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PubMed2004

Assessment of catechol induction and glucuronidation in rat liver microsomes.

Catechols are substances with a 1,2-dihydroxybenzene group from natural or synthetic origin. The aim of this study was to determine whether catechols (4-methylcatechol, 4-nitrocatechol, 2,3-dihydroxynaphthalene) and the antiparkinsonian drugs, entacapone and tolcapone, at doses 150 to 300 mg/kg/day, for 3 days, are able to enhance their own glucuronidation. The induction potency of catechols on rat liver UDP-glucuronosyltransferases (UGTs) was compared with that of a standard polychlorinated biphenyl (PCB) inducer, Aroclor 1254. The glucuronidation rate of these catechols was enhanced up to 15-fold in the liver microsomes of PCB-treated rats, whereas treatment with catechols had little effect. Entacapone, tolcapone, 4-methylcatechol, catechol, 2,3-dihydroxynaphthalene, and 4-nitrocatechol were glucuronidated in control microsomes at rates ranging from 0.12 for entacapone to 22.0 nmol/min/mg for 4-nitrocatechol. Using 1-naphthol, entacapone, and 1-hydroxypyrene as substrates, a 5-, 8-, and 16-fold induction was detected in the PCB rats, respectively, whereas the catechol-induced activities were 1.1- to 1.5-fold only. Entacapone was glucuronidated more efficiently by PCB microsomes than by control microsomes (Vmax/Km, 0.0125 and 0.0016 ml/min/mg protein, respectively). Similar kinetic results were obtained for 1-hydroxypyrene. The Eadie-Hofstee plots suggested the contribution of multiple UGTs for the glucuronidation of 1-hydroxypyrene (Km1, Km2, Km3 = 0.8, 9.7, and 63 microM, and Vmax1, Vmax2, Vmax3 = 11, 24, and 55 nmol/min/mg, respectively), whereas only one UGT could be implicated in the glucuronidation of entacapone (Km = 130 microM, Vmax = 1.6 nmol/min/mg). In conclusion, catechols are poor inducers of their own glucuronidation supported by several UGT isoforms. Their administration is unlikely to affect the glucuronidation of other drugs administered concomitantly.

Alanine Transaminase↗
PubMed2000

Catechol-O-methyltransferase inhibition attenuates levodopa toxicity in mesencephalic dopamine neurons.

Inhibition of catechol-O-methyltransferase (COMT; EC 2.1.1.6) is a new therapeutic strategy in the treatment of Parkinson's disease. However, nothing is known about the effects of COMT inhibition on levodopa (L-dopa)-induced toxicity in dopamine (DA) neurons. Therefore we evaluated the effects of the selective COMT inhibitors Ro 41-0960, OR-486, and tolcapone alone and in combination with L-dopa in primary mesencephalic cultures from rat. Neither COMT inhibitor affected the growth of tyrosine hydroxylase immunoreactive (THir) cells with concentrations up to 10 microM when studied alone. However, Ro 41-0960 reduced the L-dopa-induced THir cell loss after 24 h in a dose-dependent manner, shifting the TD(50) value from 21 microM in the absence to 71 microM in the presence of 1 microM Ro 41-0960 (P <.01) without affecting survival of non-DA neurons. OR-486 and the clinically used COMT inhibitor tolcapone showed similar effects. In contrast, toxicity induced by D-dopa was not altered by COMT inhibitors. Furthermore, the primary metabolite of L-dopa formed by COMT, 3-O-methyldopa, and the methyl group donor S-adenosyl-L-methionine used by COMT did not alter THir neuron survival and L-dopa-induced toxicity, respectively, with concentrations up to 100 microM. These data demonstrate that COMT inhibition attenuates L-dopa toxicity toward DA neurons in vitro, but probably not by preventing 3-O-methyldopa production or cellular S-adenosyl-L-methionine depletion.

Animals↗
PubMedDate not supplied

Assessment of catechol-O-methyltransferase activity and its inhibition in erythrocytes of animals and humans.

