Biotransformation of 1-nitropyrene in intestinal anaerobic bacteria

Nitroreductase-instructed supramolecular assemblies for microbiome regulation to enhance colorectal cancer treatments

The development of human microbiome has collectively correlated the sophisticated interactions between Fusobacterium nucleatum and colorectal cancers (CRCs). However, the treatment of CRC via disruption of gastrointestinal flora remains less explored. Aiming at the up-regulated activity of nitroreductase in F. nucleatum-infected tumors, here, we developed the nitroreductase-instructed supramolecular self-assembly. The designed assembly precursors underwent enzymatic transformation to form assemblies, which agglutinated F. nucleatum and eradicated the targeted bacteria. These assemblies with anti-F. nucleatum activity could further alleviate the bacteria-induced drug resistance effect, thus sensitizing CRC cells against chemo-drugs. Eventually, in mice bearing F. nucleatum-infected CRC, the local introduction of nitroreductase-instructed assemblies could efficiently inhibit the tumor growth. Overall, this study incorporated nitroreductase to broaden the toolbox of enzyme-instructed supramolecular self-assembly. The local introduction of nitroreductase-instructed assemblies could target F. nucleatum to eliminate its contribution to CRC drug resistance and ameliorate chemotherapy outcomes.

The mechanism of berberine alleviating metabolic disorder based on gut microbiome

With socioeconomic advances and improved living standards, metabolic syndrome has increasingly come into the attention. In recent decades, a growing number of studies have shown that the gut microbiome and its metabolites are closely related to the occurrence and development of many metabolic diseases, and play an important role that cannot be ignored, for instance, obesity, type 2 diabetes (T2DM), non-alcoholic fatty liver disease (NAFLD), cardiovascular disease and others. The correlation between gut microbiota and metabolic disorder has been widely recognized. Metabolic disorder could cause imbalance in gut microbiota, and disturbance of gut microbiota could aggravate metabolic disorder as well. Berberine (BBR), as a natural ingredient, plays an important role in the treatment of metabolic disorder. Studies have shown that BBR can alleviate the pathological conditions of metabolic disorders, and the mechanism is related to the regulation of gut microbiota: gut microbiota could regulate the absorption and utilization of berberine in the body; meanwhile, the structure and function of gut microbiota also changed after intervention by berberine. Therefore, we summarize relevant mechanism research, including the expressions of nitroreductases-producing bacteria to promote the absorption and utilization of berberine, strengthening intestinal barrier function, ameliorating inflammation regulating bile acid signal pathway and axis of bacteria-gut-brain. The aim of our study is to clarify the therapeutic characteristics of berberine further and provide the theoretical basis for the regulation of metabolic disorder from the perspective of gut microbiota.

Microbial nitroreductases: A versatile tool for biomedical and environmental applications

Nitroreductases, enzymes found mostly in bacteria and also in few eukaryotes, use nicotinamide adenine dinucleotide (NADH) or nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor for their activity and metabolize an enormous list of a diverse nitro group-containing compounds. Nitroreductases that are capable of metabolizing nitroaromatic and nitro heterocyclic compounds have drawn great attention in recent years owing to their biotechnological, biomedical, environmental, and human impact. These enzymes attracted medicinal chemists and pharmacologists because of their prodrug selectivity for activation/reduction of nitro compounds that wipe out pathogens/cancer cells, leaving the host/normal cells unharmed. It is applied in diverse fields of study like prodrug activation in treating cancer and leishmaniasis, designing fluorescent probes for hypoxia detection, cell imaging, ablation of specific cell types, biodegradation of nitro-pollutants, and interpretation of mutagenicity of nitro compounds. Keeping in view the immense prospects of these enzymes and a large number of research contributions in this area, the present review encompasses the enzymatic reaction mechanism, their role in antibiotic resistance, hypoxia sensing, cell imaging, cancer therapy, reduction of recalcitrant nitro chemicals, enzyme variants, and their specificity to substrates, reaction products, and their applications.

Gut Microbiota-Mediated Personalized Treatment of Hyperlipidemia Using Berberine

Nitroreductases (NRs) are bacterial enzymes that reduce nitro-containing compounds. We have previously reported that NR of intestinal bacteria is a key factor promoting berberine (BBR) intestinal absorption. We show here that feeding hamsters with high fat diet (HFD) caused an increase in blood lipids and NR activity in the intestine. The elevation of fecal NR by HFD was due to the increase in either the fraction of NR-producing bacteria or their activity in the intestine. When given orally, BBR bioavailability in the HFD-fed hamsters was higher than that in those fed with normal chow (by +72%, *P<0.05). BBR (100 mg/kg/day, orally) decreased blood lipids in the HFD-fed hamsters (**P<0.01) but not in those fed with normal diet. Clinical studies indicated that patients with hyperlipidemia had higher fecal NR activity than that in the healthy individuals (**P<0.01). Similarly, after oral administration, the blood level of BBR in hyperlipidemic patients was higher than that in healthy individuals (*P<0.05). Correlation analysis revealed a positive relationship between blood BBR and fecal NR activity (r=0.703). Thus, the fecal NR activity might serve as a biomarker in the personalized treatment of hyperlipidemia using BBR.

