Reduced plasma homocysteine levels in levodopa/entacapone treated Parkinson patients

The vicious circle between homocysteine, methyl group-donating vitamins and chronic levodopa intake in Parkinson's disease

A biomarker for declined methylation capacity is elevation of homocysteine levels. They increase the risk for onset of vascular disease and contribute to progression of chronic neurodegeneration and aging. This narrative review discusses associations between homocysteine, consumption of methyl group-donating vitamins and impact on disease-generating mechanisms in levodopa-treated patients with Parkinson's disease. We conclude to recommend levodopa-treated patients to substitute themselves with methyl group-donating vitamins. This is harmless in terms of application of folic acid, methylcobalamin or hydroxocobalamin. Moreover, we suggest a crucial discussion on the value of the various popular hypotheses on Parkinson's disease-generating mechanisms. Findings from studies with acute levodopa exposure describe oxidative stress generation and impaired methylation capacity, which causes gene dysfunction. Their repeated occurrences contribute to onset of mitochondrial dysfunction, iron enrichment and pathologic protein accumulation in the long term. Current research underestimates these epigenetic, metabolic consequences of chronic levodopa application. Supplementary treatment strategies are recommended to avoid levodopa-related side effects.

Homocysteine, vitamin B metabolites, dopamine-substituting compounds, and symptomatology in Parkinson's disease: clinical and therapeutic considerations

Emerging studies suggest a correlation between elevated plasma homocysteine (hcy) levels and the risk of atherosclerosis, vascular disorders, and neurodegenerative diseases, including Parkinson's disease (PD). This narrative review delves into the intricate relationships between Hcy, vitamin B metabolites, dopamine-substituting compounds, and various symptoms of PD. Patients undergoing a long-term L-dopa/dopa-decarboxylase inhibitor (DDI) regimen, especially without a concurrent catechol-O-methyl transferase (COMT) inhibitor or methyl group-donating vitamin supplementation, such as vitamins B6 and B12, exhibit an elevation in Hcy and a decline in vitamin B metabolites. These altered concentrations appear to be associated with heightened risks of developing non-motor symptoms, including peripheral neuropathy and cognitive disturbances. The review underscores the impact of levodopa metabolism via COMT on homocysteine levels. In light of these findings, we advocate for the supplementation of methyl group-donating vitamins, notably B6 and B12, in patients undergoing a high-dose L-dopa/DDI regimen, particularly those treated with L-dopa/carbidopa intestinal gel (LCIG) infusion.

Levodopa, homocysteine and Parkinson's disease: What's the problem?

Elevated circulating homocysteine levels have been associated with cognitive impairment and cardio-cerebro-vascular events. Levodopa treatment of Parkinson's disease tends to further elevate circulating homocysteine levels due to the metabolism of levodopa via catechol-O-methyltransferase (COMT). COMT co-factors are vitamins B12, B6 and folic acid. Accumulating deficiencies of these vitamins are presumed to be the substrate for the homocysteine elevation. B-vitamin therapy reduces homocysteine levels. This begs the question of whether Parkinson's disease patients on levodopa should be concurrently treated with ongoing B-vitamin therapy (versus long-term monitoring of B-vitamins/homocysteine). There is a substantial literature on this topic that has accumulated over the last quarter-century, and this topic is still debated. This review summarizes the relevant literature with the aim of approximating closure on this issue. Also, noteworthy is that Parkinson's disease patients with renal insufficiency may not tolerate cyanocobalamin, the standard oral B12 supplement due to facilitation of renal decline; alternatives are discussed.

Two Faces of Catechol-O-Methyltransferase Inhibitor on One-Carbon Metabolism in Parkinson's Disease: A Meta-Analysis

Levodopa (L-dopa) and catechol-O-methyltransferase (COMT) inhibition are widely used therapeutics in Parkinson's disease (PD). Despite their therapeutic effects, it was raised that nutrients involved in one-carbon metabolism can be deteriorated by PD therapies. The aim of this meta-analysis was to investigate the impact of L-dopa and COMT inhibitors on levels of homocysteine (Hcy), vitamin B₁₂ and folate in patients with PD. A total of 35 case-control studies from 14 different countries were selected through PubMed, MEDLINE and Google Scholar and were meta-analyzed. In the L-dopa group, the Hcy level was higher compared to the PD without L-dopa group (SMD: 5.11 μmol/L, 95% CI: 3.56 to 6.66). Moreover, vitamin B₁₂ and folate levels in the L-dopa group were lower compared to the healthy control (SMD: -62.67 pg/mL, 95% CI: -86.53 to -38.81; SMD: -0.89 ng/mL, 95% CI: -1.44 to -0.33, respectively). The COMT inhibitor group showed lower levels of Hcy (SMD: -3.78 μmol/L, 95% CI: -5.27 to -2.29) and vitamin B₁₂ (SMD: -51.01 pg/mL, 95% CI: -91.45 to -10.57), but higher folate levels (SMD: 1.78 ng/mL, 95% CI: -0.59 to 4.15) compared to the L-dopa group. COMT inhibitors may ameliorate L-dopa-induced hyper-homocysteine and folate deficiency but exacerbate vitamin B₁₂ deficiency.

Tolcapone improves outcomes in patients with Parkinson disease treated by levodopa/carbidopa intestinal gel: A pilot study

BACKGROUND

Patients with Parkinson disease (PD) treated with levodopa/carbidopa intestinal gel (LCIG) have higher prevalence of hyperhomocysteinemia and peripheral nerves damage.

OBJECTIVE

The aim of our study was to test the effect of catechol-O-methyl transferase inhibitor tolcapone-as an add-on therapy to LCIG in patients with PD-on homocysteine (HCY) metabolism and nerve conduction study (NCS) parameters.

