Calcium antagonists: stroke therapy coming of age

[Histopathologic comparison of dexmedetomidine's and thiopental's cerebral protective effects on focal cerebral ischemia in rats]

This study was designed to investigate whether dexmedetomidine and thiopental have cerebral protective effects after focal cerebral ischemia in rats. Thirty male Sprague Dawley rats were randomly assigned to three groups: control group (Group C, n=10), dexmedetomidine group (Group D, n=10), thiopental group (Group T, n=10). After all rats were anesthetized, they were intubated, then mechanically ventilated. A catheter was inserted into the right femoral artery for continuous mean arterial pressure, physiological parameters and blood sampling at baseline, 5min after occlusion and 20min after reperfusion. A catheter was inserted into the left femoral vein for intravenous (IV) medication administration. Right common carotid artery of each rat was isolated and clamped for 45min. At the end of the duration common carotid artery were unclamped and the brain reperfusion was achieved for 90min. Dexmedetomidine was administered for Group D IV infusion, and Group T received thiopental IV. According to histopathologic scores cerebral ischemia was documented in all rats in Group C, but no ischemia was found in three rats in Group T and in four rats in Group D. Grade 3 cerebral ischemia was documented in three rats in Group C, and in only one rat in both groups T and D. For histopathologic grades the difference between Group T and Group D was not significant (p>0.05). But the differences between Group C and Group T (p<0.05) and Group C and Group D (p<0.01) were statically significant. In conclusion, we demonstrated that dexmedetomidine and thiopental have experimental histopathologic cerebral protective effects on experimental focal cerebral ischemia in rats.

Histopathologic comparison of dexmedetomidine's and thiopental's cerebral protective effects on focal cerebral ischemia in rats

This study was designed to investigate whether dexmedetomidine and thiopental have cerebral protective effects after focal cerebral ischemia in rats. Thirty male Sprague Dawley rats were randomly assigned to three groups: control group (Group C, n=10), dexmedetomidine group (Group D, n=10), thiopental group (Group T, n=10). After all rats were anesthetized, they were intubated, then mechanically ventilated. A catheter was inserted into the right femoral artery for continuous mean arterial pressure, physiological parameters and blood sampling at baseline, 5min after occlusion and 20min after reperfusion. A catheter was inserted into the left femoral vein for intravenous (IV) medication administration. Right common carotid artery of each rat was isolated and clamped for 45min. At the end of the duration common carotid artery were unclamped and the brain reperfusion was achieved for 90min. Dexmedetomidine was administered for Group D IV infusion, and Group T received thiopental IV. According to histopathologic scores cerebral ischemia was documented in all rats in Group C, but no ischemia was found in three rats in Group T and in four rats in Group D. Grade 3 cerebral ischemia was documented in three rats in Group C, and in only one rat in both groups T and D. For histopathologic grades the difference between Group T and Group D was not significant (p>0.05). But the differences between Group C and Group T (p<0.05) and Group C and Group D (p<0.01) were statically significant. In conclusion, we demonstrated that dexmedetomidine and thiopental have experimental histopathologic cerebral protective effects on experimental focal cerebral ischemia in rats.

Effects of Intracellular Calcium Reduction by Dantrolene on Prevention/Treatment of Ischemic Stroke

BACKGROUND: It has been suggested that cerebral blood vessels and brain cells might depend more on intracellular calcium than extracellular calcium to modulate intracellular free calcium concentrations, [Ca(2+)](i). METHODS AND RESULTS: A potent intracellular calcium antagonist, dantrolene, was used to prevent the ischemic stroke induced in the rat model. It was found that treatment of rats with dantrolene at -1 hour and +1 hour after 60 minutes of ischemic insult prevented by the formation of cortical necrosis 98% and 85%, respectively. Further, the [Ca(2+)](i) of embryonic aorta cells was markedly reduced, and cAMP of the same cultured cells were significantly increased by dantrolene treatment. CONCLUSIONS: These results indicate that ischemic stroke is preventable by dantrolene through reduction of [Ca(2+)](i) and increase of cAMP.

