Bioactivation of diesel exhaust particle extracts and their major nitrated polycyclic aromatic hydrocarbon components, 1-nitropyrene and dinitropyrenes, by human cytochromes P450 1A1, 1A2, and 1B1

Defining the in vivo mechanism of air pollutant toxicity using murine stress response biomarkers

Air pollution can cause a wide range of serious human diseases. For the informed instigation of interventions which prevent these outcomes there is an urgent need to develop robust in vivo biomarkers which provide insights into mechanisms of toxicity and relate pollutants to specific adverse outcomes. We exemplify for a first time the application of in vivo stress response reporters in establishing mechanisms of air pollution toxicity and the application of this knowledge in epidemiological studies. We first demonstrated the utility of reporter mice to understand toxicity mechanisms of air pollutants using diesel exhaust particles compounds. We observed that nitro-PAHs induced Hmox1 and CYP1a1 reporters in a time- and dose-dependent, cell- and tissue-specific manner. Using in vivo genetic and pharmacological approaches we confirmed that the NRF2 pathway mediated this Hmox1-reporter induction stress reporter activity. We then correlated the activation of stress-reporter models (oxidative stress/inflammation, DNA damage and Ah receptor -AhR- activity) with responses in primary human nasal cells exposed to chemicals present in particulate matter (PM; PM2.5-SRM2975, PM10-SRM1648b) or fresh roadside PM10. To exemplify their use in clinical studies, Pneumococcal adhesion was assessed in exposed primary human nasal epithelial cells (HPNEpC). The combined use of HPNEpC and in vivo reporters demonstrated that London roadside PM10 particles induced pneumococcal infection in HPNEpC mediated by oxidative stress responses. The combined use of in vivo reporter models with human data thus provides a robust approach to define the relationship between air pollutant exposure and health risks. Moreover, these models can be used in epidemiological studies to hazard ranking environmental pollutants by considering the complexity of mechanisms of toxicity. These data will facilitate the relationship between toxic potential and the level of pollutant exposure in populations to be established and potentially extremely valuable tools for intervention studies for disease prevention.

Nitroreduction: A Critical Metabolic Pathway for Drugs, Environmental Pollutants, and Explosives

Nitro group containing xenobiotics include drugs, cancer chemotherapeutic agents, carcinogens (e.g., nitroarenes and aristolochic acid) and explosives. The nitro group undergoes a six-electron reduction to form sequentially the nitroso-, N-hydroxylamino- and amino-functional groups. These reactions are catalyzed by nitroreductases which, rather than being enzymes with this sole function, are enzymes hijacked for their propensity to donate electrons to the nitro group either one at a time via a radical mechanism or two at time via the equivalent of a hydride transfer. These enzymes include: NADPH-dependent flavoenzymes (NADPH: P450 oxidoreductase, NAD(P)H-quinone oxidoreductase), P450 enzymes, oxidases (aldehyde oxidase, xanthine oxidase) and aldo-keto reductases. The hydroxylamino group once formed can undergo conjugation reactions with acetate or sulfate catalyzed by N-acetyltransferases or sulfotransferases, respectively, leading to the formation of intermediates containing a good leaving group which in turn can generate a nitrenium or carbenium ion for covalent DNA adduct formation. The intermediates in the reduction sequence are also prone to oxidation and produce reactive oxygen species. As a consequence, many nitro-containing xenobiotics can be genotoxic either by forming stable covalent adducts or by oxidatively damaging DNA. This review will focus on the general chemistry of nitroreduction, the enzymes responsible, the reduction of xenobiotic substrates, the regulation of nitroreductases, the ability of nitrocompounds to form DNA adducts and act as mutagens as well as some future directions.

Diesel exhaust particles distort lung epithelial progenitors and their fibroblast niche

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease characterized by inflammation and impaired tissue regeneration, and is reported as the fourth leading cause of death worldwide by the Centers for Disease Control and Prevention (CDC). Environmental pollution and specifically motor vehicle emissions are known to play a role in the pathogenesis of COPD, but little is still known about the molecular mechanisms that are altered following diesel exhaust particles (DEP) exposure. Here we used lung organoids derived from co-culture of alveolar epithelial progenitors and fibroblasts to investigate the effect of DEP on the epithelial-mesenchymal signaling niche in the distal lung, which is essential for tissue repair. We found that DEP treatment impaired the number as well as the average diameter of both airway and alveolar type of lung organoids. Bulk RNA-sequencing of re-sorted epithelial cells and fibroblasts following organoid co-culture shows that the Nrf2 pathway, which regulates antioxidants' activity, was upregulated in both cell populations in response to DEP; and WNT/β-catenin signaling, which is essential to promote epithelial repair, was downregulated in DEP-exposed epithelial cells. We show that pharmacological treatment with anti-oxidant agents such as N-acetyl cysteine (NAC) or Mitoquinone mesylate (MitoQ) reversed the effect of DEP on organoids growth. Additionally, a WNT/β-catenin activator (CHIR99021) successfully restored WNT signaling and promoted organoid growth upon DEP exposure. We propose that targeting oxidative stress and specific signaling pathways affected by DEP in the distal lung may represent a strategy to restore tissue repair in COPD.

The Activation of Procarcinogens by CYP1A1/1B1 and Related Chemo-Preventive Agents: A Review

CYP1A1 and CYP1B1 are extrahepatic P450 family members involved in the metabolism of procarcinogens, such as PAHs, heterocyclic amines and halogen-containing organic compounds. CYP1A1/1B1 also participate in the metabolism of endogenous 17-β-estradiol, producing estradiol hydroquinones, which are the intermediates of carcinogenic semiquinones and quinones. CYP1A1 and CYP1B1 proteins share approximately half amino acid sequence identity but differ in crystal structures. As a result, CYP1A1 and CYP1B1 have different substrate specificity to chemical procarcinogens. This review will introduce the general molecular biology knowledge of CYP1A1/1B1 and the metabolic processes of procarcinogens regulated by these two enzymes. Over the last four decades, a variety of natural products and synthetic compounds which interact with CYP1A1/1B1 have been identified as effective chemo-preventive agents against chemical carcinogenesis. These compounds are mainly classified as indirect or direct CYP1A1/1B1 inhibitors based on their distinct mechanisms. Indirect CYP1A1/1B1 inhibitors generally impede the transcription and translation of CYP1A1/1B1 genes or interfere with the translocation of aryl hydrocarbon receptor (AHR) from the cytosolic domain to the nucleus. On the other hand, direct inhibitors inhibit the catalytic activities of CYP1A1/1B1. Based on the structural features, the indirect inhibitors can be categorized into the following groups: flavonoids, alkaloids and synthetic aromatics, whereas the direct inhibitors can be categorized into flavonoids, coumarins, stilbenes, sulfur containing isothiocyanates and synthetic aromatics. This review will summarize the in vitro and in vivo activities of these chemo-preventive agents, their working mechanisms, and related SARs. This will provide a better understanding of the molecular mechanism of CYP1 mediated carcinogenesis and will also give great implications for the discovery of novel chemo-preventive agents in the near future.