A non-radiometric method to measure the catechol-O-methyltransferase (COMT) activity in erythrocytes was modified to increase its sensitivity four-fold as well as its reproducibility and applicability. The method is based on the COMT-mediated O-methylation of 4-(naphtho [1,2-d] thiazol-2-yl) pyrocatechol, the product of which was determined fluorometrically. COMT activities down to less than 1% of those present at baseline could be measured precisely and accurately. The intra- and inter-assay coefficients were below 3 and 5.3%, respectively. Basal COMT activity and the distribution between soluble and membrane-bound COMT was shown to be variable among different species (ten species tested). The applicability of the method was demonstrated by the characterization of COMT activity-time courses in human erythrocytes after oral administration of the COMT inhibitor tolcapone. The assay developed will be useful in the rapid screening and clinical development of new COMT inhibitors.

Animals↗
PubMed2003

Rapid screening and characterization of drug metabolites using a new quadrupole-linear ion trap mass spectrometer.

The application of a new hybrid RF/DC quadrupole-linear ion trap mass spectrometer to support drug metabolism and pharmacokinetic studies is described. The instrument is based on a quadrupole ion path and is capable of conventional tandem mass spectrometry (MS/MS) as well as several high-sensitivity ion trap MS scans using the final quadrupole as a linear ion trap. Several pharmaceutical compounds, including trocade, remikiren and tolcapone, were used to evaluate the capabilities of the system with positive and negative turbo ionspray, using either information-dependent data acquisition (IDA) or targeted analysis for the screening, identification and quantification of metabolites. Owing to the MS/MS in-space configuration, quadrupole-like CID spectra with ion trap sensitivity can be obtained without the classical low mass cutoff of 3D ion traps. The system also has MS(3) capability which allows fragmentation cascades to be followed. The combination of constant neutral loss or precursor ion scan with the enhanced product ion scan was found to be very selective for identifying metabolites at the picogram level in very complex matrices. Owing to the very high cycle time and, depending on the mass range, up to eight different MS experiments could be performed simultaneously without compromising chromatographic performance. Targeted product ion analysis was found to be complementary to IDA, in particular for very low concentrations. Comparable sensitivity was found in enhanced product ion scan and selected reaction monitoring modes. The instrument is particularly suitable for both qualitative and quantitative analysis.

Animals↗
PubMed2005

The combination of liquid chromatography/tandem mass spectrometry and chip-based infusion for improved screening and characterization of drug metabolites.

An approach has been developed for drug metabolism studies of non-radiolabeled compounds using on-line liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with chip-based infusion following fraction collection. The potential of this approach, which improves the data quality compared with only LC/MS analysis, has been investigated for the analysis of in vitro metabolites of tolcapone and talinolol, two compounds with well-characterized metabolism. The information-dependent LC/MS/MS analysis enables the characterization of the major metabolites while the chip-based infusion is used to obtain good product ion spectra for lower level metabolites, to generate complementary MS information on potential metabolites detected in the LC/MS trace, or to screen for unexpected metabolites. Fractions from the chromatographic analysis are collected in 20 second steps, into a 96-well plate. The fractions of interest can be re-analyzed with chip-based infusion on a variety of mass spectrometers including triple quadrupole linear ion trap (QqLIT or Q TRAP) and QqTOF systems. Acquiring data for several minutes using multi-channel acquisition (MCA), or signal averaging while infusing the fractions at approximately 200 nL/min, permits about a 50 times gain in sensitivity (signal-to-noise) in MS/MS mode. A 5-10 microL sample fraction can be infused for more than 30 min allowing the time to perform various MS experiments such as MS(n), precursor ion or neutral loss scans and accurate mass measurement, all in either positive or negative mode. Through fraction collection and infusion, a significant gain in data quality is obtained along with a time-saving benefit, because the original sample needs neither to be re-analyzed by re-injection nor to be pre-concentrated. Therefore, a novel hydroxylated talinolol metabolite could be characterized with only one injection.

Animals↗
PubMed2003

The relevance of preclinical studies for the treatment of Parkinson's disease.

