Voltammetric measurement of entacapone in the presence of other medicines against Parkinson's disease by a screen-printed electrode modified with sulfur-tin oxide nanoparticles.

A screen-printed electrode (SPE) is described modified with sulfur-tin oxide nanoparticles (S@SnO2NP) for the determination of entacapone (ENT) in the presence of other medicines against Parkinson's disease (PD). The S@SnO2NP was synthesized through the hydrothermal method and used in the modification of the SPE. The smart utilization of the S@SnO2NP and the SPE provided excellent properties such as high surface area and current density amplification by embedding an efficient sensing interface for highly selective electrochemical measurement. Under optimized experimental conditions, the anodic peak current related to the ENT oxidation onto the sensor surface at 0.46 V presented a linear response towards different ENT concentration sin the range 100 nM to 75 µM. The limit of detection (LOD) and electrochemical sensitivity were estimated to be 0.010 µM and 2.27 µA·µM-1·cm-2, respectively. The applicability of the sensor was evaluated during ENT determination in the presence of other conventional medicines againts, including levodopa (LD), carbidopa (CD), and pramipexole (PPX). The results of the analysis of human urine and pharmaceutical formulation as real samples using the developed sensor were in good agreement withre sults of high-performance liquid chromatography (HPLC) as a standard method. These findings demonstrated that the strategy based on the SPE is a cost-effective platform creating a promising candidate for practical determination of ENT in routine clinical testing.Graphical abstract.

Substantial renal conversion of L-threo-3,4-dihydroxyphenylserine (droxidopa) to norepinephrine in patients with neurogenic orthostatic hypotension.

BACKGROUND: The pressor effect of L-threo-3,4-dihydroxyphenylserine (L-DOPS, droxidopa, Northera™) results from conversion of L-DOPS to norepinephrine (NE) in cells expressing L-aromatic-amino-acid decarboxylase (LAAAD). After L-DOPS administration the increase in systemic plasma NE is too small to explain the increase in blood pressure. Renal proximal tubular cells abundantly express LAAAD. Since NE generated locally in the kidneys could contribute to the pressor effect of L-DOPS, in this study we assessed renal conversion of L-DOPS to NE. METHODS: Ten patients who were taking L-DOPS for symptomatic orthostatic hypotension had blood and urine sampled about 2 h after the last L-DOPS dose. L-DOPS and NE were assayed by alumina extraction followed by liquid chromatography with electrochemical detection. Data were compared in patients off vs. on levodopa/carbidopa. RESULTS: In patients off levodopa/carbidopa the ratio of NE/L-DOPS in urine averaged 63 times that in plasma (p = 0.0009 by t test applied to log-transformed data). In marked contrast, in the three patients on levodopa/carbidopa the ratio of NE/L-DOPS in urine did not differ from that in plasma. CONCLUSION: There is extensive renal production of NE from L-DOPS. Carbidopa seems to attenuate the conversion of L-DOPS to NE in the kidneys. Further research is needed to assess whether the proposed paracrine effect of L-DOPS in the kidneys contributes to the systemic pressor response.

Excretion of himantane and its metabolites with the urine and feces in rats.

The levels of himantane and its metabolites in daily urine and feces of rats were measured after intraperitoneal and oral dose of 25 mg/kg. The injected dose of the initial substance and 1.3% its metabolites were eliminated with excrements within 24 h after administration via both routes 0.23%.

[Pharmacokinetics of hemantane in rats].

The pharmacokinetics ofhemantane after administration in different ways has been studied in rats. It is established that hemantane introduced both orally (p.o.) and intravenously (i.v.) is very intensively metabolized, with the main metabolites characterized by m/z = 250 and 266 and detected for 6 hours after the administration in both ways. Hemantane shows high rate of permeability into its target organ--brain--whereas the permeation of its metabolites is extremely low. The absolute bioavailability ofhemantane upon p.o. administration was 14.1%. The substance is subject to the "first-pass effect". The unchanged substance was determined in daily urine and feces in very small fractions of the administered dose: 0.23% in urine and 0.08% in feces after i.v. administration and 0.02% in feces after p.o. administration. Thus, it may be concluded that the substance is completely absorbed in rats from the gastro-intestinal tract into systemic blood circulation.

