Remacemide hydrochloride reduces cortical lesion volume following brain trauma in the rat

Acute Non-Convulsive Status Epilepticus after Experimental Traumatic Brain Injury in Rats

Severe traumatic brain injury (TBI) induces seizures or status epilepticus (SE) in 20-30% of patients during the acute phase. We hypothesized that severe TBI induced with lateral fluid-percussion injury (FPI) triggers post-impact SE. Adult Sprague-Dawley male rats were anesthetized with isoflurane and randomized into the sham-operated experimental control or lateral FPI-induced severe TBI groups. Electrodes were implanted right after impact or sham-operation, then video-electroencephalogram (EEG) monitoring was started. In addition, video-EEG was recorded from naïve rats. During the first 72 h post-TBI, injured rats had seizures that were intermingled with other epileptiform EEG patterns typical to non-convulsive SE, including occipital intermittent rhythmic delta activity, lateralized or generalized periodic discharges, spike-and-wave complexes, poly-spikes, poly-spike-and-wave complexes, generalized continuous spiking, burst suppression, or suppression. Almost all (98%) of the electrographic seizures were recorded during 0-72 h post-TBI (23.2 ± 17.4 seizures/rat). Mean latency from the impact to the first electrographic seizure was 18.4 ± 15.1 h. Mean seizure duration was 86 ± 57 sec. Analysis of high-resolution videos indicated that only 41% of electrographic seizures associated with behavioral abnormalities, which were typically subtle (Racine scale 1-2). Fifty-nine percent of electrographic seizures did not show any behavioral manifestations. In most of the rats, epileptiform EEG patterns began to decay spontaneously on Days 5-6 after TBI. Interestingly, also a few sham-operated and naïve rats had post-operation seizures, which were not associated with EEG background patterns typical to non-convulsive SE seen in TBI rats. To summarize, our data show that lateral FPI-induced TBI results in non-convulsive SE with subtle behavioral manifestations; this explains why it has remained undiagnosed until now. The lateral FPI model provides a novel platform for assessing the mechanisms of acute symptomatic non-convulsive SE and for testing treatments to prevent post-injury SE in a clinically relevant context.

Elucidating opportunities and pitfalls in the treatment of experimental traumatic brain injury to optimize and facilitate clinical translation

The aim of this review is to discuss the research presented in a symposium entitled "Current progress in characterizing therapeutic strategies and challenges in experimental CNS injury" which was presented at the 2016 International Behavioral Neuroscience Society annual meeting. Herein we discuss diffuse and focal traumatic brain injury (TBI) and ensuing chronic behavioral deficits as well as potential rehabilitative approaches. We also discuss the effects of stress on executive function after TBI as well as the response of the endocrine system and regulatory feedback mechanisms. The role of the endocannabinoids after CNS injury is also discussed. Finally, we conclude with a discussion of antipsychotic and antiepileptic drugs, which are provided to control TBI-induced agitation and seizures, respectively. The review consists predominantly of published data.

Effect of lacosamide on structural damage and functional recovery after traumatic brain injury in rats

In a subgroup of patients, traumatic brain injury (TBI) results in the occurrence of acute epileptic seizures or even status epilepticus, which are treated with antiepileptic drugs (AEDs). Recent experimental data, however, suggest that administration of AEDs at the early post-injury phase can compromise the recovery process. The present study was designed to assess the profile of a novel anticonvulsant, lacosamide (Vimpat) on post-TBI structural, motor and cognitive outcomes. Moderate TBI was induced by lateral fluid-percussion injury in adult rats. Treatment with 0.9% saline or lacosamide (30 mg/kg, i.p.) was started at 30 min post-injury and continued at 8h intervals for 3d (total daily dose 90 mg/kg/d). Rats were randomly assigned to 4 treatment groups: sham-operated controls treated with vehicle (Sham-Veh) or lacosamide (Sham-LCM) and injured animals treated with vehicle (TBI-Veh) or lacosamide (TBI-LCM). As functional outcomes we tested motor recovery with composite neuroscore and beam-walking at 2, 7, and 15 d post-injury. Cognitive recovery was tested with the Morris water-maze at 12-14 d post-TBI. To assess the structural outcome, animals underwent magnetic resonance imaging (MRI) at 2 d post-TBI. At 16d post-TBI, rats were perfused for histology to analyze cortical and hippocampal neurodegeneration and axonal damage. Our data show that at 2 d post-TBI, both the TBI-Veh and TBI-LCM groups were equally impaired in neuroscore. Thereafter, motor recovery occurred similarly during the first week. At 2 wk post-TBI, recovery of the TBI-LCM group lagged behind that in the TBI-VEH group (p<0.05). Performance in beam-walking did not differ between the TBI-Veh and TBI-LCM groups. Both TBI groups were similarly impaired in the Morris water-maze at 2 wk post-TBI. MRI and histology did not reveal any differences in the cortical or hippocampal damage between the TBI-Veh and TBI-LCM groups. Taken together, acute treatment with LCM had no protective effects on post-TBI structural or functional impairment. Composite neuroscore in the TBI-LCM group lagged behind that in the TBI-Veh group at 15 d post-injury, but no compromise was found in other indices of post-TBI recovery in the LCM treated animals.

