Platelet mitochondrial respiratory chain function in Parkinson's disease

A blood-based marker of mitochondrial DNA damage in Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, and neuroprotective or disease-modifying interventions remain elusive. High-throughput markers aimed at stratifying patients on the basis of shared etiology are required to ensure the success of disease-modifying therapies in clinical trials. Mitochondrial dysfunction plays a prominent role in the pathogenesis of PD. Previously, we found brain region-specific accumulation of mitochondrial DNA (mtDNA) damage in PD neuronal culture and animal models, as well as in human PD postmortem brain tissue. To investigate mtDNA damage as a potential blood-based marker for PD, we describe herein a PCR-based assay (Mito DNADX) that allows for the accurate real-time quantification of mtDNA damage in a scalable platform. We found that mtDNA damage was increased in peripheral blood mononuclear cells derived from patients with idiopathic PD and those harboring the PD-associated leucine-rich repeat kinase 2 (LRRK2) G2019S mutation in comparison with age-matched controls. In addition, mtDNA damage was elevated in non-disease-manifesting LRRK2 mutation carriers, demonstrating that mtDNA damage can occur irrespective of a PD diagnosis. We further established that Lrrk2 G2019S knock-in mice displayed increased mtDNA damage, whereas Lrrk2 knockout mice showed fewer mtDNA lesions in the ventral midbrain, compared with wild-type control mice. Furthermore, a small-molecule kinase inhibitor of LRRK2 mitigated mtDNA damage in a rotenone PD rat midbrain neuron model and in idiopathic PD patient-derived lymphoblastoid cell lines. Quantifying mtDNA damage using the Mito DNADX assay may have utility as a candidate marker of PD and for measuring the pharmacodynamic response to LRRK2 kinase inhibitors.

3α,7-Dihydroxy-14(13→12)abeo-5β,12α(H),13β(H)-cholan-24-oic Acids Display Neuroprotective Properties in Common Forms of Parkinson's Disease

Parkinson's Disease is the most common neurodegenerative movement disorder globally, with prevalence increasing. There is an urgent need for new therapeutics which are disease-modifying rather than symptomatic. Mitochondrial dysfunction is a well-documented mechanism in both sporadic and familial Parkinson's Disease. Furthermore, ursodeoxycholic acid (UDCA) has been identified as a bile acid which leads to increased mitochondrial function in multiple in vitro and in vivo models of Parkinson's Disease. Here, we describe the synthesis of novel C-nor-D-homo bile acid derivatives and the 12-hydroxy-methylated derivative of lagocholic acid (7) and their biological evaluation in fibroblasts from patients with either sporadic or LRRK2 mutant Parkinson's Disease. These compounds boost mitochondrial function to a similar level or above that of UDCA in many assays; notable, however, is their ability to boost mitochondrial function to a higher level and at lower concentrations than UDCA specifically in the fibroblasts from LRRK2 patients. Our study indicates that novel bile acid chemistry could lead to the development of more efficacious bile acids which increase mitochondrial function and ultimately cellular health at lower concentrations proving attractive potential novel therapeutics for Parkinson's Disease.

Is there a special relationship between complex I activity and nigral neuronal loss in Parkinson's disease? A critical reappraisal

Parkinson’s disease (PD) is a progressive neurodegenerative disease manifesting both motor and non-motor symptoms. The motor features are generally ascribed to the selective loss of dopamine neurons within the substantia nigra pars compacta. While the precise etiology of PD remains elusive, multiple genetic and environmental elements have emerged as contributing factors. The discovery of MPTP-induced parkinsonism directed intense inquiry towards mitochondrial pathways, with a specific focus on mitochondrial complex I. Consisting of more than 40 subunits, complex I is the first enzyme of the electron transport chain that is required for mitochondrial ATP production. In this review, we present a critical analysis of studies assessing the prevalence and specificity of mitochondrial complex I deficiency in PD. In addition, we take the novel view of incorporating the features of genetically-defined bona fide complex I disorders and the prevalence of nigral involvement in such cases. Through this innovative bi-directional view, we consider both complex I changes in a disease of the substantia nigra and nigral changes in diseases of complex I. We assess the strength of association between nigral cell loss and complex I deficits, as well as the oft under-appreciated heterogeneity of complex I deficiency disorders and the variability of the PD data.

Mitophagy and the Brain

Stress mechanisms have long been associated with neuronal loss and neurodegenerative diseases. The origin of cell stress and neuronal loss likely stems from multiple pathways. These include (but are not limited to) bioenergetic failure, neuroinflammation, and loss of proteostasis. Cells have adapted compensatory mechanisms to overcome stress and circumvent death. One mechanism is mitophagy. Mitophagy is a form of macroautophagy, were mitochondria and their contents are ubiquitinated, engulfed, and removed through lysosome degradation. Recent studies have implicated mitophagy dysregulation in several neurodegenerative diseases and clinical trials are underway which target mitophagy pathways. Here we review mitophagy pathways, the role of mitophagy in neurodegeneration, potential therapeutics, and the need for further study.

A Ketone Ester Drink Enhances Endurance Exercise Performance in Parkinson's Disease

Objectives

Routine exercise is thought to be among the only disease-modifying treatments for Parkinson's disease; however, patients' progressive loss of physical ability limits its application. Therefore, we sought to investigate whether a ketone ester drink, which has previously been shown to enhance endurance exercise performance in elite athletes, could also improve performance in persons with Parkinson's disease.

Participants

14 patients, aged 40-80 years, with Hoehn and Yahr stage 1-2 Parkinson's disease.

Intervention

A randomized, placebo-controlled, crossover study in which each participant was administered a ketone ester drink or an isocaloric carbohydrate-based control drink on separate occasions prior to engaging in a steady state cycling test at 80 rpm to assess endurance exercise performance.

