Relative genotoxicity of polycyclic aromatic hydrocarbons inferred from free energy perturbation approaches.

Utilizing molecular dynamics and free energy perturbation, we examine the relative binding affinity of several covalent polycyclic aromatic hydrocarbon - DNA (PAH-DNA) adducts at the central adenine of NRAS codon-61, a mutational hotspot implicated in cancer risk. Several PAHs classified by the International Agency for Research on Cancer as probable, possible, or unclassifiable as to carcinogenicity are found to have greater binding affinity than the known carcinogen, benzo[a]pyrene (B[a]P). van der Waals interactions between the intercalated PAH and neighboring nucleobases, and minimal disruption of the DNA duplex drive increases in binding affinity. PAH-DNA adducts may be repaired by global genomic nucleotide excision repair (GG-NER), hence we also compute relative free energies of complexation of PAH-DNA adducts with RAD4-RAD23 (the yeast ortholog of human XPC-RAD23) which constitutes the recognition step in GG-NER. PAH-DNA adducts exhibiting the greatest DNA binding affinity also exhibit the least RAD4-RAD23 complexation affinity and are thus predicted to resist the GG-NER machinery, contributing to their genotoxic potential. In particular, the fjord region PAHs dibenzo[a,l]pyrene, benzo[g]chrysene, and benzo[c]phenanthrene are found to have greater binding affinity while having weaker RAD4-RAD23 complexation affinity than their respective bay region analogs B[a]P, chrysene, and phenanthrene. We also find that the bay region PAHs dibenzo[a,j]anthracene, dibenzo[a,c]anthracene, and dibenzo[a,h]anthracene exhibit greater binding affinity and weaker RAD4-RAD23 complexation affinity than B[a]P. Thus, the study of PAH genotoxicity likely needs to be substantially broadened, with implications for public policy and the health sciences. This approach can be broadly applied to assess factors contributing to the genotoxicity of other unclassified compounds.

Chlororesistoflavins A and B, Chlorinated Benzopyrene Antibiotics Produced by the Marine-Derived Actinomycete Streptomyces sp. Strain EG32.

As part of a collaborative biomedical investigation of actinomycete bacteria isolated from sediments collected along the northern coast of Egypt (Mediterranean Sea), we explored the antibacterial metabolites from a bacterium identified as a Streptomyces sp., strain EG32. HPLC analysis and antibacterial testing against methicillin-resistant Staphylococcus aureus (MRSA) resulted in the identification of six compounds related to the resistoflavin and resistomycin class. Two of these metabolites were the chlorine-containing analogues chlororesistoflavins A (1) and B (2). The absolute configurations of the lone stereogenic center (C-11b) in these metabolites were assigned by analysis of their ECD spectra. Interestingly, the ECD spectrum of chlororesistoflavin A (1) shows a Cotton effect of the n-π* transition antipodal to that of the parent natural product, a consequence of 1,3-allylic strain induced by the adjacent bulky chlorine atom that distorts the coplanarity of the carbonyl group with the π-system. The chiroptical analysis thus resolves the paradox and uniformly aligns the configuration of all analogues as identical to that reported for natural resistoflavin. Chlororesistoflavins A (1) and B (2) exhibited antibacterial activity against MRSA with a minimum inhibitory concentration of 0.25 and 2.0 µg/mL, respectively.

First-principles study of benzo[a]pyrene-7,8-dione and DNA adducts.

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in environments, and some of them are causative agents of human cancer. Previous studies concluded that benzo[a]pyrene-7,8-dione (BPQ), which is one kind of carcinogenic PAH metabolites, forms covalently bonded adducts with DNA, and the major adduct formed is a deoxyguanosine adduct. In this work, we investigate the interactions between BPQ and DNA molecules via first-principles calculations. We identify six possible DNA adducts with BPQ. In addition to the four adducts forming covalent bonds, there are two adducts bound purely by van der Waals (vdW) interactions. Remarkably, the two vdW-bound adducts have comparable, if not larger, binding energies as the covalent adducts. The results may help us gain more understanding of the interactions between PAH metabolites and DNA.

NADPH-quinone oxidoreductase-1 mediates Benzo-[a]-pyrene-1,6-quinone-induced cytotoxicity and reactive oxygen species production in human EA.hy926 endothelial cells.

