Neuronal death, cytoplasmic calcium and internucleosomal DNA fragmentation: evidence for DNA fragments being released from cells

Mitochondrial function in spinal cord injury and regeneration

Many people around the world suffer from some form of paralysis caused by spinal cord injury (SCI), which has an impact on quality and life expectancy. The spinal cord is part of the central nervous system (CNS), which in mammals is unable to regenerate, and to date, there is a lack of full functional recovery therapies for SCI. These injuries start with a rapid and mechanical insult, followed by a secondary phase leading progressively to greater damage. This secondary phase can be potentially modifiable through targeted therapies. The growing literature, derived from mammalian and regenerative model studies, supports a leading role for mitochondria in every cellular response after SCI: mitochondrial dysfunction is the common event of different triggers leading to cell death, cellular metabolism regulates the immune response, mitochondrial number and localization correlate with axon regenerative capacity, while mitochondrial abundance and substrate utilization regulate neural stem progenitor cells self-renewal and differentiation. Herein, we present a comprehensive review of the cellular responses during the secondary phase of SCI, the mitochondrial contribution to each of them, as well as evidence of mitochondrial involvement in spinal cord regeneration, suggesting that a more in-depth study of mitochondrial function and regulation is needed to identify potential targets for SCI therapeutic intervention.

Cerebrolysin enhances spinal cord conduction and reduces blood-spinal cord barrier breakdown, edema formation, immediate early gene expression and cord pathology after injury

Spinal cord evoked potentials (SCEP) are good indicators of spinal cord function in health and disease. Disturbances in SCEP amplitudes and latencies during spinal cord monitoring predict spinal cord pathology following trauma. Treatment with neuroprotective agents preserves SCEP and reduces cord pathology after injury. The possibility that cerebrolysin, a balanced composition of neurotrophic factors improves spinal cord conduction, attenuates blood-spinal cord barrier (BSCB) disruption, edema formation, and cord pathology was examined in spinal cord injury (SCI). SCEP is recorded from epidural space over rat spinal cord T9 and T12 segments after peripheral nerves stimulation. SCEP consists of a small positive peak (MPP), followed by a prominent negative peak (MNP) that is stable before SCI. A longitudinal incision (2mm deep and 5mm long) into the right dorsal horn (T10 and T11 segments) resulted in an immediate long-lasting depression of the rostral MNP with an increase in the latencies. Pretreatment with either cerebrolysin (CBL 5mL/kg, i.v. 30min before) alone or TiO₂ nanowired delivery of cerebrolysin (NWCBL 2.5mL/kg, i.v.) prevented the loss of MNP amplitude and even enhanced further from the pre-injury level after SCI without affecting latencies. At 5h, SCI induced edema, BSCB breakdown, and cell injuries were significantly reduced by CBL and NWCBL pretreatment. Interestingly this effect on SCEP and cord pathology was still prominent when the NWCBL was delivered 2min after SCI. Moreover, expressions of c-fos and c-jun genes that are prominent at 5h in untreated SCI are also considerably reduced by CBL and NWCBL treatment. These results are the first to show that CBL and NWCBL enhanced SCEP activity and thwarted the development of cord pathology after SCI. Furthermore, NWCBL in low doses has superior neuroprotective effects on SCEP and cord pathology, not reported earlier. The functional significance and future clinical potential of CBL and NWCBL in SCI are discussed.

Neuronal Calcium and cAMP Cross-Talk Mediated by Cannabinoid CB1 Receptor and EF-Hand Calcium Sensor Interactions

Endocannabinoids are important players in neural development and function. They act via receptors, whose activation inhibits cAMP production. The aim of the paper was to look for calcium- and cAMP-signaling cross-talk mediated by cannabinoid CB₁ receptors (CB₁R) and to assess the relevance of EF-hand CaM-like calcium sensors in this regard. Using a heterologous expression system, we demonstrated that CB₁R interacts with calneuron-1 and NCS1 but not with caldendrin. Furthermore, interaction motives were identified in both calcium binding proteins and the receptor, and we showed that the first two sensors competed for binding to the receptor in a Ca²⁺-dependent manner. Assays in neuronal primary cultures showed that, CB₁R-NCS1 complexes predominate at basal Ca²⁺ levels, whereas in the presence of ionomycin, a calcium ionophore, CB₁R-calneuron-1 complexes were more abundant. Signaling assays following forskolin-induced intracellular cAMP levels showed in mouse striatal neurons that binding of CB₁R to NCS1 is required for CB₁R-mediated signaling, while the binding of CB₁R to calneuron-1 completely blocked G_i-mediated signaling in response to a selective receptor agonist, arachidonyl-2-chloroethylamide. Calcium levels and interaction with calcium sensors may even lead to apparent Gs coupling after CB₁R agonist challenge.

Antidepressants, sertraline and paroxetine, increase calcium influx and induce mitochondrial damage-mediated apoptosis of astrocytes

The impacts of antidepressants on the pathogenesis of dementia remain unclear despite depression and dementia are closely related. Antidepressants have been reported may impair serotonin-regulated adaptive processes, increase neurological side-effects and cytotoxicity. An ‘astroglio-centric’ perspective of neurodegenerative diseases proposes astrocyte dysfunction is involved in the impairment of proper central nervous system functioning. Thus, defining whether antidepressants are harmful to astrocytes is an intriguing issue. We used an astrocyte cell line, primary cultured astrocytes and neuron cells, to identify the effects of 11 antidepressants which included selective serotonin reuptake inhibitors, a serotonin-norepinephrine reuptake inhibitor, tricyclic antidepressants, a tetracyclic antidepressant, a monoamine oxide inhibitor, and a serotonin antagonist and reuptake inhibitor. We found that treatment with 10 μM sertraline and 20 μM paroxetine significantly reduced cell viability. We further explored the underlying mechanisms and found induction of the [Ca²⁺]_i level in astrocytes. We also revealed that sertraline and paroxetine induced mitochondrial damage, ROS generation, and astrocyte apoptosis with elevation of cleaved-caspase 3 and cleaved-PARP levels. Ultimately, we validated these mechanisms in primary cultured astrocytes and neuron cells and obtained consistent results. These results suggest that sertraline and paroxetine cause astrocyte dysfunction, and this impairment may be involved in the pathogenesis of neurodegenerative diseases.

