The formation of 2-hydroxypropylmercapturic acid from 1-halogenopropanes in the rat

Quantitation of the tetrachloroethylene metabolite N-acetyl-S-(trichlorovinyl)cysteine in rat urine via negative ion chemical ionization gas chromatography/tandem mass spectrometry

A sensitive and selective negative ion chemical ionization gas chromatographic/tandem mass spectrometric (NICI GC/MS/MS) method was developed for the determination of the tetrachlorethylene metabolite, N-acetyl-S-(trichlorovinyl)cysteine (TCVC), in rat urine. Urine samples were fortified with a 13C,D2-analog of TCVC, acidified and extracted with ethyl acetate. The extract were derivatized with methanolic HCl, and the resulting methyl esters analyzed via NICI GC/MS/MS. Detection of the TCVC analogs was performed by monitoring the Cl- product ion of M-Cl2C2HS-. The limit of detection for TCVC by this method was estimated to be 0.1 ng ml-1 urine (3 x noise). The quantitation limit was determined to be 0.3 ng TCVC per milliliter of urine. The method was found to be linear for TCVC concentrations from 0.3 to 104 ng ml-1 urine. Relative recovery of TCVC from urine ranged from 95.4% to 108.5%. Additional data are given for GC/MS and GC/MS/MS analysis of the pentafluoro-benzyl ester derivative of TCVC. Data are also presented for the isolation and analysis of this compound obtained from dosed rats.

Quantitative determination of N-acetyl(-L-)cysteine derivatives in human urine by tandem mass spectrometry

Collision-induced dissociation (CID) methods are described for the quantification of nanogram per millilitre (ppb) concentrations of 2-acetamido-3-(3'-hydroxypropylthio)-propanoic acid (I) and 2-acetamido-3-phenylthiopropanoic acid (II) in human urine extracts. I and II are potential detoxification products of acrolein and benzene in conjugation with N-acetyl(-L-)cysteine derived from glutathione. We have studied the potential of tandem mass spectrometry (MS/MS) under electron impact (EI) and chemical ionization (CI) conditions as a confirmatory screening technique for these compounds. Our main goals were high selectivity and low detection limits along with little or no sample clean-up. The effects of the mode of ionization and of collision conditions on the CID spectra have been investigated. Direct insertion probe without any derivatization or short-column gas chromatographic separation techniques are used. Total instrument and data analysis time is about 15 min for direct insertion probe MS/MS and about 30 min for short-column gas chromatography (GC)/MS/MS. Detection limits are: direct insertion probe MS/MS (EI mode), 50 ppb (100 pg) for compound I; short-column GC/MS/MS (EI mode), 1.5 ppb (5 pg) for compound II; and short-column GC/MS/MS (CI mode), 0.6 ppb (2 pg) for the methyl ester of compound II. Results are compared with non-mass spectrometric methods. The MS/MS methods were applied for the determination of I (EI mode) and II (CI mode) in urinary samples of a smoker and eight non-smokers. After smoking, the urinary levels of I and II were elevated, whereas no increase was observed after experimental passive smoking.

Alkylation of an active-site cysteinyl residue during substrate-dependent inactivation of Escherichia coli S-adenosylmethionine decarboxylase

S-Adenosylmethionine decarboxylase from Escherichia coli is a member of a small class of enzymes that uses a pyruvoyl prosthetic group. The pyruvoyl group is proposed to form a Schiff base with the substrate and then act as an electron sink facilitating decarboxylation. We have previously shown that once every 6000-7000 turnovers the enzyme undergoes an inactivation that results in a transaminated pyruvoyl group and the formation of an acrolein-like species from the methionine moiety. The acrolein then covalently alkylates the enzyme [Anton, D. L., & Kutny, R. (1987) Biochemistry 26, 6444]. After reduction of the alkylated enzyme with NaBH4, a tryptic peptide with the sequence Ala-Asp-Ile-Glu-Val-Ser-Thr-[S-(3-hydroxypropyl)Cys]-Gly-Val-Ile-Ser-Pro - Leu-Lys was isolated. This corresponds to acrolein alkylation of a cysteine residue in the second tryptic peptide from the NH2 terminal of the alpha-subunit [Anton, D. L., & Kutny, R. (1987) J. Biol. Chem. 262, 2817-2822]. The modified residue derived is from Cys-140 of the proenzyme [Tabor, C. W., & Tabor, H. (1987) J. Biol. Chem. 262, 16037-16040] and lies in the only sequence conserved between rat liver and E. coli S-adenosylmethionine decarboxylase [Pajunen et al. (1988) J. Biol. Chem. 263, 17040-17049]. We suggest that the alkylated Cys residue could have a role in the catalytic mechanism.