Hypoglycaemic brain damage: effect of a dihydropyridine calcium channel antagonist in rats

Hypoglycaemic brain damage consists of selective necrosis of cerebral neurons related to the extracellular release of excitatory amino acids. Neuronal excitatory amino acid receptors are activated and calcium channels are opened. The present investigation was designed to test the effectiveness of dihydropyridine blockade of voltage-sensitive calcium channels in hypoglycaemic brain damage. Sixty-four rats were given either high-dose nimodipine, consisting of an initial bolus of 300 micrograms/kg nimodipine administered at the stage of EEG slowing (blood glucose levels of 1.0-1.5 mmol/l), followed by continuous intravenous nimodipine infusion at 1.5 micrograms.kg-1.min-1, low-dose nimodipine, consisting of an initial bolus of 30 micrograms/kg at the time of EEG slowing, followed by 0.15 microgram.kg-1.min-1, an equal volume of vehicle solution, or 154 mmol/l NaCl. Animals receiving either low- or high-dose nimodipine had higher mortality, and increased brain damage compared with controls. Examination of the perfusion-fixed brains 1 week after recovery with glucose revealed that quantitated neuronal necrosis was worsened by nimodipine in the hippocampus, caudate nucleus and cerebral cortex. The present results in profound hypoglycaemia (accompanied by a flat EEG) contrast with the beneficial effect of nimodipine in brain ischaemia.

A review of brain retraction and recommendations for minimizing intraoperative brain injury

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.

A randomized controlled trial of high-dose intravenous nicardipine in aneurysmal subarachnoid hemorrhage. A report of the Cooperative Aneurysm Study

Because of their action as cerebral vasodilators, dihydropyridine calcium antagonists have received intense scrutiny for their potential benefit in ameliorating the devastating consequences of delayed cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH). From October, 1987, to September, 1989, 41 North American neurosurgical centers in the Cooperative Aneurysm Study accrued 906 patients with recent (Days 0 to 7) aneurysmal SAH into a prospective randomized double-blind placebo-controlled trial of high-dose intravenous nicardipine to test whether treatment with this agent improved overall outcome. Eligible patients received 0.15 mg/kg/hr of either nicardipine or placebo by continuous infusion for up to 14 days following hemorrhage. The 449 patients randomly assigned to the nicardipine-treated group and the 457 patients assigned to the placebo-treated group were balanced with regard to prognostic factors for ischemic deficits from vasospasm and for overall outcome. Other medical and surgical interventions were used with similar frequency in both groups, except that antihypertensive agents were used less frequently in the nicardipine-treated patients (26% of the nicardipine-treated group vs. 43% of the placebo-treated group, p < 0.001), and more patients in the placebo-treated group had intentional hypervolemia, induced hypertension, and/or hemodilution administered therapeutically for symptomatic vasospasm (38% of the placebo-treated group vs. 25% of the nicardipine-treated group, p < 0.001). The incidence of symptomatic vasospasm during the treatment period was higher in the placebo-treated group (46%) than in the nicardipine-treated group (32%) (p < 0.001). Despite the reduction in symptomatic vasospasm in the nicardipine-treated group, overall outcome at 3 months was similar between the two groups. Fifty-five percent of nicardipine-treated patients were rated as having a good recovery according to the Glasgow Outcome Scale at follow-up review and 17% were dead, compared to 56% and 18%, respectively, in the placebo-treated group (not statistically significant). These data suggest that high-dose intravenous nicardipine treatment is associated with a reduced incidence of symptomatic vasospasm in patients with recent aneurysmal SAH, but not with an improvement in overall outcome at 3 months when compared to standard management in North America. It is postulated that, while nicardipine prevents vasospasm, hypertensive/hypervolemic therapy may be effective in reversing ischemic deficits from vasospasm once they occur.