An essential element of pharmaceutical development, defined as the period between the discovery of a new agent and its market release, is provided by the "preclinical studies". They consist of the in vitro and in vivo studies performed before examination of the agent in human subjects. Regulatory authorities prescribe specific requirements regarding the nature and number of preclinical studies. In the present paper, we discuss the relevance of these studies for the treatment of Parkinson's disease (PD) on the basis of three examples: the L-DOPA ( L-3,4-dihydroxyphenylalanine, levodopa) story; the development of selegiline as a palliative and neuroprotective drug; and the safety concerns regarding tolcapone, an inhibitor of central and peripheral catechol-O-methyltransferase (COMT).

Antiparkinson Agents↗
PubMed2006

Optimal design for multivariate response pharmacokinetic models.

We address the problem of designing pharmacokinetic experiments in multivariate response situations. Criteria, based on the Fisher information matrix, whose inverse according to the Rao-Cramer inequality is the lower bound of the variance-covariance matrix of any unbiased estimator of the parameters, have previously been developed for univariate response for an individual and a population. We extend these criteria to design individual and population studies where more than one response is measured, for example, when both parent drug and metabolites are measured in plasma, multi-compartment models, where measurements are taken at more than one site, or when drug concentration and pharmacodynamic data are collected simultaneously. We assume that measurements made at distinct times are independent, but measurements made of each concentration are correlated with a response variance-covariance matrix. We investigated a number of optimisation algorithms, namely simplex, exchange, adaptive random search, simulated annealing and a hybrid, to maximise the determinant of the Fisher information matrix as required by the D-optimality criterion. The multiresponse optimal design methodology developed was applied in two case studies, where the aim was to suggest optimal sampling times. The first was a restrospective iv infusion experiment aimed to characterise the disposition kinetics of tolcapone and its two metabolites in healthy volunteers. The second was a prospective iv bolus experiment designed to estimate the tissue disposition kinetics of eight beta-blockers in rat.

Adrenergic beta-Antagonists↗
PubMed2000

Direct analysis of nitrocatechol-type glucuronides in urine by capillary electrophoresis-electrospray ionisation mass spectrometry and tandem mass spectrometry.

Direct, quantitative capillary electrophoresis-electrospray ionisation mass spectrometric (CE-ESI-MS) and tandem mass spectrometric (CE-ESI-MS-MS) methods are described for the quantitation of 3-O-glucuronides of E- and Z-entacapone isomers (EEG and EZG) and tolcapone (TG) in urine. 3-O-Glucuronide of nitecapone was used as internal standard. Good separation of glucuronides was achieved with 20 mM ammonium acetate as separation solution at pH 6.84. Stacking was used to increase the sensitivity of the method by introducing samples in 5 mM ammonium acetate. CE-ESI-MS and CE-ESI-MS-MS methods are linear with correlation coefficients better than 0.9983 and 0.9982, and repeatable with relative standard deviations below 9 and 14%, respectively. The limit of detection (LOD) in CE-ESI-MS at signal-to-noise ratio 3 is 100 ng/ml for EEG and EZG and 250 ng/ml for TG. The CE-ESI-MS-MS method was the more sensitive; LOD was 7 ng/ml for all compounds, without any concentration of the sample.

Benzophenones↗
PubMed2003

The psychometric properties of the Parkinson's Impact Scale (PIMS) as a measure of quality of life in Parkinson's disease.

We have previously designed and validated a 10-item bilingual questionnaire, the Parkinson's Impact Scale (PIMS), as a disease-specific instrument to measure the impact of Parkinson's disease (PD) on the quality of life of patients with PD. In this paper we extend the psychometric assessment of PIMS to a new set of patients, in the context of a cross-over trial by Hoffman-La Roche Ltd, comparing two doses of tolcapone in 116 PD patients who had developed wearing off effect on levodopa. Using data from this trial, we evaluate PIMS' test-retest reliability, construct validity, sensitivity and responsiveness to change. Validation is carried out by correlating the PIMS scores with corresponding UPDRS subscales and with the Schwab and England scale. We show that PIMS has excellent psychometric properties, and can therefore be used not only in clinical trials but also to identify quickly potential problems in major subjective areas of PD patients' lives, in order to refer them effectively to appropriate providers of assistance.

