The Role of 3-O-Methyldopa in the Side Effects of l-dopa

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

Sevoflurane Alters Serum Metabolites in Elders and Aging Mice and Increases Inflammation in Hippocampus

Purpose

Postoperative cognitive dysfunction (POCD) is a central nervous system complication that occurs after anesthesia, particularly among the elderly. However, the neurological pathogenesis of postoperative cognitive dysfunction remains unclear. The aim of this study was to evaluate the effects of sevoflurane exposure on serum metabolites and hippocampal gene expression in elderly patients and aging mice by metabolomics and transcriptomic analysis and to explore the pathogenesis of sevoflurane induced POCD.

Patients and Methods

Human serum samples from five patients over 60 years old were collected before sevoflurane anesthesia and 1 hour after anesthesia. Besides, mice aged at 12 months (n=6 per group) were anesthetized with sevoflurane for 2 hours or with sham procedure. Subsequently, serum and hippocampal tissues were harvested for analysis. Further investigation into the relationship between isatin and neuroinflammation was conducted using BV2 microglial cells.

Results

Sevoflurane anesthesia led to the activation of inflammatory pathways, an increased presence of hippocampal astrocytes and microglia, and elevated expression of neuroinflammatory cytokines. Comparative analysis identified 12 differential metabolites that exhibited changes in both human and mouse serum post-sevoflurane anesthesia. Notably, isatin levels were significantly decreased after anesthesia. Notably, isatin levels significantly decreased after anesthesia, a factor known to stimulate proliferation and proinflammatory gene expression in microglia-the pivotal cell type in inflammatory responses.

Conclusion

Sevoflurane-induced alterations in serum metabolites in both elderly patients and aging mice, subsequently contributing to increased inflammation in the hippocampus.

Optimization of oral entacapone administration in patients undergoing levodopa-carbidopa intestinal gel treatment

BACKGROUND

Levodopa-carbidopa intestinal gel (LCIG) treatment markedly reduces motor fluctuations in patients with Parkinson's disease; however, some patients undergoing LCIG treatment may demonstrate clinical deterioration in the afternoon. Entacapone, a catechol-O-methyltransferase inhibitor, may be a promising adjunctive option for LCIG-treated patients; however, the optimal timing of oral entacapone administration to ameliorate clinical symptoms in the afternoon remains unexplored. This study aimed to investigate the optimal timing of oral entacapone administration in patients with Parkinson's disease undergoing LCIG treatment.

METHODS

Pharmacokinetic analysis and symptom assessment were performed on three days: a day without entacapone administration, day with oral entacapone administration at 13:00, and day with oral entacapone administration at 15:00.

RESULTS

Eight LCIG-treated patients were enrolled, of whom seven completed this study. The relative plasma concentrations of levodopa with entacapone administration at 13:00 were gradually increased, especially at 18:00 and were significantly higher than those without entacapone administration (127.10 ± 25.06% vs. 97.51 ± 22.20%). The relative plasma concentrations of 3-O-methyldopa were gradually increased without entacapone administration, whereas those with entacapone administration at 13:00 were lower than those without entacapone administration, especially at 17:00 (97.47 ± 3.70% vs. 110.71 ± 9.84%). Administering oral entacapone at 15:00 increased and decreased the relative plasma concentrations of levodopa and 3-O-methyldopa, respectively, but without significant difference. The "Off" time was shorter with entacapone administration at 13:00 (0.43 ± 0.79 h) and at 15:00 (0.57 ± 0.79 h) than that without entacapone administration (1.14 ± 1.46 h).

CONCLUSIONS

The concomitant use of oral entacapone in the early afternoon may be effective in improving afternoon symptoms in patients undergoing LCIG treatment.

Adopting the Rumsfeld approach to understanding the action of levodopa and apomorphine in Parkinson's disease

Dopaminergic therapies dominate the treatment of the motor and non-motor symptoms of Parkinson's disease (PD) but there have been no major advances in therapy in many decades. Two of the oldest drugs used appear more effective than others-levodopa and apomorphine-but the reasons for this are seldom discussed and this may be one cause for a lack of progress. This short review questions current thinking on drug action and looks at whether adopting the philosophy of ex-US Secretary of State Donald Rumsfeld reveals 'unknown' aspects of the actions of levodopa and apomorphine that provide clues for a way forward. It appears that both levodopa and apomorphine have a more complex pharmacology than classical views would suggest. In addition, there are unexpected facets to the mechanisms through which levodopa acts that are either forgotten as 'known unknowns' or ignored as 'unknown unknowns'. The conclusion reached is that we may not know as much as we think about drug action in PD and there is a case for looking beyond the obvious.

Amelioration of AlCl3-induced Memory Loss in the Rats by an Aqueous Extract of Guduchi, a Medhya Rasayana

Background

In ayurvedic practice, the Guduchi ( Tinospora cordifolia (Willd.) Miers) stem is used as a Medhya drug for its beneficial effects on memory improvement.

Objectives

The current study was planned to explore the Medhya properties of the Guduchi stem extract by observing its ameliorating effect on AlCl3-induced neurotoxicity in rats that acted as a chronic model of memory loss.

