Two structurally different T-type Ca 2+ channel inhibitors, mibefradil and pimozide, protect CA1 neurons from delayed death after global ischemia in rats

Cav3.2 channel regulates cerebral ischemia/reperfusion injury: a promising target for intervention

JOURNAL/nrgr/04.03/01300535-202419110-00028/figure1/v/2024-03-08T184507Z/r/image-tiff Calcium influx into neurons triggers neuronal death during cerebral ischemia/reperfusion injury. Various calcium channels are involved in cerebral ischemia/reperfusion injury. Cav3.2 channel is a main subtype of T-type calcium channels. T-type calcium channel blockers, such as pimozide and mibefradil, have been shown to prevent cerebral ischemia/reperfusion injury-induced brain injury. However, the role of Cav3.2 channels in cerebral ischemia/reperfusion injury remains unclear. Here, in vitro and in vivo models of cerebral ischemia/reperfusion injury were established using middle cerebral artery occlusion in mice and high glucose hypoxia/reoxygenation exposure in primary hippocampal neurons. The results showed that Cav3.2 expression was significantly upregulated in injured hippocampal tissue and primary hippocampal neurons. We further established a Cav3.2 gene-knockout mouse model of cerebral ischemia/reperfusion injury. Cav3.2 knockout markedly reduced infarct volume and brain water content, and alleviated neurological dysfunction after cerebral ischemia/reperfusion injury. Additionally, Cav3.2 knockout attenuated cerebral ischemia/reperfusion injury-induced oxidative stress, inflammatory response, and neuronal apoptosis. In the hippocampus of Cav3.2-knockout mice, calcineurin overexpression offset the beneficial effect of Cav3.2 knockout after cerebral ischemia/reperfusion injury. These findings suggest that the neuroprotective function of Cav3.2 knockout is mediated by calcineurin/nuclear factor of activated T cells 3 signaling. Findings from this study suggest that Cav3.2 could be a promising target for treatment of cerebral ischemia/reperfusion injury.

Nanomedicines, an emerging therapeutic regimen for treatment of ischemic cerebral stroke: A review

Owing to its intricate pathophysiology, cerebral stroke is a serious medical condition caused by interruption or obstruction of blood supply (blockage of vasculature) to the brain tissues which results in diminished supply of essential nutrients and oxygen (hypoxia) and ultimate necrosis of neuronal tissues. A prompt risks assessment and immediate rational therapeutic plan with proficient neuroprotection play critically important role in the effective management of this neuronal emergency. Various conventional medications are being used for treatment of acute ischemic cerebral stroke but fibrinolytic agents, alone or in combination with other agents are considered the mainstay. These clot-busting agents effectively restore blood supply (reperfusion) to ischemic regions of the brain; however, their clinical significance is hampered due to various factors such as short plasma half-life, limited distribution to brain tissues due to the presence of highly efficient physiological barrier, blood brain barrier (BBB), and lacking of target-specific delivery to the ischemic brain regions. To alleviate these issues, various types of nanomedicines such as polymeric nanoparticles (NPs), liposomes, nanoemulsion, micelles and dendrimers have been designed and evaluated. The implication of these newer therapies (nanomedicines) have revolutionized the therapeutic outcomes by improving the plasma half-life, permeation across BBB, efficient distribution to ischemic cerebral tissues and neuroprotection. Furthermore, the adaptation of some diverse techniques including PEGylation, tethering of targeting ligands on the surfaces of nanomedicines, and pH responsive features have also been pondered. The implication of these emerging adaptations have shown remarkable potential in maximizing the targeting efficiency of drugs to ischemic brain tissues, simultaneous delivery of drugs and imaging agents (for early prognosis as well as monitoring of therapy), and therapeutic outcomes such as long-term neuroprotection.

Emerging Drugs for the Treatment of Amyotrophic Lateral Sclerosis: A Focus on Recent Phase 2 Trials

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease involving both upper and lower motor neurons and resulting in increasing disability and death 3-5 years after onset of symptoms. Over 40 large clinical trials for ALS have been negative, except for Riluzole that offers a modest survival benefit, and Edaravone that modestly reduces disease progression in patients with specific characteristics. Thus, the discovery of efficient disease modifying therapy is an urgent need.