Antiparkinson Agents↗
PubMedDate not supplied

Enzyme-assisted synthesis and structural characterization of nitrocatechol glucuronides.

Enzyme-assisted synthesis and characterization are described for 3-O-beta-D-glucuronides 1b-4b of the aglycons E- and Z-2-cyano-N, N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)propenamide (entacapone), 1a and 2a, respectively, 3-(3,4-dihydroxy-5-nitrobenzylidene)-2, 4-pentanedione (nitecapone) 3a and 4'-methyl-3, 4-dihydroxy-5-nitrobenzophenone (tolcapone) 4a, and 1-o- and 2-o-glucuronides 5b and 6b of the aglycon 1, 2-dihydroxy-4-nitrobenzene 5a. Liver microsomes from rats pretreated with Aroclor 1254 were used as catalyst in the synthesis. Glucuronidation was regio- and stereoselective in the case of 1a-4a; only one product was observed by HPLC, HPTLC, and NMR. The glucuronidation of 1,2-dihydroxy-4-nitrobenzene 5a resulted in equal amounts of 1-O-beta-D- and 2-O-beta-D-glucuronides. Purification of the crude products by C18 solid-phase extraction and/or flash chromatography gave compounds 1b-6b in 38-98% yields (50-84 mg). The structures of the glucuronides were characterized on the basis of UV and IR spectra and confirmed with FAB-MS and NMR spectroscopy.

Animals↗
PubMed2000

Release and elimination of dopamine in vivo in mice lacking the dopamine transporter: functional consequences.

In mice lacking the dopamine transporter (DAT), the amplitude of dopamine (DA) release and the kinetics of dopamine elimination were measured in vivo using carbon fibre electrodes combined with amperometry. DA release was evoked by electrical stimulation of the medial forebrain bundle. The amplitude of DA release per pulse was lower (7% in striatum and 21% in nucleus accumbens) than in wild-type mice. Inhibition of monoamine oxidases (MAOs) by pargyline, but not of catechol-O-methyltransferase (COMT) by tolcapone, slowed down DA elimination in knockout mice. As DA half-life was two orders of magnitude higher in these mice, the DA diffusion distance was 10-times higher than in wild-types (100 and 10 microm, respectively). In knockout mice, alpha-methyl-p-tyrosine induced a much faster decline of DA release and haloperidol was less effective in potentiating DA release. Therefore, DA release was more dependent on DA synthesis than in normal animals but was less influenced by D2 autoregulation. Dopaminergic neurons exhibit two kinds of discharge activity, i.e. single spikes and bursts of 2-6 action potentials. In wild-type mice, stimuli mimicking bursts evoked significant increases in extracellular DA over its basal level sustained by tonic activity. However, in mice lacking the DAT, low frequency firing resulted in consistently high extracellular DA levels that could not be distinguished from DA levels achieved by high frequency firing. Therefore, the burst firing activity cannot be specifically translated into phasic changes in extracellular DA. This deficit might contribute to the difficulties of these mice in spatial cognitive function.

Animals↗
PubMed2001

Catechol-O-methyltransferase inhibitors in the management of Parkinson's disease.

Parkinson's disease is the most common neurodegenerative disease in which the chemical pathology is known and effective symptomatic treatment, levodopa, is available. Therapy in the initial years after initiation with dopa decarboxylase inhibitors, carbidopa or benserazide, combined with levodopa results in favorable, stable responses. However, by 5 years after the initiation of treatment, over two thirds of patients experience motor fluctuations beginning initially with a "wearing-off" effect followed by more complex fluctuations including dyskinesias and "on-off" responses. A number of strategies have been developed in an attempt to deal with these complications including changing doses and frequencies, adding agonist medications, adding or substituting controlled-release levodopa, and surgical therapies. A more recent strategy has centered on increasing the availability of intracellular levodopa and synaptic dopamine by inhibiting the peripheral and central metabolism of levodopa to 3-O-methyldopa with the use of a catechol-O-methyltransferase inhibitor. To date, two of these inhibitors, tolcapone and entacapone, are available to treat the wearing-off phase of levodopa therapy.

