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

To understand the delay in the clinical benefit that commonly occurs after initiation of levodopa (L-Dopa) treatment, we examined the pharmacokinetic profile of L-Dopa after the first oral dose ever taken of L-Dopa/carbidopa in untreated patients with Parkinson's disease and followed these parameters after 1 month of treatment. This was performed in correlation with the clinical therapeutic effect. Plasma levels of L-Dopa were measured with use of high-performance liquid chromatography with electrochemical detection after administration of the "first ever" 125 mg L-Dopa/12.5 mg carbidopa tablet in 15 patients with de novo Parkinson's disease (mean age, 69 +/- 11 y, mean disease duration, 1.5 +/- 0.8 years). Blood samples were drawn before administration and thereafter at various intervals for a period of 4 hours. Repeated measurements after the same oral dose were performed after 1 month of continued therapy with L-Dopa/carbidopa 125/12.5 mg three times daily. Patients were clinically evaluated by unified Parkinson's disease rating scale motor scores. There was a modest clinical improvement after 1 month of continuous L-Dopa treatment (motor scores, 13.1 +/- 11.6 vs. 17.6 +/- 11.7; p < 0.01). Peak plasma L-Dopa levels and area under the curve did not differ significantly between the first-ever dose and after 1 month of continuous treatment (0.9 +/- 0.1 vs. 1.0 +/- 0.1 microg/mL and 66.0 +/- 30.9 vs. 86.2 +/- 34.9 microg/mL, respectively; p < 0.1. There was also no change in time to peak levels between measurements. Results indicate that the first-ever dose of oral L-Dopa is well absorbed and that pharmacokinetic mechanisms such as reduced absorption of L-Dopa probably do not play a major role in the initial delay in clinical response to oral L-Dopa/carbidopa in patients with Parkinson's disease. The latter phenomena may be linked to central pharmacodynamic mechanisms.
 ...
PMID:The pharmacokinetic profile of the "first ever" oral dose of levodopa in de novo patients with Parkinson's disease. 1130 44

We performed a double-blind, placebo-controlled, randomized, crossover, multiple-dose study on entacapone in 25 patients with Parkinson's disease with levodopa (L-Dopa) treatment-related fluctuations. A run-in period was followed by four 2-week treatment periods during which the patients took 4 to 6 daily doses of L-Dopa concomitantly with 100, 200, or 400 mg of entacapone or with placebo. The effects were assessed at the end of each period; the inhibition of soluble catechol-O-methyltransferase (S-COMT) activity in red blood cells and the plasma concentrations of entacapone, L-Dopa, and 3-O-methyldopa (3-OMD) were measured and clinical effects assessed on an 18-hour home diary. Twenty-one patients completed the study. Entacapone decreased the COMT activity from predose level: 100 mg by 25%, 200 mg by 33%, and 400 mg by 32% (p < 0.001 vs. placebo for each dose). Correspondingly, the 3-OMD concentrations decreased by 39%, 54%, and 66% with 100-, 200-, and 400-mg doses, respectively. The elimination half-life of L-Dopa was prolonged by 23% (p < 0.05), 26% (p < 0.001), and 48% (p < 0.001), and the area under the curve of L-Dopa increased by 17% (p < 0.05), 27% (p < 0.001), and 37% (p < 0.001) with the increasing doses. Despite a significant decrease in the daily dose of L-Dopa, entacapone decreased the proportion of daily "off" time: 100 mg by 11%, 200 mg by 18%, and 400 mg by 20% compared with placebo. However, this decrease was not statistically significant for any of the doses in this small patient population. The dyskinetic "on" time did not increase with different doses of entacapone. All doses were well tolerated, and no severe adverse events were reported. The study showed that repeated dosing of entacapone inhibits the COMT activity in a dose-dependent manner and thereby reduces the loss of L-Dopa to 3-OMD. Therefore, the area under the curve of L-Dopa is increased and the patient's clinical condition improved.
 ...
PMID:The effects of different repeated doses of entacapone on the pharmacokinetics of L-Dopa and on the clinical response to L-Dopa in Parkinson's disease. 1139 Nov 26

