MRZ 2/579, a novel uncompetitive N-methyl-D-aspartate antagonist, reduces infarct volume and brain swelling and improves neurological deficit after focal cerebral ischemia in rats

Microglia through MFG-E8 signaling decrease the density of degenerating neurons and protect the brain from the development of cortical infarction after stroke

Neuronal loss is a hallmark of stroke and other neurodegenerative diseases, and as such, neuronal loss caused by microglia has been thought to be a contributing factor to disease progression. Here, we show that microglia indeed contribute significantly to neuronal loss in a mouse model of stroke, but this microglial-dependent process of neuronal clearance specifically targets stressed and degenerating neurons in the ischemic cortical region and not healthy non-ischemic neurons. Nonspecific stimulation of microglia decreased the density of neurons in the ischemic cortical region, whereas specific inhibition of MFG-E8 signaling, which is required for microglial phagocytosis of neurons, had the opposite effect. In both scenarios, the effects were microglia specific, as the same treatments had no effect in mice whose microglia were depleted prior to stroke. Finally, even though the inhibition of MFG-E8 signaling increased neuronal density in the ischemic brain region, it substantially exacerbated the development of cortical infarction. In conclusion, microglia through MFG-E8 signaling contribute to the loss of ischemic neurons and, in doing so, minimize the development of cortical infarction after stroke.

Anesthesia-Induced Hypothermia Attenuates Early-Phase Blood-Brain Barrier Disruption but Not Infarct Volume following Cerebral Ischemia

Blood-brain barrier (BBB) disruption is thought to facilitate the development of cerebral infarction after a stroke. In a typical stroke model (such as the one used in this study), the early phase of BBB disruption reaches a peak 6 h post-ischemia and largely recovers after 8–24 h, whereas the late phase of BBB disruption begins 48–58 h post-ischemia. Because cerebral infarct develops within 24 h after the onset of ischemia, and several therapeutic agents have been shown to reduce the infarct volume when administered at 6 h post-ischemia, we hypothesized that attenuating BBB disruption at its peak (6 h post-ischemia) can also decrease the infarct volume measured at 24 h. We used a mouse stroke model obtained by combining 120 min of distal middle cerebral arterial occlusion (dMCAo) with ipsilateral common carotid arterial occlusion (CCAo). This model produced the most reliable BBB disruption and cerebral infarction compared to other models characterized by a shorter duration of ischemia or obtained with dMCAO or CCAo alone. The BBB permeability was measured by quantifying Evans blue dye (EBD) extravasation, as this tracer has been shown to be more sensitive for the detection of early-phase BBB disruption compared to other intravascular tracers that are more appropriate for detecting late-phase BBB disruption. We showed that a 1 h-long treatment with isoflurane-anesthesia induced marked hypothermia and attenuated the peak of BBB disruption when administered 6 h after the onset of dMCAo/CCAo-induced ischemia. We also demonstrated that the inhibitory effect of isoflurane was hypothermia-dependent because the same treatment had no effect on ischemic BBB disruption when the mouse body temperature was maintained at 37°C. Importantly, inhibiting the peak of BBB disruption by hypothermia had no effect on the volume of brain infarct 24 h post-ischemia. In conclusion, inhibiting the peak of BBB disruption is not an effective neuroprotective strategy, especially in comparison to the inhibitors of the neuronal death signaling cascade; these, in fact, can attenuate the infarct volume measured at 24 h post-ischemia when administered at 6 h in our same stroke model.

Neramexane: a moderate-affinity NMDA receptor channel blocker: new prospects and indications

