title: Detection and identification of benzo[a]pyrene-DNA adducts by [35S]phosphorothioate labeling and HPLC.
abstract: Two generally applicable [35S]phosphorothioate postlabeling procedures for the HPLC analysis of polycyclic aromatic hydrocarbon (PAH)-DNA adducts have been developed based upon [32P]phosphate postlabeling assays described by Gupta and Randerath et al. In one procedure, benzo[a]pyrene (B[a]P)-modified DNA was digested to nucleoside 3'-phosphates by micrococcal nuclease and spleen phosphodiesterase and the adducted nucleotides were extracted with 1-butanol. The adducted nucleoside-3'-phosphates were 5'-thiophosphorylated by T4 polynucleotide kinase (T4PNK) and adenosine 5'-O-(3-[35S]thiotriphosphate) to yield [35S]B[a]P-nucleoside-5'-phosphorothioate-3'-phosphate adducts. Although thiophosphorylation of B[a]P-DNA adducts was slower than the corresponding phosphorylation reaction, similar recoveries of the postlabeled adducts were achieved with longer incubation times and higher concentrations of T4PNK. A major advantage of this procedure over the 32P-postlabeling procedure is that the resistance of phosphorothioates to degradation by phosphatases allows selective removal of the unlabeled 3'-phosphate from the [35S]B[a]P-nucleoside-5'-phosphorothioate-3'-phosphate adducts by brief treatment with alkaline phosphatase. [35S]B[a]P-nucleoside-5'-phosphorothioate adducts were also prepared using a nuclease P1/prostatic acid phosphatase DNA degradation method. For anti-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-modified DNA, overall adduct recoveries were substantially higher with the nuclease P1/prostatic acid phosphatase method (48-51%) than with the micrococcal nuclease/spleen phosphodiesterase/alkaline phosphatase method (22-29%). There were no significant differences in the HPLC profiles of the [35S]phosphorothioate-postlabeled adducts obtained from these two procedures. HPLC analysis of B[a]P-DNA adducts formed in B[a]P-treated hamster embryo cell cultures demonstrated the formation of two major adducts, (+)syn-BPDE-deoxyguanosine-5'-phosphorothioate and (+)anti-BPDE-deoxyguanosine-5'-phosphorothioate, along with other minor adducts. Based upon an overall adduct recovery of 20% and 0.5 mol as the detection limit of this 35S-postlabeling/HPLC assay, the sensitivity of this assay is 1 adduct/10(8) nucleotides for a 60 micrograms DNA sample. This method offers the advantages of using 35S which has a longer half-life and lower radioactive decay energy than 32P and the ability to prepare PAH-DNA adducts at the monophosphorothioate level which greatly facilitates separation of individual 35S-postlabeled PAH-DNA adducts by HPLC.
authors.affiliation: Department of Medicinal Chemistry and Pharmacognosy, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, IN 47907.
authors.forename: H H
authors.initials: HH
authors.lastname: Lau
authors.forename: W M
authors.initials: WM
authors.lastname: Baird
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000737:chemistry; D000818:Animals; D001564:Benzo(a)pyrene / Q000737:chemistry*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D004247:DNA / Q000737:chemistry*; D018736:DNA Adducts; D013462:Sulfur Radioisotopes; D013873:Thionucleotides / Q000737:chemistry*
chemical_list: D018736:DNA Adducts; D013462:Sulfur Radioisotopes; D013873:Thionucleotides; C056612:benzo(a)pyrene-DNA adduct; D001564:Benzo(a)pyrene; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D004247:DNA