Outcomes Measures

The primary outcome variable was length of time participants could sustain a therapeutic 80 rpm cadence. Secondary, metabolic outcomes measures included cardiorespiratory parameters as well as serum β-hydroxybutyrate, glucose, and lactate.

Results

The ketone ester increased the time that participants were able to sustain an 80 rpm cycling cadence by 24 ± 9% (p = 0.027). Correspondingly, the ketone ester increased β-hydroxybutyrate levels to >3 mmol/L and decreased respiratory exchange ratio, consistent with a shift away from carbohydrate-dependent metabolism.

Conclusion

Ketone ester supplementation improved endurance exercise performance in persons with Parkinson's disease and may, therefore, be useful as an adjunctive therapy to enhance the effectiveness of exercise treatment for Parkinson's disease.

Multivariate meta-analyses of mitochondrial complex I and IV in major depressive disorder, bipolar disorder, schizophrenia, Alzheimer disease, and Parkinson disease

Complex I (NADH dehydrogenase, NDU) and complex IV (cytochrome-c-oxidase, COX) of the mitochondrial electron transport chain have been implicated in the pathophysiology of major psychiatric disorders, such as major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ), as well as in neurodegenerative disorders, such as Alzheimer disease (AD) and Parkinson disease (PD). We conducted meta-analyses comparing complex I and IV in each disorder MDD, BD, SZ, AD, and PD, as well as in normal aging. The electronic databases Pubmed, EMBASE, CENTRAL, and Google Scholar, were searched for studies published between 1980 and 2018. Of 2049 screened studies, 125 articles were eligible for the meta-analyses. Complex I and IV were assessed in peripheral blood, muscle biopsy, or postmortem brain at the level of enzyme activity or subunits. Separate meta-analyses of mood disorder studies, MDD and BD, revealed moderate effect sizes for similar abnormality patterns in the expression of complex I with SZ in frontal cortex, cerebellum and striatum, whereas evidence for complex IV alterations was low. By contrast, the neurodegenerative disorders, AD and PD, showed strong effect sizes for shared deficits in complex I and IV, such as in peripheral blood, frontal cortex, cerebellum, and substantia nigra. Beyond the diseased state, there was an age-related robust decline in both complexes I and IV. In summary, the strongest support for a role for complex I and/or IV deficits, is in the pathophysiology of PD and AD, and evidence is less robust for MDD, BD, or SZ.

Procyanidin protects against 6-hydroxydopamine-induced dopaminergic neuron damage via the regulation of the PI3K/Akt signalling pathway

Over the past 200 years, Parkinson's disease (PD) has remained an insurmountable challenge. Despite the existence of numerous therapeutic drugs, there are still not enough treatments in the face of the complex pathogenesis of PD. Therefore, the search for more effective therapeutic drugs for PD has extremely important practical significance. Procyanidin (PC), widely found in plants such as grapes, is a bioflavonoid antioxidant with a special molecular structure that can effectively remove free radicals in the human body. To explore its possible mechanism in PD, we used 6-hydroxydopamine (6-OHDA, 8 μg) to mimic dopaminergic (DA) neuronal damage and validated this model in vivo and in vitro. in vivo, we detected an effect of PC (60 mg/kg) on the behavioural changes exhibited in 6-OHDA model rats, the number of DA neurons and the phosphorylation of protein kinase B (Akt). in vitro, we detected changes in cell viability, mitochondrial membrane potential (MMP) and total superoxide dismutase (SOD) and explored the role of PC (50 μM) by inhibiting the phosphoinositide 3-kinase (PI3K)/Akt signalling pathway with LY294002 (20 μM). The present study demonstrates that PC plays a protective role against 6-OHDA-induced neurotoxicity, which may be mediated through the activation of the PI3K/Akt signalling pathway. This study indicates a potential use for PC in the treatment and prevention of PD.

A Useful Device to Measure Kinetics of Platelet Contraction

Platelet contraction provides a minimally invasive source for physiologic information. In this article, we describe a device that directly measures the kinetics of platelet contraction. Whole blood is injected between acrylic plates and an adherent clot forms. The bottom plate is fixed, and the top plate is attached to a wire cantilever. Platelet contraction drives deflection of the wire cantilever which is captured by a camera. Force generated by the clot with time is derived using beam equations. Force derivations were verified using a microelectromechanical (MEMS) force sensor. Kinetics of clot contraction were defined, including maximum contraction force (FMAX), lift-off time (TLIFTOFF), and contraction rate (CR). Metrics were compared with optical aggregometry and thromboelastography. FMAX correlates with optical aggregometry maximal amplitude with a Spearman's rho of 0.7904 and p = 0.0195 and thromboelastography maximal amplitude with a Spearman's rho of 0.8857 and p = 0.0188. Lift-off time correlates with optical aggregometry lag time with a Spearman's rho of 0.9048 and p = 0.002. This preliminary study demonstrates the repeatability of a useful platelet contraction device and its correlation with thromboelastography and optical aggregometry, the gold standard platelet function test.

Mitochondrial abnormalities in Parkinson's disease and Alzheimer's disease: can mitochondria be targeted therapeutically?

Mitochondrial abnormalities have been identified as a central mechanism in multiple neurodegenerative diseases and, therefore, the mitochondria have been explored as a therapeutic target. This review will focus on the evidence for mitochondrial abnormalities in the two most common neurodegenerative diseases, Parkinson's disease and Alzheimer's disease. In addition, we discuss the main strategies which have been explored in these diseases to target the mitochondria for therapeutic purposes, focusing on mitochondrially targeted antioxidants, peptides, modulators of mitochondrial dynamics and phenotypic screening outcomes.