Proinflammatory and proapoptotic markers in relation to mono and di-cations in plasma of autistic patients from Saudi Arabia

Objectives

Autism is a developmental disorder characterized by social and emotional deficits, language impairments and stereotyped behaviors that manifest in early postnatal life. This study aims to clarify the relationship amongst absolute and relative concentrations of K⁺, Na⁺, Ca²⁺, Mg²⁺ and/or proinflammatory and proapoptotic biomarkers.

Materials and methods

Na⁺, K⁺, Ca²⁺, Mg²⁺, Na⁺/K⁺, Ca²⁺/Mg²⁺ together with IL6, TNFα as proinflammatory cytokines and caspase3 as proapoptotic biomarker were determined in plasma of 25 Saudi autistic male patients and compared to 16 age and gender matching control samples.

Results

The obtained data recorded that Saudi autistic patients have a remarkable lower plasma caspase3, IL6, TNFα, Ca²⁺ and a significantly higher K⁺ compared to age and gender matching controls. On the other hand both Mg²⁺ and Na⁺ were non-significantly altered in autistic patients. Pearson correlations revealed that plasma concentrations of the measured cytokines and caspase-3 were positively correlated with Ca²⁺ and Ca²⁺/K⁺ ratio. Reciever Operating Characteristics (ROC) analysis proved that the measured parameters recorded satisfactory levels of specificity and sensitivity.

Conclusion

Alteration of the selected measured ions confirms that oxidative stress and defective mitochondrial energy production could be contributed in the pathogenesis of autism. Moreover, it highlights the relationship between the measured ions, IL6, TNFα and caspase3 as a set of signalling pathways that might have a role in generating this increasingly prevalent disorder. The role of ions in the possible proinflammation and proapoptic mechanisms of autistics' brains were hypothesized and explained.

Antiproliferative effect of diallyl disulfide (DADS) on prostate cancer cell line LNCaP

Garlic has been used throughout the world to treat coughs, toothache, earache, dandruff, hypertension, hysteria, diarrhoea, dysentery, diptheria, vaginitis and many other conditions. Garlic contains a complex mixture of oil and water-soluble organosulfur compounds. Diallyl disulfide (DADS), an oil-soluble constituent of garlic seems to be effective in reducing tumour cells originating from colon, lung and skin. Hence our present study focuses on the dose-dependent effect of DADS on an androgen-dependent prostate cancer cell line. Various concentrations of DADS ranging from 25 to 100 microM were given to LNCaP cells and the activity of lactate dehydrogenase (LDH) prostatic acid phosphatase (PAcP) and the level of prostate specific antigen were studied. DADS reduced the secretory activity of LNCaP cells with the gradual increase in dosage. DADS was found to act as a good antiproliferative agent, which was confirmed by proliferation assay. DADS also induced apoptosis and nuclear segmentation in the higher doses.

Activation of voltage-sensitive sodium channels during oxygen deprivation leads to apoptotic neuronal death

Sodium (Na(+)) entry into neurons during hypoxia is known to be associated with cell death. However, it is not clear whether Na(+) entry causes cell death and by what mechanisms this increased Na(+) entry induces death. In this study we used cultures of rat neocortical neurons to show that an increase in intracellular sodium (Na(i)(+)) through voltage-sensitive sodium channels (VSSCs), during hypoxia contributes to apoptosis. Hypoxia increased Na(i)(+) and induced neuronal apoptosis, as assessed by electron microscopy, annexin V staining, and terminal UDP nick end labeling staining. Reducing Na(+) entry with the VSSC blocker, tetrodotoxin (TTX), attenuated apoptotic neuronal death via a reduction in caspase-3 activation. Since the attenuation of apoptosis by TTX during hypoxia suggested that the activation of VSSCs and Na(+) entry are crucial events in hypoxia-induced cell death, we also determined whether the activation of VSSCs per se could lead to apoptosis under resting conditions. Increasing Na(+) entry with the VSSC activator veratridine also induced neuronal apoptosis and caspase-3 activation. These data indicate that a) Na(+) entry via VSSCs during hypoxia leads to apoptotic cell death which is mediated, in part, by caspase-3 and b) activation of VSSCs during oxygen deprivation is a major event by which hypoxia induces cell death.

N(2)O(2)-induced apoptosis of thymocytes involves mobilization of divalent cations

More than 90% of thymocytes undergo apoptosis while undergoing differentiation in the thymus. Although several factors act in concert to induce thymocyte apoptosis, it remains speculative if reactive oxygen intermediates produced by thymic macrophages may play a role in this process. The present investigation was carried out to determine if H(2)O(2) is capable of inducing apoptosis of thymocytes in vitro. It was observed that H(2)O(2) could induce apoptosis of thymocytes in vitro in a dose and time dependent manner. It was further found that H(2)O(2)-induced thymocyte apoptosis was dependent on the mobilization of divalent cations. The result of this study will help further in the understanding of the mechanism of H(2)O(2)-induced apoptosis

In vitro models of brain ischemia: the peptidergic drug cerebrolysin protects cultured chick cortical neurons from cell death