Materials and Methods

The aqueous extract of the Guduchi stem was prepared per the Ayurvedic Pharmacopoeia of India and administered to the AlCl3-treated Wistar rats for 42 days. The biochemical assessment of the brain tissues of the treated animals was done by the acetylcholinesterase (AChE) inhibition assay, protein expression, and oxidative stress assays, namely lipid peroxidation, reduced glutathione, superoxide dismutase, and catalase assay. The neurobehavioral assessment was done using the elevated plus maze (EPM) test.

Results

The EPM test revealed that treatment with Guduchi extract showed marked improvement of memory status in rats along with reduced oxidative stress, and a marked modulation of the AChE inhibition and expression of AChE tubulin proteins.

Conclusion

The results substantiate the Medhya properties of the Guduchi. Detailed investigations are required to be carried out to explore the precise mechanism of the neuroprotective action of the Guduchi stem extract against the AlCl3-induced neurotoxicity in rats.

Effects of a New Natural Catechol-O-methyl Transferase Inhibitor on Two In Vivo Models of Parkinson's Disease

A tetrahydroisoquinoline identified in Mucuna pruriens ((1R,3S)-6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline-1,3-dicarboxylic acid, compound 4) was synthesized and assessed for its in vitro pharmacological profile and in vivo effects in two animal models of Parkinson's disease. Compound 4 inhibits catechol-O-methyltransferase (COMT) with no affinity for the dopaminergic receptors or the dopamine transporter. It restores dopamine-mediated motor behavior when it is co-administered with L-DOPA to C. elegans worms with 1-methyl-4-phenylpyridinium-damaged dopaminergic neurons. In a 6-hydroxydopamine rat model of Parkinson's disease, its co-administration at 30 mg/kg with L-DOPA enhances the effect of L-DOPA with an intensity similar to that of tolcapone 1 at 30 mg/kg but for a shorter duration. The effect is not dose-dependent. Compound 4 seems not to cross the blood-brain barrier and thus acts as a peripheral COMT inhibitor. COMT inhibition by compound 4 further validates the traditional use of M. pruriens for the treatment of Parkinson's disease, and compound 4 can thus be considered as a promising drug candidate for the development of safe, peripheral COMT inhibitors.

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.

Determination of levodopa by chromatography-based methods in biological samples: a review

Levodopa (L-DOPA) is the most effective drug for Parkinson's disease; however, various side effects occur during therapy. L-DOPA metabolites and the high cumulative dose of L-DOPA were responsible for its side effects. It is necessary to monitor the concentration of L-DOPA and its metabolites for individualized therapy. This review focuses on L-DOPA analysis by chromatography-based methods in biological matrices. Literature published up to September 2021 was collected in the PubMed, Web of Science, and Embase by using search strategy ("levodopa" OR "L-DOPA") AND ("chromatography"). A total of 1249 articles were identified and 32 articles were included. The contents for method development and validation were summarized and analyzed. Due to the instability of catecholamines (L-DOPA, dopamine, and 3-O-methyldopa) and carbidopa, antioxidation (0.5 mg sodium metabisulfite for 100 μL sample) and environment temperature control were used alone or in combination to enhance stability. Sample was mainly pretreated by protein precipitation (0.4-0.7 M perchloric acid). Separation was usually achieved using methanol or acetonitrile:water (with formic acid) on C18 columns. Mass spectrometry, electrochemical detector, ultraviolet-visible detector and fluorescence detector were used for detection. For L-DOPA, the calibration range was 2.5-10,000 ng/mL, the matrix effect and its coefficient of variation was 85-115 and -9.0-8.5%, and the recovery was 66.8-127.0%. Without stabilization strategy, L-DOPA was stable in plasma at room temperature for 1-7 h (4-6 h for most studies), at - 70 °C to - 80 °C for 10-20 days and after 3-5 freeze-thaw cycles. With stabilization strategies, the stability of L-DOPA in plasma was significantly improved. Metabolites of L-DOPA and enzyme inhibitors (carbidopa, entacapone, tolcapone and benserazide) were all stable in biological matrix. This study might be useful for researchers to develop their methods for individualized therapy of patients with Parkinson.

Pharmacokinetics of Levodopa and 3-O-Methyldopa in Parkinsonian Patients Treated with Levodopa and Ropinirole and in Patients with Motor Complications