Platelet biomechanics, platelet bioenergetics, and applications to clinical practice and translational research

The purpose of this review is to explore the relationship between platelet bioenergetics and biomechanics and how this relationship affects the clinical interpretation of platelet function devices. Recent experimental and technological advances highlight platelet bioenergetics and biomechanics as alternative avenues for collecting clinically relevant data. Platelet bioenergetics drive energy production for key biomechanical processes like adhesion, spreading, aggregation, and contraction. Platelet function devices like thromboelastography, thromboelastometry, and aggregometry measure these biomechanical processes. Platelet storage, stroke, sepsis, trauma, or the activity of antiplatelet drugs alters measures of platelet function. However, the specific mechanisms governing these alterations in platelet function and how they relate to platelet bioenergetics are still under investigation.

Mitochondrial Respiration in Intact Peripheral Blood Mononuclear Cells and Sirtuin 3 Activity in Patients with Movement Disorders

OBJECTIVE

Mitochondrial dysfunction is considered a unifying pathophysiological explanation for movement disorders. Sirtuin 3 (SIRT3) exhibits deacetylase activity and antioxidant properties. The aim of the study was to analyze the mitochondrial respiration in peripheral blood mononuclear cells (PBMCs) and the SIRT3 activity in patients with movement disorders.

METHODS

Mitochondrial respiration was analyzed in intact PBMCs using the ROUTINE, LEAK, electron transfer system (ETS), and residual oxygen consumption (ROX) protocol by means of high-resolution respirometry. The SIRT3 expression and PBMC activity were measured using fluorometry. Ultrasound measurements of the echogenicity of the substantia nigra and the diameter of the 3rd ventricle were also performed.

RESULTS

Patients with movement disorders exhibited a lower ROUTINE respiration than controls (P = 0.0237). Reduced oxygen fluxes in the LEAK (P = 0.033) and ROX (P = 0.0486) states were observed in patients with movement disorders compared with controls. Decreased ROUTINE respiration (P = 0.007) and oxygen flux in the LEAK state (P = 0.0203) were observed in patients with PD with substantia nigra hyperechogenicity compared with controls. Decreased SIRT 3 deacetylase activity was found in patients with movement disorders.

CONCLUSION

Impaired mitochondrial respiration in intact PBMCs was associated with inhibited SIRT3 activity and neurodegeneration measures evaluated using ultrasound in patients with PD.

Parkinson's disease: Microglial/macrophage-induced immunoexcitotoxicity as a central mechanism of neurodegeneration

Parkinson's disease is one of the several neurodegenerative disorders that affects aging individuals, with approximately 1% of those over the age of 60 years developing the disorder in their lifetime. The disease has the characteristics of a progressive disorder in most people, with a common pattern of pathological change occurring in the nervous system that extends beyond the classical striatal degeneration of dopaminergic neurons. Earlier studies concluded that the disease was a disorder of alpha-synuclein, with the formation of aggregates of abnormal alpha-synuclein being characteristic. More recent studies have concluded that inflammation plays a central role in the disorder and that the characteristic findings can be accounted for by either mutation or oxidative damage to alpha-synuclein, with resulting immune reactions from surrounding microglia, astrocytes, and macrophages. What has been all but ignored in most of these studies is the role played by excitotoxicity and that the two processes are intimately linked, with inflammation triggered cell signaling enhancing the excitotoxic cascade. Further, there is growing evidence that it is the excitotoxic reactions that actually cause the neurodegeneration. I have coined the name immunoexcitotoxicity to describe this link between inflammation and excitotoxicity. It appears that the two processes are rarely, if ever, separated in neurodegenerative diseases.

Proteinopathy, oxidative stress and mitochondrial dysfunction: cross talk in Alzheimer's disease and Parkinson's disease

Alzheimer’s disease and Parkinson’s disease are two common neurodegenerative diseases of the elderly people that have devastating effects in terms of morbidity and mortality. The predominant form of the disease in either case is sporadic with uncertain etiology. The clinical features of Parkinson’s disease are primarily motor deficits, while the patients of Alzheimer’s disease present with dementia and cognitive impairment. Though neuronal death is a common element in both the disorders, the postmortem histopathology of the brain is very characteristic in each case and different from each other. In terms of molecular pathogenesis, however, both the diseases have a significant commonality, and proteinopathy (abnormal accumulation of misfolded proteins), mitochondrial dysfunction and oxidative stress are the cardinal features in either case. These three damage mechanisms work in concert, reinforcing each other to drive the pathology in the aging brain for both the diseases; very interestingly, the nature of interactions among these three damage mechanisms is very similar in both the diseases, and this review attempts to highlight these aspects. In the case of Alzheimer’s disease, the peptide amyloid beta (Aβ) is responsible for the proteinopathy, while α-synuclein plays a similar role in Parkinson’s disease. The expression levels of these two proteins and their aggregation processes are modulated by reactive oxygen radicals and transition metal ions in a similar manner. In turn, these proteins – as oligomers or in aggregated forms – cause mitochondrial impairment by apparently following similar mechanisms. Understanding the common nature of these interactions may, therefore, help us to identify putative neuroprotective strategies that would be beneficial in both the clinical conditions.

Mitochondrial Dysfunction and α-Synuclein Synaptic Pathology in Parkinson's Disease: Who's on First?

