Nicotine-N'-Oxidation by Flavin Monooxygenase Enzymes

BACKGROUND

The major mode of metabolism of nicotine is by hydroxylation via cytochrome P450 (CYP) 2A6, but it can also undergo glucuronidation by UDP-glucuronosyltransferases and oxidation by flavin monooxygenases (FMO). The goal of this study was to examine the potential importance of FMOs in nicotine metabolism and assess the potential impact of missense polymorphisms in active FMOs on nicotine-N'-oxide (NOX) formation.

METHODS

Urine samples from 106 current Chinese smokers were analyzed for nicotine metabolites by mass spectrometry. Wild-type FMOs 1-5 and their most prevalent nonsynonymous variants were cloned and overexpressed in HEK293 cells, and were tested in oxidation reactions against nicotine.

RESULTS

A strong inverse correlation was observed between the ratio of urinary 3'-hydroxycotinine/cotinine, a measure of CYP2A6 activity, and the urinary levels of NOX alone (r = -0.383; P < 0.001) or NOX measured as a ratio of total nicotine metabolites (r = -0.414; P < 0.001) in smokers. In addition to FMO1 and FMO3, the functional FMO2^427Q isoform was active against nicotine, whereas FMO4 and FMO5 exhibited low activity against nicotine (K _m > 5.0 mmol/L). Significant (P < 0.05) decreases in N'-oxidation activity (V _max/K _m) were observed for the FMO1^I303V, FMO3^N61S, FMO3^D132H, FMO3^V257M, and FMO3^E308G variants in vitro when compared with their respective wild-type isoforms; the truncated FMO2^Q472stop isoform exhibited no enzyme activity.

CONCLUSIONS

These data indicate that increases in nicotine-N'-oxidation occur in subjects with deficient CYP2A6 activity, and that several FMO enzymes are active in nicotine-N'-oxidation.

IMPACT

Several common missense FMO variants are associated with altered enzyme activity against nicotine and may play an important role in nicotine metabolism in low-CYP2A6 activity subjects.

[Development of analytical method for determination nicotine metabolites in urine]

The assay of biomarkers in biological material is the most popular and reliable method in estimate exposure to tobacco smoke. Nicotine and its metabolites qualify to the most specific biomarkers for tobacco smoke. Currently the most often used are cotinine and trans-3'-hydroxycotinine. The aim of this study was development of easy and quick method of determining nicotine and its main metabolites with high performance liquid chromatography--available in most laboratories. Nicotine and its metabolites in urine (cotinine, trans-3'-hydroxycotinine, nornicotine and nicotine N-oxide) was determined by means of high performance liquid chromatography with spectrometry detection (HPLC-UV). The determined compounds were extracted from urine by means of the liquid-liquid technique, before analysed by the HPLC method. Developed technique of high performance liquid chromatography proved to be useful to assessment nicotine and its four metabolites in smokers, though further research are necessary. The further modification of procedure is required, because of the interferences of cotinine N-oxide with matrix, which prevent determination. Increasing the efficiency of extraction nicotine and nornicotine could enable the determination in people exposed on environmental tobacco smoke (ETS). This study confirm other authors' observations that 3'-hydroxycotinine might be equivalent with cotinine predictor of tobacco smoke exposure, however further studies are required.

The metabolomics of (+/-)-arecoline 1-oxide in the mouse and its formation by human flavin-containing monooxygenases