Quinazolinone derivative BNUA-3 ameliorated [NDEA+2-AAF]-induced liver carcinogenesis in SD rats by modulating AhR-CYP1B1-Nrf2-Keap1 pathway

Cytochrome P450 1B1, considered as one of the novel chemotherapeutic targets involved in cancer prevention and therapy is also associated with the conversion of procarcinogens into their active metabolites. The aryl hydrocarbon receptor (AhR) is responsible for mediating different biological responses to a wide variety of environmental pollutants and also causes transcriptional activation of cytochrome P450 enzymes including CYP1B1 and thus plays a pivotal role for initiating cancer and its progression. On the other hand, active carcinogenic metabolites and reactive oxygen species-mediated stress alter different molecular signalling pathways and gene expressions. Quinazoline derivatives are recognized for their diversified biological activities including anticancer properties. The current study was designed for evaluation of chemotherapeutic efficacy of a synthetic quinazolinone derivative BNUA-3 against hepatocellular cancer in Sprague-Dawley (SD) rats. A detailed in vivo analysis was performed by administrating BNUA-3 (15, 30 mg/kg b.w. for 28 days, i.p.) in N-Nitrosodiethylamine + 2-Acetylaminofluorene induced partially hepatectomized liver cancer in SD rats. This was followed by morphological evaluations, biochemical estimations and analysis of different mRNA and protein expressions. The results demonstrated the potency of BNUA-3 in efficient restoration of the altered morphology of liver, its protective effect against lipid peroxidation, enzymic and non-enzymic antioxidants levels in liver tissue which was disrupted after cancer induction. The study also demonstrated downregulation of AhR, CYP1B1 and Keap1 expressions with subsequent augmentation of protective Nrf2, HO-1, NQO1 and GSTA1 expressions thus, revealing the chemotherapeutic potency of BNUA-3 in inhibiting liver carcinogenesis through AhR/CYP1B1/Nrf2/Keap1 pathway.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

Metabolism of the lipophilic phycotoxin 13-Desmethylspirolide C using human and rat in vitro liver models

13-Desmethylspirolide C (13-SPX-C) is a phycotoxin produced by dinoflagellates which can accumulate in shellfish. 13-SPX-C induces neurotoxic effects in rodents through blockade of nicotinic acetylcholine receptors. As no human intoxication has been to date attributed to the consumption of 13-SPX-C-contaminated seafood, this toxin is not regulated according to the Codex Alimentarius. Nevertheless, shellfish consumers can be exposed to 13-SPX-C via shellfish consumption. In order to follow the fate of the toxin after ingestion and to verify whether metabolic detoxification could explain the lack of human intoxications, we assessed the metabolism of 13-SPX-C using several in vitro liver systems. First, both phase I and II reactions occurring with rat and human liver S9 fractions were screened. Our results indicated that 13-SPX-C was almost completely metabolized with both rat and human liver S9. Using a receptor binding assay towards nicotinic acetylcholine receptors we demonstrated that the resulting metabolites showed less affinity towards nicotinic acetylcholine receptors than 13-SPX-C. Finally, we showed that 13-SPX-C induced a pronounced increase of gene expression of the drug-metabolizing enzyme cytochrome P450 (CYP) CYP1A2. The role of this CYP in 13-SPX-C metabolism was clarified using an innovative in vitro tool, CYP1A2-Silensomes™. In summary, this study highlights that liver first-pass metabolism can contribute to the detoxification of 13-SPX-C.

Advanced Approaches to Model Xenobiotic Metabolism in Bacterial Genotoxicology In Vitro

During the past 30 years there has been considerable progress in the development of bacterial test systems for use in genotoxicity testing by the stable introduction of expression vectors (cDNAs) coding for xenobiotic-metabolizing enzymes into bacterial cells. The development not only provides insights into the mechanisms of bioactivation of xenobiotic compounds but also evaluates the roles of enzymes involved in metabolic activation or inactivation in chemical carcinogenesis. This review describes recent advances in bacterial genotoxicity assays and their future prospects, with a focus on the development and application of genetically engineering bacterial cells to incorporate some of the enzymatic activities involved in the bio-activation process of xenobiotics. Various genes have been introduced into bacterial umu tester strains encoding enzymes for genotoxic bioactivation, including bacterial nitroreductase and O-acetyltransferase, human cytochrome P450 monooxygenases, rat glutathione S-transferases, and human N-acetyltransferases and sulfotransferases. Their application has provided new tools for genotoxicity assays and for studying the role of biotransformation in chemical carcinogenesis in humans.

Toxic Effects of the Major Components of Diesel Exhaust in Human Alveolar Basal Epithelial Cells (A549)

We investigated the toxicity of benzo[a]pyrene (B[a]P), 1-nitropyrene (1-NP) and 3-nitrobenzanthrone (3-NBA) in A549 cells. Cells were treated for 4 h and 24 h with: B[a]P (0.1 and 1 μM), 1-NP (1 and 10 μM) and 3-NBA (0.5 and 5 μM). Bulky DNA adducts, lipid peroxidation, DNA and protein oxidation and mRNA expression of CYP1A1, CYP1B1, NQO1, POR, AKR1C2 and COX2 were analyzed. Bulky DNA adducts were induced after both treatment periods; the effect of 1-NP was weak. 3-NBA induced high levels of bulky DNA adducts even after 4-h treatment, suggesting rapid metabolic activation. Oxidative DNA damage was not affected. 1-NP caused protein oxidation and weak induction of lipid peroxidation after 4-h incubation. 3-NBA induced lipid peroxidation after 24-h treatment. Unlike B[a]P, induction of the aryl hydrocarbon receptor, measured as mRNA expression levels of CYP1A1 and CYP1B1, was low after treatment with polycyclic aromatic hydrocarbon (PAH) nitro-derivatives. All test compounds induced mRNA expression of NQO1, POR, and AKR1C2 after 24-h treatment. AKR1C2 expression indicates involvement of processes associated with reactive oxygen species generation. This was supported further by COX2 expression induced by 24-h treatment with 1-NP. In summary, 3-NBA was the most potent genotoxicant, whereas 1-NP exhibited the strongest oxidative properties.

Revealing the role of oxidation state in interaction between nitro/amino-derived particulate matter and blood proteins

Surface oxidation states of ultrafine particulate matter can influence the proinflammatory responses and reactive oxygen species levels in tissue. Surface active species of vehicle-emission soot can serve as electron transfer-mediators in mitochondrion. Revealing the role of surface oxidation state in particles-proteins interaction will promote the understanding on metabolism and toxicity. Here, the surface oxidation state was modeled by nitro/amino ligands on nanoparticles, the interaction with blood proteins were evaluated by capillary electrophoresis quantitatively. The nitro shown larger affinity than amino. On the other hand, the affinity to hemoglobin is 10(3) times larger than that to BSA. Further, molecular docking indicated the difference of binding intensity were mainly determined by hydrophobic forces and hydrogen bonds. These will deepen the quantitative understanding of protein-nanoparticles interaction from the perspective of surface chemical state.

Reproductive toxicity of 1-nitronaphthalene and 1-nitropyrene exposure in the mummichog, Fundulus heteroclitus

After pregnant mummichog were implanted with 1-nitronaphthalene or 1-nitropyrene via cholesterol pellet, we investigated the effects of the chemicals on embryo normality, hatchability and days to hatch of normal embryos, and growth and survival of hatched larvae from normal embryos of the implanted mummichog. Hatchability was the parameter most sensitive to the effects of both 1-nitronaphthalene and 1-nitropyrene. The 4-week lowest-observed-effect concentration (LOEC) of 1-nitronaphthalene, based on the actual concentrations in the eggs in the test, was 447 ng g(-1) wet wt.; and the LOEC and no-observed-effect concentration (NOEC) of 1-nitropyrene were 958 and 344 ng g(-1) wet wt., respectively. The 4-week LOEC of 1-nitronaphthalene, based on the concentration in the water, was estimated at 4.8 µg L(-1) by using the reported bioconcentration factor; and the LOEC and NOEC of 1-nitropyrene, based on the concentration in the water, were estimated at 3.1 and 8.6 µg L(-1), respectively. The reported environmental concentrations of 1-nitropyrene and 1-nitronaphthalene are over three magnitudes lower than the toxicity values we obtained. Therefore, the effects of environmental levels of 1-nitropyrene and 1-nitronaphthalene on fish reproduction, not including genomic effects on embryos, appear to be almost negligible. However, DNA damage has been detected in marine organisms exposed to 1-nitropyrene. Further studies of the genotoxicity of nitrated polycyclic aromatic hydrocarbons at environmental levels are therefore needed to evaluate their ecotoxicological risks.

