Role of mitochondria in the etiology and pathogenesis of Parkinson's disease

Metabolic profiling of Parkinson's disease: evidence of biomarker from gene expression analysis and rapid neural network detection

Background

Parkinson's disease (PD) is a neurodegenerative disorder. The diagnosis of Parkinsonism is challenging because currently none of the clinical tests have been proven to help in diagnosis. PD may produce characteristic perturbations in the metabolome and such variations can be used as the marker for detection of disease. To test this hypothesis, we used proton NMR and multivariate analysis followed by neural network pattern detection.

Methods & Results

¹H nuclear magnetic resonance spectroscopy analysis was carried out on plasma samples of 37 healthy controls and 43 drug-naive patients with PD. Focus on 22 targeted metabolites, 17 were decreased and 5 were elevated in PD patients (p < 0.05). Partial least squares discriminant analysis (PLS-DA) showed that pyruvate is the key metabolite, which contributes to the separation of PD from control samples. Furthermore, gene expression analysis shows significant (p < 0.05) change in expression of PDHB and NPFF genes leading to increased pyruvate concentration in blood plasma. Moreover, the implementation of ¹H- NMR spectral pattern in neural network algorithm shows 97.14% accuracy in the detection of disease progression.

Conclusion

The results increase the prospect of a robust molecular definition in detection of PD through the early symptomatic phase of the disease. This is an ultimate opening for therapeutic intervention. If validated in a genuinely prospective fashion in larger samples, the biomarker trajectories described here will go a long way to facilitate the development of useful therapies. Moreover, implementation of neural network will be a breakthrough in clinical screening and rapid detection of PD.

Selective activation of p38 mitogen-activated protein kinase in dopaminergic neurons of substantia nigra leads to nuclear translocation of p53 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc). Activation of the mixed lineage kinase and c-Jun N-terminal kinase (JNK) has been reported in models of PD. Our focus was to discern whether distinct pathways were activated in cell-specific manner within the SNpc. We now demonstrate the selective phosphorylation of p38 MAP kinase within the dopaminergic neurons, whereas JNK activation occurs predominantly in the microglia. p38 activation results in downstream phosphorylation of p53 and increased p53 mediated transcription of Bax and Puma in the ventral midbrain. Treatment with p38 inhibitor, SB239063 protected primary dopaminergic neurons derived from human progenitor cells from MPP(+) mediated cell death and prevented the downstream phosphorylation of p53 and its translocation to the nucleus in vivo, in the ventral midbrain. The increased staining of phosphorylated p38 in the surviving neurons of SNpc in human brain sections from patients with PD and in MPTP treated mice but not in the ventral tegmental area provides further evidence suggesting a role for p38 in the degeneration of dopaminergic neurons of SNpc. We thus demonstrate the cell specific activation of MAP kinase pathways within the SNpc after MPTP treatment emphasizing the role of multiple signaling cascades in the pathogenesis and progression of the disease. Selective inhibitors of p38 may therefore, help preserve the surviving neurons in PD and slow down the disease progression.

Protective role of endogenous gangliosides for lysosomal pathology in a cellular model of synucleinopathies

Gangliosides may be involved in the pathogenesis of Parkinson's disease and related disorders, although the precise mechanisms governing this involvement remain unknown. In this study, we determined whether changes in endogenous ganglioside levels affect lysosomal pathology in a cellular model of synucleinopathy. For this purpose, dementia with Lewy body-linked P123H beta-synuclein (beta-syn) neuroblastoma cells transfected with alpha-synuclein were used as a model system because these cells were characterized as having extensive formation of lysosomal inclusions bodies. Treatment of these cells with D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), an inhibitor of glycosyl ceramide synthase, resulted in various features of lysosomal pathology, including compromised lysosomal activity, enhanced lysosomal membrane permeabilization, and increased cytotoxicity. Consistent with these findings, expression levels of lysosomal membrane proteins, ATP13A2 and LAMP-2, were significantly decreased, and electron microscopy demonstrated alterations in the lysosomal membrane structures. Furthermore, the accumulation of both P123H beta-syn and alpha-synuclein proteins was significant in PDMP-treated cells because of the suppressive effect of PDMP on the autophagy pathway. Finally, the detrimental effects of PDMP on lysosomal pathology were significantly ameliorated by the addition of gangliosides to the cultured cells. These data suggest that endogenous gangliosides may play protective roles against the lysosomal pathology of synucleinopathies.

Glutaredoxin-1 mediates NADPH-dependent stimulation of calcium-dependent insulin secretion

Nicotinamide adenine dinucleotide phosphate (NADPH) enhances Ca(2+)-induced exocytosis in pancreatic beta-cells, an effect suggested to involve the cytosolic redox protein glutaredoxin-1 (GRX-1). We here detail the role of GRX-1 in NADPH-stimulated beta-cell exocytosis and glucose-stimulated insulin secretion. Silencing of GRX-1 by RNA interference reduced glucose-stimulated insulin secretion in both clonal INS-1 832/13 cells and primary rat islets. GRX-1 silencing did not affect cell viability or the intracellular redox environment, suggesting that GRX-1 regulates the exocytotic machinery by a local action. By contrast, knockdown of the related protein thioredoxin-1 (TRX-1) was ineffective. Confocal immunocytochemistry revealed that GRX-1 locates to the cell periphery, whereas TRX-1 expression is uniform. These data suggest that the distinct subcellular localizations of TRX-1 and GRX-1 result in differences in substrate specificities and actions on insulin secretion. Single-cell exocytosis was likewise suppressed by GRX-1 knockdown in both rat beta-cells and clonal 832/13 cells, whereas after overexpression exocytosis increased by approximately 40%. Intracellular addition of NADPH (0.1 mm) stimulated Ca(2+)-evoked exocytosis in both cell types. Interestingly, the stimulatory action of NADPH on the exocytotic machinery coincided with an approximately 30% inhibition in whole-cell Ca(2+) currents. After GRX-1 silencing, NADPH failed to amplify insulin release but still inhibited Ca(2+) currents in 832/13 cells. In conclusion, NADPH stimulates the exocytotic machinery in pancreatic beta-cells. This effect is mediated by the NADPH acceptor protein GRX-1 by a local redox reaction that accelerates beta-cell exocytosis and, in turn, insulin secretion.

Mitochondrial UCP4 attenuates MPP+ - and dopamine-induced oxidative stress, mitochondrial depolarization, and ATP deficiency in neurons and is interlinked with UCP2 expression

Mitochondrial uncoupling proteins (UCPs) uncouple oxidative phosphorylation from ATP synthesis. We explored the neuroprotective role of UCP4 with its stable overexpression in SH-SY5Y cells, after exposure to either MPP(+) or dopamine to induce ATP deficiency and oxidative stress. Cells overexpressing UCP4 proliferated faster in normal cultures and after exposure to MPP(+) and dopamine. Differentiated UCP4-overexpressing cells survived better when exposed to MPP(+) with decreased LDH release. Contrary to the mild uncoupling hypothesis, UCP4 overexpression resulted in increased absolute ATP levels (with ADP/ATP ratios similar to those of controls under normal conditions and ADP supplementation) associated with increased respiration rate. Under MPP(+) toxicity, UCP4 overexpression preserved ATP levels and mitochondrial membrane potential (MMP) and reduced oxidative stress; the preserved ATP level was not due to increased glycolysis. Under MPP(+) toxicity, the induction of UCP2 expression in vector controls was absent in UCP4-overexpressing cells, suggesting that UCP4 may compensate for UCP2 expression. UCP4 function does not seem to adhere to the mild uncoupling hypothesis in its neuroprotective mechanisms under oxidative stress and ATP deficiency. UCP4 overexpression increases cell survival by inducing oxidative phosphorylation, preserving ATP synthesis and MMP, and reducing oxidative stress.

