Protective effects of a selective L-type voltage-sensitive calcium channel blocker, S-312-d, on neuronal cell death

Targeting calciumopathy for neuroprotection: focus on calcium channels Cav1, Orai1 and P2X7

As the uncontrolled entry of calcium ions (Ca2+) through plasmalemmal calcium channels is a cell death trigger, the conjecture is here raised that mitigating such an excess of Ca2+ entry should rescue from death the vulnerable neurons in neurodegenerative diseases (NDDs). However, this supposition has failed in some clinical trials (CTs). Thus, a recent CT tested whether isradipine, a blocker of the Cav1 subtype of voltage-operated calcium channels (VOCCs), exerted a benefit in patients with Parkinson's disease (PD); however, outcomes were negative. This is one more of the hundreds of CTs done under the principle of one-drug-one-target, that have failed in Alzheimer's disease (AD) and other NDDs during the last three decades. As there are myriad calcium channels to let Ca2+ ions gain the cell cytosol, it seems reasonable to predict that blockade of Ca2+ entry through a single channel may not be capable of preventing the Ca2+ flood of cells by the uncontrolled Ca2+ entry. Furthermore, as Ca2+ signaling is involved in the regulation of myriad functions in different cell types, it seems also reasonable to guess that a therapy should be more efficient by targeting different cells with various drugs. Here, we propose to mitigate Ca2+ entry by the simultaneous partial blockade of three quite different subtypes of plasmalemmal calcium channels that is, the Cav1 subtype of VOCCs, the Orai1 store-operated calcium channel (SOCC), and the purinergic P2X7 calcium channel. All three channels are expressed in both microglia and neurons. Thus, by targeting the three channels with a combination of three drug blockers we expect favorable changes in some of the pathogenic features of NDDs, namely (i) to mitigate Ca2+ entry into microglia; (ii) to decrease the Ca2+-dependent microglia activation; (iii) to decrease the sustained neuroinflammation; (iv) to decrease the uncontrolled Ca2+ entry into neurons; (v) to rescue vulnerable neurons from death; and (vi) to delay disease progression. In this review we discuss the arguments underlying our triad hypothesis in the sense that the combination of three repositioned medicines targeting Cav1, Orai1, and P2X7 calcium channels could boost neuroprotection and delay the progression of AD and other NDDs.

Neuro-Restorative Effect of Nimodipine and Calcitriol in 1-Methyl 4-Phenyl 1,2,3,6 Tetrahydropyridine-Induced Zebrafish Parkinson's Disease Model

OBJECTIVE

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The treatment of PD aims to alleviate motor symptoms by replacing the reduced endogenous dopamine. Currently, there are no disease-modifying agents for the treatment of PD. Zebrafish (Danio rerio) have emerged as an effective tool for new drug discovery and screening in the age of translational research. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to cause a similar loss of dopaminergic neurons in the human midbrain, with corresponding Parkinsonian symptoms. L-type calcium channels (LTCCs) have been implicated in the generation of mitochondrial oxidative stress, which underlies the pathogenesis of PD. Therefore, we investigated the neuro-restorative effect of LTCC inhibition in an MPTP-induced zebrafish PD model and suggested a possible drug candidate that might modify the progression of PD.

METHODS

All experiments were conducted using a line of transgenic zebrafish, Tg(dat:EGFP), in which green fluorescent protein (GFP) is expressed in dopaminergic neurons. The experimental groups were exposed to 500 μmol MPTP from 1 to 3 days post fertilization (dpf). The drug candidates : levodopa 1 mmol, nifedipine 10 μmol, nimodipine 3.5 μmol, diethylstilbestrol 0.3 μmol, luteolin 100 μmol, and calcitriol 0.25 μmol were exposed from 3 to 5 dpf. Locomotor activity was assessed by automated tracking and dopaminergic neurons were visualized in vivo by confocal microscopy.

RESULTS

Levodopa, nimodipine, diethylstilbestrol, and calcitriol had significant positive effects on the restoration of motor behavior, which was damaged by MPTP. Nimodipine and calcitriol have significant positive effects on the restoration of dopaminergic neurons, which were reduced by MPTP. Through locomotor analysis and dopaminergic neuron quantification, we identified the neuro-restorative effects of nimodipine and calcitriol in zebrafish MPTP-induced PD model.

CONCLUSION

The present study identified the neuro-restorative effects of nimodipine and calcitriol in an MPTP-induced zebrafish model of PD. They restored dopaminergic neurons which were damaged due to the effects of MPTP and normalized the locomotor activity. LTCCs have potential pathological roles in neurodevelopmental and neurodegenerative disorders. Zebrafish are highly amenable to high-throughput drug screening and might, therefore, be a useful tool to work towards the identification of diseasemodifying treatment for PD. Further studies including zebrafish genetic models to elucidate the mechanism of action of the diseasemodifying candidate by investigating Ca2+ influx and mitochondrial function in dopaminergic neurons, are needed to reveal the pathogenesis of PD and develop disease-modifying treatments for PD.

The relationship of salusins with Parkinson's Disease, Alzheimer's Disease, and acute ischemic stroke: A preliminary study

Neuroinflammation, oxidative stress, and apoptosis play important roles in the pathophysiology of Alzheimer's Disease (AD), Parkinson's Disease (PD), and Acute Ischemic Stroke (AIS). Salusin-α and salusin-β peptides, which were shown to be present in many tissues, including the central nervous system, were also shown to be associated with apoptosis, inflammation, and oxidative stress. In the present study, the relationship between Salusin-α and salusin-β peptides and AD, PD, and AIS were investigated. A total of 179 people were included in the present study, including 46 AD, 44 PD, 42 AIS, and 47 controls. Plasma Salusin-α and salusin-β levels were measured with the ELISA Method. The plasma salusin-β levels of AD, PD, and AIS patients were lower than the control group at significant levels (p < 0.05). It was also found that there were correlations between salusin-α and salusin-β levels and age, triglyceride, LDL-c, total cholesterol, and hemoglobin levels. In this study, we found that salusin- β, an endogenous neuropeptide, was associated with AD, PD and AIS. The low level of salusin-β in these diseases in which neuronal damage occurs may be related to the neuroprotective properties of this endogenous peptide. Further studies are needed to fully understand the relationship between salusin-β and the pathophysiology of these diseases.

Delineation of Neuroprotective Effects and Possible Benefits of AntioxidantsTherapy for the Treatment of Alzheimer's Diseases by Targeting Mitochondrial-Derived Reactive Oxygen Species: Bench to Bedside

Alzheimer's disease (AD) is considered the sixth leading cause of death in elderly patients and is characterized by progressive neuronal degeneration and impairment in memory, language, etc. AD is characterized by the deposition of senile plaque, accumulation of fibrils, and neurofibrillary tangles (NFTs) which are responsible for neuronal degeneration. Amyloid-β (Aβ) plays a key role in the process of neuronal degeneration in the case of AD. It has been reported that Aβ is responsible for the production of reactive oxygen species (ROS), depletion of endogenous antioxidants, increase in intracellular Ca²⁺ which further increases mitochondria dysfunctions, oxidative stress, release of pro-apoptotic factors, neuronal apoptosis, etc. Thus, oxidative stress plays a key role in the pathogenesis of AD. Antioxidants are compounds that have the ability to counteract the oxidative damage conferred by ROS. Therefore, the antioxidant therapy may provide benefits and halt the progress of AD to advance stages by counteracting neuronal degeneration. However, despite the beneficial effects imposed by the antioxidants, the findings from the clinical studies suggested inconsistent results which might be due to poor study design, selection of the wrong antioxidant, inability of the molecule to cross the blood-brain barrier (BBB), treatment in the advanced state of disease, etc. The present review insights into the neuroprotective effects and limitations of the antioxidant therapy for the treatment of AD by targeting mitochondrial-derived ROS. This particular article will certainly help the researchers to search new avenues for the treatment of AD by utilizing mitochondrial-derived ROS-targeted antioxidant therapies.

