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

Soft computing in the design of nontoxic chemicals

This research focuses on the use of soft computing to aid in the development of novel, state-of-the-art, nontoxic dyes which are of commercial importance to the U.S. textile industry. Where appropriate, modern molecular orbital (MO) and density functional (DF) techniques are employed to establish the necessary databases of molecular properties to be used in conjunction with the neural network approach. In this research, we focused on the following: (1) using molecular modeling to establish databases of various molecular properties of azo dyes required as input for our neural network approach; (2) designing and implementing a neural network architecture suitable to process these databases; and (3) investigating combinations of molecular descriptors needed to predict various properties of the azo dyes.

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.

Different effects of DNA adducts induced by carcinogenic and noncarcinogenic azo dyes on in vitro DNA synthesis

M13mp10 phage DNA modified with the carcinogen 3-methoxy-4-aminoazobenzene (3-MeO-AAB) or the noncarcinogen 2-methoxy-4-aminoazobenzene (2-MeO-AAB) was used as a template for E.coli DNA polymerase I. Analysis of the reaction products on DNA sequencing gels showed that with both types of compound the induced lesions blocked DNA synthesis, mainly at one base prior to guanine adducts, but that the inhibition by 3-MeO-AAB-adducts was substantially greater than that by 2-MeO-AAB-adducts. Thus different effects on DNA replication between 3-MeO-AAB- and 2-MeO-AAB-adducts might be a reflection of differences in their carcinogenic potency.

32P-postlabeling analysis of DNA adducts in rat livers after treatment with genotoxic and non-genotoxic 4-aminoazobenzene derivatives

Formation of hepatic DNA adducts was studied in rats following intraperitoneal administration of a hepatocarcinogen, 3-methoxy-4-aminoazobenzene (3-MeO-AAB) and a non-hepatocarcinogen, 2-methoxy-4-aminoazobenzene (2-MeO-AAB). The 32P-post-labeling assay revealed 3-MeO-AAB to give more than 20-fold higher amounts of DNA adducts than did 2-MeO-AAB. Furthermore, five adducts, one of which accounted for over 70% of the total modified bases, were found in DNA from 3-MeO-AAB-treated rats, whereas only one adduct was apparent in 2-MeO-AAB-treated DNA. Our data thus suggested that the difference in hepatocarcinogenic activity between 3-MeO-AAB and 2-MeO-AAB might be, at least in part, dependent on quantitative and qualitative differences in their azo dye-DNA adduct formation in the rat liver.

Changes in the quantity and activity of cytochrome P-450 isozymes in primary cultured rat hepatocytes

Hepatocytes from male Sprague-Dawley rats pretreated with a cytochrome P-450 inducer, 3-methoxy-4-aminoazobenzene (3-MeO-AAB), 3-methylcholanthrene (MC) or phenobarbital (PB), were cultured in vitro, and changes in the quantity and activity of microsomal cytochrome P-450 isozymes in the cells were determined by means of immunochemical methods and a bacterial mutation test, respectively. The results of enzyme-linked immunosorbent assay using monoclonal antibodies against rat P-450 isozymes revealed that the amount of cytochrome P-450d induced by 3-MeO-AAB or MC declined rapidly during culture and fell to 10 to 15% of the initial value after 24 h. A similar tendency was observed with PB-induced cytochrome P-450b/e. By contrast, cytochrome P-450c in MC-induced hepatocytes declined more slowly than cytochrome P-450d and remained at 45 to 60% of the initial value after 24 h. Similar quantitative changes of the individual cytochrome P-450 isozymes in culture were also observed by immunoblotting using the anti-cytochrome P-450 monoclonal antibodies. Changes in the activities of individual cytochrome P-450 isozymes in hepatocytes by culture were in accordance with the quantitative changes of the cytochromes, as determined by a mutation test using Salmonella typhimurium TA 98 and carcinogenic aromatic amines. These results indicate that microsomal cytochrome P-450c in primary cultured rat hepatocytes is more stable in culture, in terms of both quantity and activity, than cytochrome P-450d and P-450b/e.

A simple method for assessment of rat cytochrome P-448 isozymes responsible for the mutagenic activation of carcinogenic chemicals

Cytochrome P-448H/L-enriched and cytochrome P-448L-enriched microsomes were prepared from the livers of Sprague-Dawley rats treated with 3-methylcholanthrene (MC) and with a combination of MC and carbon tetrachloride, respectively, and their activities for mediating mutagenic activation of 9 carcinogenic aromatic amines and benzo[a]pyrene, which are found to be different from cyt. P-450 isozymes as to mutagenic activation, were compared on the basis of microsomal cytochrome P-450 content using Salmonella typhimurium TA98 as a tester bacterium. With regard to the substrate-specificity of cytochrome P-448 isozymes, the present results reflected the reported results with use of a cytochrome P-450-reconstituted system. These findings indicate that the mutation test with cytochrome P-448H/L-enriched and cytochrome P-448L-enriched microsomes could be used as a simple method for the determination of the cytochrome P-448 isozymes responsible for the mutagenic activation of carcinogens and mutagens without the use of a cytochrome P-450-reconstituted system.

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.

Induction of a high spin form of microsomal cytochrome P-448 in rat liver by 4-aminoazobenzene derivatives

Male Sprague-Dawley rats were treated with 4-aminoazobenzene derivatives or other drug metabolizing enzyme inducers such as phenobarbital, 3-methylcholanthrene and isosafrole. The expression of hepatic microsomal cytochrome P-450 of the rats, principally that of a high spin form of cytochrome P-448 (cytochrome P-448H), was assessed by a bacterial mutation test and by immunological methods. The results of the mutation test with use of Salmonella typhimurium TA9 and 3 aromatic amine substrates showed that 2-methoxyl, 3-methoxyl and 2',3-dimethoxyl derivatives of AAB and methyl derivatives of AAB such as o-aminoazotoluene, N-methyl-4-aminoazobenzene and N,N-dimethyl-4-aminoazobenzene have a large capacity for the selective induction of cytochrome P-448H. Activity of the cytochrome increased by 6 hr after an azo dye treatment, reached a maximum after 24 hr, and then declined. In contrast, 4'-methoxy-AAB has a small, and AAB has no, capacity for the cytochrome induction. The aminoazo dye-induced enzymes differ in their substrate specificities from those induced with 3-methylcholanthrene or phenobarbital, and the induced enzyme was identified to be cytochrome P-448H, as determined by an enzyme-linked immunosorbent assay and immunoblotting with use of anti-cytochrome P-448 monoclonal antibodies. These observations indicate that several methoxyl and methyl derivatives of 4-aminoazobenzene are potent and selective inducers of cytochrome P-448H in the rat.