Mitochondrial DNA and Parkinson's disease

SNHG14 Elevates NFAT5 Expression Through Sequestering miR-375-3p to Promote MPP + -Induced Neuronal Apoptosis, Inflammation, and Oxidative Stress in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons. LncRNA small nucleolar RNA host gene 14 (SNHG14) was found to promote neuron injury in PD. Here, we investigated the mechanisms of SNHG14 in PD process. In vivo or in vitro PD model was established by using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice or 1-methyl-4-phenylpyridinium (MPP +)-stimulated SK-N-SH cells. The expression of genes and proteins was measured by qRT-PCR and Western blot. In vitro assays were conducted using ELISA, CCK-8, colony formation, EdU, flow cytometry, and Western blot assays, respectively. The oxidative stress was evaluated by determining the production of superoxide dismutase (SOD) and malondialdehyde (MDA). The direct interactions between miR-375-3p and NFAT5 (Nuclear factor of activated T-cells 5) or SNHG14 was verified using dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. SNHG14 and NFAT5 were elevated, while miR-375-3p was decreased in MPTP-mediated PD mouse model and MPP + -induced SK-N-SH cells. Knockdown of SNHG14 or NFAT5, or overexpression of miR-375-3p reversed MPP + -induced neuronal apoptosis, inflammation, and oxidative stress. Mechanistically, SNHG14 directly bound to miR-375, which targeted NFAT5. Inhibition of miR-375-3p abolished the inhibitory activity of SNHG14 knockdown on MPP + -evoked neuronal damage. Besides that, NFAT5 up-regulation counteracted the effects of miR-375-3p on MPP + -mediated neuronal damage. SNHG14 contributed to MPP + -induced neuronal injury by miR-375/NFAT5 axis, suggesting a new insight into the pathogenesis of PD.

Monogenic Disorders of ROS Production and the Primary Anti-Oxidative Defense

Oxidative stress, characterized by an imbalance between the production of reactive oxygen species (ROS) and the cellular anti-oxidant defense mechanisms, plays a critical role in the pathogenesis of various human diseases. Redox metabolism, comprising a network of enzymes and genes, serves as a crucial regulator of ROS levels and maintains cellular homeostasis. This review provides an overview of the most important human genes encoding for proteins involved in ROS generation, ROS detoxification, and production of reduced nicotinamide adenine dinucleotide phosphate (NADPH), and the genetic disorders that lead to dysregulation of these vital processes. Insights gained from studies on inherited monogenic metabolic diseases provide valuable basic understanding of redox metabolism and signaling, and they also help to unravel the underlying pathomechanisms that contribute to prevalent chronic disorders like cardiovascular disease, neurodegeneration, and cancer.

Systems level analysis of sex-dependent gene expression changes in Parkinson's disease

Parkinson's disease (PD) is a heterogeneous disorder, and among the factors which influence the symptom profile, biological sex has been reported to play a significant role. While males have a higher age-adjusted disease incidence and are more frequently affected by muscle rigidity, females present more often with disabling tremors. The molecular mechanisms involved in these differences are still largely unknown, and an improved understanding of the relevant factors may open new avenues for pharmacological disease modification. To help address this challenge, we conducted a meta-analysis of disease-associated molecular sex differences in brain transcriptomics data from case/control studies. Both sex-specific (alteration in only one sex) and sex-dimorphic changes (changes in both sexes, but with opposite direction) were identified. Using further systems level pathway and network analyses, coordinated sex-related alterations were studied. These analyses revealed significant disease-associated sex differences in mitochondrial pathways and highlight specific regulatory factors whose activity changes can explain downstream network alterations, propagated through gene regulatory cascades. Single-cell expression data analyses confirmed the main pathway-level changes observed in bulk transcriptomics data. Overall, our analyses revealed significant sex disparities in PD-associated transcriptomic changes, resulting in coordinated modulations of molecular processes. Among the regulatory factors involved, NR4A2 has already been reported to harbor rare mutations in familial PD and its pharmacological activation confers neuroprotective effects in toxin-induced models of Parkinsonism. Our observations suggest that NR4A2 may warrant further research as a potential adjuvant therapeutic target to address a subset of pathological molecular features of PD that display sex-associated profiles.

Colorimetric Detection of ATP by a Chlorophosphonazo III -based Mg2+ Complex in Aqueous Solution via Indicator Displacement Approach

A simple and effective colorimetric detection of adenosine 5-triphosphate (ATP) in 100% aqueous media was developed based on an indicator displacement approach (IDA). A commercially available dye, Chlorophosphonazo III (CPA), was utilized as the indicator and the ATP detection was achieved using the complex of CPA with Mg²⁺ in a 2:1 stoichiometric ratio (CPA₂-Mg²⁺) through the regeneration of CPA by the binding of ATP to Mg²⁺. Upon addition of a series of anions to the CPA₂-Mg²⁺ complex, only the appearance of the solution of the complex with ATP exhibited a color change from blue to purple which can be detected by the naked eye. Moreover, the ATP recognition was not hampered by the presence of other anions. Hence, CPA₂-Mg²⁺ is efficient in ATP highly selective and sensitive colorimetric detection in 100% aqueous media.

Functional Interaction among lncRNA HOTAIR and MicroRNAs in Cancer and Other Human Diseases

Simple Summary

This review aimed to describe the contribution of functional interaction between the lncRNA HOTAIR and microRNAs in human diseases, including cancer. HOTAIR/miRNAs complexes interfere with different cellular processes during carcinogenesis, mainly deregulating a series of oncogenic signaling pathways. A great number of ncRNAs-related databases have been established, supported by bioinformatics technologies, to identify the ncRNA-mediated sponge regulatory network. These approaches need experimental validation through cells and animal models studies. The optimization of systems to interfere with HOTAIR/miRNAs interplay could represent a new tool for the definition of diagnostic therapeutics in cancer patients.

Abstract

LncRNAs are a class of non-coding RNAs mostly involved in regulation of cancer initiation, metastatic progression, and drug resistance, through participation in post-transcription regulatory processes by interacting with different miRNAs. LncRNAs are able to compete with endogenous RNAs by binding and sequestering miRNAs and thereby regulating the expression of their target genes, often represented by oncogenes. The lncRNA HOX transcript antisense RNA (HOTAIR) represents a diagnostic, prognostic, and predictive biomarker in many human cancers, and its functional interaction with miRNAs has been described as crucial in the modulation of different cellular processes during cancer development. The aim of this review is to highlight the relation between lncRNA HOTAIR and different microRNAs in human diseases, discussing the contribution of these functional interactions, especially in cancer development and progression.