Low temperature acclimation with electrical stimulation enhance the biocathode functioning stability for antibiotics detoxification

Improvement of the stability of functional microbial communities in wastewater treatment system is critical to accelerate pollutants detoxification in cold regions. Although biocathode communities could accelerate environmental pollutants degradation, how to acclimate the cold stress and to improve the catalytic stability of functional microbial communities are remain poorly understood. Here we investigated the structural and functional responses of antibiotic chloramphenicol (CAP) reducing biocathode communities to constant low temperature 10 °C (10-biocathode) and temperature elevation from 10 °C to 25 °C (S25-biocathode). Our results indicated that the low temperature acclimation with electrical stimulation obviously enhanced the CAP nitro group reduction efficiency when comparing the aromatic amine product AMCl2 formation efficiency with the 10-biocathode and S25-biocathode under the opened and closed circuit conditions. The 10-biocathode generated comparative AMCl maximum as the S25-biocathode but showed significant lower dehalogenation rate of AMCl2 to AMCl. The continuous low temperature and temperature elevation both enriched core functional community in the 10-biocathode and S25-biocathode, respectively. The 10-biocathode functioning stability maintained mainly through selectively enriching cold-adapted functional species, coexisting metabolically similar nitroaromatics reducers and maintaining the relative abundance of key electrons transfer genes. This study provides new insights into biocathode functioning stability for accelerating environmental pollutants degradation in cold wastewater system.

Distribution of nitroreductive activity toward nilutamide in rat

Nilutamide is a pneumotoxic and hepatotoxic nitroaromatic (R-NO2) antiandrogen used in the treatment of prostate carcinoma in man. Previously, we established that in the rat lung, the drug is metabolized into the corresponding hydroxylamine (R-NHOH) and amine (R-NH2) derivatives. These results evidenced a cytosolic oxygen-sensitive (type II) nitroreductase activity in lung. In the present studies, we extended the characterization of nilutamide metabolism in liver, brain, kidney, heart, blood, intestine (small, cecum, and large, and their respective luminal contents) of male Sprague-Dawley rats. Subcellular fractions for all tissues (except blood) examined (postmitochondrial, cytosolic, and microsomal) were prepared by differential ultracentrifugation. Blood and intestinal contents were sonicated before investigation. Incubations were run in the presence or absence of O2 to assess type I and II nitroreductase activities. Organic extracts were analyzed by HPLC methods and results were expressed as pmoles of R-NH2 formed per milligram protein per minute. Four distinct nitroreductive activities were evidenced. Cytosolic and microsomal type II nitroreductase activities were detected in all tissue samples studied. Type I NR activity was not observed in any of the cytosols, but was detected in the small intestine, lung, kidney, and liver microsomes. Nilutamide was also reduced in the intestinal lumen, possibly by a bacterial type I nitroreductase. Highest activities were observed in cytosols and were oxygen sensitive. These results evidence and characterize previously unknown nitroreductive activities toward nilutamide in rat tissues that might provide some explanation to the side effects of nilutamide and other nitroaromatic compounds observed in human therapeutics.

Biological degradation of 2,4,6-trinitrotoluene

Nitroaromatic compounds are xenobiotics that have found multiple applications in the synthesis of foams, pharmaceuticals, pesticides, and explosives. These compounds are toxic and recalcitrant and are degraded relatively slowly in the environment by microorganisms. 2,4,6-Trinitrotoluene (TNT) is the most widely used nitroaromatic compound. Certain strains of Pseudomonas and fungi can use TNT as a nitrogen source through the removal of nitrogen as nitrite from TNT under aerobic conditions and the further reduction of the released nitrite to ammonium, which is incorporated into carbon skeletons. Phanerochaete chrysosporium and other fungi mineralize TNT under ligninolytic conditions by converting it into reduced TNT intermediates, which are excreted to the external milieu, where they are substrates for ligninolytic enzymes. Most if not all aerobic microorganisms reduce TNT to the corresponding amino derivatives via the formation of nitroso and hydroxylamine intermediates. Condensation of the latter compounds yields highly recalcitrant azoxytetranitrotoluenes. Anaerobic microorganisms can also degrade TNT through different pathways. One pathway, found in Desulfovibrio and Clostridium, involves reduction of TNT to triaminotoluene; subsequent steps are still not known. Some Clostridium species may reduce TNT to hydroxylaminodinitrotoluenes, which are then further metabolized. Another pathway has been described in Pseudomonas sp. strain JLR11 and involves nitrite release and further reduction to ammonium, with almost 85% of the N-TNT incorporated as organic N in the cells. It was recently reported that in this strain TNT can serve as a final electron acceptor in respiratory chains and that the reduction of TNT is coupled to ATP synthesis. In this review we also discuss a number of biotechnological applications of bacteria and fungi, including slurry reactors, composting, and land farming, to remove TNT from polluted soils. These treatments have been designed to achieve mineralization or reduction of TNT and immobilization of its amino derivatives on humic material. These approaches are highly efficient in removing TNT, and increasing amounts of research into the potential usefulness of phytoremediation, rhizophytoremediation, and transgenic plants with bacterial genes for TNT removal are being done.

Metabolism of 2-nitrofluorene, 2-aminofluorene and 2-acylaminofluorenes in rat and dog and the role of intestinal bacteria

1. The in vivo metabolism of 2-nitrofluorene (NF), an environmental pollutant, and 2-aminofluorene (AF) and its acylated derivatives, 2-formylaminofluorene (FAF) and 2-acetylaminofluorene (AAF), was examined in rat and dog. 2. 7-Hydroxy-2-nitrofluorene, 5-hydroxy-2-nitrofluorene, AF, AAF, FAF, 7-hydroxy-2-aminofluorene, 5-hydroxy-2-aminofluorene, 7-hydroxy-2-acetylaminofluorene, 5-hydroxy-2-acetylaminofluorene, 7-hydroxy-2-formylaminofluorene and 5-hydroxy-2-formylaminofluorene were identified as urinary and faecal metabolites of NF in rat and dog. 3. AAF and its hydroxylated derivatives were detected as major metabolites of NF in rat, but FAF and its hydroxylated metabolites were mainly excreted in dog. 4. AF, AAF, FAF and their hydroxylated metabolites were also identified as urinary and faecal metabolites of AF, AAF or FAF in rat, suggesting that AAF and FAF are interconverted via AF. 5. Treatment of rat and dog with antibiotics significantly decreased the urinary and faecal excretion of AF and its derivatives after oral administration of NF, and partly decreased the excretion of acylated metabolites after an oral dose of AF. 6. The caecal contents of untreated rats and some species of intestinal bacteria exhibited nitro-reductase activity toward NF, and acylating activity toward AF, affording AAF and FAF.

