Effects of verapamil on the release of different neurotransmitters

Multitargeting in cardioprotection: An example of biaromatic compounds

A multitarget drug design approach is actively developing in modern medicinal chemistry and pharmacology, especially with regard to multifactorial diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. A detailed study of many well-known drugs developed within the single-target approach also often reveals additional mechanisms of their real pharmacological action. One of the multitarget drug design approaches can be the identification of the basic pharmacophore models corresponding to a wide range of the required target ligands. Among such models in the group of cardioprotectors is the linked biaromatic system. This review develops the concept of a "basic pharmacophore" using the biaromatic pharmacophore of cardioprotectors as an example. It presents an analysis of possible biological targets for compounds corresponding to the biaromatic pharmacophore and an analysis of the spectrum of biological targets for the five most known and most studied cardioprotective drugs corresponding to this model, and their involvement in the biological effects of these drugs.

Verapamil attenuates scopolamine induced cognitive deficits by averting oxidative stress and mitochondrial injury - A potential therapeutic agent for Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial disorder where amyloid beta (Aβ) plaques, Ca2+ dysregulation, excessive oxidative stress, mitochondrial dysfunction and synaptic loss operate synergistically to bring about cholinergic deficits and dementia. New therapeutic interventions are gaining prominence as the morbidity and mortality of AD increases exponentially every year. Treating AD with antihypertensive drugs is thought to be a promising intervention; however, its mechanism of action of ameliorating AD needs further investigation. In this context, the present study explores the protective effect of verapamil, an antihypertensive agent of Ca2+ channel blocker (CCB) class against scopolamine-induced in vitro neurotoxicity and in vivo cognitive impairment. Supplementation of verapamil was found to attenuate oxidative stress by preventing mitochondrial injury, and augment the expression of genes involved in the cholinergic function (mACR1), synaptic plasticity (GAP43, SYP) and Ca2+-dependent memory-related genes (CREB1, CREBBP, BDNF). Further, verapamil treatment in mice attenuated the cognitive and behavioural deficits induced by scopolamine as measured by the elevated plus maze and passive avoidance test (P < 0.05). Thus, the present study demonstrates the neuroprotective effect of verapamil against the pathogenesis of AD such as oxidative stress, mitochondrial dysfunction and cognitive decline. These observations emphasize the importance of ‛Ca2+ dysregulation' and ‛mitochondrial dysfunction' theories in AD and recommends the supplementation of compounds that regulate Ca2+ homeostasis and mitochondrial function in susceptible AD individuals.

Verapamil Blocks Scopolamine Enhancement Effect on Memory Consolidation in Passive Avoidance Task in Rats

Our recent data have indicated that scopolamine, a non-selective muscarinic receptor antagonist, improves memory consolidation, in a passive avoidance task, tested in rats. It has been found that verapamil, a phenylalkylamine class of the L-type voltage-dependent calcium channel antagonist, inhibits [3H] N-methyl scopolamine binding to M1 muscarinic receptors. However, there are no data about the effect of verapamil on memory consolidation in the passive avoidance task, in rats. The purpose of the present study was to examine the effects of verapamil (0.5, 1.0, 2.5, 5.0, 10, or 20 mg/kg i.p.) as well as the interaction between scopolamine and verapamil on memory consolidation in the step-through passive avoidance task, in Wistar rats. Our results showed that verapamil (1.0 and 2.5 mg/kg) administered immediately after the acquisition task significantly increased the latency of the passive avoidance response, on the 48 h retested trial, improving memory consolidation. On the other hand, verapamil in a dose of 5 mg/kg, that per se does not affect memory consolidation, significantly reversed the memory consolidation improvement induced by scopolamine (1 mg/kg, i.p., administered immediately after verapamil treatment) but did not change the passive avoidance response in rats treated by an ineffective dose of scopolamine (30 mg/kg). In conclusion, the present data suggest that (1) the post-training administration of verapamil, dose-dependently, improves the passive avoidance response; (2) verapamil, in ineffective dose, abolished the improvement of memory consolidation effect of scopolamine; and (3) exists interaction between cholinergic muscarinic receptors and calcium homeostasis-related mechanisms in the consolidation of emotional memory.

