Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0030567 (Parkinson's disease)
 63,064 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Increased and sustained central delivery of L-dihydroxyphenylalanine (L-DOPA) is a desirable therapeutic strategy in Parkinson's disease. We investigated the effects of peripheral catechol-O-methyltransferase (COMT) inhibition, by the non-toxic drug nitecapone on the metabolism of 6-[18F]fluoro-L-dihydroxyphenylalanine (6FD) and on its positron emission tomography (PET) imaging in non-human primates. Nitecapone produced a dose-dependent inhibition in the formation of 3-O-methyl-6-[18F]fluorodihydroxyphenylalanine (OMFD). This inhibition of OMFD formation was attended by increased production of other metabolites, in particular 6-[18F]fluorodopamine (6FDA), 6-[18F]fluorodihydroxyphenylacetic acid (FDOPAC), 6-[18F]fluorohomovanillic acid (FHVA) and [18F]-sulfated conjugates (FSC). Although nitecapone had no effect on plasma 6FD pharmacokinetics, high-dose nitecapone increased contrast of cerebral 18F uptake and retention between regions with high (striatum) versus sparse (parieto-occipital lobes) dopaminergic innervation. 18F uptake contrast was also improved between structures known to possess an intermediate dopaminergic innervation, including the upper brainstem, frontal and temporal lobes, versus sparsely innervated regions. This increased contrast was secondary to decreased activity in sparsely innervated structures and not to increased activity in highly innervated structures. Contrast was correlated inversely with the plasma OMFD/6FD concentration ratio, OMFD being the main 6FD metabolite which can cross the blood brain barrier. We conclude that nitecapone is an effective inhibitor of COMT in non-human primates. This inhibition results in increased 6FD flux through other catabolic pathways. Because of decreased OMFD formation, however, COMT inhibition improves the specificity of 6FD-PET and facilitates in-vivo detection of a wide range of dopaminergic innervation densities in cerebral structures.
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PMID:6-[18F]fluoro-L-dihydroxyphenylalanine metabolism and positron emission tomography after catechol-O-methyltransferase inhibition in normal and hemiparkinsonian monkeys. 828 20

We studied the effect of entacapone, a selective catechol-O-methyltransferase inhibitor, on the bioavailability and clinical effect of levodopa in Parkinson's disease (PD). On day 1 (control day), nine patients received their own levodopa (plus benserazide) medication only; for the next 7 days they received 200 mg of entacapone with each dose of levodopa (tid or qid). We evaluated disability in the morning (8 AM) before drug administration and then at 1-hour intervals until 6 PM on days 1, 2, and 8, using a modified motor part of the Unified Parkinson's Disease Rating Scale. Repeated blood samples were taken before and during the 4 hours after the morning drugs for pharmacokinetic evaluation of entacapone and of levodopa and its metabolites. Added to the levodopa treatment, entacapone decreased clinical disability by about 16% (p < 0.05) from day 1 to day 8. The area under the curve (AUC) of levodopa increased by 38% (p < 0.01) after administration of a single dose of entacapone and by 40% (p < 0.05) after 7 days of multiple dosing with entacapone. Entacapone did not change the Tmax and Cmax values of levodopa. After 7 days of treatment with entacapone, the AUC of 3-O-methyldopa had decreased by 44% (p < 0.01) and of homovanillic acid by 26% (p < 0.05) as compared with treatment with levodopa alone. Four patients became slightly more dyskinetic during entacapone treatment than before it. The combination of entacapone and levodopa was well tolerated, judged by the lack of significant changes in hemodynamic and safety variables.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of entacapone, a COMT inhibitor, on clinical disability and levodopa metabolism in parkinsonian patients. 829 96

L-Dopa is metabolized to 3-O-methyldopa (3OMD) by catechol-O-methyltransferase (COMT). This reduces the amount of L-dopa available for entry into brain. We studied the effect of OR-611, a new COMT inhibitor, on plasma and brain 6-[18F]-fluoro-L-dopa (6FD) metabolism in cynomolgus monkeys with positron emission tomography (PET). OR-611 pretreatment substantially reduced plasma 6FD metabolism to 3-O-methylfluorodopa (3OMFD). PET measurements of striatal 6FD concentrations showed an average 2.3-fold increase following OR-611 pretreatment, compared to the same animals in the control state. OR-611 inhibits plasma metabolism of 6FD and increases brain uptake of this L-dopa analog. OR-611 appears to be a promising agent as an adjunct to L-dopa for the treatment of patients with Parkinson's disease.
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PMID:Administration of the new COMT inhibitor OR-611 increases striatal uptake of fluorodopa. 834 Dec 94

