3-Aminobenzanthrone, a human metabolite of the carcinogenic environmental pollutant 3-nitrobenzanthrone, induces biotransformation enzymes in rat kidney and lung

Abstract

3-aminobenzanthrone (3-ABA) is the metabolite of the carcinogenic air pollutant 3-nitrobenzanthrone (3-NBA). 3-ABA was investigated for its ability to induce cytochrome P450 1A1 (CYP1A1) and NAD(P)H:quinone oxidoreductase (NQO1) in kidney and lung of rats, and for the influence of such induction on DNA adduct formation by 3-ABA and 3-NBA. NQO1 is the enzyme that reduces 3-NBA to N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) and CYP1A enzymes oxidize 3-ABA to the same intermediate. When activated by cytosolic and and/or microsomal fractions isolated from rat lung, the target organ for 3-NBA carcinogenicity, and kidney, both compounds generated the same DNA-adduct pattern, consisting of five adducts. When pulmonary cytosols isolated from rats that had been treated i.p. with 40 mg/kg bw of 3-ABA were incubated with 3-NBA, DNA adduct formation was up to 1.7-fold higher than in incubations with cytosols from control animals. This increase corresponded to an increase in protein level and enzymatic activity of NQO1. In contrast, no induction of NQO1 expression by 3-ABA treatment was found in the kidney. Incubations of 3-ABA with renal and pulmonary microsomes of 3-ABA-treated rats led to an increase of up to a 4.5-fold in DNA-adduct formation relative to controls. The stimulation of DNA-adduct formation correlated with a higher protein expression and activity of CYP1A1 induced by 3-ABA. These results show that by inducing lung and kidney CYP1A1 and NQO1, 3-ABA increases its own enzymatic activation as well as that of the environmental pollutant, 3-NBA, thereby enhancing the genotoxic and carcinogenic potential of both compounds.

Mechanisms of Enzyme-Catalyzed Reduction of Two Carcinogenic Nitro-Aromatics, 3-Nitrobenzanthrone and Aristolochic Acid I: Experimental and Theoretical Approaches

“…Human NQO1 in the presence of its cofactor, NADPH, reductively activates 3-NBA to the reactive intermediate N -hydroxy-3-aminobenzanthrone ( N -OH-3-ABA) (see reaction step 2 in Figure 1) that dissociates to a ion that exhibits both nitrenium and carbenium character because the positive charge is delocalized to both nitrogen and carbon sites (step 3a in Figure 1), forming DNA adducts both in vitro and in vivo (Figure 1 and Figure 2; Table 1) [15,21,48,49,50,51,52,53]. N -OH-3-ABA can be further reduced to 3-aminobenzanthrone (3-ABA; step 4 in Figure 1) [14,51,52,54].…”

“…N -OH-3-ABA can be further reduced to 3-aminobenzanthrone (3-ABA; step 4 in Figure 1) [14,51,52,54]. Of the 3-NBA-derived DNA adducts generated by NQO1, three major adducts were identified as 2-(2'-deoxyadenosin- N 6 -yl)-3-aminobenzanthrone (dA- N 6 -3-ABA), dG- N 2 -3-ABA and dG-C8- N -3-ABA [16,20,55,56,57,58] (Figure 1).…”

“…Interestingly, 3-NBA and its amino metabolite, 3-ABA, are potent inducers of NQO1 in liver, lung and kidney of rats. Such induction finally resulted in a more than 10-fold increase in the levels of 3-NBA-DNA adducts in ex vivo incubations of 3-NBA with DNA and liver, kidney and lung cytosols isolated from these animals [50,51,53], emphasizing the importance of NQO1 in the genotoxicity of 3-NBA.…”

“…Of the CYP enzymes reducing 3-NBA, CYP1A1 and 1A2 were also found to oxidize 3-ABA to N -OH-3-ABA dissociating to the ion binding to DNA (Figure 1) [80]. In addition, CYP1A1 and 1A2 are induced in liver, lung and kidney of rats not only treated with 3-NBA, but also with 3-ABA [49,50,51,53]. DNA adduct levels increased up to 12-fold due to the induction of CYP1A1/2 in lung, kidney and liver in 3-NBA- or 3-ABA-treated rats using different routes of administration including intratracheal instillation of 3-NBA [49,50,51,53].…”

Induction of biotransformation enzymes by the carcinogenic air-pollutant 3-nitrobenzanthrone in liver, kidney and lung, after intra-tracheal instillation in rats

“…1). In animal experiments with Wistar rats the major role of CYP1A1 in 3-ABA activation in lungs and kidneys rather than peroxidases was elucidated [24,28]. In the same rat model we treated rats with single i.p.…”