Effects of Levetiracetam, Carbamazepine, Phenytoin, Valproate, Lamotrigine, Oxcarbazepine, Topiramate, Vinpocetine and Sertraline on Presynaptic Hippocampal Na(+) and Ca(2+) Channels Permeability

Ion channels are targets of various antiepileptic drugs. In cerebral presynaptic nerve endings Na(+) and Ca(2+) channels are particularly abundant, as they control neurotransmitter release, including the release of glutamate (Glu), the most concentrated excitatory amino acid neurotransmitter in the brain. Several pre-synaptic channels are implicated in the mechanism of action of the pro-convulsive agent, 4-aminopyridine (4-AP). In the present study the effects of levetiracetam and other established and newer (vinpocetine) anti-epileptic drugs, as well as of the anti-depressant, sertraline on the increase in Ca(2+) induced by 4-AP in hippocampal isolated nerve endings were investigated. Also the effects of some of the anti-seizure drugs on the selective increase in Ca(2+) induced by high K(+), or on the selective increase in Na(+) induced by veratridine were tested. Sertraline and vinpocetine effectively inhibited the rise in Ca(2+) induced by 4-AP, which was dependent on the out-in Na(+) gradient and tetrodotoxin sensitive. Carbamazepine, phenytoin, lamotrigine and oxcarbazepine inhibited the rise in Ca(2+) induced by 4-AP too, but at higher concentrations than sertraline and vinpocetine, whereas levetiracetam, valproic acid and topiramate did not. The three latter antiepileptic drugs also failed in modifying other responses mediated by the activation of brain presynaptic Na(+) or Ca(2+) channels, including Glu release. This indicates that levetiracetam, valproic acid and topiramate mechanisms of action are unrelated with a decrease in presynaptic Na(+) or Ca(2+) channels permeability. It is concluded that depolarized cerebral isolated nerve endings represent a useful tool to unmask potential antiepileptic drugs targeting presynaptic Na(+) and/or Ca(2+) channels in the brain; such as vinpocetine or the anti-depressant sertraline, which high effectiveness to control seizures in the animal in vivo has been demonstrated.

Verapamil enhances acute stress or glucocorticoid-induced deficits in retrieval of long-term memory in rats

This study was designed to investigate an interaction between acute restraint stress and corticosterone with verapamil, a blocker of L-type voltage-dependent calcium (VDC) channels on retrieval of long-term memory. Young adult male rats were trained in one trial inhibitory avoidance task (0.5 mA, 3 s footshock). On retention test given 48 h after training, the latency to re-enter dark compartment of the apparatus was recorded. In Experiment 1, verapamil pretreatment (5, 10, or 20 mg/kg) enhanced the impairing effects of acute stress (which was applied for 10 min in a Plexiglass tube 30 min before the retention test) on memory retrieval. The applied stress increased circulating corticosterone levels as assessed immediately after the retention test, indicating that stress-induced impairment of memory retrieval is mediated, in part, by increased plasma levels of glucocorticoids. Verapamil did not change this response. In Experiment 2, pretreatment of an intermediate dose of verapamil also enhanced corticosterone-induced impairment of memory retrieval. In Experiments 3 and 4, acute stress or corticosterone did not change motor activity with or without prior treatment of verapamil, suggesting that stress or glucocorticoid-induced impairment of memory retrieval is not due to any gross disturbances in motor performance of animals. These findings indicate that blockade of L-type VDC channels enhances stress or glucocorticoid-induced impairment of memory retrieval, and provide evidence for the existence of an interaction between glucocorticoids and L-type VDC channels on memory retrieval.

