Veratridine induces apoptotic death in bovine chromaffin cells through superoxide production

Pre-clinical safety and therapeutic efficacy of a plant-based alkaloid in a human colon cancer xenograft model

A high-throughput drug screen revealed that veratridine (VTD), a natural plant alkaloid, induces expression of the anti-cancer protein UBXN2A in colon cancer cells. UBXN2A suppresses mortalin, a heat shock protein, with dominant roles in cancer development including epithelial–mesenchymal transition (EMT), cancer cell stemness, drug resistance, and apoptosis. VTD-dependent expression of UBXN2A leads to the deactivation of mortalin in colon cancer cells, making VTD a potential targeted therapy in malignant tumors with high levels of mortalin. VTD was used clinically for the treatment of hypertension in decades past. However, the discovery of newer antihypertensive drugs and concerns over potential neuro- and cardiotoxicity ended the use of VTD for this purpose. The current study aims to determine the safety and efficacy of VTD at doses sufficient to induce UBXN2A expression in a mouse model. A set of flow-cytometry experiments confirmed that VTD induces both early and late apoptosis in a dose-dependent manner. In vivo intraperitoneal (IP) administration of VTD at 0.1 mg/kg every other day (QOD) for 4 weeks effectively induced expression of UBXN2A in the small and large intestines of mice. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) assays on tissues collected from VTD-treated animals demonstrated VTD concentrations in the low pg/mg range. To address concerns regarding neuro- and cardiotoxicity, a comprehensive set of behavioral and cardiovascular assessments performed on C57BL/6NHsd mice revealed that VTD generates no detectable neurotoxicity or cardiotoxicity in animals receiving 0.1 mg/kg VTD QOD for 30 days. Finally, mouse xenograft experiments in athymic nude mice showed that VTD can suppress tumor growth. The main causes for the failure of experimental oncologic drug candidates are lack of sufficient safety and efficacy. The results achieved in this study support the potential utility of VTD as a safe and efficacious anti-cancer molecule.

Synthesis and Neuroprotective Properties of N-Substituted C-Dialkoxyphosphorylated Nitrones

Herein, we report the synthesis and neuroprotective power of some N-substituted C-(dialkoxy)phosphorylated nitrones 4a-g, by studying their ability to increase the cell viability, as well as their capacity to reduce necrosis and apoptosis. We have identified (Z)-N-tert-butyl-1-(diethoxyphosphoryl)methanimine oxide (4e) as the most potent, nontoxic, and neuroprotective agent, with a high activity against neuronal necrotic cell death, a result that correlates very well with its great capacity for the inhibition of the superoxide production (72%), as well as with the inhibition of lipid peroxidation (62%), and the 5-lipoxygenase activity (45%) at 100 μM concentrations. Thus, nitrone 4e could be a convenient promising compound for further investigation.

Development of a rapid and economic in vivo electrocardiogram platform for cardiovascular drug assay and electrophysiology research in adult zebrafish

Zebrafish is a popular and favorable model organism for cardiovascular research, with an increasing number of studies implementing functional assays in the adult stage. For example, the application of electrocardiography (ECG) in adult zebrafish has emerged as an important tool for cardiac pathophysiology, toxicity, and chemical screen studies. However, few laboratories are able to perform such functional analyses due to the high cost and limited availability of a convenient in vivo ECG recording system. In this study, an inexpensive ECG recording platform and operation protocol that has been optimized for adult zebrafish ECG research was developed. The core hardware includes integration of a ready-to-use portable ECG kit with a set of custom-made needle electrode probes. A combined anesthetic formula of MS-222 and isoflurane was first tested to determine the optimal assay conditions to minimize the interference to zebrafish cardiac physiology under sedation. For demonstration, we treated wild-type zebrafish with different pharmacological agents known to affect cardiac rhythms in humans. Conserved electrophysiological responses to these drugs were induced in adult zebrafish and recorded in real time. This economic ECG platform has the potential to facilitate teaching and training in cardiac electrophysiology with adult zebrafish and to promote future translational applications in cardiovascular medicine.

Chromaffin cells as a model to evaluate mechanisms of cell death and neuroprotective compounds

In this review, we show how chromaffin cells have contributed to evaluate neuroprotective compounds with diverse mechanisms of action. Chromaffin cells are considered paraneurons, as they share many common features with neurons: (i) they synthesize, store, and release neurotransmitters upon stimulation and (ii) they express voltage-dependent calcium, sodium, and potassium channels, in addition to a wide variety of receptors. All these characteristics, together with the fact that primary cultures from bovine adrenal glands or chromaffin cells from the tumor pheochromocytoma cell line PC12 are easy to culture, make them an ideal model to study neurotoxic mechanisms and neuroprotective drugs. In the first part of this review, we will analyze the different cytotoxicity models related to calcium dyshomeostasis and neurodegenerative disorders like Alzheimer's or Parkinson's. Along the second part of the review, we describe how different classes of drugs have been evaluated in chromaffin cells to determine their neuroprotective profile in different neurodegenerative-related models.

