Clomethiazole protects the brain in transient forebrain ischemia when used up to 4 h after the insult

The science of cerebral ischemia and the quest for neuroprotection: navigating past failure to future success

Ischemic stroke remains a leading cause of morbidity and death for which few therapeutic options are available. The development of neuroprotective agents, a once promising field of investigation, has failed to translate from bench to bedside successfully. This work reviews the ischemic cascade, agents targeting steps within the cascade, and potential reasons for lack of translation. Additional therapeutic targets are highlighted and areas requiring further investigation are discussed. It is clear that alternative targets need to be pursued, such as the role glia play in neurological injury and recovery, particularly the interactions between neurons, astrocytes, microglia, and the vasculature. Similarly, the biphasic nature of many signaling molecules such as matrix metalloproteinases and high-mobility group box 1 protein must be further investigated to elucidate periods of detrimental versus beneficial activity.

Diazepam attenuates the post-traumatic hyperactivity of excitatory synapses in rat hippocampal CA1 neurons

The effect of diazepam, a benzodiazepine derivative, on the post-traumatic hyperactivity of excitatory synaptic transmission was examined in rat hippocampal CA1 area. Optical recordings showed that the activity of hippocampal neurons was enhanced in rats treated with fluid percussion injury (FPI) as compared with that of sham-operated rats. The optical response was characterized by fast and slow components. FPI did not affect the fast component that reflects presynaptic action potentials, but enhanced the slow component that reflects excitatory synaptic responses. Intracellular recordings showed that the amplitude and duration of the excitatory postsynaptic potential (EPSP) were increased after FPI. However, FPI did not affect the resting membrane potential and action potentials of hippocampal neurons. Intraperitoneal (i.p.) administration of diazepam (30 and 90 min after FPI) attenuated the post-traumatic hyperactivity of the slow optical response. The slope of input-to-output relation of excitatory synapses was decreased by acute administration of diazepam to FPI rats, but not by delayed administration of diazepam (4 and 5 h after FPI). The fast optical responses were not affected by either FPI or i.p. administration of diazepam. These results suggest that administration of diazepam at early post-traumatic period prevents the FPI-induced delayed enhancement of excitatory synaptic transmission in rat hippocampal CA1 neurons.

Ion channels involved in stroke

Ion channels are membrane proteins that flicker open and shut to regulate the flow of ions down their electrochemical gradient across the membrane and consequently regulate cellular excitability. Every living cell expresses ion channels, as they are critical life-sustaining proteins. Ion channels are generally either activated by voltage or by ligand interaction. For each group of ion channels the channels' molecular biology and biophysics will be introduced and the pharmacology of that group of channels will be reviewed. The in vitro and in vivo literature will be reviewed and, for ion channel groups in which clinical trials have been conducted, the efficacy and therapeutic potential of the neuroprotective compounds will be reviewed. A large part of this article will deal with glutamate receptors, focusing specifically on N-methyl-D-aspartate (NMDA) receptors. Although the outcome of clinical trials for NMDA receptor antagonists as therapeutics for acute stroke is disappointing, the culmination of these failed trials was preceded by a decade of efforts to develop these agents. Sodium and calcium channel antagonists will be reviewed and the newly emerging efforts to develop therapeutics targeting potassium channels will be discussed. The future development of stroke therapeutics targeting ion channels will be discussed in the context of the failures of the last decade in hopes that this decade will yield successful stroke therapeutics.

Behavioral effects of photothrombotic ischemic cortical injury in aged rats treated with the sedative-hypnotic GABAergic drug zopiclone

Sedative-hypnotic drugs commonly used in the elderly may affect functional recovery following cerebrovascular events. Previous research has shown that prolonged exposure to diazepam can interfere with recovery of function and exaggerate tissue loss after brain injury. The present study evaluated the effect of zopiclone, a widely used hypnotic drug, on functional and histological outcome after cortical photothrombosis in aged rats, which might be particularly vulnerable to brain insults and inhibitory sedative-hypnotic drugs. Aged Wistar rats were treated with zopiclone at a dose of 3 mg/kg (i.p., once a day) beginning 4 days before ischemia induction and continuing for 23 days. Sensorimotor recovery was assessed by a new ledged beam-walking test and spatial learning by the Morris water-maze. After a 7-day washout period all rats were administered a single dose of zopiclone (3 mg/kg, i.p.) and retested. Infarct volumes were measured from nitroblue tetrazolium-stained sections at the end of the experiment. Beam-walking data showed that ischemic rats treated with zopiclone were not more impaired than untreated rats. Indeed, they showed fewer faults with the impaired hindlimb than ischemic controls on post-operative day 16. Water-maze performance was not affected by zopiclone. After the washout period a single dose of zopiclone did not worsen forelimb or hindlimb function, but seemed to improve performance in the water-maze test. Cortical infarct volumes were similar in ischemic controls and ischemic rats treated with zopiclone. In conclusion, zopiclone was not detrimental and even seemed to improve behavioral outcome without affecting ischemic damage in aged rats subjected to cortical photothrombosis.

The pharmacology of chlormethiazole: a potential neuroprotective agent?