AREAS COVERED

Although the cause of ALS remains unclear, many studies have demonstrated that neuroinflammation, proteinopathies, glutamate-induced excitotoxicity, microglial activation, oxidative stress, and mitochondrial dysfunction may play a key role in the pathogenesis. This review highlights recent discoveries relating to these diverse mechanisms and their implications for the development of therapy. Ongoing phase 2 clinical trials aimed to interfere with these pathophysiological mechanisms are discussed.

EXPERT OPINION

This review describes the challenges that the discovery of an efficient drug therapy faces and how these issues may be addressed. With the continuous advances coming from basic research, we provided possible suggestions that may be considered to improve performance of clinical trials and turn ALS research into a 'fertile ground' for drug development for this devastating disease.

T-type Ca2+ channel activity increases in rat hippocampal CA1 region during kindling epileptogenesis

Epileptogenesis is a dynamical process that involves synaptic plasticity changes such as synaptic reorganization of excitatory and inhibitory systems and axonal sprouting in the hippocampus, which is one of the most studied epileptogenic regions in the brain. However, the early events that trigger these changes are not understood well. We investigated short-term and long-term synaptic plasticity parameters and T-type Ca²⁺ channel activity changes in the early phase of a rat kindling model. Chronic pentylenetetrazole (PTZ) application was used in order to induce the kindling process in rats. The recordings were obtained from hippocampal slices in the CA1 region at 25th day of PTZ application. Tetraethylammonium was used in order to induce long-term potentiation and T-type Ca²⁺ channel activity was assessed in the presence of mibefradil. We found that tetraethylammonium-induced long-term potentiation was not prevented by mibefradil in the kindling group in contrast to control group. We also found an increase in paired-pulse ratios in the PTZ-applied group. Our findings indicate an increase in the "T-type Ca²⁺ channel component of LTP" in the kindling group, which may be an early mechanism in epileptogenesis.

NNC 55-0396, a T-type calcium channel blocker, protects against the brain injury induced by middle cerebral artery occlusion and reperfusion in mice

We tested whether NNC 55-0396 (NNC), a T-type calcium channel (T-channel) blocker, reduces the brain injury caused by middle cerebral artery occlusion and reperfusion (MCAO/R) in mice. NNC, administered i.c.v. before the occlusion, greatly reduced the MCAO/R-induced brain infarct and neurological dysfunctions, although it, given toward the end of occlusion, was less effective. Systemic administration of NNC before the occlusion also attenuated the infarct and neurological dysfunctions. Our data imply that blood-brain-barrier-permeable T-channel blockers such as NNC are capable of reducing MCAO/R-induced brain damage, and that T-channels are involved in neuronal damage induced by ischemia rather than reperfusion.

Chronic Administration of Pimozide Fails to Attenuate Motor and Pathological Deficits in Two Mouse Models of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease which presently does not have any efficient therapeutic approach. Pimozide, a Food and Drug Administration (FDA)-approved neuroepileptic drug, has been recently proposed as a promising treatment for ALS patients based on apparent stabilization of right hand muscles after a short-time administration. A new clinical trial started at the end of 2017 to recruit patients with a prolonged drug delivery schedule. Here, our aim was to investigate the effects of chronic administration of pimozide on disease progression and pathological events in two mouse models of ALS. Pimozide was administered every 2 days to transgenic mice bearing the ALS-linked A315T mutation on the human TAR DNA-binding protein 43 (TDP-43) gene and to mice carrying the human superoxide dismutase 1 (SOD1) gene with the ALS-linked G93A mutation. Chronic administration of pimozide exacerbated motor performances in both animal models and reduced survival in SOD1G93A mice. In TDP-43A315T, it decreased the percentage of innervated neuromuscular junctions (NMJs) and increased the accumulation of insoluble TDP-43. In SOD1G93A mice, pimozide had no effects on NMJ innervation or motoneuron loss, but it increased the levels of misfolded SOD1. We conclude that a chronic administration of pimozide did not confer beneficial effects on disease progression in two mouse models of ALS. In light of a new clinical trial on ALS patients with a chronic regime of pimozide, these results with mouse models suggest prudence and careful monitoring of ALS patients subjected to pimozide treatment.