Ca2+-permeable TRPV1 pain receptor knockout rescues memory deficits and reduces amyloid-β and tau in a mouse model of Alzheimer's disease

The transient receptor potential vanilloid 1 (TRPV1) protein is a pain receptor that elicits a hot sensation when an organism eats the capsaicin of red chili peppers. This calcium (Ca2+)-permeable cation channel is mostly expressed in the peripheral nervous system sensory neurons but also in the central nervous system (e.g. hippocampus and cortex). Preclinical studies found that TRPV1 mediates behaviors associated with anxiety and depression. Loss of TRPV1 functionality increases expression of genes related to synaptic plasticity and neurogenesis. Thus, we hypothesized that TRPV1 deficiency may modulate Alzheimer's disease (AD). We generated a triple-transgenic AD mouse model (3xTg-AD+/+) with wild-type (TRPV1+/+), hetero (TRPV1+/-) and knockout (TRPV1-/-) TRPV1 to investigate the role of TRPV1 in AD pathogenesis. We analyzed the animals' memory function, hippocampal Ca2+ levels and amyloid-β (Aβ) and tau pathologies when they were 12 months old. We found that compared with 3xTg-AD-/-/TRPV1+/+ mice, 3xTg-AD+/+/TRPV1+/+ mice had memory impairment and increased levels of hippocampal Ca2+, Aβ and total and phosphorylated tau. However, 3xTg-AD+/+/TRPV1-/- mice had better memory function and lower levels of hippocampal Ca2+, Aβ, tau and p-tau, compared with 3xTg-AD+/+/TRPV1+/+ mice. Examination of 3xTg-AD-derived primary neuronal cultures revealed that the intracellular Ca2+ chelator BAPTA/AM and the TRPV1 antagonist capsazepine decreased the production of Aβ, tau and p-tau. Taken together, these results suggested that TRPV1 deficiency had anti-AD effects and promoted resilience to memory loss. These findings suggest that drugs or food components that modulate TRPV1 could be exploited as therapeutics to prevent or treat AD.

Association between chronic kidney disease and Alzheimer's disease: an update

It has been accepted that kidney function is connected with brain activity. In clinical studies, chronic kidney disease (CKD) patients have been found to be prone to suffering cognitive decline and Alzheimer's disease (AD). The cognitive function of CKD patients may improve after kidney transplantation. All these indicators show a possible link between kidney function and dementia. However, little is known about the mechanism behind the relation of CKD and AD. This review discusses the associations between CKD and AD from the perspective of the pathophysiology of the kidney and complications and/or concomitants of CKD that may lead to cognitive decline in the progression of CKD and AD. Potential preventive and therapeutic strategies for AD are also presented. Further studies are warranted in order to confirm whether the setting of CKD is a possible new determinant for cognitive impairment in AD.

Alterations of Calcium Channels in a Mouse Model of Huntington's Disease and Neuroprotection by Blockage of CaV1 Channels

Huntington’s disease (HD) is a neurodegenerative autosomal dominant disorder, characterized by symptoms of involuntary movement of the body, loss of cognitive function, psychiatric disorder, leading inevitably to death. It has been previously described that higher levels of brain expression of Cav1 channels are involved in major neurodegenerative disorders, such as Alzheimer’s disease and Parkinson’s disease. Our results demonstrate that a bacterial artificial chromosome (BAC)-mediated transgenic mouse model (BACHD mice) at the age of 3 and 12 months exhibits significantly increased Cav1.2 protein levels in the cortex, as compared with wild-type littermates. Importantly, electrophysiological analyses confirm a significant increase in L-type Ca2+ currents and total Ca2+ current density in cortical neurons from BACHD mice. By using an in vitro assay to measure neuronal cell death, we were able to observe neuronal protection against glutamate toxicity after treatment with Cav1 blockers, in wild-type and, more importantly, in BACHD neurons. According to our data, Cav1 blockers may offer an interesting strategy for the treatment of HD. Altogether, our results show that mutant huntingtin (mHtt) expression may cause a dysregulation of Cav1.2 channels and we hypothesize that this contributes to neurodegeneration during HD.

Role of GPCR signaling and calcium dysregulation in Alzheimer's disease

Alzheimer's disease (AD), a late onset neurodegenerative disorder is characterized by the loss of memory, disordered cognitive function, caused by accumulation of amyloid-β (Aβ) peptide and neurofibrillary tangles (NFTs) in the neocortex and hippocampal brain area. Extensive research has been done on the findings of the disease etiology or pathological causes of aggregation of Aβ and hyperphosphorylation of tau protein without much promising results. Recently, calcium dysregulation has been reported to play an important role in the pathophysiology of AD. Calcium ion acts as one of the major secondary messengers, regulates many signaling pathways involved in cell survival, proliferation, differentiation, transcription and apoptosis. Calcium signaling is one of the major signaling pathways involved in the formation of memory, generation of energy and other physiological functions. It also can modulate function of many proteins upon binding. Dysregulation in calcium homeostasis leads to many physiological changes leading to neurodegenerative diseases including AD. In AD, GPCRs generate secondary messengers which regulate calcium homeostasis inside the cell and is reported to be disturbed in the pathological condition. Calcium channels and receptors present on the plasma membrane and intracellular organelle maintain calcium homeostasis through different signaling mechanisms. In this review, we have summarized the different calcium channels and receptors involved in calcium dysregulation which in turn play a critical role in the pathogenesis of AD. Understanding the role of calcium channels and GPCRs to maintain calcium homeostasis is an attempt to develop effective AD treatments.

Calcium signaling in Alzheimer's disease & therapies

Alzheimer's disease (AD) is the most common type of dementia and is characterized by the accumulation of amyloid (Aβ) plaques and neurofibrillary tangles in the brain. Much attention has been given to develop AD treatments based on the amyloid cascade hypothesis; however, none of these drugs had good efficacy at improving cognitive functions in AD patients suggesting that Aβ might not be the disease origin. Thus, there are urgent needs for the development of new therapies that target on the proximal cause of AD. Cellular calcium (Ca²⁺) signals regulate important facets of neuronal physiology. An increasing body of evidence suggests that age-related dysregulation of neuronal Ca²⁺ homeostasis may play a proximal role in the pathogenesis of AD as disrupted Ca²⁺ could induce synaptic deficits and promote the accumulation of Aβ plaques and neurofibrillary tangles. Given that Ca²⁺ disruption is ubiquitously involved in all AD pathologies, it is likely that using chemical agents or small molecules specific to Ca²⁺ channels or handling proteins on the plasma membrane and membranes of intracellular organelles to correct neuronal Ca²⁺ dysregulation could open up a new approach to AD prevention and treatment. This review summarizes current knowledge on the molecular mechanisms linking Ca²⁺ dysregulation with AD pathologies and discusses the possibility of correcting neuronal Ca²⁺ disruption as a therapeutic approach for AD.