A plant alkaloid, veratridine, potentiates cancer chemosensitivity by UBXN2A-dependent inhibition of an oncoprotein, mortalin-2

Veratridine (VTD), an alkaloid derived from the Liliaceae plant shows anti-tumor effects; however, its molecular targets have not been thoroughly studied. Using a high-throughput drug screen, we found that VTD enhances transactivation of UBXN2A, resulting in upregulation of UBXN2A in the cytoplasm, where UBXN2A binds and inhibits the oncoprotein mortalin-2 (mot-2). VTD-treated cancer cells undergo cell death in UBXN2A- and mot-2-dependent manners. The cytotoxic function of VTD is grade-dependent, and the combined treatment with a sub-optimal dose of the standard chemotherapy, 5-Fluorouracil (5-FU) and etoposide, demonstrated a synergistic effect, resulting in higher therapeutic efficacy. VTD influences the CD44+ stem cells, possibly through UBXN2A-dependent inhibition of mot-2. The VTD-dependent expression of UBXN2A is a potential candidate for designing novel strategies for colon cancer treatment because: 1) In 50% of colon cancer patients, UBXN2A protein levels in tumor tissues are significantly lower than those in the adjacent normal tissues. 2) Cytoplasmic expression of the mot-2 protein is very low in non-cancerous cells; thus, VTD can produce tumor-specific toxicity while normal cells remain intact. 3) Finally, VTD or its modified analogs offer a valuable adjuvant chemotherapy strategy to improve the efficacy of 5-FU-based chemotherapy for colon cancer patients harboring WT-p53.

The endoplasmic reticulum stress and the HIF-1 signalling pathways are involved in the neuronal damage caused by chemical hypoxia

BACKGROUND AND PURPOSE

Hypoxia inducible factor-1 (HIF-1) promotes transitory neuronal survival suggesting that additional mechanisms such as the endoplasmic reticulum (ER) stress might be involved in determining neuronal survival or death. Here, we examined the involvement of ER stress in hypoxia-induced neuronal death and analysed the relationship between ER stress and the HIF-1 pathways.

EXPERIMENTAL APPROACH

Cultures of rat cortical neurons were exposed to chemical hypoxia induced by 200 μM CoCl2 , and its effect on neuronal viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and counting apoptotic nuclei. Protein levels were determined by Western blot analysis. RT-PCR was performed to analyse the content and the t1/2 of HIF-1α mRNA.

KEY RESULTS

Chemical hypoxia induced neuronal apoptosis in a time-dependent manner and activated the ER stress PRK-like endoplasmic reticulum kinase (PERK)-dependent pathway. At later stages, chemical hypoxia increased the expression of the C/EBP homologous protein (CHOP) and caspase 12 activity. CoCl2 reduced HIF-1α mRNA t1/2 leading to a decrease in HIF-1α mRNA and protein content, simultaneously activating the ER stress PERK-dependent pathway. Salubrinal, a selective inhibitor of phospho-eIF2α phosphatase, protected neurons from chemical hypoxia by reducing CHOP levels and caspase 12 activity, and increasing the t1/2 of HIF-1α mRNA and the levels of HIF-1α protein. Knocking down HIF-1α blocked the neuroprotective effects of salubrinal.

CONCLUSIONS AND IMPLICATIONS

Neuronal apoptosis induced by chemical hypoxia is a process regulated by HIF-1α stabilization early on and by ER stress activation at later stages. Our data also suggested that HIF-1α levels were regulated by ER stress.

Transient receptor potential melastatin 4 and cell death

Cell death proceeds by way of a variety of “cell death subroutines,” including several types of “apoptosis,” “regulated necrosis,” and others. “Accidental necrosis” due to profound adenosine triphosphate (ATP) depletion or oxidative stress is distinguished from regulated necrosis by the absence of death receptor signaling. However, both accidental and regulated necrosis have in common the process of “oncosis,” a physiological process characterized by Na⁺ influx and cell volume increase that, in necrotic cell death, is required to produce the characteristic features of membrane blebbing and membrane rupture. Here, we review emerging evidence that the monovalent cation channel, transient receptor potential melastatin 4 (TRPM4), is involved in the cell death process of oncosis. Potential involvement of TRPM4 in oncosis is suggested by the fact that the two principal regulators of TRPM4, intracellular ATP and Ca²⁺, are both altered during necrosis in the direction that causes TRPM4 channel opening. Under physiological conditions, activation of TRPM4 promotes Na⁺ influx and cell depolarization. Under pathological conditions, unchecked activation of TRPM4 leads to Na⁺ overload, cell volume increase, blebbing and cell membrane rupture, the latter constituting the irreversible end stage of necrosis. Emerging data indicate that TRPM4 plays a crucial role as end executioner in the accidental necrotic death of ATP-depleted or redox-challenged endothelial and epithelial cells, both in vitro and in vivo. Future studies will be needed to determine whether TRPM4 also plays a role in regulated necrosis and apoptosis.

