Effect of flunarizine on global brain ischemia in the dog: a quantitative morphologic assessment

Flunarizine improves the survival of grafted dopaminergic neurons

Embryonic nigral grafts can survive, reinnervate the striatum and reverse functional deficits in both experimental and clinical Parkinsonism. A major drawback is that only around 10% of the implanted dopaminergic neurons survive. The underlying mechanisms leading to this 90% cell death are not fully understood, but oxidative stress and a substantial loss of neurotrophic support are likely to be involved. Hypoxia and mechanical trauma, which are unavoidable during tissue preparation, may be a trigger for cell death. Recent studies have provided evidence that the type of cell death occurring is, to a large extent, apoptotic. Flunarizine is an antagonist of L-, T- and N-type calcium channels, which permits calcium entry into cells via a voltage-dependent mechanism. Flunarizine has been shown to protect neurons against death induced by serum deprivation, nerve growth factor deprivation, oxidative stress, axotomy and ischemia. This study was designed to investigate whether flunarizine can protect grafted embryonic dopaminergic neurons from death when implanted in a rat model of Parkinson's disease. Addition of 1 microM flunarizine inhibited cell death in a suspension of cells derived from the rat's ventral mesencephalon and when such a treated suspension was injected into the neostriatum there was a 2.6-fold greater number of surviving dopaminergic neurons, a doubling of the graft volume and a doubling of the volume of the host neostriatum innervated by dopaminergic fibers from the graft, compared with suspensions not exposed to flunarizine. Furthermore, rats injected with cells that had been exposed to flunarizine displayed a greater recovery of function in the amphetamine-induced rotation test.

Low dose flunarizine protects the fetal brain from ischemic injury in sheep

Flunarizine, a calcium channel blocker, reduced cerebral damage caused by hypoxic-ischemic insults in neonatal rats and in fetal sheep near term. However, the high dose regimen used in these studies produced cardiovascular side effects that might have counteracted the neuroprotective properties of flunarizine. Therefore, the neuroprotective effect was tested in a low dose protocol (1 mg/kg estimated body weight). Twelve fetal sheep near term were instrumented chronically. Six fetuses were pretreated with 1 mg of flunarizine per kg of estimated body weight 1 h before ischemia, whereas the remainder (n=6) received solvent. Cerebral ischemia was induced by occluding both carotid arteries for 30 min. To exclude the possibility that the neuroprotective effects of flunarizine were caused by cerebrovascular alterations we measured cerebral blood flow by injecting radiolabeled microspheres before (-1 h), during (3 min and 27 min) and after (40 min, 3 h, and 72 h) cerebral ischemia. At the end of the experiment (72 h) the ewe was given a lethal dose of sodium pentobarbitone and saturated potassium chloride i.v., and the fetal brain was perfused with formalin. Neuronal cell damage was assessed in various brain structures by light microscopy after cresyl violet/fuchsin staining using a scoring system: 1, 0-5% damage; 2, 5-50% damage; 3, 50-95% damage; 4, 95-99% damage; and 5, 100% damage. In 10 other fetal sheep effects of low dose flunarizine on circulatory centralization caused by acute asphyxia could be excluded. In the treated group neuronal cell damage was reduced significantly in many cerebral areas to varying degrees (range for control group, 1.03-2.14 versus range for treated group, 1.00-1.13; p < 0.05 to p < 0.001, respectively). There were only minor differences in blood flow to the various brain structures between groups. We conclude that pretreatment with low dose flunarizine protects the brain of fetal sheep near term from ischemic injury. This neuroprotective effect is not mediated by changes in cerebral blood flow. We further conclude that low dose flunarizine may be clinically useful as a treatment providing fetal neuroprotection, particularly because the fetal cardiovascular side effects are minimal.