Chlormethiazole is a thiazole derivative with a long history of use as a sedative agent. The mode of action of the drug has been partly worked out and has been established with recognition that its mechanism of action involves potentiation of GABA activity, the major intrinsic inhibitory neurotransmitter. Animal models of stroke ranging from rodents to primates have suggested an optimistic role for chlormethiazole in preventing both anatomical and functional deleterious effects of stroke. Phase III clinical trials, therefore, proceeded but unfortunately with very little success. Recently, the animal models have been revisited in an attempt to identify causes for this discrepancy between the results from preclinical and clinical studies. This review studies the pharmacological roots of chlormethiazole from its origin through to its licensed and novel applications. Emphasis is placed on discussing the animal experiments which led to its grooming as a neuroprotective agent and also on the human trials. The review seeks to explain the discrepancies between animal and human studies, which include short survival times of experimental subjects, speed of drug administration and fundamental differences between species. The primate model of stroke perhaps offers the nearest alternative to phase III trials and has recently been used to compare a number of newer neuroprotective agents with greater efficacy than chlormethiazole. In addition, novel approaches involving human neurochemical analyses in vivo are described which may help bridge the gap between animal models and future phase III trials.

Differential neuroprotective effects for three GABA-potentiating compounds in a model of hypoxia–ischemia

Clomethiazole (CMZ) is a GABA(A)-potentiating compound; however, it is unclear whether this mode of action is responsible for its neuroprotective effects in animal models of ischemia. This study compared the neuroprotective efficacies of muscimol and midazolam, two potent GABA(A)-potentiating compounds, to that of CMZ in a model of hypoxia-ischemia (H-I). To establish a neuroprotective profile for CMZ, CMZ (60, 95, or 125 mg kg-1, i.p.) was administered to post-natal day 25 male rats at numerous post-hypoxic time points and the rats were sacrificed 1 or 4 weeks later. Varying degrees of histological protection were evident when CMZ was administered 1, 2, or 3 h post-hypoxia with the 125 mg kg-1 dose producing complete histological protection if administered 3 h post-hypoxia. To determine whether midazolam or muscimol could match the protection provided by CMZ administered 3 h post-hypoxia, H-I rats received varying doses of these compounds 3 h post-hypoxia and were sacrificed 1 week later. Under identical conditions, no dose of muscimol or midazolam provided equivalent neuroprotection to that provided by CMZ. In fact, muscimol showed no neuroprotective ability whatsoever. Thus, CMZ, administered as late as 3 h post-hypoxia, was able to completely prevent H-I-induced cell death while a full dose range of other GABA-potentiating agents did not. Such direct comparison of these compounds in this model suggests the mechanism underlying the protective effects of CMZ may not rely solely on GABA(A)-potentiating properties. Elucidation of a novel mechanism of action for CMZ may expose new therapeutic targets in stroke treatment.

Neuro-overprotection? A functional evaluation of clomethiazole-induced neuroprotection following hypoxic-ischemic injury

Hypoxic-ischemic (H-I) injury produces extensive damage to the hippocampus of young rats. We have recently shown that administration of 125 mg kg-1 clomethiazole (CMZ), a GABA(A)-agonist, provides complete histological protection against H-I injury if administered 3 h post-H-I (Brain Res 1035 (2005) 194). However, whether that histological protection translates into lasting functional preservation is unclear. To determine whether hippocampal-based circuits remain functionally intact in CMZ-protected H-I rats, we administered 125 mg kg-1 (high dose [CMZ-HD]) or 65 mg kg-1 (low dose [CMZ-LD]) CMZ, 3 h post-H-I, and examined numerous kindling parameters in the dorsal hippocampus 60 days following H-I. Kindling parameters included afterdischarge (AD) thresholds (ADTs), AD durations and kindling rates. Additional groups assessed included vehicle-injected H-I (VIH), hypoxic, ligated and naive rats. VIH, CMZ-HD, CMZ-LD and hypoxic rats all exhibited significantly faster kindling rates than naive rats. Thus, a previous traumatic event, even hypoxia alone, facilitated subsequent seizure propagation. Still, a significantly slower kindling rate was evident in CMZ-HD rats than in hypoxic, VIH or CMZ-LD rats. Moreover, while longer pre-kindling AD durations were observed in the damaged hippocampus of VIH compared with naive rats, this was not true for either CMZ-treated groups, hypoxic or ligated rats. Collectively, these findings suggest CMZ can suppress the epileptogenic effects of H-I. Surprisingly, however, both groups of CMZ-treated rats exhibited a four to nine times greater ADT than any other group and this effect was most profound in the CMZ-protected hippocampus. Thus, CMZ administration protected local neurons against terminal insult and left network excitability relatively normal with respect to seizure offset mechanisms but also caused profound elevation of local ADTs, which suggests a local hypoexcitability/increased inhibition. Finally, this study demonstrates, for the first time, that the kindling model can serve as a sensitive measure of function-related neuroprotective efficacy in animal models of ischemia.

