Mechanism of cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction

Cyclopentenone Isoprostanes Inhibit the Inflammatory Response in Macrophages

Although both inflammation and oxidative stress contribute to the pathogenesis of many disease states, the interaction between the two is poorly understood. Cyclopentenone isoprostanes (IsoPs), highly reactive structural isomers of the bioactive cyclopentenone prostaglandins PGA2 and PGJ2, are formed non-enzymatically as products of oxidative stress in vivo. We have, for the first time, examined the effects of synthetic 15-A2- and 15-J2-IsoPs, two groups of endogenous cyclopentenone IsoPs, on the inflammatory response in RAW264.7 and primary murine macrophages. Cyclopentenone IsoPs potently inhibited lipopolysaccharide-stimulated IkappaB alpha degradation and subsequent NF-kappaB nuclear translocation and transcriptional activity. Expression of inducible nitric-oxide synthase and cyclooxygenase-2 were also inhibited by cyclopentenone IsoPs as was nitrite and prostaglandin production (IC50 approximately 360 and 210 nM, respectively). 15-J2-IsoPs potently activated peroxisome proliferator-activated receptor gamma (PPARgamma) nuclear receptors, whereas 15-A2-IsoP did not, although the anti-inflammatory effects of both molecules were PPARgamma-independent. Interestingly 15-A2-IsoPs induced oxidative stress in RAW cells that was blocked by the antioxidant 4-hydroxy-TEMPO (TEMPOL) or the mitochondrial uncoupler carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone. TEMPOL also abrogated the inhibitory effect of 15-A2-IsoPs on lipopolysaccharide-induced NF-kappaB activation, inducible nitricoxide synthase expression, and nitrite production, suggesting that 15-A2-IsoPs inhibit the NF-kappaB pathway at least partially via a redox-dependent mechanism. 15-J2-IsoP, but not 15-A2-IsoP, also potently induced RAW cell apoptosis again via a PPAR gamma-independent mechanism. These findings suggest that cyclopentenone IsoPs may serve as negative feedback regulators of inflammation and have important implications for defining the role of oxidative stress in the inflammatory response.

Advanced electrochemical sensors for cell cancer monitoring

The possibility of using minimally invasive analytical instruments to monitor cancerous cells and their interactions with analytes provide great advances in cancer research and toxicology. The real success in the development of a reliable sensor for cell monitoring depends on the ability to design powerful instrumentation that will facilitate efficient signal transduction from the biological process that occurs in the cellular environment. The resulting sensor should not affect cell viability and must function as well as adapt the system to the specific conditions imposed by the cell culture. Due to their performance, electrochemical biosensors could be used as an effective instrument in cell cancer research for studying biochemical processes, cancer development and progression as well as toxicity monitoring. Current research in this direction is conducted through high-throughput, compact, portable, and easy to use sensors that enable measurement of cells' activity in their optimum environment. This paper discusses the potential of a high-throughput electrochemical multisensor system, so-called the DOX system for monitoring cancerous cells and their interaction with chemical toxins. We describe the methodology, experiments, and the operation principle of this device, and we focus on the challenges encountered in optimizing and adapting the system to the specific cell-culture conditions. The DOX system is also compared with conventional cell-culture techniques.

Nucleation-dependent polymerization is an essential component of amyloid-mediated neuronal cell death

Accumulating evidence suggests that amyloid protein aggregation is pathogenic in many diseases, including Alzheimer's disease. However, the mechanisms by which protein aggregation mediates cellular dysfunction and overt cell death are unknown. Recent reports have focused on the potential role of amyloid oligomers or protofibrils as a neurotoxic form of amyloid-beta (Abeta) and related amyloid aggregates. Here we describe studies indicating that overt neuronal cell death mediated by Abeta(1-40) is critically dependent on ongoing Abeta(1-40) polymerization and is not mediated by a single stable species of neurotoxic aggregate. The extent and rate of neuronal cell death can be controlled by conditions that alter the rate of Abeta polymerization. The results presented here indicate that protofibrils and oligomeric forms of Abeta most likely generate neuronal cell death through a nucleation-dependent process rather than acting as direct neurotoxic ligands. These findings bring into question the use of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide formazan assay (MTT assay) as a reporter of Abeta-mediated neuronal cell death and suggest that diffusible Abeta protofibrils and oligomers more likely mediate subtle alterations of synaptic function and long-term potentiation rather than overt neuronal cell death. These results have been extended to Abeta(1-42), the non-Abeta component of Alzheimer's disease amyloid plaques, and human amylin, suggesting that nucleation-dependent polymerization is a common mechanism of amyloid-mediated neuronal cell death. Our findings indicate that ongoing amyloid fibrillogenesis may be an essential mechanistic process underlying the pathogenesis associated with protein aggregation in amyloid disorders.

Cobra cardiotoxin-induced cell death in fetal rat cardiomyocytes and cortical neurons: different pathway but similar cell surface target

Cobra cardiotoxins (CTXs) are basic polypeptides with diverse pharmacological functions that are cytotoxic to many different cell types through both necrotic and apoptotic cell death pathways. In this comparative study of the action of CTX A3 from the Taiwan cobra (Naja atra) on fetal rat cardiomyocytes and cortical neurons, it was shown that CTX A3 induced different patterns of elevation of intracellular Ca2+ concentration ([Ca2+]i), CTX internalization, caspase-3 activity and viability. Application of an anti-sulfatide monoclonal antibody, O4 specific for 3-sulfo-galactose lipid, but not in the control experiments using anti-GM3 monoclonal antibody, reduces CTX-induced [Ca2+]i elevation, CTX internalization and toxicity. Therefore, CTX may target similar sulfo-containing cell surface receptors in both fetal rat cardiomyocytes and cortical neurons, but induce cell death through different pathways specific to each cell type.

Glutamate modulates sodium-potassium-ATPase through cyclic GMP and cyclic GMP-dependent protein kinase in rat striatum

Excessive excitatory action of glutamate and nitric oxide (NO) has been implicated in degeneration of striatal neurons. Evidence had been provided that Na+K+-ATPase might be involved in this process. Here we investigated whether glutamate-regulated messengers, such as NO and cyclic GMP, could modulate the activity of membrane Na+K+-ATPase. Our results demonstrated that NO donors sodium nitroprusside (SNP at 30 and 300 microM) and S-nitroso-N-acetylpenicillamine (SNAP at 200 microM) increased alpha2,3Na+K+-ATPase activity which was blocked by the NO chelator, haemoglobin and was independent of [Na+]. This regulation was associated with cGMP synthesis and mimicked by glutamate (300 microM) and 8-Br-cyclic GMP (4 mM). 8-Br-cGMP-induced stimulation of Na+K+-ATPase activity could be blocked by KT5823 (an inhibitor of cGMP-dependent protein kinase, PKG), but not by KT5720 (an inhibitor of cAMP-dependent protein kinase, PKA). N-Methyl-D-aspartate (NMDA) receptors appeared to be involved in the effect of glutamate, since MK-801 (NMDA receptor antagonist) produced a partial reduction in glutamate-induced activation of the enzyme. MK-801 was not synergistic to L-NAME (NOS inhibitor), suggesting that glutamate stimulates the NMDA-NOS pathway to activate alpha2,3 Na+K+-ATPase in rat striatum. This regulation was associated with cyclic GMP (but not cyclic AMP) synthesis. These data indicate the existence, in vitro, of a regulatory pathway by which glutamate, acting through NO and cGMP, can cause alterations in striatal alpha2,3 Na+K+-ATPase activity.

Oxidative stress induced by beta-amyloid peptide1–42 is involved in the altered composition of cellular membrane lipids and the decreased expression of nicotinic receptors in human SH-SY5Y neuroblastoma cells

The neurotoxic effects and influence of beta-amyloid peptide (Abeta)(1-42) on membrane lipids and nicotinic acetylcholine receptors (nAChRs) in human SH-SY5Y neuroblastoma cells were investigated in parallel. Exposure of the cultured cells to varying concentrations of Abeta(1-42) evoked a significantly decrease in cellular reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5,diphenyl tetrazolium bromide), together with enhanced lipid peroxidation and protein oxidation. Significant reductions in the total contents of phospholipid and ubiquinone-10, as well as in the levels of the alpha3 and alpha7 subunit proteins of nAChRs were detected in cells exposed to Abeta(1-42). In contrast, such treatment had no effect on the total cellular content of cholesterol. Among these alterations, increased lipid peroxidation and decreased levels of cellular phospholipids were most sensitive to Abeta(1-42), occurring at lower concentrations. In addition, when SH-SY5Y cells were pretreated with the antioxidant Vitamin E, prior to the addition of Abeta(1-42), these alterations in neurotoxicity, oxidative stress, composition of membrane lipids and expression of nAChRs were partially prevented. These findings suggest that stimulation of lipid peroxidation by Abeta may be involved in eliciting the alterations in membrane lipid composition and the reduced expression of nAChRs associated with the pathogenesis of AD.

