Fluorescence Study on the Interaction of Bovine Serum Albumin with P-Aminoazobenzene

In this paper, the interaction between p-aminoazobenzene (PAAB) and BSA was investigated mainly by fluorescence quenching spectra, circular dichroism (CD) and three-dimensional fluorescence spectra under simulative physiological conditions. It was proved that the fluorescence quenching of BSA by PAAB was mainly a result of the formation of a PAAB-BSA complex. The modified Stern-Volmer quenching constant K(a) and the corresponding thermodynamic parameters DeltaH, DeltaG and DeltaS at different temperatures were calculated. The results indicated that van der Waals interactions and hydrogen bonds were the predominant intermolecular forces in stabilizing the complex. The distance r=4.33 nm between the donor (BSA) and acceptor (PAAB) was obtained according to Förster's non-radioactive energy transfer theory. The synchronous fluorescence, CD and three-dimensional fluorescence spectral results showed that the hydrophobicity of amino acid residues increased and the losing of alpha-helix content (from 63.57 to 51.83%) in the presence of PAAB. These revealed that the microenvironment and conformation of BSA were changed in the binding reaction.

Partial degradation of p-aminoazobenzene by a defined mixed culture of Bacillus subtilis and Stenotrophomonas maltophilia

A defined mixed culture of Bacillus subtilis and Stenotrophomonas maltophilia was used to accomplish the partial biodegradation of the azo-dye p-aminoazobenzene (pAAB). Kinetic experiments were conducted, under aerobic conditions, to study the mineralization of p-aminoazobenzene by the above-defined mixed culture, under aerobic conditions. The combination of two previously developed models, (Zissi et al., 1997), which describes pAAB biodegradation by Bacillus subtilis into aniline and p-phenylenediamine, and (Zissi and Lyberatos, 1999), which describes aniline biodegradation by Stenotrophomonas maltophilia, is shown to predict well the anticipated mixed culture growth and partial biodegradation of pAAB. In previous work (Zissi et al., 1997) it was observed that pphenylenediamine was unstable during the experiments therefore the fate of p-phenylenediamine was not studied. The overall kinetic model of the defined mixed culture was then used to study the behavior of the mixed culture system in a range of operating conditions in the chemostat. The partial degradation of pAAB (regarding one of the two products, aniline) was described by an interaction between the two bacteria with competitive and commensalistic elements. The two bacteria are shown to coexist in a CSTR for some ranges of the operating variables.

Mutagenic activation of 3-methoxy-4-aminoazobenzene by mouse renal cytochrome P450 CYP4B1: cloning and characterization of mouse CYP4B1

A new P450 responsible for mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) which is a potent procarcinogen was purified from renal microsomes of male mice using an index of umu gene expression. The purified P450 had high bioactivation toward 3-MeO-AAB and also 2-aminofluorene and 2-aminoanthracene. The antibody against this P450 completely inhibited mutagenic activation of 3-MeO-AAB of mouse renal microsomes. With immunoblotting, this form was present abundantly in renal microsomes of male mice but not in those of female mice. This P450 was also present in pulmonary microsomes of male and female mice but not in hepatic microsomes. The NH2-terminal amino acid sequence analysis indicated that this form belonged to the CYP4B subfamily. Thus, mouse kidney cDNA library was screened with rat CYP4B1 probe. The cDNA-deduced amino acid sequence of isolated cDNA consisted of 511 amino acids and bore 90, 86, and 84% similarities to rat, rabbit, and human CYP4B1, respectively. The NH2-terminal amino acid sequence of the purified renal P450 and amino acid sequence of BrCN-digested peptides from the purified P450 agreed with the cDNA-deduced amino acid sequence. These results suggest that CYP4B1 is a major form in renal microsomes of male mice and plays a major role in mutagenic activation of 3-MeO-AAB. In extrahepatic tissue, CYP4B1 may contribute to chemical carcinogenesis.

DNA adduct formation of hepatocarcinogenic aromatic amines in rat liver: effect of cytochrome P450 inducers

F344 rats were treated with an i.p. injection of 2-amino-6- methyldipyrido[1,2-a:3',2'-d]imidazole (Glu P-1) or 3-methoxy-4-aminoazobenzene (3-MeO-AAB) and examined for the formation of the DNA adduct in the liver. To examine the effect of pretreatment with a cytochrome P450 (CYP) inducer on the formation of DNA adduct, these rats were pretreated with 3-methylcholanthrene (MC; CYP1A1/1A2 inducer) or phenobarbital (PB; CYP2B inducer). Administration of Glu P-1 and 3-MeO-AAB gave 2 and 5 adducts, respectively, as determined by 32P-postlabeling assay. By Glu P-1 administration, pretreatment of rats with MC, but not with PB, increased the total amount of DNA adducts including 3 new adducts as minor products. In contrast, pretreatment of rats with PB increased the total amount of DNA adducts derived by 3-MeO-AAB. The increase of aromatic amine DNA adducts by pretreatment with a CYP inducer was proportional to the activity of induced CYP isozyme(s) responsible for the mutagenic activation of each aromatic amine.

Immunological detection and quantitation of DNA adducts formed by 4-aminoazobenzene species in vivo

Antibodies to 3-methoxy-4-aminoazobenzene (3-MeO-AAB) and 2-methoxy-4-aminoazobenzene (2-MeO-AAB) DNA adducts were raised in rabbits against in vitro-adducted DNA samples. The enzyme-linked immunosorbent assay (ELISA) was used to determine the sensitivity and specificity of these antibodies. They proved highly specific for the modified DNA used as the immunogen, but cross-reacted with each other. Moreover, they showed cross reactivity with DNA modified by 4-(o-tolylazo)-o-toluidine, but not by other carcinogens, such as 4-aminobiphenyl or 4-nitroquinoline 1-oxide. The 50% inhibition level of antibody binding in the competitive ELISA was at 10-20 fmol of modified base per assay (equivalent to 1-2 adducts per 10(6) bases). Immunohistochemical staining indicated that these antibodies bind specifically to nuclear components of the liver in rats given either 3-MeO-AAB or 2-MeO-AAB at the dose of 50 mg/kg body weight.