Benzophenones↗
PubMed1995

The fate of [3H]-(-)-noradrenaline in the perfused rat liver.

1. Hepatic removal and metabolism as well as biliary excretion of noradrenaline were studied. Rat livers were perfused in situ for 60 min with Krebs-Henseleit buffer at 37 degrees C containing 2 nM [3H]-(-)-noradrenaline. [3H]-noradrenaline and its [3H]-metabolites were determined in liver, venous effluent and bile. 2. Removal of [3H]-noradrenaline by the liver, calculated as the sum of total radioactivity in the liver at the end of perfusion plus total radioactivity in the bile formed during perfusion plus [3H]-metabolites in the venous effluent formed during perfusion, was 40.2 +/- 6.9 pmol g-1 h-1. This removal corresponded to about 25% of the amount of [3H]-noradrenaline offered to the liver. 3. A proportion of the [3H]-noradrenaline (86.8%) taken up by the liver was metabolized, 13.2% remained unmetabolized in the liver and 0.019% was excreted unmetabolized into the bile. The most abundant metabolites were those present in the [3H]-OMDA fraction (72.5%), followed by [3H]-NMN (15.8%), [3H]-DOPEG (6.1%) and [3H]-DOMA (5.6%). Some of these metabolites (66.6%) were recovered from the venous effluent, 32.7% from the liver and only 1.3% from the bile. The amount of [3H]-noradrenaline present in the liver at the end of the perfusion produced a tissue:perfusion medium ratio of 2.6. 4. Simultaneous inhibition of monoamine oxidase and catechol-O-methyl transferase with pargyline (75 mg kg-1, i.p., 3 h before) and tolcapone (1 microM), respectively, markedly reduced the formation of [3H]-NMN, [3H]-DOPEG and [3H]-DOMA, but did not affect the hepatic removal of [3H]-noradrenaline, the content of [3H]-noradrenaline in the liver, the formation of [3H]-OMDA or the excretion of [3H]-noradrenaline and its [3H]-metabolites into the bile. 5. Treatment with an uptake2 blocker, corticosterone (40 microM), did not change the hepatic removal and metabolism of [3H]-noradrenaline or the biliary excretion of [3H]-noradrenaline and its [3H]-metabolites. 6. These findings indicate that the perfused rat liver efficiently removed and metabolized [3H]-noradrenaline, both monoamine oxidase and catechol-O-methyl transferase being involved in the metabolism of this amine. The apparent lack of effect of monoamine oxidase and catechol-O-methyl transferase inhibition on the formation of [3H]-OMDA may be due to the presence, especially in the liver, of conjugated metabolites of [3H]-noradrenaline in the [3H]-OMDA fraction. These results also show that uptake2 does not seem to be involved in the hepatic uptake of [3H]-noradrenaline, confirming previous findings. Finally, the results indicate that the rat liver perfused with Krebs-Henseleit buffer is not a suitable experimental model for studies on the biliary excretion of catecholamines.

Adrenergic Uptake Inhibitors↗
PubMed2000

Catechol-O-methyltransferase (COMT) inhibitors in Parkinson's disease.

Catechol-O-methyltransferase (COMT) inhibitors are a new therapeutic option in the treatment of patients with Parkinson's disease. COMT inhibitors act by extending the duration of action of levodopa, thus improving the amount of time a patient can experience benefit from levodopa. COMT inhibitors are only used in conjunction with levodopa. They do have a propensity to augment dopaminergic effects, such that levodopa doses might need to be adjusted downward. Other side effects of COMT inhibitors include diarrhea and liver function abnormalities. Due to the latter, recent guidelines have been developed to monitor patients on tolcapone for this rare side effect, and these guidelines will be discussed. This article also provides representative case histories for the appropriate use of COMT inhibitors that illustrate how these drugs can be used to manage patients with a fluctuating response to levodopa.

Antiparkinson Agents↗
PubMed1998

Highlights of the North American and European experiences.