Regional prevalence and distribution of ischemic neurons in dog brains 96 hours after cardiac arrest of 0 to 20 minutes

BACKGROUND AND PURPOSE

In this established outcome model of cardiac arrest in dogs, we have used total (summed regional) brain histopathologic damage scores. The present study describes the regional progression of necrotic (ischemic) neuron prevalence with increasing duration of cardiac arrest. It tests the hypothesis that increases in the total prevalence of necrotic neurons better correspond to increasing arrest duration and better correlate with neurological deficit than do any individual regional scores.

METHODS

Blinded evaluation with light microscopy was used to score the prevalence (five categories) and note the distribution of necrotic neurons in dog brains 96 hours after normothermic ventricular fibrillation cardiac arrest followed by standard reperfusion and control of extracerebral variables. Six coronal brain sections including 19 regions were examined from dogs subjected to 0 (n = 2), 5 (n = 5), 10 (n = 6), 12.5 (n = 12), 15 (n = 8), 17 (n = 5), or 20 (n = 1) minutes of cardiac arrest. Dogs were neurologically evaluated before death.

RESULTS

Necrotic neurons were widespread and scattered among normal neurons. Individual regions varied in their sensitivity to different durations of cardiac arrest. There were consistent increases in the mean prevalence of necrotic neurons with increased arrest duration in the hippocampal dentate gyrus and for cerebellar granule neurons. Regionally, the caudate nucleus had the best correlation with clinical neurological deficit (rho = +.85, P < .01).

CONCLUSIONS

Compared with total (summed regional) necrotic neuron prevalence scores, increased regional prevalence scores for cerebellar granule neurons with increasing arrest duration were equally significant, and scores for the caudate nucleus had nearly the same correlation with individual clinical neurological deficit.

U-92032, a T-type Ca2+ channel blocker and antioxidant, reduces neuronal ischemic injuries

Several diphenylmethylpiperazine derivatives are potential therapeutic agents for prevention of ischemic injuries in the heart and brain, because of their ability to block Ca2+ currents and their antioxidant activity. In this study, the current lead compound, U-92032 ((7-((bis-4-fluorophenyl)methyl)-1-piperazinyl)-2-(2-hydroxyethylamin o)- 4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one), has been compared with flunarizine and nifedipine (well-known T- and L-type Ca2+ channel antagonists, respectively) for their effects on Ca2+ channels in a mouse neuronal cell line, N1E-115 cells, and their ability to preserve the phenomenon of long-term potentiation and to improve neurological symptoms in gerbil ischemic models. U-92032, like flunarizine, blocked transient Ba2+ currents (IBa) through T-type Ca2+ channels with no effect on nifedipine-sensitive non-inactivating currents. Transient IBa was reduced by U-92032 at a constant rate, the magnitude of which depended on the drug concentration, probably because of a time-dependent accumulation of the lipophilic drug in the membrane phase. For instance, the drug at 6 microM reduced IBa by 21% per min and abolished it in less than 5 min, about 3 times faster than flunarizine at the same concentration. Otherwise, U-92032 behaved like flunarizine, showing a use-dependent block without noticeable effects on the current-voltage relationship for transient IBa. Oral administration of U-92032 (1 and 25 mg/kg) or flunarizine (25 mg/kg), but not nifedipine (50 mg/kg), to gerbils 1 h prior to bilateral carotid artery occlusion, preserved long-term potentiation in hippocampal CA1 neurons, which were largely abolished by ischemia without the drug treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral resuscitation after cardiac arrest: research initiatives and future directions

