O-glucuronide Conjugates Research Articles

Resveratrol glucuronidation in vitro: potential implications of inhibition by probenecid.

Resveratrol is a naturally occurring antioxidant with therapeutic potential in prevention and treatment of neoplastic disease and other human disorders. However, net clearance of resveratrol in humans is very high, mainly due to glucuronide conjugation. This leads to extensive presystemic extraction and low plasma concentrations after oral dosage. The present study evaluated the effect of probenecid, an inhibitor of glucuronide conjugation, on resveratrol metabolism invitro. Biotransformation of resveratrol to its 3-O-glucuronide and 4'-O-glucuronide conjugates was studied invitro using human liver microsomal preparations. The mechanism and inhibitory potency of probenecid were evaluated based on a mixed competitive-noncompetitive inhibition model. Probenecid inhibition of resveratrol 3-O-glucuronidation was predominantly noncompetitive, with an inhibition constant (Ki ) averaging 3.1mm. The ratio of invivo maximum concentration of probenecid [I] during usual clinical use to the invitro Ki value ([I]/Ki ) exceeds the boundary value of 0.1, used by regulatory agencies to identify the possibility of clinical drug interactions. This finding, together with the known property of probenecid as an inhibitor of glucuronide conjugation in humans, suggests that probenecid could serve as a pharmacokinetic boosting agent to enhance systemic exposure to resveratrol in humans.

Toxicological evaluation of two novel bitter modifying flavour compounds: 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)imidazolidine-2,4-dione and 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)-5,5-dimethylimidazolidine-2,4-dione.

A toxicological evaluation of two novel bitter modifying flavour compounds, 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)imidazolidine-2,4-dione (S6821, CAS 1119831-25-2) and 3-(1-((3,5-dimethylisoxazol-4-yl)methyl)-1H-pyrazol-4-yl)-1-(3-hydroxybenzyl)-5,5-dimethylimidazolidine-2,4-dione (S7958, CAS 1217341-48-4), were completed for the purpose of assessing their safety for use in food and beverage applications. S6821 undergoes oxidative metabolism in vitro, and in rat pharmacokinetic studies both S6821 and S7958 are rapidly converted to the corresponding O-sulfate and O-glucuronide conjugates. S6821 was not found to be mutagenic or clastogenic in vitro, and did not induce micronuclei in bone marrow polychromatic erythrocytes in vivo. S7958, a close structural analog of S6821, was also found to be non-mutagenic in vitro. In short term and subchronic oral toxicity studies in rats, the no-observed-adverse-effect-level (NOAEL) for both S7958 and S6821 was 100 mg/kg bw/day (highest dose tested) when administered as a food ad-mix for either 28 or 90 consecutive days, respectively. Furthermore, S6821 demonstrated a lack of maternal toxicity, as well as adverse effects on fetal morphology at the highest dose tested, providing a NOAEL of 1000 mg/kg bw/day for both maternal toxicity and embryo/fetal development when administered orally during gestation to pregnant rats.

Design, Synthesis, and Pharmacological Evaluation of 5,6-Disubstituted Pyridin-2(1H)-one Derivatives as Phosphodiesterase 10A (PDE10A) Antagonists.

We report the design and synthesis of novel 5,6-diarylated pyridin-2(1H)-one derivatives as pharmacophoric PDE10A inhibitors. This highly potent molecular scaffold was developed from an inactive diarylpyridine-2-amine derivative 3b by extensive and systematic analogue synthesis and SAR analysis. Further optimization of the scaffold resulted in identification of pyridin-2(1H)-one 18b as a lead compound with good potency (IC50 = 1.6 nM) and selectivity (>6000-fold) over other related PDEs but with a poor pharmacokinetic profile. Careful metabolite profiling of 18b revealed that poor systemic exposure in rats (Cmax = 44 ng/mL; AUC0-t = 359 ng · h/mL) at 10 mg/kg was due to the formation of O-glucuronide conjugate by phase 2 metabolism. The structure of the glucuronide metabolite was confirmed by retention time and LC-MS/MS fragmentation matching with the synthetic glucuronide 26. The problem of low exposure of 18b was effectively addressed by its conversion to an acetate prodrug 25b, which upon oral dosing resulted in an improved pharmacokinetic profile (Cmax = 359 ng.h/mL; AUC0-t = 2436 ng.h/mL) and a desirable brain to plasma ratio of 1.2. The prodrug 25b showed good efficacy in selected rodent models of psychosis.