Colorimetric lactate dehydrogenase (LDH) assay for evaluation of antiviral activity against bovine viral diarrhoea virus (BVDV) in vitro

A rapid and sensitive screening assay has been established for in vitro evaluation of antiviral compounds against bovine viral diarrhoea virus (BVDV), which is widely used as a surrogate for hepatitis C virus (HCV). The procedure is based on photospectrometrical assessment for the viability of virus-infected cells via extracellular leakage of lactic dehydrogenase (LDH). The level of LDH in culture supernatants of BVDV-infected Madin-Darby bovine kidney (MDBK) cells was significantly higher than those of mock-infected MDBK cells. Under optimized assay conditions, the LDH level was found to correlate well with the degree of viral replication. When the 50% effective concentrations (EC50s) of ribavirin, cyclosporine A and human interferon-alpha for BVDV replication were determined by the established LDH method and compared with those obtained by a conventional tetrazolium colorimetric (MTT) method, there was a complete correlation in EC50s between the two methods. Furthermore, a much higher ratio of background activity (noise) to sample activity (signal) could be achieved with the LDH method than with the MTT method, indicating that the present LDH assay permits a sensitive, rapid and reliable screening of compounds for their anti-BVDV activity and may be useful for the discovery of novel anti-HCV agents.

Effects of root-end filling materials and eugenol on mitochondrial dehydrogenase activity and cytotoxicity to human periodontal ligament fibroblasts

Various root-end filling materials have been used to prevent the entry of root-canal pathogens into periapical regions. Five root-end filling materials were compared regarding the cytotoxicity, apoptosis, and mitochondrial dehydrogenase (MDH) activities of human periodontal ligament (PDL) fibroblasts, with the use of a novel transwell culture system. Exposure to IRM (a ZnO eugenol-based intermediate restorative material), a 2-ethoxybenzoic acid cement (Super EBA), and amalgam for 3 days inhibited the MDH activity of PDL fibroblasts as indicated by decrease in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction by 97%, 95%, and 51%, respectively. Evident suppression of MTT reduction by amalgam and glass ionomer cement (GIC) was noted after 5 days of exposure, with 73% and 46% of inhibition, respectively. Mineral trioxide aggregates (MTA) showed little effect on MDH activity. IRM and Super EBA were cytotoxic to PDL fibroblasts as indicated by a trypan blue dye exclusion technique. GIC and amalgam showed mild cytotoxicity. IRM, GIC, and amalgam further induced apoptosis of PDL cells, as revealed by the presence of sub-G0/G1 DNA content in flow cytometric histogram. Twenty-four-hour exposure to IRM and Super EBA elevated the MDH activities to 156% and 117%, correspondingly, of that of control. Eugenol, a phenolic ingredient in Super EBA and IRM, also increases MDH activity of PDL fibroblasts by 45% and 51%, at concentrations of 0.5 and 1 mM. However, at concentrations higher than 0.5 mM, eugenol decreased the number of viable PDL fibroblasts. These results suggest that MTA is a biocompatible root-end filling material, followed by self-curing Fuji II GIC and amalgam. IRM and Super EBA ingredients induced marked cytotoxicity and transiently stimulate MDH activities, which is possibly due to their content of eugenol and induction of cellular adaptive response.

Kinetics of MTT-formazan exocytosis in phagocytic and non-phagocytic cells

MTT is taken up by cells by endocytosis and reduced to formazan in the endosomal/lysosomal compartment. Formazan is deposited intracellularly as blue granules and is later exocytosed as needle-like formazan crystals. The present study involves an analysis of the pattern of exocytosis of MTT in different cell types showing clearcut differences in the response that can be associated to their ability to phagocytose. To further assess the characteristics of the exocytic mechanism of MTT/formazan, different experimental conditions were assayed. When culture medium with decreasing serum concentration was used as a metabolic modulator no variations were observed in the proportion of cells with formazan crystals. Conversely, the markedly sensitivity of phagocytic cells to increasing concentrations of genistein constituted a remarkable difference with non-phagocytic cells. These results must be considered when the modulation of MTT exocytosis is used as a signal of the progress of human diseases.

Age-related changes in cyclic GMP and PKG-stimulated cerebellar Na,K-ATPase activity

Energy deficiency and dysfunction of the Na,K-ATPase are common consequences of many pathological insults. Glutamate through cyclic GMP and cyclic GMP-dependent protein kinase (PKG) has been shown to stimulate alpha(2/3)-Na,K-ATPase activity in the central nervous system. Thus, a slight impairment of this pathway may amplify the disruption of ion homeostasis in the presence of a non-lethal insult. We investigate the effect of aging (4, 12 and 24 months) on the glutamate-cyclic GMP-PKG modulation of alpha1, alpha(2/3)-Na,K-ATPase activity in rat cerebellum and the stimulation of the glutamate-cyclic GMP-PKG pathway at different levels. Cyclic GMP levels and alpha(2/3)-Na,K-ATPase activity were progressively decreased from 4 and 24 month-old animals. However, PKG basal activity was reduced between 4 and 12 months, and no additional change was observed at 24 months. The ability of 8-Br-cyclic GMP to stimulate PKG activity was only reduced between 12 and 24 months. Moreover, glutamate or 8-Br-cyclic GMP promoted a smaller increase of alpha(2/3)-Na,K-ATPase activity at 24 months, when compared to 4 and 12 months. In spite of the age-related reduced basal levels of cyclic GMP, the production induced by CO or NO was not age-related. Finally, inhibition of PKG activation by KT5823 revealed a lower sensitivity of the enzyme at the older age. Taken together, these data show that basal age-related decline in sodium pump activity is a consequence of changes in different steps of the cyclic GMP-PKG pathway. On the other hand, age-related reduction in glutamate positive modulation of cerebellar alpha(2/3)-Na,K-ATPase is linked to a defective PKG signaling pathway.

Short-term serum supplementation improves glucose-oxygen deprivation in primary cortical cultures grown under serum-free conditions

Brain ischemia can be studied in vitro by depriving primary neurons of oxygen and glucose by replacing oxygen with argon and glucose with its antimetabolite 2-deoxy-D-glucose. In this contribution, we explain how to construct a reliably functioning ischemia chamber and use it to study neuronal cell death in neuron-enriched fetal primary cortical cultures grown under serum-free conditions. We observed that these cultures exhibited a significant cell death even during exposure to oxygenated balanced salt solution used as control for oxygen-glucose deprivation. We show that addition of only 2% fetal calf serum 24 h prior, during, and after treatment almost abolished this undesirable cell loss and proportionally increased cell death induced by oxygen-glucose deprivation. Western blots and immunocytochemistry showed that these effects were mainly due to an increase in neuronal viability under control conditions accompanied by a limited glial proliferation independent of the treatment condition. Under these modified conditions, the cultures could also still be effectively preconditioned by a short-term oxygen-glucose deprivation. In summary, this modified protocol combines the advantages of serum-free neuronal culture, where potentially toxic antimitotic substances can be omitted, with a serum-mediated protection of neurons against unspecific factors and concomitant sensitization for oxygen-glucose deprivation.

