Instability of ({+/-})-7{beta}, 8{alpha}-dihydroxy-9{beta}, 10{beta}-epoxy-7, 8, 9, 10-tetrahydrobenzo[a]pyrene (syn-BaPDE)- DNA adducts formed in benzo[a]pyrene-treated Wistar rat embryo cell cultures

One of the peaks present in HPLC profiles of [³H]benzo[a]-pyrene(BaP)-deoxyribonucleosides prepared by enzymatic degradationof [³H)BaP-DNA isolated from Wistar rat embryo cell culturesexposed to [G-³H)BaP was found to be r-7, c-9, c-10 t-8-tetrahydroxy-7,8, 9, 10-tetrahydroBaP, a BaP-DNA adduct decomposition product(Pruess-Schwartz, D. and Baird, W.M., Cancer Res., 46, 545–552,1986). To investigate the stability of the hydrocarbon-deoxyribo-nucleosidelinkages in intact BaP-modified DNA, DNA was isolated from Wistarrat embryo cells that had been exposed to [G-³H]BaP- and incubatedin darkness at 37°C at a range of pH values from 5 to 11for 72 h or for 1– 150 h at pH 7. The rate of breakdownof (³H)BaP-DNA adducts (0.25%/h) was linear over 150 h. Theamounts of the two major BaP-DNA adduct decomposition products,I and II (present in a ratio of 1: 3), increased with lengthof time of incubation. Formation of I was not affected by pH.whereas, formation of II was highest at acidic and neutral pH.Analysis of the decomposition products by immobilized boronatechromatography and reverse-phase HPLC demonstrated that bothI and II contained cis-vicinal hydroxyl groups and decompositionproduct II cochromatographed with r-7, c-9, c-10, t-8-tetrahydroxy-7, 8, 9, 10-tetrahydroBaP, a (±)- 7ß,8-dihydroxy-9ß, 10ß-epoxy-7, 8, 9, 10-tetrahydroBaP(syn-BaPDE)-derivedtetraol. At neutral pH [³H](±)-syn-BaPDE-modified calfthymus DNA formed a decomposition product identical to II. Analysisof the BaP-DNA adducts that remained covalently bound to theDNA after the above incubations demonstrated that the amountsof both major syn-BaPDE-deoxyguanosine adducts decreased withlength of time of incubation. Thus, syn-BaPDE-deoxyribonucleosideadducts formed in the DNA of [³H)BaP-treated Wistar rat embryocells are unstable and breakdown spontaneously in the absenceof light to yield syn-BaPDE-tetraol decomposition products.