Cellular metabolism of arsenocholine.

The biotransformation of arsenocholine and arsenobetaine, which are organic arsenic compounds present in certain aquatic organisms, has been studied in vitro using synthetic reference substances. Incubation of arsenocholine with different liver cell fractions showed arsenocholine to be biotransformed only in presence of the mitochondrial fraction. The biotransformation products were arsenobetaine aldehyde, arsenobetaine, trimethylarsine oxide and trimethylarsine. Arsenobetaine was the major metabolite and it was formed via arsenobetaine aldehyde. Trimethylarsine oxide was formed via a side reaction from arsenobetaine aldehyde. Further reduction of trimethylarsine oxide, produced trimethylarsine. In vitro studies of arsenobetaine, did not show any formation of trimethylarsine oxide or trimethylarsine. Furthermore, cytotoxicity of arsenobetaine or arsenocholine in isolated hepatocytes was not observed.

Biotransformation of dimethylarsinic acid in mouse, hamster and man.

The metabolism of dimethylarsinic acid (DMA) a common pesticide and the main metabolite of inorganic arsenic in mammals, has been studied in mice, hamsters and man. Mice and hamsters were administered a single dose of 74As-DMA (40 mg As/kg body weight) orally, while a human subject ingested DMA corresponding to 0.1 mg As/kg body weight. Ion exchange chromatography, paper electrophoresis, thin layer chromatography as well as arsine generation--gas chromatography combined with atomic absorption spectrophotometry or mass spectrometry were used to characterize the arsenic metabolites in urine and feces collected over 48 hours after treatment. In mice and hamsters 3.5% and 6.4% of the dose, respectively, were excreted in urine in the form of trimethylarsine oxide (TMAO). No TMAO was found in feces. A DMA-complex was detected in urine and feces. It amounted to about 13% of the dose in mice and 15% in hamsters. About 80-85% of the dose was eliminated in urine and feces in the form of unmetabolized DMA. No demethylation of DMA to inorganic arsenic was observed. In man, about 4% of the dose was excreted in urine as TMAO and about 80% as DMA.

Characterization and mechanism of formation of reactive products formed during peroxidase-catalyzed oxidation of p-phenetidine. Trapping of reactive species by reduced glutathione and butylated hydroxyanisole.

OFF products of horseradish peroxidase (EC 1.11.1.7)-catalyzed oxidation of p-phenetidine were isolated and reactive species were trapped with reduced glutathione (GSH) and butylated hydroxyanisole (BHA). When BHA was added to a reaction mixture after 5 min, subsequent TLC and mass spectrometric analysis revealed the formation of an adduct of BHA and 4-(ethoxyphenyl)-p-benzoquinone diimine (A). The diimine derivative (A) was unstable and its expected degradation products, 4-(ethoxyphenyl)-p-benzoquinone imine (B) and ammonia, were recovered from the reaction in stoichiometric amounts. Ethanol was an early product of the reaction presumably resulting from radical coupling reactions and its formation agreed with the combined production of A and B, suggesting that this was its sole route of formation. The addition of GSH to a reaction at various times and subsequent TLC and high performance liquid chromatographic analysis revealed the presence of at least seven conjugates. Two conjugates were identified by fast atom bombardment mass spectrometry, one as a mono-GSH conjugate of A and another as a mono-GSH conjugate of B. When purified [14C]B was mixed with [3H]GSH, three conjugates were isolated by high performance liquid chromatography, two of which were tentatively identified as di-GSH conjugates. The conjugates isolated existed in both oxidized and reduced forms which could be easily interconverted by redox processes. The production of such reactive species and their conjugates in vivo may be a useful indicator of peroxidase-catalyzed metabolism.

Fast atom bombardment mass spectra of mercapturic acid-pathway metabolites of propachlor (2-chloro-N-isopropylacetanilide).

1. Fast atom bombardment (FAB) mass spectra, obtained from mercapturic acid-pathway metabolites (glutathione-, mercapturic acid- and cysteine-conjugates, and a sulphoxide of the mercapturate) of propachlor, are presented. 2. Each underivatized mercapturic acid-pathway metabolite of propachlor gave a FAB mass spectrum containing an (M + H)+ ion (7-100% relative intensity), an (M + Na)+ ion and characteristic fragment ions. 3. The advantage of the FAB technique in obtaining mass spectra of these mercapturic acid-pathway metabolites of propachlor and other xenobiotics is discussed. 4. Ions in the FAB spectra resulting from sample fragment/glycerol interactions were characterized.

Negative ion mass spectrometry of phenothiazines.

Mass spectra of a number of phenothiazines have been obtained by negative chemical ionization and compared with the corresponding mass spectra by positive chemical ionization and conventional electron impact. NH3, CH4, and N2O were used as reagent gases for negative chemical ionization, iso-C4H10 and CH4 for positive chemical ionization. The negative chemical ionization technique gives significant information regarding the molecular weight and the ring system of this group of compounds. As a complementary method to positive electron impact, negative chemical ionization is more informative than positive chemical ionization. Phenothiazines with two, but not three, methylene groups between the ring and the sidechain nitrogens given an intense rearrangement anion due to loss of the substituted nitrogen in the sidechain and two additional hydrogens. A 5-membered ring structure is postulated for this anion, which is formed with the reagents NH3 and CH4. but not with N2O. Apart from this peculiarity, the negative chemical ionization spectra are easy to understand. With NH3 as reagent, the anions representing the ring system and [M -- 1]- dominate the anion current. With CH4, both quasimolecular ions [M + 1]- and [M -- 1]- can be detected along with the much more intense ring anion. The reagent N2O yields cluster anions by oxidation of the ring and the molecule with the negatively charged oxygen formed in the ion source.

Negative-ion mass spectrometry of amphetamine congeners.

Negative-ion chemical ionization mass spectrometry with a conventional combined gas chromatograph-mass spectrometer has been used for the analysis of amphetamine-like compounds. Ammonia was used as the reagent gas, which gives rise to few but specific sample-fragment ions, such as (M--1)- as the base peak, m/z 91, and a smaller peak corresponding to the end part of the side chain. Five reference compounds and a urine sample from an overdose case were analyzed. Comparative positive-ion chemical ionization reference spectra were also recorded.

Variations in human metabolism of methaqualone given in therapeutic doses and in overdose cases studied by gas chromatography-mass spectrometry.

The individual variations in human metabolism of methaqualone were studied after oral administration of therapeutic doses. The effect of antabuse on the drug metabolism as well as metabolites in some autopsy cases were also studied. The metabolites were identified using the GC-MS computer technique, and the relative amounts of the indicated metabolites were calculated from the sum of the peak heights in the gas chromatogram. The results show that the individual variations were small in the cases of therapeutic doses and that antabuse did not interact with the metabolism of methaqualone. Large amounts of one single metabolite 2-methyl-3-[phenyl(2'-methyl-4-hydroxy)]-4(3H)-quinazolinone was found in the bile from the two autopsy cases where the bile was also collected.