Renal and hepatic microsomal enzymes responsible for bioactivation of 3-methoxy-4-aminoazobenzene in the rodent

Activities of the renal and hepatic microsomal enzymes responsible for the N-hydroxylation and mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) were examined in male mice, rats, hamsters and guinea pigs. In all these rodent species, hepatic microsomes showed definite N-hydroxylation of 3-MeO-AAB, whereas the renal activity was detected only in mice. The hepatic enzyme responsible for N-hydroxylation of 3-MeO-AAB (3-MeO-AAB N-hydroxylase) was induced in all species except mice by phenobarbital and selectively in mice and hamsters by 3-methylcholanthrene, whereas these cytochrome P450 inducers did not affect the renal enzyme in mice, rats or hamsters. In individual microsome samples, activities for N-hydroxylation and mutagenic activation of 3-MeO-AAB correlated well. These results indicate that the renal and hepatic enzymes responsible for the metabolic activation of 3-MeO-AAB differed among different species of rodent animals in terms of their activity and inducibility with cytochrome P450 inducers.

Lack of release from hepatocytes in vitro or excretion in vivo of mutagenic chrysoidine metabolites

Rat liver postmitochondrial supernatant (S9) converted the azo dyes chrysoidine Y and R to products that were mutagenic towards Salmonella typhimurium strain TA100. No such release of mutagens was demonstrated using intact rat hepatocytes as an activation system despite the fact that chrysoidine dyes cause unscheduled DNA synthesis in these cells. It appears that genotoxic products produced within hepatocytes either react within the cell or are detoxified prior to release. Following intraperitoneal administration of chrysoidine Y to rats (100 mg/kg i.p.) there was also no evidence of mutagenic or por-mutagenic products excreted in bile or urine. The S9-derived mutagens appear to be largely independent of bacterial acetylation since they were active in the acetylation-deficient strain TA98/1,8-DNP6 in addition to strain TA98. The ultimate mutagenic form(s) are therefore unlikely to be acetoxyarylamines.

Monomorphic and polymorphic isozymes of arylamine N-acetyltransferases in hamster liver: purification of the isozymes and genetic basis of N-acetylation polymorphism

Two forms of cytosolic acetyltransferases, AT-I and AT-II, have been purified from hamster livers, and a comparison made of their chemical and catalytic properties and genetically expressed difference. Homogeneous AT-I and AT-II were 31 and 30 kd respectively on SDS-PAGE and catalyzed efficiently various N- and O-acetylations in their reconstitution systems. AT-I used both acetyl CoA and arylhydroxamic acids as acetyl donors, while AT-II did not utilize arylhydroxamic acids as acetyl donors. In the reconstitution system, purified AT-I, but not AT-II, catalyzed acetyl CoA-dependent O-acetylation of 2-N-hydroxyamino-6-methyldipyrido[1,2-alpha:3', 2'-d]imidazole (N-OH-Glu-P-1) and arylhydroxamic acid-dependent N-acetylation of 4-aminoazobenzene (AAB). On the other hand purified AT-II showed high activities of acetyl CoA-dependent N-acetylation of 2-aminofluorene (AF) and p-aminobenzoic acid (PABA). Polyclonal antibodies raised against AT-I inhibited cytosolic acetylations of N-OH-Glu-P-1 and AAB, and to a lesser extent of AF, while PABA N-acetylation was only marginally inhibited. Using Western blots, both AT-I and AT-II were recognized by the antibodies. AT-I was detectable in all the livers examined, and the content did not differ among the individuals (monomorphic distribution). In contrast, AT-II was distributed polymorphically, and the trimodal distribution of AT-II (high, intermediate and low) was correlated with the phenotype identified by cytosolic N-acetylations of AF and PABA (rapid, intermediate and slow). In addition, cross-mating experiments with intra- and inter-phenotype animals confirmed that hepatic AT-II isozyme is inherited by a Mendelian co-dominant trait. These results indicate that the polymorphic appearance of an acetyltransferase, AT-II, is responsible for the N-acetylation polymorphism in individual hamsters.

Analogues of N-hydroxy-4-acetylaminobiphenyl as substrates and inactivators of hamster hepatic acetyltransferases

1. A series of analogues of N-hydroxy-4-acetylaminobiphenyl (1, N-OH-AAB) has been synthesized and evaluated in vitro as substrates and inactivators of hamster hepatic N,N-acetyltransferase (N,N-AT) activity. The analogues of 1 are N-arylhydroxamic acids in which an atom or small functional group has been incorporated between the phenyl rings of 1. 2. The structural and molecular properties of the atoms between the two phenyl rings had little influence on the ability of the compounds to serve as acetyl donors in the N-arylhydroxamic acid-dependent transacetylation of 4-aminoazobenzene (AAB) catalysed by N,N-AT. An exception was the SO2 analogue (6) which was inactive. 3. All of the compounds except 6 were mechanism-based inactivators (suicide inhibitors) of hamster hepatic N,N-AT. The inhibition of N,N-AT by the hydroxamic acids was irreversible. The properties of the atom or functional group between the phenyl rings had a substantial influence on the relative effectiveness of the compounds as inactivators of N,N-AT. trans-N-Hydroxy-4-acetylaminostilbene (N-OH-AAS, 7) was the most potent and effective mechanism-based inactivator among the compounds studied. The ketone analogue (2) was the least effective among the compounds that exhibited inactivating activity. 4. The presence of the nucleophile cysteine in the incubation mixtures reduced the extent of inactivation of N,N-AT by 1 and by the ether (4) analogue but had little effect on the inactivation caused by 7. The inactivation of N,N-AT by N-OH-AAS (7) does not appear to involve electrophiles that are released from the active site and subsequently become covalently bound to the enzyme.