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.

Biochemistry and bioenergetics of glutaryl-CoA dehydrogenase deficiency

Glutaryl-CoA dehydrogenase (GCDH) is a central enzyme in the catabolic pathway of L-tryptophan, L-lysine, and L-hydroxylysine which catalyses the oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA and CO2. Glutaryl-CoA dehydrogenase deficiency (GDD) is an autosomal recessive disease characterized by the accumulation of glutaric and 3-hydroxyglutaric acids in tissues and body fluids. Untreated patients commonly present with severe striatal degeneration during encephalopathic crises. Previous studies have highlighted primary excitotoxicity as a trigger of striatal degeneration. The aim of this PhD study was to investigate in detail tissue-specific bioenergetic and biochemical parameters of GDD in vitro, post mortem, and in Gcdh-/- mice. The major bioenergetic finding was uncompetitive inhibition of alpha-ketoglutarate dehydrogenase complex by glutaryl-CoA. It is suggested that a synergism of primary and secondary excitotoxic effects in concert with age-related physiological changes in the developing brain underlie acute and chronic neurodegenerative changes in GDD patients. The major biochemical findings were highly elevated cerebral concentrations of glutaric and 3-hydroxyglutaric acid despite low permeability of the blood-brain barrier for these dicarboxylic acids. It can be postulated that glutaric and 3-hydroxyglutaric acids are synthesized de novo and subsequently trapped in the brain. In this light, neurological disease in GDD is not 'transported' to the brain in analogy with phenylketonuria or hepatic encephalopathy as suggested previously but is more likely to be induced by the intrinsic biochemical properties of the cerebral tissue and the blood-brain barrier.

Cannabinoids ameliorate cerebral dysfunction following liver failure via AMP‐activated protein kinase

Hepatic encephalopathy (HE) is a neuropsychiatric disorder of complex pathogenesis caused by acute or chronic liver failure. We studied the etiology of cerebral dysfunction in a murine model of HE induced by either bile duct ligation or thioacetamide administration. We report that stimulation of cerebral AMP-activated protein kinase (AMPK), a major intracellular energy sensor, is a compensatory response to liver failure. This function of AMPK is regulated by endocannabinoids. The cannabinoid system controls systemic energy balance via the cannabinoid receptors CB-1 and CB-2. Under normal circumstances, AMPK activity is mediated by CB-1 while CB-2 is barely detected. However, CB-2 is strongly stimulated in response to liver failure. Administration of delta9-tetrahydrocannabinol (THC) augmented AMPK activity and restored brain function in WT mice but not in their CB-2 KO littermates. These results suggest that HE is a disease of energy flux. CB-2 signaling is a cerebral stress response mechanism and makes AMPK a promising target for its treatment by modulating the cannabinoid system.

Knockdown of uncoupling protein-5 in neuronal SH-SY5Y cells: Effects on MPP+-induced mitochondrial membrane depolarization, ATP deficiency, and oxidative cytotoxicity

Uncoupling proteins (UCPs) uncouple oxidative phosphorylation from ATP synthesis by dissipating proton gradient across mitochondrial inner membrane. The physiological role of neuronal specific UCP5 is unknown. We explored the effects of reduced UCP5 expression on mitochondrial membrane potential (MMP), oxidative stress, ATP levels, and cell viability, under normal and MPP+-induced cytotoxic conditions, in human catecholaminergic SH-SY5Y cells. UCP5 expression was reduced by 56% by siRNA, compared to scrambled-siRNA controls. UCP5 knockdown induced apoptosis but did not affect basal levels of ATP, oxidative stress and MMP in the cells under normal conditions. However, UCP5 knockdown increased MPP+-induced cytotoxicity by 15% and oxidative stress levels by 40%, and partially restored MPP+-induced mitochondrial depolarization by 57%. UCP2 and UCP4 expression were unaffected by UCP5 knockdown. Exacerbation of cytotoxicity, oxidative stress and modification of MMP with reduced UCP5 expression in the face of MPP+ toxicity suggest that UCP5 might be physiologically important in the pathology of oxidative stress-induced neurodegeneration.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

Protective effect of alpha-keto-beta-methyl-n-valeric acid on BV-2 microglia under hypoxia or oxidative stress

The alpha-ketoglutarate dehydrogenase complex (KGDHC) is a mitochondrial enzyme in the TCA cycle. Inhibition of KGDHC activity by alpha-keto-beta-methyl-n-valeric acid (KMV) is associated with neuron death. However, the effect of KMV in microglia is unclear. Therefore, we investigated the effect of KMV on BV-2 microglial cells exposed to hypoxia or oxidative stress. The results showed that KMV (1-20 mM) enhanced the cell viability under hypoxia. KMV dose-dependently reduced ROS and LDH releases from hypoxic BV-2 cells. KMV also reduced ROS production and enhanced the cell viability under H2O2 but failed to reduce the SIN-1 and sodium nitroprusside (SNP) toxicity. KMV also reduced caspase-3 and -9 activation under stress. These results suggest that KMV protects BV-2 cells from stress and acts by reducing ROS production through inhibition of KDGHC.

Attenuation of MPTP-induced neurotoxicity and locomotor dysfunction in Nucling-deficient mice via suppression of the apoptosome pathway

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity is one of the experimental models most commonly used to study the pathogenesis of Parkinson's disease (PD). Although the biochemical mechanisms underlying the cell death induced by MPTP remain to be clarified, it has been found that the mitochondrial apoptotic signaling pathway plays an important role in the neurotoxicity of MPTP. Nucling is a novel type of apoptosis-associated molecule, essential for cytochrome c, apoptosis protease activating factor 1 (Apaf-1), pro-caspase-9 apoptosome induction and caspase-9 activation following pro-apoptotic stress. Here we found that Nucling-deficient mice treated with MPTP did not exhibit locomotor dysfunction in an open-field test. The substantia nigra dopaminergic neurons of Nucling-deficient mice were resistant to the damaging effects of the neurotoxin MPTP. Up-regulated expression of apoptosome was attenuated in Nucling-deficient mice treated with MPTP. These results indicate an important role for Nucling in MPTP-induced neuronal degeneration and suggest that the suppression of Nucling would be of therapeutic benefit for the treatment of neurodegeneration in PD.

Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production

In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

Calcium, mitochondria and oxidative stress in neuronal pathology. Novel aspects of an enduring theme

The interplay among reactive oxygen species (ROS) formation, elevated intracellular calcium concentration and mitochondrial demise is a recurring theme in research focusing on brain pathology, both for acute and chronic neurodegenerative states. However, causality, extent of contribution or the sequence of these events prior to cell death is not yet firmly established. Here we review the role of the alpha-ketoglutarate dehydrogenase complex as a newly identified source of mitochondrial ROS production. Furthermore, based on contemporary reports we examine novel concepts as potential mediators of neuronal injury connecting mitochondria, increased [Ca2+]c and ROS/reactive nitrogen species (RNS) formation; specifically: (a) the possibility that plasmalemmal nonselective cationic channels contribute to the latent [Ca2+]c rise in the context of glutamate-induced delayed calcium deregulation; (b) the likelihood of the involvement of the channels in the phenomenon of 'Ca2+ paradox' that might be implicated in ischemia/reperfusion injury; and (c) how ROS/RNS and mitochondrial status could influence the activity of these channels leading to loss of ionic homeostasis and cell death.

Geographic and ethnic differences in frequencies of two polymorphisms (D/N394 and L/I272) of the parkin gene in sporadic Parkinson's disease

In this report, we evaluated the allele frequency of the D/N394 single nucleotide polymorphism (SNP) in exon 11 of the parkin gene in 200 Japanese patients with sporadic Parkinson's disease (PD) and 200 normal controls. Although the reported allele frequency of G-to-A (D/N394) is 2% in Caucasians, this SNP was not detected in Japanese patients and healthy controls. Evaluation of L/I272 polymorphism, a C-to-A transition in exon 7, showed the polymorphism in only six controls, but not in PD patients. Our results suggest that the frequencies of parkin polymorphisms are different among Asians and Caucasians.

Vasoactive intestinal peptide family as a therapeutic target for Parkinson’s disease

Parkinson's disease (PD) is a common neurodegenerative disorder with no effective protective treatment, characterised by a massive degeneration of dopaminergic neurons in the substantia nigra and the subsequent loss of their projecting nerve fibres in the striatum. Because current treatments for PD are not effective, considerable research has been focused recently on a number of regulatory molecules that regulate inflammation characteristic of PD, induce neurotrophic and survival factors and reduce oxidative stress. Vasoactive intestinal peptide (VIP), a neuropeptide with a potent anti-inflammatory, antiapoptotic and neurotrophic effect, has been found to be protective in several inflammatory disorders. This review examines the putative protective effect of VIP and analogues in different models for PD. VIP emerges as a potential valuable neuroprotective agent for the treatment of pathological conditions in the CNS, such as PD, in which inflammation-induced neurodegeneration occurs.

PACAP protects neuronal differentiated PC12 cells against the neurotoxicity induced by a mitochondrial complex I inhibitor, rotenone

In vivo and in vitro studies have suggested a neuroprotective role for Pituitary adenylate cyclase activating polypeptide (PACAP) against neuronal insults. Here, we showed that PACAP27 protects against neurotoxicity induced by rotenone, a mitochondrial complex I inhibitor that has been implicated in the pathogenesis of Parkinson's disease (PD). The neuroprotective effect of PACAP27 was dose-dependent and blocked by its specific receptor antagonist, PACAP6-27. The effects of PACAP27 on rotenone-induced cell death were mimicked by dibutyryl-cAMP (db-cAMP), forskolin and prevented by the PKA inhibitor H89, the ERK inhibitor PD98059 and the p38 inhibitor SB203580. PACAP27 administration blocked rotenone-induced increases in the level of caspase-3-like activity, whereas could not restore mitochondrial activity damaged by rotenone. Thus, our results demonstrate that PACAP27 has a neuroprotective role against rotenone-induced neurotoxicity in neuronal differentiated PC12 cells and the neuroprotective effects of PACAP are associated with activation of MAP kinase pathways by PKA and with inhibition of caspase-3 activity; the signaling mechanism appears to be mediated through mitochondrial-independent pathways.

Bioenergetics in glutaryl-coenzyme A dehydrogenase deficiency: a role for glutaryl-coenzyme A

Inherited deficiency of glutaryl-CoA dehydrogenase results in an accumulation of glutaryl-CoA, glutaric, and 3-hydroxyglutaric acids. If untreated, most patients suffer an acute encephalopathic crisis and, subsequently, acute striatal damage being precipitated by febrile infectious diseases during a vulnerable period of brain development (age 3 and 36 months). It has been suggested before that some of these organic acids may induce excitotoxic cell damage, however, the relevance of bioenergetic impairment is not yet understood. The major aim of our study was to investigate respiratory chain, tricarboxylic acid cycle, and fatty acid oxidation in this disease using purified single enzymes and tissue homogenates from Gcdh-deficient and wild-type mice. In purified enzymes, glutaryl-CoA but not glutaric or 3-hydroxyglutaric induced an uncompetitive inhibition of alpha-ketoglutarate dehydrogenase complex activity. Notably, reduced activity of alpha-ketoglutarate dehydrogenase activity has recently been demonstrated in other neurodegenerative diseases, such as Alzheimer, Parkinson, and Huntington diseases. In contrast to alpha-ketoglutarate dehydrogenase complex, no direct inhibition of glutaryl-CoA, glutaric acid, and 3-hydroxyglutaric acid was found in other enzymes tested. In Gcdh-deficient mice, respiratory chain and tricarboxylic acid activities remained widely unaffected, virtually excluding regulatory changes in these enzymes. However, hepatic activity of very long-chain acyl-CoA dehydrogenase was decreased and concentrations of long-chain acylcarnitines increased in the bile of these mice, which suggested disturbed oxidation of long-chain fatty acids. In conclusion, our results demonstrate that bioenergetic impairment may play an important role in the pathomechanisms underlying neurodegenerative changes in glutaryl-CoA dehydrogenase deficiency.

Reduction in the E2k subunit of the alpha-ketoglutarate dehydrogenase complex has effects independent of complex activity

The activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC) declines in brains of patients with several neurodegenerative diseases. KGDHC consists of multiple copies of E1k, E2k, and E3. E1k and E2k are unique to KGDHC and may have functions independent of the complex. The present study tested the consequences of different levels of diminished E2k mRNA on protein levels of the subunits, KGDHC activity, and physiological responses. Human embryonic kidney cells were stably transfected with an E2k sense or antisense expression vector. Sense control (E2k-mRNA-100) was compared with two clones in which the mRNA was reduced to 67% of control (E2k-mRNA-67) or to 30% of control (E2k-mRNA-30). The levels of the E2k protein in clones paralleled the reduction in mRNA, and E3 proteins were unaltered. Unexpectedly, the clone with the greatest reduction in E2k protein (E2k-mRNA-30) had a 40% increase in E1k protein. The activity of the complex was only 52% of normal in E2k-mRNA-67 clone, but was near normal (90%) in E2k-mRNA-30 clone. Subsequent experiments tested whether the physiological consequences of a reduction in E2k mRNA correlated more closely to E2k protein or to KGDHC activity. Growth rate, increased DCF-detectable reactive oxygen species, and cell death in response to added oxidant were proportional to E2k proteins, but not complex activity. These results were not predicted because subunits unique to KGDHC have never been manipulated in mammalian cells. These results suggest that in addition to its essential role in metabolism, the E2k component of KGDHC may have other novel roles.

