1-Nitropyrene reduction

Although 1-aminopyrene is a reduced metabolite of 1-nitropyrene, this arylamine will not covalently bind to DNA in vitro (72). In contrast, when incubations were conducted with the intermediate reduction product, N-hydroxy-l-aminopyrene, extensive covalent binding to DNA was detected (72). This observation is consistent with the previous report that several N-hydroxy arylamines formed DNA adducts and induced mutations in S. typhimurium (116), and suggests that, at least for 1-nitropyrene, reduction to N-hydroxy-l-aminopyrene is a critical step in mutation induction. 

Reduction of nitroarenes has been demonstrated in species of Clostridium and Eubacte-rium, and was associated with the reduction in the mutagenic activity of 1-nitropyrene, and... 

Compared to the extensive data that have been obtained on the mutagenicity of nitro PAHs in S. typhimurium, relatively little is known about the metabolism of these compounds in this organism. Messier et al. (67) reported that incubation of 1-nitropyrene with S. typhimurium TA98 yielded 1-aminopyrene and 1-acetylaminopyrene as major and minor metabolites, respectively. The reduction of 1-nitropyrene was slow and was accompanied by a slow formation of DNA adducts. When incubations were conducted with the nitroreductase-deficient strain, TA100 F50, both the extent of 1-amino-pyrene formation and DNA binding decreased. Howard ej al. (71,115) also found reduction of 1-nitropyrene to 1-aminopyrene in strains TA98, TA1538 and ATCC 14028. 

Recently, Bryant t al. (70) examined the metabolism of 1,8-dinitropyrene in several S. typhimurium strains and found reduction to l-amino-8-nitropyrene and 1,8-diaminopyrene. In addition, other unidentified metabolites were detected in strains which were sensitive to 1,8-dinitropyrene-induced mutations (TA98 and TA98NR) but not in the resistant strains, TA98/1,8-DNP and TA98NR/1,8-DNP6. 

Other bacteria. Intestinal bacteria may play a critical role in the metabolic activation of certain nitroaromatic compounds in animals (119) and several reports have appeared on the metabolism of nitro PAHs by rat and human intestinal contents and microflora (120-123). Kinouchi et al. (120) found that 1-nitropyrene was reduced to 1-aminopyrene when incubated with human feces or anaerobic bacteria. More recently, Kinouchi and Ohnishi (121) isolated four nitroreductases from one of these anaerobic bacteria (Bacteroides fragilis). Each nitroreductase was capable of converting 1-nitropyrene into 1-aminopyrene, and one form catalyzed the formation of a reactive intermediate capable of binding DNA. Howard ej al. (116) confirmed the reduction of 1-nitropyrene to 1-aminopyrene by both mixed and purified cultures of intestinal bacteria. Two additional metabolites were also detected, one of which appeared to be 1-hydroxypyrene. Recently, similar experiments have demonstrated the rapid reduction of 6-nitro-BaP to 6-amino-BaP (123). 

Nitropyrene. 1-Nitropyrene is the principal nitro PAH found in diesel exhaust (40) and, therefore, has been the subject of intense study. Nachtman and Wei (133) found that under anaerobic conditions, 1-nitropyrene was reduced by hepatic S9, cytosol or microsomes to principally 1-aminopyrene. Only limited reduction occurred in the absence of cofactors, while maximum metabolism was observed in the presence of both FMN and NADPH. Although the microsomal fraction had the greatest specific activity toward 1-nitropyrene metabolism, the cytosol had 30 times the total activity. 

Saito et al. (134) found that the cytosolic nitroreductase activity was due to DT-diaphorase, aldehyde oxidase, xanthine oxidase plus other unidentified nitroreductases. As anticipated, the microsomal reduction of 1-nitropyrene was inhibited by 0 and stimulated by FMN which was attributed to this cofactor acting as an electron shuttle between NADPH-cytochrome P-450 reductase and cytochrome P-450. Carbon monoxide and type II cytochrome P-450 inhibitors decreased the rate of nitroreduction which was consistent with the involvement of cytochrome P-450. Induction of cytochromes P-450 increased rates of 1-aminopyrene formation and nitroreduction was demonstrated in a reconstituted cytochrome P-450 system, with isozyme P-448-IId catalyzing the reduction most efficiently. 

In the PO-CL system, the compounds showing native fluorescence or that fluoresce after chemical derivatization can be detected. As examples of the PO-CL detection of native fluorescence compounds, dipyridamole and benzydamine in rat plasma [57] and fluphenazine [58] have been reported in the former method, the detection limits of dipyridamole and benzydamine were 345 pM and 147 nM in plasma, respectively. Diamino- and aminopyrenes were sensitively determined using TCPO and their detection limits were in the sub-fmol range [59], Carcinogenic compounds such as 1- nitropyrene and its metabolites, can also be determined by the HPLC-PO-CL system. Nonfluorescent nitropyrenes were converted into the corresponding fluorescent aminopyrenes by online reduction on a Zn column followed by detection 2-50-fmol detection limits were achieved in the determination of ethanol extracts from airborne particulates (Fig. 13) [60],... 