Mitochondrial Aspects of Synaptic Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by brain deposition of amyloid plaques and tau neurofibrillary tangles along with steady cognitive decline. Synaptic damage, an early pathological event, correlates strongly with cognitive deficits and memory loss. Mitochondria are essential organelles for synaptic function. Neurons utilize specialized mechanisms to drive mitochondrial trafficking to synapses in which mitochondria buffer Ca2+ and serve as local energy sources by supplying ATP to sustain neurotransmitter release. Mitochondrial abnormalities are one of the earliest and prominent features in AD patient brains. Amyloid-β (Aβ) and tau both trigger mitochondrial alterations. Accumulating evidence suggests that mitochondrial perturbation acts as a key factor that is involved in synaptic failure and degeneration in AD. The importance of mitochondria in supporting synaptic function has made them a promising target of new therapeutic strategies for AD. Here, we review the molecular mechanisms regulating mitochondrial function at synapses, highlight recent findings on the disturbance of mitochondrial dynamics and transport in AD, and discuss how these alterations impact synaptic vesicle release and thus contribute to synaptic pathology associated with AD.

Neurotransmitters in the mediation of cerebral ischemic injury

Under physiological conditions, neurotransmitters shape neuronal networks and control several cellular and synaptic functions. In the mammalian central nervous system (CNS), excitatory and inhibitory neurotransmission are mediated in large part by glutamate and gamma-aminobutyric acid (GABA), which are excitatory and inhibitory neurotransmitters, respectively. Glutamate and GABA also play crucial roles in neurological disorders such as cerebral ischemia. Glutamate in particular causes excitotoxicity, known as one of the hallmark mechanisms in the pathophysiology of cerebral ischemic injury for more than thirty years. Excitotoxicity occurs due to excessive glutamate release leading to overactivation of postsynaptic glutamate receptors, which evokes a downstream cascade that eventually leads to neuronal dysfunction and degeneration. Also, a reduction in GABA receptor response after ischemia impedes these inhibitory effectors from attenuating excitotoxicity and thereby further enabling the excitotoxic insult. This review focuses on the mechanisms by which glutamate and GABA mediate excitotoxicity and ischemic injury. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Inhibitory Effect of Lychee Seed Saponins on Apoptosis Induced by Aβ25-35 through Regulation of the Apoptotic and NF-κB Pathways in PC12 Cells

Neuronal apoptosis plays a critical role in the pathogenesis of Alzheimer's disease (AD). Previous studies have shown that lychee seed saponins (LSS), isolated and extracted from traditional Chinese medicine lychee seeds, possess many beneficial activities including anti-oxidation, anti-diabetes, anti-AD, etc. In the present study, we established an in vitro neuronal apoptotic model of PC12 cells induced by Aβ25-35 and studied the effect of LSS on apoptosis by the methods of Hoechst 33342/propidium iodide (PI) fluorescence double staining, Annexin V/PI double staining, and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL). We also investigated the effects of LSS on mitochondria membrane potential, the expressions of Bcl-2 and Bax proteins, and the mRNA expression and the nuclear translocation of NF-κBp65 in PC12 cells. The results showed that LSS markedly inhibited apoptosis, improved the mitochondria membrane potentials, upregulated the expression of Bcl-2 protein, downregulated the expression of Bax protein, and decreased the mRNA expression and nuclear translocation of NF-κBp65 in PC12 cells. The study demonstrated that LSS significantly inhibited apoptosis induced by Aβ25-35 via regulation of the apoptotic and NF-κB pathways in PC12 cells. Therefore, LSS has the potential to be developed as a novel agent or nutrient supplement for the prevention and/or treatment of AD.

L-type Ca2+ currents at CA1 synapses, but not CA3 or dentate granule neuron synapses, are increased in 3xTgAD mice in an age-dependent manner

Abnormal neuronal excitability and impaired synaptic plasticity might occur before the degeneration and death of neurons in Alzheimer's disease (AD). To elucidate potential biophysical alterations underlying aberrant neuronal network activity in AD, we performed whole-cell patch clamp analyses of L-type (nifedipine-sensitive) Ca(2+) currents (L-VGCC), 4-aminopyridine-sensitive K(+) currents, and AMPA (2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid) and NMDA (N-methyl-D-aspartate) currents in CA1, CA3, and dentate granule neurons in hippocampal slices from young, middle-age, and old 3xTgAD mice and age-matched wild type mice. 3xTgAD mice develop progressive widespread accumulation of amyloid β-peptide, and selective hyperphosphorylated tau pathology in hippocampal CA1 neurons, which are associated with cognitive deficits, but independent of overt neuronal degeneration. An age-related elevation of L-type Ca(2+) channel current density occurred in CA1 neurons in 3xTgAD mice, but not in wild type mice, with the magnitude being significantly greater in older 3xTgAD mice. The NMDA current was also significantly elevated in CA1 neurons of old 3xTgAD mice compared with in old wild type mice. There were no differences in the amplitude of K(+) or AMPA currents in CA1 neurons of 3xTgAD mice compared with wild type mice at any age. There were no significant differences in Ca(2+), K(+), AMPA, or NMDA currents in CA3 and dentate neurons from 3xTgAD mice compared with wild type mice at any age. Our results reveal an age-related increase of L-VGCC density in CA1 neurons, but not in CA3 or dentate granule neurons, of 3xTgAD mice. These findings suggest a potential contribution of altered L-VGCC to the selective vulnerability of CA1 neurons to tau pathology in the 3xTgAD mice and to their degeneration in AD patients.

Mechanisms, treatment and prevention of cellular injury and death from delayed events after aneurysmal subarachnoid hemorrhage

INTRODUCTION

Subarachnoid hemorrhage (SAH) patients often develop brain injury as a result of a number of delayed complications, resulting in significant morbidity and mortality. Many of these complications arise due to delayed cerebral ischemia, which occurs secondary to the hemorrhage.

AREAS COVERED

The mechanisms of the delayed injury are reviewed, including angiographic vasospasm, cortical spreading ischemia, small arteriolar constriction, microthromboemboli, free radical injury and inflammation. Some current and prospective therapies for SAH are discussed, in the context of these complications. Statins have been particularly promising in experimental studies.

EXPERT OPINION

Multiple mechanisms are involved in the pathogenesis of the delayed insult after SAH. New drugs may need to target multiple pathways to injury. Trials aiming to treat complications after SAH could benefit from taking into account the multifactorial pathogenesis of delayed insults.

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.