Numerous studies conducted in the past have reported deaths in the human population due to cardiovascular diseases (CVD) on exposure to air particulate matter (APM). BP-1,6-quinone (BP-1,6-Q) is one of the significant components of APM. However, the mechanism(s) by which it can exert its toxicity in endothelial cells is not yet completely understood. NAD(P)H: quinone oxidoreductase-1 (NQO1) is expressed highly in myocardium and vasculature tissues of the heart and plays a vital role in maintaining vascular homeostasis. This study, demonstrated that BP-1,6-Q diminishes NQO1 enzyme activity in a dose-dependent manner in human EA.hy926 endothelial cells. The decrease in the NQO1 enzyme causes potentiation in BP-1,6-Q-mediated toxicity in EA.hy926 endothelial cells. The enhancement of NQO1 in endothelial cells showed cytoprotection against BP-1,6-Q-induced cellular toxicity, lipid, and protein damage suggesting an essential role of NQO1 in cytoprotection against BP-1,6-Q toxicity. Using various biochemical assays and genetic approaches, results from this study further demonstrated that NQO1 also plays a crucial role in BP-1,6-Q-induced production of reactive oxygen species (ROS). These findings will contribute to elucidating BP-1,6-Q mediated toxicity and its role in the development of atherosclerosis.

Conditional and unconditional genome-wide association study reveal complicate genetic architecture of human body weight and impacts of smoking.

To reveal the impacts of smoking on genetic architecture of human body weight, we conducted a genome-wide association study on 5,336 subjects in four ethnic populations from MESA (The Multi-Ethnic Study of Atherosclerosis) data. A full genetic model was applied to association mapping for analyzing genetic effects of additive, dominance, epistasis, and their ethnicity-specific effects. Both the unconditional model (base) and conditional model including smoking as a cofactor were investigated. There were 10 SNPs involved in 96 significant genetic effects detected by the base model, which accounted for a high heritability (61.78%). Gene ontology analysis revealed that a number of genetic factors are related to the metabolic pathway of benzopyrene, a main compound in cigarettes. Smoking may play important roles in genetic effects of dominance, dominance-related epistasis, and gene-ethnicity interactions on human body weight. Gene effect prediction shows that the genetic effects of smoking cessation on body weight vary from different populations.

Degradation of benzopyrene and acrylamide in roasted coffee beans by corona discharge plasma jet (CDPJ) and its effects on biochemical and sensory properties.

This study was aimed to reduce the concentrations of benzopyrene (BaP) and acrylamide (ACR) in roasted coffee beans by corona discharge plasma jet (CDPJ). The initial concentrations of BaP and ACR in roasted beans were decreased by 53.6% and 32.0%, respectively, following CDPJ (powered by 20 kV DC/1.5 A) treatment for 60 min. The levels of total solid, total acid, chlorogenic acid, caffeine, trigonelline, and pH were insignificantly changed upon CDPJ treatment compared to controls. However, the concentration of total phenolic content and Agtron color values were altered significantly. The treatment of beans did not alter descriptive sensory properties of the corresponding coffee brews, except aroma and aftertaste characteristics. As the treatment time increased from 15 to 60 min, scores for aroma profiles in PCA plot were shifted from right to left, although overlapping was observed between 15- and 30-min-treated samples. Additionally, none of the treated samples were discriminated from the control by electronic tongue.

Investigation of Environmental Pollutant-Induced Lung Inflammation and Injury in a 3D Coculture-Based Microfluidic Pulmonary Alveolus System.

The health impact of environmental pollution involving an increase in human diseases has been subject to extensive study in recent decades. The methodology in biomimetic investigation of these pathophysiologic events is still in progress to uncover the gaps in knowledge associated with pollution and its influences on health. Herein, we describe a comprehensive evaluation of environmental pollutant-caused lung inflammation and injury using a microfluidic pulmonary alveolus platform with alveolar-capillary interfaces. We performed a microfluidic three-dimensional coculture with physiological microenvironment simulation at microscale control and demonstrated a reliable reconstruction of tissue layers including alveolar epithelium and microvascular endothelium with typical mechanical, structural, and junctional integrity, as well as viability. On-chip detection and analysis of pulmonary alveolus responses focusing on various inflammatory and injurious dynamics to the respective pollutant stimulations were achieved in the coculture-based microfluidic pulmonary alveolus model, in comparison with common on-chip monoculture and off-chip culture tools. We confirmed the synergistic effects of the epithelial and endothelial interfaces on the stimuli resistance and verified the importance of creating complex tissue microenvironments in vitro to explore pollution-involved human pathology. We believe the microfluidic approach presents great promise in environmental monitoring, drug discovery, and tissue engineering.