Effects of creatine treatment on the survival of dopaminergic neurons in cultured fetal ventral mesencephalic tissue

Parkinson's disease is a disabling neurodegenerative disorder of unknown etiology characterized by a predominant and progressive loss of dopaminergic neurons in the substantia nigra. Recent findings suggest that impaired energy metabolism plays an important role in the pathogenesis of this disorder. The endogenously occurring guanidino compound creatine is a substrate for mitochondrial and cytosolic creatine kinases. Creatine supplementation improves the function of the creatine kinase/phosphocreatine system by increasing cellular creatine and phosphocreatine levels and the rate of ATP resynthesis. In addition, mitochondrial creatine kinase together with high cytoplasmic creatine levels inhibit mitochondrial permeability transition, a major step in early apoptosis. In the present study, we analyzed the effects of externally added creatine on the survival and morphology of dopaminergic neurons and also addressed its neuroprotective properties in primary cultures of E14 rat ventral mesencephalon. Chronic administration of creatine [5 mM] for 7 days significantly increased survival (by 1.32-fold) and soma size (by 1.12-fold) of dopaminergic neurons, while having no effect on other investigated morphological parameters. Most importantly, concurrent creatine exerted significant neuroprotection for dopaminergic neurons against neurotoxic insults induced by serum and glucose deprivation (P < 0.01), 1-methyl-4-phenyl pyridinium ion (MPP+) [15 microM] and 6-hydroxydopamine (6-OHDA) [90 microM] exposure (P < 0.01). In addition, creatine treatment significantly protected dopaminergic cells facing MPP+-induced deterioration of neuronal morphology including overall process length/neuron (by 60%), number of branching points/neuron (by 80%) and area of influence per individual neuron (by 60%). Less pronounced effects on overall process length/neuron and number of branching points/neuron were also found after 6-OHDA exposure (P < 0.05) and serum/glucose deprivation (P < 0.05). In conclusion, our findings identify creatine as a rather potent natural survival- and neuroprotective factor for developing nigral dopaminergic neurons, which is of relevance for therapeutic approaches in Parkinson's disease and for the improvement of cell replacement strategies.

Effect of coenzyme Q10 on the mitochondrial function of skin fibroblasts from Parkinson patients

Several lines of evidence suggest an impairment of mitochondrial function in the brain of patients with Parkinson's disease (PD). However, the presence of a detectable mitochondrial defect in extracerebral tissue of these patients remains a matter of dispute. Therefore, we investigated mitochondrial function in fibroblasts of 18 PD patients applying biochemical micromethods. Putative beneficial effects of coenzyme Q(10) (CoQ(10)), a potent antioxidant, on the mitochondrial function of skin fibroblast cultures were evaluated. Applying inhibitor titrations of the mitochondrial respiration to calculate flux control coefficients of respiratory chain complexes I and IV, we observed deficiencies of both complexes in cultivated skin fibroblasts of PD patients. Cultivation of fibroblasts in the presence of 5 microM CoQ(10) restored the activity of impaired respiratory chain complexes in the fibroblast cultures of 9 out of 18 PD patients. Our data support the presence of a generalised mitochondrial defect in at least a subgroup of patients with PD that can be partially ameliorated in vitro by coenzyme Q(10) treatment.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

Genotyping Parkinson disease-associated mitochondrial polymorphisms

OBJECTIVE

The purpose of this study was to establish a system for rapidly detecting single nucleotide polymorphisms (SNPs) in mitochondrial DNA (mtDNA) using hybridization probes and melting temperature (T(m)) analysis. This technology should prove useful for population-based studies on the interaction between genetic factors and environmental exposures and the risk of Parkinson disease (PD).

METHODS

Mitochondrial DNA (mtDNA) was extracted from whole blood. Rapid polymerase chain reaction (PCR) and melting curve analyses were performed with primers and fluorochrome-labeled probes on a LightCycler (Roche Molecular Biochemical, Mannheim, Germany). Genotyping of 10 SNPs in 15 subjects was based on the analysis of allele-specific T(m) of detection probes. The results of melting curve analyses were verified by sequencing all 150 PCR products.

RESULTS

Real-time monitoring showed optimal PCR amplification of each mtDNA fragment. The nucleotide changes at positions 1719, 4580, 7028, 8251, 9055, 10398, 12308, 13368, 13708, and 16391 from wild-type to mutant genotype resulted in 6.51, 8.29, 3.26, 7.82, 4.79, 2.84, 2.73, 9.04, 8.53, and 9.52 degrees C declines in T(m) of the detection probes, respectively. Genotyping of all 150 samples was verified by 100% correspondence with the results of sequencing. Fourteen subjects were haplogrouped by combining results for all 10 SNPs.

CONCLUSION

A rapid and reliable detection system for identifying mitochondrial polymorphisms and haplotypes was developed based on hybridization probe technology. This method may be suitable for mitochondrial genotyping of samples from large-scale epidemiology studies, and may prove useful for exploring the molecular etiopathogenesis of PD, identifying markers of genetic susceptibility, and protecting susceptible individuals from PD.

Effects of (1R,9S)-β-hydrastine on l-DOPA-induced cytotoxicity in PC12 cells

(1R,9S)-beta-Hydrastine in lower concentrations of 10-50 microM inhibits dopamine biosynthesis in PC12 cells. In this study, the effects of (1R,9S)-beta-hydrastine on L-DOPA (L-3,4-dihydroxyphenylalanine)-induced cytotoxicity in PC12 cells were investigated. (1R,9S)-Hydrastine at concentrations up to 250 microM did not reduce cell viability. However, at concentrations higher than 500 microM it caused cytotoxicity in PC12 cells, as determined with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, TUNEL (terminal deoxynucleotidyltransferase dUTP nick-end labeling) method and flow cytometry. Exposure of PC12 cells to cytotoxic concentrations of (1R,9S)-beta-hydrastine (500 and 750 microM) in combination with L-DOPA (20, 50 and 100 microM) after 24 or 48 h resulted in a significant decrease in cell viability compared with the effects of (1R,9S)-beta-hydrastine or L-DOPA alone, and apoptotic cell death was observed. However, the decrease in cell viability induced by (1R,9S)-beta-hydrastine was not prevented by the antioxidant N-acetyl-L-cysteine, indicating that it is not mediated by membrane-based oxygen free radical damage. These data suggest that (1R,9S)-beta-hydrastine has a mild cytotoxic effect and at higher concentration ranges aggravates L-DOPA-induced cytotoxicity in PC12 cells.

Mice deficient in dihydrolipoamide dehydrogenase show increased vulnerability to MPTP, malonate and 3-nitropropionic acid neurotoxicity

Altered energy metabolism, including reductions in activities of the key mitochondrial enzymes alpha-ketoglutarate dehydrogenase complex (KGDHC) and pyruvate dehydrogenase complex (PDHC), are characteristic of many neurodegenerative disorders including Alzheimer's Disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Dihydrolipoamide dehydrogenase is a critical subunit of KGDHC and PDHC. We tested whether mice that are deficient in dihydrolipoamide dehydrogenase (Dld+/-) show increased vulnerability to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), malonate and 3-nitropropionic acid (3-NP), which have been proposed for use in models of PD and HD. Administration of MPTP resulted in significantly greater depletion of tyrosine hydroxylase-positive neurons in the substantia nigra of Dld+/- mice than that seen in wild-type littermate controls. Striatal lesion volumes produced by malonate and 3-NP were significantly increased in Dld+/- mice. Studies of isolated brain mitochondria treated with 3-NP showed that both succinate-supported respiration and membrane potential were suppressed to a greater extent in Dld+/- mice. KGDHC activity was also found to be reduced in putamen from patients with HD. These findings provide further evidence that mitochondrial defects may contribute to the pathogenesis of neurodegenerative diseases.