METHODS

We evaluated NCS and serum B12, folic acid, and homocysteine in 16 patients with advanced PD on LCIG. Quality of life (QoL) was also assessed. Six subjects were treated with tolcapone add-on therapy (and LCIG dose reduction), 5 with B vitamin supplementation, and 5 without additional treatment.

RESULTS

The level of HCY increased among patients without treatment (4.95 ± 12.54), and decreased in the vitamin (-17.73 ± 11.82) and tolcapone groups (-8.81 ± 8.36). Patients with tolcapone demonstrated improvement in polyneuropathic symptoms and signs compared with patients treated with vitamins or those without additional treatment (-0.83, d = 0.961). Although the most robust improvement in NCS parameters were observed with tolcapone, the findings were inconsistent to prove the effect of any intervention. Only tolcapone treatment was associated with improvement in QoL (d = 1.089).

CONCLUSION

Our study indicates potential of tolcapone add-on therapy in LCIG treated patients in control of homocysteine levels, and improvement of polyneuropathic symptoms, as well as QoL.

Parkinsonism and cerebrovascular disease

The relationship between cerebrovascular disease and parkinsonism is commonly seen in everyday clinical practice but remains ill-defined and under-recognised with little guidance for the practising neurologist. We attempt to define this association and to illustrate key clinical, radiological and pathological features of the syndrome of Vascular Parkinsonism (VaP). VaP is a major cause of morbidity in the elderly associated with falls, hip fractures and cognitive impairment. Although acute parkinsonism is reported in the context of an acute cerebrovascular event, the vast majority of VaP presents as an insidious syndrome usually in the context of vascular risk factors and radiological evidence of small vessel disease. There may be an anatomic impact on basal ganglia neuronal networks, however the effect of small vessel disease (SVD) on these pathways is not clear. There are now established reporting standards for radiological features of SVD on MRI. White matter hyperintensities and lacunes have been thought to be the representative radiological features of SVD but other features such as the perivascular space are gaining more importance, especially in context of the glymphatic system. It is important to consider VaP in the differential diagnosis of Parkinson disease (PD) and in these situations, neuroimaging may offer diagnostic benefit especially in those patients with atypical presentations or refractoriness to levodopa. Proactive management of vascular risk factors, monitoring of bone density and an exercise program may offer easily attainable therapeutic targets in PD and VaP. Levodopa therapy should be considered in patients with VaP, however the dose and effect may be different from use in PD. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Involvements of Hyperhomocysteinemia in Neurological Disorders

Homocysteine (HCY), a physiological amino acid formed when proteins break down, leads to a pathological condition called hyperhomocysteinemia (HHCY), when it is over a definite limit. It is well known that an increase in HCY levels in blood, can contribute to arterial damage and several cardiovascular disease, but the knowledge about the relationship between HCY and brain disorders is very poor. Recent studies demonstrated that an alteration in HCY metabolism or a deficiency in folate or vitamin B12 can cause altered methylation and/or redox potentials, that leads to a modification on calcium influx in cells, or into an accumulation in amyloid and/or tau protein involving a cascade of events that culminate in apoptosis, and, in the worst conditions, neuronal death. The present review will thus summarize how much is known about the possible role of HHCY in neurodegenerative disease.

Twelve-Week Daily Consumption of ad hoc Fortified Milk with ω-3, D, and Group B Vitamins Has a Positive Impact on Inflammaging Parameters: A Randomized Cross-Over Trial

Background and Aim: A state of chronic, subclinical inflammation known as inflammaging is present in elderly people and represents a risk factor for all age-related diseases. Dietary supplementation with ad hoc fortified foods seems an appealing strategy to counteract inflammaging. The purpose of this study was to test the efficacy of elderly-tailored fortified milk on inflammaging and different health parameters. Methods: A double-blind randomized cross-over study was performed on forty-eight volunteers aged 63–80 years. The fortified milk was enriched with ω-3 polyunsaturated fatty acids (eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA), vitamins (25-hydroxyvitamin D, E, C, B6, B9, B12), and trace elements (zinc, selenium). The two intervention periods lasted for 12 weeks, with a 16-week washout intermission. Results: Compared to placebo, the consumption of fortified milk increased the circulating levels of different micronutrients, including vitamins and the ω-3 index of erythrocyte membranes. Conversely, it reduced the amount of arachidonic acid, homocysteine, and ω-6/ω-3 ratio. Conclusion: Twelve-week daily consumption of adhoc fortified milk has an overall positive impact on different health parameters related to inflammaging in the elderly.

Estrogen Signaling in Alzheimer's Disease: Molecular Insights and Therapeutic Targets for Alzheimer's Dementia

Estrogens play a crucial physiological function in the brain; however, debates exist concerning the role of estrogens in Alzheimer's disease (AD). Women during pre-, peri-, or menopause periods are more susceptible for developing AD, suggesting the connection of sex factors and a decreased estrogen signaling in AD pathogenesis. Yet, the underlying mechanism of estrogen-mediated neuroprotection is unclarified and is complicated by the existence of estrogen-related factors. Consequently, a deeper analysis of estrogen receptor (ER) expression and estrogen-metabolizing enzymes could interpret the importance of estrogen in age-linked cognitive alterations. Previous studies propose that hormone replacement therapy may attenuate AD onset in postmenopausal women, demonstrating that estrogen signaling is important for the development and progression of AD. For example, ERα exerts neuroprotection against AD by maintaining intracellular signaling cascades and study reported reduced expression of ERα in hippocampal neurons of AD patients. Similarly, reduced expression of ERβ in female AD patients has been associated with abnormal function in mitochondria and improved markers of oxidative stress. In this review, we discuss the critical interaction between estrogen signaling and AD. Moreover, we highlight the potential of targeting estrogen-related signaling for therapeutic intervention in AD.

