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

Methods based on reversed-phase liquid chromatography with amperometric detection have been developed for determination of nitecapone, 3-(3,4-dihydroxy-5-nitrobenzylidene)-2,4-pentanedione, a COMT inhibitor, in human plasma and urine. Nitecapone was extracted with ethyl acetate-hexane mixtures from plasma after acidification with hydrochloric acid and from urine as the tetrabutylammonium ion-pair of its diphenylborate derivative. The recoveries of both methods exceeded 70% and the relative standard deviations for within-day precision were less than 4% and 8% at 50 ng ml-1 and at the quantitation limits, respectively. The methods are selective, sensitive and precise enough for determination of 4-5 ng ml-1 of nitecapone in plasma and urine and are thus suitable for the kind of pharmacokinetic studies exemplified in this paper.

Identification of major metabolites of the catechol-O-methyltransferase-inhibitor nitecapone in human urine

Metabolites of nitecapone [3-(3,4-dihydroxy-5-nitrobenzylidene)-2,4-pentanedione], a potent new catechol-O-methytransferase-inhibitor, were isolated from human urine both after hydrolysis with beta-glucuronidase and as intact conjugates. Seven phase-I metabolites and corresponding glucuronides were identified using electron ionization and fast atom bombardment mass spectrometry, IR spectroscopy, and proton NMR spectrometry. The most abundant metabolite in urine was the glucuronide of unchanged nitecapone, representing 60-65% of the metabolites found. The main phase-I metabolic reaction was reduction of the side chain double bond and carbonyl groups. One of the major metabolites was formed by cleavage of the side chain by retro aldol condensation. All phase-I metabolites were present mainly as their glucuronic acid conjugates. The 3-nitrocatechol-structure of nitecapone seems to hinder nitro-reduction, catechol-O-methylation, and sulfation reactions.

Biological monitoring of exposure to monochlorobenzene

We assessed the exposure to monochlorobenzene (MBC) of 44 male subjects performing maintenance work in a diphenylmethane-4-4'diisocyanate producing plant. In total, 251 whole shift personal air sampling measurements (passive diffusion) were carried out and at the end of the shift, during which the time-weighted average exposure (TWA) to MCB was determined, a urine sample was collected for the analysis of 4-chlorophenol and 4-chlorocatechol, the two main urinary metabolites of MCB in human. The MCB-TWA values were log normally distributed with a median of 1.2 ppm and a range from less than 0.05 to 106 ppm. The Pearson's correlation coefficient between the log MCB-TWA (ppm) and the log concentration (mg/g creatinine) of the metabolites in post shift-urine samples amounted to 0.65 (P less than 0.001) for 4-chlorophenol (log 4-chlorophenol = 0.22 + 0.43 log MCB-TWA) and 0.72 (P less than 0.001) for 4-chlorocatechol (log 4-chlorocatechol = 0.53 + 0.58 log MCB-TWA), respectively. On the average the workers excreted three times more 4-chlorocatechol than 4-chlorophenol. The follow up of 21 workers over several days did not show any tendency for the metabolite concentration in urine to increase during the workweek.

Role of the clinical laboratory in the diagnosis and management of malignant melanoma

The biosynthesis of melanin from tyrosine is reviewed as the basis for assessment of laboratory tests that might potentially aid in the diagnosis and management of patients with malignant melanoma. These tests include qualitative and quantitative assays for the intermediates in metabolism of melanin and catecholamines, enzyme assays, metal ion analyses, and, most recently, immunoassays. Although currently no role exists for the clinical laboratory in the early diagnosis of malignant melanoma, serial quantitative analyses of total or individual melanogens or of catecholamine metabolites in urine or plasma specimens may be of value in the management of patients with this disorder. Immunologically based methods for the diagnosis and management of malignant melanoma hold some promise for the future.

Quantitative estimation of catechol/methylcatechol pathways in human phenytoin metabolism

A gas-liquid chromatographic (GLC) assay utilizing an on-column methylation technique has been developed to assay urinary concentration of a phenytoin (5,5-diphenylhydantoin, PHT) metabolite, 5-(4-hydroxy-3-methoxyphenyl)-5-phenylhydantoin (MCAT). Assay of MCAT in 35 24-h urine samples from patients receiving chronic phenytoin (PHT) therapy indicated that 0.3-4.0% of the daily dose could be accounted for as MCAT. The GLC assay was specific for MCAT, and provided a minimal estimate of the fraction of the PHT dose being metabolized via the catechol/MCAT route. Multiple regression analyses indicated that the amount of urinary MCAT was dependent on the quantities of both dihydrodiol (DHD) and p-phenolic (p-HPPH) metabolites. Oxidative pathways involving both DHD and p-HPPH as substrates appear to be responsible for catechol/MCAT production.

