Effects of the novel NMDA antagonists CP-98,113, CP-101,581 and CP-101,606 on cognitive function and regional cerebral edema following experimental brain injury in the rat

Efficacy of N-Methyl-D-Aspartate (NMDA) Receptor Antagonists in Treating Traumatic Brain Injury-Induced Brain Edema: A Systematic Review and Meta-analysis of Animal Studies

Traumatic brain injury leads to glutamate release, which overstimulates N-methyl-D-aspartate (NMDA) receptors, leading to neurotoxicity and cytotoxic edema. NMDA receptor antagonists may offer neuroprotection by blocking this pathway. The objective of this systematic review is to assess the efficacy of NMDA receptor antagonists for traumatic brain injury-induced brain edema in rodent models. This systematic review followed Cochrane Handbook guidelines and registered its protocol in PROSPERO (ID: CRD42023440934). Here, we included controlled rodent animal models comparing NMDA antagonist use with a placebo treatment. Outcome measures included the reduction of cerebral edema, Neurobehavioral Severity Scale, and adverse effects. The search strategy used Medical Subject Headings terms related to traumatic brain injury and NMDA receptor antagonists. The Collaborative Approach to Meta Analysis and Review of Animal Experimental Studies (CAMARADES) checklist and Systematic Review Centre for Laboratory Animal Experimentation's (SYRCLE's) tools were used to measure the quality and bias of included studies. The synthesis of results was presented in a meta-analysis of standard mean difference. Sixteen studies were included, with the predominant drugs being ifenprodil, MK-801, magnesium, and HU-211. The subjects consisted of Sprague-Dawley or Sabra rats. The analysis showed a significant reduction in brain edema with NMDA antagonist treatment (Standardized mean difference [SMD] - 1.17, 95% confidence interval [CI] - 1.59 to - 0.74, p < 0.01), despite high heterogeneity (I2 = 72%). Neurobehavioral Severity Scale also significantly improved (mean difference - 3.32, 95% CI - 4.36 to - 2.28, p < 0.01) in animals receiving NMDA antagonists. Administration within 1 h after injury showed a modest enhancement in reducing brain edema compared with the baseline (SMD - 1.23, 95% CI - 1.69 to - 0.77, p < 0.01). Studies met standards for animal welfare and model appropriateness. Although baseline comparability and selective reporting bias were generally addressed, key biases such as randomization, allocation concealment, and blinding were often unreported. Overall, NMDA antagonists exhibit promising efficacy in the treatment of traumatic brain injury. Notably, our systematic review consistently demonstrated a significant reduction in brain edema with compounds including HU-211 and NPS 150.

Novel Positive Allosteric Modulators of Glutamate Transport Have Neuroprotective Properties in an in Vitro Excitotoxic Model

Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and several neurodegenerative disorders. EAAT2 is the main transporter subtype responsible for glutamate clearance in the brain, and plays a key role in regulating neurotransmission and preventing excitotoxicity. Therefore, compounds that increase the activity of EAAT2 have therapeutic potential for neuroprotection. In previous studies, we used virtual screening approaches to identify novel positive allosteric modulators (PAMs) of EAAT2. These compounds were shown to selectively increase the activity of EAAT2 and increase V_max of transport, without changing substrate affinity. In this work, our major effort was to investigate whether increasing the activity of EAAT2 by allosteric modulation would translate to neuroprotection in in vitro primary culture models of excitotoxicity. To investigate potential neuroprotective effects of one EAAT2 PAM, GT949, we subjected cultures to acute and prolonged excitotoxic insults by exogenous application of glutamate, or oxidative stress by application of hydrogen peroxide. GT949 administration did not result in neuroprotection in the oxidative stress model, likely due to damage of the glutamate transporters. However, GT949 displayed neuroprotective properties after acute and prolonged glutamate-mediated excitotoxicity. We propose that this compound prevents excess glutamate signaling by increasing the rate of glutamate clearance by EAAT2, thereby preventing excitotoxic damage and cell death. This novel class of compounds is therefore an innovative approach for neuroprotection with potential for translation in in vivo animal models of excitotoxicity.

Diurnal variation of NMDA receptor expression in the rat cerebral cortex is associated with traumatic brain injury damage

OBJECTIVE

Data from our laboratory suggest that recovery from a traumatic brain injury depends on the time of day at which it occurred. In this study, we examined whether traumatic brain injury -induced damage is related to circadian variation in N-methyl-D-aspartate receptor expression in rat cortex.

RESULTS

We confirmed that traumatic brain injury recovery depended on the time of day at which the damage occurred. We also found that motor cortex N-methyl-D-aspartate receptor subunit NR1 expression exhibited diurnal variation in both control and traumatic brain injury-subjected rats. However, this rhythm is more pronounced in traumatic brain injury-subjected rats, with minimum expression in those injured during nighttime hours. These findings suggest that traumatic brain injury occurrence times should be considered in future clinical studies and when designing neuroprotective strategies for patients.

Exendin-4 inhibits high-altitude cerebral edema by protecting against neurobiological dysfunction

The anti-inflammatory and antioxidant effects of exendin-4 (Ex-4) have been reported previously. However, whether (Ex-4) has anti-inflammatory and antioxidant effects on high-altitude cerebral edema (HACE) remains poorly understood. In this study, two rat models of HACE were established by placing rats in a hypoxic environment with a simulated altitude of either 6000- or 7000-m above sea level (MASL) for 72 hours. An altitude of 7000 MASL with 72-hours of hypoxia was found to be the optimized experimental paradigm for establishing HACE models. Then, in rats where a model of HACE was established by introducing them to a 7000 MASL environment with 72-hours of hypoxia treatment, 2, 10 and, 100 μg of Ex-4 was intraperitoneally administrated. The open field test and tail suspension test were used to test animal behavior. Routine methods were used to detect change in inflammatory cells. Hematoxylin-eosin staining was performed to determine pathological changes to brain tissue. Wet/dry weight ratios were used to measure brain water content. Evans blue leakage was used to determine blood-brain barrier integrity. Enzyme-linked immunosorbent assay (ELISA) was performed to measure markers of inflammation and oxidative stress including superoxide dismutase, glutathione, and malonaldehyde values, as well as interleukin-6, tumor necrosis factor-alpha, cyclic adenosine monophosphate levels in the brain tissue. Western blot analysis was performed to determine the levels of occludin, ZO-1, SOCS-3, vascular endothelial growth factor, EPAC1, nuclear factor-kappa B, and aquaporin-4. Our results demonstrate that Ex-4 preconditioning decreased brain water content, inhibited inflammation and oxidative stress, alleviated brain tissue injury, maintain blood-brain barrier integrity, and effectively improved motor function in rat models of HACE. These findings suggest that Ex-4 exhibits therapeutic potential in the treatment of HACE.

