent to it, and in the vehicle injection site. The VP of the normal brain was unaffected by r-hMnSOD or dexamethasone treatment, unlike the VP in the tumor, the adjacent brain, and the injection sites of control animals, where it was reduced by 50, 54, and 23%, respectively (P < 0.04), for r-hMnSOD and 50, 41, and 71%, respectively (P < 0.05), for dexamethasone. A one- to threefold increase in synthesis of thromboxane and PGE2 was measured within the tumor, the adjacent brain, and the injection sites of control animals (P < 0.0001). Treatment with r-hMnSOD had no effect on tumor PG production, but it reduced the synthesis in the brain tissue adjacent to the tumor and in traumatized control animals (P < 0.04). Immunohistochemical evaluation revealed vascular proliferation with abnormal basal membrane, atypical astrocytes, and large numbers of reactive macrophages present in the adjacent brain and at the injection sites of control animals but not within the tumor mass.

CONCLUSION

Oxygen free radicals probably enhance vasogenic brain edema resulting from tumor and penetration injury. The edema can be attenuated by systemic r-hMnSOD therapy, which has been proven to be as effective as steroid treatment. An inflammatory response may account for oxygen free radical production in brain tissue adjacent to the tumor and at the injection site of vehicle solution, but other mechanisms probably generate oxygen free radicals within the tumor mass.

Reduction of traumatic brain injury-induced cerebral oedema by a free radical scavenger

Oxygen derived free radicals have been proposed to be in part responsible for the cerebral oedema resulting from head injury. In the present study the effects of free radical suppression with MDL 74,180 (2,3-dihydro-2,2,4,6,7-pentamethyl-3-(4-methylpiperazino)-methyl-1 - benzofuran-5-ol dihydrochloride), an alpha-tocopherol analogue free radical scavenger, on the development of cerebral oedema resulting from head injury has been assessed. Fluid percussion head injury in rats caused a regional oedema 48 h after injury. Infusion of MDL 74,180 for 2 h after the injury significantly attenuated oedema development in a dose-related manner. Using magnetic resonance imaging, cerebral oedema development was monitored in head injured mice. Oedema was apparent 4 h after head injury and was greatest in the vicinity of the olfactory bulb and surrounding the ventricles. Treatment with MDL 74,180 (1-10 micrograms/kg intravenously, administered 3-5 min after the injury) significantly reduced the oedema development. MDL 74,180 is a potential treatment for the oedema caused as a result of head injury.

Effect of GSH on cerebral vasospasm in dogs

Reduced glutathinone (tau-glutamylcysteinglycine, GSH) is a scavenger for oxygen radicals and plays in important role in protection of cells from ischemia and from the harmful effects of free oxygen radicals. Free oxygen radicals due to cerebral vasospasm increase in both vasospasm and proliferative vasculopathy. This experiment was performed to determine whether GSH plays a role in cerebral vasospasm after subarachnoid hemorrhage by preventing the harmful effects of free oxygen radicals. In this study, GSH was administered intraarterially and intracisternally following vasospasm of the canine basilar artery. Less vasospasm was observed in the group treated with GSH intraarterially following subarachnoid hemorrhage than in the one treated with GSH intracisternally and in the control group. The arterial wall was investigated ultrastructurally. We evaluated the effect of the anti-oxidating substance through the activity of superoxide dismutase in the arterial wall. We compared the effect of glutathione reductase in the two groups treated with GSH intraarterially and intracisternally. Arterial degeneration was more prominent in the group in which GSH was used intracisternally, while the superoxide dismutase levels were low. In contrast, arterial degeneration was less in the other group in which GSH was used intraarterially, while the superoxide dismutase levels were high.

Fluid percussion injury causes loss of forebrain choline acetyltransferase and nerve growth factor receptor immunoreactive cells in the rat

Memory dysfunction is a common sequela of human traumatic brain injury (TBI). Cholinergic forebrain neurons are recognized for their role in memory. We tested the hypothesis that forebrain cholinergic neurons are vulnerable to fluid percussion injury (FPI), a model of human TBI. Rodents were subjected to a moderate parasagittal FPI, sham injury, or fimbria/fornix axotomy and then killed 10 days after the procedure. Additional animals underwent FPI or sham injury and were killed 7, 14, and 28 days after the procedure. Neurons in the medial septal nucleus and vertical limb of the nucleus of the diagonal band of Broca were identified and quantitated using choline acetyltransferase (ChAT) and low affinity nerve growth factor receptor (NGF-R) immunohistochemistry. Our results showed a significant decrease in ChAT (17% +/- 5%) and NGF-R (24% +/- 8%) immunoreactive cells in FPI animals killed after 10 days when compared to sham-injured animals. Animals undergoing fimbria/fornix axotomy showed a greater reduction in ChAT (53% +/- 13%) and NGF-R (55% +/- 5%) immunoreactive cells 10 days postaxotomy. The number of ChAT and NGF-R immunoreactive neurons was reduced at all time points. However, statistical significance was present 10 and 14 days postinjury for ChAT immunoreactive neurons and 10 days only for NGF-R immunoreactive neurons. These studies have shown that FPI produces transient loss of ChAT and NGF-R immunoreactive neurons.