At present, fewer than 10% of cardiopulmonary resuscitation (CPR) attempts prehospital or in hospitals outside special care units result in survival without brain damage. Minimizing response times and optimizing CPR performance would improve results. A breakthrough, however, can be expected to occur only when cerebral resuscitation research has achieved consistent conscious survival after normothermic cardiac arrest (no flow) times of not only five minutes but up to ten minutes. Most cerebral neurons and cardiac myocytes tolerate normothermic ischemic anoxia of up to 20 minutes. Particularly vulnerable neurons die, in part, because of the complex secondary post-reflow derangements in vital organs (the postresuscitation syndrome) which can be mitigated. Brain-orientation of CPR led to the cardiopulmonary-cerebral resuscitation (CPCR) system of basic, advanced, and prolonged life support. In large animal models with cardiac arrest of 10 to 15 minutes, external CPR, life support of at least three days, and outcome evaluation, the numbers of conscious survivors (although not with normal brain histology) have been increased with more effective reperfusion by open-chest CPR or emergency cardiopulmonary bypass, an early hypertensive bout, early post-arrest calcium entry blocker therapy, or mild cerebral hypothermia (34 C) immediately following cardiac arrest. More than ten drug treatments evaluated have not reproducibly mitigated brain damage in such animal models. Controlled clinical trials of novel CPCR treatments reveal feasibility and side effects but, in the absence of a breakthrough effect, may not discriminate between a treatment's ability to mitigate brain damage in selected cases and the absence of any treatment effect. More intensified, coordinated, multicenter cerebral resuscitation research is justified.

Post cardiac arrest hyperoxic resuscitation enhances neuronal vulnerability of the respiratory rhythm generator and some brainstem and spinal cord neuronal pools in the dog

Selective neuronal vulnerability of the motor cortex, basal ganglia, brainstem, medulla, cerebellum, C6 and L6 segments of the spinal cord were studied after 15 min of cardiac arrest followed by 1 h of normoxic or hyperoxic resuscitation using the suppressive Nauta method in dogs. Hyperoxic resuscitation causes characteristic somatodendritic argyrophilia of the interneuronal pool in the spinal cord and lower medulla. Cuneate, lateral reticular, supraspinal, and caudal trigeminal nuclei as well as the dorsal and ventral respiratory neuronal groups were heavily involved. Similarly, the Purkinje cells, neurons in the middle and deep portions of the mesencephalic tectum, perirubral, pretectal, posterior commissure, middle-sized striatal and giant pyramidal (Betz's) neurons in the motor cortex became argyrophilic. Hyperoxic resuscitation versus normoxic resuscitation causes statistically significant somatodendritic argyrophilia of the dorsal respiratory group, cuneate, dorsal lateral geniculate and thalamic reticular nuclei.

Silver impregnability of ischemia-sensitive neocortical neurons after 15 minutes of cardiac arrest in the dog

The development of postischemic neuronal argyrophilia and the subsequent fate of argyrophilic neurons were studied in dogs after 15 min of complete cerebral ischemia and survival varying from 1 h to 7 days. Histopathological examination of the vulnerable neocortical region was performed using the Nauta degeneration method, and the time course of cellular changes was described. Clear-cut neuronal argyrophilia was found to precede cell body shrinkage and gradual disintegration corresponding to selective neuronal death. To clarify this initial stage of neuronal impregnability, the samples from the animals surviving 8 h postarrest were stained with toluidine blue or processed for electron microscopy, and the distribution of argyrophilic cells was confirmed to be identical with that of hyperchromatic or electron-dense cells. On the other hand, infrequently observed "tissue infarctions" exhibited no silver affinity in spite of apparent cellular damage. These findings indicate that enhanced impregnability is related to cytochemical processes incidental to the phenomenon of "selective neuronal death", which can be readily detected by the Nauta method.

Brain mitochondrial DNA is not damaged by prolonged cardiac arrest or reperfusion

