Levodopa and 3-O-methyldopa plasma levels in parkinsonian patients with stable and fluctuating motor response

Diurnal motor variations to repeated doses of levodopa in Parkinson's disease

Patients with Parkinson's disease (PD) in long-term levodopa therapy often complain of worsening of motor symptoms in the afternoon and evening. The pathophysiology of this phenomenon is not known. We evaluated the motor response to repeated doses of levodopa during a 12-hour period in 52 parkinsonian patients (19 de novo, 20 stable, and 13 wearing-off). On the day of the study, all patients received standard doses of levodopa/carbidopa at 8:00 a.m., 12:00 noon, and 4:00 p.m. Motor measurements such as tapping test, walking time, and tremor score, and blood samples for levodopa and 3-O-methyldopa (3OMD) plasma analysis, were performed hourly. Mean motor scores and pharmacokinetic data, evaluated for a period of 3 hours after each levodopa dose, were compared. In de novo patients, we did not observe diurnal changes in motor score, whereas a progressive daytime worsening was visible in stable and wearing-off patients. No significant difference in levodopa pharmacokinetics after each levodopa dose was observed within each patient group, whereas 3OMD plasma levels significant increased with repeated levodopa administrations. However, no significant correlation between motor scores and 3OMD plasma levels was observed, suggesting that the diminishing motor response to afternoon and evening doses of levodopa in patients in long-term levodopa therapy does not relate to the pharmacokinetics of the drug. It is possible that this phenomenon may be an expression of the occurrence of tolerance to repeated doses of levodopa.

A comparative study on neurochemistry of cerebrospinal fluid in advanced Parkinson's disease

This study addresses two issues: (1) the comparative neurochemistry of classic tremor type of Parkinson's disease or PD-A and akinetic type of Parkinson's disease or PD-B; and (2) the neurochemistry of levodopa failure syndrome (LDFS). Cerebrospinal fluid from the lateral ventricle was collected from 50 patients with idiopathic Parkinson's disease of PD-A and PD-B. Levels of monoamine neurotransmitters and metabolites were determined using high performance liquid chromatography. We have found that (1) 5-hydroxylindoleacetic acid (5-HIAA) level is significantly lower in PD-B than in PD-A; (2) 5-HIAA level is inversely associated with score of part one of United Parkinson's Disease Rating Score (UPDRS); (3) 5-HIAA level is inversely associated with score of part four of UPDRS; (4) 3-O-methyldopa (3-OMD) level is positively associated with levodopa failure syndrome (LDFS) assessed by part four of UPDRS and inversely associates with 5-HIAA. From these data, it can be inferred that serotonergic activity is decreased in PD-B to a greater extent than in PD-A and that decreased serotonergic activity plays a role in LDFS.

Effects of the catechol-O-methyltransferase inhibitor tolcapone in Parkinson's disease: correlations between concentrations of dopaminergic substances in the plasma and cerebrospinal fluid and clinical improvement

We compared the concentrations of dopaminergic substances in the plasma and cerebrospinal fluid (CSF) with clinical severity in patients with Parkinson's disease (PD) under L-dopa/carbidopa treatment and under L-dopa/carbidopa+tolcapone treatment. Compared with treatment with L-dopa/carbidopa alone, the co-administration of tolcapone produced a significant decrease in clinical severity; a remarkable reduction in the 3-O-methyldopa (3-OMD) concentration and significant increase in the L-dopa concentration both in the plasma and CSF; and a significant increase in the dopamine concentration in the CSF. The clinical effects of tolcapone were closely correlated with the reduction in the 3-OMD concentration, but not with the increase in the dopamine and L-dopa concentrations in the CSF.

Chronic administration does not alter the pharmacokinetic profile of L-dopa in the rat

Chronic administration of L-dopa (200 mg kg-1 day-1 for 12 months) plus carbidopa (25 mg kg-1 day-1) or carbidopa (25 mg kg-1 day-1) alone did not alter the t1/2, AUC0-infinity k10, k12, k21, CLp or Vdss of L-dopa following intra-aortic (i.a.) administration (50 mg kg-1) alone or after carbidopa (25 mg kg-1, i.p.) pretreatment, or the t1/2, AUC0-infinity, tmax or the bioavailability (F) of L-dopa (50 mg kg-1) administered orally, alone or after acute pretreatment with carbidopa (25 mg kg-1 i.p.). The peripheral metabolism of L-dopa was unaltered by chronic administration of L-dopa plus carbidopa or carbidopa alone as measured by unaltered AUC0-360 min for 3-O-methyldopa, dopamine, DOPAC or homovanillic acid in the plasma of rats following acute administration of L-dopa (50 mg kg-1, p.o. or i.a.) alone or following pretreatment with carbidopa, and unaltered hepatic dopa decarboxylase activity.

Drug delivery to brain and the role of carrier-mediated transport

In summary, the results suggest that carrier-mediated transport can be used to augment the brain delivery of a wide variety of hydrophilic therapeutic drugs. A large number of carriers are now known to be present at the brain capillary endothelium, and in many instances these carriers have been shown to mediate the brain uptake of exogenous drugs. The findings with D,L-NAM demonstrate that brain delivery can be improved through design of selective, high affinity agents. Although NAM was developed for the large neutral amino acid carrier, high affinity drugs could be produced for other systems, as shown by the work of Schein et al. with nitrogen mustard monosaccharides and by the work of Deves and Krupka on choline derivatives. Lastly, the method may allow some selectivity of delivery because of differential expression of transport carriers between tissues and in various disease states.