Neurotoxicity induced by bupivacaine via T-type calcium channels in SH-SY5Y cells

There is concern regarding neurotoxicity induced by the use of local anesthetics. A previous study showed that an overload of intracellular calcium is involved in the neurotoxic effect of some anesthetics. T-type calcium channels, which lower the threshold of action potentials, can regulate the influx of calcium ions. We hypothesized that T-type calcium channels are involved in bupivacaine-induced neurotoxicity. In this study, we first investigated the effects of different concentrations of bupivacaine on SH-SY5Y cell viability, and established a cell injury model with 1 mM bupivacaine. The cell viability of SH-SY5Y cells was measured following treatment with 1 mM bupivacaine and/or different dosages (10, 50, or 100 µM) of NNC 55-0396 dihydrochloride, an antagonist of T-type calcium channels for 24 h. In addition, we monitored the release of lactate dehydrogenase, cytosolic Ca²⁺ ([Ca2+]_i), cell apoptosis and caspase-3 expression. SH-SY5Y cells pretreated with different dosages (10, 50, or 100 µM) of NNC 55-0396 dihydrochloride improved cell viability, reduced lactate dehydrogenase release, inhibited apoptosis, and reduced caspase-3 expression following bupivacaine exposure. However, the protective effect of NNC 55-0396 dihydrochloride plateaued. Overall, our results suggest that T-type calcium channels may be involved in bupivacaine neurotoxicity. However, identification of the specific subtype of T calcium channels involved requires further investigation.

Ca(2+) channel currents of cortical neurons from pure and mixed cultures

Voltage-gated Ca(2+) channels (VGCCs) are key regulators of many neuronal functions, and involved in multiple central nervous system diseases. In the last 30 years, a large number of injury and disease models have been established based on cultured neurons. Culture with serum develops a mixture of neurons and glial cells, while culture without serum develops pure neurons. Both of these neuronal-culture methods are widely used. However, the properties of Ca(2+) currents in neurons from these two cultures have not been compared. In this study, we cultured rat cortical neurons in serum-containing or -free medium and then recorded the Ca(2+) channel currents using patch-clamp technique. Our results showed that there were significant differences in the amplitude and activation properties of whole-cell Ca(2+) channel currents, and of non-L-type Ca(2+) channel currents between the neurons from these two culture systems. Our data suggested that the difference of whole-cell Ca(2+) currents may result from the differences in non-L-type currents. Understanding of these properties will considerably advance studies of VGCCs in neurons from pure or mixed culture.

The role of glutamate in neuronal ischemic injury: the role of spark in fire

Although being a physiologically important excitatory neurotransmitter, glutamate plays a pivotal role in various neurological disorders including ischemic neurological diseases. Its level is increased during cerebral ischemia with excessive neurological stimulation causing the glutamate-induced neuronal toxicity, excitotoxicity, and this is considered the triggering spark in the ischemic neuronal damage. The glutamatergic stimulation will lead to rise in the intracellular sodium and calcium, and the elevated intracellular calcium will lead to mitochondrial dysfunction, activation of proteases, accumulation of reactive oxygen species and release of nitric oxide. Interruption of the cascades of glutamate-induced cell death during ischemia may provide a way to prevent, or at least reduce, the ischemic damage. Various therapeutic options are suggested interrupting the glutamatergic pathways, e.g., inhibiting the glutamate synthesis or release, increasing its clearance, blocking of its receptors or preventing the rise in intracellular calcium. Development of these strategies may provide future treatment options in the management of ischemic stroke.

Effects of amyloid-β peptides on voltage-gated L-type Ca(V)1.2 and Ca(V)1.3 Ca(2+) channels

Overload of intracellular Ca(2+) has been implicated in the pathogenesis of neuronal disorders, such as Alzheimer's disease. Various mechanisms produce abnormalities in intracellular Ca(2+) homeostasis systems. L-type Ca(2+) channels have been known to be closely involved in the mechanisms underlying the neurodegenerative properties of amyloid-β (Aβ) peptides. However, most studies of L-type Ca(2+) channels in Aβ-related mechanisms have been limited to Ca(V)1.2, and surprisingly little is known about the involvement of Ca(V)1.3 in Aβ-induced neuronal toxicity. In the present study, we examined the expression patterns of Ca(V)1.3 after Aβ(25-35) exposure for 24 h and compared them with the expression patterns of Ca(V)1.2. The expression levels of Ca(V)1.3 were not significantly changed by Aβ(25-35) at both the mRNA levels and the total protein level in cultured hippocampal neurons. However, surface protein levels of Ca(V)1.3 were significantly increased by Aβ(25-35), but not by Aβ(35-25). We next found that acute treatment with Aβ(25-35) increased Ca(V)1.3 channel activities in HEK293 cells using whole-cell patch-clamp recordings. Furthermore, using GTP pulldown and co-immunoprecipitation assays in HEK293 cell lysates, we found that amyloid precursor protein interacts with β(3) subunits of Ca(2+) channels instead of Ca(V)1.2 or Ca(V)1.3 α(1) subunits. These results show that Aβ(25-35) chronically or acutely upregulates Ca(V)1.3 in the rat hippocampal and human kidney cells (HEK293). This suggests that Ca(V)1.3 has a potential role along with Ca(V)1.2 in the pathogenesis of Alzheimer's disease.

Role of oxidant scavengers in the prevention of Ca²+ homeostasis disorders

A number of disorders, such as Alzheimer disease and diabetes mellitus, have in common the alteration of the redox balance, resulting in an increase in reactive oxygen species (ROS) generation that might lead to the development of apoptosis and cell death. It has long been known that ROS can significantly alter Ca²+ mobilization, an intracellular signal that is involved in the regulation of a wide variety of cellular functions. Cells have a limited capability to counteract the effects of oxidative stress, but evidence has been provided supporting the beneficial effects of exogenous ROS scavengers. Here, we review the effects of oxidative stress on intracellular Ca²+ homeostasis and the role of antioxidants in the prevention and treatment of disorders associated to abnormal Ca²+ mobilization induced by ROS.

Cerebral arachidonate cascade in dementia: Alzheimer's disease and vascular dementia

Phospholipase A(2) (PLA(2)), cyclooxygenase (COX) and prostaglandin (PG) synthase are enzymes involved in arachidonate cascade. PLA(2) liberates arachidonic acid (AA) from cell membrane lipids. COX oxidizes AA to PGG(2) followed by an endoperoxidase reaction that converts PGG(2) into PGH(2). PGs are generated from astrocytes, microglial cells and neurons in the central nervous system, and are altered in the brain of demented patients. Dementia is principally diagnosed into Alzheimer's disease (AD) and vascular dementia (VaD). In older patients, the brain lesions associated with each pathological process often occur together. Regional brain microvascular abnormalities appear before cognitive decline and neurodegeneration. The coexistence of AD and VaD pathology is often termed mixed dementia. AD and VaD brain lesions interact in important ways to decline cognition, suggesting common pathways of the two neurological diseases. Arachidonate cascade is one of the converged intracellular signal transductions between AD and VaD. PLA(2) from mammalian sources are classified as secreted (sPLA(2)), Ca(2+)-dependent, cytosolic (cPLA(2)) and Ca(2+)-independent cytosolic PLA(2) (iPLA(2)). PLA(2) activity can be regulated by calcium, by phosphorylation, and by agonists binding to G-protein-coupled receptors. cPLA(2) is upregulalted in AD, but iPLA(2) is downregulated. On the other hand, sPLA(2) is increased in animal models for VaD. COX-2 is induced and PGD(2) are elevated in both AD and VaD. This review presents evidences for central roles of PLA(2)s, COXs and PGs in the dementia.