In vivo metabolite identification of bakuchiol in rats by UPLC/ESI–PDA–QTOF–MS

Psoralea corylifolia L. is a traditional Chinese medicine for the treatment of various skin diseases such as psoriasis, vitiligo and chronic graft-versus-host. Bakuchiol, isolated from the seeds of P. corylifolia L., is one of the most important active compounds. To study the metabolic fate of bakuchiol in rats, an ultra performance liquid chromatography/electrospray ionization–photo diode array–quadrupole time of flight–mass spectrometry (UPLC/ESI–PDA–QTOF–MS) combined with MetaboLynx XS software was used, peak area–time curves of major metabolites in plasma from bakuchiol were determined. A total of 11 metabolites were identified after a single oral administration of bakuchiol, including 6 in plasma, 10 in bile, 8 in urine and 2 in feces, the metabolic transformation pathways of bakuchiol in rats included oxidation, hydroxylation, methylation, O-glucuronide conjugation and O-sulfate conjugation. In conclusion, this study expands our knowledge about the metabolism of bakuchiol which will be conducive to reveal its in vivo pharmacological and toxicological material basis, in addition, UPLC/ESI–PDA–QTOF–MS coupled with MetaboLynx XS software can be adopted as a useful tool for quick detection and identification of metabolites from medicine in vivo.

UPLC-Q-TOF/MS-based screening and identification of two major bioactive components and their metabolites in normal and CKD rat plasma, urine and feces after oral administration of Rehmannia glutinosa Libosch extract.

Rehmannia glutinosa is a widely used traditional Chinese medicine (TCM) in clinical practice to tackle chronic kidney disease for thousands of years. However, the in vivo metabolism of its two major bioactive components (catalpol and acteoside) remains unknown. In this paper, a highly sensitive, rapid and robust ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) with MetaboLynx™ software combined with mass defect filtering (MDF) method was established. This validated analysis method was successfully applied to investigate the in vivo metabolic profiles of R. glutinosa extract in normal and chronic kidney disease (CKD) rats. The results showed that a total of 17 metabolites of two parent compounds in normal rats in vivo were tentatively detected and identified according to the characteristics of their protonated ions and relevant literature. While 11 of the metabolites were observed in the CKD rat samples. These metabolites suggested that catalpol was firstly deglycosylated to its aglycone and subsequently to two main metabolites (M1 and M4) by conjugation and hydrogenation respectively and acteoside was mainly metabolized by O-glucuronide conjugation and O-sulphate conjugation. In conclusion, this study showed an insight into the metabolism of R. glutinosa extract in vivo and the proposed metabolic pathways of bioactive components might play a key role in further pharmacokinetic experiments evaluations.

Pharmacokinetics, metabolism and excretion of [14C]-lanicemine (AZD6765), a novel low-trapping N-methyl-d-aspartic acid receptor channel blocker, in healthy subjects

1. (1S)-1-phenyl-2-(pyridin-2-yl)ethanamine (lanicemine; AZD6765) is a low-trapping N-methyl-d-aspartate (NMDA) channel blocker that has been studied as an adjunctive treatment in major depressive disorder. The metabolism and disposition of lanicemine was determined in six healthy male subjects after a single intravenous infusion dose of 150 mg [14C]-lanicemine.2. Blood, urine and feces were collected from all subjects. The ratios of Cmax and AUC(0–∞) of lanicemine to plasma total radioactivity were 84 and 66%, respectively, indicating that lanicemine was the major circulating component with T1/2 at 16 h. The plasma clearance of lanicemine was 8.3 L/h, revealing that lanicemine is a low-clearance compound. The mean recovery of radioactivity from urine was 93.8% of radioactive dose.3. In urine samples, 10 metabolites of lanicemine were identified. Among which, an O-glucuronide conjugate (M1) was the most abundant metabolite (∼11% of the dose in excreta). In plasma, the circulatory metabolites were identified as a para-hydroxylated metabolite (M1), an O-glucuronide (M2), an N-carbamoyl glucuronide (M3) and an N-acetylated metabolite (M6). The average amount of each of metabolite was less than 4% of total radioactivity detected in plasma or urine.4. In conclusion, lanicemine is a low-clearance compound. The unchanged drug and metabolites are predominantly eliminated via urinary excretion.