Neuroleptics as therapeutic compounds stabilizing neuromuscular transmission in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, fatal disorder with no effective treatment. We used simple genetic models of ALS to screen phenotypically for potential therapeutic compounds. We screened libraries of compounds in C. elegans, validated hits in zebrafish, and tested the most potent molecule in mice and in a small clinical trial. We identified a class of neuroleptics that restored motility in C. elegans and in zebrafish, and the most potent was pimozide, which blocked T-type Ca2+ channels in these simple models and stabilized neuromuscular transmission in zebrafish and enhanced it in mice. Finally, a short randomized controlled trial of sporadic ALS subjects demonstrated stabilization of motility and evidence of target engagement at the neuromuscular junction. Simple genetic models are, thus, useful in identifying promising compounds for the treatment of ALS, such as neuroleptics, which may stabilize neuromuscular transmission and prolong survival in this disease.

The T-type calcium channel enhancer SAK3 inhibits neuronal death following transient brain ischemia via nicotinic acetylcholine receptor stimulation

The T-type calcium channel enhancer SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo[1,2-a]pyridin]-2-ene-3-carboxylate) promotes acetylcholine (ACh) release in mouse hippocampus, enhancing cognitive function. Here, we tested SAK3 neuroprotective activity in the context of transient brain ischemia using a 20-min bilateral common carotid arteries occlusion (BCCAO) mouse model. Mice were administered with SAK3 (0.1, 0.5 or 1.0 mg/kg, p.o.) 24 h after BCCAO ischemia. Oral SAK3 (0.5 or 1.0 mg/kg/day, p.o.) administration significantly blocked loss of hippocampal CA1 neurons and memory deficits seen in BCCAO mice. Treatment with α7 nicotinic ACh receptor (nAChR)-selective inhibitor methyllycaconitine (MLA: 6.0 mg/kg/day, i.p.) significantly antagonized both neuroprotection and improvement in memory promoted by SAK3 (0.5 mg/kg/day, p.o.). Acute SAK3 (0.5 mg/kg, p.o.) administration significantly enhanced protein kinase B (Akt) phosphorylation levels in CA1 of control and BCCAO mice. Importantly, treatment of control and BCCAO mice with the non-selective nAChR antagonist mecamylamine (MEC: 1.0 mg/kg, i.p.) or the α7-selective nAChR antagonist MLA (6.0 mg/kg, i.p.), but not the M1 muscarinic ACh receptor (mAChR) antagonist pirenzepine (PZ: 10 mg/kg, i.p.), blocked enhanced Akt activity elicited by SAK3 (0.5 mg/kg, p.o.). We also confirmed that decreased phosphorylated Akt immunoreactivities were rescued by SAK3 (0.5 mg/kg, p.o.) administration in NeuN-positive CA1 neurons of BCCAO mice, an effect blocked by MLA (6.0 mg/kg, i.p.). Finally, we observed α7 nAChR and phosphorylated Akt expression in CA1 pyramidal neurons. We conclude that the T-type calcium channel enhancer SAK3 is neuroprotective in the context of brain ischemia by stimulating nicotinic cholinergic neurotransmission.

Activity-dependent regulation of T-type calcium channels by submembrane calcium ions

Voltage-gated Ca²⁺ channels are involved in numerous physiological functions and various mechanisms finely tune their activity, including the Ca²⁺ ion itself. This is well exemplified by the Ca²⁺-dependent inactivation of L-type Ca²⁺ channels, whose alteration contributes to the dramatic disease Timothy Syndrome. For T-type Ca²⁺ channels, a long-held view is that they are not regulated by intracellular Ca²⁺. Here we challenge this notion by using dedicated electrophysiological protocols on both native and expressed T-type Ca²⁺ channels. We demonstrate that a rise in submembrane Ca²⁺ induces a large decrease in T-type current amplitude due to a hyperpolarizing shift in the steady-state inactivation. Activation of most representative Ca²⁺-permeable ionotropic receptors similarly regulate T-type current properties. Altogether, our data clearly establish that Ca²⁺ entry exerts a feedback control on T-type channel activity, by modulating the channel availability, a mechanism that critically links cellular properties of T-type Ca²⁺ channels to their physiological roles.

DOI:http://dx.doi.org/10.7554/eLife.22331.001

Neurons, muscle cells and many other types of cells use electrical signals to exchange information and coordinate their behavior. Proteins known as calcium channels sit in the membrane that surrounds the cell and can generate electrical signals by allowing calcium ions to cross the membrane and enter the cell during electrical activities. Although calcium ions are needed to generate these electrical signals, and for many other processes in cells, if the levels of calcium ions inside cells become too high they can be harmful and cause disease.