2D Graphene Oxide/Fe-MOF Nanozyme Nest with Superior Peroxidase-Like Activity and Its Application for Detection of Woodsmoke Exposure Biomarker.

Emerging nanomaterials such as nanozymes have recently been applied for the immunoassay-based detection of biomarkers. However, the inferior catalytic activity and low water solubility of nanozymes remain as the major limitations compared to natural enzymes. To overcome these limitations, we successfully synthesized a superior nanozyme with a structure of enriched 2D catalytic interface, namely Nanozyme Nest, which was composed of Fe-based metal-organic frameworks (Fe-MOF) and graphene oxide (GO). Then, we applied it in an ultrasensitive enzyme-linked immunosorbent assay (ELISA) for the detection of benzo[a]pyrene-7,8-diol 9,10-epoxide-DNA adduct (BPDE-DNA), which is a metabolite of benzo[a]pyrene (BP) and used as a typical biomarker of woodsmoke exposure in human blood. The Nanozyme Nest features amplified peroxidase-like catalytic ability from graphene and Fe-MOF due to their large surface area and abundant active sites. By using the proposed Nanozyme Nest-based ultrasensitive ELISA, the BPDE-DNA could be detected at a level as low as 0.268 ng/mL, and the obtained sensitivity was much higher than most of the widely used methods. Our work provides a novel strategy to design ultrasensitive immunosensors with advantages of amplified catalytic activity and improved water solubility compared to classic nanozymes. This illustrates the promising applications of the Nanozyme Nest-based immunosensors in point-of-care settings to conveniently detect exposures and diagnose diseases.

Wurster-Type Anthanthrene Polyradicaloid Cations.

4,10-dibromoanthanthrone, a highly robust building block, is used to synthesize a bis(triarylamine) polymer. The polymer can be oxidized twice to form a polycationic macromolecule showing magnetic properties by electron paramagnetic resonance spectroscopy. In its dicationic state, the presence of isolated radicals is possible because of the interrupted conjugation between the diphenylamine with the anthanthrone core. The high steric hindrance prevents the planarity of the adjacent groups resulting in a polyradical cationic polymer. The oxidized polymer has a strong absorption in the near-infrared region along with reversible redox stages.

Benzopyrone represents a privilege scaffold to identify novel adenosine A1/A2A receptor antagonists.

Adenosine receptor antagonists are under investigation as potential drug candidates for the treatment of certain cancers, neurological disorders, depression and potentially improve tumour immunotherapy. The benzo-γ-pyrone scaffold is well-known in medicinal chemistry with diverse pharmacological activities attributed to them, however, their therapeutic potential as adenosine receptor antagonists have not been investigated in detail. To expand on the structure-activity relationships, the present study explored the adenosine A1 and A2A receptor binding affinities of a selected series of benzo-γ-pyrone analogues. In vitro evaluation led to the identification of 5-hydroxy-2-(3-hydroxyphenyl)-4H-1-benzopyran-4-one with the best adenosine A2A receptor affinity among the test compounds and was found to be non-selective (A1Ki = 0.956 µM; A2AKi = 1.44 µM). Hydroxy substitution on ring A and/or B play a key role in modulating the binding affinity at adenosine A1 and A2A receptors. Adenosine A1 receptor affinity was increased to the nanomolar range with hydroxy substitution on C6 (ring A), while meta-hydroxy substitution on ring B governed adenosine A2A receptor affinity. The double bond between C2 and C3 of ring C as well as C2 phenyl substitution was shown to be imperative for both adenosine A1 and A2A receptor affinity. Selected benzo-γ-pyrone derivatives behaved as adenosine A1 receptor antagonists in the performed GTP shift assays. It may be concluded that benzo-γ-pyrone based derivatives are suitable leads for designing and identifying adenosine receptor antagonists as treatment of various disorders.

Structural Insight into the Mechanism of Dibenzo[a,l]pyrene and Benzo[a]pyrene-Mediated Cell Proliferation Using Molecular Docking Simulations.