Metabolism and Excretion of Canagliflozin in Mice, Rats, Dogs, and Humans

Canagliflozin is an oral antihyperglycemic agent used for the treatment of type 2 diabetes mellitus. It blocks the reabsorption of glucose in the proximal renal tubule by inhibiting the sodium-glucose cotransporter 2. This article describes the in vivo biotransformation and disposition of canagliflozin after a single oral dose of [(14)C]canagliflozin to intact and bile duct-cannulated (BDC) mice and rats and to intact dogs and humans. Fecal excretion was the primary route of elimination of drug-derived radioactivity in both animals and humans. In BDC mice and rats, most radioactivity was excreted in bile. The extent of radioactivity excreted in urine as a percentage of the administered [(14)C]canagliflozin dose was 1.2%-7.6% in animals and approximately 33% in humans. The primary pathways contributing to the metabolic clearance of canagliflozin were oxidation in animals and direct glucuronidation of canagliflozin in humans. Unchanged canagliflozin was the major component in systemic circulation in all species. In human plasma, two pharmacologically inactive O-glucuronide conjugates of canagliflozin, M5 and M7, represented 19% and 14% of total drug-related exposure and were considered major human metabolites. Plasma concentrations of M5 and M7 in mice and rats from repeated dose safety studies were lower than those in humans given canagliflozin at the maximum recommended dose of 300 mg. However, biliary metabolite profiling in rodents indicated that mouse and rat livers had significant exposure to M5 and M7. Pharmacologic inactivity and high water solubility of M5 and M7 support glucuronidation of canagliflozin as a safe detoxification pathway.

Metabolites identification of harmane in vitro/in vivo in rats by ultra-performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Harmane, a β-carboline alkaloid with a wide spectrum of pharmacological activities, is naturally present in the human diet, in numerous foodstuffs and in hallucinogenic plants such as Peganum harmala, Banisteriopsis caapi and Tribulus terrestris. However, the precise metabolic fate of harmane remains unknown. In order to know whether harmane is extensively metabolized, a rapid and sensitive method using ultra-performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC/ESI-QTOF-MS) was used to analyze the metabolic profile of harmane in vitro and in vivo in rats. A total of 21 metabolites were identified from the rat liver microsomes and rat liver S9 (9), rat urine (11), feces (16), bile (16), and plasma (10) after a single oral administration of harmane using MetaboLynx™ and MassFragment ™ software tools. It indicated that the biliary and faecal clearance were the major excretion routes for harmane as well as its metabolites. The specific CLogP values combined with different acidic and alkaline mobile phase were helpful and useful for distinguishing N-oxidation and monohydroxylation metabolites. The metabolic transformation pathways of harmane included monohydroxylation, dihydroxylation, N-oxidation, O-glucuronide conjugation, O-sulphate conjugation, and glutathione conjugation. In conclusion, this study showed an insight into the metabolism of harmane.