Long-term effects of clomethiazole in a model of global ischemia

The failure of neuroprotective drugs in clinical trials has raised questions about the predictive value of animal models. To address this issue we reexamined the efficacy of clomethiazole using functional and histological outcome measures in combination with long-term survival times. Gerbils were exposed to 5 min of global ischemia and received 400 mg/ml clomethiazole (via osmotic minipump) plus a bolus injection (60 mg/kg) 30 min after ischemia. Brain temperature was maintained at approximately 36.5 degrees C during ischemia and for the first 30 min after ischemia, and was monitored in all groups for 24 h. Subgroups of clomethiazole-treated gerbils had their temperatures regulated in the normothermic range while in other animals temperature was not controlled. Open-field habituation tests were conducted 5, 10, 30, and 60 days after occlusion. CA1 cell counts and CA1 slice recordings were done at the conclusion of behavioral testing. Clomethiazole significantly attenuated CA1 cell loss at 10-, 30-, and 60-day survival. A modest reduction in habituation deficits was evident only on Day 10 (P < 0.05). Similarly, field potential amplitude was not maintained in the rostral CA1 region. Clomethiazole produced mild hypothermia that developed over several hours. Based on short-term CA1 cell counts, clomethiazole provided significant histological protection with limited functional preservation. Neuroprotection disappeared when longer survival times (60 day) were employed and temperature confounds eliminated. These data demonstrate the necessity of utilizing more clinically relevant survival times and carefully monitoring/regulating postischemic temperature when assessing potential neuroprotective compounds.

The effect of clomethiazole on plasma concentrations of interleukin-6, -8, -1beta, tumor necrosis factor-alpha, and neutrophil adhesion molecule expression during experimental extracorporeal circulation

Clomethiazole (CMZ), a neuroprotective drug, has antiinflammatory actions. We investigated the effects of CMZ administration on plasma concentrations of interleukin (IL)-6, IL-8, IL-1beta, tumor necrosis factor-alpha, and neutrophil adhesion molecule expression during experimental extracorporeal circulation. Five healthy volunteers each donated 500 mL of blood, which was subsequently divided into equal portions. Identical extracorporeal circuits were simultaneously primed with donated blood (250 mL) and circulated for 2 h at 37 degrees C. CMZ was added to 1 of the circuits of each pair to achieve a total plasma concentration of 40 micro mol/L. Blood samples were withdrawn at (i) donation, (ii) immediately after addition of CMZ, and at (iii) 30, 60, 90, and 120 min after commencing circulation. Plasma concentrations of IL-6, IL-8, and tumor necrosis factor-alpha were less in the CMZ group compared with control after 60 min of circulation (2.2 [0.3] versus 3.2 [0.4], 14.9 [4.8] versus 21.9 [18.4], 63.3 [43.5] versus 132.2 [118.9] pg/mL, respectively, P < 0.05). After 120 min of circulation, neutrophils from CMZ-treated circuits showed significantly less CD18 expression compared with control (237.5 [97.4] versus 280.5 [111.5], P = 0.03). The addition of CMZ to experimental extracorporeal circuits decreases the inflammatory response. This effect may be of clinical benefit by decreasing inflammatory-mediated neurological injury during cardiopulmonary bypass.

IMPLICATIONS

Enhancement of gamma-aminobutyric acid(A)-mediated effects by clomethiazole (CMZ) and associated neuroprotection has been established in animal models of cerebral ischemia. In an ex vivo study, we demonstrated antiinflammatory activity of CMZ in experimental extracorporeal circulation. This represents a potential neuroprotective mechanism of CMZ in patients undergoing coronary artery bypass surgery.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Diazepam does not reduce infarct size in rats subjected to transient occlusion of the middle cerebral artery when normothermia is maintained

Activation of the gamma-amino butyric acid (GABA)-ergic system might protect against the damage that occurs after cerebral ischaemia. We examined this hypothesis by administering diazepam to rats subjected to transient middle cerebral artery occlusion (MCAO) using the intraluminal thread method. Diffusion MRI (DWI) and perfusion imaging (PI) were acquired during MCAO to assess brain tissue status and haemodynamics, respectively. Rats were intraperitoneally injected with either 10 mg kg(-1) diazepam (n = 5) or vehicle (n = 5) both 30 min and 90 min after the onset of MCAO. To exclude the possibility that neuroprotection was due to the hypothermic action of the drug, body temperature was maintained at 37-38 degrees C for up to 7 h postischaemia with a feed-back controlled thermoregulatory unit. Infarct volumes quantified 2 days after MCAO from T(2)-weighted images were similar in ischaemic control rats and in ischaemic rats treated with diazepam. We conclude that diazepam-induced enhancement of GABA(A) activity does not effectively protect against neuronal damage that occurs after transient MCAO in normothermic rats.

Neuroprotective effects of progesterone on damage elicited by acute global cerebral ischemia in neurons of the caudate nucleus

BACKGROUND

In addition to the hippocampus, the dorsolateral caudate nucleus (CN) and the pars reticularis of the substantia nigra (SNr) are among the most vulnerable brain areas to ischemia. A possible association of the neuronal injury in these two subcortical nuclei has been proposed, the primary damage affecting the CN GABAergic neurons innervating the SNr, and secondarily the SNr neurons as a result of an imbalance of GABAergic and glutamatergic input to the SNr. Progesterone (P(4)) exerts a GABAergic action on the central nervous system (CNS) and is known to protect neurons in the cat hippocampus from the damaging effect of acute global cerebral ischemia (AGCI). The effects of AGCI on the neuronal populations of the CN and SNr, in addition to the possible neuroprotective effects of P(4), were assessed in cats in the present study.