Glutamate (1 mM), iodoacetate (0.01 mM) and ionomycin (0.25 micro M) are reported to induce several characteristics of ischemia and neuronal degeneration in vitro, e.g. glutamate and ionomycin lesion result in a disturbance of Ca(2+) homeostasis, iodoacetate impairment leads to an inhibition of energy metabolism, suppression of protein synthesis and generation of oxygen free radicals. In this study these three lesion models were used to investigate the effects of the nootropic drug Cerebrolysin (Cere) on the survival of cortical neurons in culture and on the occurrence of apoptosis. The viability of the cells was evaluated with the colorimetric MTT-reduction assay. Apoptosis was detected with Bisbenzimide (Hoechst:33258), a fluorescent DNA stain. Administration of Cere resulted in dose dependent neuroprotection independent from the kind of lesion. In the glutamate model the drug almost doubled neuronal viability compared to lesioned controls. After acute glutamate exposure Cere reduced the number of apoptotic cells significantly. In spite of the protective efficacy after cytotoxic hypoxia induced by iodoacetate, the drug significantly increased the number of apoptotic neurons, indicating a shift from necrosis to apoptosis. In contrast to previous studies investigating acute ionomycin lesions, the chronic Ca(2+)-overload used here did not increase the abundance of apoptosis compared to the unlesioned control. Summarizing the findings it can be suggested that Cere is able to stabilize Ca(2+) homeostasis, to protect protein synthesis and to counteract neuronal death in different in vitro medels of ischemia.

Phospholipase A2-mediated Ca2+ influx by 2,2',4,6-tetrachlorobiphenyl in PC12 cells

Polychlorinated biphenyls (PCBs) are a group of persistent and widespread environmental pollutants, and known to affect signaling molecules. Phospholipase A2 (PLA2) mediates cellular destructive processes as well as normal physiological responses in neuronal cells. In this study, we examined whether PLA2 can be activated by PCBs in PC12 cells. Of the congeners tested, ortho-substituted PCBs were found to induce PLA2 activation. PLA2 activation by 2,2',4,6-tetrachlorobiphenyl (TeCB), the most potent congener, was inhibited by bromoenol lactone (BEL), a calcium-independent PLA2 (iPLA2) inhibitor, and methyl arachidonyl fluorophosphonate (MAFP), a cytosolic PLA2 and iPLA2 inhibitor. In the case of Ca2+, although 2,2',4,6-TeCB increased [Ca2+]i in the presence of extracellular Ca2+, PLA2 activation was not inhibited by EGTA and 1,2-bis (o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra (acetoxy-methyl) ester, an extracellular and an intracellular Ca2+ chelator, respectively. On the other hand, 2,2',4,6-TeCB-induced Ca2+ increase was partially inhibited by BEL and MAFP. In addition, 2,2',4,6-TeCB induced apoptotic cell death in these cells. Taken together, our results suggest that ortho-substituted PCBs might induce apoptosis through PLA2-mediated Ca2+ influx, which provides a clue to understand the mechanism of neurotoxic effects of ortho-substituted PCBs.

A population of PC12 cells that is initiating apoptosis can be rescued by nerve growth factor

Programmed cell death, or apoptosis, occurs asynchronously in neuronal cells. To overcome this asynchrony, rat pheochromocytoma (PC12) cells were separated at different stages of apoptosis on the basis of cell density. Live cells that exhibited no apoptotic features floated to the top of density gradients. The most dense cells showed extensive loss of cytochrome c from mitochondria, caspase activation, chromatin condensation, and DNA fragmentation. These cells were committed to apoptosis and could not be rescued by reculturing in with nerve growth factor (NGF). Cells of intermediate density displayed no DNA fragmentation, but had begun to show cytochrome c loss, caspase activation, and chromatin condensation. This population displayed upregulation of the prodeath factor, c-Jun, and downregulation of prosurvival kinase, Akt. Importantly, apoptosis was reversible by NGF in this population. These studies suggest that increased cell density correlates with an initial step in the apoptosis mechanism that precedes irreversible commitment to suicide.

Tetrahydrobiopterin enhances apoptotic PC12 cell death following withdrawal of trophic support

(6R)-Tetrahydro-l-biopterin (BH(4)) is the rate-limiting cofactor in the production of catecholamine and indoleamine neurotransmitters and is also essential for the synthesis of nitric oxide by nitric-oxide synthase. We have previously reported that BH(4) administration induces PC12 cell proliferation and that nerve growth factor- or epidermal growth factor-induced PC12 cell proliferation requires the elevation of intracellular BH(4) levels. We show here that BH(4) accelerates apoptosis in undifferentiated PC12 cells deprived of serum and in differentiated neuron-like PC12 cells after nerve growth factor withdrawal. Increased production of catecholamines or nitric oxide cannot account for the enhancement of apoptosis by BH(4). Furthermore, increased calcium influx by exogenous BH(4) administration is not involved in the BH(4) proapoptotic effect. Our data also argue against the possibility that increased oxidative stress, due to BH(4) autoxidation, is responsible for the observed BH(4) effects. Instead, they are consistent with the hypothesis that BH(4) induces apoptosis by increasing cell cycle progression. Elevation of intracellular BH(4) during serum withdrawal increased c-Myc (and especially Myc S) expression earlier than serum withdrawal alone. Furthermore, N-acetylcysteine and the cyclin-dependent kinase inhibitor olomoucine ameliorated the BH(4) proapoptotic effect. These data suggest that BH(4) affects c-Myc expression and cell cycle-dependent events, possibly accounting for its effects on promoting cell cycle progression or apoptosis.

