Evidence that the blockade of mitochondrial respiration by the neurotoxin 1-methyl-4-phenylpyridinium (MPP+) involves binding at the same site as the respiratory inhibitor, rotenone

Vesicular monoamine transporter (VMAT) regional expression and roles in pathological conditions

Vesicular monoamine transporters (VMATs) are key regulators of neurotransmitter release responsible for controlling numerous physiological, cognitive, emotional, and behavioral functions. They represent important therapeutic targets for numerous pathological conditions. There are two isoforms of VMAT transporter proteins that function as secondary active transporters into the vesicle for storage and release via exocytosis: VMAT1 (SLC18A1) and VMAT2 (SLC18A2) which differ in their function, quantity, and regional expression. VMAT2 has gained considerable interest as a therapeutic target and diagnostic marker. Inhibitors of VMAT2 have been used as an effective therapy for a range of pathological conditions. Additionally, the functionality and phenotypic classification of classical and nonclassical catecholaminergic neurons are identified by the presence of VMAT2 in catecholaminergic neurons. Dysregulation of VMAT2 is also implicated in many neuropsychiatric diseases. Despite the complex role of VMAT2, many aspects of its function remain unclear. Therefore, our aim is to expand our knowledge of the role of VMAT with a special focus on VMAT2 in different systems and cellular pathways which may potentially facilitate development of novel, more specific therapeutic targets. The current review provides a summary demonstrating the mechanism of action of VMAT, its functional role, and its contribution to disease progression and utilization as therapeutic targets.

Standardization and validation of novel ex-vivo method for mitochondrial bioenergetics using mitochondrial modulators

Mitochondria is an essential organelle; it produces 95% of the adenine triphosphate (ATP) of cells, their dysfunction is related to the pathogenesis of multiple diseases, such as diabetes mellitus, cardiovascular and neurological disorders. Various pharmacologic agents are known to target mitochondrial function. Moreover, the toxic side effects of multiple drugs used to treat diseases are related to the impairment of mitochondrial function. Thus, there is a need to develop a method to evaluate the effect of pharmacologic agents for their potential and side effects to identify effective mitochondrial-modulating agents. Therefore, the objective of this study was to develop and validate an ex-vivo method for studying the effect of pharmacologic agents on mitochondrial function and rescue of dysfunction. Dimethyl sulfoxide (DMSO) concentrations that drugs were soluble in and maintained mitochondrial function were determined. Metformin (MET) is a known mitochondrial complex-1 inhibitor tested for its ability to compromise mitochondrion function. Coenzyme Q10 (Q10) and Resveratrol (RSV), which are known to enhance mitochondrial function, were added alone and dose-dependent, tested for the ability to rescue metformin-induced mitochondrial dysfunction. Ex-vivo liver and brain mitochondrial function was assessed using an oxytherm Clark-type oxygen electrode. DMSO was found to be toxic above 10% and drugs insoluble below 5%. The addition of 0.5 mg/ml MET decreased liver and brain mitochondrial respiratory control rate (RCR). At the same time, Q10 improved RCR in normal mitochondria and a concentration-dependent manner in MET-induced dysfunctional mitochondria. RSV was added in the last step of the experiment to confirm that compromised function is due to MET. Hence this method can be used to screen pharmacological agents for their potential therapeutics or toxic effect on mitochondria.

Bacopa Protects against Neurotoxicity Induced by MPP+ and Methamphetamine

The neurotoxins methamphetamine (METH) and 1-methyl-4-phenylpyridinium (MPP⁺) damage catecholamine neurons. Although sharing the same mechanism to enter within these neurons, METH neurotoxicity mostly depends on oxidative species, while MPP⁺ toxicity depends on the inhibition of mitochondrial activity. This explains why only a few compounds protect against both neurotoxins. Identifying a final common pathway that is shared by these neurotoxins is key to prompting novel remedies for spontaneous neurodegeneration. In the present study we assessed whether natural extracts from Bacopa monnieri (BM) may provide a dual protection against METH- and MPP⁺-induced cell damage as measured by light and electron microscopy. The protection induced by BM against catecholamine cell death and degeneration was dose-dependently related to the suppression of reactive oxygen species (ROS) formation and mitochondrial alterations. These were measured by light and electron microscopy with MitoTracker Red and Green as well as by the ultrastructural morphometry of specific mitochondrial structures. In fact, BM suppresses the damage of mitochondrial crests and matrix dilution and increases the amount of healthy and total mitochondria. The present data provide evidence for a natural compound, which protects catecholamine cells independently by the type of experimental toxicity. This may be useful to counteract spontaneous degenerations of catecholamine cells.

The PINK1-Mediated Crosstalk between Neural Cells and the Underlying Link to Parkinson's Disease

Mitochondrial dysfunction has a fundamental role in the development of idiopathic and familiar forms of Parkinson's disease (PD). The nuclear-encoded mitochondrial kinase PINK1, linked to familial PD, is responsible for diverse mechanisms of mitochondrial quality control, ATP production, mitochondrial-mediated apoptosis and neuroinflammation. The main pathological hallmark of PD is the loss of dopaminergic neurons. However, novel discoveries have brought forward the concept that a disruption in overall brain homeostasis may be the underlying cause of this neurodegeneration disease. To sustain this, astrocytes and microglia cells lacking PINK1 have revealed increased neuroinflammation and deficits in physiological roles, such as decreased wound healing capacity and ATP production, which clearly indicate involvement of these cells in the physiopathology of PD. PINK1 executes vital functions within mitochondrial regulation that have a detrimental impact on the development and progression of PD. Hence, in this review, we aim to broaden the horizon of PINK1-mediated phenotypes occurring in neurons, astrocytes and microglia and, ultimately, highlight the importance of the crosstalk between these neural cells that is crucial for brain homeostasis.