Enriched environment, nitric oxide production and synaptic plasticity prevent the aging-dependent impairment of spatial cognition

In rodents, neuronal plasticity decreases and spatial learning and working memory deficits increase upon aging. Several authors have shown that rats reared in enriched environments have better cognitive performance in association with increased neuronal plasticity than animals reared in standard environments. We hypothesized that enriched environment could preserve animals from the age-associated neurological impairments, mainly through NO-dependent mechanisms of induction of neuronal plasticity. We present evidence that 27 months old rats from an enriched environment show a better performance in spatial working memory than standard reared rats of the same age. Both mtNOS and cytosolic nNOS activities were found significantly increased (73% and 155%, respectively) in female rats from enriched environment as compared with control animals kept in a standard environment. The enzymatic activity of complex I was 80% increased in rats from enriched environment as compared with control rats. We conclude that an extensively enriched environment prevents old rats from the aging-associated impairment of spatial cognition, synaptic plasticity and nitric oxide production.

Inhibition of alpha-ketoglutarate dehydrogenase complex promotes cytochrome c release from mitochondria, caspase-3 activation, and necrotic cell death

Mitochondrial dysfunction has been implicated in cell death in many neurodegenerative diseases. Diminished activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key and arguably rate-limiting enzyme of the Krebs cycle, occurs in these disorders and may underlie decreased brain metabolism. The present studies used alpha-keto-beta-methyl-n-valeric acid (KMV), a structural analogue of alpha-ketoglutarate, to inhibit KGDHC activity to test effects of reduced KGDHC on mitochondrial function and cell death cascades in PC12 cells. KMV decreased in situ KGDHC activity by 52 +/- 7% (1 hr) or 65 +/- 4% (2 hr). Under the same conditions, KMV did not alter the mitochondrial membrane potential (MMP), as assessed with a method that detects changes as small as 5%. KMV also did not alter production of reactive oxygen species (ROS). However, KMV increased lactate dehydrogenase (LDH) release from cells by 100 +/- 4.7%, promoted translocation of mitochondrial cytochrome c to the cytosol, and activated caspase-3. Inhibition of the mitochondrial permeability transition pore (MPTP) by cyclosporin A (CsA) partially blocked this KMV-induced change in cytochrome c (-40%) and LDH (-15%) release, and prevented necrotic cell death. Thus, impairment of this key mitochondrial enzyme in PC12 cells may lead to cytochrome c release and caspase-3 activation by partial opening of the MPTP before the loss of mitochondrial membrane potentials.

Gene therapy for Parkinson's disease

We review recent progress in gene therapy utilizing experimental parkinsonian models including our data. Investigation of ex vivo gene therapy for Parkinson's disease (PD) is to provide L-dopa by transplantation of genetically modified cells into the striatum. Recently, neuronal progenitor cells (NPC) are recognized as the most appropriate target population for such genetic and cellular therapy of PD. We have developed modified pseudo-typed retrovirus production system. Using this gene transfer system, it is easy and efficient to introduce the gene into NPC because high titer virus vector is easily obtained. For the in vivo gene therapy, adeno-associated virus (AAV) vector is best virus vector because it is easy to introduce gene into neurons without inflammatory reaction. We established in vivo models of the inhibition of the caspase-cascade by overexpression of apoptotic protease activating factor-1-dominant negative inhibitor (Apaf-1-DN) using AAV vector. We showed that Apaf-1-DN delivery using an AAV vector system could prevent nigrostriatal degeneration in MPTP mice, suggesting that it might be an anti-mitochondrial apoptotic gene therapy for PD.

Relationship between NMDA receptor expression and MPP+ toxicity in cultured dopaminergic cells

It has been suggested that excitotoxicity could be contributing to dopamine cell loss after methylphenylpyridinium ion (MPP+) exposure, although the literature regarding this is contradictory. Given that in cell culture excitotoxicity has been reported to be dependent on culture age, we postulated that these discrepant results might be explained by a difference in developmental expression of N-methyl-D-aspartate (NMDA) receptors. To test this, mesencephalic cells were cultured and the number of dopaminergic neurons (tyrosine hydroxylase-immunoreactive cells [TH-IR] cells) expressing the NMDA R1 subunit (NR1) was determined using double-label immunofluorescence microscopy. An increase in the percentage of TH-IR cells expressing NR1 occurred over time in culture and this correlated with the toxicity of NMDA. At 7 days in vitro (DIV 7), only 17% (n=167 cells/4 experiments) of TH-IR cells expressed NR1 and these cells were insensitive to NMDA toxicity. This increased to 80% (n=254 cells/6 experiments) by DIV 11 and cultures were now susceptible to NMDA-induced injury. Cultures grown for either 7 or 11 days were treated for 48 hr with increasing concentrations of MPP= (0.5-20 microM) and the loss of dopaminergic neurons was determined by cell counting. Cultures at DIV 7 were more sensitive to MPP= than 11-day-old cultures (LD50= approximately 0.75 microM vs. 15 microM, respectively). Co-exposure to MK-801 (5 microM) did not protect against MPP+ toxicity in young cultures, but attenuated MPP+ toxicity in the older cultures, becoming statistically significant at 20 microM MPP+. These data indicate that the activation of NMDA receptors is not required for, but can contribute to, MPP(+)-induced neurodegeneration of dopaminergic cells in culture.

Deficits in a tricarboxylic acid cycle enzyme in brains from patients with Parkinson's disease

Parkinson's disease (PD) is associated with mitochondrial dysfunction, specifically a deficiency of complex I of the electron transport chain. Most, although not all, studies indicate that this deficiency is limited to brain regions with neurodegeneration. The current studies tested for deficiencies in other mitochondrial components in PD brain in a neuropathologically unaffected region where the abnormality cannot be attributed to secondary effects of neurodegeneration. The activity of a key (and arguably rate-limiting) tricarboxylic acid cycle enzyme, the alpha-ketoglutarate dehydrogenase complex (KGDHC), was measured in the cerebellum of patients with PD. Activity in 19 PD brains was 50.5% of that in 18 controls matched for age, sex, post-mortem interval, and method of preservation (P<0.0019). The protein subunits of KGDHC were present in normal amounts in PD brains, indicating a relatively discrete abnormality in the enzyme. The activities of another mitochondrial enzyme, glutamate dehydrogenase (GDH), were normal in PD brains. These results demonstrate that specific reductions in KGDHC occur even in pathologically unaffected areas in PD, where the decline is unlikely to be a non-specific result of neurodegeneration. Reductions in the activity of this enzyme, if widespread in the brain, may predispose vulnerable regions to further damage.