Aliskiren prevents the toxic effects of peritoneal dialysis fluids during chronic dialysis in rats

The benefits of long-term peritoneal dialysis (PD) in patients with end-stage renal failure are short-lived due to structural and functional changes in the peritoneal membrane. In this report, we provide evidence for the in vitro and in vivo participation of the renin-angiotensin-aldosterone system (RAAS) in the signaling pathway leading to peritoneal fibrosis during PD. Exposure to high-glucose PD fluids (PDFs) increases damage and fibrosis markers in both isolated rat peritoneal mesothelial cells and in the peritoneum of rats after chronic dialysis. In both cases, the addition of the RAAS inhibitor aliskiren markedly improved damage and fibrosis markers, and prevented functional modifications in the peritoneal transport, as measured by the peritoneal equilibrium test. These data suggest that inhibition of the RAAS may be a novel way to improve the efficacy of PD by preventing inflammation and fibrosis following peritoneal exposure to high-glucose PDFs.

Cofilin activation mediates Bax translocation to mitochondria during excitotoxic neuronal death

During excitotoxic neuronal death, Bax translocates to the mitochondria where it plays an important role by contributing to the release of proapoptotic factors. However, how Bax translocates to the mitochondria during excitotoxicity remains poorly understood. Herein, our data suggest the presence of a novel signalling mechanism by which NMDA receptor stimulation promotes Bax translocation. This signalling pathway is triggered by dephosphorylation of cofilin. Once dephosphorylated, cofilin might interact physically with Bax acting as a carrier for it, translocating it to the mitochondria, where it contributes to mitochondrial membrane despolarization, permeabilization and to the release of apoptotic factors, thus leading to neuronal death. Lack-of-function studies indicate that only the Slingshot family of phosphatases, more specifically the enzyme Slingshot 1L phosphatase, but not cronophin participates in the cofilin activation process during excitotoxicity. Indeed, cofilin-mediated Bax translocation seems to be a key event in excitotoxic neuronal death as knock down of either cofilin or Slingshot 1L phosphatase has a marked neuroprotective effect on NMDA-mediated neuronal death. This novel biochemical pathway may therefore be a good target to develop future therapeutic molecules for neurodegenerative diseases.

HIF-1α is neuroprotective during the early phases of mild hypoxia in rat cortical neurons

Hypoxia-inducible factor 1α (HIF-1α) is a transcription factor that plays a key role in regulating the adaptive response to hypoxia. HIF-1α is stabilised during hypoxia and, after dimerisation with hypoxia-inducible factor 1β (HIF-1β), triggers the expression of various genes involved in cell cycle control and energy metabolism associated with cell survival. However, HIF-1α also regulates the expression of proapoptotic genes. The aim of this study was to ascertain the influence of HIF-1α on neurotoxicity evoked by hypoxia in rat cortical neurons. We found that mild hypoxia induces time-dependent neuronal death involving free radical production, mitochondrial depolarisation, cytochrome c release and caspase-3 activation. Lentivirus-mediated HIF-1α knockdown markedly strengthened all of these effects during the initial 24h of hypoxia, which suggests that HIF-1α plays a neuroprotective role in hypoxia-mediated neuronal death. After this initial period, the protective actions of HIF-1α disappeared over the course of the hypoxia-mediated HIF-1α stabilisation. Moreover, lentiviral-mediated overexpression of HIF-1α increased lactate dehydrogenase (LDH) A, one of the target genes for HIF-1α, but did not show protective actions on hypoxia-mediated neuronal death, indicating that the level of endogenous HIF-1α stabilisation achieved during hypoxia was already the maximum required for HIF-1α transcription activities. These results indicate that HIF-1α is neuroprotective in the early phases of hypoxia.

Inhibition of p42 MAPK using a nonviral vector-delivered siRNA potentiates the anti-tumor effect of metformin in prostate cancer cells

AIMS

The aim of this work was to study if a G1-polyamidoamine dendrimer/siRNA dendriplex can remove the p42 MAPK protein in prostate cancer cells and to potentiate the anti-tumoral effect of the antidiabetic drug metformin and taxane docetaxel.

MATERIAL & METHODS

The dendriplex uptake was studied using flow cytometry analysis. Transfection efficiency was determined by measuring p42 MAPK mRNA and protein levels. Anti-tumoral effects were determined by measuring cellular proliferation and damage.

RESULTS

The dendriplex siRNA/G1-polyamidoamine dendrimer decreased both p42 MAPK mRNA and protein levels by more than 80%, which potentiates the anti-tumoral effects of metformin.

CONCLUSION

Blockade of the MAPK pathway using a dendrimer-vehiculized siRNA to block the MAPK signaling pathway in prostate cancer cells can potentiate the anti-tumoral activity of anticancer drugs, indicating that the combination of siRNA-mediated blockade of survival signals plus anti-tumoral therapy might be a useful approach for cancer therapy.