Acidosis during reoxygenation has an early detrimental effect on neuronal metabolic activity

We recently showed that acidosis is protective during hypoxia and detrimental during reoxygenation. We hypothesized that the detrimental effect of acidosis during reoxygenation was due to a negative effect on mitochondrial function. Human postmitotic NT2-N neurons were exposed to 3 h of hypoxia and glucose deprivation and then reoxygenated for 0, 1, 4, 9, or 21 h. The detrimental effect of acidotic reoxygenation on metabolic activity was evident already after 1 h of reoxygenation, when MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] reduction (percentage of normoxic controls) was significantly higher in cells reoxygenated with neutral compared with acidotic medium both after acidotic hypoxia (83+/-26% versus 67+/-27%, p=0.006) and after neutral hypoxia (51+/-12% versus 41+/-7%, p=0.005). Hypoxanthine, a marker of cellular energy failure, increased more with acidotic compared with neutral reoxygenation both after acidotic hypoxia (after 21 h: 7.7+/-2.7 versus 3.1+/-1.9 microM, p<0.001) and after neutral hypoxia (10.4+/-2.6 versus 7.9+/-2.8 microM, p=0.001). During hypoxia and reoxygenation, there was an earlier reduction in the activity of complex IV compared with complexes II+III, and the ratio between these complexes fell during the first hour of reoxygenation. The reduction in complex IV activity was alleviated with acidotic hypoxia. Acidosis during reoxygenation, however, had no effect on the activity of either complex IV or complexes II+III. We conclude that acidosis during hypoxia increases neuronal survival and preserves complex IV activity. Acidosis during reoxygenation has an early detrimental effect on metabolic activity, but this is not mediated through an effect on the mitochondrial complexes IV or II+III.

A human single-chain antibody specific for integrin alpha3beta1 capable of cell internalization and delivery of antitumor agents

Selective antitumor chemotherapy can be achieved by using antibody-drug conjugates that recognize surface proteins upregulated in cancer cells. One such receptor is integrin alpha3beta1, which is overexpressed on malignant melanoma, prostate carcinoma, and glioma cells. We previously identified a human single-chain Fv antibody (scFv), denoted Pan10, specific for integrin alpha3beta1 that is internalized by human pancreatic cancer cells. Herein, we describe the chemical introduction of reactive thiol groups onto Pan10, the specific conjugation of the modified scFv to maleimide-derivatized analogs of the potent cytotoxic agent duocarmycin SA, and the properties of the resultant conjugates. Our findings provide evidence that Pan10-drug conjugates maintain the internalizing capacity of the parent scFv and are cytotoxic at nanomolar concentrations. Our Pan10-drug conjugates may be promising candidates for targeted chemotherapy of malignant diseases associated with overexpression of integrin alpha3beta1.

In brain mitochondria the branched-chain fatty acid phytanic acid impairs energy transduction and sensitizes for permeability transition

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) accumulates at high levels throughout the body in the adult form of Refsum disease, a peroxisomal genetic disorder. However, it is still unclear why increased levels of phytanic acid have cytotoxic effects. In the present study, we examined the influence of non-esterified phytanic acid on energy-related functions of mitochondria from adult rat brain. Phytanic acid at low concentrations (5-20 microM, i.e. 5-20 nmol/mg of mitochondrial protein) de-energized mitochondria, as indicated by depolarization, stimulation of non-phosphorylating oxygen uptake and inhibition of the reduction of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide. The unbranched homologue palmitic acid exerted much smaller effects. In addition, phytanic acid reduced state 3 respiration, which was partly due to inhibition of the ADP/ATP carrier. Phytanic acid decreased the rate of adenine nucleotide exchange and increased the degree of control, which the ADP/ATP carrier has on state 3 respiration. Important for functional consequences is the finding that mitochondria, which are preloaded with small amounts of Ca2+ (100 nmol/mg of protein), became highly sensitized to rapid permeability transition even when only low concentrations of phytanic acid (below 5 microM) were applied. In conclusion, the incorporation of phytanic acid into the inner mitochondrial membrane increases the membrane H+ conductance and disturbs the protein-linked functions in energy coupling. This is most probably essential for the short-term toxicity of phytanic acid. Thus in neural tissue, which becomes enriched with phytanic acid, the reduction in mitochondrial ATP supply and the facilitation of the opening of the permeability transition pore are two major mechanisms by which the branched-chain fatty acid phytanic acid induces the onset of degenerative processes.

Peroxisome proliferator-activated receptor expression and activation in normal human colonic epithelial cells and tubular adenomas

OBJECTIVE

Peroxisome proliferator-activated receptor (PPAR) ligands, widely used in type 2 diabetes treatment, have variably been shown to promote or prevent colon tumor formation in animal models and cell lines, but their role in normal human colon is unknown. The aim of this study was to determine PPAR expression and function in normal human colonic epithelial cells and tubular adenomas.

MATERIAL AND METHODS

Short-term cultures of normal human colonic epithelial cells were established from biopsies obtained in 42 patients with normal colonoscopy. PPAR and adipophilin mRNA expression was assessed by real-time RT-PCR. PPARs were activated by ligands for PPAR alpha (Wy-14643), PPAR delta (GW-501516) and PPAR gamma (rosiglitazone or troglitazone). Cell viability was measured using the methyltetrazoleum assay, proliferation by thymidine incorporation, and DNA profiles by flow cytometry. PPAR mRNA levels in tubular adenomas or metaplastic polyps (n=12) were compared with those in controls.

RESULTS

PPAR alpha and gamma were consistently expressed in normal colonocytes while no PPAR delta expression could be detected. PPAR gamma activation induced a 7.5-fold increase in adipophilin expression (a PPAR-activated gene). PPAR gamma activation had no effect on viability or DNA profiles, but led to a 25% significant decrease in cell proliferation. Finally, a selective and significant 2.5-fold decrease in PPAR alpha expression was observed in tubular adenomas, but not in metaplastic polyps, compared to controls.

CONCLUSIONS

Our findings support the view that PPAR gamma ligands act as anti-proliferative agents rather than as promoters of tumorigenesis in normal human colon. Moreover, they raise interest in investigation of PPAR alpha as a therapeutic target to prevent adenoma formation.

A role for caveolin-1 in post-injury reactive neuronal plasticity

Remodeling and plasticity in the adult brain require cholesterol redistribution and synthesis for the formation of new membrane components. Caveolin-1 is a cholesterol-binding membrane protein involved in cellular cholesterol transport and homeostasis. Evidence presented here demonstrates an up-regulation of caveolin-1 in the hippocampus, which was temporally correlated with an increase in synaptophysin during the reinnervation phase in a mouse model of hippocampal deafferentation. Using an in vitro model of neuronal reactive plasticity, we examined the effect of virally mediated overexpression of caveolin-1 on injured differentiated PC12 cells undergoing terminal remodeling. Three days post lesion, caveolin-1-overexpressing cells revealed increases in synaptophysin and GAP-43, two markers of neurite sprouting and synaptogenesis. Morphologically, caveolin-1-overexpressing cells showed a decrease in primary neurite outgrowth and branching as well as an increase in neurite density. Caveolin-1-overexpressing cells also revealed the presence of terminal swelling and beading along processes, consistent with a possible alteration of microtubules stability. Moreover, a focal enrichment of caveolin-1 immunofluorescence was observed at the bases of axonal and dendritic terminals of mouse primary hippocampal neurons. Altogether, these results indicate that caveolin-1 plays an active role in the regulation of injury-induced synaptic and terminal remodeling in the adult CNS.

Protracted lithium treatment protects against the ER stress elicited by thapsigargin in rat PC12 cells: roles of intracellular calcium, GRP78 and Bcl-2

We investigated the cytoprotective effects of lithium, the mood-stabilizer, on thapsigargin-induced stress on the endoplasmic reticulum (ER) in rat PC12 cells. Protracted lithium pretreatment of PC12 cells elicited cytoprotection against thapsigargin-induced cytotoxicity. Lithium protection was concurrent with inhibition of thapsigargin-induced intracellular calcium increase and with elevated expression of the molecular chaperone GRP78. Moreover, lithium pretreatment upregulated the antiapoptotic protein Bcl-2, and blocked Bcl-2 downregulation elicited by thapsigargin. Prior to the induction of GRP78, lithium treatment alone increased the expression of c-Fos whose induction by ER stress is necessary for GRP78 induction. Curcumin, an inhibitor of transcription factor AP-1, blocked lithium cytoprotection against thapsigargin cytotoxicity. Thus, the induction of GRP78 and Bcl-2, and activation of AP-1 likely contribute to lithium-induced protection against cytotoxicity resulting from ER stress. Additionally, thapsigargin-induced cytotoxicity was suppressed by pretreatment with another mood-stabilizer, valproate, indicating that cytoprotection against ER stress is a common action of mood-stabilizing drugs.