1,2-Dichloropropane: investigation of the mechanism of mercapturic acid formation in the rat

1. Three mercapturic acid metabolites were identified in the urine of male and female Fischer 344 rats given 1,2-dichloropropane (DCP) orally (100 mg/kg) or by inhalation exposure (100 ppm, 6 h). 2. These compounds (N-acetyl-S-(2-hydroxypropyl)-L-cysteine, N-acetyl-S-(2-oxopropyl)-L-cysteine and N-acetyl-S-(1-carboxyethyl)-L-cysteine) were isolated from the urine following acidification and extraction with ethyl acetate. The extracts were derivatized with diazomethane and N,O-bis(trimethylsilyl)trifluoroacetamide and analysed by chemical ionization g.l.c.-mass spectrometry. 3. Further mechanistic studies were carried out with the stable isotope-labelled analogue, D6-DCP (105 mg/kg, orally). Analysis of the resulting mass spectra indicated retention of primarily three deuterium atoms in the 2-hydroxypropyl-mercapturic acid formed from D6-DCP. Similar isotope retention was observed for the 2-oxopropyl-mercapturic acid metabolite. 4. These results do not support a sulphonium ion intermediate in the formation of the 2-hydroxypropyl-mercapturic acid metabolite of DCP. Instead, this metabolite is thought to arise via direct oxidation of DCP, either prior to or following conjugation with glutathione.

Disposition of inhaled 1-chloro-2-propanol in F344/N rats

Propylene chlorohydrins, of which 1-chloro-2-propanol (1-CP) is a constituent, used as intermediates in the manufacture of propylene oxide and have been identified as potential air pollutants. The objective of these studies was to determine whether changes in the inhaled exposure concentration would affect the disposition of 1-CP in rats. In addition, experiments were conducted to identify the carbon atom of 1-CP that is metabolized to CO2. Rats were exposed nose-only to [14C]1-CP for 6 hr to 8.3 +/- 1.0 ppm (26.1 +/- 3.2 micrograms/liter air) or 77 +/- 4 ppm (245 +/- 13 micrograms/liter air) (mean +/- SE). There were two major routes of elimination of 14C, urinary and exhalation of CO2, which together accounted for about 80% of the total 14C in excreta and carcass. Half-times for elimination of 14C in urine as 14CO2 were between 3 and 7 hr with no effect of exposure concentration on the elimination half-times for either route. After the end of exposure, kidneys, livers, trachea, and nasal turbinates contained high concentrations of [14C]1-CP equivalents at both exposure concentrations (30-50 nmol 14C/g tissue for the 8 ppm exposure level and 200-350 nmol 14C/g tissue for the 80 ppm exposure level). Elimination of 14C from tissues was biphasic with about 50% of the material in a tissue being rapidly eliminated with a half-time of 1 to 3 hr and the remaining material slowly eliminated with a half-time of 40 to 80 hr. There was no effect of exposure concentration on elimination half-times in tissues. Major metabolites detected in urine and tissues (liver, kidney, and lung) were N-acetyl-S-(hydroxypropyl)cysteine and/or S-(2-hydroxypropyl)-cysteine. Little unmetabolized 1-CP (less than 1%) was detected in analyzed tissues or urine. We propose a metabolic scheme in which the major pathway for metabolism of 1-CP is to CO2 (which is exhaled) and to cysteine conjugates and mercapturic acids that are excreted in the urine. Both carbon-2 and carbon-3 are metabolized in part to CO2.

