nitecapone and Parkinson-Disease

Degradation of levodopa in the periphery is known to be associated with motor fluctuations and dyskinesia in Parkinson's disease (PD) patients. The enzyme catechol-O-methyltransferase (COMT) is responsible for much of this degradation. Therefore, inhibiting COMT activity is one method of extending the action of levodopa. The new nitrocatechol-type COMT inhibitors entacapone, nitecapone, and tolcapone inhibit COMT in the periphery; tolcapone also inhibits COMT activity centrally. COMT inhibitors increase patients' duration of response to levodopa and reduce response fluctuations. Administration may prolong levodopa-induced dyskinesia, but peak-dose dyskinesia does not appear to increase. To reduce dyskinesia, the total daily dose of levodopa can be reduced.

Topics: Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Catechols; Dose-Response Relationship, Drug; Drug Interactions; Drug Therapy, Combination; Enzyme Inhibitors; Humans; Levodopa; Nitriles; Nitrophenols; Parkinson Disease; Pentanones; Tolcapone

PET studies were performed to investigate the effects of a new cathechol-O-methyltransferase (COMT) inhibitor, nitecapone (OR-462 [3-(3,4-dihydroxy-5-nitrobenzylidene)- 2,4-pentadione]), on the accumulation of dopamine in the striatum and whether it is able to improve [18F]6-fluorodopa imaging of the brain. Altogether, three patients with Parkinson's disease (PD) and three normal volunteers were examined, first without nitecapone and then with an oral dose of 100 mg of nitecapone 1 hour before the IV injection of 3 mCi of [18F]6-fluorodopa. High-pressure liquid chromatography analysis of arterial plasma samples showed a significant reduction in the metabolic conversion rate from [18F]6-fluorodopa to [18F]3-O-methylfluorodopa after the administration of nitecapone. PET studies showed that nitecapone significantly (p less than 0.05) increased the [18F]6-fluorodopa accumulation in the striatum both in PD patients and normal controls; the magnitude of this increase was 20.0 +/- 5.5% (mean +/- SEM). The ratio of radioactivity in the striatum and arterial plasma was increased 39.0 +/- 5.0% (mean +/- SEM) after the administration of nitecapone. Consequently, the quality of PET images after OR-462 was better, which has implications for future [18F]6-fluorodopa studies. In addition, COMT inhibition may have clinical advantages by improving levodopa treatment in PD.

Topics: Adult; Aged; Catechol O-Methyltransferase Inhibitors; Catechols; Cerebellum; Chromatography, High Pressure Liquid; Corpus Striatum; Dihydroxyphenylalanine; Female; Fluorine Radioisotopes; Humans; Male; Middle Aged; Parkinson Disease; Pentanones; Tomography, Emission-Computed

We studied the effectiveness of OR-611 and OR-462, two novel inhibitors of the enzyme catechol-O-methyltransferase (COMT), on 3-O-methyldopa (OMD) formation in cynomolgus monkeys following intravenous levodopa administration. OR-611 dose-dependently reduced the area under the OMD concentration-vs-time curve, reduced maximum plasma OMD concentrations, delayed the time to peak OMD levels, reduced systemic levodopa clearance, and prolonged the elimination half-life of levodopa. Similar effects on peripheral levodopa metabolism were seen with doses of 15 mg/kg of OR-611 and OR-462, its sister compound, which lacks the ability to penetrate the central nervous system (CNS).

Topics: Animals; Catechol O-Methyltransferase Inhibitors; Catechols; Levodopa; Macaca fascicularis; Male; Nitriles; Parkinson Disease; Pentanones; Tyrosine

A selective catechol-O-methyltransferase inhibitor, OR-462, was studied for its ability to affect pharmacokinetic properties of L-dopa after the p.o. administration of the inhibitor to rats and mice. When OR-462 was given to rats at the dose range of 0.3 to 30 mg/kg in conjunction with L-dopa and carbidopa, a dose-related and long-lasting (greater than 5 hr) increase in striatal L-dopa and dopamine levels as well as a reduction in 3-O-methyldopa levels were shown. For a 50% reduction of the 3-O-methyldopa levels a dose of 6 mg/kg of OR-462 was needed. The increase in striatal homovanillic acid, an O-methylated metabolite of dopamine which poorly penetrates the blood brain barrier, indicates that O-methylation was not inhibited in the brain. In order to get the same dopamine levels in striatum the L-dopa dose could be lowered to one-fourth when OR-462 was added. The L-dopa-sparing effect of OR-462 given p.o. was also demonstrated in two behavioral parkinsonian models. OR-462 given at doses of 3 to 30 mg/kg in conjunction with L-dopa and carbidopa, dose-dependently potentiated the L-dopa-induced reversal of hypoactivity in reserpinized mice. Likewise, the same doses of OR-462 caused a marked potentiation of L-dopa-induced contralateral turning behavior in rats with unilateral nigrostriatal lesions produced by 6-hydroxydopamine. The data suggest a possible beneficial effect of OR-462 in the therapy of Parkinson's disease.

Topics: Animals; Carbidopa; Catechol O-Methyltransferase Inhibitors; Catechols; Corpus Striatum; Disease Models, Animal; Dose-Response Relationship, Drug; Ketones; Levodopa; Male; Mice; Motor Activity; Parkinson Disease; Pentanones; Rats; Rats, Inbred Strains; Rotation