LncRNA HOTAIR promotes MPP+-induced neuronal injury in Parkinson's disease by regulating the miR-874-5p/ATG10 axis

Parkinson's disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic neurons. Long non-coding RNAs (lncRNAs) play an important role in many neurological diseases, including PD. This study aimed to investigate the role of lncRNA HOX transcript antisense RNA (HOTAIR) in PD pathogenesis and its potential mechanism. SK-N-SH cells were exposed to 1-methyl-4-phenylpyridinium (MPP⁺) to mimic PD model in vitro. The levels of HOTAIR, miR-874-5p and autophagy-related 10 (ATG10) were determined by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell viability and apoptosis were assessed by Cell Counting Kit-8 (CCK-8) assay and flow cytometry. The expression of apoptosis-related proteins was measured by western blot. The levels of neuroinflammation-related factors were detected by enzyme-linked immunosorbent assay (ELISA). Commercial kits was used to monitor lactate dehydrogenase (LDH) activity, reactive oxygen (ROS) generation and superoxide dismutase (SOD) activity. The interaction among HOTAIR, miR-874-5p and ATG10 were verified by dual-luciferase reporter assay or RNA immunoprecipitation (RIP) assay. HOTAIR and ATG10 were up-regulated, and miR-874-5p was down-regulated in dose- and time-dependent manners in MPP⁺-treated SK-N-SH cells. HOTAIR knockdown reduced MPP⁺-induced neuronal damage. HOTAIR aggrandized MPP⁺-triggered neuronal injury by sponging miR-874-5p. Also, miR-874-5p attenuated MPP⁺-triggered neuronal damage by targeting ATG10. Moreover, HOTAIR regulated ATG10 expression via sponging miR-874-5p. HOTAIR promoted MPP⁺-induced neuronal injury via modulating the miR-874-5p/ATG10 axis in SK-N-SH cells.

Age-related accumulation of de novo mitochondrial mutations in mammalian oocytes and somatic tissues

Mutations create genetic variation for other evolutionary forces to operate on and cause numerous genetic diseases. Nevertheless, how de novo mutations arise remains poorly understood. Progress in the area is hindered by the fact that error rates of conventional sequencing technologies (1 in 100 or 1,000 base pairs) are several orders of magnitude higher than de novo mutation rates (1 in 10,000,000 or 100,000,000 base pairs per generation). Moreover, previous analyses of germline de novo mutations examined pedigrees (and not germ cells) and thus were likely affected by selection. Here, we applied highly accurate duplex sequencing to detect low-frequency, de novo mutations in mitochondrial DNA (mtDNA) directly from oocytes and from somatic tissues (brain and muscle) of 36 mice from two independent pedigrees. We found mtDNA mutation frequencies 2- to 3-fold higher in 10-month-old than in 1-month-old mice, demonstrating mutation accumulation during the period of only 9 mo. Mutation frequencies and patterns differed between germline and somatic tissues and among mtDNA regions, suggestive of distinct mutagenesis mechanisms. Additionally, we discovered a more pronounced genetic drift of mitochondrial genetic variants in the germline of older versus younger mice, arguing for mtDNA turnover during oocyte meiotic arrest. Our study deciphered for the first time the intricacies of germline de novo mutagenesis using duplex sequencing directly in oocytes, which provided unprecedented resolution and minimized selection effects present in pedigree studies. Moreover, our work provides important information about the origins and accumulation of mutations with aging/maturation and has implications for delayed reproduction in modern human societies. Furthermore, the duplex sequencing method we optimized for single cells opens avenues for investigating low-frequency mutations in other studies.

The MPTP Story

The identification of MPTP, a relatively simple compound which causes selective degeneration of the substantia nigra after systemic administration, has had an a significant impact on the understanding and treatment of Parkinson’s disease (PD) over the last 30 years. This article is prefaced by the intriguing “medical detective story” that lead to the discovery of the biological effects of MPTP in humans. The steps that lead to the unraveling its mechanism of action and their impact on research into pathways underlying nigrostriatal degeneration are reviewed. The impact of the animal models that have been developed utilizing MPTP is also described with a focus on the translational implications of MPTP-related research. These include use of MAO-B inhibitors aimed at neuroprotection in PD and the importance of a stable primate model for PD which was utilized to better understand the circuitry of the basal ganglia, and the identification of the subthalamic nucleus as a target for deep brain stimulation. Finally, the results of a broad range of epidemiologic studies aimed as assessing the impact of environmental factors in PD that have been inspired by MPTP are summarized, including the discovery of other neurotoxicants (rotenone and paraquat) with parkinsonogenic effects. Overall, this article attempts to describe how the discovery of this nigral neurotoxicant began, where it is currently, and what the future may hold.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

High levels of mitochondrial DNA are associated with adolescent brain structural hypoconnectivity and increased anxiety but not depression

BACKGROUND

Adolescent anxiety and depression are highly prevalent psychiatric disorders that are associated with altered molecular and neurocircuit profiles. Recently, increased mitochondrial DNA copy number (mtDNA-cn) has been found to be associated with several psychopathologies in adults, especially anxiety and depression. The associations between mtDNA-cn and anxiety and depression have not, however, been investigated in adolescents. Moreover, to date there have been no studies examining associations between mtDNA-cn and brain network alterations in mood disorders in any age group.

METHODS

The first aim of this study was to compare salivary mtDNA-cn between 49 depressed and/or anxious adolescents and 35 well-matched healthy controls. The second aim of this study was to identify neural correlates of mtDNA-cn derived from diffusion tensor imaging (DTI) and tractography, in the full sample of adolescents.

RESULTS

There were no diagnosis-specific alterations in mtDNA-cn. However, there was a positive correlation between mtDNA-cn and levels of anxiety, but not depression, in the full sample of adolescents. A subnetwork of connections largely corresponding to the left fronto-occipital fasciculus had significantly lower fractional anisotropy (FA) values in adolescents with higher than median mtDNA-cn.

LIMITATIONS

Undifferentiated analysis of free and intracellular mtDNA and use of DTI-based tractography represent this study's limitations.

CONCLUSIONS

The results of this study help elucidate the relationships between clinical symptoms, molecular changes, and neurocircuitry alterations in adolescents with and without anxiety and depression, and they suggest that increased mtDNA-cn is associated both with increased anxiety symptoms and with decreased fronto-occipital structural connectivity in this population.

Riboflavin in Human Health: A Review of Current Evidences

Riboflavin is a water-soluble vitamin, which was initially isolated from milk. There are two coenzyme forms of riboflavin, flavin mononucleotide and flavin adenine dinucleotide, in which riboflavin plays important roles in the enzymatic reactions. Riboflavin is found in a wide variety of animal and plant foods. Meat and dairy products are the major contributors of riboflavin dietary intake. In this chapter, the latest evidence on the relationship between riboflavin status and specific health risks will be reviewed. Also, some of the mechanisms by which riboflavin exerts its roles will be discussed. The evidence accrued suggests that riboflavin is an antioxidant nutrient which may prevent lipid peroxidation and reperfusion oxidative injury. Moreover, riboflavin deficiency may increase the risk of some cancers. Riboflavin may also exert a neuroprotective effects in some neurological disorders (e.g., Parkinson disease, migraine, and multiple sclerosis) through its role in some pathways that are hypothesized to be impaired in neurological disorders such as antioxidation, myelin formation, mitochondrial function, and iron metabolism.

