Rapid reduction of ATP synthesis and lack of free radical formation by MPP+ in rat brain synaptosomes and mitochondria

Low-Intensity Ultrasound Decreases α-Synuclein Aggregation via Attenuation of Mitochondrial Reactive Oxygen Species in MPP(+)-Treated PC12 Cells

Many studies have shown that mitochondrial dysfunction and the subsequent oxidative stress caused by excessive reactive oxygen species (ROS) generation play a central role in the pathogenesis of Parkinson's disease (PD). We have previously shown that low-intensity ultrasound (LIUS) could reduce ROS generation by L-buthionine-(S,R)-sulfoximine (BSO) in retinal pigment epithelial cells. In this study, we studied the effects of LIUS stimulation on the ROS-dependent α-synuclein aggregation in 1-methyl-4-phenylpyridinium ion (MPP⁺)-treated PC12 cells. We found that LIUS stimulation suppressed the MPP⁺-induced ROS generation and inhibition of mitochondrial complex I activity in PC12 cells in an intensity-dependent manner at 30, 50, and 100 mW/cm². Furthermore, LIUS stimulation at 100 mW/cm² suppressed inhibition of mitochondrial complex activity by MPP⁺ and actually resulted in a decrease of α-synuclein phosphorylation and aggregation induced by MMP⁺ treatment in PC12 cells. LIUS stimulation also inhibited expression of casein kinase 2 (CK2) that appears to mediate ROS-dependent α-synuclein aggregation. Finally, LIUS stimulation alleviated the death of PC12 cells by MPP⁺ treatment in an intensity-dependent manner. We, hence, suggest that LIUS stimulation inhibits ROS generation by MPP⁺ treatment, thereby suppressing α-synuclein aggregation in PC12 cells.

Diagnostic Accuracy of Brain-derived Neurotrophic Factor and Nitric Oxide in Patients with Schizophrenia: A pilot study

Background

Brain-derived neurotrophic factor (BDNF) and nitric oxide (NO) play multiple roles in the developing and adult CNS. Since BDNF and NO metabolisms are dysregulated in schizophrenia, we measured these markers simultaneously in the blood of schizophrenics and assessed their diagnostic accuracy.

Methods

Thirty-eight patients with schizophrenia classified according to demographic characteristics, symptomatologyand therapy and 39 age- and gender-matched healthy controls were enrolled. BDNF was determined by the ELISA technique while the concentration of nitrite/nitrate (NO2−/NO3−) was measured by the colorimetric method.

Results

Serum BDNF levels were significantly lower (20.38±3.73 ng/mL, P = 1.339E-05), whilst plasma NO2−/NO3− concentrations were significantly higher (84.3 (72–121) μmol/L, P=4.357E-08) in patients with schizophrenia than in healthy controls (25.65±4.32 ng/mL; 60.9 (50–76) μmol/L, respectively). The lowest value of BDNF (18.14±3.26 ng/mL) and the highest NO2−/NO3− concentration (115.3 (80–138) μmol/L) were found in patients treated with second-generation antipsychotics (SGA). The patients diseased before the age of 24 and the patients suffering for up to one year had significantly lower serum BDNF levels than those diseased after the age of 24 and the patients who were ill longer than one year. Both BDNF and NO2−/NO3− showed good diagnostic accuracy, but BDNF had better ROC curve characteristics, especially in patients with negative symptomatology.

Conclusions

BDNF and nitrite/nitrate showed inverse changes in schizophrenic patients. The most pronounced changes were found in patients treated with second-generation antipsychotics. Although BDNF is not specific of schizophrenia, it may be a clinically useful biomarker for the diagnosis of patients expressing predominantly negative symptoms.

Toxicity of manganese metallodrugs toward Danio rerio

Manganese is an essential metal which can be neurotoxic in some instances. As Mn-based metallodrugs are ever more prevalent in clinical practice, concern regarding the toxic effects of Mn discharges to water bodies on the biota prompted us to study the physicochemical parameters of these complexes and to assess their acute toxicity toward adult Danio rerio individuals, particularly in terms of brain tissue damage. Our results show that the Mn(III)-salen acetate complex EUK108 is toxic, which can be rationalized in terms of its lipophilicity, stability and redox activity.