N-methyl-D-aspartate (NMDA) receptor antagonists have a potentially wide range of therapeutic applications. Unfortunately, potent NMDA receptor channel blockers produce phencyclidine-like psychotropic symptoms in humans and rodents, and thereby produce numerous side effects. However, recent data indicate that moderate-affinity, voltage-dependent, open-channel blockers, such as memantine and neramexane (MRZ 2/579) are useful therapeutics as they prevent the pathological activation of NMDA receptors but allow their physiological activity and should prove to be useful therapeutics in a wide range of CNS disorders. Indeed, memantine was recently registered in both Europe and the USA for the treatment of moderate-to-severe Alzheimer's disease (AD). Neramexane is under development as a potential neuroprotectant against various CNS disorders. Although the predicted therapeutic doses of neramexane were very well tolerated in male volunteers, unfortunately, recent Phase II/III clinical trials for moderate-to-severe AD delivered contradictory results. Neramexane also failed in a recent randomized controlled Phase II trial against drug abuse and depression. Although Phase Ib clinical trials for the indications of chronic pain showed positive results, Phase II results indicate no superiority to existing treatments. However, positive study results have been presented recently in a Phase IIb study on the treatment of tinnitus. A Phase III study for this indication is presently ongoing. Another promising application for neramexane as a neuroprotectant might be chronic neurodegeneration, such as Parkinson's disease, Huntington's disease, vascular dementia, frontal lobe dementia, Down's syndrome and AD.

ENDOTHELIN-1-INDUCED CEREBRAL ISCHEMIA: EFFECTS OF KETANSERIN AND MK-801 ON LIMB PLACING IN RATS

The long-term effects of the 5-HT(2A) receptor antagonist ketanserin on deficits in sensorimotor integration (limb placing tests) following transient focal cerebral ischemia in rats were compared to the effects of the NMDA antagonist MK-801. Middle cerebral artery occlusion was induced in conscious rats by microinjection of endothelin-1 in the vicinity of the artery (EMCAO model). The EMCAO/vehicle rats exhibited impaired tactile and proprioceptive limb placing. In contrast to ketanserin, MK-801 exerted severe early behavioral disturbances, but both drugs significantly improved the neurological scores much earlier than the spontaneous recovery of function occurred. The present results suggest that pharmacotherapy by means of ketanserin lacking the severe side effects of the NMDA antagonists can be used to enhance functional recovery after stroke.

Inhibition of the alpha9alpha10 nicotinic cholinergic receptor by neramexane, an open channel blocker of N-methyl-D-aspartate receptors

In this study we report the effects of neramexane, a novel amino-alkyl-cyclohexane derivative that is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, on recombinant rat alpha9alpha10 nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes. We compared its effects with those of memantine, a well-studied pore blocker of NMDA receptors, currently used in therapeutics for the treatment of Alzheimer's disease. Our results indicate that both compounds block acetylcholine-evoked responses at micromolar concentrations with a rank order of potency of neramexane>memantine, P<0.05. Block by neramexane of acetylcholine responses was not overcome at high concentrations of the agonist, indicative of a non-competitive inhibition. The lack of interaction of neramexane with the ligand binding domain was confirmed by radioligand binding experiments in transfected tsA201 cells. Moreover, block did not involve an increase in desensitization kinetics, it was independent of the resting potential of the membrane at low concentrations of neramexane and slightly voltage-dependent at concentrations higher than 1 microM. Finally, clinically-relevant concentrations of neramexane blocked native alpha9alpha10-containing nicotinic acetylcholine receptors of rat inner hair cells, thus demonstrating a possible in vivo relevance in potentially unexplored therapeutic areas.

Delayed treatment with magnesium: reduction of brain infarction and improvement of electrophysiological recovery following transient focal cerebral ischemia in rats

Object. The authors examined whether delayed treatment with Mg++ would reduce brain infarction and improve electrophysiological and neurobehavioral recovery following cerebral ischemia—reperfusion.

Methods. Male Sprague—Dawley rats were subjected to right middle cerebral artery occlusion for 90 minutes followed by 72 hours of reperfusion. Magnesium sulfate (750 µmol/kg) or vehicle was given via intracarotid infusion at the beginning of reperfusion. Neurobehavioral outcome and somatosensory evoked potentials (SSEPs) were examined before and 72 hours after ischemia—reperfusion. Brain infarction was assessed after the rats had died.