Postischemic reperfusion is known to cause iron-mediated peroxidation of polyunsaturated fatty acids in membranes, including mitochondrial membranes, in the brain cortex. Consequently, we tested the hypothesis that this radical-mediated damage would extend to DNA. Mitochondrial DNA (mtDNA) was chosen because of its presence at a known site of free radical formation, its sensitivity and ease of assay, and its known lack of any repair systems. In model experiments we utilized endonuclease III or piperidine to amplify topological form conversions in mtDNA damaged by in vitro reactions with hydroxyl radical. We then applied the amplified detection assays to dog brain mtDNA isolated after 2 or 8 h of reperfusion following a 20-min cardiac arrest. We found that ischemia and reperfusion caused no topological form conversions in mtDNA. Similarly, nucleotide incorporation by a gap-filling reaction showed no sensitivity to digestion of the mtDNA by exonuclease III, an enzyme known to remove blocked 3' termini at the site of radical-generated nicks. Furthermore, the recovery of mtDNA was similar in all experimental groups, suggesting that putatively damaged forms had not been removed by rapid degradation. Thus, despite mitochondrial membrane damage, brain mtDNA does not accumulate oxygen radical damage during postischemic brain reperfusion.

Prolonged postischemic hyperventilation reduces acute neuronal damage after 15 min of cardiac arrest in the dog

Hyperventilation is commonly used as a constituent of antiedematous therapy after global cerebral ischemia. The effect of hyperventilation on brain functions, however, is complex, and a number of mechanisms involved remains unclear. In this study, we attempted to determine whether postischemic hyperventilation influences acute neuronal changes developing during recirculation. Two groups of dogs underwent 15 min of cardiac arrest and cardiopulmonary resuscitation with an 8 h survival. After resuscitation, in group A the internal environment was maintained in the physiological ranges. In group B the animals were artificially hyperventilated maintaining a high level of respiratory alkalosis during recirculation. Histopathological examination of the vulnerable structures was performed using the Nauta degenerating method and the argyrophilic neurons were counted. Statistically significant amelioration in group B suggests that postischemic hyperventilation may act as a neuroprotective factor.

Thymine glycols and pyrimidine dimers in brain DNA during post-ischemic reperfusion

Free-radical reactions, known to occur in the reperfused brain, damage DNA in vitro. We therefore examined the hypothesis that thymine glycols and thymine dimers, which are known to block transcription and are formed by free radical mechanisms, are formed in brain DNA during reoxygenation following ischemia. Such biochemical lesions could account for the failure of protein synthesis that occurs following an ischemic insult. Large dogs were anesthetized, instrumented, and divided into four groups: (1) non-ischemic controls; (2) 20-min cardiac arrest without resuscitation; (3) 20-min cardiac arrest, resuscitation and 2 h reperfusion; and (4) 20-min cardiac arrest, resuscitation and 8 h reperfusion. Genomic DNA was isolated from the cerebral cortex. Thymine glycols were labeled by reduction with [3H]NaBH4. Pyrimidine dimers were determined by ELISA using antibody prepared against ultraviolet irradiated DNA. The data was evaluated by Kruskal-Wallis ANOVA with alpha = 0.05. The rabbit antibodies detected the thymine dimer content in 10 pg UV irradiated DNA but did not react with normal DNA. Borohydride labeling qualitatively detected thymine glycols generated by treatment of DNA with osmium tetroxide. There was no difference between the DNAs from the experimental groups in the content of thymine glycols or pyrimidine dimers (P = 0.608 and P = 0.219, respectively). We conclude that significant quantities of thymine glycols and thymine dimers are not formed in brain DNA during post-ischemic reperfusion. Therefore, the inhibition of brain protein synthesis during reperfusion, observed by other investigators, is unlikely to be caused by interruption of transcription by these species.

