Instability of (±)-7β, 8α-dihydroxy-9β, 10β-epoxy-7, 8, 9, 10-tetrahydrobenzo[a]pyrene (syn-BaPDE)- DNA adducts formed in benzo[a]pyrene-treated Wistar rat embryo cell cultures

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Abstract
One of the peaks present in HPLC profiles of [ 3 H]benzo[a]-pyrene (BaP)-deoxyribonucleosides prepared by enzymatic degradation of [ 3 H)BaP-DNA isolated from Wistar rat embryo cell cultures exposed to [G- 3 H)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-nucleoside linkages in intact BaP-modified DNA, DNA was isolated from Wistar rat embryo cells that had been exposed to [G- 3 H]BaP- and incubated in darkness at 37°C at a range of pH values from 5 to 11 for 72 h or for 1– 150 h at pH 7. The rate of breakdown of ( 3 H)BaP-DNA adducts (0.25%/h) was linear over 150 h. The amounts of the two major BaP-DNA adduct decomposition products, I and II (present in a ratio of 1: 3), increased with length of 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 boronate chromatography and reverse-phase HPLC demonstrated that both I and II contained cis -vicinal hydroxyl groups and decomposition product II cochromatographed with r-7, c-9, c-10, t-8-tetra hydroxy-7, 8, 9, 10-tetrahydroBaP, a (±)- 7β, 8α-dihydroxy-9β, 10β-epoxy-7, 8, 9, 10-tetrahydroBaP( syn -BaPDE)-derived tetraol. At neutral pH [ 3 H](±)- syn -BaPDE-modified calf thymus DNA formed a decomposition product identical to II. Analysis of the BaP-DNA adducts that remained covalently bound to the DNA after the above incubations demonstrated that the amounts of both major syn -BaPDE-deoxyguanosine adducts decreased with length of time of incubation. Thus, syn -BaPDE-deoxyribonucleoside adducts formed in the DNA of [ 3 H)BaP-treated Wistar rat embryo cells are unstable and breakdown spontaneously in the absence of light to yield syn -BaPDE-tetraol decomposition products.