CHARACTERIZATION OF HIGHLY POLAR BIS-DIHYDRODIOL EPOXIDE - DNA ADDUCTS FORMED AFTER METABOLIC-ACTIVATION OF DIBENZ[A,H]ANTHRACENE

Dibenz[a,h]anthracene as well as a biologically important metabolite of dibenz[a,h]anthracene, namely the M-region dihydrodiol trans-3,4-dihydroxy-3,4-dihydrodibenz[a,h]anthracene were in addition to further metabolism to a bay region diol epoxide, extensively transformed to a distal bisdihydrodiol, 3,4,10,11-tetrahydroxy-3,4,10,11-tetrahydro-dibenz[a,h]anthracene, which exhibited after renewed metabolic activation high DNA binding efficiency, leading to a new class of very polar DNA adducts. After incubation of dibenz[a,h]anthracene with DNA in the presence of liver microsomes from Aroclor 1254 treated male Sprague-Dawley rats highly polar DNA adducts probably originating from 3R,4R,10R,11R-tetrahydroxy-3,4,10,11-tetrahydrodibenz[a,h]anthracene and 3R,4R,10S,11S-tetrahydroxy-3,4,10,11-tetrahydrodibenz[a,h]anthracene were identified by reversed phase HPLC and by the P-32-postlabelling method. The adducts obtained were further characterized by comparing their fluorescence spectra with those obtained from 3,4,10,11-tetrahydroxy-3,4,10,11-tetrahydrodibenz[a,h]anthracene and from 3,4-dihydroxy-3,4-dihydrobenz[a]anthracene, the putative chromophore of the polar adduct. DNA adducts formed via 3S,4S,10S,11S-tetrahydroxy-3,4,10,11-tetrahydrobenz[a,h]anthracene were not found. After incubation of C-14-labelled dibenz[a,h]anthracene highly polar DNA adducts derived from the bisdihydrodiol contributed 38% to the adducts found in the HPLC profile. Bay region diol epoxide adducts represented a fraction of 25%. Using the P-32-postlabelling technique a higher DNA binding yield for the racemic bisdihydrodiol (38 +/- 12 pmol/mg DNA) was calculated than for the most active 3,4-dihydrodiol enantiomer, 3R,4R-dihydroxy-3,4-dihydrodibenz[a,h]anthracene (23 +/- 6 pmol/mg DNA).