Showing papers in "Xenobiotica in 1986"
TL;DR: In this article, the authors present a detailed analysis of the reactions of glutathione and transferases to different types of enzymes. But they focus on the transferases and not on the enzymes.
Abstract: (1986). Detoxication reactions of glutathione and glutathione transferases. Xenobiotica: Vol. 16, No. 10-11, pp. 957-973.
166 citations
TL;DR: The disposition of the new anti-epileptic agent oxcarbazepine has been studied in two healthy volunteers following an oral 400 mg dose of 14C-labelled drug.
Abstract: 1. The disposition of the new anti-epileptic agent oxcarbazepine (10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine-5-carboxamide) has been studied in two healthy volunteers following an oral 400 mg dose of 14C-labelled drug. The dose was excreted almost completely in the urine (94.6 and 97.1%) within six days. Faecal excretion amounted to 4.3 and 1.9% of the dose in the two subjects.2. In the 0–6 days urine samples the biotransformation products have been isolated and identified. 10,11-Dihydro-10-hydroxycarbamazepine (GP 47 779) and its two diastereoisomeric O-glucuronides were found as main metabolites. Taken together, they accounted for 79% of urinary 14C. Unchanged oxcarbazepine, and its sulphate and glucuronide conjugates were isolated in smaller amounts only (13%). Other minor metabolites were the trans- and cis-isomers of 10,11-dihydro-10,11-dihydroxy-carbamazepine (∼4%), and a phenolic derivative of GP 47 779 (<1%).3. The biotransformation of oxcarbazepine proceeds mainly by reduction to GP 47 779, and s...
141 citations
TL;DR: The enzymic deficiency of the debrisoquine/sparteine-type polymorphism is characterized by comparing kinetic data of subjects in vivo with their microsomal activities in vitro and with reconstituted activities of cytochrome P-450 isozymes purified from human liver.
Abstract: 1. Using the stereospecific metabolism of (+)- and (-)-bufuralol and (+)- and (-)metoprolol as model reactions, we have characterized the enzymic deficiency of the debrisoquinelsparteine-type polymorphism by comparing kinetic data of subjects in wiwo with their microsomal activities in uitro and with reconstituted activities of cytochrome P4SO isozymes purified from human liver. 2. The metabolism of bufuralol in liver microsomes of in viuo phenotyped ‘poor metabolizers’ of debrisoquine and/or sparteine is characterized by a marked increase in K,, a decrease in V,. and a virtual loss of the stereoselectivity of the reaction. These parameters apparently allow the ‘phenotyping’ of microsomes in uitro.
132 citations
TL;DR: It was shown that chronic administration of the sweetener caused the induction of extensive metabolism and the metabolism, which showed wide inter- and intra-individual variability was performed the gut microflora.
Abstract: 1. Three organic acids (saccharin, acesulfame-K and cyclamate) are used or have been used extensively as intense sweeteners. Once absorbed from the gut they are eliminated, largely in the urine, without undergoing metabolism.2. Early studies using radiolabelled saccharin indicated the existence of limited metabolism, but this was not confirmed by later more extensive studies using highly purified compound. Metabolism could not be induced by a variety of pretreatments.3. Following an initial report of the presence of traces of cyclohexylamine in the urines of subjects given cyclamate, it was shown that chronic administration of the sweetener caused the induction of extensive metabolism. The metabolism, which showed wide inter-and intra-individual variability was performed the gut microflora.4. The peptide sweeteners (aspartame and thaumatin) are metabolized to their constitutent amino acids in the gastro intestinal tract, prior to absorption. As such they are incorporated into normal intermediary metabolis...
120 citations
TL;DR: The inhibitory effect of the drug on hepatic MAO-B activity was annulled by pretreatment of rats with PB, but not 3-MC, and augmented by Pretreatment with SKF 525-A, but to a lesser extent by methimazole.