A novel way for detection of antiparkinsonism drug entacapone via electrodeposition of silver nanoparticles/functionalized multi-walled carbon nanotubes as an amperometric sensor.

Silver (Ag) nanoparticles were electrochemically deposited on the film of a metformin functionalized multi-walled carbon nanotube modified glassy carbon electrode (Met-MWCNT/GCE), which fabricated an Ag@Met-MWCNT nanocomposite sensor (Ag@Met-MWCNT/GCE) to detect entacapone (ENT). The Ag@Met-MWCNT nanocomposite was characterized by field emission scanning electrochemical microscopy (FESEM), X-ray diffraction (XRD) analysis, FT-IR and electrochemical tests. The modified electrode showed a large electrocatalytic activity for reduction of ENT. This improved activity indicates that Met@MWCNT plays a crucial role in the dispersion and stabilization of Ag nanoparticles on GCE. Under the optimized conditions the linear range for the detection of the ENT was obtained to be 0.05 to 70.0µM with a low detection limit of 15.3nM. The proposed sensor can effectively analyse ENT concentration in pharmaceutical formulations and human urine samples, avoiding interference, and is a promising ENT sensor due to good sensitivity, stability and low cost.

Determination of drugs used as anti-Parkinson's disease drugs in urine and serum by capillary electrophoresis.

A new capillary electrophoresis method to determine simultaneously eight of the most important anti-Parkinson's disease compounds has been developed. The generic names of the drugs studied are benactyzine (BA), trihexyphenidyl (TP), fenpiverin (FP), diphemin (DF), scopolamine (BL), adiphenine (TS), diethylaminoethylester 1-phenylcyclopentane-1-carboxylate (EKK), and diethylaminoethylester tetramethoxydiphenylacetate (EKO). An untreated fused-silica capillary tube (75 microns i.d., 57 cm total length, 49.5 cm length to the detector) was used with detection at 190 nm. The optimal separation conditions were 50 mM phosphate buffer (pH 2.7) with 7 mM-beta-cyclodextrin, electrokinetic injection for 15 sec at 5 kV, temperature 25 degrees C, and 15-20 kV separation voltage. Complete separation of all compounds was achieved in less than 16 min. The procedure was applied for the determination in urine and serum. The limits of detection (LOD, S/N = 3) for serum were 209 (FP), 234 (EKO), 168 (DF), 182 (BA), 168 (TP), 220 (BL), 174 (TS), and 163 (EKK) ppb. The method can be used for the therapeutic drug monitoring of these central active cholinolytics in clinical laboratories.

The metabolic fate of the anti-parkinsonian drug budipine in rats.

The metabolic fate of the anti-Parkinsonian drug budipine was studied in rats after oral administration. The presence of an aromatic hydroxylation product, metabolite M1, and its O-sulphate conjugate was confirmed. Three new minor metabolites, budipine N-oxide, metabolite M1 N-oxide and a secondary metabolite derived from M1 via hydroxylation of a methyl of the tert-butyl group, were isolated and identified in rat urine. The presence of a metabolite M1-glucuronic acid conjugate, was also established through different enzymatic treatments of the rat urine.

[An evaluation of methods for isolating antiparkinson preparations from cadaveric material]. / Otsenka metodov vydeleniia nekotorykh protivoparkinsonicheskikh preparatov iz trupnogo materiala.

Methods of amedine, amyzyl, and tropacine isolation from cadaveric material, blood and urine were developed. They ensure higher output of the given substances as compared with conventional methods of isolation of toxicologically significant substances. An extraction-photometric method was developed for estimation of amedine, amyzyl, and tropacine in the cadaveric material.

Pharmacokinetics, pharmacodynamics and tolerability of opicapone, a novel catechol-O-methyltransferase inhibitor, in healthy subjects: prediction of slow enzyme-inhibitor complex dissociation of a short-living and very long-acting inhibitor.