Bcl-x(L) blocks a mitochondrial inner membrane channel and prevents Ca2+ overload-mediated cell death

Apoptosis is an active process that plays a key role in many physiological and pathological conditions. One of the most important organelles involved in apoptosis regulation is the mitochondrion. An increase in intracellular Ca²⁺ is a general mechanism of toxicity in neurons which occurs in response to different noxious stimuli like excitotoxicity and ischemia producing apoptotic and necrotic cell death through mitochondria-dependent mechanisms. The Bcl-2 family of proteins modulate the release of pro-apoptotic factors from the mitochondrial intermembrane space during cell death induction by different stimuli. In this work, we have studied, using single-cell imaging and patch-clamp single channel recording, the mitochondrial mechanisms involved in the neuroprotective effect of Bcl-x_L on Ca²⁺ overload-mediated cell death in human neuroblastoma SH-SY5Y cells. We have found that Bcl-x_L neuroprotective actions take place at mitochondria where this antiapoptotic protein delays both mitochondrial potential collapse and opening of the permeability transition pore by preventing Ca²⁺-mediated mitochondrial multiple conductance channel opening. Bcl-x_L neuroprotective actions were antagonized by the Bcl-x_L inhibitor ABT-737 and potentiated by the Ca²⁺ chelator BAPTA-AM. As a consequence, this would prevent free radical production, mitochondrial membrane permeabilization, release from mitochondria of pro-apoptotic molecules, caspase activation and cellular death.

Mechanism of pyrethroid pesticide-induced apoptosis: role of calpain and the ER stress pathway

Exposure to the pyrethroid pesticide deltamethrin has been demonstrated to cause apoptosis both in vitro and in vivo. However, the molecular pathways leading to deltamethrin-induced apoptosis have not been established. To identify these pathways, SK-N-AS neuroblastoma cells were exposed to deltamethrin (100 nM-5 μM) for 24-48 h. Deltamethrin produced a time- and dose-dependent increase (21-300%) in DNA fragmentation, an indicator of apoptosis. Data demonstrate that the initiation of DNA fragmentation resulted from interaction of deltamethrin with Na⁺ channels and consequent calcium influx, as tetrodotoxin and the intracellular Ca²⁺ chelator BAPTA-AM completely prevented apoptosis. DNA fragmentation was accompanied by increased caspase-9 and -3 activities and was abolished by specific caspase-9 and -3 inhibitors. However, deltamethrin did not increase cytosolic cytochrome c levels, indicating that the mitochondrial pathway was likely not involved. Additional studies demonstrated that deltamethrin exposure activated caspase-12 activity and that pharmacological inhibition and siRNA knockdown of calpain prevented deltamethrin-induced DNA fragmentation, thus indicating a role for the endoplasmic reticulum (ER) stress pathway. This was confirmed by the observation that inhibition of eIF2α abolished deltamethrin-induced DNA fragmentation. Together, these data demonstrate that deltamethrin causes apoptosis through its interaction with Na⁺ channels, leading to calcium overload and activation of the ER stress pathway. Because ER stress and the subsequent unfolded protein response have been observed in a number of neurodegenerative diseases, these data provide mechanistic information by which high-level exposure to pyrethroids may contribute to neurodegeneration.

Acetaminophen induces apoptosis in rat cortical neurons

Background

Acetaminophen (AAP) is widely prescribed for treatment of mild pain and fever in western countries. It is generally considered a safe drug and the most frequently reported adverse effect associated with acetaminophen is hepatotoxicity, which generally occurs after acute overdose. During AAP overdose, encephalopathy might develop and contribute to morbidity and mortality. Our hypothesis is that AAP causes direct neuronal toxicity contributing to the general AAP toxicity syndrome.

Methodology/Principal Findings

We report that AAP causes direct toxicity on rat cortical neurons both in vitro and in vivo as measured by LDH release. We have found that AAP causes concentration-dependent neuronal death in vitro at concentrations (1 and 2 mM) that are reached in human plasma during AAP overdose, and that are also reached in the cerebrospinal fluid of rats for 3 hours following i.p injection of AAP doses (250 and 500 mg/Kg) that are below those required to induce acute hepatic failure in rats. AAP also increases both neuronal cytochrome P450 isoform CYP2E1 enzymatic activity and protein levels as determined by Western blot, leading to neuronal death through mitochondrial–mediated mechanisms that involve cytochrome c release and caspase 3 activation. In addition, in vivo experiments show that i.p. AAP (250 and 500 mg/Kg) injection induces neuronal death in the rat cortex as measured by TUNEL, validating the in vitro data.

Conclusions/Significance

The data presented here establish, for the first time, a direct neurotoxic action by AAP both in vivo and in vitro in rats at doses below those required to produce hepatotoxicity and suggest that this neurotoxicity might be involved in the general toxic syndrome observed during patient APP overdose and, possibly, also when AAP doses in the upper dosing schedule are used, especially if other risk factors (moderate drinking, fasting, nutritional impairment) are present.