Large-Fiber Neuropathy in Parkinson's Disease: Clinical, Biological, and Electroneurographic Assessment of a Romanian Cohort

(1) Background: Increased attention has lately been given to polyneuropathy in Parkinson’s Disease (PD). Several papers postulated that large-fiber neuropathy (PNP) in PD is related to vitamin B12 deficiency and L-Dopa exposure. (2) Methods: Using a cross-sectional, observational study, we evaluated 73 PD patients without a previously known cause of PNP using clinical scores (UPDRS II and III and Toronto Clinical Scoring System), biological evaluation of vitamin B12 and folic acid, and nerve conduction studies to assess the prevalence and features of PNP. (3) Results: The prevalence of PNP was 49.3% in the study group. In the L-Dopa group, the frequency of PNP was 67.3% as compared to PNP in the non-L-Dopa group, where one subject had PNP (χ² = 23.41, p < 0.01). PNP was predominantly sensory with mild to moderate axonal loss. Cyanocobalamin correlated with L-Dopa daily dose (r = −0.287, p < 0.05) and L-Dopa duration of administration (r = −0.316, p < 0.05). L-Dopa daily dose correlated with the amplitudes of sensory nerve action potentials of the superficial peroneal and radial nerves (r = −0.312, p < 0.05) (r = −0.336, p < 0.05), respectively. (4) Conclusions: PNP is more frequent in L-Dopa-treated patients than in L-Dopa-naïve patients. The results imply that longer exposure to high doses of L-Dopa may cause vitamin B12 and folate imbalance and PNP, secondarily.

Levodopa-Induced Neuropathy: A Systematic Review

Background

Clinical, neurophysiological, and pathological evidence suggest an association between Parkinson's disease (PD) and peripheral neuropathy (PNP), with a possible causative role of levodopa metabolic products, such as homocysteine and methylmalonic acid.

Methods

We conducted a systematic review of studies reporting cases of PNP in l-dopa-treated PD patients indexed in PubMed between January 1990 and March 2018.

Results

We identified 38 articles reporting cases of PNP in PD patients treated with oral l-dopa or with l-dopa/carbidopa intestinal gel infusion (LCIG). Prevalence of PNP was 30.2% in the former group and 42.1% in the latter. Oral l-dopa was mostly associated with slowly progressive PNP, whereas LCIG showed an acute or subacute onset in 35.7% of cases. In both groups, there was an association between PNP and higher l-dopa doses, as well as with the following biochemical alterations: increased homocysteine; reduced vitamin B12; increased methylmalonic acid; and reduced vitamin B6. A skin biopsy was performed in 181 patients, showing signs of small fibers neuropathy in 169 (93.4%). Positive, yet preliminary, results were observed in patients receiving periodic vitamin supplementation.

Conclusions

Over one third of PD patients in treatment with l-dopa may develop PNP, with a significantly higher prevalence of acute and subacute forms in those receiving LCIG. Pathogenic mechanisms remain unclear, but possibly related to a complex interplay between peripheral neurodegenerative processes and l-dopa neurotoxic metabolites. Prospective, randomized, clinical trials are required to identify factors associated with the onset and progression of PD-associated PNP and clarify the protective role of B-group vitamin supplementation.

Serum amino acid profile in patients with Parkinson's disease

Amino acids play numerous roles in the central nervous system, serving as neurotransmitters, neuromodulators and regulators of energy metabolism. The free amino acid profile in serum of Parkinson's disease (PD) patients may be influenced by neurodegeneration, mitochondrial dysfunction, malabsorption in the gastroenteric tract and received treatment. The aim of our study was the evaluation of the profile of amino acid concentrations against disease progression. We assessed the amino acid profile in the serum of 73 patients divided into groups with early PD, late PD with dyskinesia and late PD without dyskinesia. Serum amino acid analysis was performed by high-pressure liquid chromatography with fluorescence detection. We observed some significant differences amongst the groups with respect to concentrations of alanine, arginine, phenylalanine and threonine, although no significant differences were observed between patients with advanced PD with and without dyskinesia. We conclude that this specific amino acid profile could serve as biochemical marker of PD progression.

Serum methylmalonic acid correlates with neuropathic pain in idiopathic Parkinson's disease

Recent studies have shown a relatively higher prevalence of peripheral neuropathy in idiopathic Parkinson's disease (IPD). The hypothesis is that prolonged levodopa exposure causes vitamin B12 deficiency, which leads to peripheral neuropathy. The aim of our study was to find the relationship between vitamin B12 and its precursor methylmalonic acid (MMA) in IPD patients with neuropathic pain. We performed a cross-sectional study by enrolling consecutive 43 patients who were clinically tested positive for F-18 FP-CIT PET and 15 patients were diagnosed with peripheral neuropathy according to the Toronto clinical scoring system (TCSS). The severity of neuropathic pain was evaluated using total neuropathy scale, revised (TNSr), and Korean Neuropathic Pain Questionnaire (KNPQ). The correlations between age, IPD duration, levodopa equivalent dose (LED), UPDRS III, vitamin B12, MMA, and homocysteine levels were assessed. The prevalence rate of peripheral neuropathy in IPD patients was 35%. Among the serums assessed, MMA levels showed a positive correlation to TNSr and KNPQ in the IPD patients with peripheral neuropathy (TNSr r = 0.882, p < 0.001, KNPQ r = 0.710, p = 0.004), while Vitamin B12 and homocysteine showed no statistically significant correlation. Our study showed a prevalence of peripheral neuropathy in 35% of Korean IPD patients. The serum MMA positively correlated with the severity of neuropathic pain and this can be used as a useful marker in assessment of peripheral neuropathy in Parkinson's disease.