Before ischemia—reperfusion, stable SSEP waveforms were recorded after individual fore- and hindpaw stimulations. At 72 hours of perfusion the SSEPs recorded from ischemic fore- and hindpaw cortical fields were depressed in vehicle-injected animals and the amplitudes decreased to 19 and 27% of baseline, respectively (p < 0.001). Relative to controls, the amplitudes of SSEPs recorded from both ischemic fore- and hindpaw cortical field in the Mg++-treated animals were significantly improved by 23% (p < 0.005) and 39% (p < 0.001) of baselines, respectively. In addition, Mg++ improved sensory and motor neurobehavioral outcomes by 34% (p < 0.01) and 24% (p < 0.05), respectively, and reduced cortical (p < 0.05) and striatal (p < 0.05) infarct sizes by 42 and 36%, respectively.

Conclusions. Administration of Mg++ at the commencement of reperfusion enhances electrophysiological and neurobehavioral recovery and reduces brain infarction after cerebral ischemia—reperfusion. Because Mg++ has already been used clinically, it may be worthwhile to investigate it further to see if it holds potential benefits for patients with ischemic stroke and for those who will undergo carotid endarterectomy.

Lazaroid U-74389G attenuates edema in rat brain subjected to post-ischemic reperfusion injury

The aim of the present study was to determine the potential therapeutic value of 21-aminosteroid U-74389G, on blood-brain barrier (BBB) breakdown and edema in association with the changes in synaptosomal Na(+)/K(+) and Mg(2+)/Ca(2+)-ATPase activities in rat brain subjected to post-ischemic reperfusion injury. Brain ischemia was achieved by means of four-vessel occlusion model for 25 min and animals were sacrificed after 12 h reperfusion. An increase of cerebral tissue water content, blood-brain disruption and the changes of synaptosomal Na(+)/K(+) and Mg(2+)/Ca(2+)-ATPases activities were evaluated. U-74389G was given intraperitoneally at two times as 5 mg/kg at 10 min prior to ischemia and at the beginning of reperfusion. Edema was determined by means of wet-dried weight method, and BBB of extravasation of Evan's blue dye. Extravasation of Evan's blue dye into brain following ischemia and reperfusion was 2.4-fold of control value and brought close to control levels by the effect of U-74389G (p<0.001). Post-ischemic reperfusion injury caused an increase of 3.7% in tissue water content of whole brain and administration of U-74389G lowered the cerebral edema (p<0.001). The loses in the Na(+)/K(+)-ATPase and Mg(2+)/Ca(2+)-ATPase activities occurred as 42.1% (p<0.01) and 65.7% (p<0.001) of control value, respectively. While Mg(2+)/Ca(2+)-ATPase activity was enhanced compared to vehicle-treated group of animals (p<0.01), Na(+)/K(+)-ATPase activity was fully recovered when compared to control by U-74389G (p>0.05). U-74389G also significantly attenuated neuronal necrosis (p<0.001) which was determined in the hippocampal CA1 subfield. Blood-brain barrier protection, attenuation of brain edema and neuronal necrosis concomitant with the stabilizing of membrane-bound enzymes brought about by the effect of U-74389G suggest that 21-aminosteroids are worthy of consideration in the acute treatment of cerebral ischemia.

Effects of pyruvate administration on infarct volume and neurological deficits following permanent focal cerebral ischemia in rats

Recent experimental evidences indicate that pyruvate, the final metabolite of glycolysis, has a remarkable protective effect against different types of brain injury. The purpose of this study was to assess the neuroprotective effect and the neurological outcome after pyruvate administration in a model of ischemic stroke induced by permanent middle cerebral artery occlusion (pMCAO) in rats. Three doses of pyruvate (250, 500 and 1000 mg/kg, i.p.) or vehicle were administered intraperitoneally 30 min after pMCAO. In other set of experiments, pyruvate was given either before, immediately after ischemia or in a long-term administration paradigm. Functional outcome, mortality and infarct volume were determined 24 h after stroke. Even when the lowest doses of pyruvate reduced mortality and neurological deficits, no concomitant reduction in infarct volume was observed. The highest dose of pyruvate increased cortical infarction by 27% when administered 30 min after pMCAO. In addition, when pyruvate was given before pMCAO, a significant increase in neurological deficits was noticed. Surprisingly, on the contrary of what was found in the case of transient global ischemia, present findings do not support a great neuroprotective role for pyruvate in permanent focal cerebral ischemia, suggesting two distinct mechanisms involved in the effects of this glycolytic metabolite in the ischemic brain.