The alkaloid arecoline is a main constituent of areca nuts that are chewed by approximately 600 million persons worldwide. A principal metabolite of arecoline is arecoline 1-oxide whose metabolism has been poorly studied. To redress this, synthetic (+/-)-arecoline 1-oxide was administered to mice (20mg/kg p.o.) and a metabolomic study performed on 0-12h urine using ultra-performance liquid chromatography-coupled time-of-flight mass spectrometry (UPLC-TOFMS) with multivariate data analysis. A total of 16 mass/retention time pairs yielded 13 metabolites of (+/-)-arecoline 1-oxide, most of them novel. Identity of metabolites was confirmed by tandem mass spectrometry. The principal pathways of metabolism of (+/-)-arecoline 1-oxide were mercapturic acid formation, with catabolism to mercaptan and methylmercaptan metabolites, apparent CC double-bond reduction, carboxylic acid reduction to the aldehyde (a novel pathway in mammals), N-oxide reduction, and de-esterification. Relative percentages of metabolites were determined directly from the metabolomic data. Approximately, 50% of the urinary metabolites corresponded to unchanged (+/-)-arecoline 1-oxide, 25% to other N-oxide metabolites, while approximately, 30% corresponded to mercapturic acids or their metabolites. Many metabolites, principally mercapturic acids and their derivatives, were excreted as diastereomers that could be resolved by UPLC-TOFMS. Arecoline was converted to arecoline 1-oxide in vitro by human flavin-containing monooxygenases FMO1 (K(M): 13.6+/-4.9muM; V(MAX): 0.114+/-0.01nmolmin(-1)microg(-1) protein) and FMO3 (K(M): 44.5+/-8.0microM; V(MAX): 0.014+/-0.001nmolmin(-1)microg(-1) protein), but not by FMO5 or any of 11 human cytochromes P450. This report underscores the power of metabolomics in drug metabolite mining.

A foxy intoxication

Foxy is the colloquial name for the hallucinogen 5-ethoxy-diisopropyltryptamine (5-MeO-DIPT). A non-fatality involving a 23-year-old Caucasian man who ingested a capsule containing 5-MeO-DIPT is described. He presented to the Emergency Department, not with visual nor auditory hallucinations but with sensory hallucinations, that of formication and paranoia. He was observed and given supportive care for 4 h, then discharged without any known sequelae. Blood and urine were collected for laboratory analyses. Foxy and its metabolites were identified in urine by gas chromatography-mass spectrometry. The concentrations of 5-MeO-DIPT in the serum and urine were 0.14 and 1.6 microg/mL, respectively. The drug undergoes oxidative deamination to form 5-methoxy-indole acetic acid. The urinary concentration of this metabolite was 0.17 microg/mL. Also, the urine contained three other related compounds. Two of them have been described in a previous case of 5-MeO-DIPT ingestion as 5-methoxy-isopropyltryptamine (5-MeO-IPT) and 5-methoxy-diisopropyltryptamine-N'-oxide (5-MeO-DIPT-N'-oxide). The third compound was substantially present in the urine and was tentatively identified as 5-hydroxy-diisopropyltryptamine (5-OH-DIPT). Only the parent drug, 5-MeO-DIPT was detected in the serum sample.

N-Deethylation and N-oxidation of etamiphylline: identification of etamiphylline-N-oxide in greyhound urine by high performance liquid chromatography–mass spectrometry

Millophyline-V, (etamiphylline camsylate) was administered intramuscularly to two racing greyhounds at a dose of 10 mg kg(-1). Unhydrolysed pre- and post-administration urine samples were extracted using mixed mode solid phase extraction (SPE) cartridges, the basic isolates derivatised as trimethylsilyl ethers and analysed by positive ion electron ionisation gas chromatography-mass spectrometry (GC/EI+/MS). The parent drug and one metabolite, N-desethyletamiphylline, were detected in urine for up to 72 h. For semi-quantification, urine samples were extracted on-line using a Prospekt sample handler. The analytes retained on the C2 SPE cartridge were eluted by the mobile phase directly on to the analytical high performance liquid chromatography column and analysed by positive ion atmospheric pressure chemical ionisation (LC/APCI+) MS in the multiple selective-ion recording mode. A major peak containing both ions (m/z) 280 and (m/z) 252 was observed. Full scan LC/APCI+/MS of the unknown indicated that the ion at (m/z) 280 was formed by the loss of an oxygen atom [MH+ -->(MH+-O)]. Samples were analysed by positive ion electrospray ionisation LC/MS on two different instruments and the unknown compound was identified as an N-oxide of the tert. nitrogen atom of the 2-(diethylamino)ethyl substituent on N7 of the theophylline nucleus. This compound has not been reported previously either as an in vivo or in vitro metabolite of etamiphylline in any species. Thermal decomposition of the N-oxide could lead to an increase the detection period of the parent drug during routine GC/MS screening of post-competition greyhound urine samples.