Androgen-dependent renal microsomal cytochrome P-450 responsible for N-hydroxylation and mutagenic activation of 3-methoxy-4-aminoazobenzene in the BALB/c mouse

A murine renal microsomal enzyme responsible for the mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) was characterized by its catalytic activity for the mutagenic and metabolic conversion of 3-MeO-AAB. Incubation of 3-MeO-AAB with a renal or hepatic microsome fraction from male BALB/c mice in the presence of NADPH and NADH yielded N-hydroxy and 4'-hydroxy metabolites of 3-MeO-AAB as determined by two-dimensional thin layer chromatography, and the enzyme responsible for the N-hydroxylation was named 3-MeO-AAB N-hydroxylase. A mutagenicity test using Salmonella typhimurium TA98 bacteria as a tester strain has revealed that N-hydroxy-3-MeO-AAB is a potent direct mutagen but that 4'-hydroxy-3-MeO-AAB is not mutagenic. Although 3-MeO-AAB N-hydroxylase activity in liver microsomes showed no sex difference, the enzyme activity in the kidney was detected from male mice but not from females. However, administration of testosterone to female mice induced the enzyme in the kidney. Castration of male mice depressed the activity of 3-MeO-AAB N-hydroxylase in renal microsomes but it little affected the hepatic activity, and on administration of testosterone to the castrated mice the depressed renal microsomal activity recovered to a normal level. The activity of 3-MeO-AAB hydroxylase and the amount of cytochrome P-450 in renal microsomes showed a close correlation. Both renal and hepatic microsomes required NADPH as a main cofactor to mutagenize 3-MeO-AAB and to yield N-hydroxy-3-MeO-AAB from 3-MeO-AAB, and the enzyme activity was strongly inhibited by 7,8-benzoflavone. When the activities of renal and hepatic 3-MeO-AAB N-hydroxylase were compared on the basis of the amount of cytochrome P-450, the renal type enzyme showed about 8 times greater activity than hepatic type enzyme. These results indicate that the kidney contains an androgen-dependent microsomal 3-MeO-AAB hydroxylase which is different from an isozyme present in the liver and which is a new type of cytochrome P-450 isozyme.

Bacterial mutagenesis and hepatocyte unscheduled DNA synthesis induced by chrysoidine azo-dye components

5 azo dye components of Gurr chrysoidine 'Y' have been separated, synthesised and identified. Dyes with a methyl substitution (particularly between the two amino groups) were more mutagenic in Salmonella typhimurium strain TA100 with control rat liver S9 than the non-methylated counterpart (range 66-1992 revertants at 50 micrograms/plate). Mutagenicity was also catalysed by human-liver S9 and pre-treatment of rats with either phenobarbitone or beta-naphthoflavone enhanced the activation ability of S9 by greater than 4-fold. Using the most potent promutagenic component (2,4-diamino-3-methylazobenzene), the use of inhibitors of cytochrome P450 (metyrapone: 1.0 mM; alpha-naphthoflavone: 0.075 mM; DPEA: 0.125 mM) and of the flavin monooxygenase (methimazole: 0.75 mM) suggested a major role for cytochrome P448 in the activation of chrysoidine to mutagens. The ability of chrysoidine components to induce unscheduled DNA synthesis in rat hepatocytes in vitro was demonstrated and ranged between 11.92 and 23.5 net nuclear grains at a dose level of 2.5 micrograms/incubation. Since each dye was equi-potent, methyl substitution had little influence on genetic toxicity in hepatocytes.

A male-specific renal cytochrome P-450 isozyme(s) responsible for mutagenic activation of 3-methoxy-4-aminoazobenzene in mice

Renal microsomes from male mice (BALB/c, DBA/2 and BALB/c x DBA/2 F1) showed about 10-fold greater activity for mediating mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) toward Salmonella typhimurium TA98 than did the corresponding hepatic microsomes, as compared on the basis of nmol of microsomal cytochrome P-450. On the other hand, female renal microsomes and other extrahepatic microsomes (lung, small intestine and colon) in both sexes of mice showed little or no activity for converting 3-MeO-AAB to mutagen(s). The mutagenic activation of 3-MeO-AAB with the male renal enzyme(s) was definitely inhibited by cytochrome P-450 inhibitors, 7,8-benzoflavone and SKF 525A. All these findings suggest that in mice, there is a male-specific renal 3-MeO-AAB activation enzyme(s), a cytochrome P-450 isozyme(s), which is different, at least in proportion and/or in nature, from hepatic cytochrome P-450 isozymes.

Characterization and properties of the DNA adducts formed from N-methyl-4-aminoazobenzene in rats during a carcinogenic treatment regimen

Chronic oral administration of the carcinogenic aminoazo dye N-methyl-4-aminoazobenzene (MAB) to rats is known to result in the induction of liver tumors. In order to assess the role of carcinogen-DNA adduct formation in MAB hepatocarcinogenesis, male rats were fed 0.06% [3'-3H]MAB in the diet for 1, 3 or 5 weeks. Groups were sacrificed at 0, 24 and 72 h after dosing, and DNA was isolated from the liver and from two non-target tissues, the kidney and spleen. Upon enzymatic hydrolysis of the DNA, [3H]aminoazo dye-nucleoside adduct levels in these tissues were determined by h.p.l.c. Rats concurrently administered unlabeled MAB for 5 weeks and continued on a control diet for 9 months developed hepatocellular carcinomas (16/30 animals). No tumors were observed in 21 rats given only control diets. After chronic administration of [3H]MAB, three major MAB-DNA adducts were found in vivo: N-(deoxyguanosin-8-yl)-MAB (C8-dG-MAB), 3-(deoxyguanosin-N2-yl)-MAB (N2-dG-MAB) and 3-(deoxyadenosin-N6-yl)-MAB (N6-dA-MAB). In addition, several minor products were identified as: an (8,9)-purine ring-opened derivative of C8-dG-MAB that may represent an intermediate in DNA repair; N-guanosin-8-yl-MAB which is present due to trace RNA contamination; cis isomers of C8-dG-MAB and N-guanosin-8-yl-MAB, formed by photo-illumination during analyses; and N-(guanin-8-yl)-MAB, a deribosylated product resulting from thermal depurination of C8-dG-MAB. In addition, N-(deoxyguanosin-8-yl)-4-aminoazobenzene (C8-dG-AB), a major adduct previously detected in mouse liver after a single dose of 4-aminoazobenzene, was found in rat liver but appeared to be present in significant amounts only after chronic treatment with MAB. This product co-chromatographed with N6-dA-MAB but could be removed by selective decomposition in 0.1 N NaOH. For all tissues examined N2-dG-MAB and C8-dG-MAB were the major adducts observed with each accounting for 40-50% of the total carcinogen bound to DNA in rats that were sacrificed immediately after MAB feeding for 1, 3 or 5 weeks. The levels of total MAB-DNA adducts in the liver were 2-10 times greater than in the kidney or spleen and appeared to increase 2- to 3-fold over the dosing period.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of phenobarbital and beta-naphthoflavone on oxidative metabolism of N,N-dimethyl-4-aminoazobenzene by regenerating rat-liver microsomes and its response to sulphydryl compounds