Genetic variability of respiratory complex abundance, organization and activity in mouse brain

Mitochondrial dysfunction is implicated in the etiology and pathogenesis of numerous human disorders involving tissues with high energy demand. Murine models are widely used to elucidate genetic determinants of phenotypes relevant to human disease, with recent studies of C57BL/6J (B6), DBA/2J (D2) and B6xD2 populations implicating naturally occurring genetic variation in mitochondrial function/dysfunction. Using blue native polyacrylamide gel electrophoresis, immunoblots and in-gel activity analyses of complexes I, II, III, IV and V, our studies are the first to assess abundance, organization and catalytic activity of mitochondrial respiratory complexes and supercomplexes in mouse brain. Remarkable strain differences in supercomplex assembly and associated activity are evident, without differences in individual complexes I, II, III or IV. Supercomplexes I1 III2 IV2-3 exhibit robust complex III immunoreactivity and activities of complexes I and IV in D2, but with little detected in B6 for I1 III2 IV2 , and I1 III2 IV3 is not detected in B6. I1 III2 IV1 and I1 III2 are abundant and catalytically active in both strains, but significantly more so in B6. Furthermore, while supercomplex III2 IV1 is abundant in D2, none is detected in B6. In aggregate, these results indicate a shift toward more highly assembled supercomplexes in D2. Respiratory supercomplexes are thought to increase electron flow efficiency and individual complex stability, and to reduce electron leak and generation of reactive oxygen species. Our results provide a framework to begin assessing the role of respiratory complex suprastructure in genetic vulnerability and treatment for a wide variety of mitochondrial-related disorders.

The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity

Early exposure to general anesthesia (GA) causes developmental neuroapoptosis in the mammalian brain and long-term cognitive impairment. Recent evidence suggests that GA also causes functional and morphological impairment of the immature neuronal mitochondria. Injured mitochondria could be a significant source of reactive oxygen species (ROS), which, if not scavenged in timely fashion, may cause excessive lipid peroxidation and damage of cellular membranes. We examined whether early exposure to GA results in ROS upregulation and whether mitochondrial protection and ROS scavenging prevent GA-induced pathomorphological and behavioral impairments. We exposed 7-day-old rats to GA with or without either EUK-134, a synthetic ROS scavenger, or R(+) pramipexole (PPX), a synthetic aminobenzothiazol derivative that restores mitochondrial integrity. We found that GA causes extensive ROS upregulation and lipid peroxidation, as well as mitochondrial injury and neuronal loss in the subiculum. As compared to rats given only GA, those also given PPX or EUK-134 had significantly downregulated lipid peroxidation, preserved mitochondrial integrity, and significantly less neuronal loss. The subiculum is highly intertwined with the hippocampal CA1 region, anterior thalamic nuclei, and both entorhinal and cingulate cortices; hence, it is important in cognitive development. We found that PPX or EUK-134 co-treatment completely prevented GA-induced cognitive impairment. Because mitochondria are vulnerable to GA-induced developmental neurotoxicity, they could be an important therapeutic target for adjuvant therapy aimed at improving the safety of commonly used GAs.

Molecular basis for vulnerability to mitochondrial and oxidative stress in a neuroendocrine CRI-G1 cell line

Background

Many age-associated disorders (including diabetes, cancer, and neurodegenerative diseases) are linked to mitochondrial dysfunction, which leads to impaired cellular bioenergetics and increased oxidative stress. However, it is not known what genetic and molecular pathways underlie differential vulnerability to mitochondrial dysfunction observed among different cell types.

Methodology/Principal Findings

Starting with an insulinoma cell line as a model for a neuronal/endocrine cell type, we isolated a novel subclonal line (named CRI-G1-RS) that was more susceptible to cell death induced by mitochondrial respiratory chain inhibitors than the parental CRI-G1 line (renamed CRI-G1-RR for clarity). Compared to parental RR cells, RS cells were also more vulnerable to direct oxidative stress, but equally vulnerable to mitochondrial uncoupling and less vulnerable to protein kinase inhibition-induced apoptosis. Thus, differential vulnerability to mitochondrial toxins between these two cell types likely reflects differences in their ability to handle metabolically generated reactive oxygen species rather than differences in ATP production/utilization or in downstream apoptotic machinery. Genome-wide gene expression analysis and follow-up biochemical studies revealed that, in this experimental system, increased vulnerability to mitochondrial and oxidative stress was associated with (1) inhibition of ARE/Nrf2/Keap1 antioxidant pathway; (2) decreased expression of antioxidant and phase I/II conjugation enzymes, most of which are Nrf2 transcriptional targets; (3) increased expression of molecular chaperones, many of which are also considered Nrf2 transcriptional targets; (4) increased expression of β cell-specific genes and transcription factors that specify/maintain β cell fate; and (5) reconstitution of glucose-stimulated insulin secretion.