Modulatory effects of polycyclic aromatic hydrocarbons on the mutagenicity of 1-nitropyrene: a structure-activity relationship study

Benzo[a]pyrene (B[a]P) is able to inhibit the mutagenicity of 1-nitropyrene (1-NP) through the reduction of nitroreductase activity and formation of adducts with DNA. The relationships between the chemical structure of 9 polycyclic aromatic hydrocarbons (PAHs) and antagonistic effects on the 1-NP-induced mutation were evaluated by the binary mixtures of 1-NP and PAHs with Salmonella typhimurium TA98 in the absence of S9 mix. Remarkably different antagonistic effects of 9 PAHs on the mutagenicity of 1-NP were observed. Among the tested PAHs, coronene demonstrates the most antagonistic potential followed by benzo[g,h,i]perylene (B[g,h,i]P), benzo[e]pyrene (B[e]P), dibenzo[a,h]pyrene (DB[a,h]P), benzo[a]pyrene (B[a]P) and pyrene. Naphthalene, anthracene, and chrysene had only minor inhibitory activity on the 1-NP mutagenicity. The modifying effects of PAHs on the nitroreductase activity of TA98 strains in the presence of 1-NP were further examined from the production of 1-AP. The statistical analytical data showed that the inhibitory effect of PAHs on the mutagenicity of 1-NP significantly correlated with their effects on the nitroreductase activity (r = -0.69, p < 0.05). In addition, the formation of 1-NP-DNA adducts of the binary mixtures of 1-NP and PAH was determined by the 32P-postlabeling method. The results indicated that the modulatory effects of PAHs on the formation of 1-NP-DNA adducts were correlated well with their antagonistic activity (r = -0.91, P < 0.01). From the above results, the relationships between the chemical structure of PAHs and the antagonistic effects on the 1-NP mutagenicity were revealed by the surface area and electronic parameters of PAHs. The planar molecular area of PAHs was more convincingly correlated with the antagonistic effect on the mutagenicity of 1-NP (r = -0.81, p < 0.01) than that with the difference in energy, delta E, between EHOMO and ELUMO (r = 0.69, p < 0.05). According to the above, two possible mechanisms are involved in the interactive effect of the binary mixtures: (1) a higher binding affinity with nitroreductase for PAHs having a large planar surface area; and (2) a high energy of interaction between 1-NP and PAHs with a low delta E might decrease the nitroreductive capability.

Stability of 1-nitropyrene and 1,6-dinitropyrene in environmental water samples and soil suspensions

This study examined the stability of mutagenic 1-nitropyrene (1-NP) and (1,6-dinitropyrene (1,6-diNP) in environmental water samples and various soil suspensions containing 0.1% peptone and in water samples containing no peptone. The water samples or the soil suspensions were mixed with NPs and incubated at 30 degrees C. The stability of NPs was expressed as mutagenic activity remaining in the test solutions. The mutagenicity decreased rapidly when 1-NP or 1,6-diNP was incubated in unautoclaved test solutions containing 0.1% peptone but not when incubated in autoclaved test solutions. The mutagenicity in the soil suspensions, especially in the sludge, decreased faster than in the water samples. This was due to the large number of colony-forming units (CFU) in the soil suspensions. In the water samples containing 0.1% peptone, the mutagenicity of NPs in the polluted Tamiya River water decreased faster than in the unpolluted Yoshino River water. The rate of decrease was dependent on the number of CFU in the water samples. A large number of CFU decreased the mutagenicity more rapidly than did a small number of CFU in samples. The disappearance of mutagenicity was dependent on the initial concentrations of NPs. The periods required for a 50% decrease in the mutagenicity of 1-NP at the low concentration (0.2 microgram/ml) was shorter than that at the high concentration (3 micrograms/ml). 1-Aminopyrene was detected in the 1-NP test solution after incubation when it was analyzed by high-pressure liquid chromatography. In the water samples containing no peptone, the mutagenicity of 1-NP (0.2 microgram/ml) decreased gradually during 30 days of incubation. After incubation for 1540 days, the remaining mutagenicity of 1-NP in the water samples was almost the same as that in autoclaved water samples. On the other hand, the mutagenicity of 1,6-diNP (10 ng/ml) decreased and the remaining mutagenicity, except in the Yoshino River water, was less than 20% after 30 days of incubation and was completely lost during the 1540-day incubation. However, the mutagenicity of 1,6-diNP in autoclaved water samples was very stable and almost all mutagenicity, except in sea water, remained after 1540 days of incubation at 30 degrees C. These results suggest that the microflora in the environment plays an important role in the primary degradation and decontamination of relatively low concentrations of NPs.