Evaluation of the phencyclidine-like discriminative stimulus effects of novel NMDA channel blockers in rats

RATIONALE

Because of their potential therapeutic effects, N-methyl-D-aspartate (NMDA) receptor antagonists have been investigated for clinical use. Unfortunately, many channel-blocking antagonists have been associated with the production of side effects, including motor impairment and phencyclidine (PCP)-like subjective effects.

OBJECTIVE

This study investigated the relationship between NMDA receptor channel blockade and production of PCP-like side effects by evaluating a variety of NMDA channel blockers with different binding characteristics for the production of PCP-like discriminative stimulus effects.

METHODS

The NMDA channel blockers were tested in rats trained to discriminate 2 mg/kg PCP, i.p., from saline using a standard two-lever drug discrimination procedure with responding under a fixed ratio (FR) 32 schedule of food reinforcement.

RESULTS

The high-affinity channel blockers PD 138289, PD 137889 and FR 115427, produced full, dose-dependent substitution for PCP. Of the moderate-affinity channel blockers, MRZ 2/579 fully substituted for PCP while 1-(4-methoxyphenyl)-1,2,3,4-tetrahydroisoquinoline, 8-(2-methoxyphenyl)-1,2,3,4-tetrahydroisoquinoline and alaproclate produced partial substitution. Drugs with the lowest affinity for the channel site and/or higher affinity for non-NMDA CNS sites, antazoline, idazoxan, 1-phenyl-1,2,3,4-tetrahydroisoquinoline, alpha-benzyl- N-methylphenethylamine and orphenadrine, failed to substitute for PCP.

CONCLUSIONS

The results demonstrate that the cellular actions of the individual channel-blocking NMDA antagonists, in particular affinity for the channel site and NMDA receptor specificity, are important determinants of their discriminative stimulus effects. While higher affinity channel blockers show a correlation between affinity and PCP-like discriminative stimulus effects, behavioral disruption through action at non-NMDA receptors probably prevents achieving sufficient concentrations of the lower affinity compounds at NMDA receptors to produce PCP-like discriminative stimulus effects.

Evaluation of MCAO stroke models in normotensive rats: standardized neocortical infarction by the 3VO technique

The temporary three-vessel occlusion (3VO) technique with a surgical approach for middle cerebral artery (MCA) produces consistent cerebral infarction in the neocortex in normotensive rats. The intraluminal thread-occlusion technique with an endovascular approach targeting the MCA occlusion (MCAO) is more widely used since it does not require complicated intracranial procedures. The aim of this study was to review the methods/models for MCAO stroke in normotensive rats and to evaluate a 3VO stroke model that provides consistent degrees and variance of cortical stroke injury for additional discussion. First, we analyzed a model with modified temporary 3VO technique requiring less complicated procedures than the temporary 3VO model, i.e., temporary occlusion of the bilateral common carotid arteries (CCAs) superimposed on a permanent occlusion of the MCA, in Sprague-Dawley rats or C57BL/6J mice. In the microvascular tissue (cerebral) perfusion study, significant reductions in regional cerebral perfusion during the 3VO accompanied a rapid return to baseline after release of the CCAs, showing that the technique induces temporary focal ischemia. The average sizes and variances of the neocortical infarction in this model, together with those in the other normotensive rat models caused by the 3VO technique in the literature, indicated a standard size and variance of infarcted lesion in the control groups relative to the specific ischemic period. However, stroke injuries in the neocortex induced by the thread occlusion technique showed greater variability with less consistent lesion sizes. Inclusion/exclusion criteria to avoid inappropriate cases with too mild (no/faint infarction) or too great (huge/fatal infarction) severity in the ischemic injury may differ between laboratories in the thread occlusion model.

