Failure of levemopamil to improve histological outcome following temporary occlusion of the middle cerebral artery in cats

Calcium channel blockers in cerebral ischaemia

Ischaemic stroke usually results from the obstruction of a major cerebral vessel which leads to a decrease in cerebral blood flow, and a subsequent reduction in ATP. This energy loss leads to impaired cellular function due to reduced ATP-dependent processes and a disruption in ionic gradients across membranes. Under these conditions, there is a significant efflux of K+ from cells producing cellular depolarisation and the movement of extracellular calcium into cells through calcium channels. It is this increase in intracellular calcium that leads to the 'calcium toxicity' that has been associated with cerebral ischaemia. Increased intracellular calcium triggers the break-down of phospholipids, proteins and nucleic acids. This is activated by calcium-dependent phospholipases, proteases and endonucleases, and contributes to structural and functional damage of the cell membrane, which compromises cell function and facilitates cell death. Calcium channel blockers are used routinely to treat cardiovascular disease and hypertension. Although some experimental studies over the last decade suggest efficacy/benefit in the treatment of experimental ischaemic stroke, clinical data do not bear this out. This article discusses the role of voltage-operated calcium channel blockers in stroke, and reviews much of the available experimental and clinical data.

Neuroprotective effects of PACAP38 in a rat model of transient focal ischemia under various experimental conditions

In the study reported here, we investigated the neuroprotective effect of PACAP38 in a rat model of middle cerebral artery occlusion (MCAO) under various experimental conditions. Stroke patients often develop mild hyperthermia that increases the infarct size and worsens the outcome. We compared the neuroprotective effect of PACAP38 in normothermic and moderately hyperthermic animals. Brain damage was more extensive in the hyperthermic animals, but PACAP38 significantly reduced the infarct size, measured 48 h after MCAO, in both the normothermic and the moderately hyperthermic animals, by more than 50%. However, a significant neuroprotection with PACAP38 could only be demonstrated when animals with no definite circling behavior and/or convulsions were excluded from the evaluations. In conclusion, moderate hyperthermia did not influence the effect of PACAP38, but animals with questionable brain damage or convulsions must be excluded from the sample in order to demonstrate the neuroprotection with PACAP38.

LY393615, a novel neuronal Ca(2+) and Na(+) channel blocker with neuroprotective effects in models of in vitro and in vivo cerebral ischemia

In the present studies we have examined the effects of a new calcium channel blocker, LY393615 ((N-Butyl-[5,5-bis-(4-fluorophenyl)tetrahydrofuran-2-yl]methylamine hydrochloride, NCC1048) in a model of hypoxia-hypoglycaemia in vitro and in a gerbil model of global and in two rat models of focal cerebral ischaemia in vivo. Results indicated that LY393615 protected against hypoxia-hypoglycaemic insults in brain slices and also provided significant protection against ischaemia-induced hippocampal damage in gerbil global cerebral ischaemia when dosed at 10, 12.5 (P<0.05) or 15 mg/kg i.p. (P<0.01) 30 min before and 2 h 30 min after occlusion. The compound penetrated the brain well after a 15 mg/kg i.p. dose and had a half-life of 2.5 h. In further studies LY393615 was protective 1 h post-occlusion when administered at 15 mg/kg i.p. followed by 2 doses of 5 mg/kg i.p. 2 and 3 h later. LY393615 dosed at 15 mg/kg i.p. followed by 2 further doses of 5 mg/kg i.p. (2 and 3 h later) also produced a significant reduction in the infarct volume following Endothelin-1 (Et-1) middle cerebral artery occlusion in the rat when administration was initiated immediately (P<0.01) or 1 h (P<0.05) after occlusion. The compound was also evaluated in the intraluminal monofilament model of focal ischaemia. The animals had the middle cerebral artery occluded for 2 h, and 15 min after reperfusion LY393615 was administered at 15 mg/kg i.p. followed by 2 mg/kg/h i.v. infusion for 6 h. There was no reduction in infarct volume using this dosing protocol. In conclusion, in the present studies we have reported that a novel calcium channel blocker, LY393615, with good bioavailability protects against neuronal damage caused by hypoxia-hypoglycaemia in vitro and both global and focal cerebral ischaemia in vivo. The compound is neuroprotective when administered post-occlusion and may therefore be a useful anti-ischaemic agent.