Pigment epithelium-derived factor induces the production of chemokines by rat microglia

Many studies have shown that pigment epithelium-derived factor (PEDF) has neurotrophic effects on retinal cells and hippocampal, spinal cord, and cerebellar granule cell neurons, but much less work has examined the effects of PEDF on glia. In this study, we show that PEDF changes microglial morphology within 1 h of exposure, to a more deactivated form, while having no effect on the expression of such activation markers as OX-42 and ED-1. In contrast, urea activates acid phosphatase, and PEDF blocks that activation. PEDF also activates NFkappaB, accompanied by the induction of mRNAs and proteins for the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha, MIP-2, and MIP-3alpha. All the chemokines stimulate acid phosphatase activity, and high doses of MIP-2 and MIP-3alpha), alter the morphology of the microglia at 1 h after treatment. These results suggest that the use of PEDF for clinical treatments, such as for retinal neovascularization, brain injury, or ischemia, should be undertaken with caution because of the possibility of induction of inflammation caused by microglial or other immune cell migration in response to the chemokines induced by PEDF.

Lovastatin stimulates up-regulation of α7 nicotinic receptors in cultured neurons without cholesterol dependency, a mechanism involving production of the α-form of secreted amyloid precursor protein

The cholesterol-lowering drug lovastatin enhances the secretion of the alpha-secretase cleavage product of amyloid precursor protein (APP). To investigate whether this effect is mediated via activation of alpha7 nicotinic acetylcholine receptors (nAChRs), we treated SH-SY5Y cells and PC12 cells with lovastatin and measured the levels of alpha7 nAChRs, the alpha-form of secreted APP (alphaAPPs), and lovastatin-related lipids, including cholesterol and ubiquinone. The results showed that low concentrations of lovastatin significantly induced up-regulation of alpha7 nAChRs. No effects of lovastatin were observed on alpha3-containing nAChRs, muscarinic receptors, or N-methyl-D-aspartate receptors. alphaAPPs levels increased in the culture medium of cells treated with lovastatin, whereas no change in whole APP was observed. The increase in alphaAPPs was inhibited by prior exposure of these cells to alpha-bungarotoxin, an antagonist of alpha7 nAChRs. The concentrations of lovastatin used in the study did not change the cholesterol content, but high doses can decrease the levels of ubiquinone and cell viability. These results indicate that lovastatin may play a neuronal role that is cholesterol independent. We also show that the up-regulation of alpha7 nAChRs stimulated by lovastatin is involved in a mechanism that enhances production of alphaAPPs during APP processing.

Tetrazolium dyes as tools in cell biology: new insights into their cellular reduction

Tetrazolium salts have become some of the most widely used tools in cell biology for measuring the metabolic activity of cells ranging from mammalian to microbial origin. With mammalian cells, fractionation studies indicate that the reduced pyridine nucleotide cofactor, NADH, is responsible for most MTT reduction and this is supported by studies with whole cells. MTT reduction is associated not only with mitochondria, but also with the cytoplasm and with non-mitochondrial membranes including the endosome/lysosome compartment and the plasma membrane. The net positive charge on tetrazolium salts like MTT and NBT appears to be the predominant factor involved in their cellular uptake via the plasma membrane potential. However, second generation tetrazolium dyes that form water-soluble formazans and require an intermediate electron acceptor for reduction (XTT, WST-1 and to some extent, MTS), are characterised by a net negative charge and are therefore largely cell-impermeable. Considerable evidence indicates that their reduction occurs at the cell surface, or at the level of the plasma membrane via trans-plasma membrane electron transport. The implications of these new findings are discussed in terms of the use of tetrazolium dyes as indicators of cell metabolism and their applications in cell biology.

Substrates and inhibitors of efflux proteins interfere with the MTT assay in cells and may lead to underestimation of drug toxicity

The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay is a widely used method in assessment of cytotoxicity and cell viability, and also in anti-cancer drug studies with tumour cells. These cells often express efflux proteins, such as P-glycoprotein (MDR1) or multidrug resistance (MDR) protein 1 (MRP1). MDCKII cells that overexpress these proteins (MDCKII-MDR1 or MDCKII-MRP1) and normal cells (MDCKII-wt) were used to investigate the effects of efflux pump activity on the results of MTT assay. Efflux protein activity was confirmed with calcein-AM efflux assay, and MTT assay was compared to another cytotoxicity test, the LDH release assay. Inhibition of MRP and MDR1 efflux proteins in MDCKII cell lines was associated paradoxically with increased reduction of MTT, implying an apparent increase in cell viability. This effect was seen when MK 571 (MRP1 and MRP2 inhibitor) or verapamil (MRP1 and MDR1 inhibitor) were used to block efflux protein activity. The calcein-AM efflux assay also showed that the MTT reagent inhibits the function of MDR1 in the MDCKII-MDR1 cell line. This study shows that MDR1 and possibly MRP proteins interfere with the MTT assay. Due to wide substrate specificity of efflux proteins and popularity of the MTT assay this interference is not trivial. Presence of any efflux protein substrate may therefore lead to underestimated results in MTT assay, thereby causing potential bias and erroneous conclusions in cytotoxicity studies.

The effect of cocaine sensitization on mouse immunoreactivity

Recent studies indicate a role of the immune system in the behavioral effects of cocaine in rodents. In the present study, we attempted to find a correlation between the behavioral changes induced by repeated, intermittent administration of cocaine and some immunological consequences of sensitization to cocaine. Male Albino Swiss mice were treated repeatedly (for 5 days) with cocaine (10 or 15 mg/kg, intraperitoneally, ip). On day 9, they received a challenge dose of cocaine (10 or 15 mg/kg). Acute administration of cocaine increased the locomotor activity of mice. In animals treated repeatedly with the higher dose of cocaine, the locomotor hyperactivity induced by a challenge dose of the psychostimulant (15 mg/kg) was ca. twice as high as that after its first administration; in consequence, evidence for behavioral sensitization was obtained. Immune functions were evaluated by measuring the ability of splenocytes to proliferate and to produce cytokines such as interferon-gamma (IFN-gamma), interleukin (IL)-4 and IL-10. Acute cocaine administration significantly decreased proliferation of splenocytes to concanavalin A (Con A) and increased their ability to produce IFN-gamma. Repeated intermittent treatment with cocaine in a dose of 10 mg/kg significantly decreased the thymus weight and the proliferative response of T cells to a suboptimal dose of Con A. Sensitization with the higher dose of cocaine significantly enhanced IFN-gamma production. These data indicate that cocaine sensitization results in the development of a tolerant state to the cocaine-induced suppression of a thymus dependent T-lymphocyte response. It may be suggested that the cocaine sensitization partly depends on the altered balance of cytokine production, e.g. an increase in IFN-gamma production. Since repeated, intermittent use of cocaine by humans leads to psychoses or craving for this drug, our findings also seem to indicate considerable importance of monitoring and correcting immune changes in the therapy of cocaine addiction.

Inaccuracies in MTS assays: major distorting effects of medium, serum albumin, and fatty acids

Soluble formazan assays are widely used for cell number assessment. However, in our hands, we observed frequent occasions in which the actual cell number was at odds with the assay reading. In this study, we have determined that (i) a large proportion of the reading obtained in commonly used culture media can be caused by media component amplification of formazan production in a way that cannot be corrected for by media-only controls; (ii) the albumin present in 10% serum can reduce the assay absorbance by 50% so that an actual doubling of cell number can be obscured; and (iii) this latter effect is dependent on the concentration of fatty acids. To counter these problems, we have developed a protocol that gives consistent readings that are fully representative of cell number while retaining some of the original advantages of soluble formazan assays.

Decreased nicotinic receptors in PC12 cells and rat brains influenced by fluoride toxicity--a mechanism relating to a damage at the level in post-transcription of the receptor genes

In order to reveal mechanisms of the decreased nicotinic acetylcholine receptors (nAChRs) resulted from fluoride toxicity, we treated PC12 cells by different concentrations of fluoride (0.1-100 ppm) for 48 h, and exposed rats to high doses of fluoride (30 and 100 ppm) in their drinking water for 7 months. The expression of nAChRs at mRNA and protein levels, neurotoxicity and oxidative stress were analyzed in the study. The results indicated that there were no significant changes at mRNA level of the nAChR alpha3, alpha7, beta2 subunits in PC12 cells, and alpha4, alpha7, beta2 subunits in rat brains between the groups with fluorosis and controls. A significant decline in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, and increased levels of protein oxidation and lipid peroxidation were observe in PC12 cells treated with high doses of fluoride or rat brains with chronic fluorosis. The decreases of nAChR alpha3 and alpha7 subunit proteins in PC12 cells resulted from fluoride toxicity were mostly prevented by a pretreatment with antioxidant. The results suggest that the deficit of nAChRs induced by fluoride toxicity occurs at the level of post-transcription of the receptor gene, in which a mechanism might be involved in the damage by oxidative stress.