Positron emission tomography (PET) coupled to 6-[18F]Fluoro-L-Dopa (18F-Dopa) remains the gold standard for assessing dysfunctionality concerning the dopaminergic nigrostriatal pathway in Parkinson's disease and related disorders. The use of ligands of the dopamine transporters (DAT) is an attractive alternative target; consequently, the current aim was to validate one of them, 11C-PE2I, using a multiinjection modeling approach allowing accurate quantitation of DAT densities in the striatum. Experiments were performed in three controls, three MPTP-treated (parkinsonian) baboons, and one reserpine-treated baboon. 11C-PE2I B'max values obtained with this approach were compared with 18F-Dopa input rate constant values (Ki), in vitro Bmax binding of 125I-PE2I, and the number of dopaminergic neurons in the substantia nigra estimated postmortem by stereology. In the caudate nucleus and putamen, control values for 11C-PE2I B'max were 673 and 658 pmol/mL, respectively, whereas it was strongly reduced in the MPTP-treated (B'max = 26 and 36 pmol/mL) and reserpine-treated animals (B'max = 338 and 483 pmol/mL). In vivo 11C-PE2I B'max values correlated with 18F-Dopa Ki values and in vitro 125I-PE2I Bmax values in the striatum and with the number of nigral dopaminergic neurons. Altogether, these data support the use of 11C-PE2I for monitoring striatal dopaminergic disorders and the effect of potential neuroprotective strategies.
 ...
PMID:Anatomic and biochemical correlates of the dopamine transporter ligand 11C-PE2I in normal and parkinsonian primates: comparison with 6-[18F]fluoro-L-dopa. 1143 90

The efficacy and safety of two dosages of tolcapone were compared in a 12-week crossover trial involving 118 nonfluctuating patients with PD on a stable dose of levodopa (L-Dopa). At trial onset, all patients received open-label tolcapone 100 mg three times daily for 4 weeks. At week 4, 116 eligible patients entered an 8-week double-blind treatment period and were randomized to receive tolcapone three times daily at either 100 mg (group 1; n = 58) or 200 mg (group 2; n = 58) until week 8, followed by the alternative tolcapone dosage until week 12. Ratings included Unified Parkinson's Disease Rating Scale (UPDRS), Schwab & England, and patient diaries, assessed at baseline and at 4, 8, and 12 weeks. At week 4, the investigator's global assessment (IGA) of efficacy showed improvement in 76% of patients. The mean total daily L-Dopa dose and mean UPDRS scores for subscales II and III decreased significantly (p < 0.001). During the double-blind treatment period, IGA showed improvements at either or both dosages in 61% of patients; further changes in other efficacy variables were minimal and were similar with both tolcapone dosages. The most frequent adverse events were dopaminergic (nausea and dyskinesia); the most frequent nondopaminergic adverse event was diarrhea. The incidence of adverse events during double-blind treatment was slightly higher with tolcapone 200 mg three times daily (33%) than with tolcapone 100 mg three times daily (24%). The authors conclude that tolcapone dosages of 100 mg three times daily and 200 mg three times daily are well tolerated and equally effective in improving function in L-Dopa-treated nonfluctuating patients with PD.
 ...
PMID:Comparison of two dosages of tolcapone added to levodopa in nonfluctuating patients with PD. 1147 92

This study investigated whether chronic coadministration of alpha-dihydroergocryptine (DHEC) altered the plasma pharmacokinetics of individualized treatments with levodopa in 12 patients with Parkinson's disease. Steady-state pharmacokinetics of plasma levodopa (L-Dopa) under combined treatment were compared with those under treatment with L-Dopa alone. There was no evidence of increased exposure to L-Dopa caused by concomitant treatment with DHEC. In contrast, additional treatment with DHEC reduced the overall exposure to L-Dopa (17.5% reduction in area under the curve; 95% CI: 23%-6%). This effect was small but statistically significant for the area under the plasma concentration-time curve, whereas tmax (time of maximum plasma concentration) and peak-to-trough fluctuation were not affected. Cmax (maximum plasma concentration), on average, was reduced to a similar extent (-14.5%; 95% CI: 38% to -17%), albeit not significantly. The magnitude of the interaction does not suggest changing the current clinical practice of up-titrating DHEC and subsequently adapting L-Dopa to the individual needs of patients.
 ...
PMID:Influence of the dopamine agonist alpha-dihydroergocryptine on the pharmacokinetics of levodopa in patients with Parkinson's disease. 1147 96