Aluminum-induced apoptosis in cultured astrocytes and its effect on calcium homeostasis

Aluminum exposure and apoptotic cell death has been implicated in several neurodegenerative conditions including Alzheimer's disease. In this study, we use cultured astrocytes to investigate the ability of aluminum to induce the apoptosis of astrocytes. The proportion of apoptotic cells and cell cycle distribution were determined by flow cytometric analysis. Our results showed that exposure to aluminum at low levels (100 and 200 microM) for up to 6 days did not result in the apoptosis of astrocytes, and a dramatic blockage of apoptotic cells was found at 200 microM aluminum. However, at 400 microM, aluminum markedly induced the apoptosis of astrocytes, which was associated with a significant change in cell cycle distribution characterized by increase of G2/M phase cells (128%). Measurements of intracellular Ca(2+) concentration using the fluorescent calcium indicator dye Fluo-3 demonstrated a significant increase in the levels of intracellular calcium after aluminum treatment. However, no differences were observed among aluminum-treated groups. These findings suggest that aluminum induce and block selectively the apoptosis of astrocytes, which depend upon the concentrations of aluminum. Increased intracellular Ca(2+) may not be the primary mechanism of aluminum-mediated apoptotic cell death.

Oxidative stress, mitochondrial permeability transition and activation of caspases in calcium ionophore A23187-induced death of cultured striatal neurons

Disruption of intracellular calcium homeostasis is thought to play a role in neurodegenerative disorders such as Huntington's disease (HD). To study different aspects of putative pathogenic mechanisms in HD, we aimed to establish an in vitro model of calcium-induced toxicity in striatal neurons. The calcium ionophore A23187 induced a concentration- and time-dependent cell death in cultures of embryonic striatal neurons, causing both apoptosis and necrosis. Cell death was significantly reduced by the cell-permeant antioxidant manganese(III)tetrakis(4-benzoic acid) porphyrin (MnTBAP). Cyclosporin A and its analogue N-MeVal-4-cyclosporin also reduced the incidence of cell death, suggesting the participation of mitochondrial permeability transition in this process. Furthermore, addition of either of two types of caspase inhibitors, Ac-YVAD-CHO (acetyl-Tyr-Val-Ala-Asp-aldehyde) and Ac-DEVD-CHO (acetyl-Asp-Glu-Val-Asp-aldehyde), to the striatal cells blocked A23187-induced striatal cell death in a concentration-dependent manner. These results suggest that oxidative stress, opening of the mitochondrial permeability transition pore and activation of caspases are important steps in A23187-induced cell death.

Apoptosis and the nervous system

Apoptosis is now recognized as a normal feature in the development of the nervous system and may also play a role in neurodegenerative diseases and aging. This phenomenon has been investigated intensively during the last 6-7 years, and the progress made in this field is reviewed here. Besides a few in vivo studies, a variety of neuronal preparations from various parts of the brain, the majority of which were primary cultures, and some cell lines have been investigated. Several apoptosis-inducing agents have been identified, and these include lack of neurotrophic support, neurotransmitters, neurotoxicants, modulators of protein phosphorylation and calcium homeostasis, DNA-damaging agents, oxidative stress, nitric oxide, and ceramides. The precise signaling cascade is not well established, and there are lacunae in many suggested pathways. However, it appears certain that the Bcl family of proteins is involved in the apoptotic pathway, and these proteins in turn affect the processing of interleukin-1beta converting enzyme (ICE)/caspases. The available evidence suggests that there may be several apoptotic pathways that may depend on the cell type and the inducing agent, and most of the pathways may converge at the ICE/caspases step.

Trophic effects of purines in neurons and glial cells

In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.

Studies on the cytosolic phospholipase A2 in immortalized astrocytes (DITNC) revealed new properties of the calcium ionophore, A23187

Besides playing an important role in the maintenance of cell membrane phospholipids, phospholipases A2 (PLA2) are responsible for the release of arachidonic acid (AA) which is a precursor for prostaglandin biosynthesis. The cytosolic PLA2 has been the focus of recent studies, probably due to its ability to respond to protein kinases and changes in intracellular calcium levels. In this study, we examined agents for stimulation of the cytosolic phospholipase A2 in immortalized astrocytes (DITNC). Incubation of DITNC cells with [14C]arachidonic acid (AA) resulted in a time-dependent uptake of the label into phospholipids (PL) and neutral glycerides. In prelabeled cells, release of labeled AA could be stimulated by calcium mobilizing agents such as calcium ionophore A23187 (4-20 microM) and thimerosal (100 microM), and by phorbol myristate acetate (PMA, 100 nM), an agent for activation of protein kinase C. The release of AA could also be stimulated by ATP (200 microM), probably through activation of the purinergic receptor but not by glutamate (1 mM). The stimulated release of AA was dependent on extracellular Ca2+ and was inhibited by mepacrine (50 microM), a non-specific PLA2 inhibitor. Western blot analysis further confirmed the presence of an 85 kDa cPLA2 in both membrane and cytosol fractions of these cells and stimulation by A23187 resulted in translocation of this protein to the membrane fraction. Besides labeled fatty acids, A23187 also stimulated the concomitant release of labeled PL into the culture medium and this event was accompanied by the increased release in lactate dehydrogenase (LDH). Results thus revealed that besides activation of cPLA2, the calcium ionophore A23187 is capable of perturbating cell membrane integrity.

Oxygen toxicity induces apoptosis in neuronal cells

1. A high oxygen atmosphere induced apoptosis in cultured neuronal cells including PC12 cells and rat embryonic cortical, hippocampal, and basal forebrain neurons associated with DNA fragmentation and nuclear condensation. 2. The sensitivity of CNS neurons to a high-oxygen atmosphere was the following order; cortex > basal forebrain > hippocampus. 3. Cycloheximide and actinomycin-D inhibited the apoptosis, indicating that it depends on new macromolecular synthesis. In contrast, cultured postnatal CNS neurons were resistant to oxidative stress. 4. Neurotrophic factors such as nerve growth factor (NGF), fibroblast growth factor (FGF), and epidermal growth factor (EGF) blocked the apoptosis induced by a high-oxygen atmosphere.

