Deoxyribonucleic acid binding of 3-hydroxy- and 9-hydroxybenzo[a]pyrene following further metabolism by mouse liver microsomal cytochrome P 1-450

Abstract

In the presence of NADPH and microsomes from 3-methylcholanthrene-treated C57BL/6N mice, [ 3H]3-OH-benzo[a]pyrene is metabolized to reactive intermediates which covalently bind to deproteinized salmon sperm DNA in vitro. Enzymatically digested DNA, containing bound [ 3H]3-OH-benzolajpyrene derivatives, generates an elution profile from Sephadex LH20 chromatography which resembles similar chromatograms with [ 3H]benzo[a]pyrene. All peaks resulting from [ 3H]benzo[a]pyrene activation appear to be prominently represented in [ 3H]3-OH-benzo[a]pyrene activation, except that several peaks which emerge near the end of the eluting gradient of methanol and water are much reduced. Notably, a peak designated E, and attributed to benzo[a]pyrene-7, 8-diol-9, 10-oxide binding in [ 3H]benzo[a]pyrene incubations, is also prominently represented in incubations with [ 3H]3-OH-benzo[a]pyrene. Radioactivity in all of these peaks is inhibited effectively if one-seventh the concentration of 1-OH-benzo[a]pyrene is included in the incubation with [ 3H]3-OH-benzo[a]pyrene. Microsomes from 3-methylcholanthrene-treated DBA/ 2N mice cause insignificant binding. UDP-glucuronic acid markedly reduces all peaks except E, and 1, 2-epoxy-3, 3, 3-trichloropropane reduces all peaks except C and E. 9-Hydroxybenzo[a]pyrene is further metabolized to DNA binding species by microsomes from either 3-methylcholanthrene-treated DBA/2N or C57BL/6N mice. UDP-glucuronic acid prevents about 50 per cent of the binding with microsomes from DBA/2N mice but not with microsomes from C57BL/6N. In contrast, UDP-glucuronic acid does prevent binding in some of these same peaks when [ 3H]benzotaipyrene is the starting substrate with microsomes from C57BL/6N mice. UDP-glucuronic acid does not prevent binding in peak E in incubations with [ 3H]benzo[a]pyrene or [ 3H]3-hydroxybenzo[a]pyrene.