Clathrin-Dependent Uptake of Paraquat into SH-SY5Y Cells and Its Internalization into Different Subcellular Compartments

The herbicide paraquat (PQ) is an exogenous toxin that allows the selective activation of dopaminergic neurons in the mesencephalon to induce injury and also causes its apoptosis in vitro. However, uptake mechanisms between PQ and neurons remain elusive. To address this issue, we undertook a study of PQ endocytosis in a dopaminergic SH-SY5Y cell line as well as explored the subsequent subcellular location and potential functional analysis of PQ. The PQ was found to bind the SH-SY5Y cell membrane and then became internalized via a clathrin-dependent pathway. PQ was internalized by many subcellular organelles in a time- and dose-dependent manner. Interestingly, the taken up PQ and secretogranin III (SCG3), which became dysregulated with PQ treatment that induced SH-SY5Y apoptosis in our previous study, colocalized in cytoplasmic vesicles. Taken together, our findings indicate that PQ is endocytosed by SH-SY5Y cells and that its multiple, subcellular localizations indicate PQ may potentially be involved in subcellular-level functions. More importantly, PQ distributing preferentially into SCG3-positive vesicles demonstrates its selective targeting which may affect SCG3 and cargoes carried by SCG3-positive vesicles. Therefore, it is reasonable to infer that PQ toxic insults may potentially interfere with neurotransmitter storage and transport associated with secretory granules.

Parkinson's Disease: The Mitochondria-Iron Link

Mitochondrial dysfunction, iron accumulation, and oxidative damage are conditions often found in damaged brain areas of Parkinson's disease. We propose that a causal link exists between these three events. Mitochondrial dysfunction results not only in increased reactive oxygen species production but also in decreased iron-sulfur cluster synthesis and unorthodox activation of Iron Regulatory Protein 1 (IRP1), a key regulator of cell iron homeostasis. In turn, IRP1 activation results in iron accumulation and hydroxyl radical-mediated damage. These three occurrences-mitochondrial dysfunction, iron accumulation, and oxidative damage-generate a positive feedback loop of increased iron accumulation and oxidative stress. Here, we review the evidence that points to a link between mitochondrial dysfunction and iron accumulation as early events in the development of sporadic and genetic cases of Parkinson's disease. Finally, an attempt is done to contextualize the possible relationship between mitochondria dysfunction and iron dyshomeostasis. Based on published evidence, we propose that iron chelation-by decreasing iron-associated oxidative damage and by inducing cell survival and cell-rescue pathways-is a viable therapy for retarding this cycle.

Primary cultured astrocytes from old rats are capable to activate the Nrf2 response against MPP+ toxicity after tBHQ pretreatment

Astrocytes are key players for brain physiology, protecting neurons by releasing antioxidant enzymes; however, they are also susceptible to damage by neurotoxins. Nuclear factor erythroid-derived 2-like 2 (Nrf2) is a central regulator of the antioxidant response, and therefore, pharmacologic inducers are often used to activate this transcription factor to induce cellular protection. To date, it still remains unknown if cells from aged animals are capable of developing this response. Therefore, the purpose of this work was to determine if cortical astrocytes derived from old rats are able to respond to tertbuthyl-hydroquinene (tBHQ) pretreatment and stimulate the Nrf2-antioxidant response pathway to induce an antioxidant strategy against MPP+ toxicity, one of the most used molecules to model Parkinson's disease. Our results show that, although astrocytes from adult and old rats were more susceptible to MPP+ toxicity than astrocytes from newborn rats, when pretreated with tertbuthyl-hydroquinene, they were able to transactivate Nrf2, increasing antioxidant enzymes and developing cellular protection. These results are discussed in terms of the doses used to create protective responses.

The function of α-synuclein

Human genetics has indicated a causal role for the protein α-synuclein in the pathogenesis of familial Parkinson's disease (PD), and the aggregation of synuclein in essentially all patients with PD suggests a central role for this protein in the sporadic disorder. Indeed, the accumulation of misfolded α-synuclein now defines multiple forms of neural degeneration. Like many of the proteins that accumulate in other neurodegenerative disorders, however, the normal function of synuclein remains poorly understood. In this article, we review the role of synuclein at the nerve terminal and in membrane remodeling. We also consider the prion-like propagation of misfolded synuclein as a mechanism for the spread of degeneration through the neuraxis.

MPP(+) and glutamate in the degeneration of nigral dopaminergic neurons

Glutamate neurotoxicity can be an experimental oxidative stress, and we investigated glutamate toxicity against cultured rat mesencephalic neurons. Although glutamate showed similar toxicity against dopaminergic and nondopaminergic neurons, nitric oxide (NO) showed neurotoxicity restricted exclusively in nondopaminergic neurons. An inhibitor of NO synthase had no significant effect on the glutamate toxicity against dopaminergic neurons, however, it had a significant antagonistic effect on that against nondopaminergic neurons. These findings indicate the presence of two mechanisms of glutamate neurotoxicity, one being not mediated by NO, found in dopaminergic neurons, and the other being mediated via NO, found in nondopaminergic neurons. In contrast to NO, peroxynitrite (ONOO(-)), an active metabolite of NO, caused significant cytotoxicity against dopaminergic and nondopaminergic neurons, suggesting that conversion of NO to ONOO(-) is suppressed in dopaminergic neurons. After pretreatment with small doses of methyl-4-phenylpyridium ion (MPP(+)), NO caused significant cytotoxicity against dopaminergic neurons, and glutamate toxicity was enhanced only against dopaminergic neurons. Therefore, sublethal dose of MPP(+) enhances glutamate toxicity against dopaminergic neurons, probably by the facilitation of suppressed NO conversion to ONOO(-) in dopaminergic neurons. Finally, to provide basic data for neuroprotective therapy in Parkinson's disease, we investigated neuroprotection against glutamate toxicity by dopamine agonists. Preincubation with the D2 type dopamine agonists provides neuroprotection against glutamate neurotoxicity and the protective effects blocked by a D2 antagonist, indicating that D2 agonists provide protection mediated not only by the inhibition of dopamine turnover, but also via D2 type dopamine receptor.

Impact of exercise on mitochondrial transcription factor expression and damage in the striatum of a chronic mouse model of Parkinson's disease

The etiology of neurodegenerative disorders like Parkinson's disease remains unknown, although many genetic and environmental factors are suggested as likely causes. Neuronal oxidative stress and mitochondrial dysfunction have been implicated as possible triggers for the onset and progression of Parkinson's neurodegeneration. We have recently shown that long-term treadmill exercise prevented neurological, mitochondrial and locomotor deficits in a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid-induced mouse model of Parkinson's disease that was originally established in our laboratory. In the present study, we further demonstrated that long-term exercise attenuated both cytochrome c release and elevated levels of p53, which are known to be associated with mitochondrial dysfunction in the striatum of this chronic model. On the other hand, the expressions of mitochondrial transcription factor A and peroxisome proliferator-activated receptor gamma coactivator 1α were unexpectedly upregulated in the striatum of this chronic model, but long-term exercise training brought their levels down closer to normal. Our findings suggest that maintaining normal mitochondrial function is essential for preventing the process of Parkinson's disease-like neurodegeneration, whereas stimulating the mitochondrial transcription factors for biogenesis is not obligatory.