Conclusions/Significance

The molecular profile presented here will enable identification of individual genes or gene clusters that shape vulnerability to mitochondrial dysfunction and thus represent potential therapeutic targets for diabetes and neurodegenerative diseases. In addition, the newly identified CRI-G1-RS cell line represents a new experimental model for investigating how endogenous antioxidants affect glucose sensing and insulin release by pancreatic β cells.

Heterogeneous levels of oxidative phosphorylation enzymes in rat adrenal glands

Mitochondria are organelles that produce ATP and reactive oxygen species, which are thought to be responsible for a decline in physiological function with aging. In this study, we morphologically and biochemically examined mitochondria in the rat adrenal gland. Immunohistochemistry showed that the rank order for intensity of immunolabelling for complex IV was zona reticularis > zona fasciculata >> adrenal medulla, whereas for complex V α and β subunits, it was zona fasciculata > zona reticularis and adrenal medulla. The immunolabelling for complex I was homogeneous in the adrenal gland. The difference in immunolabelling between complexes I and IV indicates that the ratio of levels of complex I to that of complex IV in the zona reticularis was smaller than that in the zona fasciculata and the adrenal medulla. Electron microscopy revealed that aging rats had zona reticularis cells with many lysosomes and irregular nuclei. The result suggests that the level of proteins involved in oxidative phosphorylation is coordinated within the complex, but differs between the complexes. This might be responsible for degeneration of zona reticularis cells with aging.

Age-related deficiencies in complex I endogenous substrate availability and reserve capacity of complex IV in cortical neuron electron transport

Respiratory enzyme complex dysfunction is mechanistically involved in mitochondrial failure leading to neurodegenerative disease, but the pathway is unclear. Here, age-related differences in mitochondrial respiration were measured in both whole and permeabilized neurons from 9-month and 24-month adult rat cortex cultured in common conditions. After permeabilization, respiration increased in both ages of neurons with excess substrates. To dissect specific deficiencies in the respiratory chain, inhibitors for each respiratory chain complex were used to isolate their contributions. Relative to neurons from 9-month rats, in neurons isolated from 24-month rats, complexes I, III, and IV were more sensitive to selective inhibition. Flux control point analysis identified complex I in neurons isolated from 24-month rats as the most sensitive to endogenous substrate availability. The greatest age-related deficit in flux capacity occurred at complex IV with a 29% decrease in neurons isolated from 24-month rats relative to those from 9-month rats. The deficits in complexes I and III may contribute to a redox shift in the quinone pool within the electron transport chain, further extending these age-related deficits. Together these changes could lead to an age-related catastrophic decline in energy production and neuronal death.

Mitochondria targeted peptides protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

A large body of evidence suggests that mitochondrial dysfunction and oxidative damage play a role in the pathogenesis of Parkinson's disease (PD). A number of antioxidants have been effective in animal models of PD. We have developed a family of mitochondria-targeted peptides that can protect against mitochondrial swelling and apoptosis (SS peptides). In this study, we examined the ability of two peptides, SS-31 and SS-20, to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. SS-31 produced dose-dependent complete protection against loss of dopamine and its metabolites in striatum, as well as loss of tyrosine hydroxylase immunoreactive neurons in substantia nigra pars compacta. SS-20, which does not possess intrinsic ability in scavenging reactive oxygen species, also demonstrated significant neuroprotective effects on dopaminergic neurons of MPTP-treated mice. Both SS-31 and SS-20 were very potent (nM) in preventing MPP+ (1-methyl-4-phenylpyridinium)-induced cell death in cultured dopamine cells (SN4741). Studies with isolated mitochondria showed that both SS-31 and SS-20 prevented MPP+-induced inhibition of oxygen consumption and ATP production, and mitochondrial swelling. These findings provide strong evidence that these neuroprotective peptides, which target both mitochondrial dysfunction and oxidative damage, are a promising approach for the treatment of PD.