Solvent exposures and Parkinson disease risk in twins

OBJECTIVE

Several case reports have linked solvent exposure to Parkinson disease (PD), but few studies have assessed associations with specific agents using an analytic epidemiologic design. We tested the hypothesis that exposure to specific solvents is associated with PD risk using a discordant twin pair design.

METHODS

Ninety-nine twin pairs discordant for PD ascertained from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort were interviewed regarding lifetime occupations and hobbies using detailed job task-specific questionnaires. Exposures to 6 specific solvents selected a priori were estimated by expert raters unaware of case status.

RESULTS

Ever exposure to trichloroethylene (TCE) was associated with significantly increased risk of PD (odds ratio [OR], 6.1; 95% confidence interval [CI] 1.2-33; p = 0.034), and exposure to perchloroethylene (PERC) and carbon tetrachloride (CCl(4) ) tended toward significance (respectively: OR, 10.5; 95% CI, 0.97-113; p = 0.053; OR, 2.3; 95% CI, 0.9-6.1; p = 0.088). Results were similar for estimates of exposure duration and cumulative lifetime exposure.

INTERPRETATION

Exposure to specific solvents may increase risk of PD. TCE is the most common organic contaminant in groundwater, and PERC and CCl(4) are also ubiquitous in the environment. Our findings require replication in other populations with well-characterized exposures, but the potential public health implications are substantial.

The promise of neuroprotective agents in Parkinson's disease

Parkinson’s disease (PD) is characterized by loss of dopamine neurons in the substantia nigra of the brain. Since there are limited treatment options for PD, neuroprotective agents are currently being tested as a means to slow disease progression. Agents targeting oxidative stress, mitochondrial dysfunction, and inflammation are prime candidates for neuroprotection. This review identifies Rasagiline, Minocycline, and creatine, as the most promising neuroprotective agents for PD, and they are all currently in phase III trials. Other agents possessing protective characteristics in delaying PD include stimulants, vitamins, supplements, and other drugs. Additionally, combination therapies also show benefits in slowing PD progression. The identification of neuroprotective agents for PD provides us with therapeutic opportunities for modifying the course of disease progression and, perhaps, reducing the risk of onset when preclinical biomarkers become available.

N(ɛ)-(carboxymethyl)lysine linkage to α-synuclein and involvement of advanced glycation end products in α-synuclein deposits in an MPTP-intoxicated mouse model

This study investigated the involvement of advanced glycation end products (AGEs) that may be nonenzymatically linked to α-synuclein accumulation in the chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced C57BL/6 mouse model of parkinsonism. MPTP (20 mg/kg) was intraperitoneally administrated once daily for 30 days to the MPTP group while a saline only solution was administered to the control group. Results show that the immunoreactivities of the tyrosine hydroxylase and dopamine transporter significantly decreased in the striatum and the substantia nigra (SN) in the MPTP model compared to the subjects in the control group. α-synuclein was co-localized with N(ɛ)-(carboxymethyl)lysine (CML) and N(ɛ)-(carboxyethyl)lysine (CEL), which are well-known AGEs, in tyrosine hydroxylase-positive dopaminergic neurons in the MPTP brains. α-synuclein was also shown to be deposited in the CD11b-positive activated microglia. Some AGEs-modified proteins (CML-, CEL-, pentosidine-, or pyrraline-modified proteins) and an oligomeric form of α-synuclein appear to have almost the same molecular weight, specifically between 50 and 75 kDa; in addition, these formations were more strongly deposited in the SN region of the MPTP brains than in the control brains. Moreover, the oligomeric form of α-synuclein was modified with CML in the SNs of both the control and MPTP brains. This study, for the first time, shows that chronic dopaminergic neurodegeneration by MPTP can lead to the depositing of an oligomeric form of α-synuclein, CML-linked α-synuclein, and CEL-, pentosidine-, or pyrraline-linked proteins between 50 and 75 kDa. It is thus suggested that CML, especially a CML-linked α-synuclein oligomer between 50 and 75 kDa, may be, at least in part, involved in the aggregation of the α-synuclein induced by MPTP intoxication.

The protective role of D-glucose against 1-methyl-4-phenylpyridinium ion (MPP+): induced mitochondrial dysfunction in C6 astroglial cells

Impaired mitochondrial function in glial and neuronal cells in the substantia nigra is one of the most likely causes of Parkinson's disease. In this study, we investigated the protective role of glucose on early key events associated with MPP(+)-induced changes in rat C6 astroglial cells. Studies were carried out to examine alterations in mitochondrial respiratory status, membrane potential, glutathione levels, and cell cycle phase inhibition at 48 h in 2 and 10 mM glucose in media. The results obtained suggest that MPP(+) caused significant cell death in 2 mM glucose with LC(50) 0.14 +/- 0.005 mM, while 10 mM glucose showed highly significant protection against MPP(+) toxicity with LC(50) 0.835 +/- 0.03 mM. This protection was not observed with cocaine, demonstrating its compound specificity. MPP(+) in 2 mM glucose decreased significantly mitochondrial respiration, membrane potential and glutathione levels in a dose dependent manner, while 10 mM glucose significantly restored them. MPP(+) in 2 mM glucose arrested the cells at G0/G1 and G2/M phases, demonstrating its dual inhibitory effects. However, in 10 mM glucose, MPP(+) caused G0/G1 arrest only. In summary, the results suggest that loss of cell viability in 2 mM glucose group with MPP(+) treatments was due to mitochondrial dysfunction caused by multilevel mechanism, involving significant decrease in mitochondrial respiration, membrane potential, glutathione levels, and dual arrest of cell phases, while 10 mM glucose rescued astroglial cells from MPP(+) toxicity by significant maintenance of these factors.

