Nuclear metabolism of polycyclic hydrocarbons and interaction of polycyclic hydrocarbons with nuclear components

Abstract

Nuclear aryl hydrocarbon hydroxylase (AHH) activity which was demonstrated by a specific histofluorescent technique, is present at 15–20% of the corresponding microsomal activity. Cytochrome P 450 is also present within the nucleus and both the AHH and hemopigments are inducible by prior treatment of the rats with 3-methylcholanthrene (3MC). Other inducing agents of the nuclear AHH included pregnenolone 16α-carbonitrile, phenobarbital, arochlor 1254, β-naphthoflavone and benzo(a) pyrene (BP). The control nuclear and microsomal AHH were similarly inhibited by 1-benzylimidazole, diethylmaleate, SKF 525A, and metyrapone; α-naphthoflavone inhibited the induced nuclear and microsomal enzymes to a similar degree. Rat liver nuclei were incubated with 14C-BP or 3H-(±) trans-7–8,dihydrodiol of BP ( 3H-BP-7,8-diol) in the presence of a NADPH-generating system. The total nuclear metabolism was stimulated by 11-fold by prior administration of 3MC to the rats. The nucleic were able to oxidize BP to the 9,10-, 4,5- and 7,8-dihydrodiols, the 3,6- and 1,6-quinones as well as the 3- and 9-phenols. BP-7,8-dihydrodiol formation, under these circumstances, was enhanced by 29-fold. The rat liver nuclei were also able to produce (±)-7 β,8 α-dihydroxy-9 β,10 β-epoxy-7,8,9,10-tetrahydro BP (diol epoxide 1), (±)-7 β,8 α-dihydroxy-9 α,10 α-epoxy-7,8,9,10-tetrahydro BP (diol epoxide 2) from 3H-BP-7,8-diol. Pretreatment of the rats with 3MC resulted in an increase in this nuclear metabolic activity by 4-fold. Aralkylation of DNA, histones and nonhistone components was demonstrated after incubation of 3H-BP with liver nuclei and a NADPH-generating system in these in vitro systems. The aralkylation of each of these macromolecules was stimulated by prior treatment of the rats with 3MC. The HIV histones were aralkylated to the least extent. The alkylated deoxyribonucleosides produced after enzymatic digestion of the incubated DNA were separated by Sephadex LH-20 chromatography. Two peaks of radioactivity were noted after incubation with the parent polycyclic hydrocarbon while only 1 peak was seen after incubation with the diol derivative. These results emphasize the importance of nuclei in the metabolism of BP and in the subsequent alkylation of DNA; these reactions may be related to mutagenesis or carcinogenesis.