Abstract: 1. Deprenyl, a selective inhibitor of monoamine oxidase type B (MAO-B), was metabolized in rats to methamphetamine (MAP), amphetamine (AP) and their corresponding p-hydroxylated metabolites, p-hydroxy-MAP and p-hydroxy-AP. Recovery of metabolites in 24 h urine was 25% of the dose, and there was no urinary excretion of unchanged deprenyl.2. Deprenyl was converted into MAP, AP and nordeprenyl when incubated in vitro with rat-liver microsomes in the presence of NADPH. This metabolism was inhibited in an atmosphere of N2 and by CO, and by SKF 525-A, but to a lesser extent by methimazole.3. Liver microsomes from phenobarbital (PB)-treated rats, but not 3-methylcholan-threne (3-MC)-treated rats, stimulated the metabolism of deprenyl in vitro to MAP and AP, but not to nordeprenyl. In contrast, microsomes from SKF 525-A-treated rats showed decreased activity in the metabolism of deprenyl to all three metabolites.4. The inhibitory effect of the drug on hepatic MAO-B activity was annulled by pretreatment of rats wi...
104 citations
TL;DR: The metabolism of a 900 mg oral dose of aspirin has been investigated in 129 healthy volunteers and the recovery of gentisic acid was statistically significantly greater in female subjects than in males, whilst the opposite was found for Salicyluric acid and total salicylate.
Abstract: The metabolism of a 900 mg oral dose of aspirin has been investigated in 129 healthy volunteers. For this purpose, the 0-12 h urine was collected and analysed for the following excretion products: salicylic acid, its acyl and phenolic glucuronides, salicyluric acid, its phenolic glucuronide and gentisic acid. The total excretion of salicylate and metabolites was normally distributed within the population group studied, showing a 2.5-fold variation: a mean of 68.1% of the dose was recovered in 12 h. The excretion of salicylic acid was found to be highly variable within the study panel (1.3-31% of dose in 12 h), and was related to both urine volume and pH. Salicyluric acid was the major metabolite in the majority of the volunteers and its excretion was normally distributed amongst the study panel. The elimination of this metabolite ranged from 19.8 to 65% of the dose and was related to the total recovery of salicylate. The excretion of the two salicyl glucuronides was highly variable, ranging from 0.8 to 42% of the dose. The elimination of the glucuronides was inversely related to that of salicyluric acid. Gentisic acid and salicyluric acid phenolic glucuronide were minor metabolites of salicylate, accounting for 1 and 3% of the dose, respectively. The recovery of gentisic acid was statistically significantly greater in female subjects than in males, whilst the opposite was found for salicyluric acid and total salicylate. However, these differences were small in magnitude.
98 citations
TL;DR: The observed interphenotype differences in man and the interstrain variations in an experimental animal model indicate that dextromethorphan O-demethylation is catalysed by the debrisoquine-type cytochrome P-450 isozyme, which indicates thatdextromETHorphan might be used as a safe and innocuous substitute for debrisquine in future routine phenotyping in the field of human pharmacogenetics of oxidative drug metabolism.
Abstract: 1. The metabolism of dextromethorphan has been investigated from the aspect of genetically determined intersubject differences of oxidative drug metabolism in man. For this purpose, the urinary elimination of dextromethorphan and dextrorphan, which is the major O-demethylated metabolite in urine, has been studied in selected drug hydroxylation phenotypes.2. Dextromethorphan O-demethylation co-segregates with polymorphic debrisoquine hydroxylation, whereas no such co-segregation exists with the independently controlled mephenytoin polymorphism in man.3. The urinary dextromethorphan over dextrorphan metabolic ratio was validated for linearity of O-demethylation vs dose administered, and for varying urine collection intervals at different urinary pH values. A 94% repeatability of the dextromethorphan metabolic ratio could be established in extensive and poor metabolizer phenotypes.4. In a preliminary study, different rates of N-, O- and N,O- demethylation of dextromethorphan to yield D-methoxymorphinane, dex...
90 citations
TL;DR: Mechanism by which polycyclic hydrocarbons are activated by metabolism to epoxides of various types have been included, mainly by reference to benzo[a]pyrene, benz[ a]anthracene and chrysene.
Abstract: The metabolism and activation of the polycyclic aromatic hydrocarbons has been reviewed and the original contributions made to this area by Professor E. Boyland have been placed in context. The reactions involved in the formation, via epoxides, of hydroxylated derivatives have been outlined and conjugations with glucuronic and sulphuric acids and with glutathione have been discussed. Examples of secondary hydroxylation reactions have been given and the possible role that phenolic hydroxyl groups may play in activating epoxides considered. Mechanism by which polycyclic hydrocarbons are activated by metabolism to epoxides of various types have been included, mainly by reference to benzo[a]pyrene, benz[a]anthracene and chrysene. The tissue and species specific effects of polycyclic hydrocarbons have been referred to and the tissues that may act as targets in man for the initiation of malignancy by polycyclic hydrocarbons mentioned.