In vitro assessment of copper-induced toxicity in the human hepatoma line, Hep G2

Copper, though essential, is highly toxic when present in excess, as in Wilson disease, a genetic disorder of hepatic copper metabolism. We hypothesized that mitochondria are a major target of copper-induced cytotoxicity in Wilson disease. We used the human hepatoma line Hep G2 to examine copper-mediated cytotoxicity and three different methods to assess organelle damage: MTT assay (mitochondria), neutral red (NR; lysosomes) and Trypan blue exclusion assay (TB; plasma membrane). For all assays, cells at approximately 60% confluence in microtitre plates were incubated with CuCl(2) (concentration range: 50-100-150-200 microM) for 24 or 48 h. Results were expressed as percent of untreated control. At 24 h, cytotoxicity as detected by NR assay was significantly higher at all concentrations of copper than for MTT or TB ( p<0.005 at all concentrations). Cytotoxicity as detected by MTT was higher than that detected by TB at all concentrations except at 200 microM (p<0.05 for 50 microM, p<0.005 for 100 microM, p = 0.001 for 150 microM). Results at 48 h were similar (NR versus others: p <0.001 MTT versus TB: NS except at 150 microM where p<0.01). We investigated reactive oxygen species (ROS) production in copper-associated hepatocytoxicity by incubating sub-confluent cells with 2('),7(')-dichlorodihydrofluorescein diacetate dye plus copper (concentration range: 0-200 microM) for 1-1.5 h. Copper, but not zinc, produced significant increases in ROS (p<0.001). In summary, Hep G2 lysosomes appeared more susceptible to Cu-mediated damage than mitochondria; the cell membrane was highly resistant to damage.

Mechanism of NF-kappaB inactivation induced by survival signal withdrawal in cerebellar granule neurons

Activity of the transcription factor nuclear factor-kappaB (NF-kappaB) has been shown to be necessary for maintaining neuronal viability. In cultured rat cerebellar granule neurons, trophic factor withdrawal induces NF-kappaB inactivation, resulting in cell death. The exact mechanism of this inactivation, however, has not been revealed. Here we report that trophic factor deprivation in cultured cerebellar granule neurons leads to a rapid and sustained increase in the level of IkappaBalpha and IkappaBbeta, the inhibitory proteins of NF-kappaB, causing prolonged NF-kappaB inactivation. Transient NF-kappaB activation resulting in new IkappaBalpha mRNA and protein synthesis gives rise to the rapid increase of IkappaBalpha level. The importance of elevated IkappaB level in neuronal apoptosis was confirmed in transfection experiments. Ectopic expression of a stabilized form of IkappaBalpha protein promoted neuronal death. Our findings suggest a novel mode of initiation of neuronal apoptosis wherein survival signal withdrawal induces NF-kappaB to lethally turn itself off.

Adenosine induces apoptosis in the human gastric cancer cells via an intrinsic pathway relevant to activation of AMP-activated protein kinase

Extracellular adenosine significantly reduced cell viability in a dose (0.1-20mM)- and treatment time (24-72h)-dependent manner in GT3-TKB cells, a human gastric cancer cell line. Nuclei of cells were reactive to Hoechst 33342, a marker of apoptosis, and an anti-single-stranded DNA. Adenosine-induced GT3-TKB cell death was significantly inhibited by dipyridamole, an inhibitor of adenosine transporter, and 5'-amino-5'-deoxyadenosine, an inhibitor of adenosine kinase, but the effect was not affected by theophylline, a broad inhibitor of adenosine receptors, 8-cyclopentyltheophylline, an inhibitor of A(1) adenosine receptors or 3,7-dimethyl-1-propargylxanthine, an inhibitor of A(2a) adenosine receptors. Adenosine had no effect on mitochondrial membrane potentials. The effect of adenosine on GT3-TKB cell death was not inhibited by a pancaspase inhibitor or inhibitors of caspase-1,-3,-4,-8, and -9. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), an activator of AMP-activated protein kinase (AMPK), significantly reduced GT3-TKB cell viability, but the AICAR action was not reinforced in the presence of adenosine. The results of the present study, thus, suggest that extracellular adenosine induces apoptosis in GT3-TKB cells by its uptake into cells and conversion to AMP followed by activation of AMPK, regardless of caspase activation linked to the mitochondria and the endoplasmic reticulum.

Inhibition of lipopolysaccharide-induced expression of inducible nitric oxide synthase and tumor necrosis factor-alpha by 2'-hydroxychalcone derivatives in RAW 264.7 cells

In cultures of the murine macrophage cell line RAW 264.7, effects of four 2'-hydroxychalcone derivatives, 2'-hydroxy-4'-methoxychalcone (compound 1), 2',4-dihydroxy-4'-methoxychalcone (compound 2), 2',4-dihydroxy-6'-methoxychalcone (compound 3) and 2'-hydroxy-4,4'-dimethoxychalcone (compound 4), on lipopolysaccharide (LPS)-induced production of nitric oxide (NO) and tumor necrosis factor (TNF)-alpha were examined. Compounds 1, 2 and 3 at 3-30microM inhibited the production with almost the same potency. Compound 4 showed no inhibitory activity. Compounds 1, 2 and 3 at 3-30microM inhibited the LPS-induced expression of inducible nitric oxide synthase (iNOS) and TNF-alpha mRNA. To clarify the mechanism involved, effects of compounds 1, 2 and 3 on the activation of nuclear factor (NF)-kappaB and activator protein-1 (AP-1) were examined. Both the LPS-induced activation of NF-kappaB and AP-1 were blocked by compounds 1, 2 and 3 at 3-30microM. Moreover, the three compounds at such concentrations inhibited the LPS-induced IkappaB degradation and the phosphorylation of c-jun N-terminal kinase (JNK) and c-jun. These findings suggest that the inhibition of the LPS-induced production of NO and TNF-alpha by the 2'-hydroxychalcone derivatives is due to the inhibition of NF-kappaB and AP-1 activations.

S-allyl-L-cysteine selectively protects cultured rat hippocampal neurons from amyloid beta-protein- and tunicamycin-induced neuronal death

S-allyl-L-cysteine (SAC), one of the organosulfur compounds found in aged garlic extract, has been shown to possess various biological effects including neurotrophic activity. In our previous experiments, we found that SAC could protect against amyloid beta-protein (Abeta)- and tunicamycin-induced cell death in differentiated PC12 cells. In the study described here, we characterized the neuronal death induced by Abeta, 4-hydroxynonenal (HNE), tunicamycin, and trophic factor deprivation, and investigated whether and how SAC could prevent this in cultured rat hippocampal neurons. Treatment with SAC protected these cells against Abeta- and tunicamycin-induced neuronal death, which is mediated predominantly through caspase-12-dependent pathway in a concentration-dependent manner. In contrast, it afforded no protection against HNE- and trophic factor-deprivation-induced cell death, which has been shown to be mediated by caspase-3-dependent pathway. SAC also attenuated the Abeta-induced increase of intracellular reactive oxygen species in hippocampal neurons. SAC had no effect on Abeta-induced cell death in cultured cerebellar granule neurons, which was prevented by a caspase-3 inhibitor. These results suggest that SAC could protect against the neuronal cell death that is triggered by ER dysfunction in the hippocampus, and that it has no effect on neuronal cell death that is dependent upon the caspase-3 mediated pathway.