Parkinson’s disease (PD) is a progressive, neurodegenerative disorder primarily affecting dopaminergic neuronal systems, with impaired motor function as a consequence. The most effective treatment for PD remains the administration of oral levodopa (LD). Long-term LD treatment is frequently associated with motor fluctuations and dyskinesias, which exert a serious impact on a patient’s quality of life. The aim of our study was to determine the pharmacokinetics of LD: used as monotherapy or in combination with ropinirole, in patients with advanced PD. Furthermore, an effect of ropinirole on the pharmacokinetics of 3-OMD (a major LD metabolite) was assessed. We also investigated the correlation between the pharmacokinetic parameters of LD and 3-OMD and the occurrence of motor complications. Twenty-seven patients with idiopathic PD participated in the study. Thirteen patients received both LD and ropinirole, and fourteen administered LD monotherapy. Among 27 patients, twelve experienced fluctuations and/or dyskinesias, whereas fifteen were free of motor complications. Inter- and intra-individual variation in the LD and 3-OMD concentrations were observed. There were no significant differences in the LD and 3-OMD concentrations between the patients treated with a combined therapy of LD and ropinirole, and LD monotherapy. There were no significant differences in the LD concentrations in patients with and without motor complications; however, plasma 3-OMD levels were significantly higher in patients with motor complications. A linear one-compartment pharmacokinetic model with the first-order absorption was adopted for LD and 3-OMD. Only mean exit (residence) time for 3-OMD was significantly shorter in patients treated with ropinirole. Lag time, V/F, CL/F and t_max of LD had significantly lower values in patients with motor complications. On the other hand, AUC were significantly higher in these patients, both for LD and 3-OMD. 3-OMD C_max was significantly higher in patients with motor complications as well. Our results showed that ropinirole does not influence LD or 3-OMD concentrations. Higher 3-OMD levels play a role in inducing motor complications during long-term levodopa therapy.

Mass spectrometry imaging identifies abnormally elevated brain l-DOPA levels and extrastriatal monoaminergic dysregulation in l-DOPA-induced dyskinesia

l-DOPA treatment for Parkinson's disease frequently leads to dyskinesias, the pathophysiology of which is poorly understood. We used MALDI-MSI to map the distribution of l-DOPA and monoaminergic pathways in brains of dyskinetic and nondyskinetic primates. We report elevated levels of l-DOPA, and its metabolite 3-O-methyldopa, in all measured brain regions of dyskinetic animals and increases in dopamine and metabolites in all regions analyzed except the striatum. In dyskinesia, dopamine levels correlated well with l-DOPA levels in extrastriatal regions, such as hippocampus, amygdala, bed nucleus of the stria terminalis, and cortical areas, but not in the striatum. Our results demonstrate that l-DOPA-induced dyskinesia is linked to a dysregulation of l-DOPA metabolism throughout the brain. The inability of extrastriatal brain areas to regulate the formation of dopamine during l-DOPA treatment introduces the potential of dopamine or even l-DOPA itself to modulate neuronal signaling widely across the brain, resulting in unwanted side effects.

Impact of the catechol-O-methyltransferase Val158Met polymorphism on the pharmacokinetics of L-dopa and its metabolite 3-O-methyldopa in combination with entacapone

In the pharmacotherapy of patients with Parkinson's disease (PD), entacapone reduces the peripheral metabolism of L-dopa to 3-O-methyldopa (3-OMD), thereby prolonging the half-life (t_1/2) of L-dopa and increasing the area under the concentration curve (AUC). The effect of entacapone on the pharmacokinetics of L-dopa differs between patients with high-activity (H/H) and low-activity (L/L) catechol-O-methyltransferase (COMT) Val158Met polymorphisms, but the effects are unclear in heterozygous (H/L) patients. 3-OMD has a detrimental effect and results in a poor response to L-dopa treatment in patients with PD; however, the influence of this polymorphism on the production of 3-OMD remains unknown. Therefore, the present study aimed to clarify the effect of the COMT Val158Met polymorphism on the concentrations of L-dopa and 3-OMD in the presence of entacapone. We performed an open-label, single-period, single-sequence crossover study at two sites in Japan. The study included 54 Japanese patients with PD, who underwent an acute L-dopa administration test with and without 100 mg entacapone on two different days. Entacapone increased L-dopa AUC_0-infinity by 1.59 ± 0.26-fold in the H/H group, which was significantly higher than that in the H/L (1.41 ± 0.36-fold) and L/L (1.28 ± 0.21-fold) groups (p < 0.05). The concurrent administration of L-dopa with entacapone suppressed the increase in 3-OMD levels compared with L-dopa alone in all genotypes. Our results suggest that the COMT Val158Met polymorphism may be an informative biomarker for individualized dose adjustment of COMT inhibitors in the treatment of PD.

High throughput newborn screening for aromatic ʟ-amino-acid decarboxylase deficiency by analysis of concentrations of 3-O-methyldopa from dried blood spots

Aromatic l-amino-acid decarboxylase (AADC) deficiency is an inherited disorder of biogenic amine metabolism with a broad neurological phenotype. The clinical symptoms overlap with other diseases resulting in an often delayed diagnosis. Innovative disease-changing treatment options, particularly gene therapy, have emphasised the need for an early diagnosis. We describe the first method for 3-O-methyldopa (3-OMD) analysis in dried blood spots (DBS) suitable for high throughput newborn screening (NBS). We established a novel tandem mass spectrometry method to quantify 3-OMD in DBS and successfully tested it in 38 888 unaffected newborns, 14 heterozygous DDC variant carriers, seven known AADC deficient patients, and 1079 healthy control subjects. 3-OMD concentrations in 38 888 healthy newborns revealed a mean of 1.16 μmol/L (SD = 0.31, range 0.31-4.6 μmol/L). 1079 non-AADC control subjects (0-18 years) showed a mean 3-OMD concentration of 0.78 μmol/L (SD = 1.75, range 0.24-2.36 μmol/L) with a negative correlation with age. Inter- and intra-assay variability was low, and 3-OMD was stable over 32 days under different storage conditions. We identified seven confirmed AADC deficient patients (mean 3-OMD 9.88 μmol/L [SD = 13.42, range 1.82-36.93 μmol/L]). The highest concentration of 3-OMD was found in a NBS filter card of a confirmed AADC deficient patient with a mean 3-OMD of 35.95 μmol/L. 14 DDC variant carriers showed normal 3-OMD concentrations. We demonstrate a novel high-throughput method to measure 3-OMD in DBS, which allows integration in existing NBS programs enabling early diagnosis of AADC deficiency.