A quantum chemical study on the antioxidant activity of bioactive polyphenols from peanut ( Arachis hypogaea) and the major metabolites of trans-resveratrol

Trans-resveratrol, a polyphenolic compound, which is found in grape and red wine, exhibits inhibiting effect against tumour growth and shows strong antioxidant activity. In the human liver cells and intestinal epithelial ones this compound is converted to the following bioavailable metabolites: O-sulphates, O-disulphates, O-trisulphate and O-glucuronide conjugates. To explain the equilibrium structure–antioxidant radical scavenging capacity relationships of these metabolites and the major peanut polyphenols (arachidin-1, arachidin-2, arachidin-3 and trans-isopentadienylresveratrol), the accurate quantum-chemical calculations in the gas phase and water medium with the use of density functional theory have been performed for the first time. The hydrogen atom transfer mechanism for free radicals scavenging is found more preferable than the single-electron transfer mechanism in the media studied. The importance of 4′-OH group as a hydrogen atom donor is indicated. The metabolites and peanut polyphenols are found to be more active donors of hydrogen atoms in the gas phase than in water medium, in which the compounds studied are more susceptible to electron donation than in the gas phase. The calculations have shown that the O-sulphates, O-disulphates and O-trisulphate studied are more efficient hydrogen donors than trans-resveratrol. According to the phenolic O–H bond dissociation enthalpies of the peanut stilbenoids were found to be efficient antioxidants. It was found that arachidin-1 is the most effective antioxidant among the compounds studied. The metabolites of trans-resveratrol are shown to have a similar ability to scavenge free radicals as the parent compound and can synergistically reduce oxidative stress in human cells. This study provides rational approach for investigation of the antioxidant activity of other bioactive trans-resveratrol derivatives.

The fate of 4-hydroxycarbazole metabolite: metabolism and carcinogenicity assessment of a β-adrenergic receptor modulator containing carbazole structure

LY377604 has a potential to form 4-hydroxycarbazole, which was reported in the literature as a mutagen. This safety concern led to our investigation of the metabolism and carcinogenicity of LY377604.In in vitro studies with LY377604, 4-hydroxycarbazole was detected in the presence of liver microsomes prepared from different species. When incubated with liver slices, only the conjugate of 4-hydroxycarbazole was detected.Subsequent in vivo radio-labelled studies were conducted to characterise the formation of 4-hydroxycarbazole from LY377604. Free 4-hydroxycarbazole was not detected in vivo, but the O-glucuronide conjugate was identified as a minor metabolite in urine samples, representing 0.2% and 0.9% of the radioactive dose in rats and monkeys. The low level of circulating 4-hydroxycarbazole glucuronide conjugate was also detected in plasma.LY377604 was negative in all genetic toxicology assays and was not associated with tumour induction in a 6-month carcinogenicity study using RasH2+/− mouse model. The exposure to free 4-hydroxycarbazole was not measurable after one dose and was about 0.1%−0.2% of the parent exposure at the end of the 6-month study.These data suggested that 4-hydroxycarbazole was formed as a minor metabolite in vivo, but it was primarily conjugated and excreted in urine as the glucuronide conjugate. The absence of tumours in the carcinogenicity study combined with the exposure data suggested that the low level of free 4-hydroxycarbazole did not represent a carcinogenic risk.

Metabolism and Disposition of [14C]BMS-690514 after Oral Administration to Rats, Rabbits, and Dogs

(3R,4R)-4-Amino-1-((4-((3-methoxyphenyl)amino)pyrrolo[2,1-f] [1,2,4]triazin-5-yl)methyl)-3-piperidinol (BMS-690514) is a potent inhibitor of human epidermal growth factor receptors 1, 2, and 4 and vascular endothelial growth factor receptors 1 through 3. BMS-690514 is an oral oncologic agent currently being developed for the treatment of patients with advanced non-small cell lung cancer and breast cancer. In this investigation, a series of studies was conducted to determine the biotransformation of [(14)C]BMS-690514 after oral administration to rats, rabbits, and dogs. After administration of a single oral dose of [(14)C]BMS-690514 to rats and dogs, the majority of the radioactive dose (61-71%) was recovered in the feces, whereas 18 to 20% was eliminated in urine. In bile duct-cannulated rats, 83 and 17% of the administered radioactivity was recovered in the bile and urine, respectively, suggesting that biliary secretion was a major route for the elimination of BMS-690514-derived radioactivity in rats. The parent compound underwent extensive metabolism in both species, with <12% of the administered radioactivity recovered as BMS-690514 in the excreta samples. Metabolite profiles in plasma were qualitatively similar in rats, rabbits, and dogs. Unchanged BMS-690514 was a prominent drug-related component in the plasma profiles from all the species. However, multiple metabolites contributed significantly to the circulating radioactivity, particularly for rabbit and dog, in which metabolites comprised 73 to 93% of the area under the time curve (0-8 h). Circulating metabolites included M6, a direct O-glucuronide conjugate; M1, a hydroxylated metabolite; and glucuronide conjugates of hydroxylated and O-demethylated metabolites. Overall, the results from these studies suggested that BMS-690514 was well absorbed and highly metabolized through multiple pathways in these preclinical species.