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) provide the means to studying in vivo the neurochemical, hemodynamic or metabolic consequences of the degeneration of the nigrostriatal dopaminergic system in Parkinson's disease (PD). The extent of striatal dopaminergic denervation can be quantified with radiotracers as [18F]FDopa for PET and [123I]tropanes for SPECT. There are other radiotracers such as [11C]Dopa and meta-tyrosines as well as PET tracers for uptake sites. Striatal uptake of [18F]FDopa and [123I]tropanes is markedly decreased in PD, more in the putamen than in the caudate nucleus, and inversely correlates with the severity of motor signs and with duration of disease. PET and SPECT make possible the assessment by noninvasive means of the changes in dopamine receptor density, the effect of neuronal transplants or neuroprotective treatments in PD patients, or the nigrostriatal dopaminergic function in at-risk subjects. Activation studies using cerebral blood flow and metabolism measurements during a motor task reveal an impaired ability to activate the supplementary motor area and dorsolateral prefrontal cortex in PD. This functional disability is reversed by the use of dopaminergic medication or by surgical treatment by pallidotomy or deep brain stimulation. The differential diagnosis between PD and multiple system atrophy, progressive supranuclear palsy or corticobasal degeneration is not yet clearly established by PET and SPECT, even though these syndromes have some particular neurochemical and metabolic profiles. On the other hand, PET and SPECT are useful for distinguishing PD from Dopa-responsive dystonia, or for assessing the integrity of the nigrostriatal dopaminergic pathway in atypical cases of postural tremor or iatrogenic parkinsonian syndromes.
 ...
PMID:Contributions of PET and SPECT to the understanding of the pathophysiology of Parkinson's disease. 1181 73

L-3,4-Dihydroxyphenylalanine (L-DOPA) is a common and effective treatment for Parkinson's disease, but dyskinesia continues to be a serious adverse effect with chronic use. Evidence suggests that L-DOPA induces increases in dopamine, which then binds to supersensitive dopamine receptors, resulting in dyskinesia. We have shown previously that L-DOPA directly causes stereotypy in rats, suggesting that chronic L-DOPA-induced dyskinesia is also caused by L-DOPA itself. This raises the possibility that other L-DOPA metabolites have a role in dyskinesia. We examined the behavioral effects of five L-DOPA metabolites (3-methoxytyramine, 3-MT; 3,4-dihydroxyphenylalanine, DOPAC; dopamine; homovanillic acid, and 3-o-methyl-DOPA) in rats. A unilateral, intracerebroventricular injection of 3-MT (10-200 microg, 40 microl) over 30 min, dose-dependently increased behavioral activity and stereotypy. This effect was suppressed by the dopamine D1/5-receptor antagonist SCH 23390, but not by the dopamine D2/3/4-receptor antagonist sulpiride. Dopamine denervation resulted in behavioral supersensitivity to 3-MT. Neither dopamine nor DOPAC levels increased in the striatum after 3-MT administration, as measured using in vivo voltammetry. The behavioral changes paralleled a rise in 3-MT in the contralateral striatum. DOPAC also caused behavioral changes and stereotypy, but to a smaller degree than 3-MT. Dopamine-denervated rats did not exhibit a supersensitive response to DOPAC, however. Other L-DOPA metabolites did not cause behavioral effects. These data suggest that 3-MT directly induced dopamine-D1/5-receptor-mediated behavioral changes in rats, and that 3-MT may have a role in dyskinesia due to chronic L-DOPA treatment in Parkinson's disease patients.
 ...
PMID:Behavioral activity and stereotypy in rats induced by L-DOPA metabolites: a possible role in the adverse effects of chronic L-DOPA treatment of Parkinson's disease. 1187 3