Parkinson's disease (PD) is the most common neurodegenerative movement disorder. Its characteristic neuropathological features encompass the loss of dopaminergic neurons of the nigrostriatal system and the presence of Lewy bodies and Lewy neurites. These are intraneuronal and intraneuritic proteinaceous insoluble aggregates whose main constituent is the synaptic protein α-synuclein. Compelling lines of evidence indicate that mitochondrial dysfunction and α-synuclein synaptic deposition may play a primary role in the onset of this disorder. However, it is not yet clear which of these events may come first in the sequel of processes leading to neurodegeneration. Here, we reviewed data supporting either that α-synuclein synaptic deposition precedes and indirectly triggers mitochondrial damage or that mitochondrial deficits lead to neuronal dysfunction and α-synuclein synaptic accumulation. The present overview shows that it is still difficult to establish the exact temporal sequence and contribution of these events to PD.

Platelet mitochondrial activity and pesticide exposure in early Parkinson's disease

BACKGROUND

Mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson's disease (PD), but the cause of this dysfunction is unclear.

METHODS

Platelet mitochondrial complex I and I/III (nicotinamide adenine dinucleotide cytochrome c reductase, NCCR) activities were measured in early PD patients and matched controls enrolled in a population-based case-control study. Ambient agricultural pesticide exposures were assessed with a geographic information system and California Pesticide Use Registry.

RESULTS

In contrast to some previous reports, we found no differences in complex I and I/III activities in subjects with PD and controls. We did find that NCCR activity correlated with subjects' exposure to pesticides known to inhibit mitochondrial activity regardless of their diagnosis.

CONCLUSIONS

Electron transport chain (ETC) activity is not altered in PD in this well-characterized cohort when compared with community-matched controls but appears to be affected by environmental toxins, such as mitochondria-inhibiting pesticides.

Central pathways causing fatigue in neuro-inflammatory and autoimmune illnesses

BACKGROUND

The genesis of severe fatigue and disability in people following acute pathogen invasion involves the activation of Toll-like receptors followed by the upregulation of proinflammatory cytokines and the activation of microglia and astrocytes. Many patients suffering from neuroinflammatory and autoimmune diseases, such as multiple sclerosis, Parkinson's disease and systemic lupus erythematosus, also commonly suffer from severe disabling fatigue. Such patients also present with chronic peripheral immune activation and systemic inflammation in the guise of elevated proinflammtory cytokines, oxidative stress and activated Toll-like receptors. This is also true of many patients presenting with severe, apparently idiopathic, fatigue accompanied by profound levels of physical and cognitive disability often afforded the non-specific diagnosis of chronic fatigue syndrome.

DISCUSSION

Multiple lines of evidence demonstrate a positive association between the degree of peripheral immune activation, inflammation and oxidative stress, gray matter atrophy, glucose hypometabolism and cerebral hypoperfusion in illness, such as multiple sclerosis, Parkinson's disease and chronic fatigue syndrome. Most, if not all, of these abnormalities can be explained by a reduction in the numbers and function of astrocytes secondary to peripheral immune activation and inflammation. This is also true of the widespread mitochondrial dysfunction seen in otherwise normal tissue in neuroinflammatory, neurodegenerative and autoimmune diseases and in many patients with disabling, apparently idiopathic, fatigue. Given the strong association between peripheral immune activation and neuroinflammation with the genesis of fatigue the latter group of patients should be examined using FLAIR magnetic resonance imaging (MRI) and tested for the presence of peripheral immune activation.

SUMMARY

It is concluded that peripheral inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in many patients with neuroimmune and autoimmune diseases.This would also appear to be the case for many patients afforded a diagnosis of Chronic Fatigue Syndrome.

Platelet mitochondrial membrane potential in Parkinson's disease

Objective

Mitochondrial dysfunction is a hallmark of idiopathic Parkinson's disease (IPD), which has been reported not to be restricted to striatal neurons. However, studies that analyzed mitochondrial function at the level of selected enzymatic activities in peripheral tissues have produced conflicting data. We considered the electron transport chain as a complex system with mitochondrial membrane potential as an integrative indicator for mitochondrial fitness.

Methods

Twenty-five IPD patients (nine females; mean disease duration, 6.2 years) and 16 healthy age-matched controls (12 females) were recruited. Live platelets were purified using magnetic-activated cell sorting (MACS) and single-cell data on mitochondrial membrane potential (Δψ) were measured by cytometry and challenged with a protonophore agent.

Results

Functional mitochondrial membrane potential was detected in all participants. The challenge test reduced the membrane potential in all IPD patients and controls (P < 0.001). However, the response to the challenge was not significantly different between patients and controls.

Interpretation

While the reported protonophore challenge assay is a valid marker of overall mitochondrial function in live platelets, intact mitochondrial membrane potential in platelets derived from IPD patients suggests that presumed mitochondrial enzymatic deficiencies are compensable in this cell type. In consequence, mitochondrial membrane potential in platelets cannot be used as a diagnostic biomarker for nonstratified IPD but should be further explored in potential Parkinson's disease subtypes and tissues with higher energy demands.

Daily electromyography in females with Parkinson's disease: a potential indicator of frailty

Females with Parkinson's disease (PD) are at increased risk for frailty, yet are often excluded from frailty studies. Daily electromyography (EMG) recordings of muscle activity can dissociate stages of frailty and indicate functional decline in non-neurological conditions. The purpose of this investigation was to determine whether muscle activity can be used to identify frailty phenotypes in females with PD. EMG during a typical 6.5-h day was examined in biceps brachii, triceps brachii, vastus lateralis and biceps femoris on less-affected PD side. Muscle activity was quantified through burst (>2% maximum exertion, >0.1s) and gap characteristics (<1% maximum exertion, >0.1s). Differences across frailty phenotype (nonfrail, prefrail, frail) and muscle (biceps brachii, BB; triceps brachii, TB; vastus lateralis, VL; biceps femoris, BF) were evaluated with a 2-way repeated measure ANOVA for each burst/gap characteristic. Thirteen right-handed females (mean=67 ± 8 years) were classified as nonfrail (n = 4), prefrail (n = 6), and frail (n = 3) according to the Cardiovascular Health Study frailty index (CHSfi). Frail females had 73% decreased gaps and 48% increased burst duration compared with nonfrail. Decreased gaps may be interpreted as reduced muscle recovery time, which may result in earlier onset fatigue and eventually culminating in frailty. Longer burst durations suggest more muscle activity is required to initiate movement leading to slower movement time in frail females with PD. This is the first study to use EMG to dissociate frailty phenotypes in females with PD during routine daily activities and provides insight into how PD-associated motor declines contributes to frailty and functional decline.