Negative Allosteric Modulators Selective for The NR2B Subtype of The NMDA Receptor Impair Cognition in Multiple Domains

Antidepressant activity of N-methyl-D-aspartate (NMDA) receptor antagonists and negative allosteric modulators (NAMs) has led to increased investigation of their behavioral pharmacology. NMDA antagonists, such as ketamine, impair cognition in multiple species and in multiple cognitive domains. However, studies with NR2B subtype-selective NAMs have reported mixed results in rodents including increased impulsivity, no effect on cognition, impairment or even improvement of some cognitive tasks. To date, the effects of NR2B-selective NAMs on cognitive tests have not been reported in nonhuman primates. The current study evaluated two selective NR2B NAMs, CP101,606 and BMT-108908, along with the nonselective NMDA antagonists, ketamine and AZD6765, in the nonhuman primate Cambridge Neuropsychological Test Automated Battery (CANTAB) list-based delayed match to sample (list-DMS) task. Ketamine and the two NMDA NR2B NAMs produced selective impairments in memory in the list-DMS task. AZD6765 impaired performance in a non-specific manner. In a separate cohort, CP101,606 impaired performance of the nonhuman primate CANTAB visuo-spatial Paired Associates Learning (vsPAL) task with a selective impairment at more difficult conditions. The results of these studies clearly show that systemic administration of a selective NR2B NAM can cause transient cognitive impairment in multiple cognitive domains.

Surgical incision-induced nociception causes cognitive impairment and reduction in synaptic NMDA receptor 2B in mice

Postoperative cognitive dysfunction (POCD) is associated with impairments in daily functioning, and increased morbidity and mortality. However, the causes and neuropathogenesis of POCD remain largely unknown. Uncontrolled pain often occurs postoperatively. We therefore set out to determine the effects of surgical incision-induced nociception on the cognitive function and its underlying mechanisms in 3- and 9-month-old mice. The mice had surgical incision in the hindpaw and then were tested for nociceptive threshold, learning, and memory. Brain levels of NMDA receptor and cyclin-dependent kinase 5 (CDK5) were also assessed. We found that surgical incision-induced nociception in mice led to a decreased freezing time in the tone test (which assesses the hippocampus-independent learning and memory function), but not the context test, of Fear Conditioning System at 3 and 7 d, but not 30 d post incision in 9-month-old, but not 3-month-old mice. Consistently, the surgical incision selectively decreased synaptic NMDA receptor 2B levels in the medial prefrontal cortex, and increased levels of tumor necrosis factor-α and CDK5 in the cortex, but not hippocampus, of the mice. Finally, eutectic mixture of local anesthetics and CDK5 inhibitor, roscovitine, attenuated the surgical incision-induced reduction in the synaptic NMDA receptor 2B levels and learning impairment. These results suggested that surgical incision-induced nociception reduced the synaptic NMDA receptor 2B level in the medial prefrontal cortex of mice, which might lead to hippocampus-independent learning impairment, contributing to POCD. These findings call for further investigation to determine the role of surgical incision-induced nociception in POCD.

Ion channels as drug targets in central nervous system disorders

Ion channel targeted drugs have always been related with either the central nervous system (CNS), the peripheral nervous system, or the cardiovascular system. Within the CNS, basic indications of drugs are: sleep disorders, anxiety, epilepsy, pain, etc. However, traditional channel blockers have multiple adverse events, mainly due to low specificity of mechanism of action. Lately, novel ion channel subtypes have been discovered, which gives premises to drug discovery process led towards specific channel subtypes. An example is Na(+) channels, whose subtypes 1.3 and 1.7-1.9 are responsible for pain, and 1.1 and 1.2 - for epilepsy. Moreover, new drug candidates have been recognized. This review is focusing on ion channels subtypes, which play a significant role in current drug discovery and development process. The knowledge on channel subtypes has developed rapidly, giving new nomenclatures of ion channels. For example, Ca(2+)s channels are not any more divided to T, L, N, P/Q, and R, but they are described as Ca(v)1.1-Ca(v)3.3, with even newer nomenclature α1A-α1I and α1S. Moreover, new channels such as P2X1-P2X7, as well as TRPA1-TRPV1 have been discovered, giving premises for new types of analgesic drugs.

In vitro models of traumatic brain injury

In vitro models of traumatic brain injury (TBI) are helping elucidate the pathobiological mechanisms responsible for dysfunction and delayed cell death after mechanical stimulation of the brain. Researchers have identified compounds that have the potential to break the chain of molecular events set in motion by traumatic injury. Ultimately, the utility of in vitro models in identifying novel therapeutics will be determined by how closely the in vitro cascades recapitulate the sequence of cellular events that play out in vivo after TBI. Herein, the major in vitro models are reviewed, and a discussion of the physical injury mechanisms and culture preparations is employed. A comparison between the efficacy of compounds tested in vitro and in vivo is presented as a critical evaluation of the fidelity of in vitro models to the complex pathobiology that is TBI. We conclude that in vitro models were greater than 88% predictive of in vivo results.

N-methyl-D-aspartate receptor mechanosensitivity is governed by C terminus of NR2B subunit

N-methyl-D-aspartate receptors (NMDARs), critical mediators of both physiologic and pathologic neurological signaling, have previously been shown to be sensitive to mechanical stretch through the loss of its native Mg(2+) block. However, the regulation of this mechanosensitivity has yet to be further explored. Furthermore, as it has become apparent that NMDAR-mediated signaling is dependent on specific NMDAR subtypes, as governed by the identity of the NR2 subunit, a crucial unanswered question is the role of subunit composition in observed NMDAR mechanosensitivity. Here, we used a recombinant system to assess the mechanosensitivity of specific subtypes and demonstrate that the mechanosensitive property is uniquely governed by the NR2B subunit. NR1/NR2B NMDARs displayed significant stretch sensitivity, whereas NR1/NR2A NMDARs did not respond to stretch. Furthermore, NR2B mechanosensitivity was regulated by PKC activity, because PKC inhibition reduced stretch responses in transfected HEK 293 cells and primary cortical neurons. Finally, using NR2B point mutations, we identified a PKC phosphorylation site, Ser-1323 on NR2B, as a unique critical regulator of stretch sensitivity. These data suggest that the selective mechanosensitivity of NR2B can significantly impact neuronal response to traumatic brain injury and illustrate that the mechanical tone of the neuron can be dynamically regulated by PKC activity.