The metabolism of the hepatocarcinogen, N,N-dimethyl-4-aminoazobenzene (DAB) is catalysed by selective forms of cytochrome P-450. DAB metabolism has been studied using microsomes from regenerating rat liver prepared 1, 2, 3, 7 and 10 d after partial hepatectomy. Greatly decreased N-demethylation of DAB was seen during liver regeneration, while virtually no effect on ring-hydroxylation was observed. Glutathione stimulated N-demethylation and ring-hydroxylation of DAB, while metabolism of the corresponding secondary amine N-methyl-4-aminoazobenzene (MAB) was not affected. During regeneration, response to the thiol was depressed in the early stages but later returned to normal. beta-Naphthoflavone (BNF) specifically induced N-demethylation of DAB. Induced activity was not depressed during liver regeneration. Phenobarbital (PB) induced total metabolism, which was depressed during regeneration. This indicates greater stability of BNF-induced cytochrome P-450 compared to control and PB-induced cytochrome P-450. The results indicate that during liver regeneration the metabolism of DAB associated with activation (N-demethylation) is depressed, whereas that associated with detoxication (ring-hydroxylation) is only slightly affected. This confirms the involvement of different forms of cytochrome P-450 in DAB metabolism.

N-acetyltransferase multiplicity and the bioactivation of N-arylhydroxamic acids by hamster hepatic and intestinal enzymes

The mechanism-based inactivation (suicide inactivation) by N-hydroxyphenacetin (NHP) of N-arylhydroxamic acid N,O-acyltransferase (AHAT) and p-aminobenzoic acid N-acetyltransferase (PABA NAT) activities of a partially purified hamster liver preparation was investigated. The inactivation of both enzyme activities was irreversible, but a partial protection of PABA NAT could be achieved by inclusion of the nucleophile cysteine in the incubation mixture; cysteine did not reduce the extent of inactivation of AHAT by NHP. Hepatic AHAT and PABA NAT activities were separated by affinity chromatography, and the resolved enzyme activities were subjected to incubation in the presence of NHP, N-hydroxy-2-acetamidofluorene (N-OH-AAF), and N-hydroxy-4-acetamidobiphenyl (N-OH-AABP); AHAT, but not PABA NAT, was inactivated by NHP, N-OH-AAF and N-OH-AABP. Incubation of hamster heptic PABA NAT with radiolabeled N-OH-AAF resulted in the formation of only 15% as much fluorenylamine-tRNA adduct as was formed when N-OH-AAF was bioactivated with hamster hepatic AHAT. Hamster intestinal AHAT and PABA NAT activities also were resolved by affinity chromatography; the intestinal AHAT fractions were much more effective than the PABA NAT fractions in bioactivating N-OH-AAF. These results demonstrate that hamster liver and intestine contain at least two arylamine transacetylating activities, one of which is much more effective than the other in the bioactivation of toxic and carcinogenic N-arylhydroxamic acids.

Sulfuric acid esters as major ultimate electrophilic and hepatocarcinogenic metabolites of 4-aminoazobenzene and its N-methyl derivatives in infant male C57BL/6J x C3H/HeJ F1 (B6C3F1) mice

Liver cytosols from 12-day-old male C57BL/6 X C3H/HeJ F1 (B6C3F1) mice contain 3'-phosphoadenosine-5'-phosphosulfate (PAPS)-dependent sulfotransferase activity for N-hydroxy-4-aminoazobenzene and N-hydroxy-N-methyl-4-aminoazobenzene. No acetyl co-enzyme A-dependent transacetylase activity for these hydroxylamines was detected in the cytosols. Pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol were only moderately active inhibitors of the sulfotransferase activity; at a 100-microM concentration each compound inhibited the activity by only 50-80%. A single dose of 0.04 mumol/g body weight of PCP administered to 12-day-old male B6C3F1 mice 45 min prior to a single dose of 0.1 mumol/g body weight of [3H]4-aminoazobenzene ([3H]AB) or [3H]N,N-dimethyl-4-aminoazobenzene ([3H]DAB) inhibited DNA adduct formation by approximately 50%. Under identical conditions, PCP also reduced the average number of hepatomas induced per mouse at 9 months by AB and N-methyl-4-aminoazobenzene (MAB) by 52 and 36%, respectively. PCP strongly inhibited the hepatocarcinogenicity of DAB or AB when this agent was administered in the diet with either dye to female CD-1 mice over a 10- month period. Single doses of 0.15 mumol/g body weight of [3H]AB and [3H]DAB bound to hepatic DNA of 12-day-old brachymorphic B6C3F2 mice, which are deficient in the synthesis of PAPS, at levels 15 and 20%, respectively, of those found in their phenotypically normal litter mates. Under identical conditions, the incidence of hepatomas in brachymorphic mice at 9 months were 11 and 29%, with averages of 0.2 and 0.8 hepatomas/mouse for AB and MAB, respectively. Incidences of 77 and 86%, with averages of 6.6 and 5.4 hepatomas/mouse, respectively, were found in their phenotypically normal litter mates. These data strongly indicate that N-sulfoöxy-AB is a major ultimate electrophilic and hepatocarcinogenic metabolite of AB in mice. Similarly, this ester and N-sulfoöxy-N-methyl-4-aminoazobenzene appear to be critical metabolites for these activities of DAB and MAB.