81 citations
TL;DR: The data indicate that the basis of the differences in oxidative capacity between EM and PM subjects is more likely to be due to a variant isozyme with defective catalytic properties than to a decreased amount of the isozyme.
Abstract: 1. The formation of the two major metabolites of the antiarrhythmic and oxytocic drug sparteine (2- and 5-dehydrosparteine) exhibits a genetic polymorphism. Two phenotypes, extensive (EM) and poor metabolizers (PM) are observed in the population. The frequency of the PM phenotype in various populations (Caucasian and Japanese) ranges from 2·3 to 9%2. The metabolism of sparteine is determined by two allelic genes at a single gene locus. PM subjects are homozygous for an autosomal recessive gene.3. The metabolism of sparteine is predominantly under genetic control as treatment with drugs such as antipyrine and rifampicin known to induce oxidative drug metabolism elicited only marginal changes in sparteine metabolism.4. The formation of 2-dehydrosparteine in human liver microsomes from EM and PM subjects showed a more than 40-fold difference in Km between EM and PM subjects. However, Vmax-values were almost identical in both groups. These data indicate that the basis of the differences in oxidative capacity ...
81 citations
TL;DR: Aromatic amines are of general interest in drug metabolism and some are a health hazard, particularly as bladder carcinogens as discussed by the authors, and conditions for the biological ring-and N-oxidation of aniline and its derivatives are reviewed.
Abstract: Aromatic amines are of general interest in drug metabolism and some are a health hazard, particularly as bladder carcinogens. Conditions for the biological ring- and N-oxidation of aniline and its derivatives are reviewed. The metabolism of 2-naphthylamine and aminobiphenyls and the involvement of metabolites of aromatic amines in bladder cancer is discussed.
78 citations
TL;DR: The percentage of radioactivity exhaled as 14CO2 increased with dose in mice, which may indicate dose-dependent formation of dichloroacetic acid and saturation of deactivating mechanisms for reactive intermediates in mice.
Abstract: 1. The absorption, elimination and metabolism of 14C-trichloroethylene (Tri) was studied in adult female Wistar rats and NMRI mice after administration of 200, 20 and 2mg/kgTri.2. Dose-dependent biotransformation of Tri to metabolites was observed in both species. Induction of hepatic mono-oxygenases by phenobarbital or polychlorinated biphenyls resulted in a higher rate of biotransformation after a single oral dose of 200 mg/kg 14C-Tri to rats.3. An increase in radioactivity covalently bound to liver and kidney macromolecules of induced rats as compared to control rats parallels the toxic effects of Tri on these organs after induction of cytochrome P-450.4. The urinary metabolites were analysed by h.p.l.c. In both species, 1,1,1-trichloro compounds (trichloroacetic acid, trichloroethanol and its glucuronide, comprising 88.9±93.5% of the radioactivity excreted in the urine) constituted the main metabolites; in addition, N-(hydroxyacetyl)-aminoethanol (4.1–7.2%), dichloroacetic acid (0.1–2.0%) and oxalic a...
TL;DR: The toxicity of some of the more ubiquitous antimicrobial agents and antioxidants and the role of metabolic data in assessing the 'safety-in-use' of these and other food-additives is reviewed.
Abstract: The use of chemical preservatives serves to ensure the nutritional adequacy, palatability and safety of processed foods and beverages. The toxicity of some of the more ubiquitous antimicrobial agents (sorbic acid, p-hydroxybenzoates, sulphur dioxide) and antioxidants (propyl gallate, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT] is reviewed together with the role of metabolic data in assessing the 'safety-in-use' of these and other food-additives.
TL;DR: The metabolism of (+)-longifolene, (-)-caryophyllene, (+-caryophllene oxide, (--cyclocolorenone, (+)-nootkatone, (-), (-)-elemol, (-)abietic acid and (+)-dehydroabietIC acid was studied in rabbits to determine new metabolites.