Impact of pharmacological treatments on outcome in adult rodents after traumatic brain injury: a meta-analysis

Pharmacological treatments have been widely investigated in pre-clinical animal trials to evaluate their usefulness in reducing cognitive, behavioural and motor problems after traumatic brain injury (TBI). However, the relative efficacy of these agents has yet to be evaluated, making it difficult to assess the strength of evidence for their use in a clinical population. A meta-analytic review of research (1980-2009) was therefore conducted to examine the impact of pharmacological treatments administered to adult male rodents after experimental TBI on cognitive, behavioural, and motor outcome. The PubMed and PsycInfo databases were searched using 35 terms. Weighted Cohen's d effect sizes, percent overlap, Fail-Safe N statistics and confidence intervals were calculated for each treatment. In total, 91 treatments were evaluated in 223 pre-clinical trials, comprising 5988 rodents. Treatments that were investigated by multiple studies and showed large and significant treatment effects were of greatest interest. Of the 16 treatments that were efficacious, six improved cognition, 10 improved motor function and no treatment improved behaviour (depression/anxiety, aggression, zoosocial behaviour). Treatment benefits were found across a range of TBI models. Drug dosage and treatment interval impacted on treatment effects.

Behavioral deficits and cellular damage following developmental ethanol exposure in rats are attenuated by CP-101,606, an NMDAR antagonist with unique NR2B specificity

NMDAR-mediated excitotoxicity has been implicated in some of the impairments following fetal ethanol exposure. Previous studies suggest that both neuronal cell death and some of the behavioral deficits can be reduced by NMDAR antagonism during withdrawal, including antagonism of a subpopulation of receptors containing NR2B subunits. To further investigate NR2B involvement, we selected a compound, CP-101,606 (CP) which binds selectively to NR2B/2B stoichiometries, for both in vitro and in vivo analyses. For the in vitro study, hippocampal explants were exposed to ethanol for 10 days and then 24 h following removal of ethanol, cellular damage was quantified via propidium iodide fluorescence. In vitro ethanol withdrawal-associated neurotoxicity was prevented by CP (10 and 25 nM). In vivo ethanol exposure was administered on PNDs 1-7 with CP administered 21 h following cessation. Activity (PNDs 20-21), motor skills (PNDs 31-33), and maze navigation (PNDs 43-44) were all susceptible to ethanol insult; treatment with CP (15 mg/kg) rescued these deficits. Our findings show that CP-101,606, a drug that blocks the NR2B/2B receptor, can reduce some of the damaging effects of "3rd trimester" alcohol exposure in our rodent model. Further work is clearly warranted on the neuroprotective potential of this drug in the developing brain.

[Anti-inflammatory modulators in traumatic brain injury]

Traumatic brain injury leads to primary and secondary brain injuries. Primary brain injury results from mechanical forces applied to the head at the time of impact. Secondary brain injury occurs at some time after the primary impact. Numerous pathophysiological mechanisms have been postulated to explain the progressive tissue damage produced by secondary injuries. The endogenous neuroinflammatory response after traumatic brain injury contributes to the development of blood-brain barrier breakdown, cerebral oedema and neuronal cell death and this has led to various pharmacological therapies to try to limit this type of damage. Studies employing glutamate receptor antagonist for cerebral protection have yielded promising results in laboratory animals but failed to produce clinically significant improvements. The present review will summarize the mechanisms of post traumatic cerebral inflammation with a special focus on the anti-inflammatory drug targets.

The effect of the selective NMDA receptor antagonist traxoprodil in the treatment of traumatic brain injury

Traumatic brain injury (TBI) remains a major public health problem, and there is a great medical need for a pharmacological treatment that could improve long-term outcome. The excitatory neurotransmitter, glutamate, has been implicated in processes leading to neurodegeneration. Traxoprodil (CP-101,606) is a novel and potent glutamate receptor antagonist that is highly selective for the NR2B subunit of the NMDA receptor; it has been shown to be neuroprotective in animal models of brain injury and ischemia. A randomized, double-blind, placebo-controlled study was therefore conducted to assess the efficacy and safety of a 72-h infusion of traxoprodil compared to placebo in subjects with computed tomography scan evidence of severe TBI (GCS 4-8). A total of 404 males and non-pregnant females, aged 16-70, were treated within 8 h of injury. At baseline, subjects were stratified by motor score severity. The results showed that a greater proportion of the traxoprodil-treated subjects had a favorable outcome on the dichotomized Glasgow Outcome Scale (dGOS) at 6 months (delta 5.5%, OR 1.3, p = 0.21, 95% CI:[0.85, 2.06]) and at last visit (delta 7.5%, OR 1.47, p = 0.07, 95% CI:[0.97, 2.25]). The mortality rate with traxoprodil treatment was 7% less than with placebo treatment (OR 1.45, p = 0.08, 95% CI:[0.96, 2.18]). Differences between treatment groups were more pronounced in the severest subset (delta 11.8% for the dGOS at last visit and delta 16.6% for mortality). Traxoprodil was well tolerated. Although these results are intriguing, no definitive claim of efficacy can be made for traxoprodil for the treatment of severe TBI.

Excitatory amino acid neurotransmission

In recent years great progress has been made in understanding the function of ionotropic and metabotropic glutamate receptors; their pharmacology and potential therapeutic applications. It should be stressed that there are already N-methyl-D-aspartate (NMDA) antagonists in clinical use, such as memantine, which proves the feasibility of their therapeutic potential. It seems unlikely that competitive NMDA receptor antagonists and high-affinity channel blockers will find therapeutic use due to limiting side-effects, whereas agents acting at the glycineB site, NMDA receptor subtype-selective agents and moderate-affinity channel blockers are far more promising. This is supported by the fact that there are several glycineB antagonists, NMDA moderate-affinity channel blockers and NR2B-selective agents under development. Positive and negative modulators of AMPA receptors such as the AMPAkines and 2,3-benzodiazepines also show more promise than e.g. competitive antagonists. Great progress has also been made in the field of metabotropic glutamate receptors since the discovery of novel, allosteric modulatory sites for these receptors. Selective agents acting at these transmembrane sites have been developed that are more drug-like and have a much better access to the central nervous system than their competitive counterparts. The chapter will critically review preclinical and scarce clinical experience in the development of new ionotropic and metabotropic glutamate receptor modulators according to the following scheme: rational, preclinical findings in animal models and finally clinical experience, where available.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Evidence for improved performance in cognitive tasks following selective NR2B NMDA receptor antagonist pre-treatment in the rat

RATIONALE

We previously reported that the NR2B subunit-selective N-methyl-D-aspartate (NMDA) antagonist Ro 63-1908 produced a marked deficit in response control in the five-choice serial reaction time task (5-CSRTT).