METHODS

Ovariectomized adult cats were treated subcutaneously (s.c.) with either P(4) (10 mg/kg/day) or corn oil during the 7 days before and 7 days after being subjected to a period of AGCI by 15 min of cardiorespiratory arrest followed by 4 min of reanimation. After 14 days of survival, animals were sacrificed and their brains perfused in situ with phosphate-buffered 10% formaldehyde for histologic examination.

RESULTS

ACGI resulted in an intense glial reaction in the CN and a significant loss (43%) of medium-sized neurons of the CN, but no difference was found in the densities of SNr neurons between controls and ischemic oil- and P(4)-treated cats. Progesterone treatment completely prevented CN neuronal loss.

CONCLUSIONS

The overall results point to the higher vulnerability of CN neurons to ischemia as compared to neurons in the SNr and show the protective effects of P(4) upon CN neuronal damage after ischemia.

gamma-Aminobutyric acid(A) neurotransmission and cerebral ischemia

In this review, we present evidence for the role of gamma-aminobutyric acid (GABA) neurotransmission in cerebral ischemia-induced neuronal death. While glutamate neurotransmission has received widespread attention in this area of study, relatively few investigators have focused on the ischemia-induced alterations in inhibitory neurotransmission. We present a review of the effects of cerebral ischemia on pre and postsynaptic targets within the GABAergic synapse. Both in vitro and in vivo models of ischemia have been used to measure changes in GABA synthesis, release, reuptake, GABA(A) receptor expression and activity. Cellular events generated by ischemia that have been shown to alter GABA neurotransmission include changes in the Cl(-) gradient, reduction in ATP, increase in intracellular Ca(2+), generation of reactive oxygen species, and accumulation of arachidonic acid and eicosanoids. Neuroprotective strategies to increase GABA neurotransmission target both sides of the synapse as well, by preventing GABA reuptake and metabolism and increasing GABA(A) receptor activity with agonists and allosteric modulators. Some of these strategies are quite efficacious in animal models of cerebral ischemia, with sedation as the only unwanted side-effect. Based on promising animal data, clinical trials with GABAergic drugs are in progress for specific types of stroke. This review attempts to provide an understanding of the mechanisms by which GABA neurotransmission is sensitive to cerebral ischemia. Furthermore, we discuss how dysfunction of GABA neurotransmission may contribute to neuronal death and how neuronal death can be prevented by GABAergic drugs.

GABA potentiation: a logical pharmacological approach for the treatment of acute ischaemic stroke

It has been shown that enhancing the function of the major inhibitory neurotransmitter GABA decreases glutamatergic activity in the brain. Since increased glutamatergic activity is the major primary event that results in cell death following an acute hypoxic-ischaemic stroke, GABAmimetic drugs might therefore be expected to be neuroprotective. This review examines the evidence that GABAergic function is acutely depressed following an ischaemic insult, and also reviews the data that suggest that increasing cerebral GABA concentration has a neuroprotective effect, as does the administration of some (but not all) GABAmimetic agents. The GABA uptake inhibitor CI-966, the GABA(A) agonist muscimol and the GABA(A)mimetic clomethiazole have all been shown to be neuroprotective in animal models of stroke when given after the ischaemic insult. In contrast, benzodiazepines and particularly barbiturates, although potent GABA(A) potentiators, have shown little promise as neuroprotectants. The diversity of GABA(A) receptor subtypes and the in vivo efficacy of certain GABA(A) receptor ligands in animal models of stroke suggests that GABAmimetic drugs are an undervalued approach to stroke therapy.

Acute ethanol administration and transient ischemia: a behavioral and neuropathological study

A pressing clinical question is how acute ethanol exposure might alter the outcome of a simultaneous transient ischemic attack (TIA), since ethanol is known to dysregulate key intermediary metabolites post-ischemia. Mongolian gerbils were administered ethanol (1 or 4 g/kg, s.c.) 1 hour before induction of transient ischemia, via bilateral carotid occlusions of 5 minutes duration. A control group was administered isotonic saline and rendered ischemic. All animals were maintained normothermic during the ischemic procedure. Subjects underwent behavioral assay of acquisition to the water maze 7 days after recovery from the surgery, and neuropathological examination 1-month after the ischemic brain insult. There were no behavioral or neuropathological between-group differences suggesting that mechanisms other than adverse ethanol-induced perturbations of ischemic processes predominate in mediating epidemiological findings of elevated stroke morbidity with high ethanol consumption.