Determination of catechol and quinol in the urine of workers exposed to benzene

Time weighted average concentrations of benzene in breathing zone air (measured by diffusive sampling coupled with FID gas chromatography) and concentrations of catechol and quinol in the urine (collected at about 1500 in the second half of a working week and analysed by high performance liquid chromatography) were compared in 152 workers who were exposed to benzene (64 men, 88 women). The concentration of urinary metabolites was also determined in 131 non-exposed subjects (43 men, 88 women). There was a linear relation between the benzene concentrations in the breathing zone and the urinary concentrations of catechol and quinol (with or without correction for urine density) in both sexes. Neither catechol nor quinol concentration was able to separate those exposed to benzene at 10 ppm from those without exposure. The data indicated that when workers were exposed to benzene at 100 ppm about 25% of benzene absorbed was excreted into the urine as phenolic metabolites, of which 13.2%, 1.6%, and 10.2% are phenol, catechol, and quinol, respectively.

Mutual metabolic suppression between benzene and toluene in man

The exposure intensity during a shift and the metabolite levels in the shift-end urine were examined in male workers exposed to either benzene (65 subjects; the benzene group), toluene (35 subjects; the toluene group), or a mixture of both (55 subjects; the mixture group). In addition, 35 non-exposed male workers (the control group) were similarly examined for urinary metabolites to define background levels. A linear relationship was established between the intensity of solvent exposure and the corresponding urinary metabolite levels (i.e. phenol, catechol and quinol from benzene, and hippuric acid and o-cresol from toluene) in each case when one of the three exposed groups was combined with the control group for calculation. Comparison of regression lines in combination with regression analysis disclosed that urinary levels of phenol and quinol (but not catechol) were lower in the mixture group than in the benzene group when the intensities of exposure to benzene were comparable, indicating that the biotransformation of benzene to phenolic compounds (excluding catechol) in man is suppressed by co-exposure to toluene. Conversely, metabolism of toluene to hippuric acid was suppressed by benzene co-exposure. Conversion of toluene to o-cresol was also reduced by benzene, but to a lesser extent. The significance of the present findings on the mutual suppression of metabolism between benzene and toluene is discussed in relation to solvent toxicology and biological monitoring of exposure to the solvents.

Measurement of urinary catecholamines and their catechol metabolites and precursor by liquid chromatography with column-switching and on-line fluorimetric and electrochemical detection

A new method is described for the determination of catecholamines and their precursor (3,4-dihydroxyphenylalanine), and separately of their catechol metabolites (3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylethylene glycol and 3,4-dihydroxyphenylethanol) in urine. After a two-step pretreatment involving ethyl acetate extraction and adsorption onto alumina, the separation is performed by ion-pair reversed-phase high-performance liquid chromatography. A column-switching system enables complete separation of the most polar compounds without increase in the total analysis time. The column eluates are monitored with both fluorimetric and amperometric detectors, the relative responses of which are used as an index of peak purity. Reference values for twelve healthy adults are given.

Nephrotoxicity of phenolic bromobenzene metabolites in the mouse

Bromobenzene, at doses greater than 5.7 mmol/kg, produced renal proximal tubular necrosis and renal functional changes in mice. p-Bromophenol and o-bromophenol were the major urinary phenolic bromobenzene metabolites although m-bromophenol and 4-bromocatechol were also excreted in detectable quantities. With the exception of o-bromophenol, urinary metabolites were excreted primarily as conjugates. 4-Bromocatechol and the 3 bromophenol isomers were nephrotoxicants (measured as increased blood urea nitrogen and decreased accumulation of organic anions by renal cortical slices) but not hepatotoxicants (measured as serum glutamic pyruvate transaminase) in vivo at 0.56 mmol/kg (i.v.). Preincubation of renal cortical slices with each of these bromobenzene metabolites for 90 min resulted in dose-dependent decreases in the accumulation of p-aminohippurate and tetraethylammonium. At 10 mumol/preincubation (2.4 mM), organic ion accumulation was decreased maximally by all bromobenzene metabolites examined while equimolar amounts of bromobenzene were without effect. 4-Bromocatechol was the most potent nephrotoxicant in vitro. Administration of 0.53-2.12 mmol/kg (i.v.) 4-bromocatechol to mice resulted in a dose-dependent decrease in renal function while hepatic function was altered only slightly at the higher doses. The renal cortical necrosis produced by in vivo administration of 4-bromocatechol could not be distinguished histologically from that induced by bromobenzene. These results demonstrate that 4-bromocatechol and the 3 bromophenol isomers are nephrotoxicants that can be generated from bromobenzene in mice.