Foxy, a designer tryptamine hallucinogen

Foxy is slang for 5-methoxy-N,N-diisopropyltryptamine. It has hallucinogenic properties, similar to other tryptamine compounds, and is mildly euphoric. This case report describes a 21-year-old Caucasian man who ingested a pill called Foxy containing an unknown amount of drug. He was observed in hospital for 2 h, during which time he had mild hallucinations and could not move his limbs. A urine sample was collected approximately 4 h after drug ingestion. The patient was then discharged with no follow up assessment. The 5-methoxy-N,N-diisopropyltryptamine was identified in the urine by gas chromatography-mass spectrometry. Standards prepared from the pure material were used in the identification. Quantitative analysis using the same analytical technique resulted in a urinary concentration of 1.7 micro g/mL. Through oxidative deamination, the metabolite, 5-methoxy-indole acetic acid, was formed. It was identified in the urine, and the concentration was determined to be 1.3 micro g/mL using gas chromatography-mass spectrometry. Two other compounds were discovered in the urine sample as a result of a routine drug screen. From their mass spectra, they were tentatively identified as 5-methoxy-N-isopropyltryptamine and 5-methoxy-N,N-diisopropyltryptamine-N'-oxide.

The disposition of voriconazole in mouse, rat, rabbit, guinea pig, dog, and human

Voriconazole is a new triazole antifungal agent with potent, wide-spectrum activity. Its pharmacokinetics and metabolism have been studied in mouse, rat, rabbit, dog, guinea pig, and humans after single and multiple administration by both oral and intravenous routes. Absorption of voriconazole is essentially complete in all species. The elimination of voriconazole is characterized by non-linear pharmacokinetics in all species. Consequently, pharmacokinetic parameters are dependent upon dose, and a superproportional increase in area under the curve is seen with increasing dose in rat and dog toxicology studies. Following multiple administration, there is a decrease in systemic exposure. This is most pronounced in mouse and rat, less so in dog, and not observed in guinea pig or rabbit. Repeat-dose toxicology studies in mouse, rat, and dog have demonstrated that induction of cytochrome P450 by voriconazole (autoinduction of metabolism) is responsible for the decreased exposure in these species. Autoinduction of metabolism is not observed in humans, and plasma steady-state concentrations remain constant with time. Voriconazole is extensively metabolized in all species. The major pathways in humans involve fluoropyrimidine N-oxidation, fluoropyrimidine hydroxylation, and methyl hydroxylation. Also, N-oxidation facilitates cleavage of the molecule, resulting in loss of the fluoropyrimidine moiety and subsequent conjugation with glucuronic acid. Major pathways are represented in animal species. The major circulating metabolite in rat, dog, and human is the N-oxide of voriconazole. It is not thought to contribute to efficacy since it is at least 100-fold less potent than voriconazole against fungal pathogens in vitro.

Fragmentation of N-oxides (deoxygenation) in atmospheric pressure ionization: investigation of the activation process

The diagnostic fragmentation of N-oxides resulting from loss of the oxygen atom (MH+ --> MH+-O) in electrospray and atmospheric pressure chemical ionization (APCI) mass spectra was investigated. When the temperature of the heated capillary tube was elevated, the ratio of the intensity of the [MH+ -16] fragment to the precursor ion (MH+) increased. This 'deoxygenation' process was associated with thermal activation and did not result from collisional activation in the desolvation region of the API source. Although the extent of 'deoxygenation' is compound-dependent, it can provide evidence for the presence of an N-oxide in a sample and can be used to distinguish N-oxides from hydroxylated metabolites (Ramanathan et al. Anal. Chem. 2000; 72: 1352). To demonstrate the practical application of thermal fragmentation of N-oxides, liquid chromatography (LC)/APCI-MS was used to distinguish an N-oxide drug from its hydroxylated metabolite in an unprocessed rat urine sample, despite the fact that the drug and its metabolite were not fully resolved by HPLC.