Cerebral ischemia-reperfusion injury after severe head injury and its possible treatment with polyethyleneglycol-superoxide dismutase

Oxygen radical-mediated mechanisms play a role both in cerebral ischemia-reperfusion injury and in traumatic brain injury. Moreover, my work with measurements of cerebral blood flow with the 133Xe method and the stable xenon-computed tomography method and through measurements of arteriovenous difference of oxygen indicates that ischemia and ischemia-reperfusion are also part of traumatic brain injury but only in the first few hours after injury. The contributions of the research laboratories at the Medical College of Virginia, Richmond, to the understanding of the role of oxygen free radicals in traumatic brain injury are discussed. Finally, a trial of the oxygen radical scavenger polyethyleneglycol-superoxide dismutase in human beings with severe head injuries show that death and vegetative state occurred twice as often in the 26 patients receiving placebo compared with the group of 26 patients receiving a 10,000 U/kg bolus of polyethyleneglycol-superoxide dismutase (43%, respectively; 20% at three months; P < .03).

Improving the outcome of severe head injury with the oxygen radical scavenger polyethylene glycol-conjugated superoxide dismutase: a phase II trial

Formation of the oxygen radical superoxide anion is one of the final events of several metabolic pathways in the cascade that leads to delayed neuronal death after traumatic or ischemic brain injury. In the laboratory, scavenging of the superoxide anion with native superoxide dismutase (SOD) or polyethylene glycol (PEG)-conjugated SOD (PEG-SOD) has been shown to be beneficial in several types of traumatic and ischemic injury. Accordingly, PEG-SOD was utilized in a randomized controlled Phase II trial to evaluate its safety and efficacy in severely head-injured patients with a Glasgow Coma Scale score of 8 or less. At two institutions, 104 patients were randomly assigned to receive either placebo or PEG-SOD (2000, 5000, or 10,000 U/kg) intravenously as a bolus, an average of 4 hours after injury. Prognostic factors were evenly distributed in the four groups, except for mean age which was significantly higher in the group receiving 10,000 U/kg than in the placebo group (mean age 34 years vs. 25 years). No complications attributed to the study medication were noted. The average intracranial pressure (ICP) was similar in the four groups, but the percentage of time during which ICP was above 20 mm Hg was less in the groups receiving 5000 or 10,000 U/kg of PEG-SOD. Patients in the group receiving 10,000 U/kg also required less mannitol for ICP control than the placebo group. Outcome was assessed using the Glasgow Outcome Scale at 3 and 6 months postinjury in 91 and 93 patients, respectively, by blinded observers not involved in the clinical management of the patients. At 3 months, 44% of patients in the placebo group were vegetative or had died, while only 20% of patients in the group receiving 10,000 U/kg of PEG-SOD were in these outcome categories (p < 0.03, multiple logistic regression test); at 6 months, these figures were 36% and 21%, respectively (p = 0.04). Differences in outcome between the placebo group and either of the other two dosage groups were not statistically significant. It is concluded that PEG-SOD was generally well tolerated and appears promising in improving outcome after severe head injury. A larger, multicenter, Phase III trial, using a higher dose (20,000 U/kg) compared to placebo and to 10,000 U/kg of PEG-SOD is planned.

Superoxide dismutase decreases mortality, blood pressure, and cerebral blood flow responses induced by acute hypertension in rats

Oxygen radicals are known to be produced by the cerebral vasculature during acute, pressor-induced hypertension and are also known to inactivate endothelium-derived relaxing factor. The objective of our present study was to determine if the oxygen radical scavenger superoxide dismutase (24,000 units/kg plus 1,600 units/kg/min) alters the pressor, cerebral blood flow, and mortality responses to systemic norepinephrine in rats. Increasing doses (0.01-30 micrograms/kg i.v.) of norepinephrine were given by bolus injection to eight rats, and changes in the cortical microcirculatory blood flow were measured by laser-Doppler flowmetry. Superoxide dismutase shifted the norepinephrine-blood pressure and -cerebral blood flow dose-response curves moderately, but significantly, to the right such that it took more norepinephrine to reach a given blood pressure. However, superoxide dismutase had no effect on the autoregulation of cerebral blood flow. Additionally, whereas five (63%) of the eight control rats died after the 10 micrograms/kg norepinephrine dose, all eight rats treated with superoxide dismutase survived this dose. The mechanism by which superoxide dismutase reduced mortality is uncertain. The blood pressure and cerebral blood flow results suggest that superoxide dismutase prevents oxygen radicals from destroying endothelium-derived relaxing factors, which reduce the pressor effects of norepinephrine.

Effect of indomethacin pretreatment on acute mortality in experimental brain injury

The effect of indomethacin administration on the mortality rate of brain-injured rats was studied in four groups of animals subjected to a level of injury with a fluid-percussion apparatus predetermined to cause 50% mortality (50% lethal dose, or LD50). There were 24 animals in each of the following groups: 1) a control group, on which the LD50 was evaluated; 2) an ethanol-treated group with a mean blood serum level of 0.32 +/- 0.03 gm% (+/- standard error of the mean); 3) an indomethacin-treated group at a dose level of 3 mg/kg body weight administered intraperitoneally 10 to 15 minutes before injury; and 4) an indomethacin/ethanol-treated group. Significant differences in mortality rates were found in these experimental groups; namely, 50%, 58%, 8.3% (p less than 0.005), and 25% (p less than 0.05), respectively. The predetermined LD50 level of a 2.5- to 2.6-atm peak pressure pulse produced immediate apnea in all animals, which was either sustained (Type III), followed by temporary respiratory recovery (Type II), or followed by permanent resumption of breathing (Type I). The most important effect of indomethacin on respiratory function was manifested by a much higher percentage of Type I respiratory responses and a much lower percentage of Type II and III responses (hence a lower mortality rate). There was also a more rapid return to normal breathing in the postapneic period of recovery. Suppression of prostaglandin synthesis and of superoxide anion production at the of trauma may explain, at least in part, these favorable effects of indomethacin.