Serotonergic system modulation holds promise for L-DOPA-induced dyskinesias in hemiparkinsonian rats: A systematic review

The alleged effects of serotonergic agents in alleviating levodopa-induced dyskinesias (LIDs) in parkinsonian patients are debatable. To this end, we systematically reviewed the serotonergic agents used for the treatment of LIDs in a 6-hydroxydopamine model of Parkinson's disease in rats. We searched MEDLINE via PubMed, Embase, Google Scholar, and Proquest for entries no later than March 2018, and restricted the search to publications on serotonergic agents used for the treatment of LIDs in hemiparkinsonian rats. The initial search yielded 447 citations, of which 49 articles and one conference paper met our inclusion criteria. The results revealed ten different categories of serotonergic agents, including but not limited to 5-HT_1A/BR agonists, 5-HT_2AR antagonists, selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitor (SNRIs), and tricyclic antidepressants (TCAs), all of which improved LIDs without imposing considerable adverse effects. Although there is promising evidence regarding the role of these agents in relieving LIDs in hemiparkinsonian rats, further studies are needed for the enlightenment of hidden aspect of these molecules in terms of mechanisms and outcomes. Given this, improving the quality of the pre-clinical studies and designing appropriate clinical trials will help fill the bench-to-bedside gap.

L-DOPA in Parkinson's Disease: Looking at the "False" Neurotransmitters and Their Meaning

L-3,4-dihydroxyphenylalanine (L-DOPA) has been successfully used in the treatment of Parkinson’s disease (PD) for more than 50 years. It fulfilled the criteria to cross the blood–brain barrier and counteract the biochemical defect of dopamine (DA). It remarkably worked after some adjustments in line with the initial hypothesis, leaving a poor place to the plethora of mechanisms involving other neurotransmitters or mechanisms of action beyond newly synthesized DA itself. Yet, its mechanism of action is far from clear. It involves numerous distinct cell populations and does not mimic the mechanism of action of dopaminergic agonists. L-DOPA-derived DA is mainly released by serotonergic neurons as a false neurotransmitter, and serotonergic neurons are involved in L-DOPA-induced dyskinesia. The brain pattern and magnitude of DA extracellular levels together with this status of false neurotransmitters suggest that the striatal effects of DA via this mechanism would be minimal. Other metabolic products coming from newly formed DA or through the metabolism of L-DOPA itself could be involved. These compounds can be trace amines and derivatives. They could accumulate within the terminals of the remaining monoaminergic neurons. These “false neurotransmitters,” also known for some of them as inducing an “amphetamine-like” mechanism, could reduce the content of biogenic amines in terminals of monoaminergic neurons, thereby impairing the exocytotic process of monoamines including L-DOPA-induced DA extracellular outflow. The aim of this review is to present the mechanism of action of L-DOPA with a specific attention to “false neurotransmission.”

Pharmacokinetics, metabolism and safety of deuterated L-DOPA (SD-1077)/carbidopa compared to L-DOPA/carbidopa following single oral dose administration in healthy subjects

AIMS

SD-1077, a selectively deuterated precursor of dopamine (DA) structurally related to L-3,4-dihydroxyphenylalanine (L-DOPA), is under development for treatment of motor symptoms of Parkinson's disease. Preclinical models have shown slower metabolism of central deuterated DA. The present study investigated the peripheral pharmacokinetics (PK), metabolism and safety of SD-1077.

METHODS

Plasma and urine PK of drug and metabolites and safety after a single oral 150 mg SD-1077 dose were compared to 150 mg L-DOPA, each in combination with 37.5 mg carbidopa (CD) in a double-blind, two-period, crossover study in healthy volunteers (n = 16).

RESULTS

Geometric least squares mean ratios (GMRs) and 90% confidence intervals (90% CI) of SD-1077 vs. L-DOPA for C_max , AUC_0-t , and AUC_0-inf were 88.4 (75.9-103.1), 89.5 (84.1-95.3), and 89.6 (84.2-95.4), respectively. Systemic exposure to DA was significantly higher after SD-1077/CD compared to that after L-DOPA/CD, with GMRs (90% CI) of 1.8 (1.45-2.24; P = 0.0005) and 2.06 (1.68-2.52; P < 0.0001) for C_max and AUC_0-t and a concomitant reduction in the ratio of 3,4-dihydroxyphenylacetic acid/DA confirming slower metabolic breakdown of DA by monoamine oxidase (MAO). There were increases in systemic exposures to metabolites of catechol O-methyltransferase (COMT) reaction, 3-methoxytyramine (3-MT) and 3-O-methyldopa (3-OMD) with GMRs (90% CI) for SD-1077/CD to L-DOPA/CD for 3-MT exposure of 1.33 (1.14-1.56; P = 0.0077) and 1.66 (1.42-1.93; P < 0.0001) for C_max and AUC_0-t , respectively and GMRs (90% CI) for 3-OMD of 1.19 (1.15, 1.23; P < 0.0001) and 1.31 (1.27, 1.36; P < 0.0001) for C_max and AUC_0-t . SD-1077/CD exhibited comparable tolerability and safety to L-DOPA/CD.