Serum from patients with type 2 diabetes with neuropathy induces complement-independent, calcium-dependent apoptosis in cultured neuronal cells

We hypothesized that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that promotes complement-independent, calcium-dependent apoptosis in neuronal cell lines. Neuronal cells were cultured in the presence of complement-inactivated sera obtained from patients with type 2 diabetes with and without neuropathy and healthy adult control patients. Serum from diabetic patients with neuropathy was associated with a significantly greater induction of apoptosis, compared to serum from diabetic patients without neuropathy and controls. In the presence of calcium channel antagonists, induction of apoptosis was reduced by approximately 50%. Pretreatment of neuronal cells with serum from diabetic patients with neuropathy was associated with a significant increase in elevated K+-evoked cytosolic calcium concentration. Serum-induced enhancement in cytosolic calcium and calcium current density was blocked by treatment with trypsin and filtration of the serum using a 100,000-kd molecular weight filter. Treatment with an anti-human IgG antibody was associated with intense fluorescence on the surface of neuronal cells exposed to sera from patients with type 2 diabetes mellitus with neuropathy. We conclude that sera from type 2 diabetic patients with neuropathy contains an autoimmune immunoglobulin that induces complement-independent, calcium-dependent apoptosis in neuronal cells.

Melatonin prevents apoptosis induced by 6-hydroxydopamine in neuronal cells: implications for Parkinson's disease

It was recently reported that low doses of 6-hydroxydopamine (6-OHDA) induce apoptosis of naive (undifferentiated) and neuronal (differentiated) PC12 cells, and this system has been proposed as an adequate experimental model for the study of Parkinson's disease. The mechanism by which this neurotoxin damages cells is via the production of free radicals. Given that the neurohormone melatonin has been reported 1) to be a highly effective endogenous free radical scavenger, 2) to increase the mRNA levels and the activity of several antioxidant enzymes, and 3) to inhibit apoptosis in other tissues, we have studied the ability of melatonin to prevent the programmed cell death induced by 6-OHDA in PC12 cells. We found that melatonin prevents the apoptosis caused by 6-OHDA in naive and neuronal PC12 cells as estimated by 1) cell viability assays, 2) counting of the number of apoptotic cells, and 3) analysis and quantification of DNA fragmentation. Exploration of the mechanisms used by melatonin to reduce programmed cell death revealed that this chemical mediator prevents the 6-OHDA induced reduction of mRNAs for several antioxidant enzymes. The possibility that melatonin utilized additional mechanisms to prevent apoptosis of these cells is also discussed. Since this endogenous agent has no known side effects and readily crosses the blood-brain-barrier, we consider melatonin to have a high clinical potential in the treatment of Parkinson's disease and possibly other neurodegenerative diseases, although more research on the mechanisms is yet to be done.

Characterization of apoptosis in a motor neuron cell line

STUDY DESIGN

Serum withdrawal was introduced to a spinal cord motor neuron cell line to investigate the mode of cell death.

OBJECTIVES

To characterize the death of motor neurons in culture, to gain insight into mechanisms that could be important in spinal cord diseases.

SUMMARY OF BACKGROUND DATA

Normal reduction of cell number during central nervous system development is brought about by programmed cell death. These same apoptotic processes probably play a role in a variety of central nervous system disorders, including traumatic injury. Although certain proteolytic processes are involved, the molecular details involved in the apoptotic induction have not been fully elucidated.

METHODS

To identify apoptosis, several criteria were used, including analysis of chromatin condensation with DNA-specific stains (propidium iodide and Hoechst 33342); in situ end-labeling of DNA fragments in apoptotic nuclei with terminal deoxynucleotidyl transferase; fragmentation of DNA separated on agarose gel electrophoresis; and cleavage of a characteristic substrate for apoptotic proteases, alpha-fodrin, into signature cleavage fragments.

RESULTS

The NSC19 cell line exhibited motor neuron characteristics morphologically, with typical cellular structure, and biochemically, by synthesizing choline acetyl transferase. Under various treatments including serum withdrawal (loss of trophic factors), cell loss occurred through an apoptotic cell death pathway.

CONCLUSIONS

A murine motor neuron cell line, NSC19, has been used to investigate apoptosis in this in vitro system. Cell death occurs by apoptosis, suggesting that this cell line may provide a useful model for studying apoptotic mechanisms in spinal cord degeneration and injury.

Apoptotic cell death and caspase 3 (CPP32) activation induced by calcium ionophore at low concentrations and their prevention by nerve growth factor in PC12 cells

A23187 (a calcium ionophore) at low concentration (0.1 microM) induced apoptotic cell death (chromatin condensation and DNA fragmentation) accompanied by the activation of caspase-3 (CPP32), a member of the interleukin-1beta-converting enzyme protease. On the other hand, A23187 at high concentration (2 microM) induced necrotic cell death not accompanied by the activation of CPP32. Nerve growth factor inhibited the cell death and CPP32 activation induced by 0.1 microM A23187, but not the cell death induced by 2 microM A23187. Acylaspartyl-glutamyl-valyl-aspartyl-aldehyde, an inhibitor of CPP32, reduced the cell death induced by 0.1 microM A23187. These results suggest that calcium-ion-induced apoptotic cell death was mediated by CPP32 activation in PC12 cells.