Deep brain stimulation modulates nonsense-mediated RNA decay in Parkinson's patients leukocytes

BACKGROUND

Nonsense-Mediated decay (NMD) selectively degrades mRNA transcripts that carry premature stop codons. NMD is often triggered by alternative splicing (AS) modifications introducing such codons. NMD plays an important regulatory role in brain neurons, but the in vivo dynamics of AS and NMD changes in neurological diseases and under treatment were scarcely explored.

RESULTS

Here, we report exon arrays analysis of leukocyte mRNA AS events prior to and following Deep Brain Stimulation (DBS) neurosurgery, which efficiently improves the motor symptoms of Parkinson's disease (PD), the leading movement disorder, and is increasingly applied to treat other diseases. We also analyzed publicly available exon array dataset of whole blood cells from mixed early and advanced PD patients. Our in-house exon array dataset of leukocyte transcripts was derived from advanced PD patients' pre- and post-DBS stimulation and matched healthy control volunteers. The mixed cohort exhibited 146 AS changes in 136 transcripts compared to controls, including 9 NMD protein-level assessed events. In comparison, PD patients from our advanced cohort differed from healthy controls by 319 AS events in 280 transcripts, assessed as inducing 27 protein-level NMD events. DBS stimulation induced 254 AS events in 229 genes as compared to the pre-DBS state including 44 NMD inductions. A short, one hour electrical stimulus cessation caused 234 AS changes in 125 genes compared to ON-stimulus state, 22 of these were assessed for NMD. Functional analysis highlighted disease-induced DNA damage and inflammatory control and its reversal under ON and OFF stimulus as well as alternative splicing in all the tested states.

CONCLUSIONS

The study findings indicate a potential role for NMD both in PD and following electrical brain stimulation. Furthermore, our current observations entail future implications for developing therapies for PD, and for interfering with the impaired molecular mechanisms that underlie PD and other neurodegenerative and neurological disorders, as well as DBS-treatable conditions in general.

Platelet mitochondrial complex I and I+III activities do not correlate with cerebral mitochondrial oxidative metabolism

Assays of mitochondrial electron transport system (ETS) activity in circulating blood platelets have been used to investigate the cause of neurodegenerative diseases. However, the correspondence between platelet ETS function and cerebral mitochondrial metabolism is not well characterized. To assess the validity of using platelet ETS activity to infer cerebral mitochondrial metabolism, we measured platelet ETS activity (complex I and complex I+III), cerebral metabolic rate of oxygen (CMRO(2)), and the CMRO(2)/cerebral metabolic rate for glucose ratio in 40 subjects: 7 with never-medicated Parkinson's disease, 13 with genetically proved Huntington's disease, and 20 normal controls. We found no correlation between in vivo measures of cerebral mitochondrial oxidative metabolism and ex vivo assays of platelet complex I and complex I+III activity performed on blood collected immediately before cerebral metabolism studies. We saw no evidence of a threshold effect when comparing platelet complex I and complex I+III activity with cerebral oxidative metabolism across a 4- to 10-fold range of platelet ETS activity. On the basis of these data, we conclude that measures of mitochondrial complex I and I+III activity in platelets within the ranges we have studied do not correlate with oxidative function of cerebral mitochondria.

Oxidative stress in skin fibroblasts cultures from patients with Parkinson's disease

BACKGROUND

In the substantia nigra of Parkinson's disease (PD) patients, increased lipid peroxidation, decreased activities of the mitochondrial complex I of the respiratory chain, catalase and glutathione-peroxidase, and decreased levels of reduced glutathione have been reported. These observations suggest that oxidative stress and mitochondrial dysfunction play a role in the neurodegeneration in PD. We assessed enzymatic activities of respiratory chain and other enzymes involved in oxidative processes in skin fibroblasts cultures of patients with PD.

METHODS

We studied respiratory chain enzyme activities, activities of total, Cu/Zn- and Mn-superoxide-dismutase, gluthatione-peroxidase and catalase, and coenzyme Q10 levels in skin fibroblasts cultures from 20 Parkinson's disease (PD) patients and 19 age- and sex- matched healthy controls.

RESULTS

When compared with controls, PD patients showed significantly lower specific activities for complex V (both corrected by citrate synthase activity and protein concentrations). Oxidized, reduced and total coenzyme Q10 levels (both corrected by citrate synthase and protein concentrations), and activities of total, Cu/Zn- and Mn-superoxide-dismutase, gluthatione-peroxidase and catalase, did not differ significantly between PD-patients and control groups. Values for enzyme activities in the PD group did not correlate with age at onset, duration, scores of the Unified Parkinson's Disease Rating scales and Hoehn-Yahr staging.

CONCLUSIONS

The main result of this study was the decreased activity of complex V in PD patients. This complex synthesizes ATP from ADP using an electrochemical gradient generated by complexes I-IV. These results suggest decreased energetic metabolism in fibroblasts of patients with PD.