Efficacy of Vitamin B Supplementation on Cognition in Elderly Patients With Cognitive-Related Diseases

Increase in serum homocysteine is shown to be a potential risk factor for cognitive impairment. Evidence suggests that vitamin B supplementation may reduce cognitive decline by lowering the homocysteine levels. The current meta-analysis evaluated the efficacy of folic acid along with vitamin B12 and/or B6 in lowering homocysteine, thereby attenuating cognitive decline in elderly patients with Alzheimer disease or dementia. Randomized controlled trials (RCTs) comparing the efficacy of folate and B vitamin supplementation in patients with cognitive decline secondary to Alzheimer disease or dementia were identified using the keywords, "homocysteine, hyper-homocysteinemia, B vitamin, vitamin B6, B12, folic acid, cognitive, Alzheimer's disease, and dementia." The outcome measures analyzed were the Mini-Mental State Examination (MMSE) score and serum homocysteine. Of the 77 studies identified, 4 RCTs were included in the current meta-analysis. The baseline characteristics, age, and gender distribution of patients among the 2 groups (supplement vs placebo) were comparable. The results reveal that the intervention group achieved significantly greater reduction in homocysteine levels than the control (pooled difference in means = -3.625, 95% confidence interval [CI] = -5.642 to -1.608, P < .001). However, no significant difference in MMSE (pooled difference in means = 0.027, 95% CI = -0.518 to 0.573, P = 0.921) was observed between the groups. Taken together, vitamin B supplementation was effective in reducing serum homocysteine levels. However, it did not translate into cognitive improvement, indicating that the existing data on vitamin B-induced improvement in cognition by lowering homocysteine levels are conflicting.

Homocysteine Levels in Parkinson's Disease: Is Entacapone Effective?

Plasma homocysteine (Hcy) levels may increase in levodopa-treated patients with Parkinson's disease (PD) as a consequence of levodopa methylation via catechol-O-methyltransferase (COMT). Results from previous studies that assessed the effect of COMT inhibitors on levodopa-induced hyperhomocysteinemia are conflicting. We aimed to evaluate the effects of levodopa and entacapone on plasma Hcy levels. A hundred PD patients were enrolled to the study and divided into three treatment groups (group I: levodopa and/or dopamine agonists; group II: levodopa, entacapone, and/or a dopamine agonist; and group III: dopamine agonist alone). We measured the serum B12, folic acid, and Hcy levels in all patients. There were no statistically significant differences between groups in terms of modified Hoehn and Yahr stages, Unified Parkinson's Disease Rating Scale II/III, Standardized Mini-Mental Test scores, and serum vitamin B12 and folic acid levels. Plasma median Hcy levels were found above the normal laboratory values in groups I and II, but they were normal in group III. However, there was no statistically significant difference in plasma Hcy levels between groups. Our results showed that levodopa treatment may cause a slight increase in the Hcy levels in PD compared with dopamine agonists and that COMT inhibitors may not have a significant effect on preventing hyperhomocysteinemia.

A coumarin-based fluorescent probe as a central nervous system disease biomarker

Homocysteine and methylmalonic acid are important biomarkers for diseases associated with an impaired central nervous system (CNS). A new chemoassay utilizing coumarin-based fluorescent probe 1 to detect the levels of homocysteine is successfully implemented using Parkinson's disease (PD) patients' blood serum. In addition, a rapid identification of homocysteine and methylmalonic acid levels in blood serum of PD patients was also performed using the liquid chromatography-mass spectrometry (LC-MS). The results obtained from both analyses were in agreement. The new chemoassay utilizing coumarin-based fluorescent probe 1 offers a cost- and time-effective method to identify the biomarkers in CNS patients.

Elevated homocysteine levels in levodopa-treated idiopathic Parkinson's disease: a meta-analysis

To assess the association between the elevation of plasma homocysteine (Hcy) level and long-term levodopa (L-dopa) therapy in idiopathic Parkinson's disease (PD). We performed a systematic literature review to recruit original studies published up to May 14, 2012. Studies enrolled should be controlled, with specific information of long-term L-dopa application and plasma Hcy in patients with PD. Effects were summarized using standardized mean differences (SMDs) or weighted mean differences (WMDs). Our search enrolled 22 eligible studies. Plasma Hcy levels were significantly higher in L-dopa-treated patients than those in healthy controls [SMD 0.97; 95% confidence interval (CI) 0.80-1.14, P < 0.001], L-dopa-naïve patients with PD (SMD 0.99; 95% CI 0.54-1.44, P < 0.001), and untreated patients (SMD 0.52; 95% CI 0.18-0.86, P < 0.01). However, its levels in untreated patients with PD were not significantly higher than in healthy controls (SMD 0.24; 95% CI -0.03 to 0.51, P > 0.05). Patients with PD treated with L-dopa plus catechol-O-methyltransferase inhibitor (COMT-I) showed lower plasma Hcy concentrations compared with L-dopa-treated patients (WMD 4.62; 95% CI 2.89-6.35, P < 0.001). L-dopa treatment is associated with the increase in plasma Hcy level in patients with PD. COMT-I may attenuate L-dopa-induced elevation of Hcy level.

Recent updates in redox regulation and free radical scavenging effects by herbal products in experimental models of Parkinson's disease

Parkinson’s disease (PD) is a complex multifactorial disease marked by extensive neuropathology in the brain with selective yet prominent and progressive loss of mid-brain dopaminergic neurons. The etiological factors involved in the development of PD are still elusive, but oxidative stress arising when reactive oxygen species (ROS) exceed amounts required for normal redox signaling is considered one of the major factors. ROS cause oxidative damage to proteins, lipids, and DNA and are one of the most prominent factors related to neurodegeneration. Pre-clinical and clinical studies clearly demonstrate the effectiveness of oxidative stress in the pathogenesis of PD. Therefore, regulation of redox signaling and inhibiting excess ROS would contribute greatly not only to extend longevity but also to ameliorate the progression of dopaminergic cell death seen in patients with PD. Several herbal products are beneficial for maintaining nerve cell function and for treating various neurodegenerative disorders by reducing oxidative stress. Here, we summarize the recent knowledge concerning promising herbs that have shown significant beneficial effects based on regulation of redox status and ROS inhibition in toxin-induced PD models.