The metabolism of clomethiazole in gerbils and the neuroprotective and sedative activity of the metabolites

A single dose of clomethiazole (600 micromol kg(-1) i.p.) has previously been shown to be neuroprotective in the gerbil model of global ischaemia. In gerbils, clomethiazole (600 micromol kg(-1)) injection produced a rapid appearance (peak within 5 min) of drug in plasma and brain and similar clearance (plasma t(1/2): 40 min) from both tissues. The peak brain concentration (226+/-56 nmol g(-1)) was 40% higher than plasma. One major metabolite, 5-(1-hydroxyethyl-2-chloro)-4-methylthiazole (NLA-715) and two minor metabolites 5-(1-hydroxyethyl)-4-methylthiazole (NLA-272) and 5-acetyl-4-methylthiazole (NLA-511) were detected in plasma and brain. Evidence suggested that clomethiazole is metabolized directly to both NLA-715 and NLA-272. Injection of NLA-715, NLA-272 or NLA-511 (each at 600 micromol kg(-1)) produced brain concentrations respectively 2.2, 38 and 92 times greater than seen after clomethiazole (600 micromol kg(-1)). Clomethiazole (600 micromol kg(-1)) injected 60 min after a 5 min bilateral carotid artery occlusion in gerbils attenuated the ischaemia-induced degeneration of the hippocampus by approximately 70%. The metabolites were not neuroprotective at this dose. In mice, clomethiazole (600 micromol kg(-1)) produced peak plasma and brain concentrations approximately 100% higher than in gerbils, drug concentrations in several brain regions were similar but 35% higher than plasma. Clomethiazole (ED(50): 180 micromol kg(-1)) and NLA-715 (ED(50): 240 micromol kg(-1)) inhibited spontaneous locomotor activity. The other metabolites were not sedative (ED(50) >600 micromol kg(-1)). These data suggest that the neuroprotective action of clomethiazole results from an action of the parent compound and that NLA-715 contributes to the sedative activity of the drug. British Journal of Pharmacology (2000) 129, 95 - 100

Effect of ganaxolone in a rodent model of cerebral hematoma

BACKGROUND AND PURPOSE

Therapy with gamma-aminobutyric acid (GABA) agonists appears to improve outcome after experimental hematoma but with unacceptable side effects. We looked to synthetic GABA agonists, or positive GABA modulators, widely developed as anticonvulsants and anxiolytics, to find compounds that may be effective. Ganaxolone is a synthetic neuroactive steroid that positively modulates GABA. We sought to determine whether ganaxolone was beneficial using a model of intracerebral hematoma.

METHODS

We stereotaxically injected varying doses of bacterial collagenase into the caudate nucleus of rats to induce blood-brain barrier failure and hematoma formation. Four hours later, we administered intravenously 15 or 30 mg/kg ganaxolone (n=23 each group), 20 mg/kg pregnanolone (n=21), or vehicle (n=30). Forty-eight hours after collagenase injection, we rated each animal using a standard rodent neurological examination. The ratings were compared with the amounts of injected collagenase using the quantal bioassay procedure. Other sets of animals were tested later for visuospatial learning. Brains were then prepared for histomorphometry, and brain volumes were estimated.

RESULTS

We found that ganaxolone 30 mg/kg significantly increased the ED(50) in the bioassay, for a potency ratio of 1.8+/-0.41 compared with vehicle (P<0.05). Ganaxolone 15 mg/kg and pregnanolone did not affect neurological outcome. Ganaxolone 30 mg/kg did not clearly improve visuospatial learning several weeks after hemorrhage. Ganaxolone exhibited a weak effect on cerebral volumes 48 hours after stroke, but 3 months after hemorrhage no such effect could be detected.

CONCLUSIONS

Ganaxolone improves neurological outcome 48 hours after intracerebral hematoma but not visuospatial learning several weeks after intracerebral hematoma. Histological evidence of damage was reduced at 48 hours but not at 3 months.

Biology of ischemic cerebral cell death

With the approval of alteplase (tPA) therapy for stroke, it is likely that combination therapy with tPA to restore blood flow, and agents like glutamate receptor antagonists to halt or reverse the cascade of neuronal damage, will dominate the future of stroke care. The authors describe events and potential targets of therapeutic intervention that contribute to the excitotoxic cascade underlying cerebral ischemic cell death. The focal and global animal models of stroke are the basis for the identification of these events and therapeutic targets. The signalling pathways contributing to ischemic neuronal death are discussed based on their cellular localization. Cell surface signalling events include the activities of both voltage-gated K+, Na+, and Ca2+ channels and ligand-gated glutamate, gamma-aminobutyric acid and adenosine receptors and channels. Intracellular signalling events include alterations in cytosolic and subcellular Ca2+ dynamics, Ca2+ -dependent kinases and immediate early genes whereas intercellular mechanisms include free radical formation and the activation of the immune system. An understanding of the relative importance and temporal sequence of these processes may result in an effective stroke therapy targeting several points in the cascade. The overall goal is to reduce disability and enhance quality of life for stroke survivors.