CONCLUSIONS

SD-1077/CD demonstrated the potential to prolong exposure to central DA at comparable peripheral PK and safety to the reference L-DOPA/CD combination. A single dose of SD-1077 is safe for further clinical development in Parkinson's disease patients.

Levodopa in Parkinson's Disease: Current Status and Future Developments

BACKGROUND

Ever since the pioneering reports in the 60s, L-3,4-Dioxyphenylalanine (levodopa) has represented the gold standard for the treatment of Parkinson's Disease (PD). However, long-term levodopa (LD) treatment is frequently associated with fluctuations in motor response with serious impact on patient quality of life. The pharmacokinetic and pharmacodynamic properties of LD are pivotal to such motor fluctuations: discontinuous drug delivery, short half-life, poor bioavailability, and narrow therapeutic window are all crucial for such fluctuations. During the last 60 years, several attempts have been made to improve LD treatment and avoid long-term complications.

METHODS

Research and trials to improve the LD pharmacokinetic since 1960s are reviewed, summarizing the progressive improvements of LD treatment.

RESULTS

Inhibitors of peripheral amino acid decarboxylase (AADC) have been introduced to achieve proper LD concentration in the central nervous system reducing systemic adverse events. Inhibitors of catechol-O-methyltransferase (COMT) increased LD half-life and bioavailability. Efforts are still being made to achieve a continuous dopaminergic stimulation, with the combination of oral LD with an AADC inhibitor and a COMT inhibitor, or the intra-duodenal water-based LD/ carbidopa gel. Further approaches to enhance LD efficacy are focused on new non-oral administration routes, including nasal, intra-duodenal, intrapulmonary (CVT-301) and subcutaneous (ND0612), as well as on novel ER formulations, including IPX066, which recently concluded phase III trial.

CONCLUSION

New LD formulations, oral compounds as well as routes have been tested in the last years, with two main targets: achieve continuous dopaminergic stimulation and find an instant deliver route for LD.

Metabolomic changes demonstrate reduced bioavailability of tyrosine and altered metabolism of tryptophan via the kynurenine pathway with ingestion of medical foods in phenylketonuria

BACKGROUND

Deficiencies of the monoamine neurotransmitters, such as dopamine synthesized from Tyr and serotonin synthesized from Trp, are of concern in PKU. Our objective was to utilize metabolomics analysis to assess monoamine metabolites in subjects with PKU consuming amino acid medical foods (AA-MF) and glycomacropeptide medical foods (GMP-MF).

METHODS

Subjects with PKU consumed a low-Phe diet combined with AA-MF or GMP-MF for 3weeks each in a randomized, controlled, crossover study. Metabolomic analysis was conducted by Metabolon, Inc. on plasma (n=18) and urine (n=9) samples. Catecholamines and 6-sulfatoxymelatonin were measured in 24-h urine samples.

RESULTS

Intake of Tyr and Trp was ~50% higher with AA-MF, and AA-MF were consumed in larger quantities, less frequently during the day compared with GMP-MF. Performance on neuropsychological tests and concentrations of neurotransmitters derived from Tyr and Trp were not significantly different with AA-MF or GMP-MF. Plasma serotonin levels of gut origin were higher in subjects with variant compared with classical PKU, and with GMP-MF compared with AA-MF in subjects with variant PKU. Metabolomics analysis identified higher levels of microbiome-derived compounds synthesized from Tyr, such as phenol sulfate, and higher levels of compounds synthesized from Trp in the kynurenine pathway, such as quinolinic acid, with ingestion of AA-MF compared with GMP-MF.

CONCLUSIONS

The Tyr from AA-MF is less bioavailable due, in part, to greater degradation by intestinal microbes compared with the Tyr from prebiotic GMP-MF. Research is needed to understand how metabolism of Trp via the kynurenine pathway and changes in the intestinal microbiota affect health for individuals with PKU. This trial is registered at www.clinicaltrials.gov as NCT01428258.