OBJECTIVES

The present studies were designed to investigate this further by studying the NR2B NMDA antagonists, ifenprodil, traxoprodil (CP101,606), Ro 25-6981 as well as Ro 63-1908 in this test.

METHODS

Following training in the 5-CSRTT, separate groups of rats were either tested under (1) standard test conditions [5 s inter-trial interval (ITI), 0.5 s stimulus duration, 100 trials], (2) high (3 s ITI) and low (10 s ITI) event rate of stimulus presentation and (3) a 250-trial protocol in aged 2-year-old rats. In a final study, the effects of traxoprodil were investigated in an operant delayed match to position (DMTP) task, a test of working memory, and compared to dizocilpine and Ro 63-1908.

RESULTS

Similar to Ro 63-1908, both traxoprodil (1-10 mg/kg) and Ro 25-6981 (3--30 mg/kg) increased premature responding but also increased response speed with no error trade-off. Conversely, ifenprodil (1--10 mg/kg) slowed response speed and increased omissions with no effect on premature responding. Tested under a variable ITI, Ro 63--1908 (1 mg/kg) increased premature responding at all ITIs, but this change was proportional to controls. At short ITI (3 s), Ro 63-1908 reliably improved performance both in terms of response speed and accuracy (percent correct). In a 250-trial protocol in aged rats, both Ro 63-1908 (0.1-0.3 mg/kg) and, particularly, traxoprodil (1--3 mg/kg) improved performance-increasing response speed and increasing the number of rewards earned during test. Finally, traxoprodil (1--10 mg/kg) improved accuracy and increased response speed in the DMTP task.

CONCLUSIONS

The present studies support the view that selective NR2B NMDA antagonists promote impulsive-type responding in the 5-CSRTT; however, under certain test conditions, drugs of this class-notably traxoprodil-may also improve task performance.

A review of the neuroprotective properties of the 5-HT1A receptor agonist repinotan HCl (BAYx3702) in ischemic stroke

Repinotan HCl (repinotan, BAYx3702), a highly selective 5-HT1A receptor agonist with a good record of safety was found to have pronounced neuroprotective effects in experimental models that mimic various aspects of brain injury. Repinotan caused strong, dose-dependent infarct reductions in permanent middle cerebral artery occlusion, transient middle cerebral artery occlusion, and traumatic brain injury paradigms. The specific 5-HT1A receptor antagonist WAY 100635 blocked these effects, indicating that the neuroprotective properties of repinotan are mediated through the 5-HT1A receptor. The proposed neuroprotective mechanisms of repinotan are thought to be the result of neuronal hyperpolarization via the activation of G protein-coupled inwardly rectifying K+ channels upon binding to both pre- and post-synaptic 5-HT1A receptors. Hyperpolarization results in inhibition of neuron firing and reduction of glutamate release. These mechanisms, leading to protection of neurons against overexcitation, could explain the neuroprotective efficacy of repinotan per se, but not necessarily the efficacy by delayed administration. The therapeutic time window of repinotan appeared to be at least 5 h in in vivo animal models, but may be even longer at higher doses of the drug. Experimental studies indicate that repinotan affects various mechanisms involved in the pathogenesis of brain injury. In addition to the direct effect of repinotan on neuronal hyperpolarization and suppression of glutamate release this compound affects the death-inhibiting protein Bcl-2, serotonergic glial growth factor S-100beta and Nerve Growth Factor. It also suppresses the activity of caspase-3 through MAPK and PKCalpha; this effect may contribute to its neuroprotective efficacy. The dose- and time-dependent neuroprotective efficacy of repinotan indicates that the drug is a promising candidate for prevention of secondary brain damage in brain-injured patients suffering from acute ischemic stroke. Unfortunately, however, the first, randomized, double blind, placebo-controlled clinical trial did not demonstrate the efficacy of repinotan in acute ischemic stroke.

Selective intermediate-/small-conductance calcium-activated potassium channel (KCNN4) blockers are potent and effective therapeutics in experimental brain oedema and traumatic brain injury caused by acute subdural haematoma

Early deterioration and death after brain injury is often the result of oedema in the injured and peri-lesional tissue. So far, no pharmacotherapy is available that exhibits significant brain oedema-reducing efficacy in patients. We selected two low molecular weight compounds from different chemical classes, a triazole (1-[(2-chlorophenyl)diphenylmethyl]-1,2,3-triazole) and a cyclohexadiene (methyl 4-[4-chloro-3-(trifluoromethyl)phenyl]-6-methyl-3-oxo-1,4,7-tetrahydroisobenzofuran-5-carboxylate) to characterize their pharmacological properties on KCNN4 channels (intermediate/small conductance calcium-activated potassium channel, subfamily N, member 4) in vitro as well as in vivo. In vitro we replaced potassium by rubidium (Rb+) and determined Rb+ fluxes evoked by 10 micro m of the calcium ionophore A23187 on C6BU1 rat glioma cells. Compared with known KCNN4 blockers, such as clotrimazole (IC50=360 +/- 12 nm) and charybdotoxin (IC50=3.3 +/- 1.9 nm), the triazole and cyclohexadiene were considerably more potent than clotrimazole and displayed similar potencies (IC50=12.1 +/- 8.8 and 13.3 +/- 4.7 nm, respectively). In the rat acute subdural haematoma model, both the triazole and cyclohexadiene displayed reduction of brain water content (-26% at 0.3 mg/kg and -24% at 0.01 mg/kg) and reduction of the intracranial pressure (-46% at 0.1 mg/kg and -60% at 0.003 mg/kg) after 24 h when administered as a 4-h infusion immediately after brain injury. When infarct volumes were determined after 7 days, the triazole as well as the cyclohexadiene displayed strong neuroprotective efficacy (-52% infarct volume reduction at 1.2 mg/kg and -43% at 0.04 mg/kg, respectively). It is concluded that blockade of KCNN4 channels is a new pharmacological approach to attenuate acute brain damage caused by traumatic brain injury.