Functional benefit from clomethiazole treatment after focal cerebral ischemia in a nonhuman primate species

Clomethiazole (CMZ) (Zendra) is neuroprotective in rodents following focal and global ischemia. However, its neuroprotective effects in other species, particularly on functional outcome, have not been reported. We have therefore examined the ability of CMZ to ameliorate the functional deficits produced by a focal cerebral ischemic lesion in the marmoset, a New World primate. Six monkeys received permanent middle cerebral artery occlusion (pMCAO); six further monkeys received pMCAO with administration of CMZ, 5 min after the arterial occlusion, by intraperitoneal bolus injection and by subcutaneous implantation of an osmotic minipump, which released CMZ for 24 h. The monkeys were trained and tested preoperatively on a number of behavioral tasks which were repeated 3 and 9 weeks after surgery. CMZ-treated monkeys were better than non-drug-treated monkeys at using the disabled arm contralateral to the lesion and also showed a reduction in contralateral spatial hemineglect. Postmortem histopathological analysis at several stereotaxic levels showed a significant reduction in the area of ischemic damage in CMZ-treated monkeys compared to that in untreated animals. CMZ treatment reduced the overall volume of damage by 31.8% (MCA group, 370.8 +/- 37.4 mm3 of damage; CMZ group, 253.0 +/- 38.0 mm3 of damage). This study demonstrates that CMZ is neuroprotective in a nonhuman primate species and is able to ameliorate the level of functional disability and reduce the size of infarct produced by focal cerebral ischemia.

The clomethiazole acute stroke study in ischemic, hemorrhagic, and t-PA treated stroke: Design of a phase III trial in the united states and canada

Clomethiazole is a drug with sedative properties effective in laboratory studies of brain ischemia. A large European multicenter trial of clomethiazole in acute stroke patients showed no benefit overall, but subgroup analysis indicated that patients with large infarctions may have benefited from treatment. To confirm this preliminary finding, we have designed CLASS-IHT, the Clomethiazole for Acute Stroke Study in Ischemic, Hemorrhagic and TPA Treated Patients, to be conducted in North America. Patients who suffer large cerebral infarctions and present within 12 hours of symptom onset are eligible. Patients will be randomized to receive clomethiazole 68 mg/kg over 24 hours or vehicle, using a dosing scheme based on the pharmacokinetics measured in the first trial. Outcome assessments include stroke scales, the Barthel Index, and lesion volume. An additional study of health economic outcomes is planned. The primary endpoint for CLASS-I will be the Barthel Index 90 days after stroke. A total of 1,200 patients will be randomized to CLASS-I, and in safety-only trials, 200 patients with cerebral hemorrhage will be randomized into CLASS-H and another 100 to 200 patients will be randomized into CLASS-T. The details of the protocols for all three studies are presented.

Neuroprotection by delayed administration of topiramate in a rat model of middle cerebral artery embolization

Because topiramate (TPM) suppresses voltage-sensitive Na+ channels and non-N-methyl-D-aspartate (NMDA) receptors and enhances gamma-aminobutyric acid (GABA)-mediated inhibition, we tested whether it would protect against cerebral ischemia. The right middle cerebral artery (MCA) was embolized by an intra-arterial injection of autogenous thrombus. Two hours after thrombus injection, animals received intra-peritoneal injections (i.p.) of normal saline as control (n=6) or alternatively, a low- (20 mg/kg, i.p., n=6) or high-dose (40 mg/kg, i.p., n=6) of TPM. Neurological deficit was scored at 2 h and 24 h following the ischemic insult. The animals were sacrificed 24 h after ischemia and the coronal brain sections were stained with 2% 2,3,5-triphenyltetrazolium chloride (TTC) for determination of the percentage of infarct volume. Administration of TPM significantly improved the 24-h neurological deficit scores (low dose, 1.75+/-0.5; high dose, 1.17+/-0.41; p<0.05 for both doses). A reduction in the percentage of infarct volume (low dose, 22.9+/-8.9%, p=0.002; high dose 7.6+/-3.4%, p<0.001) was seen when compared to the controls (infarct size, 54.2+/-9.0%; neurobehavior score, 2. 67+/-0.52). Treatment with TPM at the higher dose induced more neuroprotection than that at the lower dose (p<0.05). Thus, treatment with TPM resulted in a dose- and use-dependent neuroprotective effect, when used 2 h after MCA embolization in a rat model of focal ischemia.

An investigation of the possible interaction of clomethiazole with glutamate and ion channel sites as an explanation of its neuroprotective activity

The activity of the neuroprotective agent clomethiazole at glutamate and ion channel sites has been investigated. Dizocilpine (3.25 mg/kg intraperitoneally) provided almost total protection against the damage produced by infusion of N-methyl-DL-aspartate (NMDLA; 75 micrograms) into the right hippocampus. In contrast, clomethiazole (96 mg/kg intraperitoneally) was without effect. Using ligand binding techniques, no evidence was found for clomethiazole interacting with NMDA, AMPA or sigma binding sites. Clomethiazole did inhibit the stimulatory effect of the metabotropic glutamate receptor agonist 1S3R-aminocyclopentone-1,3-dicarboxylic acid (ACPD) on phosphoinositol hydrolysis, but only at a concentration of 10(-3) M, which is unlikely to have functional relevance. Clomethiazole was also without effect on ligand binding to Ca2+ channels (N- or L- type), Na+ channels or ATP-sensitive K+ channels. Potentiation of GABA function therefore remains the most plausible explanation for the neuroprotective activity of clomethiazole.