Neuroprotective effects of resveratrol on MPTP-induced neuron loss mediated by free radical scavenging

Resveratrol is a natural polyphenol and possesses many biological functions such as anti-inflammatory activity and protection against atherosclerosis and myocardial infraction. Parkinson's disease is a common progressive neurodegenerative disease. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is the most useful neurotoxin to induce Parkinsonism. The present study was carried out to elucidate the neuroprotective effect and possible mechanism of resveratrol on MPTP-induced striatal neuron loss. Sixty adult Balb/c mice were divided into four groups: sham operation, MPTP treatment (30 mg/kg, i.p.), MPTP combined with resveratrol administration (20 mg/kg, i.v.), and resveratrol treatment alone. Microdialysis and high-performance liquid chromatography were used to analyze dihydroxybenzoic acid (DHBA) that reflected the hydroxyl radical level. In the present study, we found MPTP chronic administration significantly induced motor coordination impairment in mice. After MPTP administration, the hydroxyl radical levels in substantia nigra were also significantly elevated and animals displayed severe neuronal loss. Resveratrol administration significantly protected mice from MPTP-induced motor coordination impairment, hydroxyl radical overloading, and neuronal loss. Our results demonstrated that resveratrol could elicit neuroprotective effects on MPTP-induced Parkinsonism through free radical scavenging.

Differential effects of overexpression of wild-type and mutant human alpha-synuclein on MPP+-induced neurotoxicity in PC12 cells

The genetic background and the pathogenesis of familial Parkinson's disease (PD) have not been fully elucidated. Two missense mutations in the alpha-synuclein gene, A30P and A53T, have been linked to familial PD. Increasing evidence suggests the involvement of alpha-synuclein, the dopamine transporter (DAT), and neurotoxins in the pathogenesis of PD, but their relationships to the death of nigral cells remains poorly understood. In the present study, we used the PC12 cell line, a well recognized model of the nigral cell, to investigate the effects of overexpression of wild-type (WT) and mutant human alpha-synuclein on MPP+-induced neurotoxicity. We found that overexpression of mutant alpha-synuclein enhanced the toxicity of MPP+ to PC12 cells and elevated intracellular reactive oxygen species (ROS) levels, whereas overexpression of WT alpha-synuclein protected PC12 cells against MPP+ toxicity and lowered ROS levels. Furthermore, assays of 131I-FP-beta-CIT binding with DAT membrane fractions showed that WT and mutant alpha-synuclein had different effects on the expression of DAT on the cell membrane following exposure to MPP+. WT alpha-synuclein reduced the toxic effect of MPP+ by facilitating DAT internalization, while both A30P and A53T alpha-synuclein aggravated the toxic effect of MPP+ by reducing DAT internalization. These data indicate that alpha-synuclein regulates ROS levels and DAT surface expression in dopaminergic neurons, and thus changes the response of these cells to MPP+.

Topological and chronological features of the impairment of glucose metabolism induced by 1-methyl-4-phenylpyridinium ion (MPP+) in rat brain slices

1-Methyl-4-phenylpyridinium (MPP(+)) was added directly to fresh rat brain slices and the dynamic changes in the cerebral glucose metabolic rate (CMRglc) were serially and two-dimensionally measured with [(18)F]2-fluoro-2-deoxy-D-glucose as a tracer. MPP(+) dose-dependently increased CMRglc, reflecting enhanced glycolysis compensating for the decrease in aerobic metabolism. While the CMRglc enhancement induced by MPP(+) (<10 microM) was restricted to the striatum, MPP(+) (>or=10 microM) induced a significant CMRglc enhancement in all brain regions. MPP(+) at high concentration (1 mM) eventually initiated rapid metabolic collapse, with failure to sustain anaerobic glycolysis.

Biphasic mechanism of the toxicity induced by 1-methyl-4-phenylpyridinium ion (MPP+) as revealed by dynamic changes in glucose metabolism in rat brain slices