Melatonin inhibits maneb-induced aggregation of alpha-synuclein in rat pheochromocytoma cells

Melatonin, a secretory product of the pineal gland, is involved in the regulation of circadian and seasonal rhythms, in oncostasis, and in inducing osteoblast differentiation. Furthermore, melatonin is a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. In this study, the antioxidant nature of melatonin was shown to prevent cultured neural cells from apoptosis induced by endocrine-disrupting chemical, maneb. The neurotoxicity of the fungicide, maneb (1 microg/mL), on the PC12 cells was elicited through apoptotic cell death, concomitant with aggregation of alpha-synuclein, a feature of Parkinson's disease. Activation of caspase-3/7 was associated with this process. A fluorescence rationing technique using a mitochondrial dye revealed that maneb altered the mitochondrial membrane potential of the neural cells. However, melatonin (1 nm) largely prevented the neural cells from the neural toxicant by inhibition of both caspase-3/7 activation and disruption of the mitochondrial transmembrane potential. Furthermore, aggregation of alpha-synuclein by maneb was also inhibited by melatonin. Thus, melatonin prevents maneb-induced neurodegeneration at a nighttime physiological blood concentration, most likely by inhibiting the aggregation of alpha-synuclein as well as preventing mitochondrial dysfunction in PC 12 cells.

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.

Effects of enhancing mitochondrial oxidative phosphorylation with reducing equivalents and ubiquinone on 1-methyl-4-phenylpyridinium toxicity and complex I–IV damage in neuroblastoma cells

The effects of increasing mitochondrial oxidative phosphorylation (OXPHOS), by enhancing electron transport chain components, were evaluated on 1-methyl-4-phenylpyridinium (MPP+) toxicity in brain neuroblastoma cells. Although glucose is a direct energy source, ultimately nicotinamide and flavin reducing equivalents fuel ATP produced through OXPHOS. The findings indicate that cell respiration/mitochondrial O(2) consumption (MOC) (in cells not treated with MPP+) is not controlled by the supply of glucose, coenzyme Q(10) (Co-Q(10)), NADH+, NAD or nicotinic acid. In contrast, MOC in whole cells is highly regulated by the supply of flavins: riboflavin, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), where cell respiration reached up to 410% of controls. In isolated mitochondria, FAD and FMN drastically increased complex I rate of reaction (1300%) and (450%), respectively, having no effects on complex II or III. MPP+ reduced MOC in whole cells in a dose-dependent manner. In isolated mitochondria, MPP+ exerted mild inhibition at complex I, negligible effects on complexes II-III, and extensive inhibition of complex IV. Kinetic analysis of complex I revealed that MPP+ was competitive with NADH, and partially reversible by FAD and FMN. Co-Q(10) potentiated complex II ( approximately 200%), but not complex I or III. Despite positive influence of flavins and Co-Q(10) on complexes I-II function, neither protected against MPP+ toxicity, indicating inhibition of complex IV as the predominant target. The nicotinamides and glucose prevented MPP+ toxicity by fueling anaerobic glycolysis, evident by accumulation of lactate in the absence of MOC. The data also define a clear anomaly of neuroblastoma, indicating a preference for anaerobic conditions, and an adverse response to aerobic. An increase in CO(2), CO(2)/O(2) ratio, mitochondrial inhibition or O(2) deprivation was not directly toxic, but activated metabolism through glycolysis prompting depletion of glucose and starvation. In conclusion, the results of this study indicate that the mechanism of action for MPP+, involves the inhibition of complex I and and more specifically complex IV, leading to impaired OXPHOS and MOC. Moreover, flavin dervatives control the rate of complex I/cellular respiration and Co-Q10 augments complex II [corrected].

High doses of riboflavin and the elimination of dietary red meat promote the recovery of some motor functions in Parkinson's disease patients

Abnormal riboflavin status in the absence of a dietary deficiency was detected in 31 consecutive outpatients with Parkinson's disease (PD), while the classical determinants of homocysteine levels (B6, folic acid, and B12) were usually within normal limits. In contrast, only 3 of 10 consecutive outpatients with dementia without previous stroke had abnormal riboflavin status. The data for 12 patients who did not complete 6 months of therapy or did not comply with the proposed treatment paradigm were excluded from analysis. Nineteen PD patients (8 males and 11 females, mean age +/- SD = 66.2+/-8.6 years; 3, 3, 2, 5, and 6 patients in Hoehn and Yahr stages I to V) received riboflavin orally (30 mg every 8 h) plus their usual symptomatic medications and all red meat was eliminated from their diet. After 1 month the riboflavin status of the patients was normalized from 106.4+/-34.9 to 179.2+/-23 ng/ml (N = 9). Motor capacity was measured by a modification of the scoring system of Hoehn and Yahr, which reports motor capacity as percent. All 19 patients who completed 6 months of treatment showed improved motor capacity during the first three months and most reached a plateau while 5/19 continued to improve in the 3- to 6-month interval. Their average motor capacity increased from 44 to 71% after 6 months, increasing significantly every month compared with their own pretreatment status (P < 0.001, Wilcoxon signed rank test). Discontinuation of riboflavin for several days did not impair motor capacity and yellowish urine was the only side effect observed. The data show that the proposed treatment improves the clinical condition of PD patients. Riboflavin-sensitive mechanisms involved in PD may include glutathione depletion, cumulative mitochondrial DNA mutations, disturbed mitochondrial protein complexes, and abnormal iron metabolism. More studies are required to identify the mechanisms involved.

Profiling genes related to mitochondrial function in mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Since mitochondrial dysfunction plays an important role in the pathogenesis of dopaminergic neurodegeneration in Parkinson's disease, we determined the expression of genes related to mitochondrial function in the substantia nigra of mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) using a cDNA array. MPTP treatment significantly depleted striatal dopamine, but did not result in apparent neuronal loss in the substantia nigra at 3 and 18 days post-treatment. We also examined changes in genes in the hypothalamus, a region containing dopaminergic neurons that are relatively resistant to MPTP. Finally, we confirmed those genes identified by microarrays as differentially expressed in the substantia nigra but not in the hypothalamus using in situ hybridization. Our results demonstrated that MPTP significantly changed the expressions of six genes in nigral neurons, four of which were related to the mitochondrial electron transport chain: the NADH-ubiquinone oxidoreductase 13 kDa B subunit, the NADH-ubiquinone oxidoreductase MNLL subunit, cytochrome c, and the cytochrome c oxidase Va subunit. Two other differentially expressed genes were the dihydropyridine-sensitive L-type calcium channel alpha-2 subunit precursor and type III alpha-1 procollagen. None of these six genes are encoded by mitochondrial DNA. The potential significance of these gene alterations in the context of Parkinson's disease is discussed.