Calpain inhibition protected spinal cord motoneurons against 1-methyl-4-phenylpyridinium ion and rotenone

Parkinson's disease (PD), characterized by selective midbrain nigrostriatal dopaminergic degeneration, is consistently associated with moderate systemic mitochondrial dysfunction. Downstream degeneration of spinal cord has also been suggested in PD, although the mechanisms have not been much investigated. In the present study, two mitochondrial toxicants, 1-methyl-4-phenylpyridinium ion (MPP(+)) and rotenone were tested in ventral spinal cord (VSC 4.1) motoneuronal cells. Cell death was assessed by morphological and biochemical means to discern a lower apoptosis-inducing concentration and lethal concentration of 50% cell death (LC(50)), which were subsequently compared in further cytoprotection experiments. Mitochondrial toxicants dose-dependently induced increase in intracellular free Ca(2+) level, which was conducive for increased expression and activities of Ca(2+)-activated neutral protease calpain and downstream caspase-3. Thus, mitochondrial damage triggered apoptotic mechanisms in spinal cord motoneurons. Inhibition of calpain by calpeptin significantly attenuated damaging effects of MPP(+) and rotenone on motoneurons, especially at low apoptosis-inducing concentrations of toxicants and partly at their LC(50), as demonstrated by absence of DNA ladder formation and decrease in terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells. Cytoprotection by calpeptin was observed with marked decreases in Bax: Bcl-2 ratio and activities of calpain and caspase-3, which affirmed the role of mitochondrial dysfunction and involvement of intrinsic pathway in mediation of apoptosis. These findings strongly suggested that parkinsonian toxicants MPP(+) and rotenone at low doses induced cascade of cell-damaging effects in spinal cord motoneurons, thus, highlighting the possibility of induction of apoptotic mechanisms in these cells, when subjected to mitochondrial stress. Cytoprotection rendered by calpeptin further validated the involvement of calpain in apoptosis and suggested calpain inhibition as a potential neuroprotective strategy.

Current concepts in drug-induced mitochondrial toxicity

Mitochondria generate most of the cell's ATP and play key roles in fatty acid oxidation, steroid synthesis, heme synthesis, thermogenesis, calcium homeostasis, and apoptosis. With the development of new methods to study mitochondrial function, it is becoming clear that drug-induced mitochondrial dysfunction is one of the causes of drug toxicity. Mitochondria can be impaired by drugs in a variety of ways. These include inhibition of oxidative phosphorylation, uncoupling of electron transport from ATP synthesis, irreversible opening of the mitochondrial permeability transition pore, inhibition of transporters within the mitochondrial inner membrane, increased oxidative stress, inhibition of the citric acid cycle, inhibition of fatty acid oxidation, and impairment of either mtDNA replication or mtDNA-encoded protein synthesis. This unit provides an overview on the physiological roles of mitochondria and the mechanisms by which they can be adversely affected by drugs.

Protective effects of heme oxygenase-1 against MPP(+)-induced cytotoxicity in PC-12 cells

Heme oxygenase-1 (HO-1) catalyses the rate-limiting step of heme degradation to biliverdin, which is in turn reduced to bilirubin, CO and free iron. HO-1 can be induced by several harmful stimuli including oxidative stress, and it has a protective role against the cytotoxicity in different cells. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridinium (MPP(+)) is a neurotoxic substance that induces the degeneration of dopaminergic neurons. This study examined whether HO-1 can be induced by MPP(+) and whether HO-1 has a protective role against the MPP(+)-induced cytotoxicity in PC-12 cells. MPP(+) triggered a relatively rapid induction of HO-1. The MPP(+)-induced cytotoxicity and reactive oxygen species (ROS) production markedly increased by HO-1 inhibitor, zinc protoporphyrin-IX (ZnPP-IX). The increase of ROS production by ZnPP-IX was completely abrogated by either two products of HO (biliverdin or bilirubin) while the increase of cytotoxicity by ZnPP-IX was attenuated partially. These suggest that HO-1 expression might have some cytoprotective effect against MPP(+)-induced cytotoxicity.

Gene and protein signatures in sporadic Parkinson's disease and a novel genetic model of PD

High-throughput gene-based platform studies in human post-mortem substantia nigra from sporadic Parkinson's disease (PD) cases have revealed significant dysregulation of genes involved in biological processes linked to previously established neurodegenerative mechanisms both in sporadic and hereditary PD. These include protein aggregation, mitochondrial dysfunction, oxidative stress, cell cycle, vesicle trafficking, synaptic transmission, dopamine metabolism and cell adhesion/cytoskeleton maintenance. These observations have extended our current view on the molecular pathways underlying the etio-pathology of the disease and provided a basis for the development of a novel genetic model of sporadic PD, centered on gradual silencing/over-expression of the candidate genes. The uncovered signatures may serve as future predictive biomarkers for early PD diagnosis, disease progression and drug development.

A mitochondrial etiology of neurodegenerative diseases: evidence from Parkinson's disease

Evidence continues to accrue implicating mitochondrial dysfunction in the etiology of a number of neurodegenerative diseases. For example, Parkinson's disease (PD) can be induced by mitochondrial toxins, and nuclear DNA (nDNA) loci linked to PD have been associated with mitochondrial dysfunction. Although conclusions about the role of mitochondrial DNA (mtDNA) variants in PD vary, we argue here that this is attributable to the novel genetics of the mtDNA and the fact that clinically relevant mtDNA variation encompasses ancient adaptive polymorphisms, recent deleterious mutations, and somatic mutations. An mtDNA association with PD is supported by an analysis of the Russian Tatar population which revealed that polymorphisms associated with haplogroup H mtDNAs increased PD risk (odds ratio [OR]= 2.58, P= 0.0001), whereas those associated with haplogroup UK cluster mtDNAs were protective (OR = 0.38, P= 0.003). Moreover, mtDNA sequencing revealed that PD patients with either haplogroup H or UK cluster mtDNAs can harbor additional recent variants that might further modulate PD risk. Therefore, the complexity of PD genetics may reflect the complex mitochondrial genetics.