Regulation of thiol environment of the N-demethylation and ring hydroxylation of N,N-dimethyl-4-aminoazobenzene (DAB) by rat liver microsomes

A study was conducted on the regulation by thiol environment of microsomal metabolism of the azo dye hepatocarcinogen, N,N-dimethyl-4-aminoazobenzene (DAB). Physiological concentrations of glutathione (GSH) stimulated N-demethylation and ring hydroxylation of the dye in normal and phenobarbital (PB)-treated microsomes. However, little effect of GSH was seen with microsomes from beta-naphthoflavone (BNF)-treated rats. The synthetic thiol, dithiothreitol (DTT), stimulated ring-hydroxylation of DAB but inhibited N-demethylation at all concentrations in control nd PB-induced microsomes. A biphasic response to DTT was obtained with BNF microsomes; inhibition of N-demethylation was seen only at low concentrations (0.1 mM) and a return to control values occurred at higher concentrations. DTT inhibition was shown to be specific for the first N-demethylation step, whereas the second was slightly stimulated at concentrations greater than 3.0 mM. Agents which alkylate [N-ethylmaleimide (NEM), p-hydroxymercuribenzoate] or oxidize [5,5'-dithiobis(nitrobenzoic acid) or Ellman's reagent] protein SH groups inhibited DAB metabolism. Inhibition of microsomal NADPH-cytochrome c reductase activity by p-hydroxymercuribenzoate required an order of magnitude more inhibitor than was needed to block DAB metabolism. This suggests that DAB metabolism requires viable SH groups other than those involved in NADPH-cytochrome c reductase activity. NEM, in contrast, inhibited the N-demethylation of DAB and NADPH-cytochrome c reductase at approximately the same concentrations. Ring-hydroxylation was stimulated by high (greater than 1 mM) concentrations of NEM, implying a different enzymic mechanism for this pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Methoxy-4-aminoazobenzene, a unique carcinogenic aromatic amine as a substrate for cytochrome-P-450-mediated mutagenesis

Rat liver microsomal enzyme(s) that catalyze mutagenic activation of a carcinogenic aminoazo dye, 3-methoxy-4-aminoazobenzene (3-MeO-AAB), was studied by virtue of the Salmonella typhimurium TA98 assay using o-aminoazotoluene (OAT) as the control. Male Wistar rats were pretreated with phenobarbital (PB), 3-methylcholanthrene (MC) or polychlorinated biphenyl (PCB), and the liver microsomal activities for mutagenic activation of 3-MeO-AAB and OAT were examined. In agreement with the reported results on several carcinogenic aromatic amines, MC pretreatment resulted in greater activation of microsomal activity in the OAT mutagenesis (about a 4-fold increase as compared to the untreated control) than did PB (1.5-fold increase). By contrast, the mutagenic activation of 3-MeO-AAB is found to be more efficiently catalyzed by those enzyme(s) that are induced by PB pretreatment (4-fold increase) than by those that are induced by MC (1.8-fold increase). The induced enzymes that principally mediate the mutagenic activation of these azo dyes are indicated to be cytochrome P-450s, because the mutagenic activation was strongly inhibited by addition of cytochrome P-450 inhibitors such as 2-diethylaminoethyl-2,2-diphenylvalerate (SKF 525A) and 7,8-benzoflavone. These data suggest that 3-MeO-AAB is a unique carcinogenic aromatic amine as a substrate for mutagenic activation via catalysis of those cytochrome P-450s that are induced by PB pretreatment.

Species difference between rats and mice in activities of enzymes activating aromatic amines: effect of dietary 3-methoxy-4-aminoazobenzene

Male Donryu rats and B6C3F1 mice were treated with dietary 3-methoxy-4-aminoazobenzene (3-MeO-AAB) (0.06% or 0.09%), and subcellular fractions of the liver were examined for ability to mutagenically activate 3-MeO-AAB and 2 amino acid pyrolysate components using Salmonella typhimurium TA 98 as a tester strain. The treatment resulted in striking induction of enzyme(s) for the mutagenic activation of these aromatic amines in rats, but the effect was smaller in mice. The enzyme(s) involved in the reaction was characterized as an isotype of microsomal cytochrome P-448.

Role of cytochrome P-450 and flavin-containing monooxygenase in the N-hydroxylation of N-methyl-4-aminoazobenzene in rat liver: analysis with purified enzymes and antibodies

By means of high pressure liquid chromatography, the role of flavin-containing monooxygenase (FMO) and cytochrome P-450 (cyt. P-450) in the metabolism of N-methyl-4-aminoazobenzene (MAB) by rat liver microsomes in vitro was studied with the help of antibodies and a chemical inhibitor. Antibody against cyt. P-488 from 3-methylcholanthrene-treated rats (MC-P-448) decreased the formation of N-hydroxy-N-methyl-4-aminoazobenzene (N-OH-MAB) by about 30% in microsomes from MC-treated rats (MC-microsomes), but showed no inhibitory effect on the formation of N-OH-MAB in microsomes from untreated rats (untreated microsomes) or in microsomes from phenobarbital-treated rats (PB-microsomes). Antibody against cyt. P-450 from PB-treated rats did not inhibit N-hydroxylation of MAB by any of the microsomes tested. A competitive inhibitor of FMO, methimazole, inhibited the N-hydroxylation of MAB by 65% in the case of MC-microsomes, and the residual activity was inhibited completely by anti-NADPH-cytochrome P-450 reductase (anti-fPT) antibody. These results indicate that in MC-microsomes, the N-hydroxylation of MAB is catalyzed by both FMO and MC-P-448, but in untreated and PB-microsomes the reaction is catalyzed exclusively by FMO.