Two large, randomized, double-blind, placebo-controlled multicenter studies, one North American and one European, examined the efficacy and safety of 300 and 600 mg/day tolcapone in similar populations of patients (n = 379) with Parkinson's disease currently taking levodopa and experiencing motor fluctuations. Change in "on-off" function was the most important end-point assessment. The two studies found similar results. The percentage of "on" time improved significantly and "off" time was reduced. Daily levodopa dosage requirements decreased significantly. The most common and significant adverse event was increased dyskinesia; hallucinations were not frequently encountered.

Antiparkinson Agents↗
PubMed1998

Influence of COMT inhibition on levodopa pharmacology and therapy.

Catechol O-methyltransferase (COMT) is an important enzyme that is linked directly to therapy with levodopa. Considering the demonstrated mechanism of action and pharmacologic profiles of COMT inhibitors, it is reasonable to hypothesize that these agents would improve the disability associated with Parkinson's disease. Two basic classes of COMT inhibitors are being studied in patients with PD: those that act exclusively extracerebrally or peripherally (e.g., entacapone) and those that cross the blood-brain barrier (e.g., tolcapone). With COMT inhibition, greater peripheral bioavailability of levodopa occurs in humans without an enhancement of peak plasma levels. It is reasonable to suggest that COMT inhibition will be associated with prolonged effects of levodopa in PD, without increased peak dose toxicity in the form of dyskinesias and hallucinations.

Animals↗
PubMed1998

COMT inhibition: a new treatment strategy for Parkinson's disease.

During the initial stages of Parkinson's disease, treatment with levodopa plus a decarboxylase inhibitor (carbidopa or benserazide) provides adequate control of symptoms. However, as the disease progresses, the clinical response to treatment often begins to fluctuate, becoming increasingly correlated with fluctuations in plasma concentrations of levodopa-the "wearing-off" phenomenon. Many strategies have attempted, with various degrees of success, to increase the availability of levodopa and its active metabolites, thus reducing these fluctuations in response. This review focuses on the role of the new catechol O-methyltransferase (COMT) inhibitors tolcapone and entacapone as adjuncts to levodopa therapy. These agents act effectively and safely to increase the amount of levodopa that is available to enter the brain by extending the half-life of levodopa, resulting in more stable levels in the plasma and prolonging "on" time.

Antiparkinson Agents↗
PubMed2006

Bioactivation and hepatotoxicity of nitroaromatic drugs.

Certain drugs containing a nitroaromatic moiety (e.g., tolcapone, nimesulide, nilutamide, flutamide, nitrofurantoin) have been associated with organ-selective toxicity including rare cases of idiosyncratic liver injury. What they have in common is the potential for multistep nitroreductive bioactivation (6-electron transfer) that produces the potentially hazardous nitroanion radical, nitroso intermediate, and N-hydroxy derivative. These intermediates have been associated with increased oxidant stress and targeting of nucleophilic residues on proteins and nucleic acids. However, other mechanisms including the formation of oxidative metabolites and mitochondrial liability, as well as inherent toxicokinetic properties, also determine the drugs' overall potency. Therefore, structural modification not only of the nitro moiety but also of ring substituents can greatly reduce toxicity. Novel concepts have revealed that, besides the classical microsomal nitroreductases, cytosolic and mitochondrial enzymes including nitric oxide synthase can also bioactivate certain nitroarenes (nilutamide). Furthermore, animal models of silent mitochondrial dysfunction have demonstrated that a mitochondrial oxidant stress posed by certain nitroaromatic drugs (nimesulide) can produce significant mitochondrial injury if superimposed on a genetic mitochondrial abnormality. Finally, there may be mechanisms for all nitroaromatic drugs that do not involve bioactivation of the nitro group, e.g., AHR interactions with flutamide. Taken together, the focus of research on the hepatic toxicity of nitroarene-containing drugs has shifted over the past years from the identification of the reactive intermediates generated during the bioreductive pathway to the underlying biomechanisms of liver injury. Most likely one of the next paradigm shifts will include the identification of determinants of susceptibility to nitroaromatic drug-induced hepatotoxicity.

Benzophenones↗