Role of NMDA receptor subtypes in the induction of catalepsy and increase in Fos protein expression after administration of haloperidol

The increase of Fos expression in the striatum induced by haloperidol, an antagonist of the dopamine D2 receptor, might be related to the activation of glutamatergic neurotransmission, especially that of N-methyl-D-aspartate (NMDA) receptors. In this study, using behavioral and immunohistochemical techniques, we examined the effects of a noncompetitive NMDA antagonist, (+)-MK-801, and an NMDA receptor NR2B subunit antagonist, ifenprodil, on catalepsy, an extrapyramidal symptom; in this context, we also considered the expression of Fos protein in the forebrain after the administration of haloperidol. Catalepsy in mice, induced by the administration of haloperidol (1 mg/kg), was inhibited by pretreatment with (+)-MK-801 (0.2 mg/kg) or ifenprodil (10 mg/kg). Furthermore, pretreatment with (+)-MK-801 (0.2 mg/kg) significantly attenuated the induction of Fos-immunoreactive (IR) cells in the dorsomedial, dorsolateral, and ventrolateral striatum, but not in the shell region of the nucleus accumbens after the administration of haloperidol, whereas pretreatment with ifenprodil (10 mg/kg) significantly attenuated the induction of Fos-IR cells in all of these areas. It is known that ifenprodil binds sigma receptors and alpha-1 adrenergic receptors with high affinity. Pretreatment with the sigma receptor antagonist BD-1407 (3 mg/kg) or the alpha-1 adrenergic receptor antagonist prazosin (3 mg/kg) affected neither catalepsy nor the expression of Fos-IR cells after the administration of haloperidol. However, pretreatment with CP-101,606 (1 mg/kg), a selective antagonist for the NR2B subunit of the NMDA receptor, significantly attenuated catalepsy and the expression of Fos-IR cells in the forebrain after the administration of haloperidol. These results suggest that the NMDA receptor antagonists attenuated the induction of catalepsy and Fos-IR cells in forebrain after the administration of haloperidol. It was also suggested that haloperidol-induced expression of Fos-IR cells in the shell region of the nucleus accumbens might be differentially regulated by NMDA receptor subunits. Therefore, it appears that selective antagonists for the NR2B subunit of the NMDA receptor (e.g., CP-101,606) might be useful drugs for the treatment of extrapyramidal side effects (EPS) associated with the chronic use of typical antipsychotics such as haloperidol.

Differential Effects of the Anticonvulsant Topiramate on Neurobehavioral and Histological Outcomes following Traumatic Brain Injury in Rats

The efficacy of topiramate, a novel therapeutic agent approved for the treatment of seizure disorders, was evaluated in a model of traumatic brain injury (TBI). Adult male rats were anesthetized (sodium pentobarbital, 60 mg/kg, i.p.), subjected to lateral fluid percussion brain injury (n = 60) or sham injury (n = 47) and randomized to receive either topiramate or vehicle at 30 min (30 mg/kg, i.p.), and 8, 20 and 32 h postinjury (30 mg/kg, p.o.). In Study A, memory was evaluated using a Morris water maze at 48 h postinjury, after which brain tissue was evaluated for regional cerebral edema. In Study B, animals were evaluated for motor function at 48 h and 1, 2, 3, and 4 weeks postinjury using a composite neuroscore and the rotating pole test and for learning ability at 4 weeks. Brains were analyzed for hemispheric tissue loss and hippocampal CA3 cell loss. Topiramate had no effect on posttraumatic cerebral edema or histologic damage when compared to vehicle. At 48 h, topiramate treatment improved memory function in sham but not brain-injured animals, while at one month postinjury it impaired learning performance in brain-injured but not sham animals. Topiramate significantly improved composite neuroscores at 4 weeks postinjury and rotating pole performance at 1 and 4 weeks postinjury, suggesting a potentially beneficial effect on motor function following TBI.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

The effect of (+/-)-CP-101,606, an NMDA receptor NR2B subunit selective antagonist, in the Morris watermaze

It is well established that the NMDA receptor antagonists block hippocampal long-term potentiation and impair acquisition in the Morris watermaze task, although the role of individual NMDA receptor subtypes is largely unknown. In the present study, we compared the effects of (+/-)-CP-101,606, an antagonist selective for NMDA receptor NR1/NR2B subunit-containing receptors and the nonselective NMDA receptor antagonist MK-801, on acquisition in the Morris watermaze. Male hooded Lister rats were given 4 trials/day to find a fixed hidden platform submerged beneath the opaque water of the Morris watermaze. Twenty-four hours after the last acquisition trial, a 'probe trial' was conducted to assess the rat's spatial memory for the location of the hidden platform. Those rats treated with MK-801 (0.1 mg/kg, i.p.) 60 min prior to the acquisition and probe trials took significantly longer to find the hidden platform during training and spent significantly less time searching the platform's location during the probe trial than vehicle-treated rats. In contrast, 60-min pretreatment with (+/-)-CP-101,606 (60 mg/kg, p.o.), a dose that fully occupied hippocampal NR1/NR2B subunit-containing receptors, as determined by ex vivo NMDA receptor-specific [3H]ifenprodil binding immediately following watermaze experiments, had no effect on acquisition or the probe trial. These results suggest that antagonists selective for NR1/NR2B subunit-containing receptors may not impair spatial memory in rats in the Morris watermaze.

The glutamate AMPA receptor antagonist, YM872, attenuates cortical tissue loss, regional cerebral edema, and neurological motor deficits after experimental brain injury in rats

A massive increase in extracellular glutamate is thought to contribute to brain damage after traumatic brain injury. We examined the neuroprotective effect of the AMPA receptor antagonist YM872 in a rat head injury model using the fluid-percussion procedure. Male Sprague-Dawley rats were subjected to right lateral (parasagittal) fluid-percussion brain injury or sham injury. At 15 min postinjury, they received either YM872 (20 mg/kg/h, 20 mg/3 mL) or normal saline (vehicle) intravenously for 4 h. The administration of YM872 significantly improved the composite neuroscore at 1 and 2 weeks postinjury (p < 0.05), and markedly reduced the volume of tissue loss in the injured cortex (p < 0.05). It also significantly reduced cerebral edema in the ipsilateral parietal cortex at 48 h postinjury (p < 0.01). These results indicate that the posttraumatic administration of YM872 may be neuroprotective by ameliorating cortical tissue loss and regional cerebral edema, and suggest the importance of AMPA receptors in traumatic brain damage involving secondary injury processes.

Reduced brain infarct volume and improved neurological outcome by inhibition of the NR2B subunit of NMDA receptors by using CP101,606-27 alone and in combination with rt-PA in a thromboembolic stroke model in rats

OBJECT

A novel postsynaptic antagonist of N-methyl-D-aspartate (NMDA) receptors, CP-101,606-27 may attenuate the effects of focal ischemia. In current experiments, the authors investigated its neuroprotective effect alone and in combination with recombinant tissue plasminogen activator (rt-PA) in thromboembolic focal cerebral ischemia in rats.