Lead stimulates ERK1/2 and p38MAPK phosphorylation in the hippocampus of immature rats

Lead (Pb(2+)) is widely recognized as a neurotoxicant whose mechanisms of action are not completely established. We have previously demonstrated that Pb(2+) can activate the p38(MAPK) pathway and increase the phosphorylation of Hsp27 in bovine adrenal chromaffin cells and human SH SY5Y cells over a short incubation period (1 h). In the present work we analyzed the effects of Pb(2+) administered in vivo on the level and the phosphorylation state of ERK1/2 and p38(MAPK) in the hippocampus of immature rats. Rats were treated with lead acetate (2, 8 or 12 mg/kg, i.p.) or saline (control) over the 8th to 12th postnatal days, and hippocampal slices were prepared on the 14th day. The Pb(2+) level in the lead-treated animals increased 2.5-6-fold in the blood (3.0-6.0 microg/dl) and 2.0-3.0-fold in the forebrain (78-103 ng/g wet weight), compared to control (saline). The phosphorylation of both ERK1/2 and p38(MAPK) was significantly increased by prior exposure to Pb(2+) in vivo. In in vitro experiments, hippocampal slices from 14-day-old rats were exposed to Pb(2+) (1-10 microM) for 1 and 3 h. There were no changes in the phosphorylation state of ERK and p38(MAPK) for 1-h incubation, whereas a significant increase of ERK1/2 and p38(MAPK) phosphorylation by Pb(2+) (5 microM) was observed for the 3-h incubation. Cell viability measured using MTT was not modified in any of the conditions tested. These results indicate that the phosphorylation of hippocampal ERK1/2 and p38(MAPK) is stimulated by lead in a period of rapid brain development, an effect that may underlie, at least in part, the neurotoxicty elicited by this metal.

Glutamate uptake inhibitor L-trans-pyrrolidine 2,4-dicarboxylate becomes neurotoxic in the presence of subthreshold concentrations of mitochondrial toxin 3-nitropropionate: involvement of mitochondrial reducing activity and ATP production

An increased concentration of extracellular glutamate is associated with neuronal damage induced by cerebral ischemia. We have demonstrated previously that exposure of cultured cerebellar granule neurons to L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a glutamate uptake inhibitor, increases extracellular glutamate levels but does not induce neuronal damage. Coincubation of PDC, however, with a subthreshold concentration of the mitochondrial toxin, 3-nitropropionic acid (3-NP), results in severe damage to these neurons. We have investigated the time course of changes in mitochondrial reducing capacity and ATP levels in cerebellar granule cells after simultaneous exposure to 3-NP and PDC, and its relation to cell viability and nuclear condensation. Although individually, 3-NP and PDC treatments are not harmful to neurons, the simultaneous exposure to both compounds results in a progressive decline in mitochondrial reducing capacity during the first 4 hr, and a rapid decrease in ATP levels. At 4 hr, cells lose plasma membrane integrity and show condensed nuclei. In the presence of the energy substrates pyruvate and acetoacetate, the N-methyl-D-apartate (NMDA) receptor antagonist, MK-801, and the spin trapper alpha-phenyl-N-tert-butylnitrone (PBN), the decline in mitochondrial activity and ATP levels is prevented, the number of condensed nuclei is reduced, and plasma membrane integrity is preserved. In contrast, the broad-spectrum caspase inhibitor Z-Asp-DCB (Z-Asp-CH2-DCB) prevents nuclear condensation but has no effect on mitochondrial reducing capacity or cell survival. Our results show that glutamate uptake impairment rapidly induces neuronal death during inhibition of succinate dehydrogenase by a mechanism involving mitochondrial dysfunction that, if not prevented, leads to cell death.

Imbalance of antioxidant enzymes in tumor cells and inhibition of proliferation and malignant features by scavenging hydrogen peroxide

The aim of this study was to evaluate the endogenous alterations of the antioxidant enzymes in tumor cells and to specifically compensate the resulting changes in the levels of reactive oxygen species (ROS) to control the malignant growth. We determined and compared the activities of antioxidant enzymes and the levels of superoxide anion (O2*-) and hydrogen peroxide (H2O2) in tumor cell lines with different degrees of malignancy, paired with regard to their origin (PB/CH72T4, PDV/PDVC57, and HBL-100/MCF-7). An increase in superoxide dismutase activity and a decrease in the activities of H2O2-detoxifying enzymes, as a function of malignancy, coupled with a rise in H2O2 and a decrease in O2*- were demonstrated. Treatment of cells with exogenous catalase showed a dose-dependent inhibition of proliferation. This inhibition was also demonstrated in several cell lines of different tissue origin and species, suggesting a general role of H2O2 in cell proliferation. Moreover, stable expression of human catalase in MCF-7 cells inhibited proliferation and also reverted malignant features. We conclude that H2O2 played a crucial and general role in the regulation of proliferation and that an endogenous imbalance in antioxidant enzymes could be a relevant event in the carcinogenesis process.

Backscattered light confocal imaging of intracellular MTT-formazan crystals

Metabolically active animal and plant cells reduce MTT tetrazolium salt to a corresponding nonfluorescent formazan. Reduction of MTT by viable cells is exploited in a number of tests widely used in biological research. The aim of this study was to optimize a microscopy method of detecting small crystals of MTT-formazan formed in intact cells maintained in in vitro cultures. We examined scattering properties of small intracellular crystals of MTT formazan and found that the efficiency of light scattering was dependent on wavelength. Small (<3 microm) crystals of MTT-formazan, formed in viable cells, scattered red, but not blue, light. Large crystals, which are formed later at a stage when cells begin to lose viability, scattered both red and blue light. We conclude that optimal detection of early stages of crystallization of MTT-formazan in living cells is possible using confocal microscopy of red, but not blue, scattered light. High contrast and resolution of images can be achieved by filtering out interference effects in the frequency domain.

Receptors to steroid hormones and aromatase are expressed by cultured motoneurons but not by glial cells derived from rat embryo spinal cord

The aim of this study was to examine the expression of aromatase and receptors to steroid hormones in cultured motoneurons (MNs). We first developed an original method for obtaining rat MN cultures. Dissociated E15 rat spinal cords were purified using metrizamide and bovine serum albumin density gradients, and cells were then seeded on the culture substratum. We optimized the culture parameters and found that simple addition of rat muscle extract (ME) and conditioned culture medium (CM) from glial cell lines (GCL) derived from spinal cord were sufficient to obtain almost pure MN cultures. MNs were characterized by the presence of specific MN markers and electrophysiology. MNs could be kept alive for 2 weeks. We demonstrate that ME and CM are essential for MN development and survival respectively. Immunocytochemistry and aromatase activity assay indicated the presence of androgen and estrogen receptors as well as aromatase in MNs but not in GCL. This is the first report demonstrating the presence of both female and male sex hormone receptors and a key enzyme in steroid hormone metabolism in MNs and its absence in GCL, at least in our culture conditions. This in vitro model appears to be valuable for elucidating the impact of the sex hormone circuit in neuronal maturation. The relevance of this model for the comprehension of neurodegenerative diseases is discussed.

Cytosolic and mitochondrial ROS in staurosporine-induced retinal cell apoptosis

In this study, we investigated the involvement of reactive oxygen species (ROS) and calcium in staurosporine (STS)-induced apoptosis in cultured retinal neurons, under conditions of maintained membrane integrity. The antioxidants idebenone (IDB), glutathione-ethylester (GSH/EE), trolox, and Mn(III)tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) significantly reduced STS-induced caspase-3-like activity and intracellular ROS generation. Endogenous sources of ROS production were investigated by testing the effect of the following inhibitors: 7-nitroindazole (7-NI), a specific inhibitor of the neuronal isoform of nitric oxide synthase (nNOS); arachidonyl trifluoromethyl ketone (AACOCF(3)), a phospholipase A(2) (PLA(2)) inhibitor; allopurinol, a xanthine oxidase inhibitor; and the mitochondrial inhibitors rotenone and oligomycin. All these compounds decreased caspase-3-like activity and ROS generation, showing that both mitochondrial and cytosolic sources of ROS are implicated in this mechanism. STS induced a significant increase in intracellular calcium concentration ([Ca(2+)](i)), which was partially prevented in the presence of IDB and GSH/EE, indicating its dependence on ROS generation. These two antioxidants and the inhibitors allopurinol and 7-NI also reduced the number of TdT-mediated dUTP nick-end labeling-positive cells. Thus, endogenous ROS generation and the rise in intracellular calcium are important inter-players in STS-triggered apoptosis. Furthermore, the antioxidants may help to prolong retinal cell survival upon apoptotic cell death.

Method for measuring neurotoxicity of aggregating polypeptides with the MTT assay on differentiated neuroblastoma cells

Reliable in vitro assays are essential for study of the effects of neurotoxic compounds such as beta-amyloid peptides (Abeta). The MTT assay has been used in cultures of different cells, e.g. SH-SY5Y neuroblastoma cells, for the quantitative measurement of Abeta toxicity. In our laboratory differentiated SH-SY5Y cells were used in the MTT assay. Cell differentiation with 10 microM all-trans-retinoic acid resulted in a constant cell number. The cells possess highly developed neurites and exhibit high sensitivity against Abeta. Owing to the constant cell number in differentiated SH-SY5Y cultures the decrease of the redox activity is directly proportional to the neurotoxicity of the substances, no correction is needed. The results of the MTT assay of Abeta peptides on differentiated SH-SY5Y cells displayed a good correlation also with the in vivo results. The present experiments reveal an effective assay for the study of potentially neurotoxic compounds.