Neuroprotective effect of vasoactive intestinal peptide (VIP) in a mouse model of Parkinson's disease by blocking microglial activation

Parkinson's disease (PD) is a common neurodegenerative disorder with no effective protective treatment, characterized by a massive degeneration of dopaminergic neurons in the substantia nigra (SNpc) and the subsequent loss of their projecting nerve fibers in the striatum. To elucidate PD pathogenic factors, and thus to develop therapeutic strategies, a murine PD model based on the administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been used extensively. It has been demonstrated that activated microglia cells actively participate in the pathogenesis of MPTP-induced PD through the release of cytotoxic factors. Because current treatments for PD are not effective, considerable research focused lately on a number of regulatory molecules termed microglia-deactivating factors. Vasoactive intestinal peptide (VIP), a neuropeptide with a potent anti-inflammatory effect, has been found to be protective in several inflammatory disorders. This study investigates the putative protective effect of VIP in the MPTP model for PD. VIP treatment significantly decreases MPTP-induced dopaminergic neuronal loss in SNpc and nigrostriatal nerve-fiber loss. VIP prevents MPTP-induced activation of microglia in SNpc and striatum and the expression of the cytotoxic mediators, iNOS, interleukin 1beta, and numor necrosis factor alpha. VIP emerges as a potential valuable neuroprotective agent for the treatment of pathologic conditions in the central nervous system, such as PD, where inflammation-induced neurodegeneration occurs.

Oxidative stress in Parkinson's disease

Oxidative stress contributes to the cascade leading to dopamine cell degeneration in Parkinson's disease (PD). However, oxidative stress is intimately linked to other components of the degenerative process, such as mitochondrial dysfunction, excitotoxicity, nitric oxide toxicity and inflammation. It is therefore difficult to determine whether oxidative stress leads to, or is a consequence of, these events. Oxidative damage to lipids, proteins, and DNA occurs in PD, and toxic products of oxidative damage, such as 4-hydroxynonenal (HNE), can react with proteins to impair cell viability. There is convincing evidence for the involvement of nitric oxide that reacts with superoxide to produce peroxynitrite and ultimately hydroxyl radical production. Recently, altered ubiquitination and degradation of proteins have been implicated as key to dopaminergic cell death in PD. Oxidative stress can impair these processes directly, and products of oxidative damage, such as HNE, can damage the 26S proteasome. Furthermore, impairment of proteasomal function leads to free radical generation and oxidative stress. Oxidative stress occurs in idiopathic PD and products of oxidative damage interfere with cellular function, but these form only part of a cascade, and it is not possible to separate them from other events involved in dopaminergic cell death.

Glutaredoxin is essential for maintenance of brain mitochondrial complex I: studies with MPTP

Mitochondrial complex I dysfunction is implicated in the pathogenesis of neurodegenerative disorders such as Parkinson's disease. Identification of factors involved in maintenance and restoration of complex I function could potentially help to develop prophylactic and therapeutic strategies for treatment of this class of disorders. Down-regulation of glutaredoxin (thioltransferase, a thiol disulfide oxido-reductase) using antisense oligonucleotides results in the loss of mitochondrial complex I activity in mouse brain. 1-Methyl-4-phenyl-1,2,3,6,tetrahydro-pyridine (MPTP), the neurotoxin that causes Parkinson's disease-like symptoms in primates and dopaminergic cell loss in mice, acts through the inhibition of complex I. Regeneration of complex I activity in the striatum occurs concurrently with increase in glutaredoxin activity, 4 h after the neurotoxic insult, and is mediated through activation of activating protein-1. Down-regulation of glutaredoxin using anti-sense oligonucleotides prevents recovery of complex I in the striatum after MPTP treatment, providing support for the critical role for glutaredoxin in recovery of mitochondrial function in brain. Maintenance and restoration of protein thiol homeostasis by glutaredoxin may be important factors in preventing complex I dysfunction.

Alterations in mitochondrial function in a mouse model of hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease characterized by varying degrees of ventricular hypertrophy and myofibrillar disarray. Mutations in cardiac contractile proteins cause HCM. However, there is an unexplained wide variability in the clinical phenotype, and it is likely that there are multiple contributing factors. Because mitochondrial dysfunction has been described in heart disease, we tested the hypothesis that mitochondrial dysfunction contributes to the varying HCM phenotypes. Mitochondrial function was assessed in two transgenic models of HCM: mice with a mutant myosin heavy chain gene (MyHC) or with a mutant cardiac troponin T (R92Q) gene. Despite mitochondrial ultrastructural abnormalities in both models, the rate of state 3 respiration was significantly decreased only in the mutant MyHC mice by approximately 23%. Notably, this decrease in state 3 respiration preceded hemodynamic dysfunction. The maximum activity of alpha-ketogutarate dehydrogenase as assayed in isolated disrupted mitochondria was decreased by 28% compared with isolated control mitochondria. In addition, complexes I and IV were decreased in mutant MyHC transgenic mice. Inhibition of beta-adrenergic receptor kinase, which is elevated in mutant MyHC mouse hearts, can prevent mitochondrial respiratory impairment in mutant MyHC mice. Thus our results suggest that mitochondria may contribute to the hemodynamic dysfunction seen in some forms of HCM and offer a plausible mechanism responsible for some of the heterogeneity of the disease phenotypes.

Inhibition of the alpha-ketoglutarate dehydrogenase complex alters mitochondrial function and cellular calcium regulation

Mitochondrial dysfunction occurs in many neurodegenerative diseases. The alpha-ketoglutarate dehydrogenase complex (KGDHC) catalyzes a key and arguably rate-limiting step of the tricarboxylic acid cycle (TCA). A reduction in the activity of the KGDHC occurs in brains and cells of patients with many of these disorders and may underlie the abnormal mitochondrial function. Abnormalities in calcium homeostasis also occur in fibroblasts from Alzheimer's disease (AD) patients and in cells bearing mutations that lead to AD. Thus, the present studies test whether the reduction of KGDHC activity can lead to the alterations in mitochondrial function and calcium homeostasis. alpha-Keto-beta-methyl-n-valeric acid (KMV) inhibits KGDHC activity in living N2a cells in a dose- and time-dependent manner. Surprisingly, concentration of KMV that inhibit in situ KGDHC by 80% does not alter the mitochondrial membrane potential (MMP). However, similar concentrations of KMV induce the release of cytochrome c from mitochondria into the cytosol, reduce basal [Ca(2+)](i) by 23% (P<0.005), and diminish the bradykinin (BK)-induced calcium release from the endoplasmic reticulum (ER) by 46% (P<0.005). This result suggests that diminished KGDHC activities do not lead to the Ca(2+) abnormalities in fibroblasts from AD patients or cells bearing PS-1 mutations. The increased release of cytochrome c with diminished KGDHC activities will be expected to activate other pathways including cell death cascades. Reductions in this key mitochondrial enzyme will likely make the cells more vulnerable to metabolic insults that promote cell death.