4-aminoazobenzene and N,N-dimethyl-4-aminoazobenzene as equipotent hepatic carcinogens in male C57BL/6 X C3H/He F1 mice and characterization of N-(Deoxyguanosin-8-yl)-4-aminoazobenzene as the major persistent hepatic DNA-bound dye in these mice

In contrast to the well-established requirement for an N-methyl group for efficient hepatic tumor induction by dietary administration of derivatives of 4-aminoazobenzene (AB) to adult rats, we have now observed that AB and its N-methyl and N,N-dimethyl derivatives have high and approximately equal hepatocarcinogenicity when given as a single i.p. dose to male 12-day-old C57BL/6 X C3H/ HeF1 (B6C3F1) mice. The hepatoma multiplicity induced by these dyes was approximately linearly related to the dose from 0.017 to 0.15 mumol/g body weight; at the high dose, an average of 11 hepatomas/mouse was observed at 10 months. Female B6C3F1 mice were resistant to tumor induction under these conditions. AB and its N-methyl derivative also induced the same incidences of hepatomas on administration of a single dose of 0.45 mumol/g body weight to 12-day-old male C3H/He mice (about 15 hepatomas/mouse) or C57BL/6 mice (about 1 hepatoma/mouse). Infant male Fischer rats were much less susceptible; less than 25% of the rats given 4 i.p. injections (0.3 to 0.4 mumol/g of body weight/injection) of N-methyl-4-amino-azobenzene and less than or equal to 5% of those given these doses of N,N-dimethyl-4-aminoazobenzene or AB before 22 days of age developed hepatic carcinomas by 24 months. Reverse-phase high-performance liquid chromatography of enzymatically hydrolyzed hepatic DNA from 12-day-old male B6C3F1 mice or Fischer rats given an i.p. dose (0.08 or 0.3 mumol/g of body weight) of [prime-ring-3H]AB showed a single major adduct which was chromatographically identical to N-( deoxyguanosin -8-yl)-4-aminoazobenzene synthesized by reaction at pH 7 of N-acetoxy-4-aminoazobenzene (formed in situ from N-hydroxy-4-aminoazobenzene and acetic anhydride) with deoxyguanosine. Mouse and rat liver DNA contained 20 and 0.5 pmol, respectively, of this adduct per mg 24 hr after administration of 0.3 mumol of [prime-ring-3H]AB/g of body weight. At 24 hr after administration of N,N-[prime-ring-3H]dimethyl-4-aminoazobenzene to male B6C3F1 mice, N-( deoxyguanosin -8-yl)-4-aminoazobenzene, N-( deoxyguanosin -8-yl)-N-methyl-4-aminoazobenzene, and 3-( deoxyguanosin -N2-yl)-N-methyl-4-aminoazobenzene were present in a ratio of approximately 4:2:1, respectively. Unlike the N-( deoxyguanosin -8-yl)-N-methyl-4-aminoazobenzene adducts, the N-( deoxyguanosin -8-yl)-4-aminoazobenzene adducts were relatively stable in the DNA; the level of the latter adducts decreased about 60% between 24 hr and 21 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Arylhydroxamic acid bioactivation via acyl group transfer. Structural requirements for transacylating and electrophile-generating activity of N-(2-fluorenyl)hydroxamic acids and related compounds

The synthesis of a series of 12 N-(2-fluorenyl)hydroxamic acids, N-(2-fluorenyl)-N-hydroxyureas, and N-(2-fluorenyl)-N-hydroxycarbamates is reported. The compounds were evaluated for their ability to serve as substrates for a partially purified hamster hepatic arylhydroxamic acid N,O-acyltransferase preparation. Transacylating activity was measured spectrophotometrically with 4-aminoazobenzene as the acyl group acceptor, and electrophile-generating activity was quantified by the N-acetylmethionine trapping assay. Only the N-acetyl, N-propionyl, and N-methoxyacetyl derivatives exhibited relatively high levels of activity as measured by either of the assay methods. These results are generally consistent with previously reported conclusions regarding the steric and electronic characteristics of acyl groups that are required for activation by this enzyme system. N,O-Acyltransferase inactivation by N-hydroxy-2-acetamidofluorene depressed the bioactivation of the N-acetyl compound to a greater extent than either the N-propionyl or N-methyloxyacetyl derivative.

Formation of N-(glutathion-S-methylene)-4-aminoazobenzene following metabolic oxidation of the N-methyl group of the carcinogen, N-methyl-4-aminoazobenzene

A major biliary metabolite of the hepatocarcinogen, N,N-dimethyl-4-aminoazobenzene (DAB), in the rat was identified as N-(glutathion-S-methylene)-4-aminoazobenzene (GS-CH2-AB). This conjugate was prepared synthetically by a Mannich condensation of 4-aminoazobenzene (AB), formaldehyde (CH2O) and glutathione (GSH) and has been characterized by chemical analysis and by ultraviolet, visible and 13C-NMR spectroscopy. The same conjugate was also formed in vitro by incubating N-methyl-4-aminoazobenzene (MAB), NADPH, NADH and GSH with rat hepatic microsomes. Evidence is presented that GSH reacted with an intermediate resulting from a cytochrome P-450-dependent oxidation of the N-methyl substituent. This reactive intermediate is presumed to be either an N-methylol or a methimine derivative of AB. The significance of this detoxification mechanism is discussed. The presence of an additional major aminoazo-dye GSH conjugate is also noted.

N-Hydroxylation enzymes of carcinogenic aminoazo dyes: possible involvement of cytochrome P-448

N-Hydroxylation reactions of 3'-methyl-N,N-dimethyl-4-aminoazobenzene (3'-Me-DAB) and 3'-methyl-N-methyl-4-aminoazobenzene (3'-Me-MAB) were studied by measuring the nitroxide radical generated from N-hydroxylated products of these aminoazo compounds. N-Hydroxylation activity was remarkably high in the microsomes from 3-methylcholanthrene (3-MC)-treated rats, whereas phenobarbital (PB) treatment had a slightly enhancing effect on the N-hydroxylation of 3'-Me-DAB and a rather inhibitory effect on that of 3'-Me-MAB. Either NADPH or NADH was effective for the N-hydroxylation of 3'-Me-MAB, though the former was slightly more effective. For the reaction of 3'-Me-DAB the effect of NADPH and NADH was additive, but this was not the case for 3'-Me-MAB. Carbon monoxide, metyrapone and 2-diethylaminoethyl-2,2-diethylvalerate hydrochloride (SKF-525-A), inhibitors of cytochrome P-450, had no inhibitory effect on the N-hydroxylation of 3'-Me-DAB and 3'-Me-MAB. On the other hand, alpha-naphthoflavone, an inhibitor of cytochrome P-448, considerably inhibited the N-hydroxylation of these aminoazo dyes. In the case of partially purified mixed function amine oxidase (MFAO), 1-(1-naphthyl)-2-thiourea, an inhibitor of MFAO, completely inhibited the N-hydroxylation of 3'-Me-MAB as well as the N-oxidation of dimethylaniline. On the other hand, in a microsomal system the inhibition of the N-hydroxylation was at most 40% at the concentration giving complete inhibition of the N-oxidation of dimethylaniline. From these results, it is concluded that, in addition to MFAO, cytochrome P-448 is involved in the N-hydroxylation of MAB.