Free radicals damage both lipids and proteins and evidence has accumulated for the presence of both oxidised lipids and proteins in aged tissue samples as well as those from a variety of pathologies including atherosclerosis, diabetes, and Parkinson's disease. Oxidation of the protein and lipid moieties of low-density lipoprotein is of particular interest due to its potential role in the unregulated uptake of lipids and cholesterol by macrophages; this may contribute to the initial stage of foam cell formation in atherosclerosis. In the study reported here, we examined the comparative time-courses of lipid and protein oxidation during copper-ion-mediated oxidation of low-density lipoprotein. We show that there is an early, lipid-mediated loss of 40-50% of the Trp residues of the apoB100 protein. There is no comparable loss over an identical period during the copper-ion-mediated oxidation of lipid-free BSA. Concomitant with Trp loss, the antioxidant alpha-tocopherol is consumed with subsequent extensive lipid peroxidation. Further changes to the protein, including the copper-ion-dependent 3.5-fold increase in 3,4-dihydroxyphenylalanine and the copper-ion-independent 3-5-fold increase in o-tyrosine, oxidation products of Tyr and Phe, respectively, only occur after maximal lipid peroxidation. Long incubation periods result in depletion of 3,4-dihydroxyphenylalanine, presumably reflecting further oxidative changes. Overall, copper-ion-mediated oxidation of LDL appears to proceed initially by lipid radical-dependent processes, even though some of the earliest detectable changes occur on the apoB100 protein. This is followed by extensive lipid peroxidation and subsequent additional oxidation of aromatic residues on apoB100, though it is not yet clear whether this late protein oxidation is lipid-dependent or occurs as a result of direct radical attack.
 ...
PMID:Comparative time-courses of copper-ion-mediated protein and lipid oxidation in low-density lipoprotein. 1205 33

Historically, 3,4-dihydroxyphenylalanine (DOPA) has been considered to be an inert amino acid that alleviates the symptoms of Parkinson's disease by its conversion to dopamine via the enzyme aromatic L-amino acid decarboxylase. In contrast to this generally accepted idea, we propose that DOPA itself is a neurotransmitter and/or neuromodulator in addition to being a precursor of dopamine. Several criteria such as synthesis, metabolism, active transport, existence, physiological release, competitive antagonism and physiological or pharmacological responses must be satisfied before a compound is accepted as a neurotransmitter. Recent evidence suggests that DOPA fulfills these criteria in its involvement in baroreflex neurotransmission.
 ...
PMID:Is DOPA a neurotransmitter? 1208 31

Catechol-O-methyltransferase (COMT) inhibitors such as entacapone and tolcapone are used as adjuncts to L-DOPA ( l-3,4-dihydroxyphenylalanine, levodopa) in the treatment of Parkinson's disease. Tolcapone has been reported to associate with diarrhoea, a common reason for study withdrawal. The mechanism of this adverse effect is not yet understood. Cholera toxin causes diarrhoea by permanent activation of G(s) proteins, resulting in increased adenylyl cyclase (AC) activity. The aim of this study was to examine the effects of the COMT inhibitors entacapone and tolcapone on AC activity in membranes isolated from rat striatum, a brain structure enriched with dopaminergic G-protein-coupled receptors and AC activity. This study demonstrates differential effects of tolcapone and entacapone on Gpp(NH)p/dopamine-stimulated AC activity. Entacapone enhanced the stimulatory effect of Gpp(NH)p/dopamine, whereas tolcapone attentuated this effect, suggesting that diarrhoea associated with tolcapone treatment is not caused by permanent activation of G(s) proteins.
 ...
PMID:Different modes of action of catecholamine-O-methyltransferase inhibitors entacapone and tolcapone on adenylyl cyclase activity in vitro. 1211 68


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>