Disposition and metabolism of (2S,3S,4R)-N′′-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxy methyl-2H-benzopyran-4-yl)-N′-benzylguanidine, a novel neuroprotective agent for ischemia-reperfusion damage, in rats

The metabolism and disposition of KR31378 (a benzopyran derivative and a novel neuroprotective agent) were investigated following single oral or intravenous administration of [14C]-KR31378 to rats. [14C]-KR31378 was rapidly absorbed after oral dosing with an oral bioavailability of greater than 71%. The maximum plasma concentration and area under the curve of total radioactivity in rat plasma increased proportionally to the administered dose. KR31378 was distributed over all organs and tissues except for brain, eyeball and testis, and declined by first order kinetics up to 24 h after dosing. Excretion of the radioactivity was 29.5% of the dose in the urine and 58.5% in the feces within 2 days after oral administration. Biliary excretion of the radioactivity in bile duct-cannulated rats was about 66.0% for the first 24 h. KR31378 was extensively metabolized by ring hydroxylation, O-demethylation, oxidation and reduction with subsequent N-acetylation and O-glucuronide conjugation. N-acetylated conjugates (M2, M10, M11, M12, M14, and M15) were identified as the predominant metabolites in rats.

Synthesis, Biological Evaluation and In Silico Metabolic and Toxicity Prediction of Some Flavanone Derivatives

Flavones chemically are anthoxanthins, occur either in the free state or as glycosides associated with tannins (flavanoids). Flavanoids (derivatives of flavone) possess various pharmacological activities and due to its xanthine-oxidase enzyme inhibitory effect it also has superoxide-scavenging activities. A series of 2-phenyl-2,3-dihydrochromon-4-one derivatives (flavanone derivatives) were synthesized from chalcones by cyclization method and their activities were evaluated against some gram positive and gram-negative bacteria. IR, NMR and CHN analysis confirmed the structure of the synthesized compounds. The results of the antibacterial studies shows that compounds 2b, 2e, 2f and 2h possess activity against many bacterial strains. Among that the compound (2h) has remarkable activity against all strains viz. 25 microg/ml inhibitory concentration against S. aureus, S. sonnei, E. coli, S. typhimurium and V. cholerae. Compound 2f possess minimum inhibitory concentration of 200 microg/ml against E. coli and S. typhimurium and 25 microg/ml against S. sonnei, S. dysenteriae and V. cholerae. In silico metabolic and toxicity study of the synthesized compounds were performed and the predicted result showed that the compound having hydroxyl functional group undergo sulfate and O-glucuronide conjugation reaction and methoxy derivatives undergo demethylation reaction. The biologically active compounds are free of toxicity in oncogene, teratogen, sensitivity and immunotoxicity.

Pre-clinical assessment of DRF 4367, a novel COX-2 inhibitor: Evaluation of pharmacokinetics, absolute oral bioavailability and metabolism in mice and comparative inter-species in vitro metabolism

