Hepatic metabolism of N-hydroxy-N-methyl-4-aminoazobenzene and other N-hydroxy arylamines to reactive sulfuric acid esters

Hepatic cytosols catalyzed a 3'-phosphoadenosine 5'-phosphosulfate (PAPS)-dependent O-sulfonation of N-hydroxy-N-methyl-4-aminoazobenzene (N-HO-MAB) and of several other N-hydroxy arylamines. The presumed product from N-HO-MAB, N-methyl-4-aminoazobenzene-N-sulfate, reacted with added guanosine to yield N-(guanosin-8-yl)-N-methyl-4-aminoazobenzene, with methionine to form a sulfonium derivative that decomposed to yield 3-methylmercapto-N-methyl-4-aminoazobenzene, and with ribosomal RNA to give a bound derivative. N-Methyl-4-aminoazobenzene was converted to N-(guanosin-8-yl)-N-methyl-4-aminoazobenzene in concerted N-oxidation and O-sulfonation reactions conducted aerobically with a fortified 10,000 X g rat liver supernatant. In the absence of an added nucleophile, metabolically formed N-methyl-4-aminoazobenzene-N-sulfate (or the nitrenium ion from this unstable ester) was reduced by N-HO-MAB to form N-methyl-4-aminoazobenzene; the N-HO-MAB was oxidized, probably through a nitrone intermediate, to yield products that included N-hydroxy-4-aminoazobenzene and formaldehyde. An analogous reaction was noted between N-benzoyloxy-N-methyl-4-aminoazobenzene and N-HO-MAB in the absence of cytosol and PAPS. Hepatic N-HO-MAB sulfotransferase activities were in the order: male rat greater than female rat, male rabbit, male guinea pig, male mouse greater than male hamster. Male rat kidney and small intestine cytosols had low activities; the other tissues studied had little or no activity. Hepatic sulfotransferase activities for N-HO-MAB and N-hydroxy-N-acetyl-2-aminofluorene displayed different pH optima and inhibitor and activator responses. The rates of PAPS-dependent rat liver cytosol-catalyzed esterification of N-hydroxy-N-ethyl-4-aminoazobenzene, N-hydroxy-4-aminoazobenzene, and N-hydroxy-1- and 2-naphthylamine were 20 to 50% of that for N-HO-MAB. Activities for trans-N-hydroxy-4-aminostilbene, N-hydroxy-2-aminofluorene, N-hydroxyaniline, and N-hydroxy-N-methyl-N-benzylamine were not detected. No microsomal reduced nicotinamide adenine dinucleotide-dependent reduction or reduced nicotinamide adenine dinucleotide phosphate-dependent oxidation or cytosolic transferase reactions for N-HO-MAB, except the above-described PAPS-dependent reaction, were detected in rat liver.

Microsomal N-oxidation of the hepatocarcinogen N-methyl-4-aminoazobenzene and the reactivity of N-hydroxy-N-methyl-4-aminoazobenzene

The N-oxidation of the hepatocarcinogen N-methyl-4-aminoazobenzene (MAB) was catalyzed by hepatic microsomes in a reduced pyridine nucleotide- and oxygen-dependent reaction. The initial N-oxidation product, N-hydroxy-N-methyl-4-aminoazobenzene (N-HO-MAB), was readily oxidized to a second product that yielded N-hydroxy-4-aminoazobenzene upon subsequent acid treatment. The secondary N-oxidation product may be formed nonenzymatically and is presumed to be N-HO-MAB N-oxide or its dehydrated derivative, N-(p-phenylazophenyl)nitrone. Under the same conditions, MAB was also oxidatively N-dealkylated to 4-aminoazobenzene, which was N-oxidized to N-hydroxy-4-aminoazobenzene. Unlike the latter reactions, the microsomal N-oxidation of MAB was independent of cytochrome P-450, as shown by its lack of sensitivity to inhibition by 2-[(2,4-dichloro-6-phenyl)phenoxy]ethylamine and its inability to utilize cumene hydroperoxide in place of reduced pyridine nucleotides and oxygen. The N-oxidation of MAB was also catalyzed by the purified microsomal flavoprotein mixed-function amine oxidase of Ziegler et al. The noncarcinogenic dye N-ethyl-4-aminoazobenzene was metabolized similarly to MAB. For male animals the hepatic levels of MAB N-oxidase activity were in the order: rat greater than hamster, guinea pig greater than mouse, rabbit. Little or no MAB N-oxidase activity was present in several extrahepatic rat tissues. N-HO-MAB, N-hydroxy-N-ethyl-4-aminoazobenzene, and N-hydroxy-4-aminoazobenzene catalyzed the aerobic oxidation of cysteine and glutathione. These hydroxylamines also bound covalently to proteins. The binding of N-HO-MAB with nucleic acids was only 3 to 6% that observed with serum albumin. Under anhydrous conditions the nitrone generated aerobically from N-HO-MAB reacted with carbon-carbon or carbon-nitrogen double bonds, or both, in fatty acids, retinol, purines, and pyrimidines to yield isoxazolidine and/or oxadiazolidine addition products. The nitrone from N-hydroxy-N-ethyl-4-aminoazobenzene was much less reactive under these conditions. Syntheses of N-HO-MAB and N-hydroxy-N-ethyl-4-aminoazobenzene are reported.

