Mutagenicity of the atmospheric transformation products 2-nitrofluoranthene and 2-nitrodibenzopyranone in Salmonella and human cell forward mutation assays

Biomonitoring of detoxifying activity as measured by CYP1A1 induction in Yangtze and Jialing Rivers in Chongqing City in China

In order to determine the potential toxicities of organic pollutants in the river water of Chongqing City (China), chemicals were extracted from surface water of the Yangtze River and Jialing River between August 2004 and January 2005. Gas chromatography/mass spectrometry (GC/MS) analysis showed that the main compounds detected were polycyclic aromatic hydrocarbons (PAH) and phthalate acid esters (PAE). The ethoxyresorufin O-deethylase (EROD) test showed that the toxic equivalency (TEQ) values of the samples ranged from 0.9 to 13.3 x 10(-4) pg 2,3,7,8-TCDD/L river water. Incubation of H4IIE cells with organic extracts produced a time-dependent induction of cytochrome P-450 1A1 (CYP1A1) mRNA expression as determined by (1) reverse-transcription polymerase chain reaction (RT-PCR), (2) positive binding to aryl hydrocarbon receptor (AhR), and (3) activation of xenobiotic response element (XRE) by electrophoretic mobility shift assay (EMSA). Data indicated that organic extracts from the river water of Chongqing City induced CYP1A1 activity in hepatocytes in vitro. A possible mechanism underlying toxicity might involve the AhR signal pathway, but further studies are necessary.

Human cell mutagens in respirable airborne particles from the northeastern United States. 2. Quantification of mutagens and other organic compounds

Few reports have characterized mutagenic compounds in respirable airborne particles (<2.5 micrometers in diameter; PM2.5) collected at different sites on a regional scale (hundreds of km). Previously, we reported differences in the human (h1A1v2) cell mutagenicity of whole and fractionated organic extracts of PM2.5 samples collected in Boston, MA, Rochester, NY, and Quabbin Reservoir, a rural site in western MA. Herein we describe the analysis of mutagens and other organic compounds in these samples. Gas chromatography-mass spectrometry (GC-MS) was used to quantify approximately 150 organic compounds, including 31 known human cell mutagens. Molecular weight (MW) 226-302 amu PAHs were the most important mutagens identified: cyclopenta[cd]pyrene accounted for 1-2% of the measured mutagenicity of the samples, MW 252 PAHs accounted for 4-6%, MW 276-278 PAHs accounted for 2-5%, and MW 302 PAHs accounted for 2-3%. 6H-benzo-[cd]pyren-6-one, a PAH ketone, accounted for 3-5% of the mutagenicity. The same compounds accounted for similar portions of the total attributed mutagenicity in each sample. Mutagen levels were similar in the Boston and Rochester samples, and both were significantly higher than the Quabbin sample. This may explain whythe mutagenicities of the Boston and Rochester samples were higher than the Quabbin sample. The levels of mutagens found in semipolar fractions, however, could not explain why the mutagenicity of semipolar fractions was 2-fold higher in the Rochester sample than in the Boston sample. Known mutagens accounted for only 16-26% of the total mutagenicity of the unfractionated extracts, and only approximately 20% of the mutagenicity of the nonpolar and semipolar fractions. The remaining mutagenicity is likely attributable to other, as-yet unknown, semipolar and polar mutagens, or to interactions among chemical constituents of the samples. These findings are consistent with similar studies performed on airborne particles from Los Angeles and Washington, DC, thus indicating that PAHs, PAH-ketones, and as-yet unidentified polar organic compounds are widely distributed airborne human cell mutagens.

The genotoxicity of ambient outdoor air, a review: Salmonella mutagenicity

Mutagens in urban air pollution come from anthropogenic sources (especially combustion sources) and are products of airborne chemical reactions. Bacterial mutation tests have been used for large, multi-site, and/or time series studies, for bioassay-directed fractionation studies, for identifying the presence of specific classes of mutagens, and for doing site- or source-comparisons for relative levels of airborne mutagens. Early research recognized that although carcinogenic PAHs were present in air samples they could not account for the majority of the mutagenic activity detected. The mutagenicity of airborne particulate organics is due to at least 500 identified compounds from varying chemical classes. Bioassay-directed fractionation studies for identifying toxicants are difficult to compare because they do not identify all of the mutagens present, and both the analytical and bioassay protocols vary from study to study. However, these studies show that the majority of mutagenicity is usually associated with moderately polar/highly polar classes of compounds that tend to contain nitroaromatic compounds, aromatic amines, and aromatic ketones. Smog chamber studies have shown that mutagenic aliphatic and aromatic nitrogen-containing compounds are produced in the atmosphere when organic compounds (even non-mutagenic compounds) are exposed to nitrogen oxides and sunlight. Reactions that occur in the atmosphere, therefore, can have a profound effect on the genotoxic burden of ambient air. This review illustrates that the mutagenesis protocol and tester strains should be selected based on the design and purpose of the study and that the correlation with animal cancer bioassay results depends upon chemical class. Future emphasis needs to be placed on volatile and semi-volatile genotoxicants, and on multi-national studies that identify, quantify, and apportion mutagenicity. Initial efforts at replacing the Salmonella assay for ambient air studies with some emerging technology should be initiated.