In vivo metabolism of the cardiovascular toxin, allylamine

Previous evidence from this laboratory demonstrated that allylamine, a known cardiovascular toxin, is metabolized in vitro to acrolein, which has been hypothesized to act as a distal toxin. In this study, 3-hydroxypropylmercapturic acid was isolated and identified by MS, NMR, and 2D-NMR spectroscopy as the sole urinary metabolite of allylamine metabolism in vivo. Parallel experiments showed reduced glutathione (GSH) depletion in several organs (most marked in aorta, blood, and lung), which is consistent with GSH conjugation of the proposed acrolein intermediate. These findings indicate that allylamine was metabolized in vivo to a highly reactive aldehyde which was converted to a mercapturic acid through a GSH conjugation pathway; the exact mechanisms of cellular damage remain unclear.

The metabolism of 1,3-dibromopropane by the rat

1. The metabolism of 1,3-dibromopropane had been investigated in the rat. Two conjugated metabolites have been isolated from the urine and identified as S-(3-hydroxypropyl)cysteine and N-acetyl-S-(3-hydroxypropyl)cysteine. 2. An oxidation product, identified as beta-bromolactic acid, has been isolated as a urinary metabolite. 3. 1,3-dibromopropane is not excreted unchanged in expired air or in the urine. Approx. 15% of the dose (100 mg/kg) is excreted as metabolic products over 50 h and 3.5% as CO2 within 6 h, indicating that oxidation is the main route of detoxication.

1,2-Dichloropropane: metabolism and fate in the rat

1. The metabolism of 1,2-dichloropropane in the rat has been investigated. The major urinary metabolite has been isolated and identified as N-acetyl-S-(2-hydroxypropyl)cysteine. Two minor metabolites of 1,2-dichloropropane have been identified as beta-chlorolactate and N-acetyl-S-(2,3-dihydroxypropyl)cysteine. 2. The fate of 1-chloro-2-hydroxypropane, a proposed intermediate metabolite of 1,2-dichloropropane, has been investigated. Apart from its known urinary metabolite, N-acetyl-S-(2-hydroxypropyl)cysteine, two oxidative metabolites were detected. These were identified as beta-chlorolactaldehyde and beta-chlorolactate. 3. A pathway is proposed for the metabolism and fate of 1,2-dichloropropane in the rat. This accounts for previous observations made for the fate of radioactivity from administration of 1,2-dichloro[1-14C]propane. 4. The microbial and mammalian metabolism of several halogen-containing foreign compounds is discussed.

The fate of S-propylcysteine in the rat

1. The metabolism of S-propylcysteine in the rat has been re-investigated. The previously known major metabolite has been isolated and identified as the mercapturic acid, N-acetyl-S-propylcysteine. 2. Several further metabolites have been isolated from the urine of rats treated with S-propyl[35S]cysteine. These have been identified as S-propylcysteine-S-oxide, N-acetyl-S-(2-hydroxypropyl)cysteine, S-(propylthio)lactate, S-(2,3-dihydroxypropyl)cysteine and N-acetyl-S-(2-carboxyethyl)cysteine. 3. The metabolism of S-(2-hydroxypropyl)-, S-(3-hydroxypropyl)- and S-(2,3-dihydroxypropyl)-[35S]cysteine have been investigated in the rat. The results, integrated with those from the metabolism of S-propyl[35S]cysteine, have enabled the pathways of S-propylcysteine to be deduced. 4. The oxidative metabolism of a number of S-alkyl cysteines is discussed.

The oxidative metabolism of 1-bromopropane in the rat

1. The metabolism of 1-bromopropane in the rat has been re-investigated. The previously known metabolites have been isolated and confirmed as the three mercapturic acids N-acetyl-S-propyl cysteine, N-acetyl-S-propyl cysteine-S-oxide and N-acetyl-S-(2-hydroxypropyl)cysteine. 2. Three further metabolites have been isolated from the urine of rats treated with 4-bromopropane. These have been identified as 3-bromopropionic acid and the mercapturic acids N-acetyl-S-(3-hydroxypropyl)cysteine and N-acetyl-S-(2-carboxyethyl)cysteine. 3. The metabolites of 3-bromopropanol and 3-chloropropanol in the rat have been shown to be the mercapturic acids N-acetyl-S-(3-hydroxypropyl)cysteine and N-acetyl-S-(2-carboxyethyl)cysteine and the corresponding 2-carboxyethyl halide. 4. Studies with 1-bromopropane and the 3-halopropanols in vitro indicate that oxidation of C3 and C2 of 1-bromopropane occurs before conjugation of the alkyl group with glutathione. The implications of these studies are discussed in relation to the mechanism of the biosynthesis of the S-(2-hydroxyalkyl)mercapturic acid metabolites derived from the alkyl halides.