Distinct mechanisms of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine resistance revealed by transcriptome mapping in mouse striatum

The etiology of idiopathic Parkinson's disease is thought to involve interplay between environmental factors and predisposing genetic traits, although the identification of genetic risk factors remain elusive. The neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) produces parkinsonian-like symptoms and pathology in mice and humans. As sensitivity to MPTP is genetically determined in mice this provides an opportunity to identify genes and biological mechanisms that modify the response to an exogenous agent that produces a Parkinson's disease-like condition. MPTP primarily targets dopaminergic nerve terminals in the striatum and elicits changes in striatal gene expression. Therefore, we used Affymetrix and qRT-PCR technology to characterize temporal mRNA changes in striatum in response to MPTP in genetically MPTP-sensitive, C57BL/6J, and MPTP-resistant Swiss Webster and BCL2-associated X protein (Bax)-/- mice. We identified three phases of mRNA expression changes composed of largely distinct gene sets. An early response (5 h) occurred in all strains of mice and multiple brain regions. In contrast, intermediate (24 h) and late (72 h) phases were striatum specific and much reduced in Swiss Webster, indicating these genes contribute and/or are responsive to MPTP-induced pathology. However, Bax-/- mice have robust intermediate responses. We propose a model in which the acute entry of MPP+ into dopaminergic nerve terminals damages them but is insufficient per se to kill the neurons. Rather, we suggest that the compromised nerve terminals elicit longer lasting transcriptional responses in surrounding cells involving production of molecules that feedback on the terminals to cause additional damage that results in cell death. In Swiss Webster, resistance lies upstream in the cascade of events triggered by MPTP and uncouples the acute events elicited by MPTP from the damaging secondary responses. In contrast, in Bax-/- mice resistance lies downstream in the cascade and suggests enhanced tolerance to the secondary insult rather than its attenuation.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

The role of mitochondria in pharmacotoxicology: a reevaluation of an old, newly emerging topic

In addition to their well-known critical role in energy metabolism, mitochondria are now recognized as the location where various catabolic and anabolic processes, calcium fluxes, various oxygen-nitrogen reactive species, and other signal transduction pathways interact to maintain cell homeostasis and to mediate cellular responses to different stimuli. It is important to consider how pharmacological agents affect mitochondrial biochemistry, not only because of toxicological concerns but also because of potential therapeutic applications. Several potential targets could be envisaged at the mitochondrial level that may underlie the toxic effects of some drugs. Recently, antiviral nucleoside analogs have displayed mitochondrial toxicity through the inhibition of DNA polymerase-γ (pol-γ). Other drugs that target different components of mitochondrial channels can disrupt ion homeostasis or interfere with the mitochondrial permeability transition pore. Many known inhibitors of the mitochondrial electron transfer chain act by interfering with one or more of the respiratory chain complexes. Nonsteroidal anti-inflammatory drugs (NSAIDs), for example, may behave as oxidative phosphorylation uncouplers. The mitochondrial toxicity of other drugs seems to depend on free radical production, although the mechanisms have not yet been clarified. Meanwhile, drugs targeting mitochondria have been used to treat mitochondrial dysfunctions. Importantly, drugs that target the mitochondria of cancer cells have been developed recently; such drugs can trigger apoptosis or necrosis of the cancer cells. Thus the aim of this review is to highlight the role of mitochondria in pharmacotoxicology, and to describe whenever possible the main molecular mechanisms underlying unwanted and/or therapeutic effects.

Paraquat neurotoxicity is distinct from that of MPTP and rotenone

Paraquat, MPTP, and rotenone reproduce features of Parkinson's disease (PD) in experimental animals. The exact mechanisms by which these compounds damage the dopamine system are not firmly established, but selective damage to dopamine neurons and inhibition of complex I are thought to be involved. We and others have previously documented that the toxic metabolite of MPTP, MPP+, is transported into dopamine neurons through the dopamine transporter (DAT), while rotenone is not transported by DAT. We have also demonstrated the requirement for complex I inhibition and oxidative damage in the dopaminergic neurodegeneration produced by rotenone. Based on structural similarity to MPP+, it has been proposed that paraquat exerts selective dopaminergic toxicity through transport by the DAT and subsequent inhibition of mitochondrial complex I. In this study we report that paraquat is neither a substrate nor inhibitor of DAT. We also demonstrate that in vivo exposure to MPTP and rotenone, but not paraquat, inhibits binding of 3H-dihydrorotenone to complex I in brain mitochondria. Rotenone and MPP+ were both effective inhibitors of complex I activity in isolated brain mitochondria, while paraquat exhibited weak inhibitory effects only at millimolar concentrations. These data indicate that, despite the apparent structural similarity to MPP+, paraquat exerts its deleterious effects on dopamine neurons in a manner that is unique from rotenone and MPTP.

Acute mitochondrial and chronic toxicological effects of 1-methyl-4-phenylpyridinium in human neuroblastoma cells

At low micromolar concentrations, 1-methyl-4-phenylpyridinium (MPP+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) selectively kills nigrostriatal dopaminergic neurons by mechanisms believed to involve impairment of mitochondrial complex I. A human neuroblastoma cell line expressing the dopamine transporter (DAT) was utilized to examine the effects of MPP+ on acute physiologic responses and subsequent cell death. Acute responses were measured by microphysiometry and by monitoring mitochondrial membrane potential with [3H]tetraphenylphosphonium (TPP+) uptake. MPP+ (10 microM) increased extracellular proton excretion in DAT-expressing cells within 2-3 min, but had no effect in untransfected cells. The lipophilic complex I inhibitor, rotenone, increased proton excretion in both cell lines. In DAT-expressing cells, mitochondrial membrane potential was reduced within I h of 10 microM MPP+ exposure. Rotenone reduced mitochondrial membrane potential in both cell lines. MPP+ caused apoptotic death of DAT-transfected cells 2-3 days after drug application, but did not kill untransfected cells. Thus, MPP+ produces immediate mitochondrial impairment only in cells that express DAT, and these changes occur days before overt cellular toxicity. The magnitude, time course and nature of these changes were similar to those produced by rotenone, confirming the site of action of MPP+ as mitochondrial complex I. These immediate mitochondrial effects appear to be an accurate predictor of subsequent cell death.