DNA adducts formed from N-benzoyloxy-N-methyl-4-aminoazobenzene in vitro and from N, N-dimethyl-4-aminoazobenzene in mouse liver

Reaction of N-benzoyloxy-N-methyl-4-aminoazobenzene with (14C) deoxyguanosine yielded a series of at least 10 dye derivatives separable by high-performance liquid chromatography. The major adduct, N-(deoxyguanosin-8-yl)-N-methyl-4-aminoazobenzene, was present as both cis and trans isomers. Similar series of adducts were obtained from enzymatic digests of DNA reacted in vitro with N-benzoyloxy-N-methyl-4-aminoazobenzene or from hepatic DNA of (C57BL/6 x C3H/He)F, males given injections at 12 days of age of [prime ring-(3)H]N, N-dimethyl-4-aminoazobenzene. The concentrations of the major adduct and of the second most prominent adduct in the hepatic DNA, after correction for liver growth, were approximately 30 to 70% of the initial values after 10 days; thus the second adduct was poorly removed in comparison to the major adduct.

Identification of the DNA adducts formed in vitro from N-benzoyloxy-N-methyl-4-aminoazobenzene and in rat liver in vivo after administration of N-methyl-4-aminoazobenzene

The synthetic model ultimate carcinogen N-benzoyloxy-N-methyl-4-aminoazobenzene reacted in vitro with either calf thymus or rat liver DNA to yield approximately 1 bound residue per 1,000 nucleotides. The DNA was enzymatically hydrolyzed and subjected to high-pressure liquid chromatographic analysis which indicated the presence of at least 6 N-methyl-4-aminoazobenzene (MAB) adducts. Two of the products cochromatographed with MAB-DNA adducts formed in rat liver in vivo following oral administration of the precarcinogen MAB. These two adducts were identified by UV, mass, and nuclear magnetic resonance spectroscopy as N-(deoxyguanosin-8-yl)- and 3-(deoxyguanosin-N(2)-yl)-MAB: the first adduct was initially the predominant product in vivo, ut it could not be detected 7 days after treatment, and the second remained at a constant level for 14 days and therefore appeared to be a persistent lesion.

Amino acid conjugation of N-hydroxy-4-aminoazobenzene dyes: a possible activation process of carcinogenic 4-aminoazobenzene dyes to the ultimate mutagenic or carcinogenic metabolites

The activation process of N-hydroxy-4-aminoazobenzene (N-OH-AAB) dyes, proximate mutagenic or carcinogenic metabolites of AAB dyes, to the ultimate mutagenic or carcinogenic metabolites was studied by the use of an amino acid conjugation (aminoacylation) system catalyzed by yeast seryl-tRNA synthetase and [3H]ATP. A potent mutagen, N-hydroxy-3-methoxy-AAB (N-OH-3-MeO-AAB), as well as a non-mutagen, N-OH-2-MeO-AAB, were equally susceptible to N-O-serine conjugation. A weak mutagen, N-OH-AAB, and a moderate mutagen, N-OH-2,5-diMeO-AAB, were also susceptible to the aminoacylation, but to a lesser extent than the 2- or 3-methoxyl homologs. In contrast, N-hydroxy-N-methyl-4-aminoazobenzene and a moderate mutagen, N-OH-4'-MeO-AAB, were not susceptible to the aminoacylation. The ability of these N-OH-AAB dyes to bind with nucleic acid after serine conjugation was proportional to the susceptibility of the dyes to serine conjugation. Serine conjugates of N-OH-AAB dyes reacted with poly G, but not with poly A, poly C or poly U, suggesting that the azo dyes selectively bind with guanine base of nucleic acids. The susceptibility of N-OH-AAB dyes to aminoacylation was compared with the carcinogenic, mutagenic and unscheduled DNA synthesis-inducing activities of these and the mother AAB dyes.

Formation of 3-(glutathion-S-YL)-N-methyl-4-aminoazobenzene and inhibition of aminoazo dye-nucleic acid binding in vitro by reaction of glutathione with metabolically-generated N-methyl-4-aminoazobenzene-N-sulfate

The reaction of glutathione (GSH) with metabolically-formed N-methyl-4-aminoazobenzene-N-sulfate (MAB-N-sulfate), a presumed ultimate carcinogenic metabolite of N,N-dimethyl-4-aminoazobenzene (DAB), was investigated using a hepatic sulfotransferase incubation mixture containing GSH and the proximate carcinogen, N-hydroxy-N-methyl-4-aminoazobenzene (N-HO-MAB). Under these conditions, 6--16% of the MAB-N-sulfate formed could be trapped as an aminoazo dye-GSH adduct. Upon subsequent purification, the adduct was shown to be chromatographically and spectrally identical to 3-(glutathion-S-yl)-N-methyl-4-aminoazobenzene (3-GS-MAB), a known biliary metabolite of DAB and a product of the reaction of the synthetic ultimate carcinogen, N-benzoyloxy-N-methyl-4-aminoazobenzene(N-BzO-MAB), with GSH. Neither 2'- nor 4'-GS-MAB, both products of the latter reaction, were detected in the sulfotransferase incubation mixture. GSH-S-transferases did not appear to be involved in the reaction of MAB-N-sulfate of N-BzO-MAB with GSH. The addition of triethyltin, a potent GSH-S-transferase inhibitor, had no effect on the yield of 3-GS-MAB in (N-HO-MAB sulfotransferase)-GSH incubations; and the addition of cytosol or purified GSH transferases A and B to a (N-BzO-MAB)-GSH reaction mixture did not increase the amount of 3-GS-MAB formed.

