Preferential induction of cytochrome P450 1A1 over cytochrome P450 1B1 in human breast epithelial cells following exposure to quercetin

Abstract

Estrogen metabolism is suggested to play an important role in estrogen-induced breast carcinogenesis. Epidemiologic studies suggest that diets rich in phytoestrogens are associated with a reduced risk of breast cancer. Phytoestrogens are biologically-active plant compounds that structurally mimic 17β-estradiol (E 2 ). We hypothesize that phytoestrogens, may provide protection against breast carcinogenesis by altering the expression of estrogen-metabolizing enzymes cytochrome P450 1A1 (Cyp1A1) and 1B1 (Cyp1B1). Cyp1A1 and Cyp1B1 are responsible for the metabolism of E 2 to generate 2-hydroxyestradiol (2-OHE 2 ) and 4-hydroxyestradiol (4-OHE 2 ), respectively. Studies suggest that 2-OHE 2 and 2-methoxyestradiol may protect against breast carcinogenesis, while 4-OHE 2 is carcinogenic in rodent models. Thus, agents that increase the metabolism of E 2 by Cyp1A1 to produce 2-OHE 2 may have chemoprotective properties. The human immortalized non-neoplastic breast cell line MCF10F was treated with quercetin at 10 and 50 µM concentrations for time-points ranging from 3 to 48 hours. Total RNA and protein were isolated. Real-time PCR was used to measure the expression of Cyp1A1 and Cyp1B1 mRNA. Quercetin treatment produced differential regulation of Cyp1A1 and Cyp1B1 mRNA expression in a time-and dose-dependent manner. Treatment with 10 and 50 µM doses of quercetin produced 6-and 11-times greater inductions of Cyp1A1 mRNA over Cyp1B1 mRNA, respectively. Furthermore, quercetin dramatically increased Cyp1A1 protein levels and only slightly increased Cyp1B1 protein levels in MCF10F cells. Thus, our data suggest that phytoestrogens may provide protection against breast cancer by modulating expression of estrogen-metabolizing genes such that production of the highly carcinogenic estrogen metabolite 4-OHE 2 by Cyp1B1 is reduced and the production of the less genotoxic 2-OHE 2 by Cyp1A1 is increased.

CYP1A1 is overexpressed upon incubation of breast cancer cells with a polyphenolic cocoa extract

“…Additionally, CYP1A1 overexpression might interfere with estrogen metabolism and the production of estrogen metabolites in breast cells. The increase in CYP1A1 activity may shift estrogen metabolism toward the production of 2-OHE2, a relatively non-genotoxic metabolite [60]. Moreover, the increase in estrogen metabolism could lead to the reduction in the levels of estrogens in mammary tumors, thus contributing to the cytotoxic effect of tamoxifen.…”

Differential regulation of estrogen receptors α and β by 4-(E)-{(4-hydroxyphenylimino)-methylbenzene,1,2-diol}, a novel resveratrol analog

“…The expression levels of ERα or β relative to cyclophilin were determined by dividing the number of cDNA molecules for the gene of interest by the number of cyclophilin cDNA molecules. Standards were created for each gene and a standard curve was run on each plate to allow for accurate quantification of cDNA, as reported previously [13, 41, 43]. …”

“…Forty microgram total protein, isolated from quadruplicates of control or treated cells, was size fractionated on a 12% SDS-polyacrylamide gel, and transferred onto PVDF membranes under standard conditions [5, 13, 43–45]. Membranes were blocked in 5% dry non-fat milk/PBS/0.05% Tween-20 at four degrees in a refrigerator overnight.…”

Phytoestrogens as natural prodrugs in cancer prevention: dietary flavonoids

“…However, recent literature seems to indicate the opposite: diosmetin, apigenin, galangin, and quercetin are linked with a diminished risk of cancer. These flavonoids inhibit proliferation of tumour cells, but exert little effect on non-tumour cells in vitro Kaur et al 2008;Bestwick and Milne 2006;Gupta et al 2002;Mense et al 2008b). …”