Ah receptor binding properties of indole carbinols and induction of hepatic estradiol hydroxylation.
The effect of route of administration on the ability of indole-3-carbinol (13C), an anticarcinogen present in cruciferous vegetables, to induce estradiol 2-hydroxylase (EH) in female rat liver microsomes was investigated and compared to that of its main gastric conversion product, 3,3'-diindolylmethane (DIM). This dimer was more potent than 13C after either oral or intraperitoneal administration and was also a better in vitro inhibitor of EH in control and 13C-induced hepatic microsomes. The induction of both CYP1A1 and 1A2 in about equal amounts by 13C and DIM as well as of CYP2B1/2 was demonstrated using monoclonal antibodies. DIM, isosafrole, beta-naphthoflavone, 3-methylcholanthrene and naringenin added in vitro inhibited EH strongly in induced microsomes but gestodene was a better inhibitor of estrogen 2-hydroxylation in liver microsomes from untreated female rats. The binding affinities of 13C and DIM to the Ah receptor were compared to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by competition studies, and the IC50 values were shown to be 2.0 x 10(-9) M, 5.0 x 10(-5) M and 2.3 x 10(-3) M for TCDD, DIM and 13C, respectively. The ability of 13C or DIM to cause in vitro transformation of the Ah receptor to a form able to bind to the dioxin-responsive element-3 (DRE3) was compared to that of TCDD and shown to parallel their abilities to compete for binding of [3H]TCDD to the Ah receptor. These experiments confirm and extend the proposals that dietary indoles induce specific cytochrome P450s in rat liver by a mechanism possibly involving the Ah receptor. The induced monooxygenases, in turn, increase the synthesis of 2-hydroxylated estrogens in the competing pathways of 2- and 16 alpha-hydroxylation which decreases the levels of 16 alpha-hydroxyestrone able to form stable covalent adducts with proteins including the estrogen receptor. Such steroid-protein interaction has been correlated with mammary carcinogenesis.
Jellinck
P H
PH
Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
Forkert
P G
PG
Riddick
D S
DS
Okey
A B
AB
Michnovicz
J J
JJ
Bradlow
H L
HL
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D000072467:Cytochrome P450 Family 2; D004247:DNA / Q000378:metabolism; D004790:Enzyme Induction; D004958:Estradiol / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D007211:Indoles / Q000378:metabolism* / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D008969:Molecular Sequence Data; D000072317:Polychlorinated Dibenzodioxins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug / Q000378:metabolism*; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000096:biosynthesis*
D000975:Antioxidants; D007211:Indoles; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug; D004958:Estradiol; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; C016517:indole-3-carbinol; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D019363:Cytochrome P-450 CYP1A1; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C020120:estrogen 2-hydroxylase; C016392:3,3'-diindolylmethane