Attenuation of ischemic and postischemic damage to brain metabolism and circulation by a novel Ca2+ channel antagonist, NC-1100, in spontaneously hypertensive rats

We investigated the effect of a newly synthesized Ca2+ channel antagonist, NC-1100, on cerebral blood flow (CBF) and metabolism in spontaneously hypertensive rats. The rats received a bolus injection of 0.2 or 1.0 mg/kg NC-1100 i.v. and 1-h cerebral ischemia was then induced by bilateral carotid artery occlusion (group 1). The rats in group 2 were continuously infused with NC-1100 0.03 or 0.1 mg/kg per min, starting immediately after bilateral carotid artery occlusion, for the 1 h of ischemia and following 3-h recirculation. Group 1: during ischemia, CBF in all rats decreased to 6-8% of the resting values. At 1 h cerebral ischemia, brain tissue lactate increased 11.5-, 10.1- and 9.8-fold of the normal control given vehicle or NC-1100, 0.2 and 1.0 mg/kg, respectively. The ATP levels were better preserved by NC-1100 administration; 0.61 +/- 0.04 (mean +/- S.E.M.), 0.80 +/- 0.09 and 0.97 +/- 0.14 mmol/kg (P < 0.05 vs. vehicle), respectively. Group 2: during recirculation, CBF in NC-1100-treated rats returned to 83-90% of the resting values, but to only 65% in the vehicle group. Postischemic brain lactate at 3 h was less well preserved and ATP was dose dependently better preserved in NC-1100- than vehicle-treated rats. It is considered that pre- as well as postischemic administration of a Ca2+ channel antagonist, NC-1100, is beneficial to attenuate and also ameliorate the metabolic and circulatory derangement in the ischemic brain.

Tyrosine phosphorylation of microtubule-associated protein kinase after transient ischemia in the gerbil brain

The tyrosine phosphorylation of microtubule-associated protein (MAP) kinase was examined in the gerbil brain after transient ischemia and reperfusion. Phosphorylation of MAP kinase was maximal within 1 min of reperfusion following 5 min of ischemia and returned to control levels as early as 5 min postischemia. The greatest increase in MAP kinase phosphorylation was detected in the hippocampus, with minor increases in other ischemic regions of the brain. Several tyrosine-phosphorylated proteins were detected in the gerbil hippocampus; however, the ischemia and reperfusion injury only increased tyrosine phosphorylation of MAP kinase. The increase in tyrosine phosphorylation was prevented by the N-methyl-D-aspartate (NMDA) receptor blocker (+)-MK-801, whereas a non-NMDA receptor blocker, 6-cyano-7-nitroquinoxaline-2,3-dione, was ineffective. Pretreatment of gerbils with calcium channel blockers also prevented the tyrosine phosphorylation of MAP kinase in the ischemic brain. Altogether, these results imply an involvement of glutamate receptors and calcium during the tyrosine phosphorylation of MAP kinase. Tyrosine phosphorylation was also prevented when ischemia and reperfusion were conducted under hypothermic conditions, which protect against neurodegenerative damage. These findings implicate a role for MAP kinase in neuronal damage resulting from ischemia and reperfusion.

Role of calcium in inactivation of calcium/calmodulin dependent protein kinase II after cerebral ischemia

Transient cerebral ischemia demonstrates an increase in activated oxygen species in the brain that could lead to eventual neuronal cell death. Neuronal cells respond to oxygen free radicals through the restructuring of the cytoskeleton and membranes, mobilization of calcium and gene expression which play a role in cell injury. Ten min of bilateral carotid artery occlusion resulted in a decrease in calcium/calmodulin dependent protein kinase II (CaM kinase II) phosphorylation and activity detected in the brain immediately following ischemia and was partially restored within 24 h of reperfusion. Pretreatment of animals with an anesthetic dose of pentobarbital (40 mg/kg) resulted in partial protection of inactivation of CaM kinase II following ischemia. CaM kinase II activity was maintained following pretreatment of animals with alpha-phenyl N-tert-butyl nitrone (PBN), which traps oxygen free radicals. Infusion of superoxide dismutase or catalase prior to ischemia, blocked CaM kinase II inactivation. Blockage of calcium uptake with bepridil resulted in a marked protection of CaM kinase II inactivation. In addition, trifluoperazine, a calmodulin antagonist also diminished the inhibition of CaM kinase II phosphorylation in our model. These results suggest that ischemia and reperfusion injury results in the generation of activated oxygen and the mobilization of calcium which inactivate CaM kinase II. These results indicate that changes associated with protein kinase activity in the brain following an ischemic insult may have profound effects upon neurodegeneration and neuronal survival.

What have drugs to offer the patient with acute stroke?

