The Impact of COMT-inhibition on Gastrointestinal Levodopa Absorption in Patients with Parkinson's Disease

Effect of catechin and commercial preparation of green tea essence on the pharmacokinetics of l-dopa in rabbits

The aim of this study was to investigate drug interactions of L-dopa/carbidopa with catechin and green tea essence in rabbits following the simultaneous administration via an intramuscular injection of catechin or via an intragastric route for green tea essence with L-dopa/carbidopa. The results indicated that catechin at doses of 10, 20 and 50 mg/kg increased the area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration (AUC_0-t ) of L-dopa by about 69, 78 and 42%, respectively. The metabolic ratios of the AUC_0-t for 3-O-methyldopa (3-OMD)/L-dopa significantly decreased by about 56, 68 and 76% (P < 0.05), respectively. In addition, a single dose of 5/1.25 mg/kg L-dopa/carbidopa was co-administrated with 150 mg/kg green tea essence via an intragastric route with an oral-gastric tube. Comparing the related pharmacokinetic parameters of L-dopa, the clearance and metabolic ratio of L-dopa decreased by 20 and 19% (P < 0.05), respectively. In conclusion, catechin and green tea essence can significantly affect the metabolism of L-dopa by the catechol-O-methyltransferase (COMT) metabolic pathway. Catechin can enhance L-dopa bioavailability, and both catechin and green tea essence decreased 3-OMD formation. Therefore, catechin and green tea essence may increase L-dopa efficacy for Parkinson's disease treatment.

Simultaneous determination of MAO-A and -B activity following first time intake of an irreversible MAO-B inhibitor in patients with Parkinson's disease

We determined monoamine oxidase-A (plasma) and -B (platelets) enzyme activity in chronic levodopa treated patients with Parkinson's disease after first time intake of an irreversible monoamine oxidase-B inhibitor. One patient received 10 mg selegiline and eleven patients took 1 mg rasagiline. A significant decrease of monoamine oxidase-B activity appeared 2 and 4 h following monoamine oxidase-B inhibitor intake in comparison to baseline. We confirm with this design, that rasagiline and selegiline inhibit monoamine oxidase-B but not monoamine oxidase-A after single dosing.

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.

Motor complications, levodopa metabolism and progression of Parkinson's disease

INTRODUCTION

Oxidative stress is an essential component of neuronal death in Parkinson's disease (PD). Clinically, progression of PD is also characterised by onset of motor complications (MC). MC results from the peripheral and central degree of fluctuations of levodopa (LD) and of dopamine.

AREAS COVERED

This review highlights aspects of LD and dopamine metabolism in chronic neurodegeneration in PD. A Medline search (terms: homocysteine, LD, PD, progression [from 2000 onwards]) was performed and considered preclinical and clinical investigations. The author discusses pharmacokinetic and metabolic aspects of chronic LD administration in PD patients and provides a therapeutic concept to reduce probable PD accelerating consequences of chronic LD application.

EXPERT OPINION

The author suggests that the future 'ideal' oral LD therapy should be homocysteine-reducing, methyl-group-donating, oxidative-stress-decreasing and antiglutamatergic while also allowing continuous delivery to the brain. This may slow the progression of PD and delay the onset of MC, both of which represent unmet needs in the treatment of PD patients.