Mechanisms of calpain mediated proteolysis of voltage gated sodium channel α-subunits following in vitro dynamic stretch injury

Although enhanced calpain activity is well documented after traumatic brain injury (TBI), the pathways targeting specific substrate proteolysis are less defined. Our past work demonstrated that calpain cleaves voltage gated sodium channel (NaCh) α-subunits in an in vitro TBI model. In this study, we investigated the pathways leading to NaCh cleavage utilizing our previously characterized in vitro TBI model, and determined the location of calpain activation within neuronal regions following stretch injury to micropatterned cultures. Calpain specific breakdown products of α-spectrin appeared within axonal, dendritic, and somatic regions 6 h after injury, concurrent with the appearance of NaCh α-subunit proteolysis in both whole cell or enriched axonal preparations. Direct pharmacological activation of either NMDA receptors (NMDArs) or NaChs resulted in NaCh proteolysis. Likewise, a chronic (6 h) dual inhibition of NMDArs/NaChs but not L-type voltage gated calcium channels significantly reduced NaCh proteolysis 6 h after mechanical injury. Interestingly, an early, transient (30 min) inhibition of NMDArs alone significantly reduced NaCh proteolysis. Although a chronic inhibition of calpain significantly reduced proteolysis, a transient inhibition of calpain immediately after injury failed to significantly attenuate NaCh proteolysis. These data suggest that both NMDArs and NaChs are key contributors to calpain activation after mechanical injury, and that a larger temporal window of sustained calpain activation needs consideration in developing effective treatments for TBI.

Anti-epileptogenesis in rodent post-traumatic epilepsy models

Post-traumatic epilepsy (PTE) accounts for 10-20% of symptomatic epilepsies. The urgency to understand the process of post-traumatic epileptogenesis and search for antiepileptogenic treatments is emphasized by a recent increase in traumatic brain injury (TBI) related to military combat or accidents in the aging population. Recent developments in modeling of PTE in rodents have provided tools for identification of novel drug targets for antiepileptogenesis and biomarkers for predicting the risk of epileptogenesis and treatment efficacy after TBI. Here we review the available data on endophenotypes of humans and rodents with TBI associated with epilepsy. Also, current understanding of the mechanisms and biomarkers for PTE as well as factors associated with preclinical study designs are discussed. Finally, we summarize the attempts to prevent PTE in experimental models.

Deletion of the p53 tumor suppressor gene improves neuromotor function but does not attenuate regional neuronal cell loss following experimental brain trauma in mice