Histopathologic clues to the pathways of neuronal death following ischemia/hypoxia

This review describes histopathologic observations made with both light and electron microscopy using both conventional staining techniques and histochemistry. Several conditions are analyzed: Ischemic cell change; delayed neuronal death; selective vulnerability. The histopathologic support for the calcium hypothesis and for the excitotoxic hypothesis explaining neuronal death is also reviewed. The findings lead to several suggestions relevant to attempts at developing interventional therapies administered after the onset of ischemia/hypoxia. (1) Except in gerbils, delayed neuronal death and more rapid neuronal death appear to be on the same continuum of cellular events. The lag between ischemia and either onset or termination of these shared events depends upon the severity and/or duration of ischemia/hypoxia. We still do not know whether the "delay," when it occurs, is a delay between ischemia and initiation of the lethal sequence or is, instead, a delay between an immediate initiation of the sequence and its lethal termination. (2) Selective vulnerability (e.g., of CA1 sector in hippocampus) is only relative. The changes are again those of ischemic cell change and are identical to the changes seen elsewhere in more severe ischemia. (3) There is histopathologic support for both the calcium hypothesis and for the cytotoxic hypothesis. Indeed, there is histopathologic support linking the two hypotheses and linking these mechanisms to the appearance of ischemic cell change. However, the histopathologic data are surprisingly sparse. The role of either hypothesis in explaining neuronal death in all areas of brain, in all types of ischemic insult, and at all times following such an insult remains to be established. (3) Apoptosis may be an important mode of neuronal death following ischemia. It differs from acute ischemic cell change; nevertheless, both calcium overload and/or excitotoxic neurotransmitters may trigger apoptosis. (4) Third cell change has been described: Eosinophilic neurons that are not shrunken and whose nuclei are not pyknotic but contain clumped chromatin. The pathogenesis and fate of these neurons remains uncertain. It is possible that they represent early apoptotic neurons. Adequate assessment of apoptosis and its relationship (to both these neurons and to neurons displaying classical ischemic cell change) may depend upon dual staining with conventional aniline dyes and with histochemical techniques designed to detect intranuclear fragments of DNA.

MPP+ induced apoptotic cell death in SH-SY5Y neuroblastoma cells: an electron microscope study

PD is a common, late-onset neurodegenerative disorder that results in part from the gradual loss of dopaminergic neurons in the substantia nigra pars compacta. The neurotoxin MPTP can induce PD-like clinical symptomatology and neuropathological destruction and, thus, has been used as a PD model. The human neuroblastoma cell line SH-SY5Y possesses many of the qualities of human neurons and, as such, has served as a model for them. Apoptosis is the mode of cell death induced in SH-SY5Y cells by MPTP, and this was confirmed with nick end labeling and bisbenzimide staining. Transmission electron microscopic analysis of the ultrastructural changes occurring in neurotoxin exposed SH-SY5Ys revealed many morphological characteristics consistent with apoptosis. These changes included plasmalemmal blebbing, altered cytosolic density, nuclear condensation and fragmentation, pronounced vacuole formation, ribosomal dispersion, and the disappearance of the golgi complex, microtubules, and smooth endoplasmic reticulum. Limited amounts of rough endoplasmic reticulum and mitochondria exhibited normal morphology throughout the apoptotic changes but then were disrupted during secondary necrotic changes. The in vitro induction of apoptosis by a parkinsonism neurotoxin might be reflective of the mechanisms of in vivo nigral degeneration occurring during PD.

Apoptotic death in cerebral hemisphere cells is density dependent and modulated by transient oxygen and glucose deprivation

Flow cytometry, light and fluorescence microscopy, and designated biochemical techniques were used to examine the type of death which occurs in cerebral cortex cells when grown under crowded vs. sparse conditions or after brief anoxia/hypoglycemia. A 4 hr episode of anoxia combined with glucose deprivation enhanced apoptotic cell death as assessed by 4',6-diamidino-2-phenylindole (DAPI) staining and reduced neutral red eye uptake. An additional form of cell death involving exclusion of the nucleus was recorded by time lapse cinematography and DAPI stain. The presence of the endonuclease inhibitor aurintricarboxylic acid (0.1 mM) reduced cell death by 56.6%, while the protein and RNA synthesis inhibitors actinomycin D and cycloheximide (each at 5 micrograms/ml) effectively decreased cell death by 83.3% and 90.6%, respectively. In contrast, 5 mM glutamate had no effect on cell death in accord with the immature state of the cells. Growth of cells under crowded conditions improved cell survival; after 2 h or 4 days in culture, cells seeded at high density (34 microgram cellular DNA/cm2) showed a nearly 3-fold decline in the amount of cell death in comparison to cells seeded at low density (5 micrograms cellular DNA/cm2). At high cell density, anoxic episodes enhanced cell death most likely by preventing a cell density-mediated rescue. Neutral red dye uptake, an index for cell viability, was enhanced with increasing cell density and in vitro maturation, but was reduced in dense cultures exposed to anoxic/hypoglycemic conditions. The data suggest that cell density may play a critical role in brain organogenesis and that anoxic stress is more deleterious in dense than sparse cell assemblies.

Apoptosis in neurodegenerative disorders: potential for therapy by modifying gene transcription