BACKGROUND AND OBJECTIVES: Opicapone is a novel catechol-O-methyltransferase (COMT) inhibitor. The purpose of this study was to evaluate the tolerability, pharmacokinetics (including the effect of food) and pharmacodynamics (effect on COMT activity) following single oral doses of opicapone in young healthy male volunteers. METHODS: Single rising oral doses of opicapone (10, 25, 50, 100, 200, 400, 800 and 1,200 mg) were administered to eight groups of eight subjects per group (two subjects randomized to placebo and six subjects to opicapone), under a double-blind, randomized, placebo-controlled design. In an additional group of 12 subjects, a 50 mg single dose of opicapone was administered on two occasions, once having fasted overnight and once with a high-fat high-calorie meal. RESULTS: Opicapone was well tolerated at all doses tested. The extent of systemic exposure (area under the plasma concentration-time curve and maximum plasma concentration) to opicapone and metabolites increased in an approximately dose-proportional manner and showed a decrease following concomitant ingestion of a high-fat high-calorie meal. The apparent terminal elimination half-life of opicapone was 0.8-3.2 h. Sulphation appeared to be the main metabolic pathway for opicapone, and both opicapone and the main sulphated metabolite are likely excreted by the biliary route. Maximum COMT inhibition by opicapone was dose dependent, ranged from 36.1% (10 mg) to 100% (200 mg and above), and reached statistical significance at all doses tested. The long duration of COMT inhibition by opicapone, however, tended to be independent from the dose taken. The observed half-life of opicapone-induced COMT inhibition in human erythrocytes was 61.6 h (standard deviation [SD] = 37.6 h), which reflects an underlying dissociative process with a kinetic rate constant of 3.1 × 10(-6) s(-1) (SD = 1.9 × 10(-6) s(-1)). Such a process compares well to the estimated dissociation rate constant (k(off)) of the COMT-opicapone molecular complex (k(off) = 1.9 × 10(-6) s(-1)). CONCLUSIONS: Opicapone was well-tolerated and presented dose-proportional kinetics. Opicapone demonstrated marked and sustained inhibition of erythrocyte soluble COMT activity. Based on the observation that the half-life of COMT inhibition is independent of the dose and that it reflects an underlying kinetic process that is consistent with the k(off) value of the COMT-opicapone complex, we propose that the sustained COMT inhibition, far beyond the observable point of clearance of circulating drug, is due to the long residence time of the reversible complex formed between COMT and opicapone. Globally, these promising results provide a basis for further clinical development of opicapone.

Target urinary analytes for the gas chromatographic- mass spectrometric detection of procyclidine and benzhexol in drug abuse cases.

The two antiparkinsonian drugs procyclidine and benzhexol are presently finding considerable favor for their euphoric hallucinogenic effects among drug abusers in some countries. In anticipation of their possible scheduling in national drug laws, gas chromatography-mass spectrometry (GC-MS) methods for their detection in urine will be required. However, because of uncertainty of the metabolic fate of the two drugs in humans, the urinary target analytes for GC-MS detection were not well defined. The problem was addressed in the present study in which it was found that mono-hydroxy metabolites, where hydroxylation took place at the cyclohexane ring in both drugs, could be endorsed as the major target analytes. The metabolites could only be detected as the mono- and/or di-trimethylsilyl (TMS) derivatives. The predominance of either derivative depended on the temperature and time of heating with the derivatizing reagent. Because of the basic properties of the hydroxy metabolites, analytic method optimization was needed for their detection in urine included extraction under basic pH conditions. Urine hydrolysis with ß-glucuronidase did not have an effect on the recovery of the metabolites, but was usually performed in search for other drugs. Because of the relative abundance of ions, the electron impact mass spectra of the mono-TMS derivatives and the chemical ionization (CI) mass spectra of the mono- and di-TMS derivatives of the hydroxy metabolites of both drugs were found to be more structurally informative. The CI mass spectra of the di- TMS derivatives have the additive advantage of being potentially useful for quantitative analysis.

Analysis of the anti-Parkinson drug pramipexole in human urine by capillary electrophoresis with laser-induced fluorescence detection.