METHODS

Forty-eight male Wistar rats underwent embolization of the right middle cerebral artery to produce focal cerebral ischemia. After random division into six groups (eight rats in each group), animals received: vehicle; low-dose (LD) CP-101, 606-27, 14.4 mg/kg; high-dose (HD) CP- 101,606-27, 28.8 mg/kg; rt-PA, 10 mg/kg; low-dose combination (LDC) CP- 101,606-27, 14.4 mg/kg plus rt-PA, 10 mg/kg; or high-dose combination (HDC) CP- 101,606-27, 28.8 mg/kg plus rt-PA, 10 mg/kg) 2 hours after induction of embolic stroke. Animals were killed 48 hours after the onset of focal ischemia. Brain infarction volume, neurobehavioral outcome, poststroke seizure activity, poststroke mortality, and intracranial hemorrhage incidence were observed and evaluated. Compared with vehicle-treated animals (39.4 +/- 8.6%) 2 hours posttreatment with CP-101,606-27 or rt-PA or in combination a significant reduction in the percentage of brain infarct volume was seen (LD CP-101,606-27: 20.8 +/- 14.3%, p < 0.05; HD CP-101,606-27: 10.9 +/- 3.2%, p < 0.001; rt-PA: 21.1 +/- 7.3%, p < 0.05; LDC, 18.6 +/- 11.5%, p < 0.05; and HDC: 15.2 +/- 10.1%, p < 0.05; compared with control: 39.4 +/- 8.6%). Combination of CP-101,606-27 with rt-PA did not show a significantly enhanced neuroprotective effect. Except for the control and LDC treatment groups, neurobehavioral outcome was significantly improved 24 hours after embolic stroke in animals in all other active therapeutic groups receiving CP-101,606-27 or rt-PA or in combination. The authors also observed that treatment with HD CP-101,606-27 decreased poststroke seizure activity.

CONCLUSIONS

The data in this study suggested that postischemia treatment with CP-101,606-27 is neuroprotective in the current stroke model; however, the authors also note that although rt-PA may offer modest protection when used alone, combination with CP-101,606-27 did not appear to enhance its effects.

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.

Pharmacological treatment of traumatic brain injury: a review of agents in development

Successful treatment strategies for patients with traumatic brain injury (TBI) remain elusive despite standardised clinical treatment guidelines, improved understanding of mechanisms of cellular response to trauma, and a decade of clinical trials aimed at identifying therapeutic agents targeted at mediators of secondary injury. The information explosion relative to mechanisms of secondary injury has identified several potential targets for intervention. Depending on the type of injury to the brain and the intensity and the success of resuscitation, necrosis, apoptosis, inflammatory and excitotoxic cellular damage can be seen. These same processes may continue postinjury, depending on the adequacy of clinical care. Each of these mechanisms of cellular damage can initiate a cascade of events mediated by endogenous signals that lead to secondary neurological injury. Several factors contributed to the failure of earlier clinical trials. Now that these have been recognised, a positive impact on future drug development in TBI has been realised. Both the US and Europe have organised brain injury consortiums where experts in the treatment of TBI provide insight into study design, implementation, conduct and oversight in conjunction with the pharmaceutical industry. Consequently, future clinical trials of new investigational treatments have greater potential for identifying therapies of merit in specific populations of patients with TBI. Pharmacological strategies under investigation are targeting sites involved in the secondary cascade that contribute to overall poor outcome following the primary injury. These treatments include ion channel antagonists including calcium channel antagonists, growth factors, antioxidants, stem cells, apoptosis inhibitors, and inhibitors of other signal modulators. In conclusion, the complexity of TBI pathology and the mechanisms contributing to secondary injury present unique therapeutic challenges. Appropriate research targets for intervention continue to be investigated, however, the likelihood of improving outcomes with a single approach is extremely small. There is a need for collaborative efforts to investigate the optimal time for drug administration and the logical sequence or combination of treatments that will ultimately lead to improved neurological outcomes in this population.

The selective 5-HT(1A) receptor agonist repinotan HCl attenuates histopathology and spatial learning deficits following traumatic brain injury in rats

The selective 5-HT(1A) receptor agonist Repinotan HCl (BAY x3702) has been reported to attenuate cortical damage and improve functional performance in experimental models of cerebral ischemia and acute subdural hematoma. Using a clinically relevant contusion model of traumatic brain injury, we tested the hypothesis that a 4-h continuous infusion of Repinotan HCl (10 microg/kg/h i.v.) commencing 5 min post-injury would ameliorate functional outcome and attenuate histopathology. Forty isoflurane-anesthetized male adult rats were randomly assigned to receive either a controlled cortical impact (2.7 mm tissue deformation, 4 m/s) or sham injury (Injury/Vehicle=10, Injury/MK-801=10, Injury/Repinotan HCl=10, Sham/Vehicle=10), then tested for vestibulomotor function on post-operative days 1-5 and for spatial learning on days 14-18. Neither Repinotan HCl nor the non-competitive N-methyl-D-aspartate receptor antagonist MK-801, which served as a positive control, improved vestibulomotor function on beam balance and beam walk tasks relative to the Injury/Vehicle group, but both did significantly attenuate spatial learning and memory deficits on a water maze task. Repinotan HCl also reduced hippocampal CA(1) and CA(3) neuronal loss, as well as cortical tissue damage, compared to the Injury/Vehicle group at 4 weeks post-trauma. No significant difference in histological outcome was revealed between the Repinotan HCl- and MK-801-treated groups.These findings extend the therapeutic efficacy of Repinotan HCl to a contusion model of experimental brain injury and demonstrate for the first time that 5-HT(1A) receptor agonists confer neuroprotection and attenuate spatial learning deficits following controlled cortical impact injury. This treatment strategy may be beneficial in a clinical context where memory impairments are common following human traumatic brain injury.