Comparison of endothelial progenitor cells in Parkinson's disease patients treated with levodopa and levodopa/COMT inhibitor

Background

Levodopa treatment in Parkinson's disease (PD) increases in serum homocysteine levels due to its metabolism via catechol O-methyltransferase. Endothelial progenitor cells (EPCs) have the capacity to differentiate into mature endothelial cells and are markers for endothelial functions and cardiovascular risks. Along with traditional vascular risk factors, hyperhomocysteinemia is known to decrease the level of EPCs. In the present study, we hypothesized that that levodopa-induced hyperhomocysteinemia leads to a change in EPC levels.

Methodology/Principal Findings

We prospectively enrolled PD patients who had been prescribed either levodopa/carbidopa (PD-L group, n = 28) or levodopa/carbidopa/COMT inhibitor (PD-LC group, n = 25) for more than 1 year. The number of circulating EPCs was measured by flow cytometry using dual staining of anti-CD34 and anti-KDR antibodies. The EPCs were divided into tertiles based on their distributions and a logistic regression analysis was used to estimate independent predictors of the highest tertile of EPCs. The number of endothelial progenitor cells was significantly decreased in PD-L patients (118±99/mL) compared with either PD-LC patients (269±258/mL, p = 0.007) or controls (206±204/mL, p = 0.012). The level of homocysteine was significantly increased in PD-L patients (14.9±5.3 µmol/L) compared with either PD-LC patients (11.9±3.0 µmol/L, p = 0.028) or controls (11.1±2.5 µmol/L, p = 0.012). The level of homocysteine was negatively correlated with endothelial progenitor cell levels (r = −0.252, p = 0.028) and was an independent predictor of the highest tertile of endothelial progenitor cell levels (OR; 0.749 [95% CI: 0.584–0.961]).

Conclusions/Significance

These data indicate that a higher consumption of EPC for restoration of endothelial damage may be associated with chronic levodopa treatment in PD patients.

Therapeutic interventions and adjustments in the management of Parkinson disease: role of combined carbidopa/levodopa/entacapone (Stalevo)

Parkinson disease (PD) is a neurodegenerative disorder characterized by 3 cardinal motor symptoms: resting tremor, rigidity, and bradykinesia. Since its introduction 40 years ago, levodopa has represented the gold standard for dopaminergic stimulation therapy in patients with PD. Levodopa is routinely combined with a dopa-decarboxylase inhibitor (DDCI) to prevent the conversion of levodopa into dopamine in peripheral circulation. However, up to 80% of patients treated with continuous levodopa manifest the onset of disabling motor complications capable of producing an adverse effect on quality of life as the disease progresses. In recent years, a new, safe, and efficacious armamentarium of treatment options has been provided by the marketing of the catechol-O-methyltransferase (COMT) inhibitor, entacapone, a peripheral blocker of dopa to 3-0-methyldopa metabolism, which increments levodopa brain availability. When administered with levodopa, entacapone conjugates the rapid onset of levodopa-induced effects with a protracted efficiency, thus providing additional benefits to classic levodopa treatment by increasing "on" time in fluctuating PD patients, and theoretically providing a more continuous and physiological-like stimulation of dopamine receptors implying a reduced risk of motor complications. In this context, the use of a single administration of combined carbidopa/ levodopa/entacapone (Stalevo(®)) in the treatment of PD affords clinical improvements similar to those obtained by 2 separate tablets (ie, levodopa/DDCI and entacapone), although the former produces a more positive effect on quality of life than the latter. Additionally, the STalevo Reduction In Dyskinesia Evaluation (STRIDE-PD) study was designed with the aim of demonstrating that the combination of levodopa, carbidopa, and entacapone, used as initial levodopa therapy, significantly delays the onset of dyskinesias compared with the conventional levodopa/carbidopa formulation. Unfortunately, STRIDEPD failed to prove the benefit of continuous dopaminergic stimulation with triple therapy in a clinical setting. Recently, the effect of combined COMT inhibitor with levodopa administration in reducing homocysteine synthesis has been described. To this regard, clear evidence has been presented indicating homocysteine as a risk factor for vascular diseases, cognitive impairment, and dementia. Several studies have discussed the potential of entacapone as adjunct to levodopa/ DDCI in reducing plasma homocysteine levels with contrasting results.

Levodopa/carbidopa and entacapone in the treatment of Parkinson's disease: efficacy, safety and patient preference

Levodopa (LD) is the oldest, most efficacious and best-tolerated drug for dopaminergic substitution of patients with Parkinson's disease (PD). Its main drawback is its short half-life, which supports onset of motor complications in the long term. Therefore well-informed PD patients mostly accept LD therapy as late as possible. Recent LD trials indicate that a combination of LD with carbidopa (CD) and the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) may reduce the onset of these motor complications to a certain extent. This observation is further supported by pharmacokinetic trials and experimental research, but there is still a need to confirm this in a clinical trial, which is under way. Additionally, combined LD/CD/EN was superior to LD/CD administration regarding cognition, muscle behavior and gastrointestinal function in small clinical trials. Moreover there is accumulating evidence that combined COMT inhibition with LD administration reduces homocysteine synthesis. In the long term, homocysteine elevation supports onset of arteriosclerosis-related disorders, which are more frequent in PD patients according to epidemiological studies than in the normal healthy population. The introduction of LD/CD/EN in one tablet supported patients' preference of COMT inhibition as an essential component of LD/DDI therapy, as this combination reduced number and size of tablets.