MITOCHONDRIAL COMPLEX I, II/III, AND IV ACTIVITIES IN FAMILIAL AND SPORADIC PARKINSON'S DISEASE

A possible role of mitochondrial respiratory chain dysfunction in the pathogenesis of sporadic Parkinson's disease (PD) has been described. There are only a few reports concerning mitochondrial involvement in familial Parkinson's disease. The present study investigated mitochondrial complex I-IV activity in patients with sporadic and familial PD, compared to controls. Platelets were isolated from venous blood and platelet mitochondria were obtained through sonication and differential centrifugation. Complex I, II/III, and IV activities were measured in 17 patients with family history of Parkinson's disease (PDF), 15 patients with sporadic Parkinson disease (PDS), and 17 age-matched, healthy controls. The mitochondrial enzyme activities did not differ significantly between patient groups and controls. In addition, there was no correlation between mitochondrial complex activities and age, severity of disease, or age at onset of disease in the patient groups. In this study, the data indicate no significant differences in mitochondrial complex I-IV activities in PDF and PDS.

The role of PTEN-induced kinase 1 in mitochondrial dysfunction and dynamics

Mutations in parkin, PTEN-induced kinase 1 (PINK1) and DJ-1 can all cause autosomal recessive forms of Parkinson's disease. Recent data suggest that these recessive parkinsonism-associated genes converge within a single pathogenic pathway whose dysfunction leads to the loss of substantia nigra pars compacta neurons. The major common functional effects of all three genes relate to mitochondrial and oxidative damage, with a possible additional involvement of the ubiquitin proteasome system. This review highlights the role of the mitochondrial kinase, PINK1, in protection against mitochondrial dysfunction and how this might relate to loss of substantia nigra neurons in recessive parkinsonism.

Mitochondrial dysfunction in the limelight of Parkinson's disease pathogenesis

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder with unknown etiology. It is marked by widespread neurodegeneration in the brain with profound loss of A9 midbrain dopaminergic neurons in substantia nigra pars compacta. Several theories of biochemical abnormalities have been linked to pathogenesis of PD of which mitochondrial dysfunction due to an impairment of mitochondrial complex I and subsequent oxidative stress seems to take the center stage in experimental models of PD and in postmortem tissues of sporadic forms of illness. Recent identification of specific gene mutations and their influence on mitochondrial functions has further reinforced the relevance of mitochondrial abnormalities in disease pathogenesis. In both sporadic and familial forms of PD abnormal mitochondrial paradigms associated with disease include impaired functioning of the mitochondrial electron transport chain, aging associated damage to mitochondrial DNA, impaired calcium buffering, and anomalies in mitochondrial morphology and dynamics. Here we provide an overview of specific mitochondrial functions affected in sporadic and familial PD that play a role in disease pathogenesis. We propose to utilize these gained insights to further streamline and focus the research to better understand mitochondria's role in disease development and exploit potential mitochondrial targets for therapeutic interventions in PD pathogenesis.

Vitamin E and neurodegenerative diseases

Vitamin E is essential for neurological function. This fact, together with a growing body of evidence indicating that neurodegenerative processes are associated with oxidative stress, lead to the convincing idea that several neurological disorders may be prevented and/or cured by the antioxidant properties of vitamin E. In this review, some aspects related to the role of vitamin E against Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and ataxia with vitamin E deficiency will be presented.

Manganese exposure and induced oxidative stress in the rat brain

Neurotoxicity linked to excessive brain manganese levels can occur as a result of high level Mn exposures and/or metabolic aberrations (liver disease and decreased biliary excretion). Increased brain manganese levels have been reported to induce oxidative stress, as well as alterations in neurotransmitter metabolism with concurrent neurobehavioral and motor deficits. Two putative mechanisms in which manganese can produce oxidative stress in the brain are: (1) via its oxidation of dopamine, and (2) interference with normal mitochondrial respiration. Measurements of antioxidant species (e.g., glutathione and metallothionein), and the abundance of proteins (enzymes) exquisitely sensitive to oxidation (e.g., glutamine synthetase) have been commonly used as biomarkers of oxidative stress, particularly in rat brain tissue. This paper examines the link between manganese neurotoxicity in the rat brain and common pathways to oxidative stress.

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.

Effect of smoking cessation on mitochondrial respiratory chain function

OBJECTIVE

Chronic smoking has been associated with diverse mitochondrial respiratory chain (MRC) dysfunction in lymphocytes, although inhibition of complex IV activity is the most consistent and relevant finding. These mitochondrial abnormalities have been proposed to contribute to pathogenesis of diseases associated with tobacco consumption. We assessed MRC function in peripheral lymphocytes from heavy smokers after cessation in smoking habit.

PATIENTS AND METHODS

We studied MRC function from peripheral lymphocytes of 10 healthy chronic smoker individuals (age 43 +/- 6 years; 50% women) before cessation of tobacco consumption (t0), and 7 (t1) and 28 (t2) days after cessation. Smoking abstinence was ascertained by measuring carboxyhemoglobin levels and carbon monoxide (CO) concentration in exhaled breath. Ten healthy nonsmoker individuals matched by age and gender were used as controls. Lymphocytes were isolated by Ficoll's gradient, and protein content was determined by Bradford's technique. MRC function was studied through double means: 1) individual enzyme activities of complex II, III, and IV were analyzed by means of spectrophotometry; 2) oxygen consumption was measured polarographically using pyruvate, succinate, and glycerol-3-phosphate (complex I, II, and III substrates, respectively) after lymphocyte permeabilization. Enzyme and oxidative activities were corrected by citrate synthase activity.

RESULTS

Smokers showed a significant decrease in complex IV activity (p = 0.05) and also in respiration of intact lymphocytes (p = 0.05) compared to controls. Eight chronic smokers remained abstinent during the study. Smoking cessation was associated with a significant recovery of complex IV (p = 0.01) and complex III (p = 0.05) activities. Oxidative activities did not show any change during the study.

