Some observations on the source of cysteine for mercapturic acid formation

1-bromoalkanes as new potent nontoxic glutathione depletors in isolated rat hepatocytes

The effect of 1-bromlalkanes on intracellular glutathione (GSH) was studied in freshly isolated rat hepatocytes. Treatment of cells with bromoalkanes depleted cellular GSH levels without causing cytotoxicity. The extent of GSH depletion was directly proportional to the concentration and increasing chain length of 1-bromoalkanes (C2-C7). Bromoheptane (100 microM) depleted GSH by 87% in 30 mins which remained depleted for the 4 hr study period without causing cytotoxicity. A 30 fold higher concentration of bromoheptane was required before cytotoxicity ensued. Bromoheptane would therefore be particularly useful for studying the role of GSH in modulating xenobiotic cytotoxicity.

The comparative metabolism of 2-bromoethanol and ethylene oxide in the rat

1. The metabolism of 2-bromo[U-14C]ethanol an [U-14C]ethylene oxide has been studied in the rat. 2. As both compounds give rise to similar amounts of two urinary metabolites, identified as S-(2-hydroxyethyl)cysteine and N-acetyl-S-(2-hydroxyethyl)cysteine, it is proposed that 2-bromoethanol is converted into ethylene oxide in vivo. 3. A minor metabolite of 2-bromoethanol has been identified as N-acetyl-S-(carboxymethyl)cysteine. 4. The metabolism of bromoacetaldehyde and bromoacetic acid has been investigated; N-acetyl-S-(carboxymethyl)cysteine had been shown to be a common urinary metabolite. 5. An oxidative metabolic pathway is proposed for 2-bromoethanol, via bromoacetaldehyde and bromoacetic acid, to N-acetyl-S-(carboxymethyl)cysteine.

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 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.

The metabolism of the soil fumigant 1,2-dibromo-3-chloropropane in the rat

The soil fumigant 1,2-dibromo-3-chloropropane (I) undergoes hydrolysis in the rat to a series of epoxide metabolites. Alkylation of glutathione by these epoxides produces 2 urinary metabolites identified as the mercapturic acids VI (R=COCH3) and VII (R-COCH3). Hydrolysis of the epoxides produces the male antifertility agents alpha-chlorohydrin (IX, X-Cl) and alpha-bromohydrin (IX, X-Br) which are oxidatively metabolized to oxalic acid (XII), thus causing renal damage. These metabolic pathways can explain the toxic nature of the fumigant as a carcinogen, a male chemosterilant and as an agent causing kidney damage.

Epoxides as obligatory intermediates in the metabolism of alpha-halohydrins

1. The metabolism of several dihalopropanols has been studied in the rat. Irrespective of their structure, each compound produced the same two mercapturic acids, excreted as urinary metabolites. 2. The mercapturic acid metabolites of the dihalopropanols were identified as N-acetyl-S-(2,3-dihydroxypropyl)cysteine and N,N'-bis-acetyl-S,S'-(1,3-bis-cysteinyl)propan-2-ol. Depending on the halogen present, each dihalopropanol produced beta-chlorolactate or beta-bromolactate as oxidative metabolites. 3. From the metabolic pathway of these compounds, it is inferred that an epoxide is an intermediate in their metabolism. 4. The metabolism of 2-chloropropane-1,3-diol has been investigated in the rat and the isolation of one mercapturic acid, N-acetyl-S-(2,3-dihydroxypropyl)cysteine, confirms that an epoxide intermediate is involved.

The metabolism of 3-amino-1-chloropropan-2-ol in relation to its antifertility activity in male rats

1. The metabolism of 3-amino[36Cl]chloropropan-2-ol (III) was studied in male rats. Three urinary metabolites were isolated and identified as alpha-chlorohydrin (I), beta-chlorolactic acid (V) and oxalic acid (VI). Much of the administered aminochloropropanol was excreted unchanged in the urine; 63% within 72 h, 75% over 250 h. 2. Monoamine oxidase is capable of converting aminochloropropanol to beta-chlorolactaldehyde (IV) which, by processes of either reduction or oxidation, suggests that the metabolic pathway is IV leads to I and IV leads to V leads to VI. 3. As assessed by the diuretic activities of the isomers of aminochloropropanol, oxalate appears to be produced by the (+)-isomer but not by the (-)-isomer. A difference in metabolic rate or route of the isomers may account for their differing physiological activities. 4. (+)- and (-)-aminochloropropanol exhibited identical in vitro inhibitory activities on the glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase and triosephosphate isomerase, and were substrates for monoamine oxidase to equivalent extents.

The oxidative metabolism of alpha-chlorohydrin in the male rat and the formation of spermatocoeles

1. The oxidative metabolism of [3-36C]chloropropan-1,2-diol (alpha-chlorohydrin, I) was studied in male rats. Two metabolites were isolated and identified as beta-chlorolactic acid (IV) and oxalic acid (V). 2. Neither alpha-chlorohydrin nor beta-chlorolactate was concentrated in any tissue. Traces of an intermediate metabolite, beta-chlorolactaldehyde (III) were detected in the urine within 4 h of administration. Studies in vitro indicated that the metabolic pathway is: alpha-chlorohydrin leads to beta-chlorolactaldehyde leads to beta-chlorolactic acid. 3. A comparative study of the metabolism of 36Cl- and 14C-beta-chlorolactate showed that oxalate was produced slowly and, as calcium oxalate, caused a type of renal glomerular nephritis. This pathological condition is responsible for the diuretic action of both alpha-chlorohydrin and beta-chlorolactate and, in higher doses, for their toxicities. 4. The role of oxalate, as a metabolite of alpha-chlorohydrin and of a number of related compounds, in inducing the formation of spermatocoeles in the male rat reproductive tract is discussed.

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.