Loss of m-AAA protease in mitochondria causes complex I deficiency and increased sensitivity to oxidative stress in hereditary spastic paraplegia

Mmutations in paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human paraplegin–AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease.

Arachidonic acid peroxides induce apoptotic Neuro-2A cell death in association with intracellular Ca2+ rise and mitochondrial damage independently of caspase-3 activation

The present study aimed at understanding the effects of arachidonic acid peroxides on neuronal cell death using the mouse neuroblastoma cell line, Neuro-2A cells. Arachidonic acid peroxides were produced by ultraviolet (UV) radiation. UV-radiated arachidonic acid significantly reduced Neuro-2A cell viability at concentrations of more than 0.1 muM, with being more potential than non-radiated arachidonic acid. Nuclei of Neuro-2A cells killed with UV-radiated arachidonic acid were reactive to Hoechst 33342, a marker of apoptosis, and the effect was much greater than that achieved with non-radiated arachidonic acid. UV-radiated arachidonic acid persistently increased intracellular Ca(2+) concentrations and dissipated mitochondrial membrane potential in Neuro-2A cells. UV-radiated arachidonic acid-induced Neuro-2A cell death, whereas it was not affected by a pancaspase inhibitor or a caspase-3 inhibitor, was significantly inhibited by an inhibitor of caspase-1, -8, or -9. The results of the present study suggest that arachidonic acid peroxides induce apoptotic neuronal cell death in association with intracellular Ca(2+) rise and mitochondrial damage, in part via a caspase-dependent pathway regardless of caspase-3.

Mitochondrial dysfunction due to mutant copper/zinc superoxide dismutase associated with amyotrophic lateral sclerosis is reversed by N-acetylcysteine

We report that the expression of mutant G93A copper/zinc superoxide dismutase (SOD1), associated with familial amyotrophic lateral sclerosis, specifically causes a decrease in MTT reduction rate and ATP levels and an increase in both cytosolic and mitochondrial reactive oxygen species (ROS) production in human neuroblastoma SH-SY5Y cells compared to cells overexpressing wild-type SOD1 and untransfected cells. Exposure to N-acetylcysteine lowers ROS production and returns mitochondrial functional assays to control levels. No large aggregates of human SOD1 are detectable under basal growth conditions in any of the investigated cell lines. After proteasome activity inhibition, SOD1 aggregates can be detected exclusively in G93A-SOD1 cells, even though they do not per se enhance cell death compared to control cell lines. Our findings indicate that mitochondrial homeostasis is affected by mutant SOD1-generated ROS independently from the formation of aggregates and that this alteration is reversed by antioxidants.

Ethanol differentially inhibits homoquinolinic acid- and NMDA-induced neurotoxicity in primary cultures of cerebellar granule cells

The potency of ethanol to inhibit N-methyl-D-aspartate (NMDA) receptor functions may depend on the subunit composition of the NMDA receptors. We used a NR2A-B subunit-selective NMDA receptor agonist, homoquinolinic acid (HQ), and a subunit-unselective agonist, NMDA, to induce neurotoxicity in cerebellar granule cells and examined the neuroprotective actions of ethanol, as well as NR2A- and NR2B-subunit selective antagonists, respectively. HQ was a more potent neurotoxic agent than NMDA, as measured by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. NR2A- and NR2B-selective NMDA receptor antagonists displayed quite similar neuroprotective potencies against the NMDA- and HQ-produced cell death, indicating that the higher potency of HQ to induce neurotoxicity cannot be simply explained by NR2A- or NR2B-subunit selectivity. As expected, ethanol (25 and 50 mM) attenuated the NMDA-induced neurotoxicity in a non-competitive manner by significantly reducing the maximum neurotoxicity produced by NMDA. By contrast, ethanol inhibited the HQ-induced neurotoxicity in a manner resembling a competitive-like interaction significantly increasing the EC50 value for HQ, without reducing the maximum neurotoxicity produced by HQ. These results suggest that HQ reveals either a novel site or a not previously observed mechanism of interaction between ethanol and NMDA receptors in rat cerebellar granule cell cultures.

The regulation of glucose metabolism by HIF-1 mediates a neuroprotective response to amyloid beta peptide

It is frequently argued that both amyloid beta (Abeta) and oxidative stress are involved in the pathogenesis of Alzheimer's disease (AD). We show here that clonal nerve cell lines and primary cortical neurons that are resistant to Abeta toxicity have an enhanced flux of glucose through both the glycolytic pathway and the hexose monophosphate shunt. AD brain also has increased enzymatic activities in both pathways relative to age-matched controls. The Abeta-induced changes in glucose metabolism are due to the activation of the transcription factor hypoxia inducible factor 1 (HIF-1). As a result of Abeta-induced changes in glucose metabolism, Abeta-resistant cells are more readily killed by glucose starvation and by classes of antipsychotic drugs that inhibit glucose uptake.

Alternative oxidase present in procyclic Trypanosoma brucei may act to lower the mitochondrial production of superoxide

The mitochondrial electron transfer chain present in the procyclic form of the African trypanosome Trypanosoma brucei contains both cytochrome c oxidase and an alternative oxidase (TAO) as terminal oxidases that reduce oxygen to water. By contrast, the electron transfer chain of the primitive mitochondrion present in the bloodstream form of T. brucei contains only TAO as the terminal oxidase. TAO functions in the bloodstream forms to oxidize the ubiquinol produced by the glycerol-3-phosphate shuttle that results in the oxidation of the reduced nicotinamide adenine dinucleotide phosphate produced by glycolysis. The function, however, of TAO in the procyclic forms is unknown. In this study, we found that inhibition of TAO by the specific inhibitor salicylhydroxamic acid stimulates the formation of reactive oxygen species (ROS) in trypanosome mitochondria, resulting in mitochondrial alteration and increased oxidation of cellular proteins. Moreover, the activity and protein content of TAO in procyclic trypanosomes were increased when cells were incubated in the presence of hydrogen peroxide or antimycin A, the cytochrome bc1 complex inhibitor, which also results in increased ROS production. We suggest that one function of TAO in procyclic cells may be to prevent ROS production by removing excess reducing equivalents and transferring them to oxygen.

Developmental changes in the Ca2+-regulated mitochondrial aspartate-glutamate carrier aralar1 in brain and prominent expression in the spinal cord

Aralar1 and citrin are two isoforms of the mitochondrial carrier of aspartate-glutamate (AGC), a calcium regulated carrier, which is important in the malate-aspartate NADH shuttle. The expression and cell distribution of aralar1 and citrin in brain cells has been studied during development in vitro and in vivo. Aralar1 is the only isoform expressed in neurons and its levels undergo a marked increase during in vitro maturation, which is higher than the increase in mitochondrial DNA in the same time window. The enrichment in aralar1 per mitochondria during neuronal maturation is associated with a prominent rise in the function of the malate-aspartate NADH shuttle. Paradoxically, during in vivo development of rat or mouse brain there is very little postnatal increase in total aralar1 levels per mitochondria. This is explained by the fact that astrocytes develop postnatally, have aralar1 levels much lower than neurons, and their increase masks that of aralar1. Aralar1 mRNA and protein are widely expressed throughout neuron-rich areas in adult mouse CNS with clear enrichments in sets of neuronal nuclei in the brainstem and, particularly, in the ventral horn of the spinal cord. These aralar1-rich neurons represent a subset of the cytochrome oxidase-rich neurons in the same areas. The presence of aralar1 could reflect a tonic activity of these neurons, which is met by the combination of high malate-aspartate NADH shuttle and respiratory chain activities.