Effects of calcium channel blockers on antidepressant action of Alprazolam and Imipramine

Alprazolam is effective as an anxiolytic and in the adjunct treatment of depression. In this study, the effects of calcium channel antagonists on the antidepressant action of alprazolam and imipramine were investigated. A forced swimming maze was used to study behavioral despair in albino mice. Mice were divided into nine groups (n = 7 per group). One group received a single dose of 1% Tween 80; two groups each received a single dose of the antidepressant alone (alprazolam or imipramine); two groups each received a single dose of the calcium channel blocker (nifedipine or verapamil); four groups each received a single dose of the calcium channel blocker followed by a single dose of the antidepressant (with same doses used for either in the previous four groups). Drug administration was performed concurrently on the nine groups. Our data confirmed the antidepressant action of alprazolam and imipramine. Both nifedipine and verapamil produced a significant antidepressant effect (delay the onset of immobility) when administered separately. Verapamil augmented the antidepressant effects of alprazolam and imipramine (additive antidepressant effect). This may be due to the possibility that verapamil might have antidepressant-like effect through different mechanism. Nifedipine and imipramine combined led to a delay in the onset of immobility greater than their single use but less than the sum of their independent administration. This may be due to the fact that nifedipine on its own might act as an antidepressant but blocks one imipramine mechanism that depends on L-type calcium channel activation. Combining nifedipine with alprazolam produced additional antidepressant effects, which indicates that they exert antidepressant effects through different mechanisms.

Effects of carbamazepine, phenytoin, valproic acid, oxcarbazepine, lamotrigine, topiramate and vinpocetine on the presynaptic Ca2+ channel-mediated release of [3H]glutamate: Comparison with the Na+ channel-mediated release

The effect of carbamazepine, phenytoin, valproate, oxcarbazepine, lamotrigine and topiramate, that are among the most widely used antiepileptic drugs (AEDs), and of the new putative AED vinpocetine on the Ca(2+) channel-mediated release of [(3)H]Glu evoked by high K(+) in hippocampal isolated nerve endings was investigated. Results show that carbamazepine, oxcarbazepine and phenytoin reduced [(3)H]Glu release to high K(+) to about 30% and 55% at concentrations of 500 microM and 1500 microM, respectively; lamotrigine and topiramate to about 27% at 1500 microM; while valproate failed to modify it. Vinpocetine was the most potent and effective; 50 microM vinpocetine practically abolished the high K(+) evoked release of [(3)H]Glu. Comparison of the inhibition exerted by the AEDs on [(3)H]Glu release evoked by high K(+) with the inhibition exerted by the AEDs on [(3)H]Glu release evoked by the Na(+) channel opener, veratridine, shows that all the AEDs are in general more effective blockers of the presynaptic Na(+) than of the presynaptic Ca(2+) channel-mediated response. The high doses of AEDs required to control seizures are frequently accompanied by adverse secondary effects. Therefore, the higher potency and efficacy of vinpocetine to reduce the permeability of presynaptic ionic channels controlling the release of the most important excitatory neurotransmitter in the brain must be advantageous in the treatment of epilepsy.

Effects of carbamazepine, phenytoin, lamotrigine, oxcarbazepine, topiramate and vinpocetine on Na+ channel-mediated release of [3H]glutamate in hippocampal nerve endings

Several of the most effective antiepileptic drugs are believed to stop the paroxysmal neuronal activity acting as Na(+) channel blockers. However, no single study comparing in parallel the potency and efficacy of the most commonly used antiepileptic drugs on brain Na(+) channel-mediated responses is available. In the present study the effects of increasing concentrations of carbamazepine, phenytoin, lamotrigine, oxcarbazepine and topiramate, which are among the most frequently used antiepileptic drugs, and of the new putative antiepileptic drug, vinpocetine, on the release of glutamate (Glu) elicited by the Na(+) channel opener, veratridine were investigated in hippocampal isolated nerve endings preloaded with the labeled excitatory amino acid neurotransmitter. The present results show that carbamazepine, phenytoin, lamotrigine and oxcarbazepine, in the range from 150 to 1500 microM, progressively inhibit [(3)H]Glu release induced by veratridine. Also vinpocetine progressively inhibits the veratridine-induced response, but in a much lower range of concentrations (from 1.5 to 15 microM), whereas topiramate only exerts a modest inhibition (20%) of Glu release to veratridine at the highest dose tested (1500 microM). These results indicate that the mechanism of action of several of the most widely used antiepileptic drugs involves reduction in cerebral presynaptic voltage sensitive Na(+) channels permeability. Considering that the high doses of antiepileptic drugs required to control seizures are frequently accompanied by adverse secondary effects, the higher potency of vinpocetine to reduce Na(+) channels permeability might be advantageous.

