Structure of an Unusual Tetracyclic Deoxyguanosine Adduct: Implications for Frameshift Mutagenicity of ortho-Cyano Nitroanilines

Effect of Guanine Adduct Size, Shape, and Linker Type on the Conformation of Adducted DNA: A DFT and Molecular Dynamics Study

DNA is damaged through various exogenous sources (e.g., automobile exhaust, tobacco smoke, and processed foods), which can yield diverse C8-dG bulky aryl adducts. Adducts are known to induce structural changes to DNA that can lead to various biological outcomes, ranging from cell death to diseases such as cancer. Unfortunately, the relationship between the chemical composition of the damaged product, the adducted DNA structure, and the biological consequences is not well understood, which limits the development of disease detection and prevention strategies. The present study uses density functional theory (DFT) calculations and quintuplicate 1 μs molecular dynamics (MD) simulations to characterize the structure of DNA containing 21 model C8-dG adducts that systematically differ in size (phenyl to pyrenyl), shape (α (2,3), β (3,4) fusion, or ring substitution), and nucleobase-aryl group linkage (N, O, and C-linked). DFT calculations reveal that the inherent structural features of the G nucleobase adducts are impacted by linker type and bulky moiety shape, but not size, with the conformational flexibility reducing with α-ring fusion and linker composition as N > O > C. These structural properties are maintained in nucleoside models, which also reveal an increased propensity for anti-to-syn rotation about the glycosidic bond with N < O < C linker type. Although these diverse chemical features do not influence the global structure of adducted DNA, the adducts differentially impact the conformation local to the adducted site, including the relative populations of structures with the bulky moiety in the major groove (B conformer) and intercalated (stacked) into the helix (S conformer). Specifically, while the smallest phenyl adducts favor the B conformation and the largest pyrenyl-derived adducts stabilize the S conformation, the B/S ratio decreases with an increase in ring size and N > O > C linker composition. The shape and size (length) of the adduct can further finetune the B/S ratio, with β-fused naphthyl or α-fused phenanthryl N-linked adducts and O or C-linked adducts containing ring substitution increasing the prevalence of the S adducted DNA conformation. Overall, this work uncovers the significant effect of bulky moiety size and linker type, as well as the lesser impact of aryl group shape, on adducted DNA structure, which suggests differential replication and repair outcomes, and thereby represents an important step toward rationalizing connections between the structure and biological consequences of diverse DNA adducts.

Reductive metabolism of azo dyes and drugs: Toxicological implications

Azo compounds are widely distributed synthetic chemicals in the modern world. Their most important applications are as dyes, but, in addition, several azo compounds are used as pharmaceuticals. Ingested azo compounds can be reduced by the action of bacteria in the gut, where the oxygen tension is low, and the development of microbiome science has allowed more precise delineation of the roles of specific bacteria in these processes. Reduction of the azo bond of an azo compound generates two distinct classes of aromatic amine metabolites: the starting material that was used in the synthesis of the azo compound and a product which is formed de novo by metabolism. Reductive metabolism of azo compounds can have toxic consequences, because many aromatic amines are toxic/genotoxic. In this review, we discuss aspects of the development and application of azo compounds in industry and medicine. Current understanding of the toxicology of azo compounds and their metabolites is illustrated with four specific examples - Disperse Dyes used for dyeing textiles; the drugs phenazopyridine and eltrombopag; and the ubiquitous food dye, tartrazine - and knowledge gaps are identified. SUBMISSION TO: FCT VSI: Toxicology of Dyes.

Effects of a Second Local DNA Damage Event on the Toxicity of the Human Carcinogen 4-Aminobiphenyl: A Molecular Dynamics Study of a Damaged DNA Structure

Exposure of humans to carcinogenic aromatic amines (AAs) occurs daily. AAs are bioactivated in cells into products that attack DNA, primarily leading to N-linked C8-dG adducts. Previous work on DNA containing a single AA-derived adduct (monoadducted DNA) has shown a structure-function relationship between the damaged DNA conformation and cellular outcomes. However, relatively little is known about the conformation and biological outcomes of DNA containing two bulky adducts (diadducted DNA) in close proximity. To fill this current void in the literature, the present work uses quintuplet 0.5 μs MD simulations to understand the structural impact of DNA exposure to the potent bladder carcinogen 4-aminobiphenyl (ABP), which is found in cigarette smoke and select dyes, and results in the widely studied N-linked ^ABPdG adduct. Specifically, 18 unique DNA duplexes were investigated that contain one or two ^ABPdG adducts in the anti and/or syn glycosidic orientation(s) in all combinations of three G positions in the NarI mutation hotspot for AAs (5'-G₁G₂CG₃CC). Monoadducted DNA displays sequence-dependent conformational heterogeneity, with the G₁ site having the greatest anti preference, and highlights the range of helical structures associated with the syn lesion orientation [i.e., stacked (S), intercalated (I), and wedge (W) conformations]. Diadducted DNA results in interesting lesion separation effects on the conformational heterogeneity, including a greater anti preference for neighboring adducts (G₁G₂) and a greater syn preference for next-nearest neighbor damaged sites (G₂G₃) compared to monoadducted DNA. As a result, an increase in the number of ^ABPdG adducts changes the conformational heterogeneity of ABP-exposed DNA depending on the relative positions of the lesions and thereby could result in increased or decreased toxicity upon human exposure to elevated levels of ABP.

Impact of DNA Adduct Size, Number, and Relative Position on the Toxicity of Aromatic Amines: A Molecular Dynamics Case Study of ANdG- and APdG-Containing DNA Duplexes

Human exposure to aromatic amines (AAs) can result in carcinogenic DNA adducts. To complement previous work geared toward understanding the mutagenicity of AA-derived adducts, which has almost exclusively studied (monoadducted) DNA containing a single lesion, the present work provides the first in-depth comparison of the structure of monoadducted and diadducted DNA duplexes. Specifically, molecular dynamics (MD) simulations were initially performed on DNA containing the nonmutagenic single-ringed N-(deoxyguanosin-8-yl)-aniline (^ANdG) or the mutagenic four-ringed N-(deoxyguanosin-8-yl)-1-aminopyrene (^APdG) lesion at G₁, G₂, or G₃ in the AA deletion hotspot (5'-G₁G₂CG₃CC) in the anti or syn glycosidic orientation (B/S duplex conformation). Subsequently, diadducted strands were assessed that span each combination of damaged sites (G₁G₂ (nearest neighbors), G₂G₃ (next-nearest neighbors), and G₁G₃ (two intervening nucleotides)) and anti/syn lesion glycosidic orientations. Despite other N-linked C8-dG adducts exhibiting sequence dependence conformational heterogeneity, a single ^ANdG or ^APdG lesion induces helical conformational homogeneity that is exclusively controlled by aryl moiety size. However, the preferred damaged DNA conformation can change upon the addition of a second adduct depending on lesion separation, with neighboring lesions stabilizing a nonmutagenic conformation and next-nearest damaged sites stabilizing a promutagenic conformation regardless of adduct size. As a result, diadducted DNA is found to adopt conformations that are unfavored for the corresponding monoadducted system, pointing to differential replication and repair outcomes for diadducted DNA compared to those for monoadducted DNA. Thus, although the toxicity of monoadducted DNA is most significantly dictated by lesion size, the toxicity can increase or decrease upon a second damaging event depending on lesion size and relative position. Overall, our work adds the number of lesions and their spatial separation to the growing list of factors that determine the structure and biological outcomes of adducted DNA.