The maxi-K channel opener BMS-204352 attenuates regional cerebral edema and neurologic motor impairment after experimental brain injury

Large-conductance, calcium-activated potassium (maxi-K) channels regulate neurotransmitter release and neuronal excitability, and openers of these channels have been shown to be neuroprotective in models of cerebral ischemia. The authors evaluated the effects of postinjury systemic administration of the maxi-K channel opener, BMS-204352, on behavioral and histologic outcome after lateral fluid percussion (FP) traumatic brain injury (TBI) in the rat. Anesthetized Sprague-Dawley rats (n = 142) were subjected to moderate FP brain injury (n = 88) or surgery without injury (n = 54) and were randomized to receive a bolus of 0.1 mg/kg BMS-204352 (n = 26, injured; n = 18, sham), 0.03 mg/kg BMS-204352 (n = 25, injured; n = 18, sham), or 2% dimethyl sulfoxide (DMSO) in polyethylene glycol (vehicle, n = 27, injured; n = 18, sham) at 10 minutes postinjury. One group of rats was tested for memory retention (Morris water maze) at 42 hours postinjury, then killed for evaluation of regional cerebral edema. A second group of injured/sham rats was assessed for neurologic motor function from 48 hours to 2 weeks postinjury and cortical lesion area. Administration of 0.1 mg/kg BMS-204352 improved neurologic motor function at 1 and 2 weeks postinjury (P < 0.05) and reduced the extent of cerebral edema in the ipsilateral hippocampus, thalamus, and adjacent cortex (P < 0.05). Administration of 0.03 mg/kg BMS-204352 significantly reduced cerebral edema in the ipsilateral thalamus (P < 0.05). No effects on cognitive function or cortical tissue loss were observed with either dose. These results suggest that the novel maxi-K channel opener BMS-204352 may be selectively beneficial in the treatment of experimental TBI.

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.

NPS 1506: a novel NMDA receptor antagonist: neuroprotective effects in a model of closed head trauma in rats

We examined whether NPS 1506, a novel uncompetitive N-methyl-D-aspartate receptor antagonist, influences neurological outcome following closed head trauma (CHT) in rats. One hundred ten rats were divided into 11 groups: CHT (yes/no), treatment with NPS 1506 (yes/no), and time of euthanization (24 h/48 h). The dose of NPS 1506 was 1 mg/kg IV at 1 and 4 hours following CHT or sham operation. Closed head trauma induced the following changes in the injured hemisphere: Decreased specific gravity (sg) (1.036 +/- 0.006) and magnesium (Mg) (0.042 +/- 0.005 microg/mg) at 24 hours, and potassium (K) at 24 (1.145 +/- 0.376 microg/mg) and 48 hours, and increased water content (W) (84.9 +/- 2.5%) and sodium (Na) (2.135 +/- 0.699 microg/mg) at 24 hours, and calcium (Ca) at 24 (0.543 +/- 0.157 microg/mg) and 48 hours. These were reversed by NPS 1506; sg of 1.043 +/- 0.004, Mg of 0.077 +/- 0.009 microg/mg, K of 1.930 +/- 0.238 microg/mg, W of 81.5 +/- 1.9%, Ca of 0.043 +/- 0.023 microg/mg, and Na of 0.688 +/- 0.110 microg/mg. In groups not given NPS 1506, a nonsignificant decrease in neurological severity score (NSS) occurred at 24 and 48 hours as compared to NSS at 1 hour after CHT. In groups given NPS 1506, NSS at 24 and 48 hours decreased significantly (improved) compared to NSS at 1 hour, but not compared to NSS at 24 and 48 hours in groups not given NPS 1506. NPS 1506 caused no significant change in ischemic tissue volume or hemorrhagic necrosis volume in the injured hemisphere at 24 hours or 48 hours. These findings indicate that NPS 1506 improved measures of brain tissue edema (at 24 hours but not at 48 hours) and ion homeostasis, and this improvement was not related to other measures of outcome.

CP-101,606, an NR2B subunit selective NMDA receptor antagonist, inhibits NMDA and injury induced c-fos expression and cortical spreading depression in rodents

(1S, 2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP-101,606) is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors containing the NR2B subunit. This compound was used to investigate the role of NR2B containing receptors in three responses to NMDA receptor activation in vivo. In mouse, CP-101,606 completely inhibited increases in fos-like immunoreactivity in dentate gyrus caused by a subconvulsant intraperitoneal dose of NMDA. In rat, the compound completely blocked cortical c-fos mRNA induction following focal injury in parietal cortex and the initiation and propagation of electrically induced cortical spreading depression. Inhibition of these responses by CP-101,606 indicates that c-fos induction and cortical spreading depression are dependent on activation of NMDA receptors containing the NR2B subunit. Since NMDA receptor dependent c-fos induction and cortical spreading depression may contribute to neuron loss after focal CNS injury, inhibition of these responses by CP-101,606 may contribute to the neuroprotective efficacy of the compound.

Glutamate as a neurotransmitter in the brain: review of physiology and pathology

Glutamate is the principal excitatory neurotransmitter in brain. Our knowledge of the glutamatergic synapse has advanced enormously in the last 10 years, primarily through application of molecular biological techniques to the study of glutamate receptors and transporters. There are three families of ionotropic receptors with intrinsic cation permeable channels [N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate]. There are three groups of metabotropic, G protein-coupled glutamate receptors (mGluR) that modify neuronal and glial excitability through G protein subunits acting on membrane ion channels and second messengers such as diacylglycerol and cAMP. There are also two glial glutamate transporters and three neuronal transporters in the brain. Glutamate is the most abundant amino acid in the diet. There is no evidence for brain damage in humans resulting from dietary glutamate. A kainate analog, domoate, is sometimes ingested accidentally in blue mussels; this potent toxin causes limbic seizures, which can lead to hippocampal and related pathology and amnesia. Endogenous glutamate, by activating NMDA, AMPA or mGluR1 receptors, may contribute to the brain damage occurring acutely after status epilepticus, cerebral ischemia or traumatic brain injury. It may also contribute to chronic neurodegeneration in such disorders as amyotrophic lateral sclerosis and Huntington's chorea. In animal models of cerebral ischemia and traumatic brain injury, NMDA and AMPA receptor antagonists protect against acute brain damage and delayed behavioral deficits. Such compounds are undergoing testing in humans, but therapeutic efficacy has yet to be established. Other clinical conditions that may respond to drugs acting on glutamatergic transmission include epilepsy, amnesia, anxiety, hyperalgesia and psychosis.