Subsequently, Benson (1985) reported 1-nitropyrene deposited on glass photodecomposed in sunlight with a half-life of 14 h. The reaction was accompanied by loss of the nitro group, formation of a phenolic derivative and possibly quinones, and a significant reduction in mutagenicity, consistent with the Chapman mechanism and previous results on nitro-BaP isomers (Finlayson-Pitts and Pitts, 1986). 

W.A. Lopes et al., Electrochemical reduction potentials of 1-nitropyrene, 9-nitroanthracene, 6-nitrochrysene and 3-nitrofluoranthene and their correlation with direct-acting mutagenicities. J. Braz. Chem. Soc. 16, 1099-1103 (2005)... 

Nitroarenes can be effectively determined by RP-HPLC-FLD after reduction to the corresponding PAA. Reduction with NaHS was found to be more efficient than with NaBHj/CuCL. The method was applied to determination of 2-nitrofluorene and 1-nitropyrene, which were converted to 2-fluorenylamine (10b) and 1-pyrenamine (13), respectively, and were found to be at ca 5 ppm levels in dust collected in the Upper Silesia region202. 

Hayakawa and co-workers have intensively developed HPLC techniques with on-line reduction of NPAC to aminoPAC (APAC) and chemiluminescence detection of APAC for trace analysis of NPAC, particularly of nitropyrenes. In this study, we examined the HPLC method for the analysis of novel NPAC, 3-NBA and 2-NTP in airborne particles including the interference of coexisting NPAC in the sample in separation and the efficiency of the on-line reduction to selective conversion of 3-nitrobenzanthrone, which has one carbonyl group, to detectable 3-aminobenzanthrone in the HPLC system. 

Belisario MA et al., Erythrocyte enzymes catalyze 1-nitropyrene and 3-nitrofluoran-threne reduction, Toxicology, 108, 101, 1996. 

Nitrosoarenes react with cellular thiols with half-lives typically a few milliseconds [130] the environmental pollutant and carcinogen, nitropyrene, forms adducts with DNA at guanine sites upon reduction [131]. Radical intermediates are certainly involved in the first two reduction steps [16,111]. 

Figure 1. Thin layer chromatograms of diesel particle extracts viewed under UV light with a fluorescent background (Left) or after reduction by NaBH /CuCl2 reagent (Right). The same samples are shown on both plates, beginning from the left a reference compound mixture of 1-nitropyrene and the three dinitro-pyrenes which ascend in the order indicated and particle extracts 1, 2, and 3 (250pg each). Samples were applied to the silica gel plates in the preabsorbant region on the bottom 3 cm of the plate.

The contrasting specificities of bacterial nitroreductases is very evident in the activity of the nitropyrenes. The nitroreductase-deficiency in strain TA98NR effects a 90% reduction in the mutagenicity of 1-nitropyrene. The compounds 1,3-dinltro- and tetranitropyrene are also less mutagenic in this strain, but 1,6-dinltro-, 1,8-dinitro-, and trinitropyrene retain their activity. In the experiment recorded in Table 2, the activities of the latter three compounds were, in fact. 

Nitrated polycyclic aromatic hydrocarbons, such as 1-nitropyrene, 1-nitrosopyr-ene and 1,3-dinitropyrene, have been measured in car exhaust deposits by HPLC with chemiluminescence detection after on-line EC reduction (PGEs, —1.6 V vs Pd)." LoDs of fmol on-column were claimed. 

Nitropyrenes Isolation, identification, and reduction of mutagenic impurities in carbon black and toners. Science 209, 1039-1043. 

Bacteria within the gastrointestinal tract perform a wide variety of biochemical reactions (77). Since the lower part of the gastrointestinal tract is anaerobic, the biochemical reactions performed by intestinal microflora are usually reductive and hydrolytic in nature. Nitro-PAH metabolism by intestinal microflora has been demonstrated both in vitro and in vivo (Table 1,2). It is well established that the nitroreductases of intestinal microflora are responsible for the metabolism and bioactivation of nitro-PAHs. However, it should be noted that the intestinal microflora are not separate from the host metabolic processes and that synergistic metabolic interactions between enzymes of the gut mucosa, hepatic tissue and microflora are important in the metabolic activation of nitro-PAHs. El-Bayoumy et al. (25) and Kinouchi et al. (45) demonstrated that the predominant metabolites formed from 1-nitropyrene-treated germ-free animals (intestinal microflora were absent) were primary ring-hydroxylated derivatives of... 

El-Bayoumy, K., C. Sharma, Y. M. Louis, B. Reddy, and S. S. Hecht. 1983. The role of intestinal microflora in the metabolic reduction of 1-nitropyrene to 1-aminopyrene in conventional and germ free rats and in humans. Cancer Lett. 19 311-316. 

Howard, P. C., R. H. Heflich, F. E. Evans, and F. A. Beland. 1983. Formation of DNA adducts in vitro and in Salmonella typhimurium upon metabolic reduction of the environmental mutagen 1-nitropyrene. Cancer Res. 43 2052-2058. 

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