In the proposed work, we have explicated the mechanism of dibenzo[a,l]pyrene (DBP) and benzo[a]pyrene (BP) modulated cell proliferation by assessing the plausible binding with CASPASES, BAX, Bcl-2, MDM2, p53, p21, p16, CylinD1-CDK4 complex, CylinE1-CDK2 complex, H-Ras, K-Ras, BRCA1, and BRCA2 through exploiting the inherent potential of AutoDock Tools 4.0. In silico findings revealed that potent carcinogenic metabolites of DBP (e.g., (-)-anti-DBPDE and (+)-syn-DBPDE) and BP (e.g., (+)-anti-BPDE) exhibited better binding interactions to Caspase-9 than Caspase-8 and Caspase-3. Feeble interactions of BAX and Bcl-2 with diol-epoxides of both PAHs were observed. Diol-epoxides of DBP and BP were found to bind to p53 with tighter interaction than MDM2 and p53-MDM2 complex. The p16 and Cyclin-CDK complexes were best docked to aforesaid metabolites as compared to p21. Moreover, stronger interactions of BRCA1 and BRCA2 with DBP and feeble interactions of BRCA1 and BRCA2 with BP were observed from docking results. Furthermore, stronger interactions of both DBP and BP with the H-Ras and K-Ras oncoproteins were found, while only DBP interacted relatively strongly with the BRCA1 and BRCA2, which were suggesting more carcinogenic nature of DBP than BP, a well-known observation in the wet lab. Besides giving structural insight into the mechanism of DBP and BP-mediated cell proliferation, these in silico findings may be helpful to understand the mechanistic nature of environmental carcinogens and their cellular targets.

Enhanced adsorbability and photocatalytic activity of TiO2-graphene composite for polycyclic aromatic hydrocarbons removal in aqueous phase.

Photodegradation via titanium dioxide (TiO2) has been used to remove polycyclic aromatic hydrocarbons (PAHs) from environmental media broadly. In this study, a series of TiO2-graphene composites (P25-GR) with different GR weight ratios were synthesized via hydrothermal reaction of graphene oxide (GO) and P25. Their structures were characterized and the proprieties were tested in aqueous phase. Phenanthrene (PHE), fluoranthene (FLAN), and benzo[a]pyrene (BaP) were selected as models of PAHs. The experiment indicated that P25-2.5%GR exhibited enhancement in both adsorption and photodegradation, ∼80% of PAHs were removed after 2h photocatalysis. The influence of photodegradation rate was studied, including PAHs initial concentration and pH. Aromatic intermediates were identified during the reaction process and the degradation pathways were portrayed. This work explored the enhanced photocatalysis performance was attributed to the PAH-selective adsorbability and the strong electron transfer ability of the composite. The analysis of the degradation intermediates confirmed that the reaction proceeded with the formation of free radicals, leading to the gradual PAH mineralization.

Structure and mechanism of error-free replication past the major benzo[a]pyrene adduct by human DNA polymerase κ.

Benzo[a]pyrene (BP) is a well-known and frequently encountered carcinogen which generates a bulky DNA adduct (+)-trans-10S-BP-N(2)-dG (BP-dG) in cells. DNA polymerase kappa (polκ) is the only known Y-family polymerase that bypasses BP-dG accurately and thus protects cells from genotoxic BP. Here, we report the structures of human polκ in complex with DNA containing either a normal guanine (G) base or a BP-dG adduct at the active site and a correct deoxycytidine. The structures and supporting biochemical data reveal a unique mechanism for accurate replication by translesion synthesis past the major bulky adduct. The active site of polκ opens at the minor groove side of the DNA substrate to accommodate the bulky BP-dG that is attached there. More importantly, polκ stabilizes the lesion DNA substrate in the same active conformation as for regular B-form DNA substrates and the bulky BPDE ring in a 5' end pointing conformation. The BP-dG adducted DNA substrate maintains a Watson-Crick (BP-dG:dC) base pair within the active site, governing correct nucleotide insertion opposite the bulky adduct. In addition, polκ's unique N-clasp domain supports the open conformation of the enzyme and the extended conformation of the single-stranded template to allow bypass of the bulky lesion. This work illustrates the first molecular mechanism for how a bulky major adduct is replicated accurately without strand misalignment and mis-insertion.

Quantitative analysis of 3-OHB[a]P and (+)-anti-BPDE as biomarkers of B[a]P exposure in rats.