1-Methyl-4-phenylpyridinium (MPP+) is a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease. The classical mechanism of MPP+ toxicity involves its entry into cells through the dopamine transporter (DAT) to inhibit aerobic glucose metabolism, while recent studies suggest that an oxidative mechanism may contribute to the toxicity of MPP+. However, it has not been adequately determined what role these two mechanisms play in the development of neurotoxicity after MPP+ loading in the brain. To clarify this issue, MPP+ was added directly to fresh rat brain slices and the dynamic changes in the cerebral glucose metabolic rate (CMRglc) produced by MPP+ were serially and two-dimensionally measured using the dynamic positron autoradiography technique with [(18)F]2-fluoro-2-deoxy-D-glucose as a tracer. MPP+ dose-dependently increased CMRglc in each of the brain regions examined, reflecting enhanced glycolysis compensating for the decrease in aerobic metabolism. Treatment with DAT inhibitor GBR 12909 significantly attenuated the enhanced glycolysis induced by 10 microM MPP+ in the striatum. Treatment with free radical spin trap alpha-phenyl-N-tert-butylnitrone (PBN) significantly attenuated the enhancement of glycolysis induced by 100 microM MPP+ in all brain regions. These results suggest that the mechanism of the toxicity of MPP+ is biphasic and consists of a DAT-mediated mechanism selective for dopaminergic regions at a lower concentration of MPP+ (10 microM), and an oxidative mechanism that occurs at a higher concentration of MPP+ (100 microM) and is not restricted to dopaminergic regions.

Possible Mechanisms of Neurodegeneration in Schizophrenia

Brain morphological alterations in schizophrenic patients have led to the neurodevelopmental hypothesis of schizophrenia. On the other hand, a progressive neurodegenerative process has also been suggested and some follow-up studies have shown progressive morphological changes in schizophrenic patients. Several neurotransmitter systems have been suggested to be involved in this disorder and some of them could lead to neuronal death under certain conditions. This review discusses some of the biochemical pathways that could lead to neurodegeneration in schizophrenia showing that neuronal death may have a role in the etiology or natural course of this disorder.

Potentiating effect of the ATP-sensitive potassium channel blocker glibenclamide on complex I inhibitor neurotoxicity in vitro and in vivo

Previous studies have demonstrated a deficiency in mitochondrial function in Parkinson's disease. We measured the ability of mitochondrial inhibitors of complexes I (rotenone, MPP(+), and HPP(+)), II (amdro), IV (Na cyanide), and an uncoupler (dinoseb) to release preloaded dopamine from murine striatal synaptosomes. These compounds were potent dopamine releasers, and the effect was calcium-dependent. The striatum also contains a significant density of K(ATP)(+) channels, which play a protective role during ATP decline. Blockage of these channels with glibenclamide only potentiated the dopamine release by complex I inhibitors, and a selective potentiating effect of glibenclamide on the toxicity of MPTP was also observed, in vivo, using C57BL/6 mice. Western blots of striatal dopamine transporter (DAT) and tyrosine hydroxylase (TH) proteins demonstrated that 30 mg/kg of glibenclamide alone did not affect the expression of DAT and TH after two weeks of daily treatments, but it significantly enhanced the reduction of DAT and TH by a single dose of 20 mg/kg of MPTP. Amdro or dinoseb alone, or in conjunction with glibenclamide did not alter the expression of DAT and TH. The possible mechanisms underlying dopamine release and the selectivity of glibenclamide were further evaluated, in vitro. (86)Rb efflux assay showed that glibenclamide inhibited rotenone-induced K(+) efflux, but not dinoseb-induced K(+) efflux. Analysis of ATP titers in treated synaptosomes did not support a correlation between mitochondrial inhibition and K(ATP)(+) channel activation. However, assay of reactive oxygen species (ROS) showed that greater amounts of ROS generated by complex I inhibitors was a contributory factor to K(ATP)(+) channel activation and glibenclamide potentiation. Overall, these findings suggest that co-exposure to mitochondrial complex I inhibitors and glibenclamide or a genetic defect in K(ATP)(+) channel function, may increase neurotoxicity in the striatal dopaminergic system.

Partial mitochondrial inhibition causes striatal dopamine release suppression and medium spiny neuron depolarization via H2O2 elevation, not ATP depletion