Thioltransferase (glutaredoxin) mediates recovery of motor neurons from excitotoxic mitochondrial injury

Mitochondrial dysfunction involving electron transport components is implicated in the pathogenesis of several neurodegenerative disorders and is a critical event in excitotoxicity. Excitatory amino acid L-beta-N-oxalylamino-L-alanine (L-BOAA), causes progressive corticospinal neurodegeneration in humans. In mice, L-BOAA triggers glutathione loss and protein thiol oxidation that disrupts mitochondrial complex I selectively in motor cortex and lumbosacral cord, the regions affected in humans. We examined the factors regulating postinjury recovery of complex I in CNS regions after a single dose of L-BOAA. The expression of thioltransferase (glutaredoxin), a protein disulfide oxidoreductase regulated through AP1 transcription factor was upregulated within 30 min of L-BOAA administration, providing the first evidence for functional regulation of thioltransferase during restoration of mitochondrial function. Regeneration of complex I activity in motor cortex was concurrent with increase in thioltransferase protein and activity, 1 hr after the excitotoxic insult. Pretreatment with alpha-lipoic acid, a thiol delivery agent that protects motor neurons from L-BOAA-mediated toxicity prevented the upregulation of thioltransferase and AP1 activation, presumably by maintaining thiol homeostasis. Downregulation of thioltransferase using antisense oligonucleotides prevented the recovery of complex I in motor cortex and exacerbated the mitochondrial dysfunction in lumbosacral cord, providing support for the critical role for thioltransferase in maintenance of mitochondrial function in the CNS.

Mitochondrial abnormalities and oxidative imbalance in neurodegenerative disease

An increasing body of evidence now suggests the involvement of mitochondrial abnormalities in the etiology of neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer disease. In this Perspective, we describe a recent study that shows that treatment of human patients with the antioxidant coenzyme Q(10'), which functions in concert with certain mitochondrial enzymes, reduced the worsening of symptoms associated with PD. These findings are consistent with the hypothesis that mitochondrial dysfunction plays a role in the pathogenesis of PD and that treatments that target mitochondrial biochemistry might ameliorate the functional decline observed in patients suffering from PD.

Selective inactivation of redox-sensitive mitochondrial enzymes during cardiac reperfusion

Reperfusion of ischemic myocardial tissue results in an increase in mitochondrial free radical production and declines in respiratory activity. The effects of ischemia and reperfusion on the activities of Krebs cycle enzymes, as well as enzymes involved in electron transport, were evaluated to provide insight into whether free radical events are likely to affect enzymatic and mitochondrial function(s). An in vivo rat model was utilized in which ischemia is induced by ligating the left anterior descending coronary artery. Reperfusion, initiated by release of the ligature, resulted in a significant decline in NADH-linked ADP-dependent mitochondrial respiration as assessed in isolated cardiac mitochondria. Assays of respiratory chain complexes revealed reduction in the activities of complex I and, to a lesser extent, complex IV exclusively during reperfusion, with no alterations in the activities of complexes II and III. Moreover, Krebs cycle enzymes alpha-ketoglutarate dehydrogenase and aconitase were susceptible to reperfusion-induced inactivation with no decline in the activities of other Krebs cycle enzymes. The decline in alpha-ketoglutarate dehydrogenase activity during reperfusion was associated with a loss in native lipoic acid on the E2 subunit, suggesting oxidative inactivation. Inhibition of complex I in vitro promotes free radical generation. alpha-Ketoglutarate dehydrogenase and aconitase are uniquely susceptible to in vitro oxidative inactivation. Thus, our results suggest a scenario in which inhibition of complex I promotes free radical production leading to oxidative inactivation of alpha-ketoglutarate dehydrogenase and aconitase.

Mice deficient in TNF receptors are protected against dopaminergic neurotoxicity: implications for Parkinson's disease

The pathogenic mechanisms underlying idiopathic Parkinson's disease (PD) remain enigmatic. Recent findings suggest that inflammatory processes are associated with several neurodegenerative disorders, including PD. Enhanced expression of the proinflammatory cytokine, tumor necrosis factor (TNF)-alpha, has been found in association with glial cells in the substantia nigra of patients with PD. To determine the potential role for TNF-alpha in PD, we examined the effects of the 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP), a dopaminergic neurotoxin that mimics some of the key features associated with PD, using transgenic mice lacking TNF receptors. Administration of MPTP to wild-type (+/+) mice resulted in a time-dependent expression of TNF-alpha in striatum, which preceded the loss of dopaminergic markers and reactive gliosis. In contrast, transgenic mice carrying homozygous mutant alleles for both the TNF receptors (TNFR-DKO), but not the individual receptors, were completely protected against the dopaminergic neurotoxicity of MPTP. The data indicate that the proinflammatory cytokine TNF-alpha is an obligatory component of dopaminergic neurodegeneration. Moreover, because TNF-alpha is synthesized predominantly by microglia and astrocytes, our findings implicate the participation of glial cells in MPTP-induced neurotoxicity. Similar mechanisms may underlie the etiopathogenesis of PD.

Antiparkinsonian drugs and their neuroprotective effects

In Parkinson's disease, while dopamine (DA) replacement therapy, such as with L-DOPA (levodopa), improves the symptoms, it does not inhibit the degeneration of DA neurons in the substantia nigra. Numerous studies have suggested that both endogenous and environmental neurotoxins and oxidative stress may participate in this disease, but the detailed mechanisms are still unclear. Recent genetic studies in familial Parkinson's disease and parkinsonism have shown several gene mutations. This new information regarding its pathogenesis offers novel prospects for effective strategies involving the neuroprotection of vulnerable DA neurons. This review summarizes current findings regarding the pathogenesis and antiparkinsonian drugs, and discusses their possibilities of targets to develop novel neuroprotective drugs.

An AAV-derived Apaf-1 dominant negative inhibitor prevents MPTP toxicity as antiapoptotic gene therapy for Parkinson's disease

Adeno-associated virus (AAV) vector delivery of an Apaf-1-dominant negative inhibitor was tested for its antiapoptotic effect on degenerating nigrostriatal neurons in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. The wild-type caspase recruitment domain of Apaf-1 was used as a dominant negative inhibitor of Apaf-1 (rAAV-Apaf-1-DN-EGFP). An AAV virus vector was used to deliver it into the striatum of C57 black mice, and the animals were treated with MPTP. The number of tyrosine hydroxylase-positive neurons in the substantia nigra was not changed on the rAAV-Apaf-1-DN-EGFP injected side compared with the noninjected side. We also examined the effect of a caspase 1 C285G mutant as a dominant negative inhibitor of caspase 1 (rAAV-caspase-1-DN-EGFP) in the same model. However, there was no difference in the number of tyrosine hydroxylase-positive neurons between the rAAV-caspase-1-DN-EGFP injected side and the noninjected side. These results indicate that delivery of Apaf-1-DN by using an AAV vector system can prevent nigrostriatal degeneration in MPTP mice, suggesting that it could be a promising therapeutic strategy for patients with Parkinson's disease. The major mechanism of dopaminergic neuronal death triggered by MPTP seems to be the mitochondrial apoptotic pathway.