Comparative neuroprotective properties of the benzodiazepine receptor full agonist diazepam and the partial agonist PNU-101017 in the gerbil forebrain ischemia model

Recent studies have demonstrated the neuroprotective properties of the novel imidazoquinoline benzodiazepine receptor partial agonist, PNU-101017, in the gerbil forebrain ischemia model. The compound effectively reduces delayed post-ischemic (5 min bilateral carotid occlusion) hippocampal CA1 neuronal degeneration even when its administration is withheld until 4 h after reperfusion and the effect is unrelated to hypothermia. The purpose of the present study was to determine the comparative abilities of PNU-101017 versus the full agonist diazepam to attenuate post-ischemic CA1 damage. Male gerbils were treated either 30 min before ischemia induction or immediately after reperfusion with an initial dose of PNU-101017 (30 mg/kg i.p.) or diazepam (10 mg/kg i.p.) with a second dose being given at 2 h after reperfusion. Possible hypothermic effects of either compound were prevented by external heating. In vehicle (0.05 N HCl)-treated gerbils, the loss of hippocampal CA1 neurons at 5 days was 85%. PNU-101017 pretreatment reduced the loss to 50% (p<0.05 vs. vehicle) whereas pretreatment with diazepam attenuated damage to only 17% (p<0.001 vs. vehicle). Delaying treatment with PNU-101017 until just after reperfusion still resulted in a reduction in CA1 degeneration statistically that was indistinguishable from that seen with pretreatment. In contrast, diazepam post-treatment did not significantly decrease CA1 neuronal loss. These results suggest that a benzodiazepine receptor partial agonist may have greater neuroprotective practicality than a full agonist for the treatment of global cerebral ischemia. The mechanistic basis for this difference may relate to the partially pro-excitatory neuronal response to endogenous GABA before and after neuronal insult.

Zonisamide as a neuroprotective agent in an adult gerbil model of global forebrain ischemia: a histological, in vivo microdialysis and behavioral study

Brief periods of global cerebral ischemia are known to produce characteristic patterns of neuronal injury both in human studies and in experimental animal models. Ischemic damage to vulnerable areas such as the CA1 sector of the hippocampus is thought to result from excitotoxic amino acid neurotransmission. The objective of this study was to determine the ability of a novel sodium channel blocking compound, zonisamide, to reduce neuronal damage by preventing the ischemia-associated accumulation of extracellular glutamate. Using a gerbil model, animals were subjected to 5 min ischemic insults. Both pre- and post-ischemic drug administration (zonisamide 150 mg/kg) were studied. Histological brain sections were prepared using a silver stain at 7 and 28 days post ischemia. The animals sacrificed at 28 days also underwent behavioral testing using a modified Morris water maze. In vivo microdialysis was performed on a separate group of animals in order to determine the patterns of ischemia-induced glutamate accumulation in the CA1 sector of the hippocampus. Pyramidal cell damage scores in the CA1 region of the hippocampus were significantly reduced in animals pre-treated with zonisamide compared to saline-treated controls, both at 7 days (drug pre-treated: 0.812 +/- 0.28, n = 8; controls: 1.625 +/- 0.24, n = 8; *P < 0.05) and 28 (drug pre-treated: 0.833 +/- 0.22, n = 12; controls: 1.955 +/- 0.26, n = 11; **P < 0.01) days post ischemia. However, animals receiving zonisamide post-treatment did not display significant differences from controls. Behavioral studies also showed significant preservation of function in drug-treated animals. Microdialysis studies confirmed a reduction in glutamate release in drug-treated animals compared to saline-treated controls. Our data suggest that zonisamide is effective in reducing neuronal damage by a mechanism involving decreased ischemia-induced extracellular glutamate accumulation and interruption of excitotoxic pathways.

High dose baclofen is neuroprotective but also causes intracerebral hemorrhage: a quantal bioassay study using the intraluminal suture occlusion method

Agonists of the GABA-A receptor are neuroprotective after experimental stroke, but studies of GABA-B agonists have contradicted each other. To further investigate whether GABA-B agonists may be neuroprotective, we devised a quantal bioassay using the intraluminal occlusion method of inducing reversible cerebral ischemia. Subjects underwent middle cerebral artery occlusion for varying amounts of time, ranging from 5 to 90 min. Behavioral outcome was measured 48 h later with a quantal observational scale: score of abnormal given for any one of asymmetric forepaw flexion on tail lift, asymmetric grip, circling, reduced exploration, seizures, or death. To the grouped response data the logistic equation was used to find the ED50, the duration of occlusion that caused one-half of the subjects to be abnormal. To find the potency ratio for each drug, we divided the ED50 for treatment by that for vehicle. We administered baclofen, a GABA-B agonist, intraperitoneally 5 min after the onset ofischemia. Baclofen (20 mg/kg) was neuroprotective (potency ratio of 3.0, P < 0.05), but a lower dose (10 mg/kg) was not. However, both doses of baclofen caused significantly more intracerebral hemorrhages than control. In awake animals, both baclofen doses caused significant increases in mean arterial pressure, but no changes in other cardiorespiratory variables. The glutamate antagonist MK-801, the GABA-A agonist muscimol, and hypothermia were all protective using the bioassay (potency ratios ranging from 1.5 to 3.0). We conclude that although baclofen (20 mg/kg) may be neuroprotective, its utility is complicated by postischemic hypertension and cerebral hemorrhages.