Deletion of the tumor suppressor gene p53 has been shown to improve the outcome in experimental models of focal cerebral ischemia and kainate-induced seizures. To evaluate the potential role of p53 in traumatic brain injury, genetically modified mice lacking a functional p53 gene (p53(-/-), n = 9) and their wild-type littermates (p53(+/+), n = 9) were anesthetized and subjected to controlled cortical impact (CCI) experimental brain trauma. After brain injury, neuromotor function was assessed by using composite neuroscore and rotarod tests. By 7 days posttrauma, p53(-/-) mice exhibited significantly improved neuromotor function, in the composite neuroscore (P = 0.002) as well as in two of three individual tests, when compared with brain-injured p53(+/+) animals. CCI resulted in the formation of a cortical cavity (mean volume = 6.1 mm(3)) 7 days postinjury in p53(+/+) as well as p53(-/-) mice. No difference in lesion volume was detected between the two genotypes (P = 0.95). Although significant cell loss was detected in the ipsilateral hippocampus and thalamus of brain-injured animals, no differences between p53(+/+) and p53(-/-) mice were detected. Although our results suggest that lack of the p53 gene results in augmented recovery of neuromotor function following experimental brain trauma, they do not support a role for p53 acting as a mediator of neuronal death in this context, underscoring the complexity of its role in the injured brain.

Cognitive deficits following coronary artery bypass grafting: prevalence, prognosis, and therapeutic strategies

There is increasing recognition that coronary artery bypass grafting (CABG) may be a risk factor for subtle cognitive decline although the presence and pattern of such decline has varied across studies. Cognitive deficits may present as short-term memory loss, executive dysfunction and psychomotor slowing. Although they are usually are not severe enough to meet criteria for mild cognitive impairment or vascular dementia, they lower quality of life and add to hospitalization and out-of-hospital costs. Proposed mechanisms include surgical-related trauma, genetic susceptibility (eg, apolipoprotein E4 allele), microembolization, other vascular or ischemic changes, and temperature during surgery. Depression and anxiety levels predict subjective perception of these deficits more than objective cognitive performance. Both nonpharmacologic (eg, emboli reduction, temperature, or glucose management) and pharmacologic (eg, dexanabinol, glypromate, nootropics) strategies to prevent post-CABG cognitive deficits are under investigation. Given the large numbers of subjects who may already have CABG associated cognitive deficits, clinical trials of agents being tested for Alzheimer's disease (eg, donepezil, rivastigmine, memantine, neramexane, ginkgo) may also be informative. The results of multicenter long-term outcome studies (with matched control groups) as well as ongoing treatment trials will more conclusively address some of these issues. These data emphasize the need for clinicians to monitor cognitive function before and after coronary bypass surgery, and to educate patients.

Traumatic brain injury: developmental differences in glutamate receptor response and the impact on treatment

Perinatal brain injury following trauma, hypoxia, and/or ischemia represents a substantial cause of pediatric disabilities including mental retardation. Such injuries lead to neuronal cell death through either necrosis or apoptosis. Numerous in vivo and in vitro studies implicate ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors in the modulation of such cell death. Expression of glutamate receptors changes as a function of developmental age, with substantial implications for understanding mechanisms of post-injury cell death and its potential treatment. Recent findings suggest that the developing brain is more susceptible to apoptosis after injury and that such caspase mediated cell death may be exacerbated by treatment with N-methyl-D-aspartate receptor antagonists. Moreover, group I metabotropic glutamate receptors appear to have opposite effects on necrotic and apoptotic cell death. Understanding the relative roles of glutamate receptors in post-traumatic or post-ischemic cell death as a function of developmental age may lead to novel targeted approaches to the treatment of pediatric brain injury.

Neuroprotective effects of lamotrigine and remacemide on excitotoxicity induced by glutamate agonists in isolated chick retina

The possible neuroprotective effects of two recently developed antiepileptic compounds, lamotrigine (LTG) and remacemide (REMA), against glutamate agonist-induced excitotoxicity have been investigated in the isolated chick embryo retina model. Retina segments from 15- or 16-day-old embryos were incubated in 1 ml of balanced salt solution, at 25 degrees C for 30 min, in the presence or absence of N-methyl-d-aspartate (NMDA), kainic acid (KA), or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (10 to 200 microM). LTG, REMA, and the active desglycinyl metabolite of REMA (d-REMA) (10-200 microM) were added separately 5 min before glutamate agonists. Retina damage was assessed after 24 h (i) by measuring LDH activity present in the medium, expressed as percentage of total retina LDH activity, and (ii) by histological analysis of retina specimens through scoring for the presence or absence of edema, necrosis, nuclear pyknosis, and cell layer damage. LTG, REMA, and d-REMA reduced LDH release produced by NMDA 58-70% in a dose-dependent manner, with d-REMA being the most potent (EC(50): d-REMA, 25.75 +/- 3.27 microM; REMA, 64.75 +/- 7.75 microM; LTG, 60.50 +/- 6.80 microM; P < 0.001). The drugs had less effect on the LDH release produced by AMPA and KA. Histological analysis confirmed these biochemical results, with all three compounds reducing edema and the number of necrotic and pyknotic nuclei in the ganglion layer. d-REMA provided almost complete protection of the ganglion cell layer against damage produced by NMDA. Combinations of d-REMA and LTG showed additive rather than potentiative effects against NMDA-induced cell injury. The present data provide pharmacological evidence that LTG, REMA, and d-REMA decrease glutamate agonist-induced excitotoxicity in isolated chick retina, findings that might have therapeutic implications for various neurological disorders.