Laboratory approach to mitochondrial diseases

Dysfunction in mitochondrial processes has been related to several pathologies. In these disorders, the cell suffers oxidative imbalance that is mostly due to defects in pyruvate metabolism, mitochondrial fatty acids oxidation, the citric acid cycle or electron transport by the mitochondrial respiratory chain. These metabolic alterations produce mitochondrial diseases that have been related to inherited syndromes, such as MERRF or MELAS. The main affected organs are brain, skeletal muscle, kidney, heart and liver, because of the high energetic demand and the oxidative metabolism. Moreover, the relationship between mitochondrial dysfunction and neurodegenerative processes, such as Parkinson disease or Alzheimer disease, as well as ageing, has been shown. Because mitochondrias are the target of several xenobiotics, such as aspirin, AZT or alcohol consumption, mitochondrial impairment has also been proposed as a mechanism of toxicity. Most laboratory tests that are available in the diagnosis of mitochondrial illness are assayed in tissue biopsies and are usually difficult to interpret. Recently, it has been shown that non-invasive techniques, such as nuclear magnetic resonance or the 2-keto[1-(13)C]isocaproic acid breath test, may be useful to assess mitochondrial function. This article attempts to show the laboratory approach to mitochondrial diseases, reviewing new techniques that could be of great value in the research of mitochondrial function, such as the 2-keto[1-(13)C]isocaproic breath test.

Modulation of mitochondrial function by hydrogen peroxide

During normal cellular metabolism, mitochondrial electron transport results in the formation of superoxide anion (O(2)) and subsequently hydrogen peroxide (H(2)O(2)). Because H(2)O(2) increases in concentration under certain physiologic and pathophysiologic conditions and can oxidatively modify cellular components, it is critical to understand the response of mitochondria to H(2)O(2). In the present study, treatment of isolated rat heart mitochondria with H(2)O(2) resulted in a decline and subsequent recovery of state 3 NADH-linked respiration. Alterations in NADH levels induced by H(2)O(2) closely paralleled changes in the rate of state 3 respiration. Assessment of electron transport chain complexes and Krebs cycle enzymes revealed that alpha-ketoglutarate dehydrogenase (KGDH), succinate dehydrogenase (SDH), and aconitase were susceptible to H(2)O(2) inactivation. Of particular importance, KGDH and SDH activity returned to control levels, concurrent with the recovery of state 3 respiration. Inactivation is not because of direct interaction of H(2)O(2) with KGDH and SDH. In addition, removal of H(2)O(2) alone is not sufficient for reactivation. Enzyme activity does not recover unless mitochondria remain intact. The sensitivity of KGDH and SDH to H(2)O(2)-mediated inactivation and the reversible nature of inactivation suggest a potential role for H(2)O(2) in the regulation of KGDH and SDH.

Brain regional development of the activity of alpha-ketoglutarate dehydrogenase complex in the rat

This study was initiated to test the hypothesis that the development of alpha-ketoglutarate dehydrogenase complex (KGDHC) activity, like that of pyruvate dehydrogenase complex, is one of the late developers of tricarboxylic acid (TCA) cycle enzymes. The postnatal development of KGDHC in rat brain exhibits four distinct region-specific patterns. The age-dependent increases in olfactory bulb (OB) and hypothalamus (HYP) form one pattern: low in postnatal days (P) 2 and 4, KGDHC activity rose linearly to attain adult level at P30. The increases in mid-brain (MB) and striatum (ST) constitute a second pattern: being <40% of adult level at P2 and P4, KGDHC activity rose steeply between P10 and P17 and attained adult level by P30. The increases in cerebellum (CB), cerebral cortex (CC), and hippocampus (HIP) form a third pattern: being 25-30% of adult level at P2 and P4, KGDHC activity doubled between P10 and P17 and rose to adult level by P30. KGDHC activity development is unique in pons and medulla (PM): being >60% of the adult level at P2, it rose rapidly to adult level by P10. Thus, KGDHC activity develops earlier in phylogenetically older regions (PM) than in phylogenetically younger regions (CB, CC, HIP). Being lowest in activity among all TCA cycle enzymes, KGDHC activity in any region at any age will exert a limit on the maximum TCA cycle flux therein. The results may have functional and pathophysiological implications in control of brain glucose oxidative metabolism, energy metabolism, and neurotransmitter syntheses.

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.

Oxidative stress and genetics in the pathogenesis of Parkinson's disease

Parkinson's Disease (PD) is the second most common chronic neurodegenerative disease characterized by the progressive loss of dopamine neurons, leading to rigidity, slowness of movement, rest tremor, gait disturbances, and imbalance. Although there is effective symptomatic treatment for PD, there is no proven preventative or regenerative therapy. The etiology of this disorder remains unknown. Recent genetic studies have identified mutations in alpha-synuclein as a rare cause of autosomal dominant familial PD and mutations in parkin as a cause of autosomal recessive familial PD. The more common sporadic form of PD is thought to be due to oxidative stress and derangements in mitochondrial complex I activity. Understanding the mechanism by which familial linked mutations and oxidative stress cause PD has tremendous potential for unraveling the mechanisms of dopamine cell death in PD. In this article, we review recent advances in the understanding of the role of genetics and oxidative stress in the pathogenesis of PD.

Dopamine-induced apoptosis is mediated by oxidative stress and Is enhanced by cyanide in differentiated PC12 cells

Dopamine (DA) oxidation and the generation of reactive oxygen species (ROS) may contribute to the degeneration of dopaminergic neurons underlying various neurological conditions. The present study demonstrates that DA-induced cytotoxicity in differentiated PC12 cells is mediated by ROS and mitochondrial inhibition. Because cyanide induces parkinson-like symptoms and is an inhibitor of the antioxidant system and mitochondrial function, cells were treated with KCN to study DA toxicity in an impaired neuronal system. Differentiated PC12 cells were exposed to DA, KCN, or a combination of the two for 12-36 h. Lactate dehydrogenase (LDH) assays indicated that both DA (100-500 microM) and KCN (100-500 microM) induced a concentration- and time-dependent cell death and that their combination produced an increase in cytotoxicity. Apoptotic death, measured by Hoechst dye and TUNEL (terminal deoxynucleotidyltransferase dUTP nick end-labeling) staining, was also concentration- and time-dependent for DA and KCN. DA plus KCN produced an increase in apoptosis, indicating that KCN, and thus an impaired system, enhances DA-induced apoptosis. To study the mechanism(s) of DA toxicity, cells were pretreated with a series of compounds and incubated with DA (300 microM) and/or KCN (100 microM) for 24 h. Nomifensine, a DA reuptake inhibitor, rescued nearly 60-70% of the cells from DA- and DA plus KCN-induced apoptosis, suggesting that DA toxicity is in part mediated intracellularly. Pretreatment with antioxidants attenuated DA- and KCN-induced apoptosis, indicating the involvement of oxidative species. Furthermore, buthionine sulfoximine, an inhibitor of glutathione synthesis, increased the apoptotic response, which was reversed when cells were pretreated with antioxidants. DA and DA plus KCN produced a significant increase in intracellular oxidant generation, supporting the involvement of oxidative stress in DA-induced apoptosis. The nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester and the peroxynitrite scavenger uric acid blocked apoptosis and oxidant production, indicating involvement of nitric oxide. These results suggest that DA neurotoxicity is enhanced under the conditions induced by cyanide and involves both ROS and nitric oxide-mediated oxidative stress as an initiator of apoptosis.