Isofurans, but not F2-isoprostanes, are increased in the substantia nigra of patients with Parkinson's disease and with dementia with Lewy body disease

F2-isoprostanes (F2-IsoPs) are well-established sensitive and specific markers of oxidative stress in vivo. Isofurans (IsoFs) are also products of lipid peroxidation, but in contrast to F2-IsoPs, their formation is favored when oxygen tension is increased in vitro or in vivo. Mitochondrial dysfunction in Parkinson's disease (PD) may not only lead to oxidative damage to brain tissue but also potentially result in increased intracellular oxygen tension, thereby influencing relative concentrations of F2-IsoPs and IsoFs. In this study, we attempted to compare the levels of F2-IsoPs and IsoFs esterified in phospholipids in the substantia nigra (SN) from patients with PD to those of age-matched controls as well as patients with other neurodegenerative diseases, including dementia with Lewy body disease (DLB), multiple system atrophy (MSA), and Alzheimer's disease (AD). The results demonstrated that IsoFs but not F2-IsoPs in the SN of patients with PD and DLB were significantly higher than those of controls. Levels of IsoFs and F2-IsoPs in the SN of patients with MSA and AD were indistinguishable from those of age-matched controls. This preferential increase in IsoFs in the SN of patients with PD or DLB not only indicates a unique mode of oxidant injury in these two diseases but also suggests different underlying mechanisms of dopaminergic neurodegeneration in PD and DLB from those of MSA.

Manganese ethylene-bis-dithiocarbamate and selective dopaminergic neurodegeneration in rat: a link through mitochondrial dysfunction

Manganese ethylene-bis-dithiocarbamate (Mn-EBDC) is the major active element of maneb, a pesticide linked to parkinsonism in certain individuals upon chronic exposure. Additionally, it has been shown to produce dopaminergic neurodegeneration in mice systemically coexposed to another pesticide, 1,1'-dimethyl-4,4'-bipyridinium (paraquat). Here, we described a rat model in which selective dopaminergic neurodegeneration was produced by delivering Mn-EBDC directly to the lateral ventricles. After establishing this model, we tested whether Mn-EBDC provoked dopamine efflux in the striatum, a well-known phenomenon produced by the mitochondrial inhibitor 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) that causes parkinsonism in humans, as well as in some animals. Finally, we investigated whether Mn-EBDC directly inhibited mitochondrial function in vitro using isolated brain mitochondria. Our data demonstrated that Mn-EBDC induced extensive striatal dopamine efflux that was comparable with that induced by MPP+, and that Mn-EBDC preferentially inhibited mitochondrial complex III. As mitochondrial dysfunction is pivotal in the pathogenesis of Parkinson's disease (PD), our results support the proposal that exposure to pesticides such as maneb, or other naturally occurring compounds that inhibit mitochondrial function, may contribute to PD development.

Mitochondrial DNA deletions/rearrangements in parkinson disease and related neurodegenerative disorders

Inhibition of mitochondrial respiratory chain function may contribute to dopaminergic neurodegeneration in the substantia nigra (SN) of patients with Parkinson disease (PD). Since large-scale structural changes (e.g. deletions and rearrangements in mitochondrial DNA [mtDNA]) have been associated with mitochondrial dysfunction, we tested the hypothesis that increased total mtDNA deletions/rearrangements are associated with neurodegeneration in PD. This study employed a well-established technique, long-extension polymerase chain reaction (LX-PCR), to detect the multiple mtDNA deletions/rearrangements in the SN of patients with PD, multiple system atrophy (MSA), dementia with Lewy bodies (DLB), Alzheimer disease (AD), and age-matched controls. We also compared the total mtDNA deletions/rearrangements in different brain regions of PD patients. The results demonstrated that both the number and variety of mtDNA deletions/rearrangements were selectively increased in the SN of PD patients compared to patients with other movement disorders as well as patients with AD and age-matched controls. In addition, increased mtDNA deletions/rearrangements were observed in other brain regions in PD patients, indicating that mitochondrial dysfunction is not just limited to the SN of PD patients. These data suggest that accumulation of total mtDNA deletions/rearrangements is a relatively specific characteristic of PD and may be one of the contributing factors leading to mitochondrial dysfunction and neurodegeneration in PD.

The mitochondrial common deletion in Parkinson's disease and related movement disorders

The mitochondrial 4977-bp common deletion has been reported in some studies to occur exclusively or with increased frequency in the midbrain of patients with Parkinson's disease (PD). Other studies could not confirm these results; rather, it was suggested that the mitochondrial common deletion is associated with aging in the midbrain and not PD. One possible explanation for these conflicting results is the difficulty in quantifying mitochondrial DNA deletions or mutations in the whole midbrain or substantia nigra (SN) while only a subset of midbrain neurons degenerate in PD. In addition, none of the studies has addressed the cell types with the common deletion within the midbrain. In this study we used in situ hybridization to detect the common deletion in sections of midbrain from patients with PD, multiple system atrophy-parkinsonian type (MSA-P), progressive supranuclear palsy (PSP), dementia with Lewy bodies (DLB), age-matched controls, and individuals of different ages. The results demonstrated that the mitochondrial common deletion accumulated primarily in neurons but not glia in both the SN and other midbrain regions. There was no significant difference in the number or distribution of neurons with the common deletion or the average of the mean densities (AMD) of staining with the common deletion in nigral neurons among patients with PD, MSA-P, PSP, DLB, or age-matched controls. In addition, there was no difference in the number or distribution of neurons with the common deletion in nigral neurons between any age group, although there was a tendency for the common deletion to increase in the non-nigral neurons in older patients. These data indicate that accumulation of the 4977-bp common deletion in mitochondrial DNA in midbrain occurred primarily in neurons, and by this cytological approach, it was not associated with nigral neurodegeneration in the common movement disorders or aging.

Gender ratio differences between Parkinson's disease patients and their affected relatives

Mitochondrial dysfunction in Parkinson's disease (PD) is suspected to arise from either acquired or inherited mutation of mitochondrial DNA (mtDNA). If inherited, epidemiologic analysis may reveal maternal transmission. We looked for maternal inheritance bias in our PD clinical database. About 13% of 600 PD probands reported an affected parent. Although 60% of the PD probands were male, only 42% of the affected parents were. The gender ratios for the proband and affected parent generations were dissimilar (p<0.005), indicating an underrepresentation of affected fathers or an overrepresentation of affected mothers. To address these possibilities we analyzed a non-PD control cohort. Four percent of the controls had a PD affected parent, and 75% of these affected parents were male. Apparent maternal inheritance bias in our PD cohort is therefore more likely due to overrepresentation of affected mothers, and is consistent with mitochondrial inheritance in some of our ascertained cases.