Apoptotic, rather than necrotic, nerve cell death now appears as likely to underlie a number of common neurological conditions including stroke, Alzheimer's disease, Parkinson's disease, hereditary retinal dystrophies and Amyotrophic Lateral Sclerosis. Apoptotic neuronal death is a delayed, multistep process and therefore offers a therapeutic opportunity if one or more of these steps can be interrupted or reversed. Research is beginning to show how specific macromolecules play a role in determining the apoptotic death process. We are particularly interested in the critical nature of gradual mitochondrial failure in the apoptotic process and propose that a maintenance of mitochondrial function through the pharmacological modulation of gene expression offers an opportunity for the effective treatment of some types of neurological dysfunction. Our research into the development of small diffusible molecules that reduce apoptosis has grown from studies of the irreversible MAO-B inhibitor (-)-deprenyl. (-)-Deprenyl can reduce neuronal death independently of MAO-B inhibition even after neurons have sustained seemingly lethal damage. (-)-Deprenyl can also influence the process outgrowth of some glial and neuronal populations and can reduce the concentrations of oxidative radicals in damaged cells at concentrations too small to inhibit MAO. In accord with earlier work of others, we showed that (-)-deprenyl alters the expression of a number of mRNAs or of proteins in nerve and glial cells and that the alterations in gene expression/protein synthesis are the result of a selective action on transcription. The alterations in gene expression/protein synthesis are accompanied by a decrease in DNA fragmentation characteristic of apoptosis and the death of responsive cells. The onco-proteins Bcl-2 and Bax and the scavenger proteins Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD-2) are among the 40-50 proteins whose synthesis is altered by (-)-deprenyl. Since mitochondrial membrane potential correlates with mitochondrial ATP production, we have used confocal laser imaging techniques in living cells to show that the transcriptional changes induced by (-)-deprenyl result in a maintenance of mitochondrial membrane potential, a decrease in intramitochondrial calcium and a decrease in cytoplasmic oxidative radical levels. We therefore propose that (-)-deprenyl acts on gene expression to maintain mitochondrial function and decrease cytoplasmic oxidative radical levels and thereby reduces apoptosis. An understanding of the molecular steps by which (-)-deprenyl selectively alters transcription may lead to the development of new therapies for neurodegenerative diseases.

Protective effect of interleukin-6 against the death of PC12 cells caused by serum deprivation or by the addition of a calcium ionophore

Interleukin-6 (IL-6) is known to differentiate the rat pheochromocytoma cell line PC12 to neuron-like cells. We examined the effect of IL-6 on the death of PC12 cells. IL-6 significantly blocked the death of PC12 cells by serum deprivation. The protective effect of IL-6 was increased by preincubation of PC12 with IL-6 for 20 hr before serum deprivation. The inhibition of protein synthesis by cycloheximide had no effect on the protective effect of IL-6 on the serum deprivation-induced cell death. IL-6 also inhibited the death of PC12 cells induced by addition of the calcium ionophore A23187 to the culture medium. Specific in situ labeling of DNA cleavage was observed in PC12 cells subjected to both serum deprivation and A23187 for 24 hr. IL-6 inhibited DNA fragmentation in PC12 cells following serum deprivation. These results suggest that the death of PC12 cells induced by serum deprivation or by the addition of calcium ionophore is apoptosis, and that IL-6 blocks apoptosis of PC12 cells.

Cytotoxic effects of an oxidative stress on neuronal-like pheochromocytoma cells (PC12)

Although the generation of oxygen derivatives during ischemia and reperfusion is generally held as a major event in the process leading to neuronal death, the biochemical mechanisms responsible for cell degeneration remain poorly understood. To better understand the toxicity induced by oxidative stress in neural tissue, we have tested the effect of an exogenous hydroperoxide, cumene hydroperoxide (CHP), on the metabolism and viability of PC12 cells. Addition of CHP in the culture medium leads to significant cell death that becomes perceptible at concentrations above 1 microM and reaches a maximum (80-90% toxicity) at 100 microM. A time-course study shows that Trypan blue uptake is preceded by a rapid phase of cell rounding and detachment from the substratum (within 30 min) followed by a progressive uptake of the dye (60-120 min). During this 2-hr period, we failed to observe any major signs of membrane lipoperoxidation (such as MDA production or fatty acid release). On the other hand, we observed that cell death is preceded by a striking decrease in cellular ATP content and in the retention of rhodamine 123 (within 15-30 min of treatment); thus, suggesting that the mitochondria may be the primary target of hydroperoxide action.

Induction of apoptosis in a Drosophila neuronal cell line by calcium ionophore

Apoptotic type cell death was induced by the calcium ionophore, A23187, in a Drosophila CNS derived cell line, ML-DmBG2-c2. It was judged by the ultrastructural observations and internucleosomal DNA fragmentation, typical characteristics of apoptosis. The ionophore failed to induce apoptosis in Ca2+- free medium, which suggests that the increase of intracellular Ca2+ concentration by the treatment of A23187 triggers apoptosis in the clonal cells.

NMDA and kainate induce internucleosomal DNA cleavage associated with both apoptotic and necrotic cell death in the neonatal rat brain

Injection of N-methyl-D-aspartate (NMDA) or kainate in the striatum of 7-day-old rats induced massive cell loss in the ipsilateral striatum, hippocampus and inner cortical layers. In order to examine whether apoptosis contributes to cell death in this model of excitotoxic injury we examined the progression of internucleosomal DNA fragmentation and changes in cellular ultrastructure. Agarose gel electrophoresis of DNA extracted from the ipsilateral striatum, cerebral cortex and hippocampus clearly showed breakdown of DNA into oligonucleosome-sized fragments, indicative of apoptosis, 12 h post-NMDA injection. In addition, an increase between 12 and 24 h was observed as well as a continuous presence 5 days later. Kainate induced a similar time course of oligonucleosomal DNA fragmentation, but the intensity of the ethidium bromide stained bands was less compared with that observed for NMDA. DNA fragmentation was not detected in animals intrastriatally injected with Tris-HCl or in animals treated with MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine hydrogen maleate, 1 mg/kg] 30 min after NMDA injection. MK-801 had no effect on DNA fragmentation induced by kainate. In addition to agarose gel electrophoresis, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labelling (TUNEL) was used for detection of DNA fragmentation in sections. A gradual increase in the density of both apoptotic and non-apoptotic TUNEL nuclei was found in the anterior cingulate (ACC) and retrosplenial (RSC) areas of the cortex, the striatum, and the CA1 area and dentate gyrus of the hippocampus over the first 24 h post-NMDA or kainate injection. In the contralateral hemisphere hardly any TUNEL nuclei were present and their density was comparable with that in animals injected with vehicle only. In the ipsilateral mammillary nucleus (MN), which showed no signs of acute cell swelling after intrastriatal injection with NMDA, internucleosomal DNA fragmentation was found 24 and 48 h after intrastriatal NMDA injection. Here, the density of TUNEL cells with apoptotic morphology was high at 12 and 24 h post-NMDA injection but returned to control levels by 5 days. Electron microscopy showed cells with a clearly apoptotic morphology in the ACC and RSC and in the MN 24 h after NMDA injection. In the CA1 area of the hippocampus a necrotic, rather than an apoptotic, ultrastructure prevailed, indicating that the TUNEL method stained both apoptotic and necrotic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of inducible transcription factors in apoptotic nerve cell death