Cells have a “feedback” mechanism that prevents calcium ion levels from becoming too high. This mechanism relies on the calcium ions that are already in the cell being able to close the calcium channels. This feedback mechanism has been extensively studied in two types of calcium channel, but it is not known whether a third group of channels – known as Cav3 channels – are also regulated in this way.

Cav3 channels are important in electrical signaling in neurons and have been linked with epilepsy, chronic pain and various other conditions in humans. Cazade et al. investigated whether calcium ions can regulate the activity of human Cav3 channels. The experiments show that these channels are indeed regulated by calcium ions, but using a distinct mechanism to other types of calcium channels. For the Cav3 channels, calcium ions alter the gating properties of the channels so that they are less easily activated . As a result, fewer Cav3 channels are “available” to provide calcium ions with a route into the cell.

The next steps following on from this work will be to identify the molecular mechanisms underlying this new feedback mechanism. Another challenge will be to find out what role this calcium ion-driven feedback plays in neurological disorders that are linked with altered Cav3 channel activity.

DOI:http://dx.doi.org/10.7554/eLife.22331.002

T-type calcium channel blockers as neuroprotective agents

T-type calcium channels are expressed in many diverse tissues, including neuronal, cardiovascular, and endocrine. T-type calcium channels are known to play roles in the development, maintenance, and repair of these tissues but have also been implicated in disease when not properly regulated. Calcium channel blockers have been developed to treat various diseases and their use clinically is widespread due to both their efficacy as well as their safety. Aside from their established clinical applications, recent studies have suggested neuroprotective effects of T-type calcium channel blockers. Many of the current T-type calcium channel blockers could act on other molecular targets besides T-type calcium channels making it uncertain whether their neuroprotective effects are solely due to blocking of T-type calcium channels. In this review, we discuss these drugs as well as newly developed chemical compounds that are designed to be more selective for T-type calcium channels. We review in vitro and in vivo evidence of neuroprotective effects by these T-type calcium channel blockers. We conclude by discussing possible molecular mechanisms underlying the neuroprotective effects by T-type calcium channel blockers.

The changing landscape of voltage-gated calcium channels in neurovascular disorders and in neurodegenerative diseases

It is a common belief that voltage-gated calcium channels (VGCC) cannot carry toxic amounts of Ca²⁺ in neurons. Also, some of them as L-type channels are essential for Ca²⁺-dependent regulation of prosurvival gene-programs. However, a wealth of data show a beneficial effect of drugs acting on VGCCs in several neurodegenerative and neurovascular diseases. In the present review, we explore several mechanisms by which the “harmless” VGCCs may become “toxic” for neurons. These mechanisms could explain how, though usually required for neuronal survival, VGCCs may take part in neurodegeneration. We will present evidence showing that VGCCs can carry toxic Ca²⁺ when: a) their density or activity increases because of aging, chronic hypoxia or exposure to β-amyloid peptides or b) Ca²⁺-dependent action potentials carry high Ca²⁺ loads in pacemaker neurons. Besides, we will examine conditions in which VGCCs promote neuronal cell death without carrying excess Ca²⁺. This can happen, for instance, when they carry metal ions into the neuronal cytoplasm or when a pathological decrease in their activity weakens Ca²⁺-dependent prosurvival gene programs. Finally, we will explore the role of VGCCs in the control of nonneuronal cells that take part to neurodegeneration like those of the neurovascular unit or of microglia.

Mitochondrial Ca2+ uptake from plasma membrane Cav3.2 protein channels contributes to ischemic toxicity in PC12 cells