1-Methyl-4-phenylpyridinium ion, a toxin that can cause parkinsonism, alters branched structures of DNA

During replication, human mitochondrial DNA (mtDNA) takes on a triple-stranded structure known as a D-loop, which is implicated in replication and transcription. 1-Methyl-4-phenylpyridinium ion (MPP+), a toxin inducing parkinsonism, inhibits mtDNA replication, possibly by resolving the D-loops. For initiation of mtDNA replication, mitochondria are thought to have another triple-stranded structure, an R-loop. The R-loop, which is resolved by a bacterial junction-specific helicase, RecG, is also resolved by MPP+. Because mitochondrial D-loops are likewise resolved by RecG, the D- and R-loops may share a similar branched structure. MPP+ resolves cruciform DNA in supercoiled DNA. MPP+ converts a stacked conformation to an extended conformation in a synthetic Holliday junction. This conversion is reversed by 1 mM Mg(2+), as is the resolution of the D-loops or cruciform DNA. These observations suggest that the junction structure of mitochondrial D- and R-loops is affected by MPP+.

The parkinsonism-inducing drug 1-methyl-4-phenylpyridinium triggers intracellular dopamine oxidation. A novel mechanism of toxicity

Uptake of the Parkinsonism-inducing toxin, 1-methyl-4-phenylpyridinium (MPP(+)), into dopaminergic terminals is thought to block Complex I activity leading to ATP loss and overproduction of reactive oxygen species (ROS). The present study indicates that MPP(+)-induced ROS formation is not mitochondrial in origin but results from intracellular dopamine (DA) oxidation. Although a mean lethal dose of MPP(+) led to ROS production in identified dopaminergic neurons, toxic doses of the Complex I inhibitor rotenone did not. Concurrent with ROS formation, MPP(+) redistributed vesicular DA to the cytoplasm prior to its extrusion from the cell by reverse transport via the DA transporter. MPP(+)-induced DA redistribution was also associated with cell death. Depleting cells of newly synthesized and/or stored DA significantly attenuated both superoxide production and cell death, whereas enhancing intracellular DA content exacerbated dopaminergic sensitivity to MPP(+). Lastly, depleting cells of DA in the presence of succinate completely abolished MPP(+)-induced cell death. Thus, MPP(+) neurotoxicity is a multi-component process involving both mitochondrial dysfunction and ROS generated by vesicular DA displacement. These results suggest that in the presence of a Complex I defect, misregulation of DA storage could lead to the loss of nigrostriatal neurons in Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced complex I inhibition is reversed by disulfide reductant, dithiothreitol in mouse brain

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes dopaminergic cell loss in mice by inhibiting mitochondrial complex-I through its metabolite, MPP+, which binds to specific sites on complex-I. Since complex-I is highly vulnerable to oxidative stress, we have examined the nature of inhibition of complex-I by MPTP. Both MPTP and MPP+ inhibited complex-I activity, in vitro, in mouse brain slices, which was abolished by prior exposure of brain slices to glutathione. Further, the inhibited complex-I activity rebounded after incubation with disulfide reductant, dithiothreitol. Systemic administration of MPTP to mice resulted in inhibition of complex-I in striatum and midbrain which was also reversed by treatment of mitochondria with dithiothreitol. Inhibition of complex I activity by MPTP may be due to oxidation of thiol group(s) in complex-I, which may be reversed by thiol antioxidants.

MPP(+)-induced mitochondrial dysfunction is potentiated by dopamine

MPP(+), the major metabolite of the Parkinsonism-inducing compound MPTP, responsible for the destruction of the nigrostriatal pathway in primates and rodents, has been assayed in isolated rat liver mitochondria in the presence of physiological concentrations of dopamine or analogous concentrations of melanin-dopamine. 5 microM MPP(+) in the presence of 70 microM dopamine or melanin-dopamine, but not alone, decreased the heat production and oxygen consumption of a mitochondrial suspension activated with succinate and ADP. Both dopamine and oxidized dopamine plus MPP(+) also decreased the mitochondrial reductive power measured with MTT. Mitochondrial swelling was observed, associated with an increase in membrane mitochondrial potential, as a synergistic effect between low concentrations of MPP(+) and dopamine. It is suggested that cytosolic dopamine, by itself or via its autooxidation products, may play a relevant role in the mitochondrial toxicity of MPP(+). A failure in the regulation of the storage/release of dopamine could aggravate a mitochondrial damage and trigger the neurodegenerative process underlying MPTP toxicity and Parkinson's disease.

The D-loop structure of human mtDNA is destabilized directly by 1-methyl-4-phenylpyridinium ion (MPP+), a parkinsonism-causing toxin

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine has been reported to cause parkinsonism via its neurotoxic form, 1-methyl-4-phenylpyridinium ion (MPP+), which inhibits complex I of the mitochondrial respiratory chain. Its parkinsonism-causing mechanisms attract a great deal of interest as a model of the disease. Recently, we reported that MPP+ strongly decreases the amount of mtDNA independent of the inhibition of complex I. Maintenance of a proper amount of mtDNA is essential for the normal function of mitochondria as exemplified in many mitochondrial diseases. The most characteristic feature in vertebral mtDNA replication is that H-strand synthesis proceeds displacing the parental H-strand as a long single strand. It forms the D-loop, a triplex replication intermediate composed of the parental L-strand, nascent H-strand and displaced H-strand. Here we show that MPP+ does not inhibit DNA synthesis by DNA polymerase gamma, but rather releases the nascent H-strands from mtDNA both in organello and in vitro. This indicates that MPP+ directly destabilizes the D-loop structure, thereby inhibiting replication. This study raises a new mechanism, i.e. destabilization of replication intermediates, for depletion of mtDNA.

Acute and reversible parkinsonism due to organophosphate pesticide intoxication: five cases

OBJECTIVE

To describe five patients who developed acute and reversible parkinsonism following organophosphate (OP) pesticide exposure, and to consider whether this syndrome represents a rare sequela of such exposure in genetically susceptible individuals.

BACKGROUND

Several toxins are known to produce parkinsonism following acute exposure. Although case-control studies have implicated OP pesticides in the etiology of PD, acute parkinsonism following brief pesticide exposure has never been reported.