In vivo L-band ESR and quantitative pharmacokinetic analysis of stable spin probes in rats and mice

Free radical species in animals have been measured by X-band ESR spectrometric method on a block of organs or a portion of homogenized samples. However, a nondestructive in vivo ESR measurement has been realized by using a recently developed L-band ESR spectrometry. With this L-band ESR method, we measured ESR spectra in animals, who received stable nitroxide radicals. L-band ESR spectra were observed at the upper abdomen of mice as well as at the heads of mice and rats at various ages immediately after the intravenous injections of nitroxide radicals such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (3-carbamoyl-PROXYL), in which ESR measurements of the radicals were performed noninvasively at the real time. On the basis of the observed time-dependent free radical clearance curves, the following important results were obtained: (1) Free radical clearances were able to analyze by the pharmacokinetic method. (2) The radicals at the head of mice, given 4-hydroxy-TEMPO, were determined quantitatively by a new analytical method using L-band ESR for the first time. (3) The elimination of the radical was found to be saturated in mice. (4) The clearance rate constant of 4-hydroxy-TEMPO detected at the head of mice was decreased in dose- and age-dependent manners. While, no age-dependent clearance rate constant of 4-hydroxy-TEMPO was observed at the upper abdomen of mice. (5) Ratios of the amount of the detected radicals to that of the administered radicals were decreased age-dependently, but they were independent of the dose of the radicals, suggesting the age-dependent decrease of distribution capacity ratio of the radical at the head of animals. (6) Clearance rate constants of 4-hydroxy-TEMPO and 3-carbamoyl-PROXYL, that were estimated by X- and L-band ESR for the collected blood of mice and rats, were found to be remarkably smaller than those in whole living animals observed by in vivo L-band ESR method. The results suggest that the clearance of the nitroxide radical is relevant to the alteration of the radical in animals following the change of organ distribution and metabolism. (7) Both the radical and its corresponding hydroxylamine, which is the reduced form of the radical, were detectable by X-band ESR method in the collected urine of mice and rats without and with an oxidizing agent, respectively. On the basis of the results on L-band ESR spectrometry, the first quantitative pharmacokinetic analysis of stable spin probes in animals is proposed.

The influence of cigarette consumption and smoking machine yields of tar and nicotine on the nicotine uptake and oral mucosal lesions in smokers