We studied the effect of inhibiting the enzyme catechol-O-methyltransferase (COMT) by a novel COMT inhibitor, entacapone, on the pharmacokinetics and metabolism of levodopa in 12 healthy male volunteers. Single increasing oral doses of entacapone (50-400 mg) were administered concomitantly with a single oral dose of levodopa/carbidopa (100/25 mg). The subjects were treated with carbidopa (100 mg t.i.d.) for 1 day prior to the administration of study drugs. Plasma concentrations of levodopa; its metabolites 3-O-methyldopa (3-OMD), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA); as well as carbidopa and entacapone were determined for pharmacokinetic calculations. Entacapone dose-dependently increased the area under the plasma concentration-time curve (AUC) of levodopa; the increase was 65% after the 400 mg dose of entacapone. Neither Cmax nor Tmax of levodopa was statistically significantly influenced by entacapone. Entacapone dose-dependently decreased the AUC of 3-OMD, maximally by 58%. The AUC of DOPAC was statistically significantly increased but no change in the AUC of HVA was observed after entacapone. No drug-related adverse events or hemodynamic effects were observed. The in vivo biochemical effects of entacapone indicate that it is an orally active COMT inhibitor and that it may improve the therapeutic efficacy of levodopa in Parkinson's disease.
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PMID:The effect of catechol-O-methyl transferase inhibition by entacapone on the pharmacokinetics and metabolism of levodopa in healthy volunteers. 847 10

Twelve parkinsonian patients with levodopa-related end-of-dose fluctuations in disability were studied in an open-label trial to examine the effects of peripheral catechol-O-methyltransferase (COMT) inhibition with entacapone on pharmacokinetics and metabolism of levodopa and on clinical response to levodopa after a single dose and after 4 weeks' medication with entacapone. The clinical response was assessed with continuous monitoring using the motor part of Unified Parkinson's Disease Rating Scale. Entacapone increased statistically significantly the mean area under the plasma concentration-time curve (AUC) of levodopa by 29% after a single dose and by 21% after 4 weeks' administration, without affecting other pharmacokinetic parameters of levodopa. The AUC of 3-O-methyldopa decreased by 45% and AUC of homovanillic acid by 21% after 4 weeks' dosing with entacapone. The duration of motor response to levodopa increased significantly from 2.3 h to 3.2 h (i.e., by 39%) after a single dose and to 3.4 h (i.e., by 48%) after 4 weeks' medication with entacapone. The magnitude of clinical response remained unchanged, but peak latency of motor response was prolonged after 4 weeks' medication. The duration and magnitude of dyskinesias also increased. Peripheral COMT inhibition with entacapone increased significantly the bioavailability of levodopa and prolonged its antiparkinsonian effect after a single dose and after repeated dosing for 4 weeks. Thus entacapone seems to be a valuable adjuvant to levodopa treatment in parkinsonian patients with end-of-dose failure.
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PMID:Effect of one month's treatment with peripherally acting catechol-O-methyltransferase inhibitor, entacapone, on pharmacokinetics and motor response to levodopa in advanced parkinsonian patients. 872 41

The multistep assay of specific catechol-O-methyltransferase (COMT) activity in human erythrocytes was validated. Enzyme preparations from lysed erythrocytes were incubated with a substrate (3,4-dihydroxybenzoic acid) in the presence of Mg2+ and S-adenosylmethionine. The reaction products (vanillic acid and isovanillic acid) were analyzable by HPLC with electrochemical detection directly in the incubation medium after protein precipitation. The precision was calculated in order to define the random variability associated with the method by intra-assay and inter-assay relative standard deviations (RSDs) for the assays of both reaction products and protein. The intra-assay RDSs for the specific activities were between 4.8 and 11.9% (n = 5-6) at two levels of COMT activity. The inter-assay RSDs were between 6.4 and 14.2% (n = 5-6), respectively. The total variation was mostly caused by the protein assay and the HPLC assay, and contributions from the sample preparation and incubation steps were minor. Some results from the clinical application of the erythrocyte COMT assay are also reported. For both normal volunteers and patients having Parkinson's disease, a single 400 mg dose of entacapone, a peripherally acting COMT inhibitor, decreased the erythrocyte COMT activity. The application demonstrates that the assay was able to detect differences between the subjects and the effect of COMT inhibition in the clinical study.
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PMID:Validation of assay of catechol-O-methyltransferase activity in human erythrocytes. 873 81