Mechanisms linked to differences in the mutagenic potential of 1,3-dinitropyrene and 1,8-dinitropyrene

This study explores and characterizes the toxicity of two closely related carcinogenic dinitro-pyrenes (DNPs), 1,3-DNP and 1,8-DNP, in human bronchial epithelial BEAS-2B cells and mouse hepatoma Hepa1c1c7 cells. Neither 1,3-DNP nor 1,8-DNP (3–30 μM) induced cell death in BEAS-2B cells. In Hepa1c1c7 cells only 1,3-DNP (10–30 μM) induced a mixture of apoptotic and necrotic cell death after 24 h. Both compounds increased the level of reactive oxygen species (ROS) in BEAS-2B as measured by CM-H₂DCFDA-fluorescence. A corresponding increase in oxidative damage to DNA was revealed by the formamidopyrimidine-DNA glycosylase (fpg)-modified comet assay. Without fpg, DNP-induced DNA damage detected by the comet assay was only found in Hepa1c1c7 cells. Only 1,8-DNP formed DNA adduct measured by ³²P-postlabelling. In Hepa1c1c cells, 1,8-DNP induced phosphorylation of H2AX (γH2AX) and p53 at a lower concentration than 1,3-DNP and there was no direct correlation between DNA damage/DNA damage response (DR) and induced cytotoxicity. On the other hand, 1,3-DNP-induced apoptosis was inhibited by pifithrin-α, an inhibitor of p53 transcriptional activity. Furthermore, 1,3-DNP triggered an unfolded protein response (UPR), as measured by an increased expression of CHOP, ATF4 and XBP1. Thus, other types of damage possibly linked to endoplasmic reticulum (ER)-stress and/or UPR could be involved in the induced apoptosis. Our results suggest that the stronger carcinogenic potency of 1,8-DNP compared to 1,3-DNP is linked to its higher genotoxic effects. This in combination with its lower potency to induce cell death may increase the probability of causing mutations.

Classification of polycyclic aromatic hydrocarbons based on mutagenicity in lung tissue through DNA microarray

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced in the combustion of organic matter. Exposure to PAHs raises the risk of lung cancer and inflammatory and allergic disorders such as asthma. DNA microarray technologies have been applied to research on toxicogenomics in the recent years. To evaluate the mutagenicity of PAHs and constituents of environmental pollutants in lung tissue, including metabolic activation, human alveolar epithelial type II cells (A549) were treated with nonmutagenic PAH pyrene and with the mutagenic PAHs benzo-[a]-pyrene, 1-nitropyrene, or 1,8-dinitropyrene. Comparison of genome-wide microarray expression profiles between a nonmutagenic and a mutagenic PAH-treated group revealed that xenobiotic response genes such as CYP1B1 were commonly upregulated in two groups and that DNA damage induced genes, especially p53-downstream genes such as p21 (CDKN1A) were upregulated only in the mutagenic PAH-treated group. Pretreatment with cytochrome P450 inhibitor α-naphthoflavone or p53 inhibitor pifithrin-α inhibited the benzo-[a]-pyrene-induced p21 expression. These data suggest that when PAHs enter the cells, lung epithelium induces PAH metabolic activating enzymes, and then the DNA damages-recognition signal is converged with p53 downstream genes. This metabolic activation and DNA damage is induced in lung epithelium, and the mutagenicity of PAHs can be classified by DNA microarray expression profiles.

Organic chemicals in diesel exhaust particles enhance picryl chloride-induced atopic dermatitis in NC/Nga mice

BACKGROUND

Diesel exhaust particles (DEP) have been reported to worsen allergic airway inflammation in mice. Recently, the organic chemical components of DEP (DEP-OC) were found to be important contributors to the aggravation of allergic airway inflammation in mice. The purpose of this study was to examine the effects of DEP-OC on atopic dermatitis (AD)-like skin lesions induced by picryl chloride (PiCl) in NC/Nga mice.

METHODS

DEP were extracted with benzene/ethanol, and the soluble organic fraction formed the DEP-OC. NC/Nga male mice received simultaneous application of DEP-OC and/or PiCl on their ears once a week for 9 or 3 weeks. We evaluated skin lesions by noting scaling, eruption, excoriation, erosion, hemorrhage, pathologic changes, production of cytokines, and IgE level in the serum.

RESULTS

PiCl application alone produced progressively severe AD-like skin lesions. The application of PiCl plus DEP-OC resulted in a marked worsening of skin lesions in the early stages of AD. Moreover, mast cell counts significantly increased in the subcutaneous tissue. Administration of PiCl combined with DEP-OC resulted in a greater increase in the local expression of interleukin-4, keratinocyte chemoattractant, and neutrophils in subcutaneous tissue compared with PiCl treatment alone. In contrast, the combination treatment produced lower levels of IFN-γ compared with PiCl treatment alone.

CONCLUSIONS

DEP-OC application to the skin aggravated PiCl-induced AD. This aggravation may be due to activation of the Th2-associated immune responses by the organic chemicals in DEP.

Genotoxic bioactivation of constituents of a diesel exhaust particle extract by the human lung

The ability of the human lung to catalyze genotoxic bioactivation of constituents of diesel exhaust particle (DEP) extract (DEPE) and the identity of the lung enzymes involved in the bioactivation were investigated using human lung tissues obtained from surgical resections. Genotoxicity was determined by lung S9-catalyzed mutagenicity of DEPE constituents to Salmonella typhimurium TA98NR in the Ames test and by DEPE-induced pneumocyte DNA damage response as determined by γH2Ax expression in ex vivo tissues. S9 was prepared from lung explants treated ex vivo with either DEPE to induce pulmonary enzymes (DEPE-S9) or vehicle only (CON-S9). TA98NR served as the tester strain for the purpose of enhancing and minimizing the contribution of lung S9 and Salmonella, respectively, to DEPE bioactivation. DEPE-S9 was 2.2-fold more active than CON-S9 or rat liver S9 in DEPE bioactivation and the bioactivation was inhibited 58, 45, 22, and 16% by α-naphthoflavone, dicumarol, ketoconazole, and ticlopidine, respectively. Alveolar S9 was less active than bronchioalveolar S9 in DEPE bioactivation. DEPE and diesel exhaust particles (DEP) induced γ-pH2Ax expression in pulmonary cells. Pulmonary CYP1A1 and NQO1 were induced by DEPE treatment, with the constitutive and induced CYP1A1 distributed throughout all peripheral lung regions, whereas NQO1 was limited in distribution to bronchiolar epithelium. The results show that the human lung is highly active in catalyzing genotoxic bioactivation of diesel emission constituents and that CYP1A and NQO1 play major roles in the reaction. The findings underscore the usefulness of human lung tissues in studies of the pneumotoxicity potential of chemicals to humans.