[Inhibition effect of IL-1beta on calcium channels currents in cultured cortical neurons of rat]

Interleukin-1beta (IL-1beta) is an important proinflammatory cytokine that exert wide biological functions in the central nervous system (CNS). Voltage-gated Ca2+ channels in plasma membrane are essential components of Ca2+ signal whose change on pathological conditions is closely related to processes of diseases. Although both IL-1beta and Ca2+ channels have key roles in injury and disease of the brain, so far their relations have been reported in few studies. The effects of IL-1beta on Ca2+ channels in cultured cortical neurons of rats were investigated using patch-clamp recording in present research. Our results showed that both 10 and 50 ng/mL of IL-1beta treatment inhibit the Ca2+ currents in time and dose dependent manner, without the change of activation properties of voltage-gated Ca2+ channels (VGCC)s.

Fibroblast growth factor 2 induces apoptosis in the early primary culture of rat cortical neurons

In the central nervous system, fibroblast growth factor 2 (FGF2) is known to have important functions in cell survival and differentiation. In addition to its roles as a neurotrophic factor, we found that FGF2 caused cell death in the early primary culture of cortical neurons. FGF2-induced neuronal cell death showed apoptotic characters, e.g., chromatin condensation and DNA fragmentation. The ultrastructural morphology of FGF2-treated neurons indicated apoptotic features such as progressive cell shrinkage, blebbing of the plasma membrane, loss of cytosolic organelles, clumping of chromatin, and fragmentation of DNA. Tyrosine kinase inhibitors significantly rescued neurons from FGF2-induced apoptosis. FGF2 potentiated a marked influx of Ca(2+) into neurons before apoptosis. Both a calcium chelator and L-type voltage-sensitive Ca(2+) channel (L-VSCC) blockers attenuated FGF2-induced apoptosis, whereas other blockers of VSCCs such as N-type and P/Q-types did not. Blockers of L-VSCCs significantly suppressed FGF2-enhanced Ca(2+) influx into neurons. Moreover, FGF2 also generated reactive oxygen species (ROS) before apoptosis. Radical scavengers reduced not only the FGF2-generated ROS, but also the FGF2-induced Ca(2+) influx and apoptosis. In conclusion, we demonstrated that FGF2 caused apoptosis via L-VSCCs in the early neuronal culture.

Dihydropyridines decrease X-ray-induced DNA base damage in mammalian cells

Compounds with the structural motif of 1,4-dihydropyridine display a broad spectrum of biological activities, often defined as bioprotective. Among them are L-type calcium channel blockers, however, also derivatives which do not block calcium channels exert various effects at the cellular and organismal levels. We examined the effect of sodium 3,5-bis-ethoxycarbonyl-2,6-dimethyl-1,4-dihydropyridine-4-carboxylate (denoted here as DHP and previously also as AV-153) on X-ray-induced DNA damage and mutation frequency at the HGPRT (hypoxanthine-guanine phosphoribosyl transferase) locus in Chinese hamster ovary CHO-K1 cells. Using formamido-pyrimidine glycosylase (FPG) comet assay, we found that 1-h DHP (10nM) treatment before X-irradiation considerably reduced the initial level of FPG-recognized DNA base damage, which was consistent with decreased 8-oxo-7,8-dihydro-2'-deoxyguanosine content and mutation frequency lowered by about 40%. No effect on single strand break rejoining or on cell survival was observed. Similar base damage-protective effect was observed for two calcium channel blockers: nifedipine (structurally similar to DHP) or verapamil (structurally unrelated). So far, the specificity of the DHP-caused reduction in DNA damage - practically limited to base damage - has no satisfactory explanation.

Calcium dysregulation in Alzheimer's disease: from mechanisms to therapeutic opportunities

Calcium is involved in many facets of neuronal physiology, including activity, growth and differentiation, synaptic plasticity, and learning and memory, as well as pathophysiology, including necrosis, apoptosis, and degeneration. Though disturbances in calcium homeostasis in cells from Alzheimer's disease (AD) patients have been observed for many years, much more attention was focused on amyloid-beta (Abeta) and tau as key causative factors for the disease. Nevertheless, increasing lines of evidence have recently reported that calcium dysregulation plays a central role in AD pathogenesis. Systemic calcium changes accompany almost the whole brain pathology process that is observed in AD, including synaptic dysfunction, mitochondrial dysfunction, presenilins mutation, Abeta production and Tau phosphorylation. Given the early and ubiquitous involvement of calcium dysregulation in AD pathogenesis, it logically presents a variety of potential therapeutic targets for AD prevention and treatment, such as calcium channels in the plasma membrane, calcium channels in the endoplasmic reticulum membrane, Abeta-formed calcium channels, calcium-related proteins. The review aims to provide an overview of the current understanding of the molecular mechanisms involved in calcium dysregulation in AD, and an insight on how to exploit calcium regulation as therapeutic opportunities in AD.

Pharmacotherapeutic targets in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder which is characterized by an increasing impairment in normal memory and cognitive processes that significantly diminishes a person's daily functioning. Despite decades of research and advances in our understanding of disease aetiology and pathogenesis, there are still no effective disease-modifying drugs available for the treatment of AD. However, numerous compounds are currently undergoing pre-clinical and clinical evaluations. These candidate pharma-cotherapeutics are aimed at various aspects of the disease, such as the microtubule-associated τ-protein, the amyloid-β (Aβ) peptide and metal ion dyshomeostasis – all of which are involved in the development and progression of AD. We will review the way these pharmacological strategies target the biochemical and clinical features of the disease and the investigational drugs for each category.

Computational models of neuronal biophysics and the characterization of potential neuropharmacological targets

The identification and characterization of potential pharmacological targets in neurology and psychiatry is a fundamental problem at the intersection between medicinal chemistry and the neurosciences. Exciting new techniques in proteomics and genomics have fostered rapid progress, opening numerous questions as to the functional consequences of ligand binding at the systems level. Psycho- and neuro-active drugs typically work in nerve cells by affecting one or more aspects of electrophysiological activity. Thus, an integrated understanding of neuropharmacological agents requires bridging the gap between their molecular mechanisms and the biophysical determinants of neuronal function. Computational neuroscience and bioinformatics can play a major role in this functional connection. Robust quantitative models exist describing all major active membrane properties under endogenous and exogenous chemical control. These include voltage-dependent ionic channels (sodium, potassium, calcium, etc.), synaptic receptor channels (e.g. glutamatergic, GABAergic, cholinergic), and G protein coupled signaling pathways (protein kinases, phosphatases, and other enzymatic cascades). This brief review of neuromolecular medicine from the computational perspective provides compelling examples of how simulations can elucidate, explain, and predict the effect of chemical agonists, antagonists, and modulators in the nervous system.