Abstract: 1. The metabolism of (+)-longifolene, (-)-caryophyllene, (-)-caryophyllene oxide, (-)-cyclocolorenone, (+)-nootkatone, (-)-elemol, (-)-abietic acid and (+)-dehydro-abietic acid was studied in rabbits.2. Each of these sesquiterpenoids was converted to primary, secondary or tertiary alcohols, among which the primary alcohol was predominant.3. A vinylic methyl group and an exomethylene group were easily hydroxylated and converted to a glycol via an epoxide in many cases.4. Eight new metabolites were determined by chemical and spectroscopic methods.
TL;DR: Nine forms of cytochrome P-450 have been purified to electrophoretic homogeneity from human-liver microsomes, including the enzymes involved in debrisoquine 4-hydroxylation, phenacetin O-deethylation and mephenytoin 4-Hydroxylase, three reactions which are characterized by genetic polymorphism in humans.
Abstract: Nine forms of cytochrome P-450 have been purified to electrophoretic homogeneity from human-liver microsomes. These include the enzymes involved in debrisoquine 4-hydroxylation, phenacetin O-deethylation and mephenytoin 4-hydroxylation, three reactions which are characterized by genetic polymorphism in humans. Evidence for the involvement of the above enzymes comes from reconstituted immunochemical inhibition studies with human-liver microsomes. These and other lines of evidence are consonant with the view that different forms of cytochrome P-450 are involved in the three reactions. The debrisoquine 4-hydroxylase has been studied most extensively in terms of its substrate specificity. In addition, an analogous rat enzyme shows some homology and serves as a useful model. The use of antibodies raised to the rat-liver enzyme in immuno-inhibition studies with human-liver microsomes provides a means of determining the extent to which this enzyme participates in other reactions. Translation of rat-liver mRNA in vitro yields the intact debrisoquine 4-hydroxylase; studies with human mRNA suggest a lower frequency than in rats. The basis for impaired catalytic activity in phenotypically poor human metabolizers appears to be an altered enzyme in all three cases, as opposed to a decreased level of a single enzyme. Using antibody screening of fusion proteins expressed in a cDNA library, it has been possible to isolate cDNA probes for all three of these cytochromes P-450 for use in screening individuals and ultimately determining the basis of these polymorphisms.
TL;DR: If standard doses of some beta-blockers are used in poor metabolizers, these patients may be susceptible to concentration-related adverse reactions and they may also require lower and less frequent dosing for control of angina pectoris.
Abstract: The contribution of debrisoquine polymorphism to the metabolism and action of beta-adrenoceptor antagonists (beta-blockers) varies widely between drugs. Oxidation phenotype is a major determinant of the metabolism, pharmacokinetics and some of the pharmacological actions of metoprolol, bufuralol and timolol. The poor metabolizer phenotype is associated with an increased area under the plasma drug concentration vs. time curve, a prolongation of elimination half-life and a more intense and sustained beta-blockade. The stereoselective metabolism of metoprolol also displays phenotypic differences, which should be taken into account when interpreting plasma concentration vs. response relationships. Studies in vivo and in vitro have identified some of the metabolic pathways which are subject to this defect, namely the alpha-hydroxylation and the O-demethylation of metoprolol and the 1'-hydroxylation of bufuralol. In contrast, the pharmacokinetics and pharmacodynamics of propranolol, which is also extensively oxidized, are not related to debrisoquine polymorphism, although 4'-hydroxypropranolol formation is deficient in the poor metabolizer phenotype. The disposition of atenolol, which is almost completely eliminated unchanged by renal and faecal excretion, is independent of oxidation phenotype. If standard doses of some beta-blockers are used in poor metabolizers, these patients may be susceptible to concentration-related adverse reactions and they may also require lower and less frequent dosing for control of angina pectoris.
TL;DR: The four substrates studied were shown to be less active in humans than the male rat, which is the most commonly used model, however, other animal species, such as the female Sprague-Dawley rat and the pig, are much more similar to man.