Mechanisms of chemokine responses by polycyclic aromatic hydrocarbons in bronchial epithelial cells: sensitization through toll-like receptor-3 priming

We have previously observed that 1-nitropyrene (1-NP) and its amine metabolite 1-aminopyrene (1-AP) induce differential chemokine responses in human bronchial epithelial cells (BEAS-2B) characterized by maximum responses for CXCL8 (IL-8) and CCL5 (RANTES), respectively. In the present study, we further explored the effects of 1-NP and 1-AP on chemokine responses. The results suggest that the differential effect of 1-NP and 1-AP on CXCL8 and CCL5 in BEAS-2B cells was mainly related to effects at higher concentrations, which in the case of 1-NP seemed to be linked to ROS-formation and/or metabolic activation by CYP-enzymes. However, at a low concentration (1 μM) where neither 1-NP, 1-AP nor unsubstituted pyrene had any effect on chemokine responses, we found that all three PAHs potentiated CXCL8 and CCL5 responses induced by the TLR3 ligand polyinosinic:polycytidylic acid (Poly I:C) in BEAS-2B cells. As neither benzo[a]pyrene nor β-naphthoflavone induced a similar effect in Poly I:C-primed cells, the response seemed independent of aryl hydrocarbon receptor-mediated mechanisms. The results show that priming cells with an inflammogenic stimuli like Poly I:C sensitizes the cells toward additional pro-inflammatory effects of certain PAHs. The study underscores that testing on healthy cells or animals may not be sufficient to fully evaluate chemokine responses and the pro-inflammatory potential of organic chemicals.

Contributions of human enzymes in carcinogen metabolism

Considerable support exists for the roles of metabolism in modulating the carcinogenic properties of chemicals. In particular, many of these compounds are pro-carcinogens that require activation to electrophilic forms to exert genotoxic effects. We systematically analyzed the existing literature on the metabolism of carcinogens by human enzymes, which has been developed largely in the past 25 years. The metabolism and especially bioactivation of carcinogens are dominated by cytochrome P450 enzymes (66% of bioactivations). Within this group, six P450s--1A1, 1A2, 1B1, 2A6, 2E1, and 3A4--accounted for 77% of the P450 activation reactions. The roles of these P450s can be compared with those estimated for drug metabolism and should be considered in issues involving enzyme induction, chemoprevention, molecular epidemiology, interindividual variations, and risk assessment.

Roles of human sulfotransferases in genotoxicity of carcinogens using genetically engineered umu test strains

Human sulfotransferase (SULT) 1A1, 1A2, and 1A3 cDNA genes were subcloned separately into the pTrc99A(KM) vector. The generated plasmids were introduced into the Salmonella typhimurium O-acetyltransferase-deficient strain NM6000 (TA1538/1,8-DNP/pSK1002), resulting in the new strains NM7001, NM7002, and NM7003. We compared the sensitivities of these three strains with the parental strain NM7000 against 51 chemicals including aromatic amines, nitroarenes, alkenylbenzenes, estrogens-like chemicals, and other compounds with and without S9 mix by making use of the umu test system that is based on the bacterial SOS induction. 2-Amino-6-methyl-dipyrido[1,2-α:3',2'-d]imidazole, 3-methoxy-4-aminoazobenzene, 3-nitrobenzanthrone, 5-nitroacenaphthene, and 3,9-dinitrofluoranthene caused high genotoxicity in the NM7001 strain. The genotoxic effects of 2-aminofluorene, 2-acetylaminofluorene, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 2-nitrofluorene, 1-nitropyrene, and 2-nitropropane were stronger in the NM7002 strain compared with the NM7001 and NM7003 strains. Among the tested benzylic and allylic compounds, 1-hydroxymethylpyrene was detected in the NM7001 strain with the highest sensitivity. Estragole and 1'-hydroxysafrole exhibited strong genotoxicity in the NM7003 strain. The estrogen-like chemicals such as bisphenol A, genistein, p,n-nonylphenol, and 4-hydroxytamoxifen were not detected as genotoxins in any strain used. Collectively, the present results suggest that the generated test strains are valuable tools in order to elucidate the role of SULT enzymes in the bioactivation of chemicals to environmental carcinogens.

Similarities in diesel exhaust particles induced alterations in expression of cytochrome P-450 and glutathione S-transferases in rat lymphocytes and lungs

Freshly prepared peripheral blood lymphocytes (PBL) are known to express cytochrome P450s (CYPs) and glutathione S-transferases (GSTs) involved in the bioactivation and detoxification of organic components of diesel exhaust particles (DEPs). To validate that blood lymphocyte expression profiles could be used as a biomarker to predict exposure to vehicular emissions, similarities in the alterations in the mRNA expression of CYPs and GSTs were studied in PBL and lungs of rats exposed to DEPs. Adult male Wistar rats were treated transtracheally with different doses of DEPs (3.75- or 7.5- or 15- or 30-mg/kg b.wt.). The animals were anaesthetized after 24 h and blood was drawn and lungs were taken out and processed. DEP produced a similar pattern of increase in the mRNA expression of CYPs (CYP1A1, 1A2, 1B1, 2E1), associated arylhydrocarbon receptor (Ahr) and arylhydrocarbon nuclear translocator (Arnt) and GSTs (GSTPi, GSTM1 and GSTM2) at all the doses in lungs and PBL. The protein expression of CYP1A1/1A2 and 2E1 and catalytic activity of CYPs and GSTs also showed a similar pattern of increase in blood lymphocyte and in lungs isolated from DEP treated rats. Our data indicating similarities in the alterations in the expression of carcinogen metabolizing CYPs and GSTs in PBL with the lung enzymes suggests the suitability of using expression profiles of blood lymphocyte CYPs and GSTs as a biomarker to predict exposure to vehicular emissions.

Diesel exhaust particulate extracts inhibit transcription of nuclear respiratory factor-1 and cell viability in human umbilical vein endothelial cells

Endothelial dysfunction precedes cardiovascular disease and is accompanied by mitochondrial dysfunction. Here we tested the hypothesis that diesel exhaust particulate extracts (DEPEs), prepared from a truck run at different speeds and engine loads, would inhibit genomic estrogen receptor activation of nuclear respiratory factor-1 (NRF-1) transcription in human umbilical vein endothelial cells (HUVECs). Additionally, we examined how DEPEs affect NRF-1-regulated TFAM expression and, in turn, Tfam-regulated mtDNA-encoded cytochrome c oxidase subunit I (COI, MTCO1) and NADH dehydrogenase subunit I (NDI) expression as well as cell proliferation and viability. We report that 17β-estradiol (E(2)), 4-hydroxytamoxifen (4-OHT), and raloxifene increased NRF-1 transcription in HUVECs in an ER-dependent manner. DEPEs inhibited NRF-1 transcription, and this suppression was not ablated by concomitant treatment with E(2), 4-OHT, or raloxifene, indicating that the effect was not due to inhibition of ER activity. While E(2) increased HUVEC proliferation and viability, DEPEs inhibited viability but not proliferation. Resveratrol increased NRF-1 transcription in an ER-dependent manner in HUVECs, and ablated DEPE inhibition of basal NRF-1 expression. Given that NRF-1 is a key nuclear transcription factor regulating genes involved in mitochondrial activity and biogenesis, these data suggest that DEPEs may adversely affect mitochondrial function leading to endothelial dysfunction and resveratrol may block these effects.

Aryl hydrocarbon receptor-dependent upregulation of Cyp1b1 by TCDD and diesel exhaust particles in rat brain microvessels

Background

AhR activates the transcription of several target genes including CYP1B1. Recently, we showed CYP1B1 as the major cytochrome P450 (CYP) enzyme expressed in human brain microvessels. Here, we studied the effect of AhR activation by environmental pollutants on the expression of Cyp1b1 in rat brain microvessels.