CONCLUSION

Chronic smoking is associated with a decrease of complex IV and III activities of MRC, which return to normal values after cessation of tobacco smoking.

Circadian rhythms of oxidative phosphorylation: effects of rotenone and melatonin on isolated rat brain mitochondria

Mitochondrial experiments are of increasing interest in different fields of research. Inhibition of mitochondrian activities seems to play a role in Parkinson's disease and in this regard several animal models have used inhibitors of mitochondrial respiration such as rotenone or MPTP. Most of these experiments were done during the daytime. However, there is no reason for mitochondrial respiration to be constant during the 24 h. This study investigated the circadian variation of oxidative phosphorylation in isolated rat brain mitochondria and the administration-time-dependent effect of rotenone and melatonin. The respiratory control ratio, state 3 and state 4, displayed a circadian fluctuation. The highest respiratory control ratio value (3.01) occurred at 04:00 h, and the lowest value (2.63) at 08:00 h. The highest value of state 3 and state 4 oxidative respiration occurred at 12:00 h and the lowest one at 20:00 h. The 24 h mean decrease in the respiratory control ratio following incubation with melatonin and rotenone was 7 and 32%, respectively; however, the exact amount of the inhibition exerted by these agents varied according to the time of the mitochondria isolation. Our results show the time of mitochondrial isolation could lead to interindividual variability. When studies require mitochondrial isolation from several animals, the time between animal experiments has to be minimized. In oxidative phosphorylation studies, the time of mitochondria isolation must be taken into account, or at least specified in the methods section.

Evidence that alpha-synuclein functions as a negative regulator of Ca(++)-dependent alpha-granule release from human platelets

alpha-Synuclein has been implicated in the pathogenesis of Parkinson disease (PD) and related neurodegenerative disorders. More recently, it has been suggested to be an important regulatory component of vesicle transport in neuronal cells. alpha-Synuclein is also highly expressed in platelets and is loosely associated with the membrane of the secretory alpha-granules. However, the functional significance of these observations is unknown. In this study, the possible function of alpha-synuclein in vesicle transport, with particular regard to alpha-granule release from the platelets, was investigated. The results showed that ionomycin- or thrombin-induced alpha-granule secretion was inhibited by exogenous alpha-synuclein addition in a dose-dependent manner. However, [(3)H]5-HT release from the dense granules and hexosaminidase release from the lysosomal granules were not affected. Two point mutants (A30P and A53T) found in some familial types of PD, in addition to beta-synuclein and alpha-synuclein112, effectively inhibited PF4 release from the alpha-granules. However, the deletion mutants, which completely lacked either the N-terminal region or the C-terminal tail, did not affect alpha-granule release. Interestingly, exogenously added alpha-synuclein appeared to enter the platelets but did not change the Ca(++) level in the platelets at the resting state and the increase in the Ca(++) level on stimulation. Electron microscopy also supported that alpha-synuclein inhibits alpha-granule release. These results suggest that alpha-synuclein may function as a specific negative regulator of alpha-granule release in platelets.

Cytoplasmic transfer of platelet mtDNA from elderly patients with Parkinson's disease to mtDNA-less HeLa cells restores complete mitochondrial respiratory function

For determination of whether platelet mtDNA in patients with Parkinson's disease (PD) possesses some lesions to reduce respiratory enzyme activities, platelet mtDNA was transferred into mtDNA-less (rho0) HeLa cells from aged PD patients and age-matched normal subjects, since their activities were controlled by both mitochondrial and nuclear genomes. The resultant mtDNA-repopulated cybrid clones containing the HeLa nuclear genome as a common background were used for comparison of respiratory enzyme activities. Remarkable variations of the enzyme activities were observed in the cybrid clones, irrespective of whether their mtDNA was transferred from normal subjects or PD patients, and some of them showed 20% reduction of average activities. Thus, the mtDNA mutations responsible for inducing 20% reduction should be polymorphic rather than pathogenic. On the other hand, pathogenic control cybrid clones possessing mtDNA mutations from patients with mitochondrial disorders showed significant and specific decline of respiratory enzyme complex I activity beyond the normal range of the variations. These observations warrant reassessment of the conventional concept that complex I activity in platelets of PD patients is defective due to mtDNA mutations.

A Yorkshire family with adult-onset cranio-cervical primary torsion dystonia

Although a family history is described in approximately 20% of patients, large families with adult-onset craniocervical primary (idiopathic) torsion dystonia (PTD) are rare. We report a new British family with cranio-cervical dystonia. Seventeen members of the family were examined. Five cases were diagnosed as definite PTD and one as probable PTD. Mean age at onset was 29 years (range, 19-40 yrs). The phenotype was characterized by adult-onset cranio-cervical dystonia in all affected cases. A few cases had additional voice tremor and/or postural arm tremor. The GAG deletion in the DYT1 gene was excluded in the index case. Linkage analysis was performed between the disease and several marker loci spanning DYT6 and DYT7 regions, and haplotypes were reconstructed in all subjects. Although linkage analysis was not completely informative, reconstructed haplotypes excluded linkage between the disease and either DYT6 or DYT7. This report confirms that familial cranio-cervical dystonia is genetically heterogeneous, and further studies of other PTD families with similar clinical features are needed to identify other new genes.

Approach to neurotoxicity tort cases

This article provides the neurologist with simple methods that can be applied to all clinical neurologic evaluations, regardless of the future potential for litigation. This article defines the appropriate application and interpretation of conventional neurologic, neurophysiologic, neuropsychological, and biochemical diagnostic tests that are sensitive to neurotoxic exposures. This article also provides the neurologist with guidance in the preparation of clinical findings and tips on the recognition and use of supportive literature that is often required for admissibility of evidence at a deposition or testimony.