The roles of NADPH oxidase and phospholipases A2 in oxidative and inflammatory responses in neurodegenerative diseases

Reactive oxygen species (ROS) are produced in mammalian cells through enzymic and non-enzymic mechanisms. Although some ROS production pathways are needed for specific physiological functions, excessive production is detrimental and is regarded as the basis of numerous neurodegenerative diseases. Among enzymes producing superoxide anions, NADPH oxidase is widespread in mammalian cells and is an important source of ROS in mediating physiological and pathological processes in the cardiovascular and the CNS. ROS production is linked to the alteration of intracellular calcium homeostasis, activation of Ca(2+)-dependent enzymes, alteration of cytoskeletal proteins, and degradation of membrane glycerophospholipids. There is evolving evidence that ROS produced by NADPH oxidase regulate neuronal functions and degrade membrane phospholipids through activation of phospholipases A(2) (PLA(2)). This review is intended to cover recent studies describing ROS generation from NADPH oxidase in the CNS and its downstream activation of PLA(2), namely, the group IV cytosolic cPLA(2) and the group II secretory sPLA(2). A major focus is to elaborate the dual role of NADPH oxidase and PLA(2) in mediating the oxidative and inflammatory responses in neurodegenerative diseases, including cerebral ischemia and Alzheimer's disease. Elucidation of the signaling pathways linking NADPH oxidase with the multiple forms of PLA(2) will be important in understanding the oxidative and degradative mechanisms that underline neuronal damage and glial activation and will facilitate development of therapeutic intervention for prevention and treatment of these and other neurodegenerative diseases.

Glutamatergic synaptic depression by synthetic amyloid beta-peptide in the medial septum

The medial septum/diagonal band region, which participates in learning and memory processes via its cholinergic and GABAergic projection to the hippocampus, is one of the structures affected by beta amyloid (betaA) deposition in Alzheimer's disease (AD). The acute effects of betaA (25-35 and 1-40) on action potential generation and glutamatergic synaptic transmission in slices of the medial septal area of the rat brain were studied using current and patch-clamp techniques. The betaA mechanism of action through M1 muscarinic receptors and voltage-dependent calcium channels was also addressed. Excitatory evoked responses decreased (30-60%) in amplitude after betaA (2 microM) perfusion in 70% of recorded cells. However, the firing properties were unaltered at the same concentration. This depression was irreversible in most cases, and was not prevented or reversed by nicotine (5 microM). In addition, the results obtained using a paired-pulse protocol support pre- and postsynaptic actions of the peptide. The betaA effect was blocked by calcicludine (50 nM), a selective antagonist of L-type calcium channels, and also by blocking muscarinic receptors with atropine (5 muM) or pirenzepine (1 microM), a more specific M1-receptor blocker. We show that in the medial septal area this oligomeric peptide acts through calcium channels and muscarinic receptors. As blocking any of these pathways blocks the betaA effects, we propose a joint action through both mechanisms. These results may contribute to a better understanding of the pathophysiology at the onset of AD. This understanding will be required for the development of new therapeutic agents.

Voltage-gated calcium channels provide an alternate route for iron uptake in neuronal cell cultures

Recent studies suggest that iron enters cardiomyocytes via the L-type voltage-gated calcium channel (VGCC). The neuronal VGCC may also provide iron entry. As with calcium, extraneous iron is associated with the pathology and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. VGCCs, ubiquitously expressed, may be an important route of excessive entry for both iron and calcium, contributing to cell toxicity or death. We evaluated the uptake of (45)Ca(2+) and (55)Fe(2+) into NGF-treated rat PC12, and murine N-2alpha cells. Iron not only competed with calcium for entry into these cells, but iron uptake (similar to calcium uptake) was inhibited by nimodipine, a specific L-type VGCC blocker, and enhanced by FPL 64176, an L-VGCC activator, in a dose-dependent manner. Taken together, these data suggest that voltage-gated calcium channels are an alternate route for iron entry into neuronal cells under conditions that promote cellular iron overload toxicity.

Transthyretin oligomers induce calcium influx via voltage-gated calcium channels

The deposition of transthyretin (TTR) amyloid in the PNS is a major pathological feature of familial amyloidotic polyneuropathy. The aim of the present study was to examine whether TTR could disrupt cytoplasmic Ca(2+) homeostasis and to determine the role of TTR aggregation in this process. The aggregation of amyloidogenic TTR was examined by solution turbidity, dynamic light scattering and atomic force microscopy. A nucleation-dependent polymerization process was observed in which TTR formed low molecular weight aggregates (oligomers < 100 nm in diameter) before the appearance of mature fibrils. TTR rapidly induced an increase in the concentration of intracellular Ca(2+) ([Ca(2+)](i)) when applied to SH-SY5Y human neuroblastoma cells. The greatest effect on [Ca(2+)](i) was induced by a preparation that contained the highest concentration of TTR oligomers. The TTR-induced increase in [Ca(2+)](i) was due to an influx of extracellular Ca(2+), mainly via L- and N-type voltage-gated calcium channels (VGCCs). These results suggest that increasing [Ca(2+)](i) via VGCCs may be an important early event which contributes to TTR-induced cytotoxicity, and that TTR oligomers, rather than mature fibrils, may be the major cytotoxic form of TTR.

Secretory PLA2-IIA: a new inflammatory factor for Alzheimer's disease

Secretory phospholipase A₂-IIA (sPLA₂-IIA) is an inflammatory protein known to play a role in the pathogenesis of many inflammatory diseases. Although this enzyme has also been implicated in the pathogenesis of neurodegenerative diseases, there has not been a direct demonstration of its expression in diseased human brain. In this study, we show that sPLA₂-IIA mRNA is up-regulated in Alzheimer's disease (AD) brains as compared to non-demented elderly brains (ND). We also report a higher percentage of sPLA₂-IIA-immunoreactive astrocytes present in AD hippocampus and inferior temporal gyrus (ITG). In ITG, the majority of sPLA₂-IIA-positive astrocytes were associated with amyloid β (Aβ)-containing plaques. Studies with human astrocytes in culture demonstrated the ability of oligomeric Aβ_1–42 and interleukin-1β (IL-1β) to induce sPLA₂-IIA mRNA expression, indicating that this gene is among those induced by inflammatory cytokines. Since exogenous sPLA₂-IIA has been shown to cause neuronal injury, understanding the mechanism(s) and physiological consequences of sPLA₂-IIA upregulation in AD brain may facilitate the development of novel therapeutic strategies to inhibit the inflammatory responses and to retard the progression of the disease.