A double-blind, placebo-controlled study of the safety, tolerability and pharmacokinetics of CP-101,606 in patients with a mild or moderate traumatic brain injury

CP-101,606 is a postsynaptic antagonist of the glutamate-mediated NR2B subunit of the N-methyl-D-aspartate (NMDA) receptor. When administered intravenously (i.v.) at the time of injury, CP-101,606 is neuroprotective in animal models of traumatic brain injury (TBI) and ischemia. Minimal adverse effects have been observed in normal human volunteers given i.v. doses of up to 3 mg/kg/hr for 72 hours. The objective of the present clinical trial was to assess the safety, pharmacokinetics, and tolerability of CP-101,606 infused for various times in patients who had suffered either an acute moderate or mild TBI (Glasgow Coma Score 9-14) or hemorrhagic stroke. Patients began receiving treatment within 12 hours of brain injury. A total of 53 subjects (45 with TBI and 8 with stroke) were randomized in a double-blind fashion to receive CP-101,606 or placebo (4 drug: 1 placebo). Drug/placebo was administered by i.v. infusion (0.75 mg/kg/hr) for 2 hours and then stopped (n = 25) or continued for 22 hours (n = 4) or 70 hours (n = 24) at a rate of 0.37 mg/kg/hr. Mean plasma drug concentrations were well above the predicted therapeutic concentration of 200 ng/ml within two hours of initiating treatment and were sustained as long as drug was infused. All the patients tolerated their drug/placebo treatment, and there were no clinically significant cardiovascular or hematological abnormalities in either group. A Neurobehavioral Rating Scale, used to detect personality changes and behavioral disturbances, indicated that all subjects showed an improvement from their postinjury, predosing baseline but did not significantly differ from each other with respect to type of head injury and/or treatment with drug or placebo. Modified Kurtzke Scoring also showed a similar pattern of improvement irrespective of type of head injury or drug/placebo treatment. This study suggests that CP-101,606, infused for up to 72 hours has no psychotropic effects and is well-tolerated in patients who have sustained a mild or moderate TBI or hemorrhagic stroke.

An open-label study of CP-101,606 in subjects with a severe traumatic head injury or spontaneous intracerebral hemorrhage

CP-101,606 is a postsynaptic antagonist of N-methyl-D-aspartate (NMDA) receptors bearing the NR2B subunit. When administered intravenously (i.v.), it decreases the effects of traumatic brain injury (TBI) and focal ischemia in animal models. Therapeutic plasma concentrations (200 ng/ml) in animals, have been well tolerated in healthy human volunteers. The purpose of the present dose escalation study was to assess the safety, tolerability, and pharmacokinetics of CP-101,606 in subjects who had suffered either an acute severe TBI (Glasgow Coma Scale 3-8) or spontaneous intracerebral hemorrhage. Thirty patients, 20 with a TBI and 10 with a stroke, were enrolled in the trial and began receiving an i.v. infusion of CP-101,606 for 2 hours, 24 hours, or 72 hours within 12 hours of brain injury. For the first two hours, the drug was given a rate of 0.75 mg/kg/hr and then stopped (n = 17) or continued for 22 (n = 2) or 70 hours (n = 11) at 0.37 mg/kg/hr. Plasma and cerebrospinal fluid (CSF) were collected at serial times during and after treatment. There were no consistent changes in blood pressure or pulse nor any clinically significant hematological or electrocardiogram (ECG) abnormalities attributable to CP-101,606. No adverse events or behavioral changes were considered to be related to the drug. Plasma concentrations of CP-101,606 over 200 ng/ml were rapidly achieved in the blood and CSF within two hours and were sustained there as long as the drug was infused. CSF concentrations were slightly higher than that in plasma by the end of infusion suggesting good penetration of CP-101,606 into the CSF. Outcome in the severe TBI patients, as measured by the Glasgow Outcome Score at six months, suggested that a two-hour infusion yielded a range of scores similar to contemporary patients with a severe TBI treated at our hospital while the outcomes of the patients treated with either a 24- or 72-hour infusion were better on average. Thus, these results indicate that CP-101,606 infused for up to 72 hours is well tolerated, penetrates the CSF and brain, and may improve outcome in the brain-injured patient.

High extracellular glutamate and neuronal death in neurological disorders. Cause, contribution or consequence?

In models of neurological disorders, increased extracellular glutamate and beneficial effects produced by glutamate-receptor antagonists are consistently taken as supporting evidence of excitotoxicity. This systematic interpretation is over-simplified and potentially misleading. High extracellular glutamate is not a reliable indicator of endogenous excitotoxicity, i.e., the intrinsic, potential neurotoxicity of endogenous glutamate whenever it accumulates extracellularly. Firstly, because the extracellular levels of glutamate necessary to produce depolarization and death in vivo, are far above those measured in models of neurological disorders. Secondly, because changes in the concentration of glutamate in the synaptic cleft (i.e., the relevant compartment for endogenous excitotoxicity) are not reflected extracellularly. Protection by glutamate-receptor antagonists does not necessarily imply inhibition of excitotoxic abnormalities. Indeed, neuronal death initiated by insults such as ischemia results from multifactorial processes that may be interrelated. Therefore, beneficial effects resulting from an interaction with glutamate-mediated transmission may actually render the cell more resistant to other deleterious mechanisms (e.g., mitochondrial injury, oxidative stress).

Apoptotic neurodegeneration following trauma is markedly enhanced in the immature brain

Age dependency of apoptotic neurodegeneration was studied in the developing rat brain after percussion head trauma. In 7-day-old rats, mechanical trauma, applied by means of a weight drop device, was shown to trigger widespread cell death in the hemisphere ipsilateral to the trauma site, which first appeared at 6 hours, peaked at 24 hours, and subsided by 5 days after trauma. Ultrastructurally, degenerating neurons displayed features consistent with apoptosis. A decrease of bcl-2 in conjunction with an increase of c-jun mRNA levels, which were evident at 1 hour after trauma and were accompanied by elevation of CPP 32-like proteolytic activity and oligonucleosomes in vulnerable brain regions, confirmed the apoptotic nature of this process. Severity of trauma-triggered apoptosis in the brains of 3- to 30-day-old rats was age dependent, was highest in 3- and 7-day-old animals, and demonstrated a subsequent rapid decline. Adjusting the mechanical force in accordance with age-specific brain weights revealed a similar vulnerability profile. Thus, apoptotic neurodegeneration contributes in an age-dependent fashion to neuropathological outcome after head trauma, with the immature brain being exceedingly vulnerable. These results help explain unfavorable outcomes of very young pediatric head trauma patients and imply that, in this group, an antiapoptotic regimen may constitute a successful neuroprotective approach.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Central nervous system resuscitation

Traumatic injury to the central nervous system induces delayed neuronal death, which may be mediated by acute and chronic neurochemical changes. Experimental identification of these injury mechanisms and elucidation of the neurochemical cascade following trauma may provide enhanced opportunities for treatment with novel neuroprotective strategies.