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IDENTIFICATION AND CHARACTERIZATION OF NOVEL STABLE DEOXYGUANNOSINE AND DEOXYADENOSINE ADDUCTS OF BENZO[A]PYRENE-7,8-QUINONE FROM REACTIONS AT PHYSIOLOGICAL PH
Citation:
Balu, N, W. T. Padgett, G. R. Lambert, A E. Swank, A M. Richard, AND S. C. Nesnow. IDENTIFICATION AND CHARACTERIZATION OF NOVEL STABLE DEOXYGUANNOSINE AND DEOXYADENOSINE ADDUCTS OF BENZO[A]PYRENE-7,8-QUINONE FROM REACTIONS AT PHYSIOLOGICAL PH. CHEMICAL RESEARCH IN TOXICOLOGY 17(6):827-838, (2004).
Impact/Purpose:
To evaluate BPQ-mediated genotoxicity and carcinogenesis
Description:
Benzo[a]pyrene (B[a]P) is an archetypal member of the family of polycyclic aromatic hydrocarbons (PAHs) and is a widely-distributed environmental pollutant. B[a]P is known to induce cancer in animals and B[a]P-containing complex mixtures are human carcinogens. B[a]P exerts its genotoxic and carcinogenic effects through metabolic activation forming reactive intermediates that damage DNA. DNA adduction by B[a]P is a complex phenomenon that involves the formation of both stable and unstable (depurinating) adducts. One pathway by which B[a]P can mediate genotoxicity is through the enzymatic formation of B[a]P-7,8-quinone (BPQ) from B[a]P-7,8-diol by members of the aldo-keto reductase family. Once formed, BPQ can act as a reactive Michael acceptor which can alkylate cellular nucleophiles including DNA and peptides. Earlier studies have reported on the formation of stable and depurinating adducts from the reaction of BPQ with DNA and nucleosides, respectively. However, the syntheses and characterization of the stable adducts from these interactions have not been addressed. In this study the reactivity of BPQ towards deoxyguanosine (dGuo) and deoxyadenosine (dAdo) nucleosides under physiological pH conditions is examined. The identification and characterization of six novel BPQ-nucleoside adducts obtained from the reaction of BPQ and dGuo or dAdo nucleosides in a solvent mixture of sodium phosphate and dimethylformamide is reported. The reaction of BPQ with dGuo afforded four unique diastereomeric Michael addition products: two diastereomers of N2-[9-(9,10-dihydro-10-hydroxybenzo[a]pyrene-7,8-quinonyl)]2'-deoxyguanosine (BPQ-9-dGuo-10-OH) and two diastereomers of N2-[10-(9,10-dihydro-9hydroxybenzo[a]pyrene-7,8-quinonyl)]-2'-deoxyguanosine (BPQ-10-dGuo-9-OH). BPQ-9-dGuo-l0-OH and BPQ-9-OH-10-dGuo represent the covalent modifications at C9 and C10 positions of BPQ by the adducting nucleoside. Most interestingly, addition of water to the C9-C10 double bond either at C9- or C10-positions is evident in all the four products obtained from the BPQ-dGuo reaction. Under similar but extended reaction conditions the reaction of BPQ with dAdo produce d only one diastereomeric pair of adducts identified as N6-[ 10-(9,10-dihydro9-hydroxybenzo[a]pyrene-7,8-quinonyl)]-2'-deoxyadenosine (BPQ-9-OH-10-dAdo). All six adducts were isolated by reverse-phase HPLC and characterized by UV, ESI-MS, 'H, 13C, COSY and NOE NMR studies. Computational methods were employed in an attempt to assign the relative stereochemistry of the new adducts by estimating the dihedral angles about the substituted C9 and C10 carbons of all possible cis and trans diastereomers of each adduct. The similarities in the calculated dihedral angles precluded the assigning of relative stereochemistry for the new BPQ-nucleoside adducts. As considerable efforts have been placed in documenting the genotoxic effects of BPQ, this first report of the identification and characterization of these stable adducts of BPQ formed under physiological pH conditions is expected to contribute significantly to the area of BPQ-mediated genotoxicity and carcinogenesis.