Estrogen mercapturic acids in the adult male rat

N-Acetylcysteine derivatives of catechol estrogens have been isolated from the urine of adult male hooded rats with ligated bile ducts, following injection of [4-¹⁴C]2-hydroxyestradiol-17β and of [4-¹⁴C]estradiol-17β-By application of double isotope methods previously described, it was shown that 2-hydroxyestradiol-17β was converted into mercapturic acids in a yield of 6–8%, confirming two previous experiments with bile duct cannulated rats, and that estradiol-17β was converted into mercapturic acids to the extent of 3–6%. Since these figures are small, and since it has been shown that in two women estrogen mercapturic acids were not formed, it appears that this class of compound will not provide an answer to the problem of unidentified water-soluble metabolites of the estrogens.     

Renal transtubular transport of mercapturic acid in vivo

When $\text{S-}\text{benzyl}\text{-N-}\text{acetyl}\text{-}\text{l}\text{-[}\text{U}\text{-}{}^{14}\text{C}\text{]}\text{cysteine}$, a mercapturic acid, was administered to rats intravenously, the plasma level of radioactivity decreased very rapidly with a concomitant increase in the renal level of radioactivity. The renal radioactivity reached its maximum within 2 min and then decreased rapidly with concomitant appearance of the radioactive mercapturic acid in the urine. Bilateral ligation of the ureters resulted in only a slight decrease in the rate of disappearance of mercapturic acid from the plasma, while bilateral nephrectomy caused a marked retardation of its clearance from the plasma. Intravenous administration of probenecid, a well known inhibitor of a renal transbular transport system for organic acids, caused a significant retardation of mercapturate clearance from the plasma in both of the control and ureter-ligated animals. The renal accumulation of this mercapturic acid as well as its excretion into urine was inhibited by probenecid.All these data suggested that a mercapturic acid in the plasma was preferentially taken up by renal tubule cells from the basolateral side of plasma membranes via the probenecid-sensitive transtubular transport system and then excreted rapidly into the lumenal space. This transtubular transport of a mercapturic acid seems to constitute an important process in the hepato-renal cooperation in the mercapturic acid biosynthesis in vivo.     

Specificity of a particulate rat renal peptidase and its localization along with other enzymes of mercapturic acid synthesis

Renal processing of S-derivatized glutathiones to mercapturic acids requires the participation of three enzymatic activities: γ-glutamyl hydrolase or transpeptidase, a peptidase which is capable of hydrolyzing S-derivatized cysteinylglycine, and an N-acetyltransferase. A particulate peptidase, which was assayed with S-benzylcysteine-p-nitroanilide, was found to be localized along with γ-glutamyltranspeptidase and N-acetyltransferase in the outer stripe region of the renal medulla. This localization suggests that these three activities may be contained primarily in the proximal straight tubules. Results of differential and isopycnic centrifugation indicate that the particulate peptidase is contained along with γ-glutamyltranspeptidase in the brush border membranes while the N-acetyltransferase is probably associated with the endoplasmic reticulum. The partially purified peptidase (200-fold) exhibits a broad substrate specificity. It has greater activity with reduced than oxidized cysteinylglycine, but S-derivatized substrates are hydrolyzed even faster. Comparison of its activity with various substrates indicates that it prefers peptides with a hydrophobic N-terminal amino acid and that it may require a free amino group. Heat-inactivation studies suggest that all of these activities are attributable to a single enzyme. These results suggest that this peptidase may participate along with γ-glutamyltranspeptidase and an N-acetyltransferase in the conversion of glutathione conjugates to mercapturic acids.     

Formation of mercapturic acids in rats after the administration of aralkyl esters

1. Benzylmercapturic acid and hippuric acid were isolated from the urine of rats that had been injected subcutaneously with benzyl acetate. 2. 1-Menaphthylmercapturic acid and 1-naphthoic acid were isolated from the urine of rats after the subcutaneous injection of each of the following compounds: 1-menaphthyl alcohol and its acetate, propionate, butyrate and benzoate esters. 3. A quantitative method for determining 1-menaphthylmercapturic acid in urine was developed and used to measure the excretion of this compound in the urine of rats in the 4-day period after the subcutaneous injection of 1-menaphthyl alcohol and its acetate, propionate, butyrate and benzoate esters. 4. Chromatographic evidence was obtained for the presence of S-(1-menaphthyl)glutathione and S-(1-menaphthyl)-l-cysteine in bile collected from rats with cannulated bile ducts after the animals had been injected subcutaneously with each of the following compounds: S-(1-menaphthyl)glutathione, 1-menaphthyl acetate, propionate and butyrate. 5. Benzylmercapturic acid and 1-menaphthylmercapturic acid were isolated from the urine of rats that had been injected with sodium benzyl sulphate and sodium 1-menaphthyl sulphate respectively.     