METHODS

The authors describe the clinical syndrome affecting five patients who presented with recent OP exposure and symptoms of an acute akinetic-rigid syndrome.

RESULTS

All patients developed parkinsonism that resembled PD clinically except for poor response to levodopa. Three genetically related patients were exposed to pesticides in a common environment before onset of parkinsonism; other family members remained unaffected. Other secondary causes of parkinsonism were excluded. Four patients recovered completely without treatment, and one patient was lost to follow-up. One patient experienced repeated episodes of parkinsonism with inadvertent reexposure to a pesticide-contaminated environment.

CONCLUSION

The clinical course of these five patients suggests their syndrome represents a heretofore undescribed toxic effect of OP pesticides. Our observations strengthen epidemiologic studies implicating OP pesticides in the etiology of PD. A genetic susceptibility to OP pesticide-induced parkinsonism may account for three family members developing this syndrome.

Neuroprotection and neuronal differentiation studies using substantia nigra dopaminergic cells derived from transgenic mouse embryos

The major pathological lesion of Parkinson's disease (PD) is the selective cell death of dopaminergic (DA) neurons in substantia nigra (SN). Although the initial cause and subsequent molecular signaling mechanisms leading to DA cell death underlying the PD process remain elusive, brain-derived neurotrophic factor (BDNF) is thought to exert neuroprotective as well as neurotrophic roles for the survival and differentiation of DA neurons in SN. Addressing molecular mechanisms of BDNF action in both primary embryonic mesencephalic cultures and in vivo animal models has been technically difficult because DA neurons in SN are relatively rare and present with many heterogeneous cell populations in midbrain. We have developed and characterized a DA neuronal cell line of embryonic SN origin that is more accessible to molecular analysis and can be used as an in vitro model system for studying SN DA neurons. A clonal SN DA neuronal progenitor cell line SN4741, arrested at an early DA developmental stage, was established from transgenic mouse embryos containing the targeted expression of the thermolabile SV40Tag in SN DA neurons. The phenotypic and morphological differentiation of the SN4741 cells could be manipulated by environmental cues in vitro. Exogenous BDNF treatment produced significant neuroprotection against 1-methyl-4-phenylpyridinium, glutamate, and nitric oxide-induced neurotoxicity in the SN4741 cells. Simultaneous phosphorylation of receptor tyrosine kinase B accompanied the neuroprotection. This SN DA neuronal cell line provides a unique model system to circumvent the limitations associated with primary mesencephalic cultures for the elucidation of molecular mechanisms of BDNF action on DA neurons of the SN.

1-Methyl-4-phenylpyridinium ion (MPP+) selectively inhibits the replication of mitochondrial DNA

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine is known to cause Parkinsonism in its neurotoxic form, 1-methyl-4-phenylpyridinium ion (MPP+). We have previously reported that MPP+ decreases the content of mitochondrial DNA (mtDNA) independently of the inhibition of complex I in human cells [Miyako, K., Kai, Y., Irie, T., Takeshige, K., and Kang, D. (1997) J. Biol. Chem. 272, 9605-9608]. Here we study the mechanism causing the decrease in mtDNA. MPP+ inhibits the incorporation of 5-bromo-2'-deoxyuridine into mtDNA but not into nuclear DNA, indicating that MPP+ inhibits the replication of mtDNA but not that of the nuclear genome. The replication of mtDNA is initiated by the synthesis of the heavy strand switched from the transcription of the light strand. MPP+ decreases the nascent heavy strands per mtDNA and increases the transcript of the ND6 gene, encoded on light strand, per mtDNA. The amount of mitochondrial transcription factor A is not decreased. These data suggest that the transcription is not inhibited and therefore the transition from transcription to replication of mtDNA is lowered in the MPP+-treated cells. Electron microscopy shows that the number of mitochondria is not decreased in the MPP+-treated cells, suggesting that MPP+ does not affect the overall biogenesis of mitochondria. Thus, MPP+ selectively inhibits the replication of mtDNA.

Inhibitors of NADH-ubiquinone reductase: an overview

This article provides an updated overview of the plethora of complex I inhibitors. The inhibitors are presented within the broad categories of natural and commercial compounds and their potency is related to that of rotenone, the classical inhibitor of complex I. Among commercial products, particular attention is dedicated to inhibitors of pharmacological or toxicological relevance. The compounds that inhibit the NADH-ubiquinone reductase activity of complex I are classified according to three fundamental types of action on the basis of available evidence and recent insights: type A are antagonists of the ubiquinone substrate, type B displace the ubisemiquinone intermediate, and type C are antagonists of the ubiquinol product.

Nitric oxide donors protect cultured rat astrocytes from 1-methyl-4-phenylpyridinium-induced toxicity

MPP+ is thought to mediate MPTP's toxicity on dopamine neurons by inhibiting mitochondrial respiration. However, astrocytic injuries are also observed in MPTP/MPP+-treated rats. Because nitric oxide (NO.) is suggested to be cytoprotective, we examined the effects of nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) on MPP+-induced toxicity in astrocytes. Incubation of astrocytes with MPP+ for 2 days produced a dose-dependent toxicity, including increase in lactate level and lipid peroxidation, decrease of metabolic activity and cell damage. SNP, SNAP, and SIN-1 all attenuated MPP+-induced toxicity. The same protection was not achieved with N-acetylpenicillamine or ferrocyanide, structural analogues of SNAP or SNP but devoid of NO.. Further, the effect was not attributed to the increased cGMP levels or blockade of MPP+ accumulation in astrocytes. Notably, catalase, dimethyl sulfoxide and ferricyanide, an extracellular electron acceptor, were also effective in inhibiting MPP+ damage. NO. donors and analogues were also tested against damage produced by rotenone, an irreversible complex I inhibitor. Only ferricyanide and SNP effectively protected rotenone's toxicity. These results concluded that (1) NO. may protect astrocytes from MPP+-induced free radical formation, and (2) prevention of energy depletion/free radicals production alleviate MPP+-induced toxicity.