The purpose of this investigation, which has been performed as two studies, was to evaluate the association between the daily exposure to nicotine (measured as cigarette smoking machine yields) and the actual uptake of nicotine by cigarette smokers, as well as the association between oral mucosal changes and the exposure to cigarette smoke. In Study 1, consumption data, soft tissue changes and nicotine intake were measured in 47 habitual smokers using cigarettes with tar and nicotine yields within the ranges 9.3-12.2 and 0.72-1.16 mg per cigarette, respectively. The subjects were divided into three groups based on daily cigarette consumption; group averages (standard deviation) were 10.8 (2.2), 17.9 (1.9) and 28.4 (6.1) cigarettes per day. The group averages of tar deliveries from their usual brands of cigarettes were 11.1, 11.0 and 10.5 mg per cigarette, and group averages of nicotine deliveries were 1.05, 1.05 and 1.06 mg per cigarette, respectively. In Study 2, the same data were measured in a group of 77 habitual smokers with an average individual consumption of 11-21 cigarettes per day. The participants in Study 2 were divided into three groups according to tar delivery from their usual brands to cigarettes, with group averages of tar being 6.4 (1.2), 11.0 (1.2) and 16.0 (1.1) mg per cigarette, and of nicotine being 0.70 (0.12), 1.05 (0.12) and 1.34 (0.08) mg per cigarette, respectively. The average consumption of all three groups was within the range 17.1 to 17.9 cigarettes per day. The daily exposures to nicotine and tar were measured as the smoking machine yields multiplied by the number of cigarettes smoked per day. Nicotine uptake was determined by monitoring nicotine and its seven main metabolites in 24-h urine samples. In Study 1 there were significant differences between the three groups in the total amount of nicotine and metabolites excreted in the 24-h urine. The average nicotine uptake was 14.9, 24.4 and 35.4 mg per day, respectively. In Study 2, the 24-h excretion of nicotine and metabolites was about the same in all three groups and averaged 24.5 mg per day. The nicotine uptake was significantly correlated to the number of cigarettes smoked per day but not to the smoking machine yields of tar and nicotine per cigarette. The average prevalences for each of the different oral mucosal lesions (leukoedema, smoker's palate and hairy tongue) were found to increase with increasing consumption and nicotine uptake (Study 1); they were also independent of tar and nicotine yields from the cigarettes smoked (Study 2). These results indicate that the actual uptake of nicotine by smokers could not be estimated from the smoking machine yields. Reduction in exposure to smoke components may best be accomplished if smokers are encouraged to smoke fewer lower-yield cigarettes and to avoid smoking more of each cigarette.

Reduction in nicotine intake and oral mucosal changes among users of Swedish oral moist snuff after switching to a low-nicotine product

The purpose of this investigation was to assess nicotine regulation among users of portion-bag Swedish oral moist snuff (snus) when switching from an ordinary snus product (Brand A) to a low-nicotine product having only half the concentration of nicotine (Brand B). Two studies were performed to compare the short-term effects on consumption and nicotine intake of switching to low-nicotine snus with those of long-term effects. In Study 1, consumption data, soft tissue changes and nicotine intake were measured in a group of 24 habitual users of Swedish portion-bag snus, both during use of their ordinary snus (Brand A) for 2 weeks and during consumption of the low-nicotine product (Brand B) for 10 weeks. In study 2, the same data were measured during 2 weeks in a reference group of 18 snus users who had been habitual users of the low-nicotine snus (Brand B) for at least one year. Although there was no increase in number of hours of daily consumption, the amount of snus consumed increased on average by 2 grams a day (+15%) when switching from Brand A to the low-nicotine Brand B (Study 1). The Brand B reference group (Study 2) consumed about 3 grams less snus a day during the same number of hours as the subjects in Study 1 who had switched to Brand B. These results indicate that snus users compensate to a small extent for the lower nicotine delivery by increasing their consumption on short-term switching but the same does not apply to long-term users.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of quinidine, dihydroquinidine, (3S)-3-hydroxyquinidine and quinidine N-oxide in plasma and urine by high-performance liquid chromatography

A specific and sensitive method for the quantitation of quinidine, (3S)-3-hydroxyquinidine, quinidine N-oxide, and dihydroquinidine in plasma and urine has been developed. The method is based on a single-step, liquid-liquid extraction procedure, followed by isocratic reversed-phase high-performance liquid chromatography, with fluorescence detection. After extraction from 250 microliters plasma and 100 microliters urine, the limit of determination is 10 nM and 25 nM, respectively. For the use as standards, commercially available quinidine was purified from dihydroquinidine; quinidine N-oxide was synthesized.