The effects of LY393613, nimodipine and verapamil, in focal cerebral ischaemia

This study evaluates the effects of N-(2-[bis (4-fluorophenyl)methoxy]ethyl)-1-butanamine hydrochloride (LY393613), a novel neuronal (N/P/Q-type) Ca(2+) channel blocker, in ischaemia. For comparison, two commonly used L-type Ca(2+) channel blockers; nimodipine and verapamil were also evaluated. Ischaemia was induced in freely moving rats by micro-injection of endothelin-1 near the middle cerebral artery. In vivo microdialysis, laser Doppler flowmetry and histology were used to monitor ischaemia. Administration of LY393613, before and after the insult, attenuated the ischaemia-induced glutamate release, but not the dopamine release. Both nimodipine and verapamil failed to affect transmitter releases significantly, when administered post-occlusion. None of the compounds tested, produced any significant change in striatal blood flow. Histology showed that ischaemic damage was significantly less in LY393613 pre-treated rats. In conclusion, LY393613, a neuronal N/P/Q-Ca(2+) channel blocker, can attenuate ischaemic brain damage. The protective mechanism appears to be mainly the attenuation of the ischaemia-induced glutamate release, rather than its effect on cerebral hemodynamics.

Effects of Ca2+ and Na+ channel inhibitors in vitro and in global cerebral ischaemia in vivo

In the present study we have examined the effects of the small organic molecules: NNC 09-0026 ((-)-trans-1-butyl-4-(4-dimethylaminophenyl)-3-[(4-trifluoromethyl-ph eno xy) methyl] piperidine dihydrochloride); SB 201823-A (4-[2-(3,4-dichlorophenoxy)ethyl]-1-pentyl piperidine hydrochloride); NS 649 (2-amino-1-(2,5-dimethoxyphenyl)-5-trifluoromethyl benzimidazole); CNS 1237 (N-acenaphthyl-N'-4-methoxynaphth-1-yl guanidine) and riluzole on human omega-conotoxin sensitive N-type voltage-dependent Ca2+ channel currents (ICa) expressed in HEK293 cells, on Na+ channel currents (INa) in acutely isolated cerebellar Purkinje neurones in vitro and in the gerbil model of global cerebral ischaemia in vivo. Estimated IC50 values for steady-state inhibition of ICa were as follows; NNC 09-0026, 1.1 microM; CNS 1237, 4.2 microM; SB 201823-A, 11.2 microM; NS 649, 45.7 microM and riluzole, 233 microM. Estimated IC50 values for steady-state inhibition of Na+ channel currents were as follows: NNC 09-0026, 9.8 microM; CNS 1237, 2.5 microM; SB 201823-A, 4.6 microM; NS 649, 36.7 microM and riluzole, 9.4 microM. In the gerbil model of global cerebral ischaemia the number of viable cells (mean +/- S.E.M.) per 1 mm of the CA1 was 215 +/- 7 (sham operated), 10 +/- 2 (ischaemic control), 44 +/- 15 (NNC 09-0026 30 mg/kg i.p.), 49 +/- 19 (CNS 1237 30 mg/kg i.p.), 11 +/- 2 (SB 201823-A 10 mg/kg i.p.), 17 +/- 4 (NS 649 50 mg/kg i.p.) and 48 +/- 18 (riluzole 10 mg/kg i.p.). Thus NNC 09-0026, CNS 1237 and riluzole provided significant neuroprotection when administered prior to occlusion while SB 201823-A and NS 649 failed to protect. These results indicate that the Ca2+ channel antagonists studied not only inhibited human N-type voltage-dependent Ca2+ channels but were also effective blockers of rat Na+ channels. Both NNC 09-0026 and CNS 1237 showed good activity at both Ca2+ and Na+ channels and this may contribute to the observed neuroprotection.