Homocysteine and cognitive impairment in Parkinson's disease: a biochemical, neuroimaging, and genetic study

The role of the plasma level of homocysteine (Hcy), as a primary outcome, and the effect of silent cerebrovascular lesions and genetic variants related to Hcy metabolism, as secondary outcomes, in the cognitive decline and dementia in Parkinson's disease (PD) were studied. This case-control study focused on 89 PD patients of minimum 10 years of evolution and older than 60 years, who were neuropsychologically classified either as cognitively normal (n = 37), having mild cognitive impairment (Petersen criteria) (n = 22), or suffering from dementia (DSM-IV) (n = 30), compared with cognitively normal age-matched control subjects (n = 30). Plasma levels of Hcy, vitamins B12 and B6, folic acid, polymorphisms in genes related to Hcy metabolism (MTHFR, MTR, MTRR, and CBS) and silent cerebrovascular events were analyzed. Plasma levels of Hcy were increased in PD patients (P = 0.0001). There were no differences between the groups of patients. The brain vascular burden was similar among PD groups. There was no association between polymorphisms in the studied genes and the Hcy plasma levels or cognitive status in PD patients. We found no evidence for a direct relationship between Hcy plasma levels and cognitive impairment and dementia in PD. No indirect effect through cerebrovascular disease or genetic background was found either.

Methylation Status and Neurodegenerative Markers in Parkinson Disease

Background: Increased concentrations of plasma total homocysteine (tHcy) have been associated with age-related diseases, including dementia, stroke, and Parkinson disease (PD). Methylation status might link Hcy metabolism to neurodegenerative proteins in patients with PD.

Methods: We tested blood samples from 87 patients with PD (median age 68 years; 35 men) for tHcy, methylmalonic acid (MMA), vitamin B12, vitamin B6, folate, S-adenosyl methionine (SAM), S-adenosyl homocysteine (SAH), and amyloid-β(1–42). We collected citrate blood from a subset of 45 patients to prepare platelet-rich plasma, and we used washed platelets to prepare cell extracts for amyloid precursor protein (APP) and α-synuclein assays. We used brain parenchyma sonography to estimate the substantia nigra echogenic area in a subset of 59 patients.

Results: Serum concentrations of tHcy were increased in PD patients (median 14.8 μmol/L). tHcy (β coefficient = −0.276) and serum creatinine (β = −0.422) were significant predictors of the ratio of SAM/SAH in plasma (P &lt; 0.01). The plasma SAM/SAH ratio was a significant determinant for DemTect scores (β = 0.612, P = 0.004). Significant negative correlations were found between concentrations of SAH in plasma and platelet APP and between SAM and platelet α-synuclein. A larger echogenic area of the substantia nigra was related to higher serum concentrations of MMA (P = 0.016).

Conclusions: Markers of neurodegeneration (APP, α-synuclein) are related to markers of methylation (SAM, SAH) in patients with PD. Better cognitive function was related to higher methylation potential (SAM/SAH ratio).

Possible treatment concepts for the levodopa-related hyperhomocysteinemia

The saga of harmful levodopa (LD) in the treatment of Parkinson's disease (PD) resulted from outcomes of animal-and cell culture studies and the clinical observation of motor complication related to the short half life of LD. Further aspects of LD long term application, the LD associated homocysteine increase and its emerging consequences on progression, and onset of neuropsychiatric symptoms and of vascular disease are only partially considered. Therapeutic approaches for this LD-mediated neurotoxic homocysteine increase are vitamin supplementation or LD application with an inhibitor of catechol-O-methyltransferase (COMT). However, forcing central dopamine metabolism further down the methylation path by central blocking of COMT and MAO-B may reduce oxidative stress and homocysteine levels. But it may also increase N-methylation of tetrahydroisoquinolines to neurotoxic N-methylated tetrahydroisoquinolines. These compounds were observed in cerebrospinal fluid and plasma of long term LD-treated PD patients. Therefore LD application with peripheral COMT inhibition may be safer.

Neuropathy as a potential complication of levodopa use in Parkinson's disease

The presence and potential etiologies of peripheral neuropathy (PN) in patients with Parkinson's Disease (PD) is unknown. We examined for presence of PN in patients with PD. From a PD patient population of 500 patients screened for features of symptomatic PN, patients were further selected for clinical, electrophysiological, and laboratory studies related to PN. This PD patient population with idiopathic PN (PD-IPN) was compared to a group of PD patients without PN (PD-only), and a large group of patients without PD with idiopathic PN (IPN) for abnormalities in Cbl, fasting homocysteine (Hcy), and fasting methylmalonic acid (MMA) levels. PD-IPN and IPN patients identified with abnormalities in Cbl, Hcy, or MMA levels were treated with intramuscular Cbl for 1 to 2 years. Of 49 PD patients with symptomatic PN, 34 patients (69%) had PD-IPN, and 32/34 (94%) had abnormal Hcy or MMA levels as compared to 26/258 (10%) of IPN patients. Cumulative lifetime L-dopa dosage and fasting MMA levels were associated with PN severity. Cbl therapy led to improvements in Hcy and MMA levels in all groups, and PN in PD-IPN patients stabilized during therapy. PN in PD patients may be associated with iatrogenic Cbl metabolic abnormalities. Alternatively PN may be a peripheral nervous system manifestation of PD.

Current status of symptomatic medical therapy in Parkinson's disease

Symptomatic medical therapies for Parkinson's disease (PD) have been disease modifying and have led to improvement in daily function, quality of life, and survival. For 40 years, these therapies have been primarily dopaminergic, and currently include the dopamine (DA) precursor levodopa (LD), DA agonists, catechol-O-methyltransferase (COMT) inhibitors, and monoamine oxidase (MAO) inhibitors. The roles of all these classes of agents have evolved, with significant changes occurring since the early 2000s. This article reviews the current literature for each of these classes of drugs, with a focus on efficacy and place in the therapeutic scheme. Levodopa is no longer considered to be toxic and, thus, its early use is not only appropriate but recommended. Ergot agonists are no longer in use, and new agents administered in patch form or subcutaneous injections have been approved. The COMT inhibitor tolcapone, with its significant efficacy, has been reintroduced, and two new MAO inhibitors have been approved. Selected safety issues are discussed, including the incidence of melanoma in relation to LD; pathological gambling and DA agonists; hepatic toxicity of tolcapone; and the tyramine or so-called cheese reaction with MAO B inhibitors. The article closes with a discussion of future directions and new drugs under development.