Species variation and stereoselectivity in the metabolism of nicotine enantiomers

1. High performance liquid radiochromatographic systems have been developed for the identification and quantification of 7 urinary metabolites of both S-(-)-[3H-N'-CH3]nicotine and R-(+)-[3H-N'-CH3] nicotine in guinea pig, hamster, rat and rabbit. 2. 3'-Hydroxycotinine was a major urinary metabolite of both S-(-)-nicotine and R-(+)-nicotine in guinea pig, hamster and rabbit. Cotinine was not generally a significant urinary metabolite of either nicotine enantiomer, except in rat, where it constituted 14.6 and 10.4%, respectively, of the total radiolabel in the urine after administration of [3H]-S-(-)-nicotine or [3H]-R-(+)-nicotine. Nicotine N'-oxide was an important urinary metabolite of both nicotine isomers in guinea pig and rat, but in both cases, was not observable in hamster and rabbit. No N-methylated urinary metabolite of S-(-)-nicotine could be detected in any of the species examined. In R-(+)-nicotine experiments, only guinea pig afforded N-methylated metabolites. Significant amounts of 2 unidentified polar, non-basic urinary metabolites of both S-(-)- and R-(+)-nicotine-treated animals were observed. 3. Analysis of the comparative metabolism of the nicotine enantiomers in the four animals species studied, showed that stereoselective differences in the formation of oxidative metabolites existed, particularly in the formation of 3'-hydroxycotinine and nicotine-N'-oxide. A clear stereospecificity was observed in the guinea pig, in that only the R-(+)-nicotine enantiomer was N-methylated in this species. 4. Sex differences appear to exist in the metabolism of nicotine enantiomers in the rat. Female rats excreted more of the unidentified polar metabolite B than male rats, whereas the converse was true for nicotine-N'-oxide. In experiments with R-(+)-nicotine, urinary levels of 3'-hydroxycotinine and R-(+)-nicotine in female rats were higher than in male rats. Conversely, higher amounts of nicotine-N'-oxide were observed in the urine of male rats compared to those in female rats.

Evaluation of a low to middle tar/medium nicotine cigarette designed to maintain nicotine delivery to the smoker

A specific objective of this 6-week crossover study was to determine how 21 regular smokers of middle tar cigarettes changed their smoking behaviour and uptake of smoke constituents, when switching to either lower tar cigarettes capable of delivering amounts of nicotine similar to a conventional middle tar cigarette (maintained nicotine product), or to conventional low tar/low nicotine cigarettes. Subjects visited the laboratory every 2 weeks for detailed assessment of their smoking behaviour. Weekly per capita consumption was similar for all three cigarettes. They were smoked with variable intensities (low tar greater than maintained nicotine greater than middle tar), the tendency being for larger puff volumes, faster puffing and increased puff duration with the low tar cigarettes. The maintained nicotine cigarette was preferred to the middle tar cigarette, although acceptability ratings of the three cigarettes only differed marginally. The nicotine absorbed from the maintained nicotine and middle tar cigarettes was similar and significantly greater than the levels achieved from the low tar cigarettes. Intake of carbon monoxide into the mouth and absorption into the blood stream was lower for the maintained nicotine cigarette than for the middle tar cigarette, with the low tar cigarette occupying an intermediate position. Derived estimates of tar intake suggested reduced intake of tar into the respiratory tract (around 25%) from the maintained nicotine product relative to the middle tar product. The possible advantages of switching to maintained nicotine cigarettes is discussed.

Kinetics and dynamics of quinidine-N-oxide in healthy subjects

The pharmacokinetics of a major metabolite of quinidine in humans, quinidine-N-oxide, were investigated after single oral doses (3 to 15 mg) in four healthy subjects. The concentration in serum and urine was determined by an HPLC assay. Because of a small volume of distribution, the elimination half-life of quinidine-N-oxide was only 2.5 +/- 0.28 hours (mean +/- SD), considerably shorter than that of quinidine. The renal clearance was 1.3 +/- 0.3 L/hr. Only 13.9% +/- 3.7% of the dose was recovered in urine as unchanged compound for up to 12 hours. Two unidentified compounds with the same retention time as quinidine and 3-hydroxyquinidine were found in the urine samples of two subjects. The free fraction in serum was 3.3% +/- 0.83%. No systematic changes in heart rate-corrected QT interval were observed up to concentrations of 500 ng/ml. The results indicate that quinidine-N-oxide, in contrast to 3-hydroxyquinidine, does not possess quinidine-like pharmacologic activity.