DNA damage in brain mitochondria caused by aging and MPTP treatment

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment leads to marked depletion of dopamine (DA) levels in the nigrostriatal pathway and dopaminergic neuronal degeneration in caudate-putamen and substantia nigra. MPTP is believed to inhibit complex I of the electron transport system leading to the generation of reactive oxygen species. We sought to test the hypotheses that MPTP treatment: (1) leads to dopamine depletion; (2) causes extensive mitochondrial DNA damage, and (3) that these effects would be age dependent. The levels of dopamine and its metabolites, DOPAC and HVA were analyzed by HPLC equipped with electrochemical detection. DNA damage was measured by quantitative PCR in both mitochondrial and nuclear (beta-polymerase) targets from the caudate-putamen, substantia nigra and cerebellum regions of control and MPTP-treated mice. The age groups studied were 22 days and 12 months. MPTP produced no significant effect on the levels of dopamine and its metabolites in young mice whereas in old, there was a significant decrease in this neurotransmitter system after MPTP administration. These 12-month-old mice, when compared to the young mice, showed a significant increase in mitochondrial DNA damage in the caudate-putamen and cerebellum. The latter region also displayed a significant increase in DNA damage in a nuclear gene. After treatment with MPTP, there was an age-dependent increase in DNA damage in mitochondria of the caudate-putamen while there was no significant DNA damage in the nuclear target. MPTP treatment led to damage in both mitochondrial and nuclear DNA of the substantia nigra, while there was no damage in either mitochondria or nucleus in cerebellum which was used as a negative control.

Increased caspase 3 and Bax immunoreactivity accompany nuclear GAPDH translocation and neuronal apoptosis in Parkinson's disease

In situ end labeling combined with YOYO staining was used to mark apoptotic DNA fragmentation and chromatin condensation respectively in human postmortem brain sections. Increased numbers of apoptotic neuronal nuclei were identified in the Parkinson's disease (PD) nigra compared with age-matched controls. Caspase 3 and Bax showed increased immunoreactivity in melanized neurons of the PD nigra compared with controls. Importantly, GAPDH nuclear accumulation was also observed in the PD nigra, suggesting apoptotic rather than necrotic cell death. Interestingly, both Lewy bodies and the intranuclear Marinesco's bodies were GAPDH immunoreactive in the PD brain.

Enhanced N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice deficient in CuZn-superoxide dismutase or glutathione peroxidase

Administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mammals causes damage to the nigrostriatal dopaminergic pathway similar to that observed in Parkinson disease (PD). Reactive oxygen species (ROS) are thought to be involved in the pathogenesis of MPTP-mediated dopaminergic neurodegeneration. To further clarify the role of superoxide anion radical (*O2-) and to study the possible involvement of hydroperoxides in MPTP-mediated neurodegeneration, MPTP neurotoxicity was induced in mice deficient in either CuZn superoxide dismutase (SOD), a scavenger enzyme for *O2-, or cellular glutathione peroxidase (GSHPx-1), a scavenger enzyme for hydroperoxides. Littermate control and homozygous deficient mice were injected intraperitoneally with a total cumulative dose of 0, 75, or 150 mg/kg of MPTP delivered over 5 d. All mice were killed 5 d after the last injection and the brains were processed for immunohistological analysis for tyrosine hydroxylase (TH) in the striatum and the substantia nigra pars compacta (SNc), as well as for direct measurements of dopamine concentrations in the striatum. The intensity of TH immunoreactivity in the striatum was evaluated by measuring the relative optical density (OD) with NIH IMAGE, and expressed as Log (OD of striatum)/Log (OD of white matter). Degeneration of TH-containing neurons was assessed by counting TH-positive neurons in the SNc. We found that this MPTP exposure protocol produced dose-dependent depletion of TH immunoreactivity and dopamine in the striatum in littermate control mice and both strains of knockout mice; however. reduction in TH immunoreactivity and dopamine content were significantly greater in CuZn-SOD or GSHPx-1 deficient mice compared with littermate controls. MPTP exposure did not significantly alter the number of TH-positive neurons in the SNc in littermate control or knockout mice. These data suggest that some of the deleterious effects of MPTP on striatal dopaminergic nerve terminals are mediated by both *O2- and hydroperoxides, and that they occur prior to dopaminergic neurodegeneration in the SNc. The similarity between the MPTP model and PD raises the possibility that both types of ROS may play a significant role in the early pathogenesis of dopaminergic neurodegeneration in PD.

Pathogenesis and preclinical course of Parkinson's disease

Idiopathic parkinsonism (IP) is defined by its classic symptomology, its responsiveness to therapies which elevate dopamine levels, and by the failure to identify a specific etiological factor. The progressive and irreversible degeneration of dopaminergic neurons projecting from the substantia nigra pars compacta (SNc) to the striatum and the presence of SNc Lewy bodies are regarded as the essential pathological bases of IP, but neither the initiator(s) nor the nature of the degeneration have been determined, nor its relationship with degenerative changes in other parts of the IP brain. This paper discusses the various hypotheses that have been proposed to explain these phenomena, arguing that IP be regarded as a multisystem disorder, both at the level of individual neurons and at the whole brain level. It is probable that IP is the result of a multifactorial process, and that a cascade of interacting and overlapping biochemical mechanisms determine the course of the disease.

Neurodegenerative disorders in humans: the role of glutathione in oxidative stress-mediated neuronal death

Oxidative stress has been implicated in both normal aging and in various neurodegenerative disorders and may be a common mechanism underlying various forms of cell death including necrosis, apoptosis, and excitotoxicity. In this review, we develop the hypothesis that oxidative stress-mediated neuronal loss may be initiated by a decline in the antioxidant molecule glutathione (GSH). GSH plays multiple roles in the nervous system including free radical scavenger, redox modulator of ionotropic receptor activity, and possible neurotransmitter. GSH depletion can enhance oxidative stress and may also increase the levels of excitotoxic molecules; both types of action can initiate cell death in distinct neuronal populations. Evidence for a role of oxidative stress and diminished GSH status is presented for Lou Gehrig's disease (ALS), Parkinson's disease, and Alzheimer's disease. Potential links to the Guamanian variant of these diseases (ALS-PD complex) are discussed. In context to the above, we provide a GSH-depletion model of neurodegenerative disorders, suggest experimental verifications of this model, and propose potential therapeutic approaches for preventing or halting these diseases.

Origin and functional consequences of the complex I defect in Parkinson's disease

The mitochondrial electron transport enzyme NADH:ubiquinone oxidoreductase (complex I), which is encoded by both mitochondrial DNA and nuclear DNA, is defective in multiple tissues in persons with Parkinson's disease (PD). The origin of this lesion and its role in the neurodegeneration of PD are unknown. To address these questions, we created an in vitro system in which the potential contributions of environmental toxins, complex I nuclear DNA mutations, and mitochondrial DNA mutations could be systematically analyzed. A clonal line of human neuroblastoma cells containing no mitochondrial DNA was repopulated with mitochondria derived from the platelets of PD or control subjects. After 5 to 6 weeks in culture, these cytoplasmic hybrid (cybrid) cell lines were assayed for electron transport chain activities, production of reactive oxygen species, and sensitivity to induction of apoptotic cell death by 1-methyl-4-phenyl pyridinium (MPP+). In PD cybrids we found a stable 20% decrement in complex I activity, increased oxygen radical production, and increased susceptibility to 1-methyl-4-phenyl pyridinium-induced programmed cell death. The complex I defect in PD appears to be genetic, arising from mitochondrial DNA, and may play an important role in the neurodegeneration of PD by fostering reactive oxygen species production and conferring increased neuronal susceptibility to mitochondrial toxins.