Abstract: 1. The cytochrome P-450 content found in human livers obtained post mortem was between 0.21–0.42 nmol/mg protein.2. The kinetic parameters of the mono-oxygenase activities—Km and Vmax—were determined in liver microsomes for N-demethylation (aminopyrine, benzphetamine, ethylmorphine), O-demethylation (4-nitroanisole), O-deethylation (7-ethoxycoumarin) and hydroxylation (benzo[a]pyrene), in an attempt to establish an inter-species comparison between man and the six animal species studied.3. The four substrates studied (aminopyrine, benzphetamine, ethylmorphine, benzo[a]pyrene) were shown to be less active in humans than the male rat, which is the most commonly used model. However, other animal species, such as the female Sprague-Dawley rat and the pig, are much more similar to man.4. From a procedural point of view, the optimal substrate concentrations vary from one experimental species to another. Due to the apparent Km observed, for example, the activities of the guinea-pig require a higher substrate conc...
TL;DR: An additional metabolic route, which differs from the expected severance of the (+)-catechin-phloroglucinol bond and well-documented total heterocyclic ring degradation of flavanoids, is proposed.
Abstract: The metabolism of 2,3-trans-3,4-trans-3,5,7,3',4'-pentahydroxy-4-(2,4,6-trihydrox yphenyl)-flavan and 2,3-trans-3,4-trans-3,5,7,3',4',-pentahydroxy-4-(2,3-trans-3,5,7,3 ', 4'-pentahydroxyflavanyl-[8])-flavan in vitro by rat-caecal microflora was investigated. Metabolites were extracted and enriched by column chromatography and preparative h.p.l.c., while structural determination was carried out using comparative g.l.c.-mass spectrometry and p.m.r. spectrometry. The metabolites identified were derivatives of benzoic acid, phenylacetic acid, phenylpropionic acid and phenyllactic acid in addition to phloroglucinol, delta-(3-hydroxyphenyl)-gamma-valerolactone and 1-(3-hydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)-propan-2-ol. An additional metabolic route, which differs from the expected severance of the (+)-catechin-phloroglucinol bond and well-documented total heterocyclic ring degradation of flavanoids, is proposed.
TL;DR: The distribution of radioactivity after injection of 3,3',4,4'-tetrachloro[14C]biphenyl (14C-TCB) in pregnant mice was determined by autoradiography and computer-assisted densitometric analysis and radioactivity was reversibly bound to fetal tissues.
Abstract: 1. The distribution of radioactivity after injection of 3,3′,4,4′-tetrachloro[14C]biphenyl (14C-TCB) in pregnant mice was determined by autoradiography and computer-assisted densitometric analysis. TCB metabolites in fetal tissue were analysed by g.l.c. and g.l.c.-mass spectrometry and compared to the synthesized reference compounds 2-, 5- and 6-methoxy-3,3′,4,4′-tetrachlorobiphenyl.2. The concentration of radioactivity was high in the uterine fluid, and in the fetuses in late gestation. Fetal radioactivity decreased after pretreatment with a high dose of unlabelled TCB. Radioactivity was reversibly bound to fetal tissues.3. A phenolic metabolite, 3,3′,4,4′-tetrachloro-2-biphenylol, and a methylsulphonyl-tetrachlorobiphenyl were found in fetuses in late gestation. No unmetabolized TCB was detected in the fetuses.
TL;DR: None of the laboratory animals, including the marmoset, provided an approximation of the enzyme profile associated with human faecal flora, indicating that it may be invalid to extrapolate the results of bacterial metabolic studies between closely related species, or from animals to man.
Abstract: A comparison was made in six species of animal (rat, mouse, hamster, guinea-pig, marmoset and man) of five enzyme activities associated with the hindgut microflora. Marked differences were found in the caecal activities of azoreductase, beta-glucosidase, beta-glucuronidase, nitrate reductase and nitroreductase in the four rodents, with no one species exhibiting consistently higher or lower enzyme activity. None of the laboratory animals, including the marmoset, provided an approximation of the enzyme profile associated with human faecal flora. The results indicate that it may be invalid to extrapolate the results of bacterial metabolic studies between closely related species, or from animals to man.
TL;DR: Treatment of eggs with 3,3',4,4'-tetrachlorobiphenyl resulted in increased metabolism of both substrates by five-day-old chick embryo livers, and the increase in aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity was 14-fold while that of 7-ethoxycoumarin O-deethylase was approximately double.