Lack of effect of smoking on the metabolism and pharmacokinetics of quinidine in patients

The urinary metabolite profile of quinidine and the oral clearance of this drug were studied under steady state conditions in five smoking and nine non-smoking patients. No significant differences were observed in the urinary recovery of unchanged quinidine, 3S-3-hydroxyquinidine, 2'-oxoquinidinone or quinidine-N-oxide between smokers and non-smokers. In addition, the plasma clearance of quinidine was not affected by the smoking status of subjects. These results suggest that cigarette smoke does not induce any of the main pathways for quinidine metabolism in a typical patient population and that the consideration of smoking status is of little utility in aiding in the selection of initial dosage regimens for this drug.

Improved method for routine determination of nicotine and its main metabolites in biological fluids

ExtrelutR extraction and glass capillary gas chromatography were applied to the routine determination of nicotine and its metabolites cotinine, nicotine-1'-N-oxide and cotinine-1-N-oxide in urine and plasma. After extraction of nicotine and cotinine both N-oxides and phendimetrazine-N-oxide (used as internal standard) were reduced to their bases by SO2 on-column and eluted by a mixture of diethyl ether and dichloromethane. The minimum detectable concentrations are 0.03 micrograms/ml for urinary nicotine and cotinine and 0.1 microgram/ml for the N-oxides. In plasma samples the corresponding values are 5 ng/ml and 15 ng/ml, respectively, with sample values as small as 2 ml. The advantage of the direct determination of all four compounds of interest in one sample reduced the amount of plasma required. The straightforward and rapid extraction and reduction procedure as well as the long-term stability of the gas chromatographic separation system make the method suitable for routine application.

Metabolic conversion of indicine N-oxide to indicine in rabbits and humans

Indicine N-oxide, a pyrrolizidine alkaloid N-oxide that exhibits antitumor activity without some of the toxic effects associated with other pyrrolizidine alkaloids, is metabolized to indicine in rabbits and humans. Indicine can be detected in the plasma and is excreted in the urine in a dose-dependent manner following the i.v. administration of indicine N-oxide. The p.o. administration of indicine N-oxide leads to an increased plasma concentration and an increased urinary excretion of indicine. The hepatic microsomal fraction and the gut flora both catalyze the anaerobic reduction of indicine N-oxide to indicine in vitro. Whole-animal studies suggest that the gut flora play a major role in the metabolic reduction of indicine N-oxide by the rabbit. Indicine N-oxide is not actively excreted in the bile, and it is probable that indicine N-oxide finds its way into the gut by passive diffusion following i.v. administration. Neomycin and erythromycin, which reduce the number of anaerobic bacteria in the gut, lead to decreased plasma levels and a decreased urinary excretion of indicine.

The gas chromatographic mass spectrometric analysis of the new antitumor drug indicine-N-oxide utilizing a novel reaction accompanying trimethylsilylation

Indicine-N-oxide was analyzed by gas chromatography mass spectrometry with nanogram sensitivity after trimethylsilylation. Two different products were produced by altering the conditions of this reaction. Mass spectral evidence is presented to show that one of these was the expected trisubstituted pyrrolizidine product while the other was a trisubstituted pyrrole. The latter derivative is useful for distinguishing between indicine-N-oxide and indicine which dies not form this novel product under the same conditions. Analogous pyrrole and pyrrolizidine products were formed from heliotrine-N-oxide, a compound that can serve as an internal standard from measuring indicine-N-oxide and its metabolites in biological samples. A method for purifying such samples by strong cation exchange chromatography prior to derivatization is also discussed.