Methods

Expression of AhR and Cyp1b1 was detected in isolated rat brain microvessels. AhR was immunovisualised in brain microvessel endothelial cells. The effect of AhR ligands on Cyp1b1 expression was studied using isolated brain microvessels after ex vivo and/or in vivo exposure to TCDD, heavy hydrocarbons containing diesel exhaust particles (DEP) or Δ⁹-tetrahydrocannabinol (Δ⁹-THC).

Results

After ex vivo exposure to TCDD (a highly potent AhR ligand) for 3 h, Cyp1b1 expression was significantly increased by 2.3-fold in brain microvessels. A single i.p. dose of TCDD also increased Cyp1b1 transcripts (22-fold) and Cyp1b1 protein (2-fold) in rat brain microvessels at 72 h after TCDD. Likewise, DEP treatment (in vivo and ex vivo) strongly induced Cyp1b1 protein in brain microvessels. DEP-mediated Cyp1b1 induction was inhibited by actinomycin D, cycloheximide, or by an AhR antagonist. In contrast, a sub-chronic in vivo treatment with Δ⁹-THC once daily for 7 seven days had no effect on Cyp1b1 expression

Conclusions

Our results show that TCDD and DEP strongly induced Cyp1b1 in rat brain microvessels, likely through AhR activation.

DNA damage and DNA damage response in human bronchial epithelial BEAS-2B cells following exposure to 2-nitrobenzanthrone and 3-nitrobenzanthrone: role in apoptosis

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are mutagenic and carcinogenic environmental pollutants found in diesel exhaust and on urban air pollution particles. In the present study, human bronchial epithelial BEAS-2B cells were exposed to 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA). DNA damage responses were compared to those observed after exposure to 1-nitropyrene (1-NP) and benzo[a]pyrene (B[a]P). Examination by microscopy revealed that 3-NBA was the most potent toxic compound while weaker responses were observed with 1-NP and B[a]P. Most interestingly, 2-NBA did not induce cell death or any other stress-related responses. 3-NBA induced a typical apoptotic cell death judged by nuclear condensation and little plasma membrane damage as well as cleavage of caspase 3 and poly-(ADP-ribose) polymerase (PARP). Exposure to 3-NBA resulted in an accumulation of cells in S-phase, and further analysis by Western blotting, immunocytochemistry and flow cytometry revealed that 3-NBA induced a DNA damage response characterized by phosphorylation of ATM (ataxia-telangiectasia mutated), checkpoint kinase (Chk) 2/Chk1, H2AX and p53. The p53 inhibitor pifithrin-α inhibited 3-NBA-induced apoptosis while small effects were seen using pifithrin-μ, suggesting that 3-NBA-induced cell death is a result of transcriptional activation of p53. In conclusion, 3-NBA is a potent inducer of apoptosis, which seemed to be triggered by the DNA damage response. Furthermore, a change of the nitro-group to the second position (i.e. 2-NBA) dramatically changed the cellular reactivity of the compound.

Differences in cytotoxicity versus pro-inflammatory potency of different PM fractions in human epithelial lung cells

Air pollution in Milan causes health concern due to the high concentrations of particulate matter (PM10 and PM2.5). The aim of this study was to investigate possible seasonal differences in PM10 and PM2.5 chemical composition and their biological effects on pro-inflammatory cytokine release and cytotoxicity. The PM was sampled during winter and summer seasons. The winter PMs had higher levels of PAHs than the summer samples which contained a greater amount of mineral dust elements. The PM toxicity was tested in the human pulmonary epithelial cell lines BEAS-2B and A549. The winter PMs were more cytotoxic than summer samples, whereas the summer PM10 exhibited a higher pro-inflammatory potential, as measured by ELISA. This inflammatory potential seemed partly due to biological components such as bacterial lipopolysaccharides (LPS), as evaluated by the use of Polymixin B. Interestingly, in the BEAS-2B cells the winter PM2.5 reduced proliferation due to a mitotic delay/arrest, while no such effects were observed in the A549 cells. These results underline that the in vitro responsiveness to PM may be cell line dependent and suggest that the PM different properties may trigger different endpoints such as inflammation, perturbation of cell cycle and cell death.

CYP2A13 expressed in human bladder metabolically activates 4-aminobiphenyl

Cigarette smoking is the predominant risk factor for bladder cancer. Aromatic amines such as 4-aminobiphenyl (ABP) is the major carcinogens found in tobacco smoke. Although it is generally accepted that ABP is metabolically activated via N-hydroxylation by CYP1A2 in human liver, previous studies using Cyp1a2-null mice indicated the involvement of other enzyme(s). Here we found that CYP2A13 can metabolically activate ABP to show genotoxicity by Umu assay. The K(m) and V(max) values for ABP N-hydroxylation by recombinant CYP2A13 in E. coli were 38.5 +/- 0.6 microM and 7.8 +/- 0.0 pmol/min/pmol CYP, respectively. The K(m) and V(max) values by recombinant CYP1A2 were 9.9 +/- 0.9 microM and 39.6 +/- 0.9 pmol/min/pmol CYP, respectively, showing 20-fold higher intrinsic clearance than CYP2A13. In human bladder, CYP2A13 mRNA, but not CYP1A2, is expressed at a relatively high level. Human bladder microsomes showed ABP N-hydroxylase activity (K(m) = 34.9 +/- 4.7 microM and V(max) = 57.5 +/- 1.9 pmol/min/mg protein), although the intrinsic clearance was 5-fold lower than that in human liver microsomes (K(m) = 33.2 +/- 2.0 microM and V(max) = 293.9 +/- 5.8 pmol/min/mg protein). The activity in human bladder microsomes was prominently inhibited by 8-methoxypsoralen, but not by fluvoxamine, anti-CYP1A2 or anti-CYP2A6 antibodies. CYP2S1, which is expressed in human bladder and has relatively high amino acid identities with CYP2As, did not show detectable ABP N-hydroxylase activity. In conclusion, although the enzyme responsible for ABP N-hydroxylation in human bladder microsomes could not be determined, we found that CYP2A13 metabolically activates ABP.

Toxicological assessment of ambient and traffic-related particulate matter: a review of recent studies

Particulate air pollution (PM) is an important environmental health risk factor for many different diseases. This is indicated by numerous epidemiological studies on associations between PM exposure and occurrence of acute respiratory infections, lung cancer and chronic respiratory and cardiovascular diseases. The biological mechanisms behind these associations are not fully understood, but the results of in vitro toxicological research have shown that PM induces several types of adverse cellular effects, including cytotoxicity, mutagenicity, DNA damage and stimulation of proinflammatory cytokine production. Because traffic is an important source of PM emission, it seems obvious that traffic intensity has an important impact on both quantitative and qualitative aspects of ambient PM, including its chemical, physical and toxicological characteristics. In this review, the results are summarized of the most recent studies investigating physical and chemical characteristics of ambient and traffic-related PM in relation to its toxicological activity. This evaluation shows that, in general, the smaller PM size fractions (<PM(10)) have the highest toxicity, contain higher concentrations of extractable organic matter (comprising a wide spectrum of chemical substances), and possess a relatively high radical-generating capacity. Also, associations between chemical characteristics and PM toxicity tend to be stronger for the smaller PM size fractions. Most importantly, traffic intensity does not always explain local differences in PM toxicity, and these differences are not necessarily related to PM mass concentrations. This implies that PM regulatory strategies should take PM-size fractions smaller than PM(10) into account. Therefore, future research should aim at establishing the relationship between toxicity of these smaller fractions in relation to their specific sources.