Abstract: Basal activities of 7-ethoxycoumarin O-deethylase and aryl hydrocarbon (benzo[a]pyrene) hydroxylase were determined in whole-liver homogenates from chick embryos of different ages, from newly hatched chicks and from chicks a few days old. The enzyme activities increased substantially in chick embryo livers between days five and 10, remained at a fairly constant level until day 19, and reached a peak in activity one day after hatching. The optimal pH value was lower than 7.0 for both enzyme activities. The total increase in activity from day five to one day after hatching was about 300-fold for 7-ethoxycoumarin O-deethylase and about 75-fold for aryl hydrocarbon (benzo[a]pyrene) hydroxylase. Treatment of eggs with 3,3',4,4'-tetrachlorobiphenyl resulted in increased metabolism of both substrates by five-day-old chick embryo livers. The increase in aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity was 14-fold while that of 7-ethoxycoumarin O-deethylase was approximately double.
TL;DR: The inability of menadione to oxidize glutathione in selenium-deficient mitochondria indicates that the metabolism of the superoxide dismutation product, H2O2, by glutathION peroxidase was probably responsible for the glutathion oxidation in seenium-replete mitochondria.
Abstract: 1. Incubation of rat-liver mitochondria with menadione in the presence of succinate and rotenone resulted in rapid glutathione and NAD(P)H oxidation followed by Ca2+ release and mitochondrial swelling.2. Ca2+ release, NAD(P)H oxidation and mitochondrial swelling, were also observed in mitochondria from selenium-deficient rats. Glutathione was only slowly oxidized, suggesting that glutathione oxidation, and subsequent NAD(P)H oxidation via the glutathione peroxidase-glutathione reductase system were not required for Ca2+ release by menadione.3. Isocitrate prevented and reversed Ca2+ release dose-dependently but dicoumarol had no effect indicating that NADH-ubiquinone oxidoreductase and not DT-diaphorase was responsible for NAD(P)H oxidation.4. Superoxide anion radical was formed by cyanide-resistant respiration, suggesting that menadione undergoes a one-electron reduction to an autoxidizable semiquinone radical by NADH-ubiquinone oxidoreductase.5. The inability of menadione to oxidize glutathione in seleni...
TL;DR: Four human volunteers given a 30 mg oral dose of nicardipine hydrochloride containing 40 microCi of the 14C-labelled material achieved peak plasma levels of compound-related radioactivity within one hour of dosing indicating rapid first-pass metabolism.
Abstract: Four human volunteers given a 30 mg oral dose of nicardipine hydrochloride containing 40 microCi of the 14C-labelled material achieved peak plasma levels of compound-related radioactivity within one hour of dosing. Parent compound comprised only a minor fraction of the circulating radioactivity indicating rapid first-pass metabolism. Plasma radioactivity declined to background levels within 96 h and was excreted both in the urine and faeces. Urinary excretion was the favoured route comprising about 60% of the dosed radioactivity. Mean total recovered radioactivity amounted to 94.8%. Both 1,4-dihydropyridine and pyridine metabolites of nicardipine hydrochloride were excreted in the urine. The major urinary metabolites, comprising some 36% of the radioactivity excreted in the 0-8 h post-dose period, were the glucuronide conjugates of +/- 2-hydroxyethyl methyl-1,4-dihydro-2,6-dimethyl-4(m-nitrophenyl)-3,5-pyridine dicarboxylate and its pyridine from 2-hydroxyethyl methyl-2,6-dimethyl-4-(m-nitrophenyl)-3,5-pyridine dicarboxylate.
TL;DR: Microbial transformation of etodolac was employed to biosynthesize sufficient amounts of two urinary metabolites to facilitate structure elucidation and false positive tests for bilirubin in urine of patients treated with etdolac were found to be due to the two phenolic metabolites.