Brain nuclear DNA survives cardiac arrest and reperfusion

Iron-mediated peroxidation of brain lipids is known to occur during reperfusion following cardiac arrest. Since in vitro damage to DNA is caused by similar iron-dependent peroxidation, we tested whether free radical damage to genomic DNA also develops during reperfusion following cardiac arrest and resuscitation. Genomic DNA was isolated from the cerebral cortex in (i) normal dogs, (ii) dogs subjected to a 20-min cardiac arrest, and (iii) dogs resuscitated from a 20-min cardiac arrest and then allowed to reperfuse for 2 or 8 h. DNA strand nicks were evaluated by in vitro labeling of newly created 3' and 5' termini. DNA base damage was evaluated utilizing reaction with piperidine prior to labeling of 5' termini. The 3' DNA termini were labeled before and after digestion with exonuclease III, and the 5' DNA termini were labeled before and after treatment with piperidine. In vitro experiments with genomic DNA damaged by oxygen radicals verified that these labeling methods identified radical damage. In the experimental animal groups, terminal incorporation and electrophoretic mobility of brain nuclear DNA are not significantly changed either by 20 min of complete brain ischemia or during the first 8 h of reperfusion. We conclude that genomic DNA is not extensively damaged during cardiac arrest and early reperfusion, and therefore such DNA damage does not appear to be an important early aspect of the neurologic injury that accompanies cardiac arrest and resuscitation.

Ca++ and Na+ channels involved in neuronal cell death. Protection by flunarizine

Flunarizine, a class IV Ca++ antagonist non-selective for slow Ca++ channels, has been shown to be beneficial in the prophylactic treatment of migraine, the treatment of vertigo, and as add-on treatment in therapy-resistant forms of epilepsy. Flunarizine protects the brain against functional and/or structural neuronal damage in various animal models of cerebral ischemia. In addition to its cerebrovascular effect, flunarizine has also direct neuroprotective actions. New data have emerged on flunarizine with regard to Ca++ and Na+ channels in neuronal cells. There are several possible mechanisms involved in the mode of action of flunarizine. Flunarizine may block Ca++ and Na+ channels, both of which may flux Ca++ as well as Na+. A decrease in Ca++ influx may prevent further release of glutamate, and activation of NMDA receptor gated Ca++ channels at physiological pH. A decrease in Na+ influx may prevent cytotoxicity secondary to a large gain in intracellular Ca++, by reverse operation of the Na+/Ca++ exchanger. This mechanism may be important when the glycolytic rate is increased with concomitant acidosis, and phospholipids are broken down as occurs typically during ischemia. Given the complexity of biochemical events leading to cell death, blocking exclusively one channel subtype is not likely to yield sufficient protection. Hence, it may be useful to develop anti-ischemic compounds which act on a series of pathways involved in Ca++ overload, rather than selectively block one such channel.

Cerebroprotective effects of flunarizine in an experimental rat model of cardiac arrest

A rat cardiopulmonary arrest model was used to study the effects of flunarizine on survival and on the development of postischemic brain damage. Ischemia was induced by a combination of hypovolemia and intracardiac injection of a cold potassiumchloride solution. To validate the model; survival rate and histological damage were assessed after ischemic periods ranging from 5 to 20 minutes. A 6-minute cardiac arrest period was withheld for further therapeutic investigations. In one group (n = 12), flunarizine was administered successively in doses of 0.5 mg/kg intravenous at 5 minutes, 10 mg/kg intraperitoneal at 1 hour, and 20 mg/kg orally at 16 and 24 hours after recirculation. The second group (n = 13) received only the vehicle. Flunarizine, although not affecting mortality; significantly reduced the mean number of ischemic neurons in CA1 hippocampus from 83% in the control to 44% in the drug-treated series (P = 0.014). The results are indicative of the usefulness of this cardiac arrest model to study morphologic aspects of cerebral injury. The results obtained with flunarizine show the effectiveness of this drug even when it is administered after a severe ischemic insult such as global complete ischemia.

Photochemical stroke model: flunarizine prevents sensorimotor deficits after neocortical infarcts in rats