Regional distributions of hippocampal Na+,K(+)-ATPase, cytochrome oxidase, and total protein in temporal lobe epilepsy

Na+,K(+)-ATPase (the sodium pump) is a ubiquitous enzyme that consumes ATP to maintain an adequate neuronal transmembrane electrical potential necessary for brain function and to dissipate ionic transients. Reductions in sodium pump function augment the sensitivity of neurons to glutamate, increasing excitability and neuronal damage in vitro. Temporal lobe epilepsy (TLE) is one disease characterized by hyperexcitability and marked hippocampal neuronal losses that could depend in part, on impaired sodium pump capacity secondary to changes in sodium pump levels and/or insufficient ATP supply. To assess whether abnormalities in the sodium pump occur in this disease, we used [3H]ouabain to determine the density of Na+,K(+)-ATPase for each anatomic region of hippocampus by in vitro autoradiography. Tissues were surgically obtained from epileptic patients with hippocampal sclerosis and compared with specimens from patients with seizures originating from temporal lobe tumors and autopsy controls. Changes in cellular population arising from neuronal losses or gliosis were assessed by protein densities derived from quantitative computerized densitometry of Coomassie-stained tissue sections. We estimated regional differences in capacity for ATP generation by determining cytochrome c oxidase (CO) activity. Principal neurons of hippocampus exhibit high levels of sodium pump enzyme. Both epilepsy groups exhibited slight but significant increases in sodium pump density/unit mass of protein in the dentate molecular layer, CA2, and subiculum as compared with autopsy controls. Greater hilar sodium pump density was also observed in sclerotic hippocampi. In contrast, CO activity was reduced in both epilepsy types throughout hippocampus. Results suggest that although sodium pump protein in surviving neurons appears to be upregulated in epilepsy, sodium pump capacity may be limited by the reduced levels of CO activity. Functional reduction in sodium pump capacity may be an important factor in hyperexcitability and neuronal death.

Positron emission tomographic evidence for progression of human MPTP-induced dopaminergic lesions

Transient exposure to the toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces a syndrome resembling idiopathic parkinsonism (IP). While IP inevitably progresses, the long-term evolution of MPTP-parkinsonism is unknown. Fluorodopa positron emission tomography (FD-PET) is a reliable tool for assessing nigrostriatal dopaminergic function. We performed FD-PET and clinical assessments on two occasions, 7 years apart, on 10 human subjects exposed to MPTP (age at the first scan, 32.7 +/- 6.9 yr [mean +/- SD], and on 10 normal individuals (age, 53 +/- 16 yr). At the time of their first scan, 5 of the subjects exposed to MPTP were clinically normal and 5 had limited signs of parkinsonism; 5 had new clinical deficits 7 years later. In the subjects exposed to MPTP, the PET index [(striatal-occipital)/occipital ratio] dropped by 2.3% per year from 0.70 +/- 0.10 (mean +/- SD) to 0.58 +/- 0.10 (p < 0.001). This was significantly faster than normal aging (p < 0.01) and similar to the progression observed in IP (p = 0.06). The findings suggest that short-term exposure to MPTP leads to a protracted decline in nigrostriatal dopaminergic function more rapid than occurs in normal aging and similar to IP progression. This is the first evidence that transient exposure to a toxin can cause progressive nigral pathology. At present, the mechanism leading to this progression is unknown. Our findings support the hypothesis that some neurodegenerative disorders may result from transient exposure to an environmental agent.

Hereditary variations in monoamine oxidase as a risk factor for Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder caused by loss of dopaminergic neurons in the brainstem. Recent studies suggest that several genes may have a role in determining individual susceptibility to this disease, and the degradative enzyme monoamine oxidase (MAO) has been implicated in the disease process. Wide differences in activity levels for both forms of this enzyme (MAO-A and MAO-B) exist in the human population, and levels of both are genetically determined. Here we have compared the frequency of haplotypes at the MAOA and MAOB loci on the X chromosome in 91 male patients with PD and 129 male controls. Alleles were marked using two restriction fragment length polymorphisms (RFLPs), a (GT)n repeat in the MAOA locus, and a (GT)n repeat in the MAOB locus. One particular haplotype marked by the RFLP's at MAOA was three times more frequent in patients with PD as compared with controls, and the overall distribution of these alleles was significantly different (p = 0.03) between these two groups. Another MAOA haplotype was about threefold more common in controls than in patients with PD (p = 0.005). No associations were observed between individual MAOB alleles and the disease state, but the frequency distribution for all alleles was significantly different in the two populations (p = 0.046). These findings support the idea that the MAO genes may be among the hereditary factors that influence susceptibility of individuals to PD.

Mitochondrial biogenesis in striated muscle

Mitochondrial biogenesis (synthesis) has been observed to occur in skeletal muscle in response to chronic use. It also occurs in cardiac muscle during growth and hypertrophy, and it may be impaired during the aging process. This review summarizes the literature on the processes of mitochondrial biogenesis at the biochemical and molecular levels, with particular reference to striated muscles. Mitochondrial biogenesis involves the expression of nuclear and mitochondrial genes and the coordination of these two genomes, the synthesis of proteins and phospholipids and their import into the organelle, and the incorporation of these lipids and proteins into their appropriate locations within the matrix, inner or outer membranes. The emphasis is on the regulation of these events, with information derived in part from other cellular systems. Although descriptions of mitochondrial content changes in heart and skeletal muscle during altered physiological states are plentiful, much work is needed at the molecular level to investigate the regulatory processes involved. A knowledge of biochemical and molecular biology techniques is essential for continued progress in the field. This is a promising area, and potential new avenues for future research are suggested.

Evidence for mitochondrial dysfunction in Parkinson's disease--a critical appraisal

There is now considerable evidence to support a defect of the mitochondrial respiratory chain, and complex I in particular, in Parkinson's Disease (PD). However, the site specificity of the defect within the chain, its anatomical selectivity within the brain, and its presence in other tissues still remain controversial. Much of the present confusion surrounding the mitochondrial defect can be dispelled by careful analysis of the available data. The molecular basis of the deficiency and its relevance to the pathogenesis of PD remain unknown. Nevertheless, the complex I deficiency in PD provides a direct biochemical link between the idiopathic disease and the MPTP toxin model. The relationship between the mitochondrial defect and other abnormalities within the PD substantia nigra suggests that a self amplifying cycle of events might be precipitated either by a genetic or environmentally induced abnormality of mitochondrial function or free radical metabolism. Alternatively, a biochemical event separate from these might precipitate a cascade which terminates in complex I dysfunction and free radical formation. An understanding of the molecular basis of the complex I defect in PD and its relationship to other biochemical changes will provide important insight into the potential chain of events that lead to dopaminergic cell death in PD.