The role of hyperhomocysteinemia and B-vitamin deficiency in neurological and psychiatric diseases

Hyperhomocysteinemia (HHcy) is related to central nervous system diseases. Epidemiological studies show a positive, dose-dependent relationship between plasma total homocysteine (tHcy) concentration and neurodegenerative disease risk. tHcy is a marker of B-vitamin (folate, B(12), B(6)) status. Hypomethylation, caused by low B-vitamin status and HHcy, is linked to key pathomechanisms of dementia; B-vitamin supplementation could potentially reduce neurological damage. In retrospective studies, the association between tHcy and cognition is impressive; there is also evidence that tHcy-lowering treatment could be effective in primary and secondary stroke prevention. Increased tHcy and low serum folate occur in patients with Parkinson's disease, especially those receiving L-dopa. There is also an association between HHcy and multiple sclerosis, and between B-vitamin status and depression. Studies also confirm a causal role for tHcy in epilepsy, and certain anti-epileptics enhance HHcy. B-vitamin status should be optimized by ensuring sufficient intake in patients with neuropsychiatric diseases. HHcy occurs commonly in the elderly and can contribute to age-related neurodegeneration. Treatment with folic acid, B(12) and B(6) lowers tHcy. For secondary and primary prevention from several neuropsychiatric disorders, it seems prudent to actively identify deficient subjects and ensure sufficient vitamin intake.

Vitaminas antioxidantes na Doença de Parkinson

Resumo A doença de Parkinson é uma enfermidade neurodegenerativa caracterizada pela presença de rigidez, tremor e bradicinesia, sendo um dos distúrbios do movimento mais encontrados na população idosa. Estudos mostraram que o estresse oxidativo, o uso prolongado da droga levodopa no tratamento dessa doença e o aumento da concentração plasmática de homocisteína são agentes que agravam os sintomas. Muitos nutrientes estão sendo pesquisados tanto na prevenção como no tratamento da doença, dentre os quais se destacam as vitaminas antioxidantes. Houve recentemente aumento do número de pesquisas sobre a ação dessas vitaminas, atenuando os danos causados ao cérebro nesses pacientes. Desta forma, o artigo teve como objetivo reunir, na literatura científica, informações recentes sobre a influência das vitaminas C, E, B6, B12 e folato na doença de Parkinson. Embora as evidências do efeito dessas vitaminas nos pacientes com a doença sejam comprovadas em algumas pesquisas, ainda há controvérsias entre os autores, sendo necessário realizar mais estudos sobre o assunto.

Proteome analysis of human substantia nigra in Parkinson's disease

Background

Parkinson's disease (PD) is the most common neurodegenerative disorder involving the motor system. Although not being the only region involved in PD, affection of the substantia nigra and its projections is responsible for some of the most debilitating features of the disease. To further advance a comprehensive understanding of nigral pathology, we conducted a tissue based comparative proteome study of healthy and diseased human substantia nigra.

Results

The gross number of differentially regulated proteins in PD was 221. In total, we identified 37 proteins, of which 16 were differentially expressed. Identified differential proteins comprised elements of iron metabolism (H-ferritin) and glutathione-related redox metabolism (GST M3, GST P1, GST O1), including novel redox proteins (SH3BGRL). Additionally, many glial or related proteins were found to be differentially regulated in PD (GFAP, GMFB, galectin-1, sorcin), as well as proteins belonging to metabolic pathways sparsely described in PD, such as adenosyl homocysteinase (methylation), aldehyde dehydrogenase 1 and cellular retinol-binding protein 1 (aldehyde metabolism). Further differentially regulated proteins included annexin V, beta-tubulin cofactor A, coactosin-like protein and V-type ATPase subunit 1. Proteins that were similarly expressed in healthy or diseased substantia nigra comprised housekeeping proteins such as COX5A, Rho GDI alpha, actin gamma 1, creatin-kinase B, lactate dehydrogenase B, disulfide isomerase ER-60, Rab GDI beta, methyl glyoxalase 1 (AGE metabolism) and glutamine synthetase. Interestingly, also DJ-1 and UCH-L1 were expressed similarly. Furthermore, proteins believed to serve as internal standards were found to be expressed in a constant manner, such as 14-3-3 epsilon and hCRMP-2, thus lending further validity to our results.

Conclusion

Using an approach encompassing high sensitivity and high resolution, we show that alterations of SN in PD include many more proteins than previously thought. The results point towards a heterogeneous aetiopathogenesis of the disease, including alterations of GSH-related proteins as well as alterations of proteins involved in retinoid metabolism, and they indicate that proteins involved in familial PD may not be differentially regulated in idiopathic Parkinson's disease.

Allosteric modulation of dopamine D2 receptors by homocysteine

It has been suggested that L-DOPA-induced hyperhomocysteinemia can increase the risk of stroke, heart disease, and dementia and is an additional pathogenetic factor involved in the progression of Parkinson's disease. In Chinese hamster ovary (CHO) cells stably cotransfected with adenosine A(2A) and dopamine D2 receptors, homocysteine selectively decreased the ability of D2 receptor stimulation to internalize adenosine A(2A)-dopamine D2 receptor complexes. Radioligand-binding experiments in the same cell line demonstrated that homocysteine acts as an allosteric D2 receptor antagonist, by selectively reducing the affinity of D2 receptors for agonists but not for antagonists. Mass spectrometric analysis showed that, by means of an arginine (Arg)-thiol electrostatic interaction, homocysteine forms noncovalent complexes with the two Arg-rich epitopes of the third intracellular loop of the D2 receptor, one of them involved in A(2A)-D2 receptor heteromerization. However, homocysteine was unable to prevent or disrupt A(2A)-D2 receptor heteromerization, as demonstrated with Fluorescence Resonance Energy Transfer (FRET) experiments in stably cotransfected HEK cells. The present results could have implications for Parkinson's disease.