Determination of indicine N-oxide and indicine in plasma and urine by electron-capture gas-liquid chromatography

A sensitive and specific method is described for the quantitative analysis of indicine N-oxide and indicine in plasma and urine. Indicine N-oxide is reduced to the tertiary amine with zinc--acetic acid (plasma) or zinc--ammonium chloride (urine). The indicine is derivatized with pentafluoropropionic anhydride to provide electron-capture detection. Assay of rabbit and human plasma and urine samples can detect 100 ng/ml (plasma) and 200 ng/ml (urine), and the method was applied to the analysis of indicine N-oxide and indicine in rabbits and one patient following administration of indicine N-oxide.

The interrelationship between the metabolism of (S)-continine-N-oxide and (S)-cotinine

The metabolism of (S)-cotinine-N-oxide was studied in the rabbit and the dog. The pattern of Koenig-positive substances in the urine of the animals suggested the presence of cotinine, demethylcotinine, hydroxycotinine, and allohydroxycotinine, compounds already previously identified as metabolites of (S)-cotinine and (S)-nicotine in many mammalian species. In the dog, 34% of the administered oral dose of (S)-cotinine-N-oxide was recovered from the urine, and 21% was recovered from the urine of the rabbit. Confirmation of the presence of (S)-cotinine, (S)-demethulcotinine, hydroxycotinine, and allohydroxycotinine in the urine of the rabbits was obtained by isolation of the metabolites as themselves of as derivatives. The data, although establishing the possibilities of an intermediary role for (S)-cotinine-N-oxide in the metabolism of nicotine, do not clearly indicate whether the metabolites such as demethylcotinine arise via the route (S)-cotinine-N-oxide leads to (S)-cotinine leads to (S)-demethylcotinine or via the alternate route (S)-cotinine-N-oxide leads to (S)-demethylcotinine-N-oxide leads to (S)-demethylcotinine.

A polarographic method for the determination of the N-oxide, N-oxide-sulphoxide and sulphoxide metabolites of chlorpromazine

Cathode ray polarography has been used to measure chlorpromazine-N-oxide, N-oxide sulphoxide and chlorpromazine sulphoxide in mixtures. The response was linear when the metabolites were present in the range 10−5 to 5 times 10−8m in aqueous solutions. Reductive polarography of the mixed oxides in solution gave an additive wave from which individual oxides were determined by subtraction. Ultraviolet and Potentiometrie titration methods were used to determine the pKa values of the oxide metabolites of chlorpromazine. The mechanism of the reduction process was investigated using d.c. polarography and preparative micro-electrolysis. Polarographic analysis was applied to the determination of the metabolites after their separation from urine, plasma and microsomal preparations.

The analysis of nicotine-1'-N-oxide in urine, in the presence of nicotine and cotinine, and its application to the study of in vivo nicotine metabolism in man

A rapid quantitative assay for nicotine-1′-N-oxide in urine, in the presence of nicotine and cotinine, is reported. The urinary excretion of nicotine, cotinine and nicotine-1′-N-oxide was determined after nicotine had been administered in cigarette smoke, orally, or intravenously to subjects with either fluctuating, controlled acidic or controlled alkaline urinary pH. The urinary excretion of the N-oxide in 24 h from smokers under normal conditions was about half that of the cotinine excretion; more trans- than cis-diastereoisomer of nicotine-1′-N-oxide was excreted.

Some aspects of the metabolism of morphine-N-oxide

After administration of morphine-N-oxide (MNO) to rats the opiates appearing in the urine were morphine (61%) and MNO (39%). After administration of morphine, the urinary opiates were morphine (80%) and normorphine (20%). When tacrine was given with morphine the urine also contained MNO (46% of total urinary opiates) and the amount of normorphine was much decreased (to 1%), the remainder being morphine (53%). Tacrine and amiphenazole inhibited demethylation of morphine and codeine by a rat liver fraction in vitro. MNO had weak inhibitory activity. Neither MNO nor codeine-N-oxide were demethylated in vitro.