Silencing of ZnT-1 expression enhances heavy metal influx and toxicity

ZnT-1 reduces intracellular zinc accumulation and confers resistance against cadmium toxicity by a mechanism which is still unresolved. A functional link between the L-type calcium channels (LTCC) and ZnT-1 has been suggested, indicating that ZnT-1 may regulate ion permeation through this pathway. In the present study, immunohistochemical analysis revealed a striking overlap of the expression pattern of LTCC and ZnT-1 in cardiac tissue and brain. Using siRNA to silence ZnT-1 expression, we then assessed the role of ZnT-1 in regulating cation permeation through the L-type Ca(2+) channels in cells that are vulnerable to heavy metal permeation. Transfection of cortical neurons with ZnT-1 siRNA resulted in about 70% reduction of ZnT-1 expression and increased Ca(2+) influx via LTCC by approximately fourfold. Moreover, ZnT-1 siRNA transfected neurons showed approximately 30% increase in synaptic release, monitored using the FM1-43 dye. An increased cation influx rate, through the LTCC, was also recorded for Zn(2+) and Cd(2+) in cells treated with the ZnT-1 siRNA. Furthermore, Cd(2+)-induced neuronal death increased by approximately twofold after transfection with ZnT-1 siRNA. In addition, ZnT-1 siRNA transfection of the ovarian granulosa cell line, POGRS1, resulted in a twofold increase in Cd(2+) influx rate via the LTCC. Finally, a robust nimodipine-sensitive Cd(2+) influx was observed using a low extracellular Cd(2+) concentration (5 muM) in neurons and testicular slice cultures, attesting to the relevance of the LTCC pathway to heavy metal toxicity. Taken together, our results indicate that endogenously-expressed ZnT-1, by modulating LTCC, has a dual role: regulating calcium influx, and attenuating Cd(2+) and Zn(2+) permeation and toxicity in neurons and other cell types.

Zinc-induced aggregation of Abeta (10-21) potentiates its action on voltage-gated potassium channel

Zinc may play an important role in the pathogenesis of Alzheimer's disease (AD) through influencing the conformation and neurotoxicity of amyloid beta-proteins (Abeta). Zn(2+) induces rapid aggregation of synthetic or endogenous Abeta in a pH-dependent fashion. Here we show for the first time that Zn(2+)-induced aggregation of Abeta (10-21) potentiates its action on outward potassium currents in hippocampal CA1 pyramidal neurons. Using the whole-cell voltage-clamp technique, we showed that Abeta (10-21) blocked the fast-inactivating outward potassium current (I(A)) in a concentration- and aggregation-dependent manner, but with no effect on the delayed rectifier potassium current (I(K)). Both the unaggregated and aggregated forms of Abeta (10-21) significantly shifted the activation curve and the inactivation curve of I(A) to more negative potentials. But the aggregated form has more effects than the unaggregated form. These data indicated that aggregation of amyloid fragments by zinc ions is required in order to obtain full modulatory effects on potassium channel currents.

Interleukin-1beta downregulates the L-type Ca2+ channel activity by depressing the expression of channel protein in cortical neurons

Interleukin-1beta (IL-1beta), a proinflammatory cytokine, has been involved in various diseases of the central nervous system (CNS). Due to the diverse, "contradictory" effects of IL-1beta on neurons during insults to the brain, the mechanisms underlying these effects have not been elucidated. Calcium influx through the L-type Ca2+ channels (LCCs) is believed to play a critical role in the cascade of biochemical events leading to neuron death in these pathophysiological conditions. So far, the mechanism of the interaction of IL-1beta and LCCs in the initiation and progression of these diseases is unclear. In this study, we investigate systemically the effects of IL-1beta on the LCCs current, which are believed to be implicated in the cascade of biochemical events leading to neuron death in neuropathological conditions. Using patch clamp, we observe that IL-1beta treatment (10 ng/ml, 24 h) suppresses LCC currents by approximately 38%, which made up half of the whole-cell Ca2+ current determined by nifedipine. IL-1beta does not alter the characteristics of single LCC including current amplitude, open probability, and conductance, but decreases the number of the functioning channel by 40%. Moreover, immunoblot assay exhibits that IL-1beta reduces the expression of LCC proteins by 38 approximately 42% in both whole neuron and plasma membrane fraction, and demonstrates that IL-1beta downregulates the LCC activity via the reduction of LCC density. According to early research pretreatments longer than 12 h may play a crucial role in the neuroprotective effects of IL-1beta, our findings may establish an explanation for the protective effects of this interleukin on neurons in the late stage of injury, and could raise a new issue to clinical treatment for insults to brain.

Potential Roles of Electrogenic Ion Transport and Plasma Membrane Depolarization in Apoptosis

Apoptosis is characterized by the programmed activation of specific biochemical pathways leading to the organized demise of cells. To date, aspects of the intracellular signaling machinery involved in this phenomenon have been extensively dissected and characterized. However, recent studies have elucidated a novel role for changes in the intracellular milieu of the cells as important modulators of the cell death program. Specially, intracellular ionic homeostasis has been reported to be a determinant in both the activation and progression of the apoptotic cascade. Several apoptotic insults trigger specific changes in ionic gradients across the plasma membrane leading to depolarization of the plasma membrane potential (PMP). These changes lead to ionic imbalance early during apoptosis. Several studies have also suggested the activation and/or modulation of specific ionic transport mechanisms including ion channels, transporters and ATPases, as mediators of altered intracellular ionic homeostasis leading to PMP depolarization during apoptosis. However, the role of PMP depolarization and of the changes in ionic homeostasis during the progression of apoptosis are still unclear. This review summarizes the current knowledge regarding the causes and consequences of PMP depolarization during apoptosis. We also review the potential electrogenic ion transport mechanisms associated with this event, including the net influx/efflux of cations and anions. An understanding of these mechamisms could lead to the generation of new therapeutic approaches for a variety of diseases involving apoptosis.

Amyloid peptides mediate hypoxic increase of L-type Ca2+ channels in central neurones

Prolonged hypoxia, encountered in individuals suffering from various cardiorespiratory diseases, enhances the likelihood of subsequently developing Alzheimer's disease (AD). However, the underlying mechanisms are unknown, as are the mechanisms of neurodegeneration of amyloid beta peptides (AbetaPs), although the latter involves disruption of Ca2+ homeostasis. Here, immunohistochemistry demonstrated that hypoxia increased production of AbetaPs, an effect which was prevented by inhibition of either beta or gamma secretase, the enzymes required for liberation of AbetaP from its precursor protein. Whole-cell patch clamp recordings showed that hypoxia selectively increased functional expression of L-type Ca2+ channels. This was prevented by inhibition of either beta or gamma secretase, indicating that hypoxic channel up-regulation is dependent upon AbetaP formation. Our results indicate for the first time that hypoxia promotes AbetaP formation in central neurons, and show that this leads to abnormally high selective expression of L-type Ca2+ channels whose blockade has previously been shown to be neuroprotective in AD models. These findings provide a cellular basis for understanding the increased incidence of AD following prolonged hypoxia.

The expression of proapoptosis genes is increased in bipolar disorder, but not in schizophrenia

Post-mortem studies conducted over the past 15 years suggest that apoptosis could play a role in the pathophysiology of bipolar disorder (BD) and, to a lesser degree, schizophrenia (SZ). To test this hypothesis, we have performed a post hoc analysis of an extant gene expression profiling database obtained from the hippocampus using a novel methodology with improved sensitivity. Consistent with the working hypothesis, BDs showed a marked upregulation of 19 out of 44 apoptosis genes; however, contrary to the hypothesis, the SZ group showed a downregulation of genes associated with apoptotic injury and death. These changes in the regulation of apoptosis genes were validated using quantitative RT-PCR. Additionally, antioxidant genes showed a marked downregulation in BDs, suggesting that accumulation of free radicals might occur in the setting of a previously reported decrease of the electron transport chain in this disorder. Overall, the changes seen in BDs and SZs do not appear to be related to exposure to either neuroleptics or mood stabilizers. We conclude that fundamental differences in the genetic regulation of apoptosis and antioxidant genes may help discriminate between the pathophysiology of BD and SZ and potentially point to new treatment strategies that are specific for each disorder.