Chiral inversion of drug: role of intestinal bacteria in the stereoselective sulphoxide reduction of flosequinan

Chiral inversion at a sulphoxide position of flosequinan enantiomers [(+/-)-7-fluoro-1-methyl-3-methylsulphinyl-4-quinolone] occurred in conventional rats but not in either germ-free rats or rats treated with antibiotics after an oral administration of each enantiomer. Thus, it was postulated that the chiral inversion occurred by mechanisms mediated by intestinal bacteria. The intestinal content isolated from conventional rats reduced R(+)- and S(-)-flosequinan to produce the sulphide, while intestinal content from rats treated with antibiotics did not reduce the drug. Several strains of facultative anaerobes possessed a high flosequinan reducing activity. Escherichia coli, Klebsiella oxytoca and Klebsiella pneumoniae reduced R(+)-flosequinan to the sulphide stereoselectively. On the other hand, Enterobacter aerogenes and Micrococcus agilis exclusively reduced S(-)-flosequinan. The sulphide, which could be produced by intestinal bacteria from R(+)- and S(-)-flosequinan, was readily absorbed upon an oral administration to rats, and was oxidized fairly rapidly to R(+)- and S(-)-flosequinan and further to the sulphone form. Based on these data, it has been confirmed that chiral inversion at the sulphoxide position of flosequinan enantiomers occur via stereoselective reduction of sulphoxide by intestinal bacteria to form the sulphide, followed by oxidation of the sulphide in the body to produce R(+)- and S(-)-flosequinan.

Bacterial mutagenicity, metabolism, and DNA adduct formation by binary mixtures of benzo[a]pyrene and 1-nitropyrene

Air pollutants are a complex mixture containing polycyclic organic compounds. Among these are 1-NP and B[a]P, which are important contributors to the mutagenicity of diesel exhaust and airborne particulate matters. To investigate the interaction of a complex mixture of airborne mutagens, the mutagenicity of 1-NP was examined with S. typhimurium TA98 and TA98NR in the presence and absence of B[aP. B[a]P exhibited a more antagonistic effect on the mutagenicity of 1-NP in strain TA98 than in strain TA98NR. Also studied were (1) the inhibitory effects of B[a]P on the nitroreductive metabolism of 1-NP and (2) DNA adduct formation by 1-NP. Nitroreductase was associated with the metabolism of 1-NP, and was reduced in a dose-dependent manner in a binary mixture of 1-NP and B[a]P. HPLC analysis showed that the amounts of 1-AP and NAAP, the metabolites of 1-NP, were significantly decreased by the addition of B[a]P in mixtures. The results indicate that the antagonistic effect of B[a]P on the mutagenicity of 1-NP is mediated through altering its nitroreductive metabolism.

Metabolism of 1-nitropyrene by human, rat, and mouse intestinal flora: mutagenicity of isolated metabolites by direct analysis of HPLC fractions with a microsuspension reverse mutation assay

The metabolism of [14C]-1-nitropyrene by human, rat and mouse intestinal microflora and a bioassay-directed chemical analysis of the isolated metabolites by assaying HPLC fractions with a microsuspension reverse mutation assay were examined. [14C]-1-Nitropyrene was metabolized by human, rat, and mouse intestinal microflora to 1-aminopyrene, N-acetyl-1-aminopyrene, N-formyl-1-aminopyrene, and two unknown metabolites identified as A and B. The predominant metabolite produced by human, rat, or mouse intestinal microflora following a 12-h incubation with [14C]-1-nitropyrene was 1-aminopyrene, which accounted for 93, 79, and 88% of the total 14C, respectively. Only minor amounts of N-formyl-1-aminopyrene (1.4, 1.2, and 1.0%), N-acetyl-1-aminopyrene (4.4, 3.0, and 3.4%), unknown A (1.0, 1.2, and 1.0%), and unknown B (3.3, 5.0, and 1.2%) were detected. These data suggest that a similar mechanism exists in the biotransformation of 1-nitropyrene by intestinal microflora from all three sources. Direct mutagenicity analysis of the HPLC fractions produced by intestinal microflora with the microsuspension reverse mutation assay indicated that mutagenic fractions can be resolved using this methodology.

Formation of amphetamine from its nitro analogue by anaerobic intestinal bacteria

1. Microbial reduction of 1-phenyl-2-nitropropane 1 was carried out using 40 strains of intestinal anaerobic bacteria. Among them, 12 strains (Mitsuokella multiacidus, Clostridium perfringens, C. innocuum, C. clostiriiforme, C. difficile, C. butyricum, C. sp., Eubacterium limosum, E. aerofaciens, E. multiforme, Peptostreptococcus anaerobius and P. productus) had the ability to reduce 1 to amphetamine 2 (0.1-1% yield). 2. Clostridium species were more active than another intestinal anaerobic bacteria. 3. When Clostridium perfringens was used in preparative fermentation, the yield of 2 was increased, and its absolute structure had an (S)-configuration with an optical purity of 68% in enantiomeric excess.

Metabolism of 1-, 3-, and 6-nitrobenzo[a]pyrene by intestinal microflora

The compounds 1-, 3-, and 6-nitrobenzo[a]pyrene (nitro-BaP) are environmental pollutants and have been shown to be potent bacterial mutagens. The anaerobic metabolism of these isomeric nitro-BaPs was investigated by the incubation of rat intestinal microflora with each isomer for 48 h. Aliquots were removed at several time intervals, extracted, fractionated by high-pressure liquid chromatography (HPLC), and the radioactivity determined. Metabolites were identified by comparison of their chromatographic, ultraviolet-visible absorption, and mass spectral properties with those of authentic standards. The order of the extent of nitroreduction for these isomers was 3-nitro-BaP greater than 6-nitro-BaP greater than 1-nitro-BaP. After 48 h of exposure, 84% of the added 3-nitro-BaP was present as 3-amino-BaP, 51% of the 6-nitro-BaP was metabolized to 6-amino-BaP, and 1-nitro-BaP was reduced to 1-amino-BaP (13%) and 1-nitro-BaP (4%). The order of the extent of microbial nitroreduction for these nitro-BaP isomers is different from the predictions based on electronic and steric hindrance effects. These results suggest that intestinal microflora nitroreductases exhibit a markedly high degree of substrate specificity toward nitro-BaPs that affects the extent of nitroreduction.