DNA damage and acute toxicity caused by the urban air pollutant 3-nitrobenzanthrone in rats: characterization of DNA adducts in eight different tissues and organs with synthesized standards

3-Nitrobenzanthrone (3-NBA) is an urban air pollutant and rat lung carcinogen that is among the most potent mutagens yet tested in the Salmonella reversion assay. In the present study, 1 mg 3-NBA was administered orally to female F344 rats and DNA adduct formation was examined in liver, lung, kidney and five sections of the gastrointestinal (GI) tract at 6 hr, and 1, 2, 3, 5, and 10 days after administration. The DNA adduct patterns, analyzed by (32)P-postlabelling followed by HPLC separation, were similar in all tissues and organs. Five of the adduct peaks cochromatographed with synthesized DNA adduct standards. Three of these unequivocally determined standards, dGp-C8-N-ABA, dGp-N2-C2-ABA, and dAp-N6-C2-ABA, were of the nonacetylated type, suggesting that at least part of the pathway for activation of 3-NBA proceeds through O-acetylation of the hydroxylamine intermediate. The two other DNA adduct standards, dGp-C8-C2-N-Ac-ABA, and dGp-N2-C2-N-Ac-ABA, were of the acetylated type, but there was some ambiguity in the characterization of these DNA adducts, since they varied inconsistently between samples and they also aligned with peaks found in controls. At 6 hr after treatment, the level of DNA adducts was highest in glandular stomach (relative adduct labeling (RAL), approximately 70 adducts/10(8) normal nucleotides (NN)); adduct levels in this organ decreased at 24 hr, but increased afterwards. DNA adduct levels in the majority of organs were characterized by an early increase (from 6 hr to 3 days), which was followed by a decrease at 5 days and a maximum level 10 days after administration (RAL approximately 120 adducts/10(8) NN for the lung, kidney and glandular stomach, approximately 80 adducts/10(8) NN for the forestomach and ceacum, and approximately 40 adducts/10(8) NN for the liver, small intestine, and colon). This pattern was consistent with pathological observations during autopsy showing high levels of tissue damage in the GI tract; the tissue damage included hemorrhages, loss of villous surface structure in the small intestine, as well as intestine fragility and oedema of the adipose tissue around the GI-tract. Tissue damage decreased and DNA adduct levels increased at 10 days after administration. These observations suggest that 3-NBA not only exerts acute toxic effects, but that the bioavailability is affected by storage in tissues and later becomes available, resulting in the increased DNA adduct levels at the later time points of collection.

Identification of mammalian cell genotoxins in respirable diesel exhaust particles by bioassay-directed chemical analysis

A bioassay-directed chemical analysis which consists of mammalian cell bioassays (comet assay, CBMN assay and EROD-microbioassay) in conjunction with analytical measurements was performed to identify the most biologically active compounds of the diesel exhaust particulate matters (DEPs) on mutagenic activity. These bioassay systems were suitable to estimate the mammalian genotoxic potentials of pollutants present in low concentrations in limited environmental samples, as is the case with DEPEs. The results from mutagenic assay showed that the aromatic and slightly polar fraction of DEPs induced chromosomal damage and DNA breakage in a non-cytotoxic dose. It was also revealed that indirect-acting mutagens may mainly contribute to the mutagenic effect of aromatic fraction via the enzyme metabolism system. In the aromatic fraction, several indirect-acting mutagenic PAHs such as dibenzo(a,h)anthracene, chrysene, and 1,2-benzanthracene were detected by GC-MS and the complex mixture effect of this fraction was quantified in terms of its biological-TCDD equivalent concentration (bio-TEQ) which was 32.82 bio-TEQ ng/g-DEPs by EROD-microbioassay. Conclusively, we confirmed that indirect-acting mutagens contained in aromatic fraction may be important causatives of the genotoxicity of extracts of DEPs by integrating the results obtained from a mammalian cell bioassay-directed fractionation.

Genotoxicity and physicochemical characteristics of traffic-related ambient particulate matter

Exposure to ambient particulate matter (PM) has been linked to several adverse health effects. Since vehicular traffic is a PM source of growing importance, we sampled total suspended particulate (TSP), PM(10), and PM(2.5) at six urban locations with pronounced differences in traffic intensity. The mutagenicity, DNA-adduct formation, and induction of oxidative DNA damage by the samples were studied as genotoxicological parameters, in relation to polycyclic aromatic hydrocarbon (PAH) levels, elemental composition, and radical-generating capacity (RGC) as chemical characteristics. We found pronounced differences in the genotoxicity and chemical characteristics of PM from the various locations, although we could not establish a correlation between traffic intensity and any of these characteristics for any of the PM size fractions. Therefore, the differences between locations may be due to local sources of PM, other than traffic. The concentration of total (carcinogenic) PAHs correlated positively with RGC, direct and S9-mediated mutagenicity, as well as the induction of DNA adducts and oxidative DNA damage. The interaction between total PAHs and transition metals correlated positively with DNA-adduct formation, particularly from the PM(2.5) fraction. RGC was not associated with one specific PM size fraction, but mutagenicity and DNA reactivity after metabolic activation were relatively high in PM(10) and PM(2.5), when compared with TSP. We conclude that the toxicological characteristics of urban PM samples show pronounced differences, even when PM concentrations at the sample sites are comparable. This implies that emission reduction strategies that take chemical and toxicological characteristics of PM into account may be useful for reducing the health risks associated with PM exposure.

Effects of exposure to diesel exhaust particles (DEP) on pulmonary metabolic activation of mutagenic agents

Exposure of rats to diesel exhaust particles (DEP) or carbon black (CB) has been shown to induce time-dependent changes in CYP1A1and CYP2B1 in the lung. The present study evaluated the role of these metabolic enzymes on the pulmonary bioactivation of mutagens. Male Sprague-Dawley rats were intratracheally instilled with saline (control), DEP or CB (35 mg/kg body weight) and sacrificed at 1, 3, or 7 days post-exposure. Both control and exposed lung S9 increased the mutagenic activity of 2-aminoanthracene (2-AA), 2-aminofluorene (2-AF), 1-nitropyrene (1-NP), and the organic extract of DEP (DEPE) in Ames tests with Salmonella typhimurium YG1024 in a dose-dependent manner. Lung microsomes prepared form control or particle-exposed S9, but not cytosolic protein, activated 2-AA mutagenicity. Compared to saline controls, CB-exposed S9 was a less potent inducer of 2-AA mutagenicity at all time points, whereas DEP-exposed S9 was less potent than control saline at 3 and 7 days but not 1 day post-exposure. At 3 days post-exposure, DEP- or CB-exposed lung S9 did not significantly affect the mutagenicity of DEPE or 1-NP, when compared to the controls. The mutgenicity of 2-AA, 2-AF, 1-NP, and DEPE were significantly decreased in the presence of inhibitors for CYP1A1 (alpha-naphthoflavone) or CYP2B (metyrapone), but markedly enhanced by CYP1A1 or CYP2B1 supersomes with all the cofactors, suggesting that both CYP1A1 and CYP2B1 were responsible for mutagen activation. These results demonstrated that exposure of rats to DEP or CB altered metabolic activity of lung S9 and S9 metabolic activity dependent mutagen activation. The bioactivation of mutagens are metabolic enzyme- and substrate-specific, and both CYP1A1 and CYP2B1 play important roles in pulmonary mutagen activation.