A sensitive method based on capillary electrophoresis with laser-induced fluorescence detection has been developed for the analysis of the non-ergoline dopamine agonist pramipexole in human urine. Separation was carried out in uncoated fused silica capillaries (75microm internal diameter, 75.0 and 60.0cm total and effective length, respectively), with a background electrolyte composed of borate buffer (50mM, pH 10.3), tetrabutylammonium bromide (30mM), and acetone (15%, v/v). Applying a 20kV voltage, the electrophoretic run is completed within 12min. A sample pre-treatment procedure based on liquid/liquid extraction with ethyl acetate, followed by derivatisation of pramipexole with fluorescein isothiocyanate at pH 9, allows the complete removal of biological interferences, with extraction yields always higher than 94.5%. Method validation gave good linearity (r(2)=0.9992) in the 25.0-1000ngmL(-1) range; limit of detection and limit of quantitation were 10.0 and 25.0ngmL(-1), respectively; precision was 90.0. The method was applied to the analysis of urine samples from patients undergoing therapy with pramipexole.

Metabolism of selegiline in humans. Identification, excretion, and stereochemistry of urine metabolites.

Nine urinary metabolites of selegiline hydrochloride [N-methyl-N-propargyl [2-phenyl-1-methyl)ethylammonium chloride], a monoamine oxidase inhibitor, after administration to humans were identified. Their identifies were confirmed by comparison of the spectra from GC/MS of peaks with those of authentic compounds. The following metabolites and unchanged drug (selegiline) were detected in urine: (R)-desmethylselegiline, (R)-methamphetamine, (R)-amphetamine, (1S,2R)-norephedrine, (1R,2R)-norpseudoephedrine, (1S,2R)-ephedrine, (1R,2R)-pseudoephedrine, (R)-p-hydroxyamphetamine, and (R)-p-hydroxymethamphetamine. The metabolites excreted 2 days after administration of 2.5-10 mg of selegiline hydrochloride amounted to 44-58% of the dose. Selegiline was metabolized by three distinct pathways: N-dealkylation, beta-carbon hydroxylation, and ring-hydroxylation. The major metabolite was (R)-methamphetamine. During metabolism, no racemic transformation occurred and beta-carbon hydroxylation showed apparently product stereoselectivity.

Stereoselective screening for and confirmation of urinary enantiomers of amphetamine, methamphetamine, designer drugs, methadone and selected metabolites by capillary electrophoresis.

Data presented in this paper demonstrate that a competitive binding, electrokinetic capillary-based immunoassay previously used for screening of urinary amphetamine and analogs cannot be employed to distinguish between the enantiomers of amphetamine and methamphetamine. However, capillary zone electrophoresis with a pH 2.5 buffer containing (2-hydroxypropyl)-beta-cyclodextrin as chiral selector is shown to permit the enantioselective analysis of urinary extracts containing methamphetamine, amphetamine, 3,4-methylenedioxymethamphetamine (Ecstasy) and other designer drugs, and methadone together with its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine. In that approach, enantiomer identification is based upon comparison of extracted polychrome UV absorption data and electropherograms obtained by rerunning of spiked extracts with spectra and electropherograms monitored after extraction of fortified blank urine. The suitability of the described chiral electrokinetic capillary method for drug screening and confirmation is demonstrated via analysis of unhydrolyzed quality control urines containing a variety of drugs of abuse. Furthermore, in a urine of a patient under selegiline pharmacotherapy, the presence of the R-(-)-enantiomers of methamphetamine and amphetamine could be unambiguously identified. Direct intake of an R-enantiomer or ingestion of drugs that metabolize to the R-enantiomers can be distinguished from the intake of S-(+)-enantiomers (drug abuse) or prescribed drugs that metabolize to the S-enantiomers of methamphetamine and amphetamine. The described approach is simple, reproducible, inexpensive and reliable (free of interferences of other major basic drugs that are frequently found in toxicological urines) and could thus be used for screening for and confirmation of urinary enantiomers in a routine laboratory.

Optimization of the hydrolysis of conjugated L-DOPA, dopamine and dihydroxyphenylacetic acid in human urine for assay by high-performance liquid chromatography with electrochemical detection.

Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and dihydroxyphenylacetic acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/l HCl for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and dihydroxyphenylacetic acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and dihydroxyphenylacetic acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of L-DOPA, dopamine and dihydroxyphenylacetic acid was decreased "concentration dependently" where the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than acid hydrolysis in generating free catechols. This indicated that there were other, non-sulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.