2-deoxyglucose enhances 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced ATP loss in the mouse brain

The effects of 2-deoxyglucose (2-DG), an inhibitor of the uptake and use of glucose, on ATP loss caused by the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were determined in the mouse brain. 2-DG alone had no effect on brain ATP levels, but when administered 30 min before MPTP exposure, 2-DG significantly enhanced MPTP-induced ATP reduction. This was reflected as an increase in ATP loss in the striatum (from 15 to 27%) as well as a significant decrease in ATP in the cerebellar cortex, an area of the brain that was not affected after exposure to MPTP alone. In mice pretreated with 2-DG, striatal ATP levels remained significantly decreased for > 8 h after MPTP administration. In contrast, ATP levels in the cerebellar cortex returned to normal values within 4 h from MPTP exposure. Mazindol, a catecholamine uptake blocker, completely protected against MPTP-induced loss of striatal ATP in the absence of 2-DG, but it only partially prevented striatal ATP decrease after administration of both 2-DG and MPTP; mazindol was also ineffective in protecting against ATP loss caused by 2-DG and MPTP in the cerebellar cortex. 2-DG/MPTP-induced ATP loss appeared to be associated with the presence of the 1-methyl-4-phenylpyridinium (MPP+) metabolite because (1) the pattern of ATP recovery in the striatum and cerebellar cortex appeared to reflect the pattern of MPP+ clearance from these areas of the brain (i.e., significant MPP+ levels persisted longer in the striatum than in the cerebellar cortex), and (2) ATP decrease was completely prevented by blocking the conversion of MPTP to MPP+ with the monoamine oxidase B inhibitor deprenyl.(ABSTRACT TRUNCATED AT 250 WORDS)

PCR analysis of platelet mtDNA: lack of specific changes in Parkinson's disease

An alteration within the mitochondrial DNA (mtDNA) has been hypothesized to underlie the deficiencies in mitochondrial complex I activity observed in the platelets, striatal muscle, and brain tissue of individuals with Parkinson's disease. Here we utilized the polymerase chain reaction (PCR) to analyze mtDNA obtained from the platelets of nonmedicated patients with early Parkinson's disease (n = 8) and aged-matched controls (n = 6) for the presence of deletion(s) or addition(s) equal to or greater than 50-100 base pairs. Initial attention was focused upon detecting a 4.977 kb deletion previously found in the brains of parkinsonian patients and some aged controls. Indeed, a large deletion of approximately 5.0 kb was observed in the platelet mtDNA from all parkinsonian individuals. However, this defect was also found in all age-matched controls as well as in a group of young healthy subjects (n = 5). In addition, we searched for the presence of smaller changes in platelet mtDNA from parkinsonian patients by PCR analysis of four mtDNA segments that code for seven of the complex I polypeptides. No large deletions or additions were detected within these four regions of mtDNA in any of the disease or age-matched control samples. We conclude that (a) a 4.977 kb deletion is apparently present in a subpopulation of platelet mtDNA from all individuals, and (b) no macrosequence alteration in mtDNA is likely to underlie the deficiency in complex I activity reported in platelet mitochondria from parkinsonian patients.

The genetics of Parkinson's disease

The possibility of a major contribution of hereditary factors to the cause of Parkinson's disease (PD) is being reconsidered by many. The studies preceding the 1980s presented conflicting evidence and suffered from procedural difficulties. The emergence of the MPTP hypothesis and the failure of three twin studies to document a strong hereditary component in the early 1980s turned attention toward an environmental cause of PD. However more recent descriptions of deficiencies in genetically-coded biochemical functions in PD, more sophisticated clinical family analyses, re-analysis and extension of the twin studies and the emergence of several large autopsy-proven PD kindreds raise the possibility of an important heritable factor in PD.

Mitochondrial poisons cause depletion of reduced glutathione in isolated hepatocytes

Antimycin A, KCN, and 1-methyl-4-phenylpyridinium ion (MPP+) all produced a marked depletion of cellular GSH levels in freshly isolated hepatocytes. This effect was consistently observed before the onset of cytotoxicity and seemed to be correlated with the loss of cellular ATP induced by these mitochondrial poisons. Concentrations of GSSG remained unchanged both intracellularly and extracellularly, indicating that oxidation was not involved in the events leading to GSH depletion. Approximately 40% of the decrease of intracellular GSH was accounted for by efflux of this tripeptide, assessed by increased formation of cysteinyl-glutathione when hepatocytes were incubated in the presence of 0.2 mM cystine. Therefore, an overall loss of glutathione was observed during incubations with all three inhibitors of mitochondrial function. Addition of 10 mM fructose to the incubation media substantially protected against GSH depletion caused by antimycin A, KCN, and MPP+. These results indicate that energy-dependent mechanisms are involved in the maintenance of intracellular GSH levels, and suggest that GSH depletion may be a general phenomenon associated with impairment of mitochondrial function.

Is Parkinson's disease a mitochondrial disorder?

Parkinson's disease (PD) is a common degenerative disease, but its etiology is still unknown. However, since the discovery of MPTP, many investigators have been interested in the mitochondrial function in PD. We investigated mitochondrial functions in PD patients using the methods which have successfully been applied to mitochondrial myopathies (MM), i.e. assay of lactate and pyruvate, measurement of muscle mitochondrial respiratory enzyme activities and Southern blot analysis of muscle mitochondrial DNA. Parkinson's disease patients did not differ from controls in the mean blood and CSF (cerebrospinal fluid) lactate and pyruvate levels at the basal resting state or during an aerobic exercise. But mitochondrial complex I activity of the skeletal muscle was significantly decreased in PD. In the Southern blot analysis, we could not find major deletions or insertions of mitochondrial DNA in PD. Our studies disclosed a differential mitochondrial impairment between PD and MM. We discuss the implication of our observation.

Glutathione in Parkinson's disease: a link between oxidative stress and mitochondrial damage?

Several links exist between the two mechanisms of neuronal degeneration (i.e., oxygen radical production and mitochondrial damage) proposed to have a role in Parkinson's disease. Indeed, mitochondria are critical targets for the toxic injury induced by oxygen radicals, and experimental evidence suggests that mitochondrial damage may cause an increased generation of oxygen radicals. A potentially important link between these two mechanisms of neurodegeneration is glutathione. Because of the scavenging activity of glutathione against accumulation of oxygen radicals, its decrease in the brains of parkinsonian patients has been interpreted as a sign of oxidative stress; however, this change may also result from or lead to mitochondrial damage. It is conceivable therefore that regardless of whether oxidative stress or mitochondrial damage represents the initial insult, these toxic mechanisms may both contribute to neuronal degeneration via changes in glutathione levels.