Quantitative study of mitochondrial complex I in platelets of parkinsonian patients

Activity of mitochondrial enzyme complex I (NADH-ubiquinone oxidoreductase) is reduced in the substantia nigra of patients with Parkinson's disease (PD). A less pronounced decrease in the activity of this enzyme has also been reported in platelets of PD patients. To obtain quantitative information on platelet complex I in PD, we studied platelet complex I in 16 PD patients and 16 age-matched controls by using a newly developed technique based on the binding of [3H]dihydrorotenone ([3H]DHR), an analog of the pesticide rotenone, to complex I. We also investigated the inhibitory effect of MPP+ (1-methyl-4-phenyl-pyridinium) on [3H]DHR specific binding to platelet complex I. PD patients and controls showed similar levels of [3H]DHR specific binding; preincubation of platelets with MPP+ caused the same degree of inhibition of [3H]DHR specific binding in the two groups. In PD patients, we observed a direct correlation between MPP+-induced inhibition of [3H]DHR specific binding and the daily intake of levodopa, which may be related to drug-induced changes in the transport of MPP+ into the platelet or in its binding to complex I. These findings demonstrate that the reported reduction in complex I activity in platelets of PD patients can not be accounted for by an abnormality at the level of the rotenone binding site (putatively the ND-1 gene product), although they do not exclude differences in complex I activity between PD patients and controls.

Methylphenylpyridium ion (MPP+) enhances glutamate-induced cytotoxicity against dopaminergic neurons in cultured rat mesencephalon

Parkinson's disease is characterized by chronic progression of dopaminergic neuronal death, the mechanism of which is still unknown. Although methyl-4-phenylpyridium ion (MPP+) or MPP(+)-like substance, that can reduce mitochondrial complex I activity, is supposed to be a causative agent for Parkinson's disease, it is difficult to explain the chronic neuronal degeneration for years. It is important to identify other putative agents capable of causing chronic cell death besides MPP+. We hypothesized that treatment with small doses of MPP+, not causing severe damage to dopaminergic neurons but merely reducing the activity of mitochondrial complex I, can be a model of Parkinson's disease, and that glutamate can be a putative agent causing chronic neuronal degeneration. Using primary culture of the rat mesencephalon, we investigated glutamate-induced cytotoxicity against dopaminergic and non-dopaminergic neurons with or without the pretreatment with MPP+. Brief exposure to glutamate showed similar cytotoxicity against both dopaminergic and non-dopaminergic neurons. An N-methyl-D-aspartate receptor antagonist completely blocked the glutamate-induced cytotoxicity against both dopaminergic and non-dopaminergic neurons. In the dopaminergic neurons, MPP+ caused cytotoxicity that was not blocked by co-administration of MK-801. After pretreatment with small doses of MPP+, sub-lethal doses of glutamate caused severe cell damage restricted to dopaminergic neurons, suggesting that MPP+ potentiates the glutamate-induced cytotoxicity only against dopaminergic neurons. As glutamate is putatively capable of causing cytotoxicity against dopaminergic neurons, the present findings might be important in considering the pathogenesis of dopaminergic neuronal degeneration and a possible therapeutic application of glutamate receptor antagonists in Parkinson's disease.

Interactive Effects of Nicotine and MPTP on Striatal Tetrahydrobiopterin in Mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin known to cause dopamine (DA) neuron degeneration, while the psychoactive compound nicotine is known to excite DA neurons. Tetrahydrobiopterin is the cofactor for tyrosine hydroxylase (TOH) in the regulation of DA biosynthesis. The present study investigated the interactions between nicotine and MPTP on striatal biopterin, DA and TOH activity in BALB/c mice. The results indicated that both acute and chronic nicotine administrations at various concentrations significantly increased biopterin and DA levels in the striatum, while MPTP markedly decreased these measures. Pretreatment with nicotine at a dose having no significant effect alone, partially protected against MPTP's toxicity on biopterin and DA. Increasing the dose of nicotine did not have a further protective action. The toxicity of MPTP on TOH was also prevented by nicotine. Further, the above effects of nicotine were probably mediated through the cholinergic nicotinic receptors since mecamylamine reversed the effects of nicotine. These results suggest that nicotine interacts with the dopaminergic system probably at the level of DA biosynthesis through activating TOH and its coenzyme tetrahydrobiopterin. Copyright 1996 S. Karger AG, Basel

A molecular analysis of vesicular amine transport

To package classical neurotransmitters into vesicles so that their release can be regulated by activity, neuronal cells express a set of specific vesicular transport proteins. We have used selection in MPP+ to clone the cDNAs encoding two vesicular monoamine transporters, the first members of this novel gene family that now also includes the vesicular transporter for acetylcholine. The sequences show similarity to several bacterial antibiotic resistance proteins, further supporting a role in detoxification and possibly Parkinson's disease. The two vesicular amine transporters show differences in their affinity for substrates, their turnover number and their pharmacology. In particular, the proteins differ in their interactions with the potent inhibitor tetrabenazine and with amphetamines, accounting for several classic pharmacological observations. Since the subcellular localization of the transport proteins determines the site of monoamine storage and the site of monoamine storage appears to differ from other classical transmitters, we have also raised polyclonal antibodies to the transporters and used these to demonstrate localization in dense core vesicles rather than synaptic vesicles. In addition to the implications for monoamine release, these observations also indicate a vesicular amine transporter as the first integral membrane protein restricted to the regulated secretory pathway.

Effects of brain-derived neurotrophic factor on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in monkeys

The effects of intrathecal infusion of brain-derived neurotrophic factor (BDNF) were examined in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian model in monkeys. Nine Japanese monkeys were divided randomly into three groups, an untreated control (n = 3), a BDNF group (n = 3), and a non-BDNF group (n = 3). Animals in the BDNF group received continuous intrathecal infusion of 10 ml of cell culture medium containing 10 micrograms of BDNF protein; the non-BDNF group received intrathecal infusion of the same culture medium without BDNF. To induce parkinsonian syndromes, a total of 1 mg/kg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was administered intravenously to each monkey in both the BDNF and non-BDNF groups. The neurological signs in the monkeys were monitored for 2 weeks and were scored according to the monkey parkinsonism rating scale; histological changes in the substantia nigra were evaluated after the 2-week observation period. The BDNF-treated animals remained asymptomatic during the 1st week and showed mild parkinsonism during the 2nd week, whereas the non-BDNF group showed typical parkinsonian syndrome during the 1st week, with deterioration in the 2nd week. Histological damage in the substantia nigra correlated well with the clinical features. Severe neuronal cell loss in the substantia nigra was observed in animals with severe parkinsonism (those in the non-BDNF group), whereas significantly less damage was observed in this region in the BDNF group.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of complex I by hydrophobic analogues of N-methyl-4-phenylpyridinium (MPP+) and the use of an ion-selective electrode to measure their accumulation by mitochondria and electron-transport particles