Mitochondrial dysfunction is a potential causal factor in Parkinson's disease. We show here that acute exposure to the mitochondrial complex I inhibitor rotenone (30-100 nM; 30 min) causes concentration-dependent suppression of single-pulse evoked dopamine (DA) release monitored in real time with carbon-fiber microelectrodes in guinea pig striatal slices, with no effect on DA content. Suppression of DA release was prevented by the sulfonylurea glibenclamide, implicating ATP-sensitive K+ (KATP) channels; however, tissue ATP was unaltered. Because KATP channels can be activated by hydrogen peroxide (H2O2), as well as by low ATP, we examined the involvement of rotenone-enhanced H2O2 generation. Confirming an essential role for H2O2, the inhibition of DA release by rotenone was prevented by catalase, a peroxide-scavenging enzyme. Striatal H2O2 generation during rotenone exposure was examined in individual medium spiny neurons using fluorescence imaging with dichlorofluorescein (DCF). An increase in intracellular H2O2 levels followed a similar time course to that of DA release suppression and was accompanied by cell membrane depolarization, decreased input resistance, and increased excitability. Extracellular catalase markedly attenuated the increase in DCF fluorescence and prevented rotenone-induced effects on membrane properties; membrane changes were also largely prevented by flufenamic acid, a blocker of transient receptor potential (TRP) channels. Thus, partial mitochondrial inhibition can cause functional DA denervation via H2O2 and KATP channels, without DA or ATP depletion. Furthermore, amplified H2O2 levels and TRP channel activation in striatal spiny neurons indicate potential sources of damage in these cells. Overall, these novel factors could contribute to parkinsonian motor deficits and neuronal degeneration caused by mitochondrial dysfunction.

Investigating the receptor-independent neuroprotective mechanisms of nicotine in mitochondria

Although nicotine has been associated with a decreased risk of developing Parkinson disease, the underlying mechanisms are still unclear. By using isolated brain mitochondria, we found that nicotine inhibited N-methyl-4-phenylpyridine (MPP(+)) and calcium-induced mitochondria high amplitude swelling and cytochrome c release from intact mitochondria. Intra-mitochondria redox state was also maintained by nicotine, which could be attributed to an attenuation of mitochondria permeability transition. Further investigation revealed that nicotine did not prevent MPP(+)- or calcium-induced mitochondria membrane potential loss, but instead decreased the electron leak at the site of respiratory chain complex I. In the presence of mecamylamine hydrochloride, a nonselective nicotinic acetylcholine receptor inhibitor, nicotine significantly postponed mitochondria swelling and cytochrome c release induced by a mixture of neurotoxins (MPP(+) and 6-hydroxydopamine) in SH-SY5Y cells, suggesting that there is a receptor-independent nicotine-mediated neuroprotective effect of nicotine. These results show that interaction of nicotine with mitochondria respiratory chain together with its antioxidant effects should be considered in the neuroprotective effects of nicotine.

Mitochondrial membrane depolarization and the selective death of dopaminergic neurons by rotenone: protective effect of coenzyme Q10

Chronic exposure to the pesticide rotenone induces a selective degeneration of nigrostriatal dopaminergic neurons and reproduces the features of Parkinson's disease in experimental animals. This action is thought to be relevant to its inhibition of the mitochondrial complex I, but the precise mechanism of this suppression in selective neuronal death is still elusive. Here we investigate the mechanism of dopaminergic neuronal death mediated by rotenone in primary rat mesencephalic neurons. Low concentrations of rotenone (5-10 nM) induce the selective death of dopaminergic neurons without significant toxic effects on other mesencephalic cells. This cell death was coincident with apoptotic events including capsase-3 activation, DNA fragmentation, and mitochondrial membrane depolarization. Pretreatment with coenzyme Q10, the electron transporter in the mitochondrial respiratory chain, remarkably reduced apoptosis as well as the mitochondrial depolarization induced by rotenone, but other free radical scavengers such as N-acetylcysteine, glutathione, and vitamin C did not. Furthermore, the selective neurotoxicity of rotenone was mimicked by the mitochondrial protonophore carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP), a cyanide analog that effectively collapses a mitochondrial membrane potential. These data suggest that mitochondrial depolarization may play a crucial role in rotenone-induced selective apoptosis in rat primary dopaminergic neurons.

Role of Mitochondrial Dysfunction in Neurotoxicity of MPP:+: Partial Protection of PC12 Cells by Acetyl-l-Carnitine

The damage to the central nervous system that is observed after administration of either methamphetamine (METH) or 1-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is known to be linked to dopamine (DA). The underlying neurotoxicity mechanism for both METH and MPP+ seem to involve free radical formation and impaired mitochondrial function. The MPP+ is thought to selectively kill nigrostriatal dopaminergic neurons by inhibiting mitochondrial complex I, with cell death being attributed to oxidative stress damage to these vulnerable DA neurons. In the present study, MPP+ was shown to significantly inhibit the response to MTT by cultured PC12 cells. This inhibitory action of MPP+ could be partially reversed by the co-incubation of the cells with the acetylated form of carnitine, acetyl-L-carnitine (ALC). Since at least part of the toxic action of MPP+ is related to mitochondrial inhibition, the partial reversal of the inhibition of MTT response by ALC could involve a partial restoration of mitochondrial function. The role carnitine derivatives, such as ALC, play in attenuating MPP+ and METH-evoked toxicity is still under investigation to elucidate the contribution of mitochondrial dysfunction in mechanisms of neurotoxicity.