Metabolism of 6-nitrochrysene by intestinal microflora

Since bacterial nitroreduction may play a critical role in the activation of nitropolycyclic aromatic hydrocarbons, we have used batch and semicontinuous culture systems to determine the ability of intestinal microflora to metabolize the carcinogen 6-nitrochrysene (6-NC). 6-NC was metabolized by the intestinal microflora present in the semicontinuous culture system to 6-aminochrysene (6-AC), N-formyl-6-aminochrysene (6-FAC), and 6-nitrosochrysene (6-NOC). These metabolites were isolated and identified by high-performance liquid chromatography, mass spectrometry, and UV-visible spectrophotometry and compared with authentic compounds. Almost all of the 6-NC was metabolized after 10 days. Nitroreduction of 6-NC to 6-AC was rapid; the 6-AC concentration reached a maximum at 48 h. The ratio of the formation of 6-AC to 6-FAC to 6-NOC at 48 h was 93.4:6.3:0.3. Interestingly, compared with results in the semicontinuous culture system, the only metabolite detected in the batch studies was 6-AC. The rate of nitroreduction differed among human, rat, and mouse intestinal microflora, with human intestinal microflora metabolizing 6-NC to the greatest extent. Since 6-AC has been shown to be carcinogenic in mice and since nitroso derivatives of other nitropolycyclic aromatic hydrocarbons are biologically active, our results suggest that the intestinal microflora has the enzymatic capacity to generate genotoxic compounds and may play an important role in the carcinogenicity of 6-NC.

Mutagenicity and nitropyrene concentration of indoor air particulates exhausted from a kerosene heater

The particulates in a room warmed with a radiant kerosene heater were collected, extracted and fractionated into diethyl ether-soluble neutral, acidic and basic fractions. The mutagenicity of these fractions was measured with Salmonella typhimurium strains TA98, TA98NR, TA98/1,8-DNP6 and TA100 in the presence and absence of S9 mix. Room air without the heater showed very low mutagenicity. However, a sample from a room at the beginning of the burning period showed very high mutagenicity (237 His+ revertants/plate/m3 of air in strain TA98 in the absence of S9 mix). In contrast, emissions from the heater after it was burning stably showed low mutagenicity (9 His+ revertants/plate/m3). The crude extract of particulates from the heater at the beginning of the burning period was analyzed by high-pressure liquid chromatography (HPLC) and showed a considerable amount of nitropyrenes (NPs); the concentrations of 1-NP and 1,6-diNP were 1.62 ng and 0.149 ng/m3 of air, respectively, and accounted for 1.2% and 17.6%, respectively, of the mutagenicity in strain TA98 in the absence of S9 mix. In addition, an HPLC-Ames histogram showed that peaks of mutagenicity corresponding to 1-NP and diNPs accounted for 75.7% (1-NP, 4.9%; 1,6-diNP, 17.1%; 1,8-diNP, 46.3%; 1,3-diNP, 7.4%) of the HPLC-recovered mutagenicity for strain TA98 without S9 mix. These results that kerosene heaters, especially immediately after ignition, create mutagenic substances such as NPs.

In vitro intestinal microflora-mediated metabolism of biliary metabolites from 1-nitropyrene-treated rats

To investigate the modifying role of the intestinal microflora in the metabolism of 1-nitropyrene (1-NP) via enterohepatic circulation, we collected bile from male Wistar rats administered [3H]1-NP orally. The bile was mixed with the intestinal contents (IC) prepared from untreated rats and the mixture was incubated anaerobically under an atmosphere of nitrogen at 37 C. Samples of the reaction mixture were removed at intervals to assay their mutagenic potential, to determine the radioactivity bound to the IC, and for analysis of the biliary metabolites. The binding of the radioactivity to the IC increased linearly as a function of time during the 1-hr incubation. The time-dependent binding does not occur with heat-treated IC and the binding was inhibited by addition of D-saccharic acid 1,4-lacton, a beta-glucuronidase inhibitor. The mutagenicity (for Salmonella typhimurium strain TA98 without S9 mix) of the bile increased early in the incubation period and then decreased very rapidly. The mutagenicity of the bile was also enhanced by treatment with a sonicated IC extract or beta-glucuronidase, but not with a heat-treated IC or aryl-sulfatase. The metabolites produced after the bile was incubated for short periods with the IC were mainly nitrohydroxypyrenes; at later times nitroreduction occurred. The level of acetylaminohydroxypyrenes, which were formed by deconjugation, did not change during the incubation. To determine the degree of contribution of the IC to the total acetylating capacity, we measured acetyltransferase activity of the IC and various organs in Wistar rats. The liver had the highest N-acetyltransferase activity among the seventeen organs examined. Considerable activity was also detected in the kidney, small intestine, lung, and testis, but the IC showed very low activity. The acetylating capacity of the IC was 0.27% of the total capacity in rats, and that of the liver was more than 80%. These results suggest that the nitrohydroxypyrenes formed from 1-NP in the liver were conjugated to glucuronic acid and excreted via the bile duct into intestine. Hydrolysis of these glucuronide conjugates by bacterial beta-glucuronidase liberated into intestine, free nitrohydroxypyrenes, which were direct-acting mutagens. The released aglycons were then rapidly nitro-reduced by intestinal microflora, but contribution of the intestinal microflora to acetylation of the reduced metabolites is very low.