The aim of this study was to develop an analytical method for the determination the levels of metabolites of benzo[a]pyrene (B[a]P), 3-hydroxybenzo(a)pyrene (3-OHB[a]P) and (+)-anti-benzo(a)pyrene diol-epoxide [(+)-anti-BPDE, combined with DNA to form adducts], in rat blood and tissues exposed to B[a]P exposure by high-performance liquid chromatography with fluorescence detection (HPLC/FD), and to investigate the usefulness of 3-OHB[a]P and (+)-anti-BPDE as markers of intragastrical exposure to B[a]P in rats. The levels of 3-OH-B[a]P and B[a]P-tetrol I-1 released after acid hydrolysis of (+)-anti-BPDE in the samples were measured by HPLC/FD. The calibration curves were linear (r(2) > 0.9904), and the lower limit of quantification ranged from 0.34 to 0.45 ng/mL for 3-OHB[a]P and from 0.43 to 0.58 ng/mL for (+)-anti-BPDE. The intra- and inter-day stability assay data suggested that the method is accurate and precise. The recoveries of 3-OHB[a]P and (+)-anti-BPDE were in the ranges of 73.6 ± 5.0 to 116.5 ± 6.3% and 73.3 ± 8.5 to 141.2 ± 13.8%, respectively. A positive correlation was found between the concentration of intragastrical B[a]P and the concentrations of 3-OH-B[a]P and (+)-anti-BPDE in the blood and in most of the tissues studied, except for the brain and kidney, which showed no correlation between B[a]P and 3-OHB[a]P and between B[a]P and (+)-anti-BPDE, respectively. A sensitive, reliable and rapid HPLC/FD was developed and validated for analysis of 3-OHB[a]P and (+)-anti-BPDE in rat blood and tissues. There was a positive correlation between the concentration of 3-OHB[a]P or (+)-anti-BPDE in the blood and the concentration of 3-OHB[a]P or (+)-anti-BPDE in the most other tissues examined. The concentration of 3-OHB[a]P or (+)-anti-BPDE in the blood could be used as an indicator of the concentration of 3-OHB[a]P or (+)-anti-BPDE in the other tissues in response to B[a]P exposure. These results demonstrate that 3-OHB[a]P and (+)-anti-BPDE are potential biomarkers of B[a]P exposure, which would also be useful to assess the carcinogenic risks from B[a]P exposure.

How Y-Family DNA polymerase IV is more accurate than Dpo4 at dCTP insertion opposite an N2-dG adduct of benzo[a]pyrene.

To bypass DNA damage, cells have Y-Family DNA polymerases (DNAPs). One Y-Family-class includes DNAP κ and DNAP IV, which accurately insert dCTP opposite N(2)-dG adducts, including from the carcinogen benzo[a]pyrene (BP). Another class includes DNAP η and DNAP V, which insert accurately opposite UV-damage, but inaccurately opposite BP-N(2)-dG. To investigate structural differences between Y-Family-classes, regions are swapped between DNAP IV (a κ/IV-class-member) and Dpo4 (a η/V-class-member); the kinetic consequences are evaluated via primer-extension studies with a BP-N(2)-dG-containing template. Four key structural elements are revealed. (1) Y-Family DNAPs have discreet non-covalent contacts between their little finger-domain (LF-Domain) and their catalytic core-domain (CC-Domain), which we call "non-covalent bridges" (NCBs). Arg37 and Arg38 in DNAP IV's CC-Domain near the active site form a non-covalent bridge (AS-NCB) by interacting with Glu251 and Asp252, respectively, in DNAP IV's LF-Domain. Without these interactions dATP/dGTP/dTTP misinsertions increase. DNAP IV's AS-NCB suppresses misinsertions better than Dpo4's equivalent AS-NCB. (2) DNAP IV also suppresses dATP/dGTP/dTTP misinsertions via a second non-covalent bridge, which is ∼8Å from the active site (Distal-NCB). Dpo4 has no Distal-NCB, rendering it inferior at dATP/dGTP/dTTP suppression. (3) dCTP insertion is facilitated by the larger minor groove opening near the active site in DNAP IV versus Dpo4, which is sensible given that Watson/Crick-like [dCTP:BP-N(2)-dG] pairing requires the BP-moiety to be in the minor groove. (4) Compared to Dpo4, DNAP IV has a smaller major groove opening, which suppresses dGTP misinsertion, implying BP-N(2)-dG bulk in the major groove during Hoogsteen syn-adduct-dG:dGTP pairing. In summary, DNAP IV has a large minor groove opening to enhance dCTP insertion, a plugged major groove opening to suppress dGTP misinsertion, and two non-covalent bridges (near and distal to the active site) to suppress dATP/dGTP/dTTP misinsertions; collectively these four structural features enhance DNAP IV's dNTP insertion fidelity opposite a BP-N(2)-dG adduct compared to Dpo4.