Divergent role of calcium on Aβ- and MPTP-induced cell death in SK-N-SH neuroblastoma

We attempted to clarify the role of Ca2+ in cell death caused by beta-amyloid protein (Abeta) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in SK-N-SH neuroblastoma, respectively. Two insults both reduced cell viability in a concentration-dependent manner and induced equal cytotoxicity in the presence of 20 microM Abeta and 0.4 mM MPTP for 72 h, respectively (68+/-7 vs. 64+/-6% viability). Time-related study showed that Abeta evoked cell death occurred quickly at 24 h. Relatively, MPTP exhibited a delayed cell death significantly after 72 h of culture. Pretreating the cells with nimodipine and chelating of Ca2+ by EGTA plus 1,2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) successfully rescued Abeta-induced cell death but failed to prevent MPTP toxicity. ELISA determination of mono/oligonucleosomes accumulation showed the mode of cell death evoked by MPTP was presumably apoptosis while by Abeta was necrosis. SK-N-SH cells constitutively expressed the alpha(1C) subunit of L-type Ca2+ channel and exposure to Abeta or MPTP for 96 h did not further modify its expression. By contrast, alpha(1D) subunit was undetectable or low level expressed in basal condition, but was induced to express after Abeta and MPTP stimulation in a time-dependent manner. Functional assay revealed that KCl-evoked [Ca2+]i rise was significantly greater in Abeta-, but not in MPTP-treated cells when compared with control. Taken together, these results showed that Abeta and MPTP elicited different mode of cell death in SK-N-SH. Nevertheless, Ca2+ overload seems to solely display a crucial role in Abeta-induced cytotoxicity and over-expressed alpha(1D) may contribute to the disruption of cellular Ca2+ homeostasis.

Verapamil prevents, in a dose-dependent way, the loss of ChAT-immunoreactive neurons in the cerebral cortex following lesions of the rat nucleus basalis magnocellularis

In the present study we analysed the neuroprotective effect of the L-type voltage-dependent calcium channel antagonist verapamil on cholineacetyltransferase (ChAT)-immunoreactive neurons in the cerebral cortex of rats with bilateral electrolytic lesions of the nucleus basalis magnocellularis (NBM). Treatment with verapamil (1.0, 2.5, 5.0 and 10.0 mg/kg/12 h i.p.) started 24 h after NBM lesions and lasted 8 days. Animals were sacrificed on day 21 after NBM-lesions. The bilateral NBM-lesions produced significant loss of ChAT-immunoreactive neurons in frontal, parietal and temporal cortex. Although the number of ChAT-positive neurons was significantly higher in NBM-lesioned animals treated with verapamil at a dose of 2.5, 5.0 and 10.0 mg/kg than in saline treated ones, the most significant effect was obtained at a dose of 5 mg/kg. This is, to our knowledge, the first report showing an inverted U-shape mode of neuroprotective action of the calcium antagonist verapamil, at morphological level in this particular model of brain damage. The demonstrated beneficial effect of verapamil treatment suggests that the regulation of calcium homeostasis during the early period after NBM lesions might be a possible treatment to prevent neurodegenerative processes in the rat cerebral cortex.

Regulation of synaptic plasticity in a schizophrenia model

The pathology of schizophrenia is characterized by increased hippocampal activity at baseline and during auditory hallucinations. Animal-model studies in which the flow of activity to the hippocampus is increased through decreased amygdalar GABAergic inhibition have shown alterations of hippocampal circuitry similar to schizophrenia, but the functional importance of this phenomenon remains unclear. We provide evidence of decreased hippocampal feed-forward and tonic GABA-mediated inhibition in this animal model, complementing increased hippocampal activity seen in neuroimaging and postmortem studies. We demonstrate that GABA dysfunction increases long-term potentiation through activation of the cholinergic system, offering a new mechanism for pharmacological strategies of this disorder.

Effect of donepezil and lercanidipine on memory impairment induced by intracerebroventricular streptozotocin in rats

Intracerebroventricular (ICV) injection of streptozotocin (STZ) causes cognitive impairment in rats. ICV STZ is known to impair cholinergic neurotransmission by decreasing choline acetyltransferase (ChAT) levels, glucose and energy metabolism in brain and synthesis of acetyl CoA. However, no reports are available regarding the cholinesterase inhibitors in this model. In aging brain, reduced energy metabolism increases glutamate release, which is blocked by L-type calcium channel blockers. These calcium channel blockers have shown beneficial effects on learning and memory in various models of cognitive impairment. The present study was designed to investigate the influence of chronic administration of donepezil (cholinesterase inhibitor, 1 and 3 mg/kg) and lercanidipine (L-type calcium channel blocker, 0.3 and 1 mg/kg) on cognitive impairment in male Sprague-Dawley rats injected twice with ICV STZ (3 mg/kg) bilaterally on days 1 and 3. ICV STZ injected rats developed a severe deficit in learning and memory indicated by deficits in passive avoidance paradigm and elevated plus maze as compared to control rats. Cholinesterase activity in brain was significantly increased in ICV STZ injected rats. Donepezil dose-dependently inhibited cholinesterase activity and improved performance in memory tests at both the doses. Lercanidipine (0.3 mg/kg) showed significant improvement in memory. When administered together, the effect of combination of these two drugs on memory and cholinesterase activity was higher than that obtained with either of the drugs when used alone.

Effects of an endothelin B receptor agonist on secretory phospholipase A2-IIA-induced apoptosis in cortical neurons

Endothelin (ET), a vasoconstrictive peptide, acts as an anti-apoptotic factor, and endothelin receptor B (ETB receptor) is associated with neuronal survival in the brain. Human group IIA secretory phospholipase A2 (sPLA2-IIA) is expressed in the cerebral cortex after brain ischemia and causes neuronal cell death via apoptosis. In primary cultures of rat cortical neurons, we investigated the effects of an ETB receptor agonist, ET-3, on sPLA2-IIA-induced cell death. sPLA2-IIA caused neuronal cell death in a concentration- and time-dependent manner. ET-3 significantly prevented neurons from undergoing sPLA2-IIA-induced cell death. These agonists reversed sPLA2-IIA-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Before cell death, sPLA2-IIA potentiated the influx of Ca2+ into neurons. Blockers of the L-type voltage-dependent calcium channel (L-VSCC) not only suppressed the Ca2+ influx, but also exhibited neuroprotective effects. As well as L-VSCC blockers, ET-3 significantly prevented neurons from sPLA2-IIA-induced Ca2+ influx. An ETB receptor antagonist, BQ788, inhibited the effects of ET-3. The present cortical cultures contained few non-neuronal cells, indicating that the ETB receptor agonist affected the survival of neurons directly, but not indirectly via non-neuronal cells. In conclusion, we demonstrate that the ETB receptor agonist rescues cortical neurons from sPLA2-IIA-induced apoptosis. Furthermore, the present study suggests that the inhibition of L-VSCC contributes to the neuroprotective effects of the ETB receptor agonist.