Genotoxicity of a variety of nitroarenes and other nitro compounds in DNA-repair tests with rat and mouse hepatocytes

Genotoxicity of a variety of nitroarenes and other compounds was examined in DNA-repair tests with rat or mouse hepatocytes. Out of 15 nitroarenes tested, 9 compounds, i.e., 1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene, 1-nitro-3-acetoxypyrene, 3-nitrofluoranthene, 2-nitrofluorene, 2,7-di-nitrofluorene and 5-nitroacenaphthene elicited positive response of DNA repair in the tests with rat and mouse hepatocytes. Among the positive chemicals, the DNA-repair level of the 3 dinitropyrene isomers was much higher than other nitroarenes. The results indicate that a number of nitroarenes are metabolically activated in the primary culture of rodent hepatocytes, and suggest potential carcinogenicity of 1-nitropyrene and 1-nitro-3-acetoxypyrene the carcinogenicity of which is either not clear or unknown. Of the other nitro compounds, 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide as well as 4-nitroquinoline 1-oxide were clearly genotoxic in the assays with hepatocytes of both species. However, 5-nitro-2-furaldehyde semicarbazone was negative in both assays with hepatocytes of 2 species.

Metabolism of nitroaromatic compounds

There appear to be two major pathways for the metabolism of nitrobenzene and substituted nitrobenzenes. The first of these is reduction of the nitro group to yield aniline or substituted anilines. For nitrobenzene and perhaps for pentachloronitrobenzene, reduction of the nitro group to the amine is accomplished by bacteria of the gastrointestinal tract. Addition of a second nitro group results in easier reduction of one of the nitro groups on dinitrobenzenes, since they can be reduced under aerobic conditions by hepatic and erythrocyte enzymes. Bacterial reduction of the dinitrobenzenes is probably not quantitatively important in vivo. The second pathway is replacement of a nitro group by glutathione. The relative importance of this pathway compared to nitro group reduction depends upon the compound. It has not been demonstrated to occur for nitrobenzene. It is the major route of metabolism for 1,2-dinitrobenzene but is not an important route for 1,3- or 1,4-dinitrobenzene in hepatocytes. Tetrachloronitrobenzene isomers in which the nitro group is flanked by chlorines and pentachloronitrobenzene undergo nitro group replacement, but 2,3,4,5-tetrachloronitrobenzene does not. The most important pathway for the metabolism of mononitrotoluenes is methyl group oxidation. All quantitatively important metabolites are apparently formed from the nitrobenzyl alcohols. The mono- and dinitrotoluenes are not significantly reduced to isolatable metabolites by mammalian enzymes in vivo; intestinal microflora reduce these compounds after biliary excretion of the nitrobenzyl glucuronides. The little available evidence suggests that this is not the case for trinitrotoluenes. Urinary metabolites retain the methyl group and bear one or two amino groups. This suggests either that mammalian enzymes are capable of reducing the nitro groups of trinitrotoluenes in vivo or that intestinal microflora gain access to unmodified trinitrotoluene. The nitropolycyclic aromatic hydrocarbons are apparently metabolized by both nitro reduction and ring oxidation. There is good evidence, at least for 1-nitropyrene and 6-nitrobenzo[a]pyrene, that nitro reduction occurs in intestinal microflora. the complexities of foreign compound metabolism are well illustrated by the biotransformation of the nitroaromatic compounds. Positional isomers are preferentially metabolized by markedly different pathways. Substitution to different degrees or with different functional groups greatly affects the types of metabolites formed. Yet these compounds also offer opportunities for understanding the mechanisms of foreign compound metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic activation of 1-nitropyrene and 1,6-dinitropyrene by nitroreductases from Bacteroides fragilis and distribution of nitroreductase activity in rats

Nitrated polycyclic aromatic compounds, 1-nitropyrene (1-NP) and 1,6-dinitropyrene (1,6-diNP), are environmental mutagens and carcinogens. Nitroreductases purified from an anaerobic bacterium, Bacteroides fragilis, catalyzed the metabolic activation of these compounds to produce DNA- and tRNA-bound adducts in vitro. Formation of the adducts was inhibited by p-chloromercuribenzoic acid, which is an inhibitor of nitroreductases from B. fragilis. The enzyme and coenzyme (NADPH) were essential for the adduct formation. These results suggest that nitroreduction is a necessary step in the metabolic activation of nitropyrenes. 1-NP bound specifically to poly(G) and poly(dG), and 1,6-diNP bound to poly(G), poly(dG), and poly(X). The other purine polynucleotides were weak acceptors. However, the reactive products of nitropyrenes formed by nitroreductases could not bind to pyrimidine polynucleotides. Enzymatic hydrolysis of 1-NP-bound DNA and subsequent analysis by high-performance liquid chromatography showed one major and two minor adducts in the hydrolysate. The peak of the major adduct corresponded to that of N-(deoxyguanosin-8-y1)-1-aminopyrene, which is the same as an adduct formed by xanthine oxidase, a mammalian nitroreductase. Nitroreductase activity in the various organs and intestinal contents of Sprague-Dawley rats was assayed in the presence of NADPH or NADH under nitrogen gas. Nitroreductase activity was widely distributed in the organs of the rats; in particular, that of the liver and of the small intestine was relatively high, but that of the respiratory organs such as lung and alveolar macrophages was very low. Intestinal contents had high nitroreductase activity, which was proportional to the number of bacteria, especially anaerobic bacteria, in the intestine. These results suggest that the nitroreductase activity of the normal bacterial flora is very high in rats and that the intestinal bacteria play a major role in the metabolism of nitropyrenes in vivo.