Overexpression of CB2 cannabinoid receptors results in neuroprotection against behavioral and neurochemical alterations induced by intracaudate administration of 6-hydroxydopamine

The role of CB2 cannabinoid receptors in the behavioral and neurochemical changes induced by intracaudate administration of 6-hydroxydopamine (6-OHDA) was evaluated. 6-OHDA (12 μg/4 μL) or its vehicle was injected in the caudate-putamen (CPu) of mice overexpressing the CB2 cannabinoid receptor (CB2xP) and wild type (WT) mice. Motor impairment, emotional behavior, and cognitive alterations were evaluated. Tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were measured by immunocytochemistry in the CPu and/or substantia nigra (SN) of CB2xP mice and WT mice. Oxidative/nitrosative and neuroinflammatory parameters were also measured in the CPu and cortex of 6-OHDA-treated and sham-treated mice. 6-OHDA-treated CB2xP mice presented significantly less motor deterioration than 6-OHDA-treated WT mice. Immunocytochemical analysis of tyrosine hydroxylase in the SN and CPu revealed significantly fewer lesions in CB2xP mice than in WT mice. GFAP and Iba-1 immunostaining revealed less astrocyte and microglia recruitment to the treated area of the CPu in CB2xP mice. Malonyldialdehyde (MDA) concentrations were lower in the striatum and cerebral cortex of sham-treated CB2xP mice than in sham-treated WT mice. The administration of 6-OHDA increased MDA levels in both WT mice and CB2xP mice; it increased the oxidized (GSSG)/reduced (GSH) glutathione ratio in the striatum in WT mice alone compared with matched sham-treated controls. The results revealed that overexpression of CB2 cannabinoid receptors decreased the extent of motor impairment and dopaminergic neuronal loss, reduced the recruitment of astrocytes and microglia to the lesion, and decreased the level of various oxidative parameters. These results suggest that CB2 receptors offer neuroprotection against dopaminergic injury.

Investigating the in vitro metabolism of veratridine: characterization of metabolites and involved cytochrome P450 isoforms

Veratridine is a lipid-soluble alkaloid extracted from Veratrum officinale and other species of the family Liliaceae. Veratridine prevents inactivation of Na(+) channel via binding the receptor site 2, causes influx of sodium ion and depolarization and induces apoptosis of neuronal cells. In the present study, we investigated the metabolism of veratridine and the effects of selective cytochrome P450 (CYP) inhibitors on the metabolism of veratridine in rat liver microsomes. The metabolites were separated and assayed by liquid-chromatography-electrospray ionization-ion trap tandem mass spectrometry (LC-ESI-QIT-MSn), and further identified by their mass spectra and chromatographic behaviors. Result showed that four CYP isoforms (CYP1A, CYP2B, CYP2E1, CYP3A) were involved in the metabolism of veratridine in vitro and seven metabolites of veratridine were detected incubating with rat liver microsomes. Some of the metabolites were presumed to be potential mediates of neurotoxicity via protein binging. Further research in vivo needs to link the metabolism of veratridine to its toxicity.

Induction of apoptosis in HepG2 cells by solanine and Bcl-2 protein

The nightshade (Solanum nigrum Linn.) has been widely used in Chinese traditional medicine as a remedy for the treatment of digestive system cancer. The anti-tumor activity of solanine, a steroid alkaloid isolated from the nightshade has been demonstrated. To observe the effect of anti-tumor and mechanism of solanine. The MTT assay was used to evaluate the IC(50) on the three digestive system tumor cell lines. The effect on the morphology was observed with a laser confocal microscopy; the rate of apoptosis and the cell cycle were measured using flow cytometry (FCM); the expression of Bcl-2 protein was measured by Western blot. The results show that the IC(50) for HepG(2), SGC-7901, and LS-174 were 14.47, >50, and >50 microg/ml, respectively; the morphology of cells in the negative control was normal; for the treated groups, typical signs for apoptosis were found. The rate of apoptosis in HepG(2) cells induced by solanine was found to be 6.0, 14.4, 17.3, 18.9, and 32.2%, respectively. Observation of the cell cycle showed that cells in the G(2)/M phases disappeared while the number of cells in the S phase increased significantly for treated groups. Western blot showed that solanine decreased the expression of Bcl-2 protein. Therefore, the target of solanine in inducing apoptosis in HepG(2) cells seems to be mediated by the inhibition in the expression of Bcl-2 protein.

Depolarization preconditioning produces cytoprotection against veratridine-induced chromaffin cell death

The hypothesis that K(+) channels and cell depolarization are involved in neuronal death and neuroprotection was tested in bovine chromaffin cells subjected to two treatment periods: the first period (preconditioning period) lasted 6 to 48 h and consisted of treatment with high K(+) solutions or with tetraethylammonium (TEA), a K(+) channel blocker; the second period consisted of incubation with veratridine for 24 h, to cause cell damage. Preconditioning with high K(+) (20-80 mM) or TEA (10-30 mM) for 24 h caused 20-60% cytoprotection against veratridine-induced cell death in bovine chromaffin cells. The absence of Ca(2+) ions during the first 9 h of an 18-h preconditioning period abolished the cytoprotection. Preconditioning with K(+) or TEA increased by 2.5-fold the expression of brain-derived neurotrophic factor and by nearly 2-fold the expression of the antiapoptotic protein Bcl-2. However, preconditioning did not modify the veratridine-evoked Ca(2+) signal. High K(+) shifted the Em by about 10 mV and TEA evoked a transient burst of action potentials superimposed on a sustained depolarization. We conclude that preconditioning may protect chromaffin cells from death by blocking K(+) channels that depolarize the cell and cause a cytosolic Ca(2+) signal, leading to enhanced expression of BDNF and Bcl-2.