Expanding the repertoire of L-DOPA's actions: A comprehensive review of its functional neurochemistry

Though a multi-facetted disorder, Parkinson's disease is prototypically characterized by neurodegeneration of nigrostriatal dopaminergic neurons of the substantia nigra pars compacta, leading to a severe disruption of motor function. Accordingly, L-DOPA, the metabolic precursor of dopamine (DA), is well-established as a treatment for the motor deficits of Parkinson's disease despite long-term complications such as dyskinesia and psychiatric side-effects. Paradoxically, however, despite the traditional assumption that L-DOPA is transformed in residual striatal dopaminergic neurons into DA, the mechanism of action of L-DOPA is neither simple nor entirely clear. Herein, focussing on its influence upon extracellular DA and other neuromodulators in intact animals and experimental models of Parkinson's disease, we highlight effects other than striatal generation of DA in the functional profile of L-DOPA. While not excluding a minor role for glial cells, L-DOPA is principally transformed into DA in neurons yet, interestingly, with a more important role for serotonergic than dopaminergic projections. Moreover, in addition to the striatum, L-DOPA evokes marked increases in extracellular DA in frontal cortex, nucleus accumbens, the subthalamic nucleus and additional extra-striatal regions. In considering its functional profile, it is also important to bear in mind the marked (probably indirect) influence of L-DOPA upon cholinergic, GABAergic and glutamatergic neurons in the basal ganglia and/or cortex, while anomalous serotonergic transmission is incriminated in the emergence of L-DOPA elicited dyskinesia and psychosis. Finally, L-DOPA may exert intrinsic receptor-mediated actions independently of DA neurotransmission and can be processed into bioactive metabolites. In conclusion, L-DOPA exerts a surprisingly complex pattern of neurochemical effects of much greater scope that mere striatal transformation into DA in spared dopaminergic neurons. Their further experimental and clinical clarification should help improve both L-DOPA-based and novel strategies for controlling the motor and other symptoms of Parkinson's disease.

Effects of acute and sub-chronic L-dopa therapy on striatal L-dopa methylation and dopamine oxidation in an MPTP mouse model of Parkinsons disease

AIMS

The molecular mechanisms for the loss of 3,4-dihydroxyphenylalanine (l-dopa) efficacy during the treatment of Parkinson's disease (PD) are unknown. Modifications related to catecholamine metabolism such as changes in l-dopa and dopamine (DA) metabolism, the modulation of catecholamine enzymes and the production of interfering metabolites are the primary concerns of this study.

MAIN METHODS

Normal (saline) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) pre-treated mice were primed with 100mg/kg of l-dopa twice a day for 14 days, and a matching group remained l-dopa naïve. l-dopa naive and primed mice received a challenge dose of 100mg/kg of l-dopa and were sacrificed 30 min later. Striatal catecholamine levels and the expression and activity of catechol-O-methyltransferase (COMT) were determined.

KEY FINDINGS

Normal and MPTP pre-treated animals metabolize l-dopa and DA similarly during l-dopa therapy. Administration of a challenge dose of l-dopa increased l-dopa and DA metabolism in l-dopa naïve animals, and this effect was enhanced in l-dopa primed mice. The levels of 3-OMD in MPTP pre-treated animals were almost identical to those in normal mice, which we found are likely due to increased COMT activity in MPTP pre-treated mice.

SIGNIFICANCE

The results of this comparative study provide evidence that sub-chronic administration of l-dopa decreases the ability of the striatum to accumulate l-dopa and DA, due to increased metabolism via methylation and oxidation. This data supports evidence for the metabolic adaptation of the catecholamine pathway during long-term treatment with l-dopa, which may explain the causes for the loss of l-dopa efficacy.

Detoxification and antioxidative therapy for levodopa-induced neurodegeneration in Parkinson's disease

Levodopa is the most efficacious drug treatment option for Parkinson's disease. However, in particular, high levodopa dosing may contribute to disease progression. Chronic levodopa metabolism reduces the methylation capacity and the antioxidant defense. Thus, this levodopa-induced free radical production complements the disease process, which considerably depends on free radical-induced, apoptotic neuronal cell death. Accordingly, clinical long-term studies with in the laboratory neuroprotective compounds failed in clinical investigations, as these studies were performed in levodopa-naive patients with Parkinson's disease over a relative short interval. Therefore, the likelihood for a positive outcome was rather low, since trials only focused on the disease process in levodopa-naive patients. However, studies on antioxidant therapeutic strategies were positive in levodopa-treated Parkinson's disease patients. To counteract these metabolic long-term levodopa-associated effects, chronic levodopa therapy should be combined with supplemental application of free radical scavengers and methyl group donating vitamins.

Beneficial effects of natural phenolics on levodopa methylation and oxidative neurodegeneration

Levodopa (L-DOPA) is widely used for symptomatic management in Parkinson's disease. We recently showed that (-)-epigallocatechin-3-gallate, a tea polyphenol, not only inhibits L-DOPA methylation, but also protects against oxidative hippocampal neurodegeneration. In the present study, we sought to determine several other common dietary phenolics, namely, tea catechins [(+)-catechin and (-)-epicatechin] and a representative flavonoid (quercetin), for their ability to modulate L-DOPA methylation and to protect against oxidative hippocampal injury. A combination of in vitro biochemical assays, cell culture-based mechanistic analyses, and in vivo animal models was used. While both tea catechins and quercetin strongly inhibit human liver catechol-O-methyltransferase (COMT)-mediated O-methylation of L-DOPA in vitro, only (+)-catechin exerts a significant inhibition of L-DOPA methylation in both peripheral compartment and striatum in rats. The stronger in vivo effect of (+)-catechin on L-DOPA methylation compared to the other dietary compounds is due to its better bioavailability in vivo. In addition, (+)-catechin strongly reduces glutamate-induced oxidative cytotoxicity in HT22 mouse hippocampal neurons in vitro through inactivation of the nuclear factor-κB signaling pathway. Administration of (+)-catechin also exerts a strong neuroprotective effect in the kainic acid-induced oxidative hippocampal neurodegeneration model in rats. In conclusion, (+)-catechin is a dietary polyphenolic that may have beneficial effects in L-DOPA-based treatment of Parkinson patients by inhibiting L-DOPA methylation plus reducing oxidative neurodegeneration.