Recent studies have shown that certain types of nerve cell death in the brain occur by an apoptotic mechanism. Researchers have demonstrated that moderate hypoxic-ischemic (HI) episodes and status epilepticus (SE) can cause DNA fragmentation as well as other morphological features of apoptosis in neurons destined to die, whereas more severe HI episodes lead to neuronal necrosis and infarction. Although somewhat controversial, some studies have demonstrated that protein synthesis inhibition prevents HI-and SE-induced nerve cell death in the brain, suggesting that apoptotic nerve cell death in the adult brain is de novo protein synthesis-dependent (i.e., programmed). The identity of the proteins involved in HI-and SE-induced apoptosis in the adult brain is unclear, although based upon studies in cell culture, a number of potential cell death and anti-apoptosis genes have been identified. In addition, a number of studies have demonstrated that inducible transcription factors (ITFs) are expressed for prolonged periods in neurons undergoing apoptotic death following HI and SE. These results suggest that prolonged expression of ITFs (in particular c-jun) may form part of the biological cascade that induces apoptosis in adult neurons. These various studies are critically discussed and in particular the role of inducible transcription factors in neuronal apoptosis is evaluated.

Ultrastructural analysis of beta-amyloid-induced apoptosis in cultured hippocampal neurons

Following treatment with the beta-amyloid (A beta) 25-35 analog, scanning and transmission electron microscopy were used to investigate the morphological changes in cultured hippocampal neurons during the course of degeneration. Ultrastructural analysis revealed focal cell surface blebbing and rapid condensation of nuclear chromatin. Changes in cytoplasmic morphology included prominent vacuole formation, dispersal of polyribosome rosettes and the disappearance of the golgi complex, smooth endoplasmic reticulum and microtubules with increased cytoplasmic electron density. Mitochondria and limited rough endoplasmic reticulum remained intact throughout the process of cell death. These results provide additional evidence suggesting A beta-induced cell death in vitro occurs via an apoptotic mechanism.

Ca2+ ionophore-induced apoptosis on cultured embryonic rat cortical neurons

The neurotoxicity of ionomycin, a Ca2+ ionophore, was investigated in cultured cortical neurons from embryonic rats. While about 90% of neurons survived 2 h after exposure to ionomycin, the surviving neurons had decreased by about 30 to 40% at 16 h. Both RNA and protein synthesis inhibitors blocked this neurotoxicity. Furthermore, c-Fos immunoreactive neurons increased not only in number but also in the intensity of immunoreactivity. These results suggest that ionomycin-induced neuronal cell death is an active process which requires de novo transcription and translation. In addition, the ultrastructural changes, such as shrinkage of cell body, compaction of nucleus, condensation of chromatin, and membrane blebbing, were observed by electron microscopy. These morphological changes are indexes of apoptosis. Furthermore, DNA fragmentation, a biochemical marker of apoptosis, was also observed. All the results suggest that ionomycin-induced neuronal cell death is apoptotic.

The brain protein S-100ab induces apoptosis in PC12 cells

Incubation of PC12 cells with S-100 protein induces a rapid (0.5-1.0 min) rise of intracellular Ca2+ which lasts for the whole period of incubation. This effect is abolished in a Ca(2+)-free medium or in the presence of 1.0 microM Ni2+, an inhibitor of calcium channels. The rise in intracellular Ca2+ is followed by a progressive increase of cells undergoing degeneration and death. This event is accompanied by the appearance of apoptotic bodies and DNA fragmentation typical of the process known as apoptosis. S-100-induced cell death is prevented by 1 microM Ni2+ or by 0.1 nM cycloheximide, suggesting the involvement of new protein synthesis. It is postulated that the binding of S-100ab to specific sites present in PC12 cells is followed by the formation of Ca2+ channels and/or the stimulation of pre-existing ones with consequent increase of Ca2+ influx and activation of a process of cell death.

Neuronal phenotypes in mouse dorsal root ganglion cell cultures: enrichment of substance P and calbindin D-28k expressing neurons in a defined medium

The primary sensory neurons in mouse dorsal root ganglia consist of diversified subpopulations which express distinct phenotypic characteristics such as substance P or calbindin D-28k. To determine whether neuronal phenotypes are altered or not in in vitro cultures carried out in a defined synthetic medium, dissociated dorsal root ganglion cells from newborn mice were grown in the alpha-modified minimum essential medium either supplemented with 10% fetal calf serum or serum-free. About 80% of the neurons survived after 5 days of culture in both media, but only 35% or 65% were rescued after 12 days in serum-free or fetal calf serum supplemented medium, respectively. The neuronal subpopulations expressing substance P or calbindin D-28k displayed similar morphological properties in both media and a higher resistance to culture conditions than the whole neuronal cell population, especially in serum-free medium. It is therefore concluded that a defined synthetic medium offers reproducible conditions to culture dorsal root ganglion cells for at least 5 days, stimulates the expression of substance P and enriches preferentially neuronal phenotypes expressing substance P or calbindin D-28k, for a longer period of culture.