Effects of veratrine and veratridine on oxygen consumption and electrical membrane potential of isolated rat skeletal muscle and liver mitochondria

We have previously shown that veratrine, a mixture of alkaloids known as Veratrum alkaloids, produces skeletal muscle toxicity, and there is evidence that veratrine interferes with the energetics of various systems, including cardiomyocytes and synaptosomes. In this work, we explored the effects of veratrine and veratridine, a component of this mixture, in rat skeletal muscle mitochondria and compared the results with those seen in liver mitochondria. Veratrine and veratridine alkaloids caused a significant concentration-dependent decrease in the rate of state 3 respiration, respiratory control (RCR) and ADP/O ratios in isolated rat skeletal muscle mitochondria (RMM), but not in rat liver mitochondria (RLM) supported by either NADH-linked substrates or succinate. The oxygen consumption experiments showed that RMM were more susceptible to the toxic action of Veratrum alkaloids than RLM. The addition of veratrine (250 microg/ml) to RMM caused dissipation of the mitochondrial electrical membrane potential during succinate oxidation, but this effect was totally reversed by adding ATP. These results indicate that there are chemical- and tissue-specific toxic effects of veratrine and veratridine on mitochondrial respiratory chain complexes. Identification of the specific respiratory chain targets involved should provide a better understanding of the molecular mechanisms of the toxicity of these agents.

Effects of veratrine on skeletal muscle mitochondria: ultrastructural, cytochemical, and morphometrical studies

The alkaloid veratrine is a lipid-soluble neurotoxin, which target voltage-gated Na+ channels for their primary action. Recently, we showed that this alkaloid may cause myonecrosis and evidences suggest mitochondria as one of its cell targets. Herein, we investigate the effects caused by variable concentration of veratrine (250 and 550 microg/mL) on mitochondrial oxygen consumption, respiratory chain enzymes activities, and ultrastructure, combining electron microscopy with cytochemical and biochemical approaches. The results showed different sort of ultrastructural changes, both in isolated and intramuscular mitochondria. Veratrine decreased mitochondrial nicotinamide adenine dinucleotide dehydrogenase (NADH-d), succinic dehydrogenase (SDH), and cytochrome oxidase (COX) activities, significantly and dose-dependently inhibited the state 3 respiration rate, respiratory control ratio (RCR), and ADP/O on isolated rat skeletal muscle mitochondria, whereas state 4 was unaffected. A tendency of increase in mitochondria diameter was seen with 250 microg/mL veratrine. We conclude that the alkaloid would probably act on mitochondrial membrane phospholipid configuration, which would explain the changes observed.

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.

Veratridine-Induced Wet Dog Shake Behaviour and Apoptosis in Rat Hippocampus

We have previously evaluated veratridine as an in vitro model of seizure using conventional electrophysiological recordings in rat hippocampal CA1 pyramidal neurones. The aim of this investigation is to further characterize this convulsant as an in vivo model of seizure. Veratridine was administered intraperitoneally to male Fisher rats in a dose range of 100-400 mug/kg. Within 5 min. after the injections, the animals entered a quiescent period which was followed 10-15 min. later by facial automatism (washing), grooming, masticatory jaw movement and profuse salivation. This phenomenon was followed by the development of wet dog shake and forelimb clonus. The time (mean+/-S.E.M.) for the onset of induction of these shakes for all tested doses was 31.65+/-2.85 min. and the number of shakes (mean+/-S.E.M.) 30 min. after the onset was 17.2+/-2.85. The onset and number of wet dog shakes induced by veratridine was dose-dependent. No rat death was recorded until 2 weeks after the experiments. Histopathological studies of animals 2 weeks after veratridine administration showed evidence of apoptosis in the hippocampus. Our results indicate that veratridine produced a behavioural pattern of a limbic seizure which mimics temporal lobe epilepsy in man. Based on our previous findings in vitro and of this investigation in vivo, veratridine can be used as an experimental tool to evaluate potential antiepileptic drugs effective against this type of limbic behaviour.

Nitric oxide and peroxynitrite induce cellular death in bovine chromaffin cells: Evidence for a mixed necrotic and apoptotic mechanism with caspases activation

Treatment of chromaffin cells with nitric oxide (NO) donors (SNP and SNAP) and peroxynitrite produces a time- and dose-dependent necrotic and apoptotic cell death. Necrotic cell death was characterized by both an increase in lactate dehydrogenase and ATP release and changes in nuclei and cell morphology (as seen with fluorescence microscopy analysis with propidium iodide and Hoechst 33342). Apoptotic cell death was characterized by nuclear fragmentation and presence of apoptotic cell bodies, by a decrease in DNA content, and by an increase in DNA fragmentation. Treatment of chromaffin cells with lipopolysaccharide (LPS) or cytokines (interferon-gamma, tumor necrosis factor-alpha) resulted only in apoptotic cell death. Apoptotic effects of NO-inducing compounds were specifically reversed, depending on the stimuli, by the NO scavenger carboxy-PTIO (CPTio) or by the NOS inhibitors L-NMA and thiocitrulline. NO-induced apoptotic death in chromaffin cells was concomitant to a cell cycle arrest in G0G1 phase and a decrease in the number of chromaffin cells in the G2M and S phases of cell cycle. All NO-producing compounds were able to induce activation of caspase 3 and cytochrome c release, and specific inhibitors of caspase 3 and 9, such as Ac-DEVD-CHO (CPP32) and Ac-Z-LEHD-FMK, respectively, prevented NO-induced apoptosis in chromaffin cells. These results suggest that chromaffin cells could be good models for investigating the molecular basis of degeneration in diseases showing death of catecholaminergic neurons, phenomenon in which NO plays an important role.