Abstract: 1. Four human subjects were given a capsule containing 200 mg of 14C-etodolac. At the peak (two hours after dosing), most of the radioactivity in serum was due to etodolac; subsequently, metabolites gradually appeared. The elimination half-life of etodolac from serum averaged six hours. Etodolac was >99% bound to human serum proteins.2. An average of 73% of the dose was excreted in the urine and 14% in faeces within seven days, with 61% appearing in the urine during the first 24 h.3. Microbial transformation of etodolac was employed to biosynthesize sufficient amounts of two urinary metabolites to facilitate structure elucidation.4. Five metabolites, representing 65% of the radioactivity in urine collected 0–24 h after dosing (61% of the dose was excreted in urine within 24 h), were isolated and characterized by t.l.c., g.c., h.p.l.c., n.m.r (1H and 13C) and m.s. Most of the identified urinary components were conjugates of etodolac and three hydroxylated metabolites (6-hydroxyetodolac, 7-hydroxyetodolac a...
TL;DR: Three stereoisomeric forms of perhexiline all had the same times to peak plasma concn of the unchanged drug or of the cis-metabolite, and all three forms had a similar plasma elimination half-life for unchanged per hexiline.
Abstract: Blood plasma and urine excretion pharmacokinetics of the (+) and (-) enantiomers of perhexiline have been determined in oral single-dose studies in eight human volunteers, and compared with the pharmacokinetics of the racemate drug in the same subjects. The (-) enantiomer is more rapidly metabolized and eliminated, and is stereoselectively hydroxylated to the cis-monohydroxy-perhexiline. The peak plasma concn of unchanged perhexiline is greater, while that of the cis-monohydroxy-perhexiline metabolite is lower, after administration of the (+) enantiomer than after the (-) enantiomer or the racemate. Similarly, the AUC values for unchanged perhexiline and for the trans-monohydroxy-perhexiline metabolite are greatest and the AUC value for the cis-monohydroxy-perhexiline metabolite is lowest for the (+) enantiomer. The three stereoisomeric forms of perhexiline all had the same times to peak plasma concn of the unchanged drug or of the cis-metabolite, and all three forms had a similar plasma elimination half-life for unchanged perhexiline. Metabolism of racemic perhexiline to the cis-monohydroxy metabolite is the major mechanism of elimination of the drug in man and has been shown to be polymorphic in human populations. The (-) enantiomer which shows stereoselective metabolism to the cis metabolite might therefore show a greater polymorphic effect. Studies with rat-liver microsomal preparations in vitro showed that, in contrast to the human studies in vivo, hydroxylation of perhexiline yields mostly the trans-monohydroxy metabolite. The DA strain of rats exhibited slower rates of hydroxylation in vitro than Wistar or Lewis strains of rats.
TL;DR: Biphasic kinetics are observed for the O-deethylation of ethoxycoumarin in intact isolated rat hepatocytes and addition of the substrate in dimethylformamide or omitting bovine serum albumin from the medium cause important changes in these kinetic parameters.
Abstract: 1. In the determination of 7-ethoxycoumarin O-deethylase activity in intact isolated rat hepatocytes various factors influence the assay, including: (i) the decay of 7-ethoxycoumarin fluorescence which is temperature and pH dependent; (ii) the measured fluorescence which has to be adjusted for the inner filter effect; (iii) glucose addition to the medium which influences the activity, (iv) all organic solvents which inhibit the enzymic activity, with dimethylformamide provoking the smallest effect (partial competitive inhibition); (v) the enzymic reaction which is inhibited by the product of reaction; and (vi) the presence of bovine serum albumin in the medium which affects the enzymic activity.2. Biphasic kinetics are observed for the O-deethylation of ethoxycoumarin in intact isolated rat hepatocytes. For the high-affinity component, Km and Vmax values are 5 μM and 43 pmol/min 106 cells and for the low-affinity component are 414 μM and 915 pmol/min 106 cells.3. Addition of the substrate in dimethylforma...
TL;DR: The metabolic fate of 1-phenyl-2-(N-methyl-N-benzylamino)propane (benzphetamine) and 1- phenyl- 2-(N)-methyl- N-furfurylamino (furfenorex) in healthy volunteers has been investigated and metabolites with traces of the unchanged drug were detected in human urine after oral administration of benzphetamine.