L-Dihydroxyphenylalanine modulates the steady-state expression of mouse striatal tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine and its metabolites in an MPTP mouse model of Parkinson's disease

AIMS

l-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective symptomatic treatment for Parkinson's disease (PD), but PD patients usually experience a successful response to L-DOPA therapy followed by a progressive loss of response. L-DOPA efficacy relies on its decarboxylation by aromatic l-amino acid decarboxylase (AAAD) to form dopamine (DA). So exogenous L-DOPA drives the reaction and AAAD becomes the rate limiting enzyme in the supply of DA. In turn, exogenous L-DOPA regulates the expression and activity of AAAD as well as the synthesis of DA and its metabolites, changes that may be linked to the efficacy and side-effects of L-DOPA.

MAIN METHODS

One-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse PD model was utilized to study the effects of L-DOPA on the steady-state level and activity of AAAD, tyrosine hydroxylase (TH), DA and the metabolites of DA. The MPTP and control mice were treated twice daily with PBS or with 100mg/kg of L-DOPA for 14days and the expression and activity of AAAD, the expression of TH and the levels of DA and its metabolites were determined 24h after L-DOPA or PBS treatment, when exogenous L-DOPA is eliminated.

KEY FINDINGS

In the MPTP model, L-DOPA reduced the steady-state expression and the activity of striatal AAAD by 52% and 50%, respectively, DA and metabolites were also significantly decreased.

SIGNIFICANCE

The outcome shows that while L-DOPA replenishes striatal DA it also down-regulates AAAD and the steady-state synthesis and metabolic capability of the dopaminergic system. These findings are important in the precipitation of L-DOPA induced side effects and the management of L-DOPA therapy.

Cysteinyl-glycine reduction as marker for levodopa-induced oxidative stress in Parkinson's disease patients

Oxidative stress is influenced by the thiol homeostasis, which determines the redox milieu. One of its components is Cysteinyl-glycine (Cys-Gly) generation, as its metabolic precursor is the free radicals scavenging glutathione. Levodopa is under suspicion to promote oxidative stress via the turnover of its metabolite dopamine in abundant mitochondria. Objective was to investigate the impact of levodopa on Cys-Gly plasma metabolism. Fifteen patients with Parkinson's disease orally took one 200-mg levodopa/50-mg carbidopa (CD) containing tablet. Levodopa, its derivative 3-O-methyldopa (3-OMD), and free Cys-Gly were measured at baseline, 60 and 120 min following levodopa/CD administration. Cys-gly concentrations decreased, levodopa and 3-OMD levels increased. Inverse relationships appeared between computed differences of Cys-gly and 3-OMD bioavailability. We conclude that Cys-Gly decline is related to levodopa metabolism to 3-OMD. Cys-Gly decay may result from the alternative transformation of glutathione to its oxidized form glutathione dissulfide as consequence of free radical scavenging.

Microdialysis with radiometric monitoring of L-[β-11C]DOPA to assess dopaminergic metabolism: effect of inhibitors of L-amino acid decarboxylase, monoamine oxidase, and catechol-O-methyltransferase on rat striatal dialysate

The catecholamine, dopamine (DA), is synthesized from 3,4-dihydroxy-L-phenylalanine (L-DOPA) by aromatic L-amino acid decarboxylase (AADC). Dopamine metabolism is regulated by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). To measure dopaminergic metabolism, we used microdialysis with radiometric detection to monitor L-[β-(11)C]DOPA metabolites in the extracellular space of the rat striatum. We also evaluated the effects of AADC, MAO, and COMT inhibitors on metabolite profiles. The major early species measured after administration of L-[β-(11)C]DOPA were [(11)C]3,4-dihydroxyphenylacetic acid ([(11)C]DOPAC) and [(11)C]homovanillic acid ([(11)C]HVA) in a 1:1 ratio, which shifted toward [(11)C]HVA with time. An AADC inhibitor increased the uptake of L-[β-(11)C]DOPA and L-3-O-methyl-[(11)C]DOPA and delayed the accumulation of [(11)C]DOPAC and [(11)C]HVA. The MAO and COMT inhibitors increased the production of [(11)C]3-methoxytyramine and [(11)C]DOPAC, respectively. These results reflect the L-DOPA metabolic pathway, suggesting that this method may be useful for assessing dopaminergic metabolism.