Neuroprotective properties of the benzodiazepine receptor, partial agonist PNU-101017 in the gerbil forebrain ischemia model

PNU-101017 is a novel, imidazoquinoline amide and benzodiazepine receptor partial agonist that has high affinity for the GABAA receptor subtypes containing the alpha 1 and alpha 3 or alpha 5 subunits. At each of these receptors, the compound is a partial agonist with approximately 50% of the intrinsic activity of the full agonist diazepam. In view of the previously demonstrated anti-ischemic effects of some GABA agonists, the purpose of this study was to determine the ability of PNU-101017 to salvage selectively vulnerable neuronal populations in the gerbil forebrain ischemia model. In an initial set of experiments, male gerbils were pretreated 30 minutes before ischemia induction (5 minutes) with PNU-101017 (3, 10, or 30 mg/kg intraperitoneally) and again 2 hours after reperfusion. In vehicle (0.05 N HC1)-treated gerbils, the loss of hippocampal CA1 neurons at 5 days was 80%. PNU-101017 was shown to produce a dose-related increase in CA1 neuronal survival; at either 10 or 30 mg/kg, the loss of CA1 neurons was only 21% (P < 0.005 versus vehicle). A second experiment, examined the therapeutic window for PNU-101017 using the dose level of 30 mg/kg intraperitoneally. Administration of the first of two doses (2 hours apart) at the time of reperfusion resulted in an identical decrease in CA1 damage at 5 days to that seen with preischemic treatment (P < 0.003 versus vehicle). Even with a delay of the initial dosing until 4 hours after reperfusion, PNU-101017 reduced CA1 neuronal loss to only 32% (P < 0.01 versus vehicle). In a third experiment in which the duration of the ischemic insult was increased to 10 minutes and the brains were not analyzed until 28 days after ischemia, daily PNU-101017 dosing for the full 28 days still significantly preserved CA1 neurons, although less effectively than in the milder 5 minute-ischemia model. The loss of dopaminergic nigrostriatal neurons was also reduced. The neuroprotective effect of PNU-101017 was not associated with any overt CNS depression and it did not correlate with hypothermia. This benzodiazepine-receptor partial agonist may have potential for the treatment of global cerebral ischemia.

Neuroprotection with felbamate: a 7- and 28-day study in transient forebrain ischemia in gerbils

The use of glutamate antagonists and GABA agonists may protect neurons from the effects of transient ischemia. Felbamate is a new antiepileptic drug with glutamate antagonist and GABA agonist properties. We tested the efficacy of felbamate in a gerbil model of transient forebrain ischemia. Damage assessment was done with silver staining at 7 and 28 days after 5 min of bilateral carotid occlusion. Cerebral cortex, hippocampus (CA1 and CA4), thalamus and striatum were evaluated on a 4-point scoring system. The animals sacrificed at 28 days were also tested in a water-maze task to assess recovery of function. The initial dose of felbamate (300 mg/kg) was given 30 min before the ischemic insult in one set of animals and 30 min after the insult in another set of animals. There were 8 animals tested per group (total: 48 animals). There was significant neuronal protection with the use of felbamate, both before and after ischemia in all regions of the brain. Protection was seen in animals sacrificed at 7 and 28 days. Protection was moderate when felbamate was used before ischemia. It was highly significant when felbamate was given 30 min after the insult. Behavioral studies however did not show any difference in the felbamate treated animals versus the saline treated controls. The structural protection with felbamate was very significant when used in the post-ischemic period. This window for protection merits further evaluation in relation to the clinical setting of stroke.

Acetyl-L-carnitine attenuates neuronal damage in gerbils with transient forebrain ischemia only when given before the insult

The underlying mechanisms leading to neuronal damage in cerebral ischemia are multifactoral. In this study, we evaluated the neuroprotective effects of acetyl-L-carnitine, a medication that may enhance metabolic recovery after cerebral ischemia. The 5-minute transient forebrain ischemia model in gerbils was used. Acetyl-L-carnitine was given 30 minutes before the insult in one set of animals and 30 minutes after the insult in a second set of animals with histological evaluation at 7 days (Group A) and 28 days (Group B). Damage assessment was done using a 4-point damage score and Mann-Whitney U test was used for statistical analysis. Compared to the controls, there was significant protection in the cerebral cortex, hippocampus and the striatum in animals treated with the medication before the insult in Group A and Group B. Post-ischemic therapy showed little evidence of neuronal protection in either group. Behavioral tests in the Group B animals showed no significant differences between the treated or the saline controls. Our study shows, that pre-ischemic treatment with acetyl-L-carnitine results in neuronal protection. This may have clinical significance in situations (such as bypass surgery) where treatment could be initiated prior to the insult.