Oral Exposure to Benzo[a]pyrene in the Mouse: Detoxication by Inducible Cytochrome P450 Is More Important Than Metabolic Activation

The cytochrome P450 (CYP1A1) enzyme metabolically activates many polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), to DNA- and protein-binding intermediates that are associated with toxicity, mutagenesis, and carcinogenesis. As a result, it is widely accepted that CYP1A1 potentiates the toxicity of this class of chemicals. In distinct contrast, we show here that CYP1A1 inducibility is essential in the detoxication of oral BaP. We compared Cyp1a1(-/-) knockout mice, having the genetic absence of the CYP1A1 enzyme, with Cyp1a1(+/+) wild-type mice. At an oral BaP dose of 125 mg/kg/day, Cyp1a1(-/-) mice died within 30 days whereas Cyp1a1(+/+) mice displayed no outward signs of toxicity. The rate of BaP clearance was 4-fold slower in Cyp1a1(-/-) than Cyp1a1(+/+) mice. The cause of death in Cyp1a1(-/-) mice receiving oral BaP seemed to be immunotoxicity, including toxic chemical depression of the bone marrow; some toxic effects in Cyp1a1(-/-) mice were noted at a BaP dose as low as 1.25 mg/kg/day. DNA post-labeling studies demonstrated dramatically higher BaP-DNA adduct levels in all Cyp1a1(-/-) tissues assayed, with the exception of the small intestine, which is probably a major site of BaP metabolism in Cyp1a1(+/+) mice. Different BaP-DNA adduct patterns were also observed between the two genotypes receiving oral BaP. Despite previous studies in vitro and in cell culture that have shown a participatory role for CYP1A1 in BaP toxicity, the present data indicate that, in the intact animal, inducible CYP1A1 is extremely important in detoxication and protection against oral BaP toxicity.

Increased expression of cytochrome P4501B1 in peripheral leukocytes from lung cancer patients

Aryl hydrocarbon receptor (AhR)-regulated cytochrome P4501A1 (CYP1A1) and P4501B1 (CYP1B1) have been shown to metabolically activate some carcinogens. In the present study, we utilized the real-time reverse transcription-polymerase chain reaction (RT-PCR) assay to compare AhR, CYP1A1 and CYP1B1 mRNA levels in peripheral leukocytes from 42 lung cancer patients and 59 non-cancer subjects. We found that CYP1A1 and CYP1B1 levels, but not AhR, were significantly higher in patients than in non-cancer subjects. After stratified by gender, CYP1A1 levels were significantly higher in female patients than in female controls. After controlling for age, smoking status and gender, lung cancer patients were more likely to be CYP1B1 high expressers (P < 0.05). Neither AhR nor CYP1A1 levels was associated with lung cancer incidence. Leu-Val polymorphism of CYP1B1 was not associated with lung cancer risk in our study. These data indicated that CYP1B1 mRNA levels were elevated in peripheral leukocytes of lung cancer patients.

Diesel exhaust particle-induced alterations of pulmonary phase I and phase II enzymes of rats

Although diesel exhaust particles (DEP) are known to produce pulmonary disorders, the xenobiotic metabolic pathways associated with DEP detoxification and bioactivation remain unclear. In this study, the effect of acute exposure of DEP on phase I and phase II enzymes of rat lung was investigated. Intratracheal administration of DEP produced an induction of cytochrome P-450 (CYP) 1A1 enzyme protein and activity at 1 d postexposure, with the enzyme level returning to control at 5 d postexposure. On the other hand, carbon black (CB), a particle control, did not show any induction of CYP1A1 protein or enzyme activity. However, both DEP and CB significantly decreased CYP2B1 protein and enzyme activity at 1 d postexposure. The decrease in CYP2B1 enzyme protein and activity by DEP or CB treatment was observed up to 7 d postexposure. DEP and CB treatments also significantly attenuated glutathione S-transferase (GST)-pi protein at 1 d postexposure. Both DEP and CB at 35 mg/kg significantly decreased the activities of GST and catalase at 1 and 7 d postexposure. DEP, but not CB, significantly induced quinone reductase (QR) activity at 7 d postexposure. This study suggests that DEP may induce CYP1A1 and QR enzymes via a chemical effect, while the carbonaceous core may be involved in the attenuation of CYP2B1, GST, and catalase proteins and enzyme activities.

The dual effect of the particulate and organic components of diesel exhaust particles on the alteration of pulmonary immune/inflammatory responses and metabolic enzymes

Exposure to diesel exhaust particles (DEP) is an environmental and occupational health concern. This review examines the cellular actions of the organic and the particulate components of DEP in the development of various lung diseases. Both the organic and the particulate components cause oxidant lung injury. The particulate component is known to induce alveolar epithelial damage, alter thiol levels in alveolar macrophages (AM) and lymphocytes, and activate AM in the production of reactive oxygen species (ROS) and pro-inflammatory cytokines. The organic component, on the other hand, is shown to generate intracellular ROS, leading to a variety of cellular responses including apoptosis. There are a number of differences between the biological actions exerted by these two components. The organic component is responsible for DEP induction of cytochrome P450 family 1 enzymes that are critical to the polycyclic aromatic hydrocarbons (PAH) and nitro-PAH metabolism in the lung as well as in the liver. The particulate component, on the other hand, causes a sustained down-regulation of CYP2B1 in the rat lung. The significance of this effect on pulmonary metabolism of xenobiotics and endobiotics remains to be seen, but may prove to be an important factor governing the interplay of the pulmonary metabolic and inflammatory systems. Long-term exposures to various particles including DEP, carbon black (CB), TiO2, and washed DEP devoid of the organic content, have been shown to produce similar tumorigenic responses in rodents. There is a lack of correlation between tumor development and DEP chemical-derived DNA adduct formation. But the organic component has been shown to generate ROS that produce 8-hydroxydeoxyguanosine (8-OHdG) in cell culture. The organic, but not the particulate, component of DEP suppresses the production of pro-inflammatory cytokines by AM and the development of Th1 cell-mediated immunity. The mechanism for this effect is not yet clear, but may involve the induction of heme oxygenase-1 (HO-1), a cellular genetic response to oxidative stress. Both the organic and the particulate components of DEP enhance respiratory allergic sensitization. Part of the DEP effects may be due to a depletion of glutathione in lymphocytes. The organic component, which is shown to induce IL-4 and IL-10 productions, may skew the immunity toward Th2 response, whereas the particulate component may stimulate both the Th1 and Th2 responses. In conclusion, the literature shows that the particulate and organic components of DEP exhibit different biological actions but both involve the induction of cellular oxidative stress. Together, these effects inhibit cell-mediated immunity toward infectious agents, exacerbate respiratory allergy, cause DNA damage, and under long-term exposure, induce the development of lung tumors.

Genotoxic activation of benzophenone and its two metabolites by human cytochrome P450s in SOS/umu assay

The genotoxic potential of benzophenone and its metabolically related compounds, benzhydrol and p-benzoylphenol, was investigated using human cytochrome P450 (P450) enzymes. Benzophenone and its two metabolites (0.1-1mM) showed a suppression of bacterial growth without any P450 system, but no induction of umu gene expression was observed in Salmonella typhimurium TA1535/pSK1002. Human liver microsomes induced the bacterial cytotoxicity of these compounds without any umu gene expression. On the other hand, with the addition of Escherichia coli membranes expressing recombinant human P450 2A6 and NADPH-cytochrome P450 reductase (NPR), benzophenone showed umu gene expression (64 umu units/min/nmol) P450 2A6). Moderate activation of benzophenone by P450 1A1/NPR membranes, 1A2/NPR membranes, or 1B1/NPR membranes was also observed. Activation of benzhydrol and p-benzoylphenol by the P450/NPR system was similar to that of benzophenone. These results suggest that benzophenone and its metabolically related benzhydrol and p-benzoylphenol can be bioactivated by P450 2A6 and P450 family 1 enzymes. Until now, benzophenone has been investigated mainly in terms of estrogenic activity and cytotoxicity, however, the genotoxic activation of benzophenone by human cytochrome P450s should be examined in terms of the risks to humans.