NPS 1506 attenuates cognitive dysfunction and hippocampal neuron death following brain trauma in the rat

Although several noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonists have been shown to be substantially efficacious in experimental models of brain trauma, side effects associated with this class of compounds have impeded clinical application. Therefore, new noncompetitive NMDA receptor antagonists have been developed, including NPS 1506, that appear to be nontoxic but retain efficacy. In the present study, we evaluated the efficacy of NPS 1506 in a model of parasagittal fluid percussion brain trauma in the anesthetized rat. Administration of 1 mg/kg NPS 1506 at both 10 min and 4 h posttrauma induced no changes in brain temperature, mean arterial pressure, pulse, or arterial blood gasses. At 1 week postinjury, animals treated with the same dosing regimen of NPS 1506 demonstrated a dramatic attenuation of memory dysfunction evaluated by a water maze task (P < 0.02) and had greatly reduced neuron death in the CA3 subfield of the hippocampus (P < 0.01). However, NPS 1506 treatment did not significantly affect the extent of cortical tissue loss following injury. Since memory dysfunction and hippocampal damage are common and potentially related consequences of brain trauma in humans, our results suggest that NPS 1506 treatment may have clinical utility.

Positive and negative modulation of the GABA(A) receptor and outcome after traumatic brain injury in rats

Glutamate-mediated excitotoxicity has been shown to contribute to cellular dysfunction following traumatic brain injury (TBI). Increasing inhibitory function through stimulation of gamma-aminobutyric acid (GABA(A)) receptors may attenuate excitotoxic effects and improve outcome. The present experiment examined the effects of diazepam, a positive modulator at the GABA(A) receptor, on survival and cognitive performance in traumatically brain-injured animals. In experiment 1, 15 min prior to central fluid percussion brain injury, rats (n=8 per group) were injected (i.p.) with saline or diazepam (5 mg/kg or 10 mg/kg). Additional rats (n=8) were surgically prepared but not injured (sham-injury). Rats pre-treated with the 5 mg/kg dose of diazepam had significantly lower mortality (0%) than injured, saline-treated rats (53%). Also, diazepam-treated (5 mg/kg) rats had significantly shorter latencies to reach the goal platform in the Morris water maze test performed 11-15 days post-injury. In experiment 2, at 15 min post-injury, rats were given either saline (n=5) or 5 mg/kg diazepam (n=6). Rats treated with diazepam did not differ in mortality from injured rats treated with vehicle. However, rats treated with diazepam at 15 min post-injury had significantly shorter latencies to reach the goal platform in the Morris water maze than injured, vehicle-treated rats. In experiment 3, the post-injury administration of bicuculline (1.5 mg/kg, n=8), a GABA(A) antagonist, increased Morris water maze goal latencies compared to injured animals treated with saline (n=8). These results suggest that enhancing inhibitory function during the acute post-injury period produces beneficial effects on both survival and outcome following experimental TBI.