Differences in urinary monochlorobenzene metabolites between rats and humans

The high performance liquid chromatographic method for the determination of p-chlorobenzene mercapturic acid and 4-chlorocatechol conjugates is described. For determination of urinary mercapturic acid, the benzene extract from urine was injected into a liquid chromatograph and for determination of urinary 4-chlorocatechol conjugates, hydrolysate was dissolved in methanol. The methanol solution containing 4-chlorocatechol was injected into a liquid chromatograph. Differences in urinary excretion of monochlorobenzene between rats and humans were studied. Monochlorobenzene was administered to rats intraperitoneally, and to humans orally or by inhalation. Urinary p-chlorophenylmercapturic acid, and 4-chlorocatechol after hydrolysis of its conjugate, were measured. The amount of total metabolites is proportional to the doses administered to rats, rabbits and mice by intraperitoneal injection. The ratio of urinary mercapturic acid to 4-chlorocatechol is in the order of rats, mice and rabbits by intraperitoneal injection, and rats and human beings by oral administration. The excretion of p-chlorophenylmercapturic acid was markedly less than that of 4-chlorocatechol in humans who received monochlorobenzene orally or by inhalation. The results indicate that the 4-chlorocatechol conjugate is a suitable index of metabolites in the urine of workers exposed to monochlorobenzene.

Quantitative analysis of catechol and 4-methylcatechol in human urine

A method was developed for the quantitative analysis of catechol and 4-methylcatechol in human urine. [U-14C]Catechol was used as in internal standard. Urine was treated with beta-glucuronidase and sulphatase, acidified and extracted with ether. The ether extract was silylated and analysed by glass capillary gas chromatography. Catechol and 4-methylcatechol occurred in urine primarily as conjugates. Levels of catechol and 4-methylcatechol in the urine of nonsmokers on unrestricted diets were 10 +/- 7.3 (mean +/- 1 SD) and 3.4 +/- 2.3 mg/24 hr, respectively. Nonsmokers on uniform restricted diets, in which the intake of plant-derived products was limited, excreted 4.4 +/- 1.2 mg catechol and 8.1 +/- 1.7 mg 4-methylcatechol/24 hr. Smokers on the same restricted diet excreted 6.8 +/- 3.0 mg catechol and 6.1 +/- 2.6 mg 4-methylcatechol/24 hr. These results indicate that diet is a major factor in determining urinary catechol levels and that the contribution of smoking is comparatively small. Catechol and 4-methylcatechol appear to have different dietary precursors.

Identification and synthesis of a methylated catechol metabolite of glutethimide isolated from biological fluids of overdose victims

Urine samples from victims severely intoxicated by glutethimide were hydrolyzed enzymatically. TLC, GLC, and mass spectral analyses revealed a methylated catechol metabolite of the parent drug. Two synthetic pathways are described for the preparation of 2-ethyl-2-(3-methoxy-4-hydroxyphenyl)glutarimide and 2-ethyl-2-(3-hydroxy-4-methoxyphenyl)glutarimde. Comparisons of GLC and mass spectral data to a compound isolated from the body fluids of glutethimide overdose victims conclusively identified a new 3-methoxy-4-hydroxyphenyl metabolite of glutethimide in humans.

Determination of 3-methoxy-4-hydroxyphenylpyruvic acid, 3,4-dihydroxyphenylethylene glycol, and 3,4-dihydroxyphenylmandelic acid in urine by mass fragmentography, with use of deuterium-labeled internal standards

We report the determination of 3-methoxy-4-hydroxyphenylpyruvic acid, 3,4-dihydroxyphenylmandelic acid, and 3,4-dihydroxyphenylethylene glycol in urine, by use of gas chromatography/mass spectrometry in combination with a simple purification method and deuterium-labeled internal standards. Normal excretion values in terms of creatinine, expressed as a function of age, are given, together with results obtained for patients with neuroblastoma, pheochromocytoma, or parkinsonism treated with L-DOPA + peripheral decarboxylase inhibitor, and for a patient receiving dopamine. We were unable to identify 3, 4-dihydroxyphenyllactic acid in urine. The results obtained and their relation to other catecholamine metabolites and catecholamine-precursor metabolites in urine are discussed.