3-O-methyldopa administration does not alter fluorodopa transport into the brain

To determine if 3-O-methyldopa (3OMD) significantly inhibits the transport of 6-[18F]fluorodopa (6-FD) into the brain at the concentration normally encountered during L-dopa administration, we performed 6-FD studies with positron emission tomography in cynomolgus monkeys in the presence and absence of 3OMD. Infusion of 3OMD was designed to produce plasma concentrations equivalent to those seen in patients on chronic L-dopa therapy. Plasma 3OMD levels of 39 +/- 4 microM did not alter the blood-brain transfer rate of 6-FD. 6-FD positron emission tomographic studies in parkinsonian patients will therefore not be altered by 3OMD present in the blood in those patients taking L-dopa preparations. These results do not support the hypothesis that transport of L-dopa into the brain is inhibited by 3OMD to cause the declining response seen in patients with advanced Parkinson's disease.

Levodopa-induced dyskinesias in Parkinson's disease: Clinical and pharmacological classification

Levodopa-induced dyskinesias (LID) in Parkinson's disease (PD) may be classified into three main categories: "On" dyskinesias, diphasic dyskinesias (DD), and "off" periods. The study of 168 parkinsonian patients showed that about half (n = 84) showed one pattern of LID only. A combination of two was present in 68, and 16 had the three presentation patterns. A fairly good correlation between type of dyskinesia and presentation pattern was established. Chorea, myoclonus, and dystonic movements occurred during the "on" period. Dystonic postures, particularly affecting the feet, were mainly present in the "off" period, but a few patients had a diphasic presentation. Repetitive stereotyped movements of the lower limbs always corresponded to DD. Acute pharmacological tests using dopamine agonists (subcutaneous apomorphine 3-8 mg; intravenous lisuride 0.1-0.15 mg) and dopamine antagonists (intravenous sulpiride 200-400 mg and intravenous chlorpromazine 25 mg) were performed in 40 patients. Dopamine agonists enhanced "on" dyskinesias and markedly reduced or abolished "off" period dystonia and DD. Dopamine antagonists reduced all types of LID but usually aggravated parkinsonism. These clinical and pharmacological results indicate that LID in PD are a heterogeneous phenomenon difficult to explain on the basis of a single pathophysiological mechanism.

The effect of benserazide on the peripheral and central distribution and metabolism of levodopa after acute and chronic administration in the rat

1. The effects of levodopa alone (50 mg kg-1) and levodopa (10 mg kg-1) plus benserazide (50 mg kg-1) were tested on the levels of dopa, dopamine, 3-methoxytyrosine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), measured by h.p.l.c. with electrochemical detection, in samples of plasma, CSF, urine, striatum and hypothalamus of rats taken 30 min after injection. Levodopa plus benserazide produced significantly higher levels of dopa in plasma and brain than levodopa alone and reduced the peripheral synthesis and metabolism of dopamine. 2. When given chronically over 6 weeks the advantages of adding benserazide (50 mg kg-1 day-1) to levodopa (40 mg kg-1 day-1) were less marked and although more dopamine was present in the striatum than with levodopa given alone (200 mg kg-1 day-1) there was no evidence of any increase in its metabolites (HVA and DOPAC) and therefore of its turnover and utilisation. 3. The most striking effect of chronic treatment with levodopa plus benserazide was the appearance of large quantities of 3-MT in plasma, CSF and brain. 4. When levodopa alone, or levodopa plus benserazide, was given as an acute challenge to animals receiving the same treatment chronically, it was found that levodopa alone still produced increases in striatal dopamine, DOPAC and HVA in those animals dosed chronically on levodopa, but it was less effective in this respect when given with benserazide to the animals dosed with levodopa plus benserazide. 5. It is concluded that this difference in levodopa distribution may depend on the persistence in benserazide-treated animals of 3-MT, which has a long half-life and may compete with dopa for transport into the blood and brain. 6. The implication of these findings to the treatment of Parkinsonism is discussed.

Ro 40-7592: inhibition of COMT in rat brain and extracerebral tissues

A random biochemical screening followed by lead optimization culminated in the discovery of Ro 40-7592 3,4-dihydroxy-4'-methyl-5-nitrobenzophenone). Ro 40-7592 was found to inhibit COMT in a competitive fashion both in the CNS and in the periphery (Ki for the liver enzyme = 30 nM). Ro 40-7592 (30 mg/kg p.o.) combined with benserazide (15 mg/kg p.o.) and a low dose of L-DOPA (10 mg/kg p.o.) almost completely blocked (for about 6 h) the formation of 3-O-methyldopa (3-OMD) in brain and plasma, producing a long-lasting increase of L-DOPA in plasma and a parallel marked increase of L-DOPA and dopamine in the brain. Ro 40-7592, combined with peripheral decarboxylase inhibitors and L-DOPA (as in Madopar and Sinemet), will offer substantial advantages in the therapy of Parkinson's disease, i.e. enhanced bioavailability and prolonged plasma half-life of L-DOPA, pronounced DOPA sparing effect and blockade of 3-OMD formation.