Single and combined effects of carbamazepine and vinpocetine on depolarization-induced changes in Na+, Ca2+ and glutamate release in hippocampal isolated nerve endings

The single and combined effects of carbamazepine and vinpocetine on the release of the excitatory amino acid neurotransmitter glutamate, on the rise in internal Na+ (Na(i), as determined with SBFI), and on the rise in internal Ca2+ (Ca(i), as determined with fura-2) induced by an increased permeability of presynaptic Na+ channels, with veratridine, or by an increased permeability of presynaptic Ca2+ channels with high K+, were investigated in isolated hippocampal nerve endings. The present study shows that carbamazepine and vinpocetine, both inhibit dose dependently the release of preloaded [3H]Glu induced by veratridine. However, carbamazepine is two orders of magnitude less potent than vinpocetine. The calculated IC(50)'s for carbamazepine and vinpocetine to inhibit veratridine-induced [3H]Glu release are 200 and 2 microM, respectively. Consistently 150 microM carbamazepine and 1.5 microM vinpocetine reduce the veratridine-induced rise in Na(i) in a similar extent. The single effects of carbamazepine and of vinpocetine on the presynaptic Na+ channel mediated responses, namely the rise in Na(i) and the release of Glu induced by veratridine, are additive. Responses that depend on the entrance of external Ca2+ via presynaptic Ca2+ channels, such as the release of [3H]Glu and the rise in Ca(i) induced by high K+, are insensitive to 300 microM carbamazepine and slightly reduced by 5 microM vinpocetine. It is concluded that the additive effects of carbamazepine, which is one of the most common antiepileptic drugs, and vinpocetine that besides its known neuroprotective action and antiepileptic potential is a memory enhancer, may perhaps be advantageous in the treatment of epileptic patients.

Contribution of L-type calcium channels to epileptiform activity in hippocampal and neocortical slices of guinea-pigs

The aim of the present investigation was to compare the antiepileptic efficacy of the specific L-type calcium channel blocker nifedipine in hippocampal and neocortical slice preparations in the Mg2+-free model of epilepsy. The main findings were as follows. (1) In hippocampal slices, in general, nifedipine (20-80 micromol/l) exerted a suppressive effect both on repetition rate and on area under epileptiform field potentials. This effect was clearly dose dependent. In the majority of cases, this suppression was preceded by an increase, which was transient in nature. Only in the lowest concentration (20 micromol/l) used, in normal K+, instead of a depression, a persistent increase occurred. (2) In neocortical slices, in the majority of experiments, nifedipine (20-80 micromol/l) showed a depressive action only on the area under the epileptiform field potentials. The depressive effect of nifedipine on the area was dose dependent, although to a lesser extent than in the hippocampus. In nearly half of the slices this suppression was preceded by a transient increase. By contrast, the repetition rate of epileptiform field potentials increased transiently in about 20% of the slices followed by a decrease. In the remaining 80% of the slices the repetition rate increased persistently. (3) An elevation of the K+ concentration accentuated the depressive actions of nifedipine only in the hippocampus. In contrast to elevated K+, in both the hippocampus and the neocortex, epileptiform field potentials were not suppressed in all experiments in normal K+. (4) The reversibility of the depressive effects of nifedipine was differential in the two tissue types. In the hippocampus, after suppression of epileptiform field potentials they reappeared in the overwhelming majority of slices. In the neocortex, this was the case in only one experiment. These findings may indicate the existence of L-type calcium channels with a differential functional significance for epileptogenesis and/or the existence of different forms of L-type channels in hippocampal and neocortical tissue. As a whole, the differential effects of L-type calcium channel blockade in the hippocampus and neocortex point to differences in the network properties of the two tissue types.