Remacemide: current status and clinical applications

Remacemide (RMC) is a non-competitive, low-affinity N-methyl-D-aspartate (NMDA) receptor antagonist that does not cause the behavioural and neuropathological side effects seen with other NMDA receptor antagonists. RMC and its active metabolite, AR-R 12495 AR, which has moderate affinity for the NMDA receptor, also interact with voltage-dependent neuronal sodium channels. Both agents show efficacy in a variety of animal models of epilepsy, parkinsonism and cerebral ischaemia. There is no evidence for teratogenicity or genotoxicity. RMC delays the absorption of L-dopa and elevates the concentrations of drugs metabolised by the hepatic cytochrome P450 3A4 isoform. RMC and AR-R 12495 AR have moderate protein binding and linear pharmacokinetics. Controlled studies show evidence of efficacy in treating epilepsy and Parkinson's disease. Post-surgical outcomes in RMC-treated patients at risk for intra-operative cerebral ischaemia are also encouraging. Adverse effects are related to the gastrointestinal and central nervous systems. RMC is a promising drug with numerous potential applications for both acute or chronic conditions associated with glutamate-mediated neurotoxicity.

Neuroprotective effect of remacemide hydrochloride in a perforant pathway stimulation model of status epilepticus in the rat

Previous studies have demonstrated that remacemide and its desglycinyl metabolite, AR-R 2495AA, reduce neuronal damage in animal models of ischemia, subarachnoid hemorrhage, and traumatic brain injury. The aim of the present study was to investigate whether remacemide hydrochloride also alleviates seizure-induced neuronal damage in a model of status epilepticus induced by the stimulation of the perforant pathway (PP) in the rat. Chronic oral remacemide treatment (3 x 25 mg/kg/day) was started either 2 days before or 2 h after the beginning of PP stimulation (2 mA, 20 Hz, 0.1 ms pulse duration for 60 min). The effects of remacemide treatment on the severity of seizures, electroencephalogram (EEG) parameters, seizure-induced neuronal damage in the temporal lobe regions, and memory impairment were compared to unstimulated and stimulated vehicle-treated controls, and carbamazepine-pre-treated (3 x 40 mg/kg/day) rats. Both remacemide and carbamazepine pretreatments, but not remacemide posttreatment, decreased pyramidal cell damage in the CA3 and CA1 subregions of the hippocampus (P < 0.05). In addition, overall neuronal damage in the extrahippocampal temporal lobe regions (the piriform cortex, entorhinal cortex, and the amygdaloid complex) was milder in remacemide-pretreated rats compared to stimulated control rats (P < 0.01). The neuroprotective effect was most evident on the side contralateral to stimulation. Remacemide or carbamazepine pretreatment had no evident effect on the number or duration of behavioral seizures during PP stimulation. Neither drug altered the spectral parameters of the baseline EEG or prevented status epilepticus-induced EEG slowing observed 2 weeks after PP stimulation. Nor did remacemide or carbamazepine treatment alleviate spatial memory impairment determined in a Morris water-maze task 2 weeks after PP stimulation. Our data provide evidence that pretreatment with remacemide has a moderate neuroprotective effect against status epilepticus-induced neuronal damage.

Riluzole attenuates cortical lesion size, but not hippocampal neuronal loss, following traumatic brain injury in the rat

The neuroprotective effects of Riluzole, a compound with several mechanisms of action including the inhibition of sodium channel activity and glutamate release, were evaluated in a rat model of parasagittal fluid-percussion (FP) brain injury. Male Sprague-Dawley rats (350-400 g, n = 17) were anesthetized with sodium pentobarbital (60 mg/kg i.p.) and subjected to parasagittal FP brain injury of moderate severity (2.3-2.5 atm). Fifteen min following injury, animals randomly received an i.v. bolus of either Riluzole (8 mg/kg, n = 8) or vehicle (n = 9), followed by subcutaneous injections (identical dose) at 6 hr and 24 hr. Two weeks after injury and drug treatment, animals were sacrificed and a series of brain sections, stained with Hematoxylin and Eosin (H&E) or cresyl violet, were evaluated for quantitative cortical lesion volume and cell counts of hippocampal CA3 neurons, respectively, using a computerized image analysis system. Administration of Riluzole significantly reduced FP-induced tissue loss in the temporal/occipital cortices ipsilateral to the site of impact by 46%, compared to vehicle-treated, brain-injured animals (P = 0.01). In contrast, the selective neuronal loss observed in the CA3 region of the ipsilateral hippocampus was unaffected by Riluzole treatment. The present study demonstrates that Riluzole can attenuate cortical lesion size following brain trauma. These neuroprotective effects may be related to the synergy of the different mechanisms of action of Riluzole.