Mutagenicity of carcinogenic azo dyes and their derivatives

The mutagenicity of N,N-dimethyl-4-aminoazobenzene and N-methyl-4-aminoazobenzene and their derivatives was shown on Salmonella typhimurium TA100 and TA98. S-9 Mix, obtained from rat liver after injection of polychlorinated biphenyl, was abligatory for their mutagenic action. N-Acetoxy-N-methyl-4-aminoazobenzene and N-benzoyloxy-N-methyl-4-aminoazobenzene and their 4'-methoxycarbonyl derivatives were also mutagenic on TA100 and TA98 and did not require metabolic activation by S-9 Mix. It is suggested that the carcinogenic effects of azo dyes may involve modification of DNA.

Ontogeny of multiple forms of monoamine oxidase in mouse brain

MAO activities in mouse brain responsible for deamination of serotonin (5-HT) and p-dimethylaminobenzylamine (DAB) were found to follow different postnatal developmental patterns. MAO activity which deaminated 5-HT reached adult levels 15 days after birth. At this age the capacity of brain to deaminate DAB was only 50% of adult levels and did not develop fully until after the 45th postnatal day. Inhibitor studies with Deprenil and clorgyline indicated that the deamination of the two substrates was due to different forms of MAO and that these forms were similar to type A and type B MAO described previously in rat brain.

Nacroautoradiographic assays in pregnant mice and their fetuses given N-acetyl-9-[14C]-2-aminofluorene and p-[14C]-dimethylaminoazobenzene

The distribution of radioactivity from N-acetyl-9-[114C]-2-aminofluorene and p-[14C]-dimethylaminoazobenzene administered i.v. or p.o. to 18-day-pregnant mice was observed by means of autoradiography of longitudinal section of the whole mouse. Radioactive substances derived from these carcinogens passed through the placenta and were distributed in the fetal organs including the kidney and intestine. Column, thin-layer, and paper chromatography revealed the presence, in while fetuses as well as in maternal livers, of N-acety-9-[14C]-2-aminofluorene. N-hydroxy-N-acetyl-9-[14C]-2-aminofluorene, ring-hydroxy-N-acetyl-9-[14C]-2-aminofluorene, and p-[14C]-dimethylaminoazobenzene. These results establish that N-acetyl-9-[14C]-2-aminofluorene and [14C]-p-dimethylaminoazobenzene are transported, metabolized, and excreted in the mouse fetus.

4-Nitrobenzoic acid reductase of Ascaris lumbricoides var suum. Substrate specificity and reaction products

1. The substrate specificity of nitro-reductase from Ascaris lumbricoides varsum was determined. This enzyme reduced nitrobenzene, 4-nitrohippuric acid and the isomers of nitrophenol, nitroanisole, nitrobenzoic acid, nitrobenzaldehyde and nitrobenzyl alcohol. The same enzyme preparation reduced azobenzene, 4-dimethylaminoazobenzene and 1,2-dimethyl-4-(4-carboxyphenylazo)-5-hydroxybenzene. Nitrobenzaldehyde isomers were not reduced to the alcohols. 2. The products of nitro- and azo-reduction were the corresponding amines, no hydroxylamino or hydrazo compounds were detected. 3. The pH optima and cofactor requirements were the same for both azo- and nitro-reduction and neither reaction was inhibited by oxygen. 4. Ammonium sulphate fractionation failed to separate azo- and nitro-reductase activities. The molecular weight of both azo- and nitro-reductase was about 130 000.

Comparative effect of phenobarbital and 3-methylcholanthrene on azo dye metabolism in rat liver. II. In vivo binding of metabolites to cellular macromolecules

The binding of 4-dimethylaminoazobenzene (DAB) metabolites to liver total protein and nuclear DNA was studied in rats pretreated with phenobarbital (PB) or 3-methylcholanthrene (3-MC), then fed with a (-14C)DAB diet (0.06%) for 3 days. Three consecutive injections of PB (80mg-kg) led to a 50% decrease of DAB metabolites bound to total protein and nuclear DNA. A single injection of 3-MC(20 mg-kg) roughly doubled the amount of metabolites bound to nuclear DNA but did not modify those bound to protein. When given in the diet (0.005%) for 8 days before the (-14C)-DAB diet, 3-MC did not change the amount of DAB metabolites bound either to protein, or to DNA. The opposite effect of PB and 3-MC injections on azodye binding to cellular constituents might be relevant to the action of these drugs on carcinogenesis. Moreover the route of 3-MC administration might be meaningful since DAB metabolite binding to DNA was only increased by intraperitoneal injection.

Comparative effect of phenobarbital and 3-methyl-cholanthrene on azodye metabolism in rat liver. I. In vitro studies on detoxication and activation processes

The effect of phenobarbital (PB) and 3-methylcholanthrene (3-MC) administration on detoxication and activation of the carcinogenic azodye 4-dimethyl-aminoazobenzene (DAB) was studies in rat liver microsomes. Azoreductase activity and in vitro DAB metabolite binding to calf thymus DNA and microsomal protein were simultaneously determined. Pretreatment of rats with 3 daily injections of PB (80 mg/kg) did not significantly modify azoreductase activity by increased DAB metabolite binding to DNA (+ 67%) and to protein (+ 123%). The effect of 3-MC differed according to the route of administration. When it was given intraperitoneally (1 times 20 mg/kg)azoreductase was not modified and DAB metabolite binding to DNA and to protein was eight-fold enhance. After continuous administration of 3-MC in the diet (3.0 MG/KG/DAY)AZOREDUCTASE ACTIVITY WAS DECREASED (MINUS 40%), DAB metabolite binding to DNA was unchanged and DAB metabolite binding to protein tripled. Thus the balance between the formation of DAB metabolites bound to DNA and azoreduction led to an increased activation/reduction ratio only by 3-MC injection. In every case, the formation of DAB metabolites bound to protein was significantly increased as compared with detoxication. Different effects of PB and 3-MC were discussed with reference to the synthesis of distinct cytochromes.