Unilateral thalamic deep brain stimulation for refractory essential tremor and Parkinson's disease tremor

OBJECTIVE

To determine the efficacy and tolerability of unilateral thalamic deep brain stimulation (DBS) for patients with medically refractory essential tremor (ET) and the tremor associated with Parkinson's disease (PD).

BACKGROUND

The tremor of ET and PD may produce functional disability despite optimal medical therapy. Several reports have demonstrated efficacy of thalamic DBS in this scenario.

METHODS

Preoperative and 3-month postoperative tremor ratings were compared in 33 patients (14 ET and 19 PD) with severe tremor. Evaluations included Unified Parkinson's Disease Rating Scale (UPDRS) scores for PD patients and a modified Unified Tremor Rating Scale in ET patients. Open-label and blinded data (unknown activation status) were obtained.

RESULTS

ET patients demonstrated an 83% reduction (p < 0.0001) in observed contralateral arm tremor. All measures of tremor including writing samples, pouring tests, subjective functional surveys, and disability scores improved significantly. PD patients demonstrated an 82% reduction (p < 0.0001) in contralateral tremor and significant improvement in disability and global impressions. There was, however, no meaningful improvement in other motor aspects of the disease, and the total UPDRS part II (activities of daily living) score did not change. Adverse events, more common in ET patients, were generally mild and were usually eliminated by adjustment of the device parameters.

CONCLUSIONS

Thalamic DBS is a safe and effective treatment of ET and the tremor of PD. In PD, its use should be limited to patients in whom high-amplitude tremor results directly in significant functional disability.

Mitochondrial DNA transmission of the mitochondrial defect in Parkinson's disease

Several groups have identified mitochondrial complex I deficiency in Parkinson's disease (PD) substantia nigra and in platelets. A search for any mitochondrial DNA (mtDNA) mutation underlying this defect has not yet produced any consistent result. We have made use of a mtDNA-less (p0) cell line to determine if the complex I deficiency follows the genomic transplantation of platelet mtDNA. From a preselected group of PD patients with low platelet complex I activity, 7 patients were used for detailed study. All 7 patients were used for mixed cybrid analysis and demonstrated a selective 25% deficiency of complex I activity. Individual clonal analysis of A549 p0/PD platelet fusion cybrids from 1 of the patients expressed combined complex I and IV deficiencies with 25% and 20% decreased activities in the PD clones, respectively. Histocytochemical, immunocytochemical, and cellular functional imaging studies of these clones showed the cells within the clones were heterogeneous with respect to cytochrome c oxidase (COX) function, COX I content, and mitochondrial respiratory chain activity. These results are in agreement with a previous study and support the proposition that an mtDNA abnormality may underlie the mitochondrial defect in at least a proportion of PD patients. This p0 technology may serve as a means to identify the subgroup of PD patients in whom an mtDNA defect may contribute to development of the disease.

Potential metabolic bioactivation pathways involving cyclic tertiary amines and azaarenes

A major theme explored in this review is the MAO-and cytochrome P450-catalyzed alpha-carbon oxidations of selected cyclic tertiary amines to give iminium metabolites that undergo further chemical modifications to form known or potentially toxic products. The most dramatic illustration of this type of bioactivation process is the conversion of the parkinsonian-inducing neurotoxin MPTP (23) by brain MAO-B to the iminium (dihydropyridinium) metabolite 24 which is oxidized further to the pyridinium species MPP+ (25). The selective destruction of nigrostriatal neurons by MPP+ is dependent on a unique sequence of events (transport into the nerve terminals by the dopamine transporter, localization in the inner mitochondrial membrane by electromotive forces, and inhibition of complex I of the mitochondrial electron transport chain) that, fortunately, are unlikely to be encountered with many substances. A second example of a well-documented metabolic bioactivation sequence involves the highly toxic pyrrolizidine alkaloids (102). These compounds undergo cytochrome P450-catalyzed alpha-carbon oxidation which converts the 3-pyrrolinyl moiety present in the parent alkaloids into a pyrrolyl-containing metabolite (105). The presence of labile functional groups results in the spontaneous conversion of 105 to reactive electrophilic products (106 and 108) that undergo Michael addition reactions with nucleophiles on biomacromolecules leading to a variety of toxic outcomes. Less clearly defined are the potential contributions to neurodegenerative processes that may be mediated by low-level, long term exposure to less potent toxins. Examples of potential proneurotoxins are the endogenously formed tetrahydroisoquinolines (such as 40-50) and tetrahydro-beta-carbolines (such as 54) that may be biotransformed to neurotoxic isoquinolinium (such as 51) and beta-carbolinium (such as 52) species in the brain. A similar argument can be made for 4-piperidinols (compounds that are at the same oxidation state as the tetrahydropyridines) which may be metabolized via iminium intermediates to amino enols that spontaneously convert to dihydropyridinium species and hence to pyridinium metabolites (67-->68-->69-->70-->71, Scheme 10). This type of reaction sequence has been well documented with the parkinsonian-inducing neuroleptic agent haloperidol (72) which is metabolized in humans, baboons, and rodents to the pyridinium species HPP+ (75), a potent inhibitor of mitochondrial respiration. Finally, an appreciation of the alpha-carbon oxidations of fully reduced azacycles such as (S)-nicotine (61) and phencyclidine (82) to chemically reactive metabolites that form covalent adducts with proteins, including the enzymes that are responsible for their formation, may prove of toxicological importance when attempting to account for the effects of chronic abuse of these potent drugs.1