Detection of 1-nitropyrene in yakitori (grilled chicken)

Pieces of raw chicken with or without a marinating sauce were grilled over a city gas flame, extracted with benzene-ethanol (4:1) by ultrasonication and fractionated into diethyl ether-soluble neutral, acidic and basic fractions. The mutagenicity of these fractions was measured with Salmonella typhimurium strains TA100, TA98, TA98NR and TA98/1,8-DNP6 in the presence and absence of a 9000 X g post-mitochondrial supernatant from Aroclor 1254-treated Sprague-Dawley rat liver (S9 mix). The basic fraction of yakitori without the sauce was more mutagenic than the other fractions for S. typhimurium strain TA98 in the presence of S9 mix. This is probably due to the presence of amino acid or protein pyrolysates. However, when the chicken was grilled with the sauce, the basic fraction showed lower mutagenicity for strain TA98 in the presence of S9 mix than did the same fraction without the sauce. The neutral fraction of yakitori with sauce showed high mutagenicity for strain TA98 in the absence of S9 mix, but low mutagenicity for strains TA98NR and TA98/1,8-DNP6, suggesting that this fraction might contain nitropyrenes (NPs). The neutral fraction of yakitori was analyzed by high-performance liquid chromatography (HPLC). The neutral fraction of the chicken grilled with the sauce for 3, 5 and 7 min contained 3.8, 19 and 43 ng, respectively, of 1-NP per gram of yakitori accounting for 3.0, 2.7 and 1.3%, respectively, of the total mutagenicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Results of the rec-assay of nitropyrenes in the Bacillus subtilis test system

The rec-assay of the nitropyrenes in Bacillus subtilis was performed. All nitropyrene derivatives were positive in this system. Especially, 3 isomers of 1,3-, 1,6- and 1,8-dinitropyrene and 4-nitropyrene were found to possess strong DNA-damaging capacities at extremely low concentrations.

Biotransformation of 1-nitropyrene to 1-aminopyrene and N-formyl-1-aminopyrene by the human intestinal microbiota

The nitropolycyclic aromatic hydrocarbon 1-nitropyrene (1-NP) is an environmental pollutant, a potent bacterial and mammalian mutagen, and a carcinogen. The metabolism of 1-NP by the human intestinal microbiota was studied using a semicontinuous culture system that simulates the colonic lumen. [3H]-1-Nitropyrene was metabolized by the intestinal microbiota to 1-aminopyrene (1-AP) and N-formyl-1-aminopyrene (FAP) as determined by high-performance liquid chromatography (HPLC) and mass spectrometry. Twenty-four hours after the addition of [3H]-1-NP, the formylated compound and 1-AP accounted for 20 and 80% of the total metabolism, respectively. This percentage increased to 66% for FAP after 24 h following 10 d of chronic exposure to unlabeled 1-NP, suggesting metabolic adaptation to 1-NP by the microbiota. Both 1-AP and FAP have been shown to be nonmutagenic towards Salmonella typhimurium TA98, which indicates that the intestinal microflora may potentially detoxify 1-NP.

Mutagenicity and carcinogenicity of nitroarenes and their sources in the environment

Nitroarenes are postulated to play a principal part among mutagens/carcinogens which are induced in the combustion process and, in addition, are widely distributed in the environment. This review deals with the following points concerning nitroarene toxicity. Data on the mutagenicity of nitroarenes obtained by short-term bioassays are expected to provide us with sufficient information for us to determine their genotoxicity and carcinogenicity. Therefore, mutagenicity detected with Salmonella, Escherichia, and yeast test systems is discussed. Genotoxicity in mammalian cells is also important for determining the mutagenic properties of nitroarenes. In this article, mutagenicity in Chinese hamster ovary cells, sister chromatid exchanges, and cell transformation is summarized. The metabolism of nitroarenes in vivo and in vitro is of importance for determining their behavior and active forms. Therefore, current studies regarding metabolism of nitroarenes are described. Carcinogenicity of nitroarenes for animals has been reported by many workers. In this review, the incidence and histological features of tumors induced by nitroarenes are described. Furthermore, the possible association between human lung cancer and nitroarenes is discussed. Sources of nitroarenes in the environment are given. The results of various chemical tests for identifying nitroarenes are summarized, and speculation on the risk of nitroarenes for humans is presented.

Fungal metabolism and detoxification of the nitropolycyclic aromatic hydrocarbon 1-nitropyrene

Nitropolycyclic aromatic hydrocarbons are ubiquitous environmental pollutants, many of which are potent mutagens in bacterial and mammalian cells and carcinogenic to rodents. In this study, we investigated the fungal metabolism of 1-nitropyrene and determined the mutagenic activity of the metabolites toward Salmonella typhimurium TA98, TA98NR, and TA100. Cunninghamella elegans metabolized 1-nitropyrene to form glucoside conjugates of 6-hydroxy-1-nitropyrene and 8-hydroxy-1-nitropyrene. The metabolites were isolated by reversed-phase high-pressure liquid chromatography and characterized by application of UV absorption, 1H-nuclear magnetic resonance, and mass spectroscopy. Mutagenicity assays performed on samples extracted from incubations of C. elegans with 1-nitropyrene indicated that mutagenic activity decreased with time. Consistent with the loss in mutagenic activity, the glucoside conjugates of 6- and 8-hydroxy-1-nitropyrene were nonmutagenic in the Salmonella reversion assay. The results indicate that the fungus C. elegans metabolizes 1-nitropyrene to detoxified products.

