Catechol-O-Methyltransferase Inhibitors in Parkinson’s Disease

Abstract

Inhibitors of catechol-O-methyltransferase (COMT) are commonly used as an adjunct to levodopa in patients with Parkinson's disease (PD) for the amelioration of wearing-off symptoms. This narrative review aims to discuss the role of COMT inhibitors on peripheral levodopa metabolism and continuous brain delivery of levodopa, and to describe their metabolic properties. Oral application of levodopa formulations with a dopa decarboxylase inhibitor (DDI) results in fluctuating levodopa plasma concentrations, predominantly due to the short half-life of levodopa and its slowing of gastric emptying. Following transport across the blood-brain barrier and its metabolic conversion to dopamine, these peripheral 'ups and downs' of levodopa are reflected in fluctuating dopamine levels in the synaptic cleft between presynaptic and postsynaptic dopaminergic neurons of the nigrostriatal system. As a result, pulsatile postsynaptic dopaminergic stimulation takes place and results in the occurrence of motor complications, such as wearing-off and dyskinesia. More continuous plasma behaviour was observed after the combination of levodopa/DDI formulations with COMT inhibitors. These compounds also weaken a levodopa/DDI-related homocysteine increase, as biomarker for an impaired methylation capacity, which is involved in an elevated oxidative stress exposure. These findings favour the concept of chronic levodopa/DDI application with concomitant inhibition of COMT and monoamine oxidase, since deamination of dopamine via this enzyme also generates free radicals. This triple combination is suggested as standard levodopa application in patients with PD who need levodopa, if they will tolerate it.

Effect of 3 Single‐Dose Regimens of Opicapone on Levodopa Pharmacokinetics, Catechol‐O‐Methyltransferase Activity and Motor Response in Patients With Parkinson Disease

“…[15][16][17] This was a short and single-dose study not designed to detect any significant differences in motor performance. However, the exploratory analysis reported here showed improvement, to some extent, in various motor outcomes.…”

Nicotinamide metabolism regulates glioblastoma stem cell maintenance

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“…In addition, for the measurement of COMT activity in various disease states or disorders, for the determination of structure–activity relationships of COMT or for the testing of efficacy of new COMT inhibitors candidates used to increase the efficacy of L-DOPA in the treatment of Parkinson's disease (Mueller, 2015). …”