The aim of this study was to characterize the pharmacokinetics and determine the absolute bioavailability and metabolism of DRF 4367, a novel COX-2 inhibitor, in mice. In addition, the in vitro metabolism of DRF 4367 was studied in mouse, rat, dog, monkey and human liver microsomes. Following oral administration, maximum concentrations of DRF 4367 were achieved after about 1 h. Upon intravenous (IV) administration, the concentration of DRF 4367 declined in a bi-exponential fashion with a terminal elimination half-life of 4.0 h. The elimination half-life was unchanged with route of administration. The volume of distribution and systemic clearance of DRF 4367 in mice were 0.80 l h−1 kg−1 and 0.14 l kg−1, respectively, after IV administration. The absolute oral bioavailability of DRF 4367 was 44%. In all species of liver microsomes examined, the primary route of metabolism for DRF 4367 was demethylation of benzyl methoxy to form a hydroxy metabolite (M1). The formation of this metabolite was mediated by CYP2D6 and CYP2C19 enzymes. M1 was not found to possess COX-2 inhibitory activity. Chemical-inhibition studies showed that quinidine (selective for CYP2D6) and ticlopidine (selective for CYP2C19) inhibited the formation of the hydroxy metabolite of DRF 4367, whereas potent inhibitors selective for other forms of CYP did not inhibit this oxidative reaction. Upon oral or IV administration of DRF 4367 to mice, unchanged DRF 4367, M1, the O-glucuronide conjugate of M1 (M1-G) and the O-sulfate conjugate of M1 (M1-S) were identified in bile.

N-O glucuronidation: a major human metabolic pathway in the elimination of two novel anticonvulsant drug candidates

1. The urinary metabolites of the anti-convulsant compound 4-amino-1-(2,6-difluorobenzyl)-1H-1,2,3-triazolo[4,5-c]-pyridine hydrochloride (GI265080) obtained following a single oral dose to man have been detected and quantified relative to each other using 19F-NMR spectroscopy. 2. The human urinary metabolites of GI265080 were isolated using semipreparative HPLC and unequivocally characterized using 1H-NMR spectroscopy, two-dimensional heteronuclear NMR spectroscopy and mass spectrometry. The assignments of the N-(5)oxide and the N-(5)-O-glucuronide metabolites of GI265080 were further confirmed by independent synthesis. The urinary metabolites obtained following single oral doses to dog and rat have also been isolated and characterized. 3. The human urinary metabolites of GI265080 comprise the N-(5)-oxide, the quaternary N+-(5)-glucuronide, the 7-hydroxy glucuronide and a glucuronide conjugate of the N-(5)-oxide. The N-(5)-O-glucuronide conjugate is a novel species in human metabolism and is a significant route of elimination of GI265080 in man. 4. The urinary metabolites of the potential anti-convulsant GW273293 (6-amino-3-(2,3,5-trichlorophenyl)pyrazin-2-ylamine) obtained following a single oral dose to man have also been isolated and characterized. The formation of a novel N-O-glucuronide was also observed and was shown to constitute a significant route of elimination of GW273293 in man.

Characterization of the major metabolite of sampangine in rats.

Sampangine (1) is a plant-derived antifungal copyrine alkaloid extracted from the stem bark of Cananga odorata. Although it possesses potent in vitro antifungal activity, 1 is devoid of significant and reproducible in vivo activity in a mouse model of cryptococcosis. Speculating that the lack of in vivo activity could be due to metabolism, a study was undertaken to begin to develop an understanding of the pharmacokinetics, and particularly metabolism of 1. Following intraperitoneal administration of 1 to rats, urine was collected, extracted, and chromatographed over a reversed-phase C(18) silica column to yield the major metabolite, SAM MM1 (2), which was identified by NMR and MS to be an O-glucuronide conjugate of sampangine. In addition, two other unstable, structurally uncharacterized minor metabolites were produced, as evidenced by HPLC analysis. Evaluation of the antifungal and antibacterial activities of 2 showed it to have remarkable in vitro activity against Cryptococcus neoformans.

Analysis of O -glucuronide conjugates in urine by electrospray ion trap mass spectrometry

The application of electrospray ionization (ESI) ion trap mass spectrometry in the characterization of O-glucuronide conjugates of some drugs in urine is described. The conjugated metabolites formed in rabbit and human were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by multi-stage mass spectrometry (MSn) experiments in negative ion mode. The ESI mass spectra showed a deprotonated molecule [M–H]–, which was chosen as precursor ion. Collision-induced dissociation (CID) of [M–H]– in MSn experiments resulted in the appearance of glucuronate ‘fingerprint’ ions at m/z 175 and 113 as well as prominent aglycone ions which were the same as those produced from authentic specimens. This information can be used to identify this type of compound directly without the need for derivatization or hydrolysis of enzymes, providing a rapid and specific method for guiding the isolation and characterization of similar compounds in complex matrices with LC/MS.