Mechanism of formation of mercapturic acids from (1-bromoethyl)benzene and (2-bromoethyl)benzene in the rat

1. Three hypotheses have been proposed for the mechanism of metabolism of alkylhalides to hydroxy-alkylmercapturic acids, two of which involve the intermediate step of dehydrohalogenation and formation of an epoxide. 2. After injection of (1-bromoethyl)benzene in rat, the only mercapturic acid appearing in the urine was N-acetyl-S-1-phenylethylcysteine. After injecting (2-bromoethyl)benzene in the rat only N-acetyl-S-2-phenylethylcysteine and N-acetyl-S-(2-phenyl-2-hydroxyethyl)cysteine were found in the urine. 3. Since the principal mercapturic acid formed from both styrene and styrene oxide could not be detected in the urine of rats receiving either 1- or 2-bromoethyl benzene, the intermediate formation of styrene or styrene oxide from the arylalkylhalides does not occur.

Dechloriation mechanisms of chlorinated olefins

The dechlorination of chlorinated hydrocarbons has been examined in detail. The reaction is catalyzed by cytochrome P-450 and occurs optimally in the presence of oxygen although some dechlorination may occur under anaerobic conditions. Halothane has been shown to undergo an oxidative dechlorination and a reductive defluorination. Enzymatic attack of chlorinated olefins and hydrocarbons is not on the carbon--halogen bond. Oxidative dechlorination of hydrocarbons is apparently initiated by an attack on the carbon atom and the halogen is then released from the oxidized carbon. The chlorinated olefins, on the other hand, are not easily dechlorinated enzymatically. The chlorines migrate readily across the double bond, therefore, cyclic chloronium ions must occur as intermediates. It is not clear at this time if epoxides are also intermediates in this conversion.

Mercapturic acid formation in the developing rat

1. Young female rats dosed with 1-bromo[1-14C]propane excrete the same metabolites as adult females but in different relative proportions. Propylcysteine was detected as one of the metabolites in rats of all ages studied but represented a higher proportion of the total metabolites excreted in rats aged 5 and 11 days. 2. Hepatic GSH-S-alkytransferase activity was low in females at birth increasing up to the age of about thirty days. No activity was detected in the livers of the males at birth and up to 6 days of age; thereafter the level of activity increased up to 35-40 days. 3. Propylcysteine was excreted as prophylmercapturic acid and propylmercapturic acid sulphoxide by female rats of all ages. The amount of sulphoxide excreted relative to mercapturic acid excreted was higher in rats up to the age of 16 days than in older animals.

The metabolism of 3-chloro,- 3-bromo- and 3-iodoprpan-1,2-diol in rats and mice

1. The metabolism of the 3-halopropan-1,2-diols (alpha-halohydrins) has been investigated in rats and mice. Apart from 3-chloropropan-1,2-diol (I), of which some 10% is excreted unchanged by both species, the compounds are completely degraded following intraperitoneal administration. 2. The alpha-halohydrins are detoxicated by conjugation with glutathione and produce two urinary metabolites, isolated and identified as S-(2,3-dihydroxypropyl)cysteine (VII) and the corresponding mercapturic acid N-acetyl-S-(2,3-dihydroxypropyl)cysteine (VIII). 3. When incubated with rat liver supernatant, the compounds do not conjugate with glutathione and their general chemical reactivity suggests that they react via a common intermediate proposed to be glycidol (2,3-epoxypropanol, IV). As the epoxide produces the same urinary metabolites as the alpha-halo-hydrins, and conjugates with glutathione either with or without liver supernatant to form the primary metabolite S-(2,3-dihydroxypropyl)glutathione (VI), glycidol is also proposed to be the reactive intermediate in vivo. 4. The role of epoxides in intermediary metabolism is discussed.