The Controversy Concerning Plasma Homocysteine in Parkinson Disease Patients Treated with Levodopa Alone or with Entacapone

Levodopa treatment of Parkinson disease results in hyperhomocysteinemia (HHcy) as a consequence of levodopa methylation by catechol-O-methyltransferase (COMT). Although inhibition of COMT should theoretically prevent or reduce levodopa-induced HHcy, results from several prospective studies are conflicting. Our review of these studies suggests that the ability of COMT inhibition to reduce or prevent levodopa-induced HHcy in Parkinson disease patients may be attributed to differences in the vitamin status of the study participants. In patients with low or low-normal folate levels, levodopa administration is associated with a greater increase in homocysteine and concomitant entacapone administration is associated with a greater reduction in homocysteine.

Tolcapone decreases plasma levels of S-adenosyl-L-homocysteine and homocysteine in treated Parkinson's disease patients

BACKGROUND

Elevated plasma total homocysteine (tHcy) appeared in levodopa/dopadecarcoxylase inhibitor (DDI) treated patients with Parkinson's disease (PD). One therapeutic approach for tHcy reduction is vitamine supplementation, since folic acid and cobalamine catalyse and enhance metabolism of tHcy to methionine. A further therapeutic alternative is inhibition of catechol-O-methyltransfrase (COMT) on a regular basis, when levodopa/DDI treatment is performed.

METHODS

We measured the concentrations of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), tHcy, levodopa and 3-O-methyldopa in plasma of 13 levodopa treated PD patients before first drug intake at 0600 hours. Blood samples were taken before and after 2 days of additional application of the centrally acting catechol-O-methyltransferase inhibitor tolcapone 100 mg t.i.d.

RESULTS

Plasma levels of SAH [day 1: 48.32+/-22.52, 23.92-98.25 (mean+/-SD, range; micromol/l); day 3: 37.72+/-15.84, 23.4-61.89; p = 0.01] and tHcy (day 1: 13.88+/-5.62, 7.63-24.81; day 3: 11.38+/-4.44, 5.98-20.45; p = 0.04) significantly reduced. Plasma levels of levodopa did not significantly (p = 0.17) increase, whereas 3-OMD concentrations significantly (p = 0.0002) reduced after additional tolcapone intake. There was no significant change of SAM plasma levels (p = 0.22).

CONCLUSION

Our prospective trial shows, that COMT inhibition with tolcapone lowers tHcy synthesis. Tolcapone may also possess beside its proven, occasional, hepatotoxic potency also beneficial effects via decrease of SAH and tHcy. This may hypothetically reduce homocysteine mediated progress of neuronal degeneration and the risk for onset of dementia, vascular disease and polyneuropathy in levodopa treated PD patients in the long term.

Acute intranigral homocysteine administration produces stereotypic behavioral changes and striatal dopamine depletion in Sprague–Dawley rats

Homocysteine has been considered a major risk factor for cardiovascular diseases, and patients with hyperhomocystinemia exhibit neurological and psychological abnormalities. Elevated level of this molecule in the blood of Parkinson's disease patients receiving long-term l-DOPA therapy prompted us to investigate whether homocysteine is neurotoxic to the nigrostriatal dopaminergic system in Sprague-Dawley rats. Animals infused unilaterally with different doses of homocysteine (0.25-1 micromol in 1 microl) intranigrally exhibited significant and dose-dependent decrease in dopamine levels in the ipsilateral striatum as assayed employing an HPLC coupled with electrochemical detector, 19 days post-infusion. While 3,4-dihydroxyphenylacetic acid level in the striatum showed a dose-dependent decrease, homovanillic acid was found to be inhibited only for the highest dose. Amphetamine administration in these animals on the 14th day caused stereotypic turning behavior ipsilateral to the side of infusion. Apomorphine challenge on the 16th day elicited stereotypic contralateral circling behavior. Neurotransmitter levels in the serotonergic perikarya or terminals were unaltered 19 days following intraraphe infusion of homocysteine, which suggested the specificity of its action to dopaminergic neurons. These results indicate nigrostriatal lesions similar to that observed following intranigral infusion of the dopaminergic neurotoxin, 6-hydroxydopamine and suggest its closeness to the parkinsonian animal model. Furthermore, these findings provide evidence for the neurotoxic nature of homocysteine to dopaminergic neurons and suggest that elevated level of this molecule in parkinsonian patients may be conducive to accelerate the progression of the disease.

Striatal dopamine transporter binding in Parkinson's disease associated with theLRRK2 Gly2019Ser mutation

We measured striatal dopamine transporter binding using [(123)I]ioflupane and SPECT in patients with Parkinson's disease associated with the LRRK2 (PARK8) Gly2019Ser gene mutation (LRRK2-PD) and in gene-negative patients with idiopathic Parkinson's disease (IPD) of comparable disease duration and severity. The LRRK2-PD group consisted of a total of 10 patients (3 sporadic) with mean age 62 +/- 14 years, disease duration 9 +/- 3 years, and UPDRS III motor score 21.60 +/- 6.65. The control IPD group consisted of 15 patients with mean age 59 +/- 9 years, disease duration 9 +/- 5 years, and UPDRS III motor score 23.80 +/- 8.69. [(123)I]ioflupane-specific uptake ratios were calculated for caudate nucleus and putamen using the occipital cortex as reference region. We found no differences between the LRRK2-PD group and IPD in all items studied. In particular, putamen and caudate uptake values as well as side asymmetry indexes and putamen/caudate ratios all revealed comparable between-group values. We conclude that in these patients carrying the LRRK2 Gly2019Ser mutation, the neurodegenerative process results in a pattern of nigrostriatal dopaminergic dysfunction similar to that observed in IPD.