Chronic verapamil modifies striatal and frontal cortex dopamine levels

In an attempt to elucidate if a change in dopamine (DA) levels was involved in the antimanic action of verapamil reported in various clinical studies, monoamine concentrations in three brain regions (striatum, frontal cortex and hippocampus) obtained from verapamil-treated rats (10 mg/kg i.p. per day for 21 days) were quantified by HPLC coupled to electrochemical detection, and compared with monoamine concentrations in haloperidol-treated animals (5 mg/kg i.p. per day for 21 days). We have found that verapamil and haloperidol, when injected for 3 weeks to rats sacrificed 2 h after the last injection, decreased the striatal DA concentration to a similar extent. This decrease was not observed in short-term (one injection 2 h before sacrifice) verapamil- or haloperidol-treated rats. Moreover, after such a single injection of verapamil the striatal DA concentration was even increased. The striatal concentration of 3,4-dihydroxyphenylacetic acid (DOPAC) was increased about two-fold by haloperidol, but not by verapamil. This haloperidol-induced increase in striatal DOPAC was similar after one injection and after 21 days of haloperidol administration. Neither verapamil nor haloperidol modified the concentrations of homovanillic acid (HVA) or 3-methoxytyramine (3-MT) in the striatum. In the frontal cortex, chronic verapamil increased the concentrations of DA two-fold, and chronic haloperidol increased the concentration of DOPAC two-fold. The other DA metabolites, namely HVA and 3-MT were not significantly changed. The concentration of serotonin (5-HT) and its main metabolite, 5-hydroxyindoleacetic acid (5-HIAA), in control, verapamil- and haloperidol-treated rats were similar in the three brain regions studied. We conclude that DA autoreceptors are implicated in verapamil's effects on frontal cortex and striatum DA levels; and that the presumed antimanic action exerted by verapamil is due to its long-term effect on these receptors.

Characterization of the type of calcium channel primarily regulating GABA exocytosis from brain nerve endings

In an attempt to further characterize the type of Ca2+ channels primarily regulating GABA exocytosis, the effects of increasing concentrations of omega CTx MVIIC,-omega-Aga IVA and other Ca2+ channel blockers (nitrendipine, Cd2+ and Ni2+), commonly used for pharmacologically discerning among the various types of Ca2+ channels, were tested on the dissected Ca2+ dependent fraction of the depolarization evoked release of GABA from mouse brain synaptosomes. Our results show that omega-CTx MVIIC inhibits GABA exocytosis with a calculated IC50 of 3 microM and omega-Aga IVA with a calculated IC50 of 50 nM. The divalent cation Cd2+ only diminishes GABA exocytosis at 70 microM, but does not modify this response at lower concentrations (i.e. 1 and 10 microM). Neither nitrendipine (10 microM) nor Ni2+ (100 microM and 500 microM) modified GABA exocytosis. The failure of nitrendipine at a high concentration to inhibit GABA exocytosis discards L-type Ca2+ channels as the main regulators of this response; likewise that of Ni2+ discards Ca2+ channels of the N-type, and the failure of nM concentrations of omega-CTx MVIIC or 500 microM Ni2+, also discards alpha 1A/Q-type Ca2+ channels as the main regulators of the GABA response. On the basis of these results and in particular of the higher potency of omega-Aga IVA than omega-CTx MVIIC, it is concluded that the type of Ca2+ channels that primarily determine the exocytosis of GABA belong to a P-like type of Ca2+ channels.