Determination of a catechol-O-methyltransferase inhibitor, nitecapone, in human plasma and urine by liquid chromatography

Synthesis and in vitro evaluation of two progressive series of bifunctional polyhydroxybenzamide catechol-O-methyltransferase inhibitors

Two progressive series of molecules with two polyhydroxybenzamide substructures were synthesized and tested as potential inhibitors of catechol-O-methyltransferase (COMT). These compounds were designed for the purpose of enhanced enzyme binding with duplicated substructures separated by a linker section of various lengths. Our results show that potency and mode of inhibition observed with the "bifunctional" compounds were a reflection of their bifunctional nature. Furthermore, potency and mode of inhibition were dependent on the length of the linker section. Of the assayed compounds, the optimum linker was found to be diaminopropane. For example, N,N'-1,3-propanediylbis(3,4-dihydroxybenzamide) and N,N'-1,3-propanediylbis(3,4,5-trihydroxybenzamide) demonstrated strong inhibitory action against COMT, with apparent Ki values of 0.3 and 6.0 microM, respectively.

The effects of the COMT inhibitor nitecapone for one week on exercise haemodynamics and catecholamine disposition

We have studied resting and exercise haemodynamics and catecholamine disposition after catechol-O-methyl-transferase (COMT) inhibition with nitecapone 100 mg t.d.s. for 7 days in 15 healthy men (aged 21 to 28 y) in a placebo-controlled, cross-over study. Nitecapone did not alter resting or exercise heart rates, blood pressure, or plasma catecholamine concentrations, but it altered the metabolic profile of endogenous catecholamines, as shown by: (1) a fall in the concentrations of the COMT-dependent metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) by 22% (P < 0.01), (2) increases in plasma concentrations of the monoamine oxidase-dependent metabolites 3,4-dihydroxyphenylglycol (DHPG) by up to 90% (P < 0.001) and 3,4-dihydroxyphenylacetic acid (DOPAC) by 67% (P < 0.05), (3) a three-fold increase in the concentration of circulating conjugated adrenaline (P < 0.001).

Liquid chromatographic determination of a new catechol-O-methyltransferase inhibitor, entacapone, and its Z-isomer in human plasma and urine

Assay procedures for analysis of entacapone, (E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)-propenamide++ +, and its Z-isomer in human plasma and urine are described. The methods were based on reversed-phase liquid chromatography with amperometric detection. Entacapone and its Z-isomer were extracted with n-hexane-ethyl acetate mixtures after acidification with hydrochloric acid. From urine extracts the analytes were back-extracted into phosphate buffer (pH 7.2). During sample treatment 1-2% of entacapone was changed to the Z-isomer. With recoveries exceeding 75% the relative standard deviations for within-day precision were less than 11% for plasma and less than 6% for urine at the quantitation limit (10 ng ml-1) and less than 6% for both methods at higher concentrations (20-2000 ng ml-1). The assays were specific with respect to all known metabolites and selective, sensitive and precise enough for determination of entacapone and its Z-isomer in plasma and urine down to 10 ng ml-1. The methods are thus suitable for the kind of pharmacokinetic studies exemplified in this paper.

Determination of nitecapone and (13C6)nitecapone in human plasma by gas chromatography/mass spectrometry

A gas chromatographic/mass spectrometric method is developed and validated for simultaneous determination of nitecapone and its 13C6-labelled analogue in human plasma using (2H6,13C6)nitecapone as internal standard. The method involves extraction of the analytes from plasma to ethyl acetate-hexane mixture (20:80) and conversion to bis(trimethylsilyl) ethers prior to determination by gas chromatography/mass spectrometry using selected ion monitoring. The quantification range is 0.5-2000 ng ml-1. Precision ranges from 11.3% (coefficient of variation) at low levels to 2.4% at high levels. Recovery is about 50% in the whole range. The method is applied to a pharmacokinetic study where nitecapone diluted with 14C-labelled nitecapone is given intravenously concomitantly with an oral dose of (13C6)nitecapone.

Inhibition of human erythrocyte and gastroduodenal catechol-O-methyltransferase activity by nitecapone

The effect of increasing single oral doses of the novel catechol-O-methyltransferase (COMT) inhibitor, nitecapone, on enzyme activity in red cells (RBC) and gastroduodenal COMT activity has been studied in healthy male volunteers. A dose-dependent decrease in RBC COMT activity was seen in all cases after 1 to 150 mg of the drug. The highest dose of 300 mg did not produce much more inhibition of COMT than 150 mg. The inhibition was not complete; at the highest doses the COMT activity was reduced by 50-60%. The effect and the duration of the inhibition in RBC COMT was strongly correlated with plasma nitecapone concentrations in the dose range up to 150 mg. RBC COMT activity recovered fully in 4 h after medication. Gastric mucosal COMT activity was several-fold higher than that in RBCs. It was also dose-dependently inhibited at the two doses (25 and 100 mg) studied. The inhibition of gastric and duodenal COMT was greater than that in RBCs. This also indicates that nitecapone is locally active in the gastroduodenal tract. The results confirm nitecapone as a potent COMT inhibitor in human tissues. New COMT inhibitors may provide a valuable approach to the treatment of Parkinson's disease in combination with L-dopa and dopa decarboxylase inhibitor therapy.