15alpha-Hydroxyoestriol and other polar oestrogens in pregnancy monitoring

Although oestriol measurements are well established for the assessment of 'at risk' pregnancies, there are a number of other oestrogens, excreted during pregnancy, which contain additional hydroxyl groups and might be more sensitive indicators of the condition of mother or fetus. Some of these result from the action of hydroxylases possibly present only in the fetus and others from maternal hydroxylations. We review the evidence for the biosynthesis of these polar oestrogens, summarise methods of measurement, and compare values obtained in normal and pathological pregnancies. There is as yet insufficient evidence to enable their potential value to be confirmed.

Identification of urinary catechol and methylated catechol metabolites of phenytoin in humans, monkeys, and dogs by GLC and GLC-mass spectrometry

A catechol metabolite, 5-(3,4-dihydroxyphenyl)-5-phenylhydantoin, and a methylated catechol metabolite, 5-(3-methoxy-4-hydroxyphenyl)-5-phenylhydantoin, were identified as urinary metabolites in humans, monkeys, and dogs following the administration of phenytoin. These metabolites were separated from each other and from other known metabolites of phenytoin as n-butyl derivatives by GLC and positively identified by combined GLC-mass spectrometry.

Synthesis and characterization of a catechol metabolite of glutethimide (Doriden) in human urine

A metabolite of glutethimide, 2-ethyl-2-(3,4-dihydroxyphenyl)-glutarimide, previously identified in enzymatically hydrolyzed human urine of overdosed victims was prepared synthetically and its chemical and spectral data compared to the proposed material. Results of these comparisons confirm the presence of a catechol metabolite of glutethimide in the urine of patients severely intoxicated by the parent drug.

In vivo phenolic metabolites of N-alkylamphetamines in the rat. Evidence in favor of catechol formation

The major in vivo metabolites of 1-phenyl-2-(n-propylamino)propane (N-n-propylamphetamine) in the rat were phenolic compounds, identified as 1-(4-hydroxyphenyl)-2-(n-propylamino)-propane (metabolite A) and 1-(4-hydroxy-3-methoxyphenyl)-2-(n-propylamino)propane (metabolite B) by gas chromatography-mass spectrometry, and by comparison with authentic synthetic samples of A and B. Metabolites A and B were formed from the substrate in 18.3% and 3.3% yields, respectively, and are excreted in the urine mainly in conjugated form. In vivo metabolism in the rat of the homolog, 1-phenyl-2-(n-butylamino)propane (N-n-butylamphetamine) resulted in the formation of two homologous metabolites in similar yields, which were tentatively identified, from their gas chromatographic and mass spectrometric behav-propane (metabolite A) and 1-(4-hydroxy-3-methoxyphenyl)-2-(n-propylamino)propane (metaboior and by comparison with metabolites A and B, as 2-(n-butylamino)-1-(4-hydroxyphenyl)propane (metabolite C) and 2-(n-butylamino)-1-(4-hydroxy-3-methoxyphenyl)propane (metabolite D). It is suggested that the methylated metabolites B and D were formed from metabolites A and C, respectively, via catecholamine intermediates.

The metabolism of vanillin and isovanillin in the rat

1. The metabolism of vanillin, isovanillin and the corresponding alcohols and acids in rats was investigated using t.l.c., g.l.c. and combined g.l.c.-mass spectrometry. 2. Oral dosage (100 mg/kg) of the aldehyde resulted in urinary excretion of most metabolites within 24 h, mainly as glucuronide and/or sulphate conjugates although the acids formed were also excreted free and as their glycine conjugates. In 48 h 94% of the dose of vanillin was accounted for as follows (%) : vanillin (7), vanillyl alcohol (19), vanillic acid (47), vanilloylglycine (10), catechol (8), 4-methylcatechol (2), guaiacol (0-5) and 4-methylguaiacol (0-6). Similarly, 89% of the dose of isovanillin was accounted for as follows: isovanillin (19), isovanillyl alcohol (10), isovanillic acid (22), vanillic acid (11), isovanilloylglycine (19), catechol(7) and 4-methylcatechol (1). Protocatechuic acid was also formed from both aldehydes. 3. By means of (a) investigation of biliary metabolites, (b) prevention of biliary excretion, (c) suppression of intestinal bacteria with neomycin sulphate and (d) inhibition of intestinal beta-glucuronidase with saccharo-1,4-lactone, it was found that glucuronides of the aldehydes and their respective alcohol and acid derivatives are excreted in the bile and that the conjugates are metabolized by the intestinal bacteria to toluene derivatives and decarboxylated products.