N-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, kills dopaminergic neurons after its accumulation in mitochondria where it inhibits Complex I of the respiratory chain. MPP+ inhibits respiration by binding to both a hydrophobic and a hydrophilic site on Complex I and this inhibition is increased by the lipophilic tetraphenylboron anion (TPB-) which facilitates movement of MPP+ through membranes and its penetration to the hydrophobic binding site on Complex I. To investigate the inhibition of respiration by MPP(+)-like compounds, we have measured simultaneously NADH-linked mitochondrial respiration and the uptake and accumulation of the N-benzyl-4-styrylpyridinium and N-ethyl-4-styrylpyridinium cations in mitochondria using ion-selective electrodes. The data provide direct evidence that TPB- increases the inhibition not by increasing matrix concentration but by facilitating access to the inhibitory sites on Complex I. We have also compared the rates of uptake of MPP+ analogues of varied lipophilicity by the inner membrane and the development of inhibition of NADH oxidation, using an inverted mitochondrial inner membrane preparation and appropriate ion-selective electrodes. These experiments demonstrated that the amount of MPP+ analogue bound to the inner membrane greatly exceeded the quantity required for complete inhibition of NADH oxidation. Moreover, binding to the membrane occurred much more rapidly than the development of inhibition with all MPP+ analogues tested. This suggests that the attainment of a correct orientation of these compounds within the membrane and the binding site may be a rate-limiting step in the development of inhibition.

Autoradiographic study of mitochondrial complex I and glutamate receptors in the basal ganglia of rats after unilateral subthalamic lesion

A unilateral lesion of the subthalamic nucleus (STN) induced, in the short-term (< or = 1 week), an ipsilateral decrease in [3H]dihydrorotenone binding to complex I in entopeduncular nucleus and substantia nigra pars reticulata (SNr). A slight reduction of [3H]MK-801 binding to N-methyl-D-aspartate (NMDA) receptors in the ipsilateral SNr was also found, whereas no changes in [3H]alpha-amino-3-hydroxy-5-methylisoxazole propionic acid binding were observed. The complex I decrease likely reflects a reduction in neuronal activity subsequent to the interruption of excitatory signaling from STN. The unexpected decrease in [3H]MK-801 binding in SNr may be related to presynaptic NMDA receptor modifications.

The transport of neurotransmitters into synaptic vesicles

Using selection in the neurotoxin MPP+, we have isolated a cDNA encoding vesicular amine transport. The transporter protects against MPP+ by sequestering the toxin in vesicles, away from its primary site of action in mitochondria. Unexpectedly, two distinct but highly related genes encode vesicular amine transport in the adrenal gland and the central nervous system. The sequence of both predicts twelve transmembrane domains and weak homology to a class of bacterial antibiotic resistance proteins. The two human genes occur on different chromosomes. In addition, the two transporters show a number of differences in function, including substrate specificity and the interaction with one inhibitor and the amphetamines.

The molecular cloning and expression of a human synaptic vesicle amine transporter that suppresses MPP+ toxicity

A synaptic vesicle amine transporter cDNA, termed hSVAT, has been isolated by the reverse transcription and polymerase chain reaction (PCR) technique from human substantia nigra and subsequent screening of a human substantia nigra library. The hSVAT sequence obtained is highly homologous to the rat SVAT sequence (92% homology) and is essentially identical to the human sequence identified recently by Surratt and colleagues [33]. This labelled hSVAT cDNA detected a single band (approximately 5.0 kb) when used as a probe for Northern analysis of human nigral RNA extract. In situ hybridization studies using hSVAT specific antisense oligonucleotides showed a strong hybridization signal concentrated over the cells of the substantia nigra pars compacta. This cDNA sequence when expressed in chinese hamster ovary (CHO) cells conferred resistance to MPP+ the toxic metabolite of MPTP and cells containing it accumulated dopamine.

Stereotaxic administration of 1-methyl-4-phenylpyridinium ion (MPP+) decreases striatal fructose 2,6-bisphosphate in rats

The stereotaxic administration of 1-methyl-4-phenylpyridinium ion (MPP+) into the neostriatum of male rats caused a lesion that resulted in a large dose-dependent loss of striatal fructose 2,6-bisphosphate; initial values were restored 5 days after the treatment. This effect was not protected by systemic administration of MK-801 or by nitroarginine. The content of hexose 6-phosphates and ATP was also reduced by MPP+ treatment, whereas lactate was increased. Biochemical and histological results suggested that MPP+ caused a nonselective cell death, followed by a pronounced astroglial response, parallel to fructose 2,6-bisphosphate recovery. The stereotaxic administration of rotenone showed a different time effect on fructose 2,6-bisphosphate cerebral content, with a significantly faster recovery. These results indicate that cerebral fructose 2,6-bisphosphate may be a sensitive metabolite related to brain damage caused by potent neurotoxins such as MPP+. On the other hand, they show that MPP+ acts in the brain through a quick, strong cytotoxic mechanism, which probably involves mechanisms other than mitochondrial chain blockage.

Chromosomal localization of the human vesicular amine transporter genes

The physiologic and behavioral effects of pharmacologic agents that interfere with the transport of monoamine neurotransmitters into vesicles suggest that vesicular amine transport may contribute to human neuropsychiatric disease. To determine whether an alteration in the genes that encode vesicular amine transport contributes to the inherited component of these disorders, we have isolated a human cDNA for the brain transporter and localized the human vesicular amine transporter genes. The human brain synaptic vesicle amine transporter (SVAT) shows unexpected conservation with rat SVAT in the regions that diverge extensively between rat SVAT and the rat adrenal chromaffin granule amine transporter (CGAT). Using the cloned sequences with a panel of mouse-human hybrids and in situ hybridization for regional localization, the adrenal CGAT gene (or VAT1) maps to human chromosome 8p21.3 and the brain SVAT gene (or VAT2) maps to chromosome 10q25. Both of these sites occur very close to if not within previously described deletions that produce severe but viable phenotypes.