The role of ethyl and fluorine substitution in the 4'-position for N,N-diethyl-4-aminoazobenzene mutagenicity and azo reduction

The mutagenicity and azo reduction rate of N,N-diethyl-4-aminoazobenzene (DEAB) were influenced by substitution in the 4'-position with a ethyl or a fluorine group. The parent dye (DEAB) was shown to be slightly mutagenic with Salmonella typhimurium TA98 using Aroclor 1254-pretreated 9000 x g supernatant fractions from rat liver. Introduction of a 4'-ethyl group in DEAB did not affect mutagenicity of the dye, but a 4-fluoro group markedly enhanced its mutagenicity. DEAB underwent azo reduction and its reduction rate was influenced by 4'-substituents. A 4'-fluoro group in DEAB increased its azo reduction rate, while a 4'-ethyl group abolished it. Inhibitors of cytochrome P-450 also inhibited 4'-fluoro-DEAB mutagenicity and azo reduction.

Characterization of DNA adducts of the carcinogen N-methyl-4-aminoazobenzene in vitro and in vivo

Since the susceptibility of specific tissues to tumor formation has been correlated with the persistence of DNA-carcinogen adducts, the identity and persistence of DNA adducts formed from the hepatocarcinogen N-methyl-4-aminoazobenzene (MAB) has been determined. The synthetic ultimate carcinogen N-benzoyloxy-N-methyl-4-aminoazobenzene (N-BxO-MAB) was reacted in vitro with either calf thymus or rat liver DNA to yield approx. 1 bound residue per 1000 nucleotides. After enzymatic hydrolysis of the DNA and high pressure liquid chromatographic analysis, at least six MAB adducts were detected. Two of the products cochromatographed with MAB-DNA adducts formed in rat liver in vivo following oral administration of the precarcinogen MAB. These two adducts were identified by mass, UV and nuclear magnetic resonance (NMR) spectroscopy as N-(deoxyguanosin-8-yl)- and 3-(deoxyguanosin-N2-yl)-MAB. The former adduct was initially the predominant product in vivo, but it could not be detected 7 days following treatment. The latter adduct remained at a constant level for 14 days and therefore appears to be a persistent lesion.

The N-hydroxy metabolites of N-methyl-4-aminoazobenzene and related dyes as proximate carcinogens in the rat and mouse

The carcinogenicities for rats and mice of N-methyl-4-aminoazobenzene (MAB) and its hepatic microsomal metabolite N-hydroxy-N-methyl-4-aminoazobenzene (N-hydroxy-MAB) were compared under several conditions. N-Ethyl-4-aminoazobenzene, 4-aminoazobenzene, and their N-hydroxy derivatives were also included in some of the assays. About 25% of the rats given MAB or N-hydroxy-MAB (3 to 5 mmol/kg body weight) by stomach tube over a 5-week period developed hepatic tumors by 18 to 22 months. Similarly treated rats subsequently given phenobarbital in the drinking water until the termination of the experiment developed about twice as many hepatic tumors. N-Hydroxy-MAB, administered p.o., but not MAB, also induced multiple papillomas and extensive carcinomas of the forestomach in approximately 50% of the rats. Only low incidence of hepatocellular carcinomas occurred in partially hepatectomized rats given a single i.p. injection of 180 mumol/kg body weight of MAB or N-hydroxy-MAB with or without subsequent administration of phenobarbital. Although repeated s.c. doses of N-benzoyloxy-N-methyl-4-aminoazobenzene induced sarcomas at the injection site in 90% of the rats, only 3 of 20 rats developed sarcomas at the site of s.c. injections of N-hydroxy-MAB. N-Ethyl-4-aminoazobenzene, 4-aminoazobenzene, and their N-hydroxy derivatives did not induce significant numbers of tumors in any of the above assay systems. Administration to preweaning male mice of MAB, N-hydroxy-MAB, N-hydroxy-N-ethyl-4-aminoazobenzene, and N-hydroxy-4-aminoazobenzene resulted in high incidences and high multiplicities of hepatic tumors (averages of 5 to 7 tumors/mouse) within 1 year. N-Ethyl-4-aminoazobenzene and 4-aminoazobenzene also induced hepatic tumors under the same conditions, but they were less active. These data support the conclusion that the N-hydroxy metabolites of these aminoazo dyes are proximate carcinogens.

Carcinogenic azo dyes--detection of new metabolites of 3'-methyl-4-(methylamino)azobenzene in rat bile

Metabolism of 3'-methyl-4-(methylamino)azobenzene (3'-Me-MAB) in the rat has been investigated by an ion cluster technique. A mixture of non-labeled and deuterium labeled 3'-Me-MAB in cottonseed oil was administered orally with a stomach tube. After administration, the rat bile was collected for 24 hr and enzymically hydrolyzed. This sample was applied to an Amberlite XAD-2 column and the column was washed with water. The metabolites were eluted with methanol and were separated by thin-layer chromatography. The mass spectrum of each metabolite was measured. By means of this technique, the metabolites oxidized at the 3'-methyl group were newly detected in the bile in addition to the N-demethylated, arly hydroxylated, and their azo-reduced metabolites. The effect of the ring methyl group on the carcinogenic action of aminoazo dyes is also discussed.

[Interaction of p-Dimethylaminoazobenzene with rat liver-chromatin and non-histones (author's transl)]

The carcinogenic p-Dimethylaminoazobenzene and the non-carcinogenic p-aminoazobenzene were radioactive labelled and applicated to Whistar rats intraperitoneally. A very significant difference in binding tendencies for the two compounds and their metabolites was observed in rat liver tissues, rat liver nuclei and rat liver chromatin. Above all a specific binding affinity of the carcinogen to nuclear non-histone protein was found.

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.