Neuroprotective activity of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (PAN-811), a cancer therapeutic agent

3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) is a highly-hydrophobic small molecule that was originally developed for cancer therapy (Triapine, Vion Pharmaceuticals) due to its ability to inhibit ribonucleotide reductase, a key enzyme required for DNA synthesis. 3-AP has a high affinity for divalent cations, chelating the Fe(2+) at the R2 subunit of the enzyme and inhibiting formation of a tyrosyl radical essential for ribonucleotide reduction. We have demonstrated that 3-AP is also a potent neuroprotectant (as such, it is referred to as "PAN-811"). In vitro it completely blocks ischemic neurotoxicity at a concentration of 0.5 microM (EC(50) approximate, equals 0.35 microM) and hypoxic toxicity at 1.2 microM (EC(50) approximate, equals 0.75 microM). Full protection of primary cortical and striatal neurons can be achieved with 3-AP when it is added to the medium at up to six hours after an ischemic insult. 3-AP also suppresses cell death induced by neurotoxic agents, including staurosporine, veratridine and glutamate, indicating activity against a central target(s) in the neurodegenerative process. 3-AP acts via neutralization of two important intracellular effectors of excitatory neurotoxicity; calcium and free radicals. Its reported ability to elevate anti-apoptotic proteins is likely to be a consequence of the suppression of excessive intracellular free calcium. In a rat model of transient ischemia, a single bolus delivery of 3-AP 1 h after the initiation of ischemic attack reduced infarct volume by 59% when administered i.c.v. (50 mug per rat) and by 35% when administered i.v. (1 mg/kg). In Phase I clinical trials in cancer therapy 3-AP had no cardiovascular, CNS or other major adverse effects. Thus, 3-AP has a high potential for development as a novel, potent neuroprotectant for the treatment of neurodegenerative diseases.

Bcl-xL blocks mitochondrial multiple conductance channel activation and inhibits 6-OHDA-induced death in SH-SY5Y cells

Apoptosis is an active process that is regulated by different signalling pathways. One of the more important organelles involved in apoptosis regulation is the mitochondrion. Electron chain transport disruption increases free radical production leading to multiple conductance channel opening, release of cytochrome c and caspase activation. This death pathway can be blocked by anti-apoptotic members of the Bcl-2 protein family that might shift redox potential to a more reduced state, preventing free radical-mediated damage. 6-Hydroxydopamine (6-OHDA) has been widely used to generate Parkinson's disease-like models. It is able to generate free radicals and to induce catecholaminergic cell death. In this paper we have used the human neuroblastoma cell line SH-SY5Y overexpressing Bcl-x(L) as a model to gain insights into the mechanisms through which Bcl-x(L) blocks 6-OHDA-induced cell death and to identify the molecular targets for this action. Herein, we present evidence supporting that the Bcl-x(L)-anti-apoptotic signal pathway seems to prevent mitochondrial multiple conductance channel opening, cytochrome c release and caspase-3 like activity following 6-OHDA treatment in the human neuroblastoma cell line SH-SY5Y.

Reactive oxygen species induce swelling and cytochrome c release but not transmembrane depolarization in isolated rat brain mitochondria

1 In this study, we have used isolated brain mitochondria to investigate the effects of superoxide anions (O(2)(-)) on mitochondrial parameters related to apoptosis, such as swelling, potential, enzymatic activity, NAD(P)H, cytochrome c release, and caspase activity. 2 Addition of the reactive oxygen species (ROS) generator KO(2) produced brain mitochondrial swelling, which was blocked by cyclosporin A (CSA), and which was Ca(2+) independent. 3 Calcium induced mitochondrial swelling only at high concentrations and in the presence of succinate. This correlated with the increase in O(2)(-) production detected with hydroethidine in mitochondrial preparations exposed to Ca(2+) and the fact that ROS were required for Ca(2+)-induced mitochondrial swelling. 4 Superoxide anions, but not Ca(2+), decreased citrate synthase and dehydrogenase enzymatic activities and dropped total mitochondrial NAD(P)H levels. 5 Calcium, but not O(2)(-), triggered a rapid loss of mitochondrial potential. Calcium-induced Deltapsi(m) dissipation was inhibited by Ruthenium Red, but not by CSA. 6 Calcium- and superoxide-induced mitochondrial swelling released cytochrome c and increased caspase activity from isolated mitochondria in a CS A-sensitive manner. 7 In summary, superoxide potently triggers mitochondrial swelling and the release of proteins involved in activation of postmitochondrial apoptotic pathways in the absence of mitochondrial depolarization.