DNA adducts from nitroreduction of 2,7-dinitrofluorene, a mammary gland carcinogen, catalyzed by rat liver or mammary gland cytosol

Nitrofluorenes are mutagenic and carcinogenic environmental pollutants arising chiefly from combustion of fossil fuels. Nitro aromatic compounds undergo nitroreduction to N-hydroxy arylamines that bind to DNA directly or after O-esterification. This study analyzes the DNA binding and adducts from the in vitro nitroreduction of 2,7-dinitrofluorene (2,7-diNF), a potent mammary carcinogen in the rat. Potential adduct(s) of 2,7-diNF was (were) generated by reduction of 2-nitroso-7-NF with ascorbate/H(+) in the presence of calf thymus DNA. The major adduct was characterized by HPLC/ESI/MS and (1)H NMR spectrometry as N-(deoxyguanosin-8-yl)-2-amino-7-NF, and a minor one was determined by HPLC/ESI/MS to be a deoxyadenosine adduct of 2-amino-7-NF. Products from enzymatic nitroreduction were monitored by HPLC and DNA adduct formation by (32)P-postlabeling. Xanthine oxidase/hypoxanthine-catalyzed nitroreduction of 2,7-diNF, 2-nitrofluorene (2-NF), and 1-nitropyrene (1-NP) yielded the respective amines to similar extents (30-50%). However, the level of the major adducts ( approximately 0.15/10(6) nucleotides) from 2-NF [N-(deoxyguanosin-8-yl)-2-aminofluorene] and 2,7-diNF [N-(deoxyguanosin-8-yl)-2-amino-7-NF] was < or = 2% that from 1-NP. In the presence of acetyl CoA, nitroreduction of 2-NF catalyzed by rat liver cytosol/NADH yielded the same adduct at a level of 2.2/10(6) nucleotides. Liver or mammary gland cytosol with acetyl CoA yielded mainly N-(deoxyguanosin-8-yl)-2-amino-7-NF from 2,7-diNF at >30 adducts/10(6) nucleotides, levels comparable to those from 1,6-dinitropyrene and 4- or 49-fold greater than the respective levels without acetyl CoA. Recovery of 2-nitroso-7-NF and 2-amino-7-NF from cytosol-catalyzed reduction of 2,7-diNF indicated nitroreduction and an N-hydroxy arylamine intermediate. Likewise, the presence of 2-acetylamino-7-NF indicated that reactivity with acyltransferase(s) was not prevented by the nitro group at C7. These data are consistent with activation of 2,7-diNF via nitroreduction to the N-hydroxy arylamine and acetyl CoA-dependent O-acetylation of the latter to bind to DNA. Enzymatic nitroreduction of 2,7-diNF was greatly enhanced by 9-oxidation. The nitroreduction of either 9-oxo-2,7-diNF or 9-hydroxy-2,7-diNF catalyzed by liver cytosol with acetyl CoA yielded two adducts (>2/10(6) nucleotides). Differences in the TLC migration of these adducts, compared to those from 2,7-diNF, and the lack of 2,7-diNF formation in the incubations suggested retention of the C9-oxidized groups. The relative ratios of the amine to amide from nitroreductions of 9-oxo-2,7-diNF and 2,7-diNF catalyzed by liver cytosol suggested that the 9-oxo group decreased reactivity with acyltransferase and, thus, the amount of N-acetoxy arylamine that binds to DNA. The mammary gland tumorigenicity of 2,7-diNF and the extent of its activation by the tumor target tissue shown herein suggest relevance of this environmental pollutant for breast cancer.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Induction of cytochrome P450 1B1 in lung, liver and kidney of rats exposed to diesel exhaust

We have shown previously that diesel exhaust particle (DEP) extracts (DEPE) and 1-nitropyrene were genotoxically activated by human cytochrome P450 1B1 in SOS/umu assay. In this study, the in vivo induction of P450 family 1 enzymes in rats by exposure to diesel exhaust was investigated with regard to mRNA levels, P450 enzyme content, drug oxidation activities in the microsomes and umu gene expression of typical P450 substrates and DEPE itself catalyzed by the microsomes. Male Fischer 344 rats (4 weeks old) were exposed to 0.3 and 3.0 mg/m(3) DEP for 12 h per day for 4 weeks; the former dose corresponded to the typical daily airborne particle concentration. The levels of mRNA of rat P450 1B1 and P450 1A1 in the lung and liver were significantly increased 1.1-1.4-fold by exposure to 0.3 mg/m(3) DEP. Diesel exhaust particle extracts induced umu gene expression in Salmonella typhimurium TA1535/pSK1002 in the absence of a functional P450 system and were further activated by human recombinant P450 1B1. Using an O-acetyltransferase overexpressing Salmonella strain, genotoxic activation of P450 1B1 marker chemicals (1-nitropyrene, 1-aminopyrene and DEPE) by lung, liver and kidney microsomes was increased 1.7-4.2-, 1.4-1.5- and 1.0-1.3-fold, respectively, by exposure to 0.3 mg/m(3) DEP. Activation of 3-amino-1,4-dimethyl-5H-pyrido [4,3-b]indole (Trp-P-1; marker for P450 1A1) by lung microsomes and the P450 1A2 content in liver microsomes were slightly increased by exposure to 3.0 mg/m(3) DEP. This is the first report to suggest that typical daily contaminant levels (0.3 mg particle/m(3)) of diesel exhaust can induce P450 1B1 in rats and that the induced P450 1B1 may catalyze the genotoxic activation of DEP.

Metabolic activation of carcinogenic 1-nitropyrene by human cytochrome P450 1B1 in Salmonella typhimurium strain expressing an O-acetyltransferase in SOS/umu assay

Metabolic activation of 1-nitropyrene (1-NP) by human cytochrome P450 (P450) family 1 enzymes co-expressed with NADPH-cytochrome P450 reductase (NPR) in Escherichia coli membranes was investigated. 1-NP induced umu gene expression in Salmonella typhimurium TA1535/pSK1002 in the absence of any P450 system, but the activities were influenced by the levels of bacterial O-acetyltransferase (OAT) and nitroreductase. Metabolic activation of 1-NP by human P450 1B1/NPR membranes was observed and was influenced by the levels of OAT levels in tester strains. Metabolic activation of 1-NP (0.3microM) by P450 1B1 was 750 umu units/min/nmol P450 1B1 in an OAT-overexpressing strain NM2009. The metabolic activation of 1-NP (3-30microM) was similar (approximately 300 umu units/min/nmol P450 1B1) using TA1535/pSK1002 or OAT-deficient strain NM2000. P450 1B1 had the highest catalytic activities among P450 family 1 enzymes for the activation of 1-aminopyrene (1-AP) in the OAT-overexpressing strain NM2009, suggesting nitrenium ion formation via N-hydroxylation/O-acetylation. High-performance liquid chromatography (HPLC) analyses revealed the formation of 1-nitropyrene-6-ol and also 1-nitropyrene-3-ol, 1-nitropyrene-8-ol, and trans-4,5-dihydroxy-4,5-diol-1-nitropyrene from 1-NP (10microM), catalyzed by P450 1B1. These results indicate that 1-NP can be activated by human P450 1B1 to a genotoxic agent by nitroreduction/O-acetylation at low substrate concentrations and probably by epoxidation (independent of OAT) at high concentrations.