Abstract: 1. The metabolic fate of 1-phenyl-2-(N-methyl-N-benzylamino)propane (benzphetamine) and 1-phenyl-2-(N-methyl-N-furfurylamino)propane (furfenorex) in healthy volunteers has been investigated.2. Nine metabolites with traces of the unchanged drug were detected in human urine after oral administration of benzphetamine, and five metabolites were found following administration of furfenorex. The major metabolites were 1-(p-hydroxyphenyl)-2-(N-benzylamino)propane for benzphetamine and 1-phenyl-2-(N-methyl-N-γ-valerolactonylamino)propane for furfenorex. In both cases, methamphetamine, amphetamine and their hydroxylated metabolites were also excreted as minor metabolites.3. Identified metabolites excreted in three days after administration of benzphetamine accounted for 30–44% of the dose and those excreted after administration of furfenorex, 31–46%.
TL;DR: The sulphur-containing heterocyclic aromatic compounds dibenzothiophene, thioxanthone and thiochromanone were oxidized at sulphur by C. elegans, and the PAHs were not metabolized by any of the fungi studied.
Abstract: Incubations of several polycyclic aromatic hydrocarbons (PAHs) and heteroaromatic compounds with a series of common micro-organisms have been performed. The PAHs were not metabolized by any of the fungi studied. The sulphur-containing heterocyclic aromatic compounds dibenzothiophene, thioxanthone and thiochromanone were oxidized at sulphur by C. elegans. Other fungi are capable of oxidation at the sulphur atom of dibenzothiophene and thioxanthone. C-1 and C-3 methyl substituted thioxanthones are hydroxylated at the methyl group by C. elegans.
TL;DR: Glucuronyltransferase activity was measured in the homogenate and in the nuclear, mitochondrial and microsomal fractions of liver and intestinal mucosa from man and rats and results were obtained in the rat.
Abstract: 1. Glucuronyltransferase (GT) activity was measured in the homogenate and in the nuclear, mitochondrial and microsomal fractions of liver and intestinal mucosa from man and rats.2. In man the average rate of morphine glucuronidation was 0.58 and 0.27 nmol/min per mg protein in the homogenates of the liver and intestinal mucosa, respectively.3. GT was evenly distributed in the different fractions of liver, whereas the major part of the activity in the intestinal mucosa was associated with the nuclear fraction. There was a larger difference between the GT activities in the microsomal fractions of the liver and intestine (0.68 and 0.06 nmol/min per mg, respectively), than between the homogenates of these organs.4. Similar results were obtained in the rat. GT activity in homogenates of the liver and intestine differed only three-fold whereas there was an 18-fold difference between the microsomal GT activities in these organs.
TL;DR: Despite pronounced interphenotypic differences in encainide's disposition and pharmacokinetics, the polymorphic oxidative metabolism appears to have limited consequences for the drug's clinical efficacy.
Abstract: The 8-h urinary metabolic profiles of encainide and its oxidized metabolites, O-desmethyl- (ODE), 3-methoxy-O-desmethyl- (MODE), N-desmethyl- (NDE) and N, O-didesmethyl- (DDE) encainide were studied in a group of 112 normal Caucasians. Nine of these subjects (8%) were defective in their ability to 4-hydroxylate debrisoquine. The cumulative frequency distribution of the 8-h recovery ratio of encainide/ODE indicated two distinct populations in complete concordance with the debrisoquine phenotyping. The subjects with an 'extensive metabolizer' (EM) phenotype had a ratio from 0.003 to 0.9 whereas the PM group had values from 7.4 to 48. In addition, no MODE was detected in the urine from 'poor metabolizers' (PM). The oxidative metabolism of encainide, specifically the O-demethylation pathway, is, therefore, polymorphically distributed and controlled by the same genetic factor(s) that determine the 4-hydroxylation of debrisoquine. In EM subjects, ODE and MODE are the major metabolites in plasma and their concentrations are much greater than those of unchanged drug. As ODE is a more potent antiarrhythmic agent than encainide and MODE is at least equipotent, these metabolites significantly contribute to the overall antiarrhythmic effect in EM patients. The low plasma concentrations of ODE and MODE in PM subjects would be expected to result in inefficacious therapy when usual doses of encainide are administered. However, in such individuals, chronic oral therapy results in accumulation of unmetabolized encainide to far higher levels than in EM subjects. As encainide itself has intrinsic antiarrhythmic activity at these concentrations, this generally results in the desired clinical response. Despite pronounced interphenotypic differences in encainide's disposition and pharmacokinetics, the polymorphic oxidative metabolism appears to have limited consequences for the drug's clinical efficacy.