Chromaffin cell death induced by 6-hydroxydopamine is independent of mitochondrial swelling and caspase activation

Our results provide evidence that 6-hydroxydopamine induced, after auto-oxidation, toxic levels of hydrogen peroxide (H2O2) that caused bovine chromaffin cell toxicity and death. 6-Hydroxydopamine (6-OHDA) treatment markedly reduced, in a dose-response fashion, chromaffin cell viability. Cell death was accompanied by cell shrinkage, nuclear condensation and DNA degradation. Under our experimental conditions, 6-OHDA auto-oxidation formed quinones and reactive oxygen species (ROS) that mainly contributed to 6-OHDA-induced cytotoxicity in bovine chromaffin cells. Accordingly, different antioxidants, including catalase, vitamin E, Mn(IIItetrakis(4-benzoic acid)porphyrin chloride (MnTBAP) or ascorbic acid, provided protection against 6-OHDA-induced toxicity. Further evidence that 6-OHDA induces oxidative stress is provided by the fact that this compound decreased total mitochondrial reduced NAD(P)H levels. Our results also suggest that mitochondrial swelling and caspase activation do not play a direct role in 6-OHDA-induced death in bovine chromaffin cells.

Mitochondrial dysfunction is involved in apoptosis induced by serum withdrawal and fatty acids in the beta-cell line INS-1

The potential toxic effects of high extracellular concentrations of fatty acids were tested in beta(INS-1)-cells cultured in the absence of serum, a condition known to alter cell survival in various systems. This may in part mimic the situation in type 1 or 2 diabetes where beta-cells are already insulted by various stressful conditions, such as cytokines and oxidative stress. Serum removal caused, over a 36-h period, oxidative stress and an early impairment of mitochondrial function, as revealed by increased superoxide production and markedly reduced mitochondrial membrane potential, but a lack of cytochrome c and apoptosis-inducing factor release in the cytosol. The fatty acids palmitate and oleate considerably accelerated the apoptosis process in serum-starved cells, as revealed by fluorescence-activated cell sorting analysis, morphological changes, chromatin condensation, DNA laddering, poly(ADP-ribose) polymerase cleavage, cytochrome c and apoptosis-inducing factor release, and increased levels of Bax and cytosolic caspase-2. The fatty acids also increased nitric oxide production, apparently independently of inducible nitric oxide synthase induction. Under the same experimental conditions, elevated glucose alone had only a marginal effect on beta-cell apoptosis. Together the results indicate that elevated concentrations of fatty acids are particularly efficient in accelerating the rate of apoptosis of already stressed beta(INS-1)-cells displaying altered mitochondrial function, and that the mitochondrial arm of the apoptosis process is involved in beta-cell lipotoxicity.

Superoxide anions mediate veratridine-induced cytochrome c release and caspase activity in bovine chromaffin cells

1. Mitochondrial mechanisms involved in veratridine-induced chromaffin cell death have been explored. 2. Exposure to veratridine (30 micro M, 1 h) produces cytochrome c release to the cytoplasm that seems to be mediated by superoxide anions and that is blocked by cyclosporin A (10 micro M), MnTBAP (10 nM), catalase (100 IU ml(-1)) and vitamin E (50 micro M). 3. Following veratridine treatment, there is an increase in caspase-like activity, blocked by vitamin E (50 micro M) and the mitochondrial permeability transition pore blocker cyclosporin A (10 micro M). 4. Superoxide anions open the mitochondrial permeability transition pore in isolated mitochondria, an effect that is blocked by vitamin E (50 micro M) and cyclosporin A (10 micro M), but not by the Ca2+ uniporter blocker ruthenium red (5 micro M). 5. These results strongly suggest that under the stress situation caused by veratridine, superoxide anions become important regulators of mitochondrial function in chromaffin cells. 6. Exposure of isolated bovine chromaffin mitochondria to Ca2+ results in mitochondrial swelling. This effect was prevented by ruthenium red (5 micro M) and cyclosporin A (10 micro M), while it was not modified by vitamin E (50 micro M). 7. Veratridine (30 micro M, 1 h) markedly decreased total glutathione and GSH content in bovine chromaffin cells. 8. In conclusion, superoxide anions seem to mediate veratridine-induced cytochrome c release, decrease in total glutathione, caspase activation and cell death in bovine chromaffin cells.

Nitric oxide and superoxide, a deadly cocktail

Free radicals and oxidants may have contrasting effects on cells. Nitric oxide is a cellular messenger that acts by several mechanisms, including activation of soluble guanylate cyclase, nitrosylation of thiols, and formation of peroxynitrite. The action of nitric oxide depends on oxidative conditions in the cell. In motor neurons, nitric oxide enhances brain-derived neurotrophic factor effects by stimulation of cGMP production. In the absence of trophic factors, nitric oxide induces motor neuron apoptosis by reacting with superoxide to form peroxynitrite. The mechanism of induction of motor neuron apoptosis by the formation of peroxynitrite is more complicated than simply the formation of a strong oxidant and it also involves decreased formation of cGMP.