Tissue Distribution, Excretion and Pharmacokinetics of the Environmental Pollutant Dibenzo[def,p]chrysene in Mice.

Dibenzo[def,p]chrysene (DBP), a representative example of the class of polycyclic aromatic hydrocarbon (PAH), is known to induce tumors in multiple organ sites including the ovary, lung, mammary glands, and oral cavity in rodents. The goal of this study was to test the hypothesis that the levels of DBP and its metabolites that reach and retain the levels for an extended time in the target organs as well as the capacity of these organs to metabolize this carcinogen to active metabolites that can damage DNA may account for its tissue selective tumorigenicity. Therefore, we used the radiolabeled [(3)H] DBP to accurately assess the tissue distribution, excretion, and pharmacokinetics of this carcinogen. We also compared the levels of DBPDE-DNA adducts in a select target organ (ovary) and nontarget organs (kidney and liver) in mice treated orally with DBP. Our results showed that after 1 week, 91.40 ± 7.23% of the radioactivity was recovered in the feces; the corresponding value excreted in the urine was less than 2% after 1 week. After 24 h, the stomach had the highest radioactivity followed by the intestine and the liver; however, after 1 week, levels of the radioactivity in these organs were the lowest among tissues examined including the ovary and liver; the pharmacokinetic analysis of DBP was conducted using a one compartment open model. The level of (-)-anti-trans-DBPDE-dA in the ovaries (8.91 ± 0.08 adducts/10(7) dA) was significantly higher (p < 0.01) than the levels of adducts in kidneys (0.69 ± 0.09 adducts/10(7) dA) and livers (0.63 ± 0.11 adducts/10(7) dA). Collectively, the results of the tissue distribution and pharmacokinetic analysis may not fully support our hypothesis, but the capacity of the target organs vs nontarget organs to metabolize DBP to active intermediates that can damage DNA may account for its tissue selective tumorigenicity.

Analysis of dibenzo[def,p]chrysene-deoxyadenosine adducts in wild-type and cytochrome P450 1b1 knockout mice using stable-isotope dilution UHPLC-MS/MS.

The polycyclic aromatic hydrocarbon (PAH), dibenzo[def,p]chrysene (DBC; also known as dibenzo[a,l]pyrene), is a potent carcinogen in animal models and a class 2A human carcinogen. Recent investigations into DBC-mediated toxicity identified DBC as a potent immunosuppressive agent similar to the well-studied immunotoxicant 7,12-dimethylbenz[a]anthracene (DMBA). DBC, like DMBA, is bioactivated by cytochrome P450 (CYP) 1B1 and forms the reactive metabolite DBC-11,12-diol-13,14-epoxide (DBCDE). DBCDE is largely responsible for the genotoxicity associated with DBC exposure. The immunosuppressive properties of several PAHs are also linked to genotoxic mechanisms. Therefore, this study was designed to identify DBCDE-DNA adduct formation in the spleen and thymus of wild-type and cytochrome P450 1b1 (Cyp1b1) knockout (KO) mice using a highly sensitive stable-isotope dilution UHPLC-MS/MS method. Stable-isotope dilution UHPLC-MS/MS identified the major DBC adducts (±)-anti-cis-DBCDE-dA and (±)-anti-trans-DBCDE-dA in the lung, liver, and spleen of both WT and Cyp1b1 KO mice. However, adduct formation in the thymus was below the level of quantitation for our method. Additionally, adduct formation in Cyp1b1 KO mice was significantly reduced compared to wild-type (WT) mice receiving DBC via oral gavage. In conclusion, the current study identifies for the first time DBCDE-dA adducts in the spleen of mice supporting the link between genotoxicity and immunosuppression, in addition to supporting previous studies identifying Cyp1b1 as the primary CYP involved in DBC bioactivation to DBCDE. The high levels of DBC-DNA adducts identified in the spleen, along with the known high levels of Cyp1b1 expression in this organ, supports further investigation into DBC-mediated immunotoxicity.