Systemic fatty acid responses to transient focal cerebral ischemia: influence of neuroprotectant therapy with human albumin

Human albumin therapy is highly neuroprotective in focal cerebral ischemia. Because albumin is the main carrier of free fatty acids (FFA) in plasma, we investigated the content and composition of plasma FFA in jugular vein (JV), femoral artery (FA) and femoral vein (FV) of rats given intravenous human albumin (1.25 g/kg) or saline vehicle (5 mL/kg) 1 h after a 2 h middle cerebral artery occlusion (MCAo) or sham surgery. Arachidonic acid was the only FFA significantly increased by MCAo in all plasma samples prior to albumin administration, remaining at the same level regardless of subsequent treatments. Albumin treatment induced in both MCAo- and sham-groups a 1.7-fold increase in total plasma FFA (mainly 16:0, 18:1, 18:2n-6) during 90-min reperfusion. MCAo selectively stimulated the albumin-mediated mobilization of n-3 polyunsaturated fatty acids (PUFA), with an early increase in 22:5n-3 and 22:6n-3 in the FA prior to detectable changes in the JV. In the MCAo-albumin group, the lower level of FFA in JV as compared with FA and FV suggests an albumin-mediated systemic mobilization and supply of FFA to the brain, which may favor the replenishment of PUFA lost from cellular membranes during ischemia and/or to serve as an alternative source of energy, thus contributing to albumin neuroprotection.

Neuroprotective effects of NS-7, voltage-gated Na+/Ca2+ channel blocker in a rodent model of transient focal ischaemia

The aim of the present study was to characterize neuroprotective activity of NS- 7, a mixed voltage-gated sodium and calcium channel blocker in a model of transient focal ischaemia in rats. Ischaemia was induced by a 75 min reversible occlusion of middle cerebral artery (MCAo) using a nylon filament. NS-7 (0.5 mg/kg i.v.) or 0.9% NaCl (1 ml/kg i.v.) were infused over 3 min. starting 30 min after the MCAo. Infarct analysis was performed 72 h after ischaemia. Application of NS- 7 produced significant protection seen in neurological tests and diminished brain damage by 37% in total infarct (17.7+/- 3.0% vs. 27.9 +/- 3.2% control; [p < 0.01]; t-test), 47.8% in cortical infarct size by (8.5 +/- 2.4% vs. 16.2 +/- 2.4% control; [p < 0.01]), and by 21.5% in striatal infarction (9.2 +/- 0.8% vs. 11.7 +/- 0.9% control; [p < 0.05]). The results indicate that NS- 7 has potential for neuroprotection against transient ischaemic insult.

Malignant infarction in cats after prolonged middle cerebral artery occlusion: glutamate elevation related to decrease of cerebral perfusion pressure

BACKGROUND AND PURPOSE

To study the putative role and predictive significance of glutamate elevation in space-occupying ischemic stroke, we investigated the correlation between perfusional disturbances and glutamate alterations in a transient ischemia model in cats that is susceptible to secondary deterioration after reperfusion.

METHODS

In 10 halothane-anesthetized cats, the left middle cerebral artery was occluded for 3 hours, followed by 6 hours of reperfusion. Laser-Doppler flowmetry (LDF) probes, microdialysis/high-performance liquid chromatography, and pressure sensors measured simultaneously regional cerebral blood flow (CBF), extracellular amino acids, mean arterial blood pressure, and intracranial pressure, respectively. Cerebral perfusion pressure (CPP) was calculated. In complementary experiments (n=2), regional CBF was assessed by sequential positron emission tomography.

RESULTS

Middle cerebral artery occlusion reduced LDF-measured CBF in all animals to <25% of control. In 5 of 10 cats, glutamate rose approximately 30-fold during ischemia. LDF-measured CBF and glutamate primarily recovered after reperfusion. Glutamate rose again in the late reperfusion phase, when CPP decreased to <60 mm Hg, and symptoms of transtentorial herniation were recognized. Positron emission tomography revealed ischemic thresholds of 15 to 20 mL/100 g per minute for secondary deterioration. In the other 5 cats, ischemic elevation of glutamate was significantly smaller, and signs of secondary deterioration were not recognized.

CONCLUSIONS

Glutamate determinations during ischemia predict fatal outcome, as do intracranial pressure and CPP measurements during early reperfusion. Secondary amino acid elevation during reperfusion is presumably caused by a drastic decrease of CPP to <50 mm Hg in the final stage of space-occupying, malignant focal ischemia. At this stage, a further progression of injury due to increased glutamate may be irrelevant with respect to fatal outcome.