The genotoxicity of 3-nitrobenzanthrone and the nitropyrene lactones in human lymphoblasts

Polycyclic aromatic hydrocarbons (PAH) and nitrated polycyclic aromatic compounds (nitro-PAC) have been found to be mutagenic in bacterial and human cells as well as carcinogenic in rodents. In this investigation, the genotoxic effects of 3-nitrobenzanthrone (3NB) and a mixture of nitropyrene lactones (NPLs) were determined using forward mutation assays performed in two human B-lymphoblastoid cell lines, MCL-5 and h1A1v2, which are responsive to the nitro-PAC class of compounds. Mutagenicity of the compounds was determined at the heterozygous tk locus and the hemizygous hprt locus, thus, identifying both large-scale loss of heterozygosity (LOH) events as well as intragenic mutagenic events. Genotoxicity was also determined using the CREST modified micronucleus assay, which detects chromosomal loss and breakage events. Results indicate 3NB is an effective human cell mutagen, significantly inducing mutations at the tk and hprt loci in both cell lines, and inducing micronuclei in the h1A1v2 cell line. The NPL isomers are also mutagenic, inducing mutations at the two loci as well as micronuclei in both cell lines. Because of their mutagenic potencies and their presence in ambient air, further assessments should be made of human exposures to these nitro-PAC and the potential health risks involved.

Evidence for oxidative metabolism in the genotoxicity of the atmospheric reaction product 2-nitronaphthalene in human lymphoblastoid cell lines

2-Nitronaphthalene (2NN) has been identified as a mutagenic atmospheric reaction product of naphthalene in the Ames bacterial reversion assay. Recent experiments have shown this nitroarene to be genotoxic in a human lymphoblastoid cell line (MCL-5) transfected with plasmids encoding epoxide hydrolase and four cytochrome P450 monooxygenase activities. The present study investigated the genotoxicity of 2NN in two related human B-lymphoblastoid cell lines, h1A1v2 containing a single P450 isozyme (cytochrome P450 1A1) and L3 cells which are isogenic with MCL-5 cells and are distinguished only by the absence of transfected plasmids. The results indicate that 2NN-induced mutagenesis at the heterozygous thymidine kinase (tk) locus was dependent on metabolic activities provided by the transfected plasmids in MCL-5; no significant induction of mutants was observed in L3 cells studied in parallel. A similar induction of mutation was observed in h1A1v2 and MCL-5 cell lines at the tk locus and no induction was observed at the hemizygous hypoxanthine phosphoribosyl transferase (hprt) locus. The induction of mutations in h1A1v2 cells suggests that cytochrome P450 1A1 alone can activate 2NN to a mutagenic species, however, this interpretation may be confounded by differences between the h1A1v2 and MCL-5 cell lines. The observed genotoxic activity induced by 2NN prompted testing of the amino analogue, beta-naphthylamine (betaNA), to investigate potential similarities in the metabolic activation pathways of the two compounds. The negative response of betaNA in all cell lines suggests that 2NN and betaNA are not activated in these human cells by similar metabolic pathways.

Mutagenicity of cyclopenta-fused polynuclear aromatic hydrocarbons and a non-polar fraction from a fuel combustion sample in a Salmonella forward mutation assay without exogenous metabolic activation

A series of cyclopenta-fused polynuclear aromatic hydrocarbons (PAH) were tested for mutagenicity in a bacterial forward mutation assay based on resistance to 8-azaguanine (8-AG) in Salmonella typhimurium TM677 in the absence of Aroclor-induced rat liver postmitochondrial supernatant (PMS). All of the aceanthrylenes tested were mutagenic in the absence of PMS, whereas none of the acephenanthrylenes were active. The following mutagenic potency series expressed as the minimum detectable mutagen concentration (MDMC) in nmol/ml was obtained: aceanthrylene (AA) (5.5); cyclopent[h,i]aceanthrylene (CPAA)(18.2); 6-methylaceanthrylene (6-MeAA)(112); 1,2,6,7-tetrahydrocyclopent[h,i]aceanthrylene (THCPAA) (166); 1,2-dihydroaceanthrylene (DHAA) (298). Saturation of the cyclopenta rings or methylation at the 6-position of AA reduced, but did not eliminate, mutagenicity measured in the absence of PMS. AA was unusual because it was approximately 4-fold more mutagenic in the absence of PMS than in its presence. The other aceanthrylenes tested were 1.3-10.7 times more mutagenic in the presence of PMS than in its absence to give an MDMC potency series of: CPAA (3.8); 6-MeAA (10.5); AA (19.9); THCPAA (52.9); DHAA (229). Approximately 20% of the PMS-independent mutagenicity in a combustion sample from ethylene burned under fuel-rich conditions was found in a fraction containing only non-polar, 4-7 ring PAHs, widely attributed to be mutagenic only in the presence of PMS. None of this mutagenicity could be attributed to aceanthrylenes, thus other non-polar PAHs appear to possess significant PMS-independent mutagenicity as well.