Enzymes of mercapturic acid production in rat mammary gland.

1. The enzymes glutathione S-transferase, gamma-glutamyl peptidyltransferase and dipeptidase, which participate in the detoxification pathway through mercapturic acid production, were measured in rat mammary gland during pregnancy and lactation. 2. Mammary-gland concentration of reduced glutathione showed, concomitantly with the enzyme activities, a significant increase during lactation. 3. The mammary-gland glutathione S-transferase exhibits characteristics quite similar to those described for the liver and kidney enzymes with respect to substrates, isoenzymes, molecular weight and probenecid and bilirubin inhibition. 4. In view of these similarities, mammary-gland glutathione S-transferase may play the same role as a cytoplasmic organic-anion receptor proposed for the hepatic enzyme. It may also represent a detoxification pathway for protecting the mammary tissue during the lactogenic cycle.     

Sensitive gas chromatographic method for determination of mercapturic acids in human urine

A method was developed for sensitive determination of the specific benzene metabolite S-phenylmercapturic acid and the corresponding toluene metabolite S-benzylmercapturic acid in human urine for non-occupational and occupational exposure. The sample preparation procedure consists of liquid extraction of urine samples followed by precolumn derivatization and a clean-up by normal-phase HPLC. Determination of analytes occurs by gas chromatography with electron-capture detection. With this highly sensitive method (detection limits 60 and 65 ng/l, respectively) urinary S-phenylmercapturic and S-benzylmercapturic acid concentrations for non-occupationally exposed persons (e.g. non-smokers) can be measured precisely in one chromatographic run. Validation of the method occured by comparison with a HPLC method we have published recently.     

Determination of the major mercapturic acids of acrylamide and glycidamide in human urine by LC-ESI-MS/MS

We developed a LC-MS/MS method for the quantitative determination of the mercapturic acid (MA) metabolites of acrylamide (AA) AAMA and of its oxidative metabolite glycidamide (GA) GAMA in urine samples from the general population. The method requires 4 mL of urine which is solid phase extracted prior to LC-MS/MS analysis. The metabolites are detected by ESI-tandem mass spectrometry in negative ionisation mode and quantified by isotope dilution. Detection limits ranged down to 1.5 microg/L urine for both AAMA and GAMA. The imprecision expressed as R.S.D. lay between 2% and 6% for both analytes (intra- and inter-assay). First results on a small group of 29 persons out of the general population ranged from 5 to 338 microg/L AAMA and 相似文献   

Phosphorus-containing isothiocyanate-derived mercapturic acids as a useful alternative for parental isothiocyanates in experimental oncology

A series of phosphonates, phosphinates and phosphine oxides isothiocyanate-derived mercapturic acids were synthesized. A temperature dependence dynamic proton decoupled ³¹P NMR studies indicated that in most cases the compounds were obtained as a mixture of rotamers. Moreover, biologically relevant reversibility of mercapturic acids synthesis from the parental isothiocyanates was confirmed. All compounds were evaluated as highly active antiproliferative agents in vitro in human colon cancer cell lines (LoVo and its doxorubicin-resistant subline LoVo/DX). The cell cycle progression and caspase-3 activity analyses revealed compounds moderate activity as apoptosis inducers and their poor influence on cell cycle progression in the LoVo cells. Our results confirm that isothiocyanate-derived mercapturic acids present a reasonable alternative for the parental compounds, and can replace them in the future studies on isothiocyanates potential as anticancer agents.     

Hemoglobin adducts and urinary mercapturic acids in rats as biological indicators of butadiene exposure

Binding of 1,2-epoxy-3-butene, the primary metabolite of butadiene, to hemoglobin (Hb) and excretion of its mercapturic acid in urine were studies as potential indicators of butadiene exposure. Four groups of Wistar rats were exposed to butadiene at 0, 250, 500 and 1000 ppm 6 h/day, 5 days/week, during 2 weeks. Blood was collected at the end of exposure and 17 days later for analysis of hemoglobin adducts and adduct stability. Urine was collected each day during exposure (afternoon samples) and in between exposures (morning samples). Adducts of 1,2-epoxy-3-butene to N-terminal valine in Hb were measured using the N-alkyl Edman procedure and GC/MS of the thiohydantoin derivatives. The corresponding mercapturic acid was analysed, after deacetylation, through derivatization with phthaldialdehyde and HPLC with fluorescence detection. The Hb adducts proved to be stable and are therefore useful for dosimetry of long-term exposure to butadiene. The adduct levels increased linearly with exposure dose up to 1000 ppm (3 nmol/g Hb at 1000 ppm). The increase with exposure dose of the mercapturic acid concentration in urine was also compatible with a linear does response up to 1000 ppm. The sensitivity of both analytical methods needs to be improved for their application to human samples.     

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.