The effect of diet on the mammalian gut flora and its metabolic activities

The review will encompass the following points: A brief introduction to the role of the gut flora in the toxicology of ingested food components, contaminants, and additives, including known pathways of activation and detoxication of foreign compounds and the implication of the flora in enterohepatic circulation of xenobiotics. The advantages and disadvantages of the various methods of studying the gut flora (classical bacteriological techniques, metabolic and enzymological methods) will be critically discussed with special reference to their relevance to dietary, toxicological, and biochemical studies. Sources of nutrients available to the gut flora will be described including host products (mucus, sloughed mucosal cells, hormones, proteins) and exogenous nutrients derived from diet. An account of the problems involved in studies of dietary modification with special reference to the use of stock laboratory animal diets, purified diets, and human dietary studies. The influence of dietary modification on the flora will be assessed on the basis of changes in numbers and types of bacteria and their metabolic activity, drawing on data from human and animal studies. The effects of manipulation of the quantity and quality of protein, fat, and indigestible residues (fiber) of the diet will be described together with their possible implications for toxicity of ingested compounds.

Metabolism of nitropolycyclic aromatic hydrocarbons by human intestinal microflora

Anaerobic bacterial suspensions from human and rat feces and intestinal contents, and pure cultures of anaerobic bacteria metabolized 1-nitropyrene and 6-nitrobenzo[a]pyrene to 1-aminopyrene and 6-aminobenzo[a]pyrene, respectively. The metabolites were isolated by reversed-phase high performance liquid chromatography and identified by comparison of their chromatographic and mass spectral properties with those of authentic compounds. The results suggest that anaerobic intestinal bacteria could play a significant role in the metabolism of potentially carcinogenic nitropolycyclic aromatic hydrocarbons.

Mutagenic 1-nitropyrene in wastewater from oil-water separating tanks of gasoline stations and in used crankcase oil

Wastewater collected from oil-water separating tanks of ten gasoline stations for a year was fractionated into diethyl ether-soluble neutral, acidic, and basic fractions. Mutagenicity of these fractions was measured with Salmonella typhimurium strains TA98 and TA100 in the presence or absence of S9 mix. The neutral fractions showed high mutagenicity in the absence of S9 mix. Each neutral fraction was subjected to high-performance liquid chromatography (HPLC) and fractionated. A 1-nitropyrene(1-NP)-corresponding fraction was collected and analyzed by gas chromatography-mass spectrometry (GC-MS) and HPLC to prove that wastewater contains 1-NP and to quantitate 1-NP in wastewater. GC-MS patterns showed the following molecular and fragment ion peaks of 1-NP: 247, 217, 201, and 189. The amount of 1-NP in 36 samples of wastewater was 4.2-25,600 ng per liter of wastewater, and 1-NP accounted for 0.3-58.5% of the total mutagenicity of the neutral fractions. The other 19 samples of wastewater did not contain any detectable 1-NP. The mutagenicity of wastewater may be due to water from car washing and contamination by used crankcase oil. A Soxhlet extract of crankcase oil used in a gasoline was fractionated into three fractions as above. Mutagenicity was measured with strains TA98, TA100, TA98NR, and TA98/1,8-DNP6 in the absence or presence of S9 mix. The neutral fraction showed the highest mutagenicity with strain TA98 in the absence of S9 mix, and its mutagenicity was decreased in strains TA98NR and TA98/1,8-DNP6. The latter result indicates that the used engine-oil contained 1-NP and dinitropyrenes. Actually, the amounts of 1-NP and 1,6-diNP in used crankcase oil were 138 and 2.0 ng per ml of oil, respectively, and these concentrations accounted for 0.45 and 2.7%, respectively, of the total mutagenicity of the neutral fraction with strain TA98 in the absence of S9 mix. Moreover, the concentrations of 1-NP and 1,6-diNP in used crankcase oil of a diesel engine were 349 and 31 ng per ml of oil, respectively, accounting for 0.9 and 12%, respectively, of the total mutagenicity of the neutral fraction in the same assay system.

Purification and characterization of 1-nitropyrene nitroreductases from Bacteroides fragilis

We isolated four nitroreductases from Bacteroides fragilis GAI0624 and examined their physicochemical and functional properties. Two major enzyme activities were found in the adsorbed and unadsorbed fractions from DEAE-cellulose column chromatography. The adsorbed fraction was subjected to Sephadex G-200 column chromatography, and two further activities were separated. One has high nitroreductase activity (nitroreductase I), and the other has low activity and relatively high molecular weight (nitroreductase III). The nitroreductase I fraction was subjected to hydroxylapatite and chromatofocusing column chromatography, and nitroreductase I was purified about 416-fold with a yield of 6.77%. The unadsorbed fraction from DEAE-cellulose column chromatography was subjected to Sepharose 2B and Sepharose 6B column chromatography. Two enzyme activities were obtained by the Sepharose 6B column chromatography. One has high activity (nitroreductase II), and the other has low activity (nitroreductase IV). Nitroreductase II was rechromatographed by Sepharose 6B gel filtration and purified about 178-fold with a yield of 9.65%. The four enzymes (nitroreductases I, II, III, and IV) were shown to be different by several criteria. Their molecular weights, determined by gel filtration, were 52,000, 320,000, 180,000, and 680,000, respectively. The substrate specificity, the effect on mutagenicity of mutagenic nitro compounds, of nitroreductases I, III, and IV was relatively high for 1-nitropyrene, dinitropyrenes, and 4-nitroquinoline 1-oxide, respectively, but nitroreductase II had broad specificity. Nitroreductase activity required a coenzyme; nitroreductases II, III, and IV were NADPH linked, but nitroreductase I was NADH linked. All enzyme activity was enhanced by addition of flavin mononucleotide and inhibited significantly by dicumarol, p-chloromercuribenzoic acid, o-iodosobenzoic acid, sodium azide, and Cu2+.(ABSTRACT TRUNCATED AT 250 WORDS)