We produced unilateral photochemical infarcts in the hindlimb sensorimotor neocortex of 186 rats by intravenous injection of the fluorescein derivative rose bengal and focal illumination of the intact skull surface. Infarcted rats showed specific, long-lasting deficits in tactile and proprioceptive placing reactions of the contralateral limbs, mostly the hindlimb. Placing deficits were most prominent during transition to immobility and/or when independent limb movements were required. Administration of flunarizine, a Class IV calcium antagonist, 30 minutes after infarction resulted in marked sparing of sensorimotor function in 30 rats. In contrast to 20 vehicle-treated rats, which remained deficient for at least 21 days, 15 (75%) of the rats treated with 1.25 mg/kg i.v. flunarizine showed normal placing on Day 1 after infarction, whereas the remaining five (25%) recovered within 5 days. Oral treatment of 10 rats with 40 mg/kg flunarizine was also effective. Neocortical infarct volume and thalamic gliosis, assessed 21 days after infarction, did not differ between 30 flunarizine- and 30 vehicle-treated rats. However, when 4-hour-old infarcts were measured in 16 rats, posttreatment with intravenous flunarizine reduced infarct size by 31%. In combination with appropriate behavioral analyses, photochemical thrombosis may constitute a relevant stroke model, in which flunarizine preserved behavioral function during a critical period, corresponding to the spread of ischemic damage.

Favourable effect of flunarizine on the recovery from hemiparesis in rats with intracerebral hematomas

In 25 rats, an intracerebral hematoma was created in the foreleg area of the motor cortex by injection of 50 microliters blood. After the lesion, 13 were treated with flunarizine and 12 with the solvent. Neurological testing was performed by measuring the running time on a rotating platform. In animals with hemiparesis, the flunarizine group (n = 7) showed a significantly (P less than 0.05) better recovery than the control group (n = 8). No significant differences occurred in animals without neurological deficits (flunarizine: n = 6, control: n = 4). So the effect of the drug is not due to a non-specific activation; it may partially cure neurological deficits caused by intracerebral hematoma.

Effect of flunarizine on the attenuation of baroreflex by transient cerebral ischemia

Baroreflex sensitivity assessed by phenylephrine-induced reflex bradycardia was markedly decreased by 5- an 10-min global cerebral ischemia in anesthetized dogs. Flunarizine, 0.1 and 1 mg/kg i.v., administered 5 min prior to 5-min ischemia, completely inhibited the decrease in baroreflex sensitivity while such a protective effect of the latter dose was incomplete against 10-min ischemia. In contrast, papaverine, 0.5 mg/kg per min i.v., infused for 5 min prior to 5-min ischemia, failed to protect the decrease in baroreflex sensitivity. Flunarizine may possess a certain direct cerebroprotective effect in addition to its cerebrocirculatory effect.

Effects of emopamil on postischemic blood flow and neuronal damage in rat brain

The effects of the calcium entry blocker emopamil on physiological variables, local cerebral blood flow (LCBF) and on hippocampal cell damage were evaluated after 10 min of forebrain ischemia in the rat. LCBF was determined with the 14C-iodoantipyrine technique after 2, 10, and 60 min of postischemic recirculation. Histological evaluation was performed 7 days after ischemia in cortical and hippocampal tissue by determination of the percentage of necrotic neurons. Preischemic application of emopamil [4 mg/kg racemate or 2 mg/kg (S)-emopamil; i.v.] caused increased in LCBF in cortical areas but did not alter blood flow in the hippocampus at 2 min of recirculation. After 10 and 30 min of flow resumption no differences in LCBF between drug-treated and control animals were observed. In the histological series (S)-emopamil was applied at doses of 2, 4 or 6 mg/kg before the induction of ischemia. After 7 days of postischemic recovery, neuronal damage was significantly reduced by the calcium antagonist in hippocampal CA1 sector at all doses tested, the most prominent effects being observed with the lowest dose. At this dose cell loss in the CA3 sector was also reduced. In cortical tissue the number of necrotic cells remained unchanged by emopamil treatment. It is concluded that the calcium antagonist emopamil can reduce ischemia-induced neuronal cell damage. The compound improves circulation in cortical tissue only during early recovery but not at later phases of reflow, i.e. the period of delayed hypoperfusion. These increases in blood flow are not of crucial importance for ultimate neuronal death in this area.(ABSTRACT TRUNCATED AT 250 WORDS)