Enhanced MTT-reducing activity under growth inhibition by resveratrol in CEM-C7H2 lymphocytic leukemia cells

Inhibition of proliferation by resveratrol of CEM-C7H2 lymphocytic leukemia cells was paradoxically associated with an enhanced cellular 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT)-reducing activity. This phenomenon was most pronounced at the sub-apoptotic concentration range of 5-20 microM resveratrol. The results of our study show that the MTT-reducing activity can be increased by the polyphenolic antioxidant resveratrol without a corresponding increase in the number of living cells and that this occurs at a concentration range of the antioxidant which is not sufficient to induce apoptosis but suffices to slow down cell growth. This phenomenon appears to be restricted to proliferation inhibitors with antioxidant properties and is cell type-specific. Thus, in determining the effects of flavonoids and polyphenols on proliferation, in certain cell types this might represent a pitfall in the MTT proliferation assay.

Differential lipid peroxidation, Mn superoxide, and bcl-2 expression contribute to the maturation-dependent vulnerability of oligodendrocytes to oxidative stress

To understand the basis of oligodendrocyte (OL) susceptibility to oxidative injury, purified rat OL cultures at different stages of maturation were exposed to nitric oxide (NO) donors with fast or slow kinetics of release and to tert-butyl-hydroperoxide, a membrane-permeant organic hydroperoxide. OL precursors (pre-OL) displayed the highest vulnerability to both oxygen or nitrogen reactive species, whereas mature OLs were uniquely vulnerable to long-lasting levels of NO. Cell death occurred by necrosis as well as apoptosis associated with increased caspase-3 activity and, only in the case of pre-OLs, with a decreased expression of the anti-apoptotic protein bcl-2. Pre-OLs were also more susceptible than mature OLs to lipid peroxidation, as measured by F2-isoprostane content in culture media. Finally, pre-OLs, but not mature OLs, expressed high levels of the mitochondrial scavenging enzyme Mn superoxide dismutase, suggesting that pre-OLs may efficiently convert anion superoxide into hydrogen peroxide and, paradoxically, be more predisposed than mature OLs to a toxic imbalance between hydrogen peroxide production and detoxification processes. These data suggest that susceptibility to lipid peroxidation, expression of the scavenging enzyme Mn superoxide dismutase and of the anti-apoptotic protein bcl-2, may contribute to the maturation-dependent vulnerability of OLs to oxidant injury.

Joint regulation of the MAP1B promoter by HNF3beta/Foxa2 and Engrailed is the result of a highly conserved mechanism for direct interaction of homeoproteins and Fox transcription factors

The MAP1B (Mtap1b) promoter presents two evolutionary conserved overlapping homeoproteins and Hepatocyte nuclear factor 3beta (HNF3beta/Foxa2) cognate binding sites (defining putative homeoprotein/Fox sites, HF1 and HF2). Accordingly, the promoter domain containing HF1 and HF2 is recognized by cerebellum nuclear extracts containing Engrailed and Foxa2 and has regulatory functions in primary cultures of embryonic mesmetencephalic nerve cells. Transfection experiments further demonstrate that Engrailed and Foxa2 interact physiologically in a dose-dependent manner: Foxa2 antagonizes the Engrailed-driven regulation of the MAP1B promoter, and vice versa. This led us to investigate if Engrailed and Foxa2 interact directly. Direct interaction was confirmed by pull-down experiments, and the regions participating in this interaction were identified. In Foxa2 the interacting domain is the Forkhead box DNA-binding domain. In Engrailed, two independent interacting domains exist: the homeodomain and a region that includes the Pbx-binding domain. Finally, Foxa2 not only binds Engrailed but also Lim1, Gsc and Hoxa5 homeoproteins and in the four cases Foxa2 binds at least the homeodomain. Based on the involvement of conserved domains in both classes of proteins, it is proposed that the interaction between Forkhead box transcription factors and homeoproteins is a general phenomenon.

Apoptosis induced by Na+/H+ antiport inhibition activates the LEI/L-DNase II pathway

L-DNase II is derived from its precursor leucocyte elastase inhibitor (LEI) by post-translational modification. In vitro, the conversion of LEI into L-DNase II can be induced by incubation of LEI at an acidic pH. In this study, we proposed to analyze the effects of intracellular acidification on this transformation. Amiloride derivatives, like hexamethylene amiloride (HMA), are known to provoke a decrease of cytosolic pH by inhibiting the Na(+)/H(+) antiport. In BHK cells, treatment with HMA-induced apoptosis accompanied by an increase in L-DNase II immunoreactivity and L-DNase II enzymatic activity. Overexpression of L-DNase II precursor led to a significant increase of apoptosis in these cells supporting the involvement of L-DNase II in HMA induced apoptosis. As previously shown in other cells, etoposide-induced apoptosis did not activate L-DNase. On the contrary, LEI overexpression significantly increased cell survival in etoposide-induced apoptosis. Together these results suggest differential roles of LEI and L-DNase II in response to different types of apoptotic inducers.

Loss of nicotinic receptors induced by beta-amyloid peptides in PC12 cells: possible mechanism involving lipid peroxidation

The mechanisms involved in the loss of nicotinic acetylcholine receptors (nAChRs), seen in brains of patients with Alzheimer's disease (AD) and in cultured cells treated by beta-amyloid peptides (A betas), remain elusive. We give results to show that lipid peroxidation induced directly by A beta might be involved in the deficits of nAChRs. In the study, PC12 cells were treated by addition of 5 microM of A beta(25-35) and A beta(1-40), respectively, with or without a antioxidant, vitamin E. Besides significantly decreased MTT (3-(4,5-dimethylthiazol-2-yl)-2,5,diphenyltetrazolium bromide) reduction, an increased lipid peroxidation was detected in the cells, but no protein oxidation. Significant reductions in [(3)H]epibatidine and [(125)I]alpha-bungarotoxin binding sites and in the protein levels of the alpha 3 and alpha 7 nAChR subunits were observed in the cells treated with A betas. Furthermore, A beta(25-35) decreased the level of ubiquinone-9 in PC12 cells, but did not change the amount of cholesterol, providing further evidence for lipid peroxidation. Interestingly, when PC12 cells were pretreated by antioxidant before the addition of A betas, the lipid peroxidation and the decreased ubiquinone resulted from A betas were prohibited. The decreases of nAChR binding sites and subunit proteins resulted from A betas were mostly prevented by the pretreatment with antioxidant. These findings suggest that lipid peroxidation stimulated by A betas might be a mechanism for the loss of nAChRs associated with the pathogenesis of AD.

Haploinsufficiency of ATP1A2 encoding the Na+/K+ pump alpha2 subunit associated with familial hemiplegic migraine type 2

Headache attacks and autonomic dysfunctions characterize migraine, a very common, disabling disorder with a prevalence of 12% in the general population of Western countries. About 20% of individuals affected with migraine experience aura, a visual or sensory-motor neurological dysfunction that usually precedes or accompanies the headache. Although the mode of transmission is controversial, population-based and twin studies have implicated genetic factors, especially in migraine with aura. Familial hemiplegic migraine is a hereditary form of migraine characterized by aura and some hemiparesis. Here we show that mutations in the gene ATP1A2 that encodes the alpha2 subunit of the Na+/K+ pump are associated with familial hemiplegic migraine type 2 (FHM2) linked to chromosome 1q23 (OMIM 602481). Functional data indicate that the putative pathogenetic mechanism is triggered by a loss of function of a single allele of ATP1A2. This is the first report associating mutations of Na+K+ pump subunits to genetic diseases.

(-)-Epigallocatechin gallate protects against NO stress-induced neuronal damage after ischemia by acting as an anti-oxidant

The present study investigated the effects of (-)-epigallocatechin gallate (EGCG), which is the major component of polyphenol in green tea, on nitric oxide (NO) stress-induced neuronal damage, by monitoring NO mobilizations in the intact rat hippocampus and assaying the viability of cultured rat hippocampal neurons. A 10-min ischemia increased NO (NO(3)(-)/NO(2)(-)) concentrations in the intact rat hippocampus, while EGCG (50 mg/kg i.p.) inhibited the increase by 77% without affecting hippocampal blood flow. The NO donor, sodium nitroprusside (SNP; 50 microM), produced NO (NO(3)(-)/NO(2)(-)), while EGCG inhibited it in a dose-dependent manner at concentrations ranging from 50 to 200 microM. Treatment with SNP (100 microM) reduced the viability of cultured rat hippocampal neurons to 22% of control levels, while EGCG caused it to recover to 51% for 10 microM, 73% for 20 microM, and 70% for 50 microM. Taken together, it appears that EGCG could protect against ischemic neuronal damage by deoxidizing peroxynitrate/peroxynitrite, which is converted to NO radical or hydroxy radical.