Effect of phytochemical intervention on dibenzo[a,l]pyrene-induced DNA adduct formation.

Dibenzo[a,l]pyrene (DBP) has been found to be the most potent carcinogen of the polycyclic aromatic hydrocarbons (PAHs). Primary sources for DBP in the environment are combustion of wood and coal burning, gasoline and diesel exhaust, and tires. Given the likelihood of environmental exposure to DBP and strong experimental evidence of its potency, it is likely to contribute to lung cancer development. Intervention with compounds of natural origin ("phytochemicals") is considered an effective means to prevent cancer development and favorably modulate the underlying mechanisms, including DNA adduct formation. In this study, several agents have been identified that inhibit environmental carcinogen-induced DNA adduct formation using a cell-free microsomal system. Of the ten agents tested, resveratrol (648 ± 26 adducts/10(9) nucleotides), oltipraz (1007 ± 348 adducts/10(9) nucleotides), delphinidin (1252 ± 142 adducts/10(9) nucleotides), tanshinone I (1981 ± 213 adducts/10(9) nucleotides), tanshinone IIA (2606 ± 478 adducts/10(9) nucleotides) and diindoylmethane (3643 ± 469 adducts/10(9) nucleotides) were the most effective compared to vehicle treatment (14,062 ± 1097 adducts/10(9) nucleotides). DBP is metabolized by phase I metabolizing enzymes CYP1A1, CYP1A2, and CYP1B1. DBP-induced DNA adducts can be inhibited by several mechanisms. We found that all the test agents inhibited DNA adducts by inhibiting one or more of these enzymes. Oltipraz inhibited DNA adducts entirely by inhibiting the CYP450s, while resveratrol and delphinidin inhibited DNA adducts by also interacting directly with the carcinogenic metabolite, anti-dibenzo(a,l)pyrene-11,12-dihydrodiol-13,14-epoxide.

Conformations of adducts formed between the genotoxic benzo[a]pyrene-7,8-dione and 2'-deoxycytidine.

Benzo[a]pyrene-7,8-dione (BPQ) is formed by the activation of benzo[a]pyrene(B[a]P), which is an environmental toxic substance that is easily exposed in daily life, due to P450/epoxide hydrolase, and is a substance that induces DNA deformation by forming adducts with DNA. In this study, to investigate the form of bonding between BPQ and DNA, the structures of adducts between BPQ and 2'-deoxycytidine were examined. To examine BPQ-dC adduct conformation, geometry optimization of a total of 16 structural isomers was performed using the density functional theory method. In the structures of BPQ-dC adducts, for the cis-form, the angle between BPQ and dC is nearly perpendicular; but for the trans-form, the bending angle is small. The trans-form had a larger energy gap between ground state and excited state than the cis-form, and had a smaller HOMO-LUMO gap than the cis-form. Therefore, it was found that the trans-form absorbs stronger light and has higher reactivity than the cis-form. Molecular electrostatic potential was calculated and analyzed. The calculated ESP contour map shows the electrophilic and nucleophilic regions of the molecule.

Phylum-specific regulation of resistomycin production in a Streptomyces sp. via microbial coculture.

Actinomycete genomes are encoded with immense potential to produce secondary metabolites, however standard laboratory culture experiments rarely provide the conditions under which associated biosynthetic pathways are expressed. Despite years of research attempting to access these pathways and aside from a few well-studied bacterial quorum sensing systems, little is known about the specificity of secondary metabolite regulation in bacteria, such as the conditions under which a bacterium produces an antibiotic and the extent to which it does so in recognition of a particular species in the immediate environment. In the current study, we observed that the cocultivation of a Streptomyces sp. (strain B033) with four pathogenic strains of the phylum Proteobacteria resulted in the production of the antibiotic resistomycin. After further coculture experiments, we determined that Proteobacteria induced the production of resistomycin in B033 at significantly higher rates (65%) than strains from the phyla Firmicutes (5.9%) and Actinobacteria (9.1%), supporting that the regulation of secondary metabolism in bacteria can be dependent on the species present in the immediate environment. These results suggest a lack of promiscuity of antibiotic biosynthetic pathway regulation and indicate that it is feasible to mine existing microbial strain libraries for antibiotics in a phylum-specific manner.