Measurement of mitochondrial respiration in permeabilized murine neuroblastoma (N-2alpha) cells, a simple and rapid in situ assay to investigate mitochondrial toxins

Most mitochondria-based methods used to investigate toxins require the use of relatively large amounts of material and hence compromised sensitivity in assay. We adopted procedures from methods initially developed to diagnose mitochondrial encephalomyopathies and unified these into a single assay. Eukaryotic cell membranes are selectively permeabilized with digitonin to render a system in which mitochondrial respiration can be measured rapidly and with considerable sensitivity. Mitochondria remain intact, uninjured, and in their natural environment where mitochondrial respiration can be measured in situ under physiologically relevant conditions. This approach furthermore allows measurement of toxin effects on individual mitochondrial complexes. Numerous compounds at varying concentrations can be screened for mitochondrial toxicity, while the site of mitochondrial inhibition can be determined simultaneously. We used this assay to investigate, in murine neuroblastoma (N-2alpha) cells, the mitochondrial inhibitory properties of the parkinsonian-inducing proneurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and its neurotoxic monoamine oxidase-B (MAO-B)-generated metabolite, the 1-methyl-4-phenylpyridinium species (MPP(+)). Within the time frame of each measurement (15 min), MPTP (< or = 1 mM) did not interfere with in situ mitochondrial respiration. As expected, MPP(+) was found to be a potent Complex I inhibitor but surprisingly also found to inhibit Complex IV. Optimized conditions for performing this assay are provided.

1-Methyl-4-phenylpyridinium-induced down-regulation of dopamine transporter function correlates with a reduction in dopamine transporter cell surface expression

The mechanisms whereby 1-methyl-4-phenylpyridinium (MPP(+)) mediates cell death and Parkinsonism are still unclear. We have shown that dopamine transporter (DAT) is required for MPP(+)-mediated cytotoxicity in HEK-293 cells stably transfected with human DAT. Furthermore, MPP(+) produced a concentration- and time-dependent reduction in the uptake of [3H]dopamine. We observed a significant decrease in [3H]WIN 35428 binding in the intact cells with MPP(+). The saturation analysis of the [3H]WIN 35428 binding obtained from total membrane fractions revealed a decrease in the transporter density (B(max)) with an increase in the dissociation equilibrium constant (K(d)) after MPP(+) treatment. Furthermore, biotinylation assays confirmed that MPP(+) reduced both plasma membrane and intracellular DAT immunoreactivity. Taken together, these findings suggest that the reduction in cell surface DAT protein expression in response to MPP(+) may be a contributory factor in the down-regulation of DAT function while enhanced lysosomal degradation of DAT may signal events leading to cellular toxicity.

Mitochondrial complex I inhibition produces selective damage to hippocampal subfield CA1 in organotypic slice cultures

The effects of mitochondrial respiratory chain inhibitors and the excitotoxin N-methyl-D-aspartate (NMDA) on cell death in hippocampal subfields CA1 and CA3 were examined in hippocampal organotypic slice cultures. Slice cultures, 2-3 week old, were exposed for 1 h to either the Complex I inhibitors, rotenone or 1-methyl-4-phenylpyridium (MPP+), the Complex II inhibitor 3-nitropropionic acid (3-NP), or the excitotoxin NMDA. Cell death was examined 24 and 48 h following treatment, by measuring propidium iodide (PI) fluorescence. Treatment with 1 micro M Rotenone caused greater cell death in hippocampal subfield CA1 than CA3. Exposure of hippocampal slice cultures to 10 micro M rotenone, to MPP+ or to NMDA resulted in damage to both CA1 and CA3 subfields. 3-NP produced little damage in either subfield. The data suggest that mitochondrial Complex I inhibition can produce selective cell damage in hippocampus and in this regard is similar to that observed following hypoxia/ischemia.