Although theoretical reasons exist for believing that selegiline slows the progression of Parkinson's disease, this has not been shown in clinical trials. Selegiline improves the symptoms of Parkinson's disease, allowing the introduction of levodopa to be delayed in de-novo patients and, later, for levodopa to be used at a lower dose. It does not lessen the long-term problems of dyskinesia and fluctuations associated with levodopa therapy. The report of an increased mortality associated with selegiline therapy awaits further evaluation. Of the dopamine agonists, pergolide appears to be more potent than bromocriptine; cabergoline looks promising. The catechol-O-methyltransferase inhibitors, tolcapone and entacopone, prolong the duration of action of levodopa and also show promise. The main objective in the drug treatment of Parkinson's disease remains the optimization of the dose and frequency of levodopa administration.
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PMID:Controversies in the treatment of Parkinson's disease. 885 90

Parkinson's disease, a clinical syndrome with 4 cardinal features (bradykinesia, resting tremor, increased muscular rigidity and impaired postural balance), is mainly caused by the loss of dopaminergic neurons in the substantia nigra pars compacta. Although levodopa remains the 'gold standard' in the treatment of the disease, several emerging strategies are currently being developed. The first concerns new symptomatic drugs that either potentiate the effects of levodopa (e.g. slow-release preparations of levodopa, catechol-O-methyltransferase inhibitors and new dopamine agonists) or target clinical symptoms resistant to dopaminergic drugs (e.g. glutamate antagonists). The second strategy is to find drugs that are able to prevent or delay the neuronal death observed in Parkinson's disease. Several neuroprotective drugs are now in development in experimental research, but clinical trials in this area are still lacking. The development of these new drugs also depends on the validation of new clinical methodologies.
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PMID:New directions in the drug treatment of Parkinson's disease. 887 11

Tremor, akinesia, rigidity and postual instability are key signs of Parkinson's disease. The most important one is akinesia, which includes decreased spontaneous locomotor activity, slowness of movement, awkwardness and freezing. On the other hand, an electrical focal lesion in the brain, neurotoxin to dopaminergic neurons such as 6-hydroxydopamine (6-OHDA) or I-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP), cholinomimetic tremorogenic agents such as oxotremorine or tremorine, monoamine depleting agents such as reserpine or tetrabenazine, or dopamine receptor antagonists such as haloperidol are applied to render animal parkinsonism. The estimation of locomotor activity can be done accurately in animal models. Tremor can be studied using the animals treated by cerebral focal lesion, neurotoxins or cholinomimetics. Skillfulness is hard to estimate in animals, however, it can be done in primates. Freezing appeared in patients with levodopa treatment over a long period. This is a specific motor sign in Parkinson's disease, and cannot be observed in animals. Supplementing dopamine by levodopa administration, retarding the metabolism of levodopa or dopamine by dopa decarboxylase inhibitor (DCI), monoamine oxidase inhibitor type B (MAO-B) inhibitor or catechol-O-methyltransferase (COMT) inhibitor, dopamine receptor agonists, anticholinergic agents, dopamine release enhancer/ uptake inhibitor, N-methyl-D-aspartate (NMDA) receptor antagonists, adenosine receptor antagonists, neurotrophic factors, GM1-ganglioside and nicotinic receptor agonists have been applied in the treatment of Parkinson's disease or are under investigation for patients. Agents to facilitate nerve growth or to inhibit the degeneration of nerves will be developed in the future.
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PMID:[Recent progress in development of psychotropic drugs (3)--Antiparkinsonian agents applied in the treatment of Parkinson's disease or are under investigation for patients or model animals]. 890

Tolcapone is a potent catechol-O-methyltransferase inhibitor that prolongs the plasma half-life of levodopa. This multicenter, double-blind, placebo-controlled study used two 10-hour clinical evaluations to compare the efficacy and safety of three doses of tolcapone (50, 200, and 400 mg tid) with placebo in patients with Parkinson's disease (PD) experiencing motor fluctuations from levodopa/carbidopa. One hundred fifty-one patients completed the study. Clinical evaluations lasting 10 hours were performed on day -1 and day 42 using United Parkinson's Disease Rating Scale motor subscale and "on/off" and dyskinesia assessments every 30 minutes. Tolcapone significantly reduced "off" time an average of 40% and increased total "on" time by about 25% at all dose levels, as compared to placebo treatment. Levodopa/carbidopa dosage and frequency were significantly reduced. Tolcapone was well tolerated, with patients experiencing typical dopaminergic side effects that could be reduced or eliminated by lowering levodopa/carbidopa dosages. Tolcapone was effective at prolonging the clinical benefit of levodopa and reducing total levodopa requirements in PD patients with motor fluctuations.
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PMID:Tolcapone improves motor function and reduces levodopa requirement in patients with Parkinson's disease experiencing motor fluctuations: a multicenter, double-blind, randomized, placebo-controlled trial. Tolcapone Fluctuator Study Group I. 900 98


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