T-type Ca(2+) channel inhibitors protect hippocampal CA1 neurons from delayed death after global ischemia in rats, suggesting that Cav3.1, Cav3.2, or Cav3.3 channels generate cytotoxic Ca(2+) elevations during anoxia. To test this hypothesis, we measured the Ca(2+) concentration changes evoked by oxygen and glucose deprivation (OGD) in the cytosol and in the mitochondria of PC12 cells. OGD evoked long-lasting cytosolic Ca(2+) elevations that were reduced by Cav3.2 inhibition (50 μm Ni(2+)) and Cav3.1/Cav3.2 silencing and potentiated by Cav3.2 overexpression. The kinetics of the sustained cytosolic Ca(2+) elevations occurring during OGD directly correlated to the extent of cell death measured 20 h after reoxygenation, which was decreased by Ni(2+) and Cav3.1/Cav3.2 silencing and increased by Cav3.2 overexpression. Ni(2+) and Cav3.1/Cav3.2 silencing delayed the decline of cellular ATP during OGD, consistent with a reduction in the Ca(2+) load actively extruded by plasma membrane Ca(2+) pumps. The cytosolic Ca(2+) elevations were paralleled by mitochondrial Ca(2+) elevations that were also increased by Cav3.2 overexpression and decreased by Ni(2+) but not by Cav3.1/Cav3.2 silencing. Overexpression and silencing of the mitochondrial Ca(2+) uniporter, the major mitochondrial Ca(2+) uptake protein, revealed that the cytotoxicity was correlated to the amplitude of the mitochondrial, rather than the cytosolic, Ca(2+) elevations. Selective activation of T-type Ca(2+) channels evoked both cytosolic and mitochondrial Ca(2+) elevations, but only the mitochondrial responses were reduced by Cav3.1/Cav3.2 silencing. We conclude that the opening of Cav3.2 channels during ischemia contribute to the entry of Ca(2+) ions that are transmitted to mitochondria, resulting in a deleterious mitochondrial Ca(2+) overload.

Calcium and potassium channels in experimental subarachnoid hemorrhage and transient global ischemia

Healthy cerebrovascular myocytes express members of several different ion channel families which regulate resting membrane potential, vascular diameter, and vascular tone and are involved in cerebral autoregulation. In animal models, in response to subarachnoid blood, a dynamic transition of ion channel expression and function is initiated, with acute and long-term effects differing from each other. Initial hypoperfusion after exposure of cerebral vessels to oxyhemoglobin correlates with a suppression of voltage-gated potassium channel activity, whereas delayed cerebral vasospasm involves changes in other potassium channel and voltage-gated calcium channels expression and function. Furthermore, expression patterns and function of ion channels appear to differ between main and small peripheral vessels, which may be key in understanding mechanisms behind subarachnoid hemorrhage-induced vasospasm. Here, changes in calcium and potassium channel expression and function in animal models of subarachnoid hemorrhage and transient global ischemia are systematically reviewed and their clinical significance discussed.

The Discovery and Characterization of ML218: A Novel, Centrally Active T-Type Calcium Channel Inhibitor with Robust Effects in STN Neurons and in a Rodent Model of Parkinson's Disease

T-type Ca(2+) channel inhibitors hold tremendous therapeutic potential for the treatment of pain, epilepsy, sleep disorders, essential tremor and other neurological disorders; however, a lack of truly selective tools has hindered basic research, and selective tools from the pharmaceutical industry are potentially burdened with intellectual property (IP) constraints. Thus, an MLPCN high-throughput screen (HTS) was conducted to identify novel T-type Ca(2+) channel inhibitors free from IP constraints, and freely available through the MLPCN, for use by the biomedical community to study T-type Ca(2+) channels. While the HTS provided numerous hits, these compounds could not be optimized to the required level of potency to be appropriate tool compounds. Therefore, a scaffold hopping approach, guided by SurflexSim, ultimately afforded ML218 (CID 45115620) a selective T-Type Ca(2+) (Ca(v)3.1, Ca(v)3.2, Ca(v)3.3) inhibitor (Ca(v)3.2, IC(50) = 150 nM in Ca(2+) flux; Ca(v)3.2 IC(50) = 310 nM and Ca(v)3.3 IC(50) = 270 nM, respectively in patch clamp electrophysiology) with good DMPK properties, acceptable in vivo rat PK and excellent brain levels. Electrophysiology studies in subthalamic nucleus (STN) neurons demonstrated robust effects of ML218 on the inhibition of T-Type calcium current, inhibition of low threshold spike and rebound burst activity. Based on the basal ganglia circuitry in Parkinson's disease (PD), the effects of ML218 in STN neurons suggest a therapeutic role for T-type Ca(2+) channel inhibitors, and ML218 was found to be orally efficacious in haloperidol-induced catalepsy, a preclinical PD model, with comparable efficacy to an A(2A) antagonist, a clinically validated PD target. ML218 proves to be a powerful new probe to study T-Type Ca(2+) function in vitro and in vivo, and freely available.