Biotransformation of 2-chloroaniline in the Fischer 344 rat: identification of urinary metabolites

1. The biotransformation of a single i.p. dose of [14C]2-chloroaniline (1.0 mmol/kg, ∼ 60 μCi/rat) was investigated in the urine and faeces of the male Fischer 344 rat. 2. During 24 h, 53.1% of the administered radioactivity was eliminated into the urine, while < 1% of the radioactivity appeared in the faeces. 3. The major biotransformation pathways were para-hydroxylation and sulphate conjugation. 4-Amino-3-chlorophenyl sulphate was the major urinary metabolite comprising 31.6% of total urinary radioactivity. The para-hydroxylated metabolite, 4-amino3-chlorophenol (10.8%), and its O-glucuronide conjugate (3.7%) were also urinary metabolites. The formation of direct conjugates of 2-chloroaniline, the N-sulphate and N-glucuronide, was significant with as much as 18.6 and 8.6%, respectively, of these metabolites excreted in the urine. The parent compound, 2-chloroaniline, accounted for 16.9% of urinary radioactivity. 4. N-Acetylated products were minor metabolites present in urine as 2-chloro-4- hydroxyacetanilide and its sulphate or glucuronide conjugate. Neither 2-chloroacetanilide nor its oxidation products, 2-chloroglycolanilide and 2-chlorooxanilic acid, were urinary metabolites.

N-nitroso compounds and man

Based on recent analytical data, total human exogenous exposure to N-nitrosamines is estimated to be 1.10 mumol/day; the major exposure sources are the diet (0.79 mumol/may, 80-120 micrograms/day; 72%), occupational exposure (0.15-0.30 mumol/day; 25%), cigarette smoking (0.02 mumol/day, 3.4 micrograms/day; 2%), and miscellaneous minor sources, including pharmaceutical products, cosmetics, indoor and outdoor air (0.001 mumol/day, 0.1 micrograms/day; 1%). Excretion of apparent total N-nitroso compounds (ATNC) in healthy adults is estimated to be 1.30 +/- 1.05 mumol/day in urine and between 1.56 +/- 1.56 and 3.17 +/- 2.58 mumol/day in faeces. The excretion of volatile N-nitrosamines (N-nitrosodimethylamine), and N-nitrosamine acids and their derivatives (N-nitrososarcosine, N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid and N-nitroso-2-methylthiazoline-4-carboxylic acid) accounts for approximately 0.03% and 16.0% of urinary ATNC, respectively. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol and its O-glucuronide conjugate, two metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone present in urine of smokers, account for 0.2% of the urinary ATNC response; < 1.5 of the excretion of currently identified N-nitroso compounds in urine. The remaining N-nitroso compounds excreted in urine and those present in faeces are still unidentified. A crude mass balance between exogenous exposure and excretion in urine and faeces indicates that 45-75% of the total human exposure to N-nitroso compounds results through in vivo formation.

The metabolism of CGS 15873 in man using stable isotope pattern recognition techniques.

CGS 15873 is a relatively specific dopamine agonist with preferential activity at the presynaptic autoreceptor and therefore may represent a novel agent for the treatment of schizophrenia and/or Parkinson's disease. Several metabolites have been identified in the rat and monkey using an isotopically enriched dosing solution and pattern recognition techniques coupled with GC/MS and LC/MS. In this study, the metabolism of CGS 15873 was investigated in man using these same techniques. In urine, specific isotope clusters were found that matched the dosing solution pattern. Three metabolites were identified: an O-glucuronide conjugate of the parent drug, N-despropyl CGS 15873, and a keto metabolite of CGS 15873. Thermospray LC/MS allowed for the direct confirmation of the conjugated metabolite. GC/MS required derivatization but afforded greater sensitivity compared to LC/MS.