Dual beneficial effects of (-)-epigallocatechin-3-gallate on levodopa methylation and hippocampal neurodegeneration: in vitro and in vivo studies

BACKGROUND

A combination of levodopa (L-DOPA) and carbidopa is the most commonly-used treatment for symptom management in Parkinson's disease. Studies have shown that concomitant use of a COMT inhibitor is highly beneficial in controlling the wearing-off phenomenon by improving L-DOPA bioavailability as well as brain entry. The present study sought to determine whether (-)-epigallocatechin-3-gallate (EGCG), a common tea polyphenol, can serve as a naturally-occurring COMT inhibitor that also possesses neuroprotective actions.

METHODOLOGY/PRINCIPAL FINDINGS

Using both in vitro and in vivo models, we investigated the modulating effects of EGCG on L-DOPA methylation as well as on chemically induced oxidative neuronal damage and degeneration. EGCG strongly inhibited human liver COMT-mediated O-methylation of L-DOPA in a concentration-dependent manner in vitro, with an average IC50 of 0.36 microM. Oral administration of EGCG moderately lowered the accumulation of 3-O-methyldopa in the plasma and striatum of rats treated with L-DOPA+carbidopa. In addition, EGCG also reduced glutamate-induced oxidative cytotoxicity in cultured HT22 mouse hippocampal neuronal cells through inactivation of the nuclear factor kappaB-signaling pathway. Under in vivo conditions, administration of EGCG exerted a strong protective effect against kainic acid-induced oxidative neuronal death in the hippocampus of rats.

CONCLUSIONS/SIGNIFICANCE

These observations suggest that oral administration of EGCG may have significant beneficial effects in Parkinson's patients treated with L-DOPA and carbidopa by exerting a modest inhibition of L-DOPA methylation plus a strong neuroprotection against oxidative damage and degeneration.

Reduced 3-O-methyl-dopa levels in OCD patients and their unaffected parents is associated with the low activity M158 COMT allele

The catechol-O-methyltransferase (COMT) gene is considered as a candidate gene in obsessive-compulsive disorder (OCD). Specifically, the COMT low-activity M158 allele has been suggested to be associated with OCD. However, there is no study reporting that COMT activity is decreased in OCD patients and that the decrease is mediated by the V158M polymorphism. Therefore, the purpose of our study was to assess COMT activity in OCD by measuring plasma levels of 3-O-methyl-dopa (3-OMD), which result from the methylation of levodopa by COMT, and to investigate the relationship between 3-OMD levels and the V158M polymorphism. We also examined whether 3-OMD levels represented an endophenotype, associated with the genetic liability to OCD, by assessing unaffected relatives of OCD patients. We assessed plasma 3-OMD levels in a sample of drug-free OCD probands (n = 34) and their unaffected parents (n = 63), and compared them with controls (n = 85). The COMT V158M polymorphism was genotyped in all participants. Lower plasma 3-OMD levels were found in OCD probands and their unaffected parents compared to controls. The COMT M158 allele was associated with reduced plasma 3-OMD levels in a co-dominant manner, both in OCD probands and their relatives, but not in controls. Our results suggest that COMT activity could act as a limiting factor for the production of 3-OMD in OCD patients and in their relatives. These findings further support a role of COMT in the susceptibility to OCD and provide evidence that 3-OMD levels could represent an endophenotype in OCD.

Excessive S-adenosyl-L-methionine-dependent methylation increases levels of methanol, formaldehyde and formic acid in rat brain striatal homogenates: possible role in S-adenosyl-L-methionine-induced Parkinson's disease-like disorders

AIMS

Excessive methylation may be a precipitating factor for Parkinson's disease (PD) since S-adenosylmethionine (SAM), the endogenous methyl donor, induces PD-like changes when injected into the rat brain. The hydrolysis of the methyl ester bond of the methylated proteins produces methanol. Since methanol is oxidized into formaldehyde, and formaldehyde into formic acid in the body, we investigated the effects of SAM on the production of methanol, formaldehyde and formic acid in rat brain striatal homogenates and the toxicity of these products in PC12 cells.

MAIN METHODS

Radio-enzymatic and colorimetric assays, cell viability, Western blot.

KEY FINDINGS

SAM increased the formation of methanol, formaldehyde and formic acid in a concentration and time-dependent manner. Concentrations of [3H-methyl]-SAM at 0.17, 0.33, 0.67 and 1.34 nM produced 3.8, 8.0, 18.3 and 34.4 fmol/mg protein/h of [3H] methanol in rat striatal homogenates, respectively. SAM also significantly generated formaldehyde and formic acid in striatal homogenates. Formaldehyde was the most toxic metabolite to differentiated PC12 pheochromocytoma cells in cell culture studies, indicating that formaldehyde formed endogenously may contribute to neuronal damage in excessive methylation conditions. Subtoxic concentration of formaldehyde decreased the expression of tyrosine hydroxylase, the limiting factor in dopamine synthesis. Formaldehyde was more toxic to catecholaminergic PC12 cells than C6 glioma cells, indicating that neurons are more vulnerable to formaldehyde than glia cells.

SIGNIFICANCE

We suggest that excessive carboxylmethylation of proteins might be involved in the SAM-induced PD-like changes and in the aging process via the toxic effects of formaldehyde.