Biosynthesis of mercapturic acids from allyl alcohol, allyl esters and acrolein

1. 3-Hydroxypropylmercapturic acid, i.e. N-acetyl-S-(3-hydroxypropyl)-l-cysteine, was isolated, as its dicyclohexylammonium salt, from the urine of rats after the subcutaneous injection of each of the following compounds: allyl alcohol, allyl formate, allyl propionate, allyl nitrate, acrolein and S-(3-hydroxypropyl)-l-cysteine. 2. Allylmercapturic acid, i.e. N-acetyl-S-allyl-l-cysteine, was isolated from the urine of rats after the subcutaneous injection of each of the following compounds: triallyl phosphate, sodium allyl sulphate and allyl nitrate. The sulphoxide of allylmercapturic acid was detected in the urine excreted by these rats. 3. 3-Hydroxypropylmercapturic acid was identified by g.l.c. as a metabolite of allyl acetate, allyl stearate, allyl benzoate, diallyl phthalate, allyl nitrite, triallyl phosphate and sodium allyl sulphate. 4. S-(3-Hydroxypropyl)-l-cysteine was detected in the bile of a rat dosed with allyl acetate.

Some metabolites of 1-bromobutane in the rabbit and the rat

1. Rabbits and rats dosed with 1-bromobutane excrete in urine, in addition to butylmercapturic acid, (2-hydroxybutyl)mercapturic acid, (3-hydroxybutyl)mercapturic acid and 3-(butylthio)lactic acid. 2. Although both species excrete both the hydroxybutylmercapturic acids, only traces of the 2-isomer are excreted by the rabbit. The 3-isomer has been isolated from rabbit urine as the dicyclohexylammonium salt. 3. 3-(Butylthio)lactic acid is formed more readily in the rabbit; only traces are excreted by the rat. 4. Traces of the sulphoxide of butylmercapturic acid have been found in rat urine but not in rabbit urine. 5. In the rabbit about 14% and in the rat about 22% of the dose of 1-bromobutane is excreted in the form of the hydroxymercapturic acids. 6. Slices of rat liver incubated with S-butylcysteine or butylmercapturic acid form both (2-hydroxybutyl)mercapturic acid and (3-hydroxybutyl)mercapturic acid, but only the 3-hydroxy acid is formed by slices of rabbit liver. 7. S-Butylglutathione, S-butylcysteinylglycine and S-butylcysteine are excreted in bile by rats dosed with 1-bromobutane. 8. Rabbits and rats dosed with 1,2-epoxybutane excrete (2-hydroxybutyl)mercapturic acid to the extent of about 4% and 11% of the dose respectively. 9. The following have been synthesized: N-acetyl-S-(2-hydroxybutyl)-l-cysteine [(2-hydroxybutyl)mercapturic acid] and N-acetyl-S-(3-hydroxybutyl)-l-cysteine [(3-hydroxybutyl)mercapturic acid] isolated as dicyclohexylammonium salts, N-toluene-p-sulphonyl-S-(2-hydroxybutyl)-l-cysteine, S-butylglutathione and N-acetyl-S-butylcysteinyl-glycine ethyl ester.

The metabolism of S-methyl-L-cysteine

1. Methylsulphinylacetic acid, 2-hydroxy-3-methylsulphinylpropionic acid and methylmercapturic acid sulphoxide (N-acetyl-S-methyl-l-cysteine S-oxide) were isolated as their dicyclohexylammonium salts from the urine of rats after they had been dosed with S-methyl-l-cysteine. 2. A fourth sulphoxide was isolated but not identified. 3. The excretion of sulphate in the urine of rats dosed with S-methyl-l-cysteine was measured. 4. The metabolism of S-methyl-l-cysteine by the hamster and guinea pig was examined chromatographically. 5. The preparation of the following compounds is reported: (-)-dicyclohexylammonium methyl-mercapturate sulphoxide; the dicyclohexylammonium salts of the optically inactive forms of 2-hydroxy-3-methylthiopropionic acid, 2-hydroxy-3-methyl-sulphinylpropionic acid and methylsulphinylacetic acid.