1. Drug treatment for acute stroke is designed to salvage neuronal tissue, and to prevent complications of stroke, which are often non-neurological. This review addresses the areas of recent advance in treatment designed to reduce the size of the cerebral infarct. With the exception of cardiac-source embolism, for which anticoagulation in the acute phase is sometimes considered, prevention of recurrent events is not discussed. 2. It is to be hoped that pharmaceutical developments will improve the current bleak picture in which there are no proven treatments for ischaemic stroke or intracerebral haemorrhage. To meet this challenge will require careful, controlled evaluation of treatment early after acute stroke in large scale clinical studies.

Nicardipine reduces the levels of leukotriene C4 and prostaglandin E2, following different ischemic periods in rat brain tissue

Ischemic depolarization of nerve membranes is associated with a rapid influx of calcium into the cell, resulting in production of arachidonic acid (AA) metabolites. These metabolites, particularly leukotriene C4 (LTC4) have a very potent vasoconstrictor effect on cerebral arteries inducing vasogenic edema that may damage the ischemic penumbra. Calcium antagonists are assumed to prevent or reduce metabolic disturbances associated with ischemia. In this study, after developing an experimental animal model simulating the concept of the ischemic penumbra in the rat, the levels of LTC4 and prostaglandin E2 (PGE2) produced in the forebrain following different ischemic periods, such as 4th, 15th, 60th and 240th min were measured by a bioassay method, including 6 rats for each ischemic group. Then the effect of the 1-4 dihydropyridine nicardipine (1 mg/kg) on these mediators was investigated by giving it to the rat 30 min before the development of the ischemic model in each corresponding group (n = 6). We showed that nicardipine significantly reduced the high levels of LTC4 and PGE2 in the 4th min and 4th h of cerebral ischemia (p less than 0.005, p less than 0.0005). So it may be concluded that institution of nicardipine may be helpful in protecting the ischemic penumbra during the early hours of cerebral ischemia.

Therapy in cerebrovascular disease: current status and future directions

OBJECTIVE

To assess the current status and future directions of therapy in cerebrovascular disease.

DATA SOURCES

English language literature search using MEDLINE, Index Medicus, reviews, texts and relevant papers.

STUDY SELECTION

Information has been drawn from approximately 200 articles.

DATA EXTRACTION AND SYNTHESIS

Those articles with most relevance to current practice and future directions in the therapy of cerebrovascular disease have been cited.

CONCLUSIONS

Much progress has been made over the last 30 years in the therapy of primary and secondary prevention of cerebrovascular disease. The introduction of antihypertensive agents has been largely responsible for the decline in mortality from stroke and, in some areas, the incidence. Anticoagulants such as warfarin protect against ischaemic stroke in patients with mitral or aortic valve disease and/or atrial fibrillation. Antiplatelet agents are clearly effective in the secondary prevention of ischaemic stroke after transient ischaemic attacks; the risk of stroke or death is reduced, on average, by 22%. In patients with subarachnoid haemorrhage, ischaemic complications caused by vasospasm are reduced by calcium channel blockers. A new wave of therapies is now on the horizon to minimise tissue damage in the early stages of ischaemic stroke ("tissue rescue") with the introduction of thrombolytic agents, calcium channel blockers, NMDA antagonists and haemodilution techniques and many of these are currently being subjected to clinical trial. If they prove to be effective, our current management of acute ischaemic stroke may alter dramatically.

Effects of glucose on calcium channels in neural cells

Hyperglycemia has been reported to alter outcome following experimental and clinical cerebral ischemia, but the mechanisms involved are incompletely understood. Since glucose influences the function of dihydropyridine-sensitive, voltage-gated Ca2+ channels in some non-neural cells, and since cellular Ca2+ overload has been implicated in the pathogenesis of ischemic neuronal injury, we examined whether glucose regulates Ca2+ channel function in a cultured neural cell line. Physiologic concentrations of glucose had no effect on free intracellular Ca2+ levels in PC12 cells, but 4-fold elevation of glucose above physiologic levels reduced the dihydropyridine-sensitive, depolarization-induced increase in Ca2+. This effect would not account for exacerbation of ischemic brain injury by hyperglycemia, but may contribute to attenuation of ischemic injury by glucose in certain settings.