Dr. Ron’s Research Review – October 2, 2013

© 2013

This week’s research review focuses on the 2-16 Ratio.

A systematic review of nine studies do not support the hypothesis that estrogen metabolite ratio can be used as a predictive marker for breast cancer risk. For the highest compared with the lowest quantile of urinary EMR, non-significant associations suggested at best a weak protective effect in premenopausal but not in postmenopausal breast cancer (range of odds ratios: 0.50–0.75 for premenopausal and 0.71–1.31 for postmenopausal). The paper includes a discussion of the issues involved, and recommends further research. (Obi, Vrieling et al. 2011)

In the Women's Health Initiative Hormone Trials, breast cancer risk was increased with estrogen plus progestin (E+P) but not with unopposed estrogen (E-alone). In a study nested in the WHI-HT, 845 confirmed breast cancer cases were matched to 1,690 controls by age and ethnicity. The 1-year increase in 16alpha-OHE1 was greater with E+P than E-alone (median 55.5 pg/mL vs. 43.5 pg/mL, P < 0.001), but both increased 2-OHE1 by approximately 300 pg/mL. Breast cancer risk was modestly associated with higher baseline levels of 2-OHE1 and the 2:16 ratio, and for estrogen receptor+/progesterone+ cases only, higher baseline 16alpha-OHE1 levels. For those randomized to active treatment, breast cancer risk was associated with greater increase in 2-OHE-1 and the 2:16 ratio, but associations were not significant. (Mackey, Fanelli et al. 2012)

Quercetin preferentially induces cytochrome P450 1A1 over cytochrome P450 1B1 in human breast epithelial cells. 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. (Mense, Chhabra et al. 2008)

Dr. Ron


Articles

Hormone therapy, estrogen metabolism, and risk of breast cancer in the Women's Health Initiative Hormone Therapy Trial

         (Mackey, Fanelli et al. 2012) Download

BACKGROUND: In the Women's Health Initiative Hormone Trials (WHI-HT), breast cancer risk was increased with estrogen plus progestin (E+P) but not with unopposed estrogen (E-alone). We hypothesized that E+P would preferentially metabolize to 16alpha-hydroxyestrone (16alpha-OHE1) rather than 2-hydroxyestrone (2-OHE1), and that breast cancer risk would be associated with baseline and 1 year changes in estrogen metabolites: positively for 16alpha-OHE1 levels and negatively for levels of 2-OHE-1 and the 2:16 ratio. METHODS: In a prospective case-control study nested in the WHI-HT, 845 confirmed breast cancer cases were matched to 1,690 controls by age and ethnicity. Using stored serum, 2-OHE1 and 16alpha-OHE1 levels were measured by enzyme immunoassay at baseline, and for those randomized to active treatment (n = 1,259), at 1 year. RESULTS: The 1-year increase in 16alpha-OHE1 was greater with E+P than E-alone (median 55.5 pg/mL vs. 43.5 pg/mL, P < 0.001), but both increased 2-OHE1 by approximately 300 pg/mL. Breast cancer risk was modestly associated with higher baseline levels of 2-OHE1 and the 2:16 ratio, and for estrogen receptor+/progesterone+ cases only, higher baseline 16alpha-OHE1 levels. For those randomized to active treatment, breast cancer risk was associated with greater increase in 2-OHE-1 and the 2:16 ratio, but associations were not significant. CONCLUSIONS: Although E+P modestly increased 16alpha-OHE1 more than E-alone, increase in 16alpha-OHE1 was not associated with breast cancer. IMPACT: Study results do not explain differences between the WHI E+P and WHI E-alone breast cancer results but metabolism of oral HT, which may explain smaller than expected increase in breast cancer compared with endogenous estrogens.


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

         (Mense, Chhabra et al. 2008) Download

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 17beta-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 50muM concentrations for time points ranging from 3 to 48h. 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 microM 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.


Urinary estrogen metabolites during a randomized soy trial

         (Morimoto, Conroy et al. 2012) Download

One of the hypothesized protective mechanisms of soy against breast cancer involves changes in estrogen metabolism to 2-hydroxy (OH) and 16alpha-OH estrogens. The current analysis examined the effect of soy foods on the 2:16alpha-OH E(1) ratio among premenopausal women during a randomized, crossover intervention study; women were stratified by equol producer status, a characteristic thought to enhance the protective effects of soy isoflavones. The study consisted of a high-soy diet with 2 soy food servings/day and a low-soy diet with <3 servings of soy/wk for 6 mo each; estrogen metabolites were measured in 3 overnight urines (baseline and at the end of the low- and high-soy diet) using gas chromatography mass spectrometry for the 82 women who completed the study. Urinary isoflavonoids were assessed by liquid chromatography mass spectrometry. When applying mixed models, the 2:16alpha-OH E(1) ratio increased (P = 0.05) because of a nonsignificant decrease in 16alpha-OH E(1) (P = 0.21) at the end of the high-soy diet. Similar nonsignificant increases in the 2:16alpha-OH E(1) ratio were observed in equol producers (P = 0.13) and nonproducers (P = 0.23). These findings suggest a beneficial influence of soy foods on estrogen metabolism regardless of equol producer status.


Estrogen metabolite ratio: Is the 2-hydroxyestrone to 16alpha-hydroxyestrone ratio predictive for breast cancer?

         (Obi, Vrieling et al. 2011) Download

Experimental studies have shown that two main estrogen metabolites hydroxylated by CYP1A1 and CYP1B1 in the breast differentially affect breast cell proliferation and carcinogenesis. Although 16alpha-hydroxyestrone (16alphaOHE1) exerts estrogenic activity through covalent estrogen receptor (ER) binding, 2-hydroxyestrone (2OHE1) presumably has antiestrogenic capabilities. The ratio of 2OHE1 to 16alphaOHE1 represents the relative dominance of one pathway over the other and is believed to be modifiable by diet. It was hypothesized that women with or at high risk of breast cancer have a lower estrogen metabolite ratio (EMR) compared with women without breast cancer. We conducted a systematic review on the EMR as a predictor for breast cancer. A total of nine studies (six prospective and three retrospective) matched our inclusion criteria, comprising 682 premenopausal cases (1027 controls) and 1189 postmenopausal cases (1888 controls). For the highest compared with the lowest quantile of urinary EMR, nonsignificant associations suggested at best a weak protective effect in premenopausal but not in postmenopausal breast cancer (range of odds ratios: 0.50-0.75 for premenopausal and 0.71-1.31 for postmenopausal). Circulating serum/plasma EMR was not associated with breast cancer risk. Associations were inconclusive for receptor subtypes of breast cancer. Uncontrolled factors known to be involved in breast carcinogenesis, such as 4-hydroxyestrone (4OHE1) concentration, may have confounded results for EMR. Results of the prospective studies do not support the hypothesis that EMR can be used as a predictive marker for breast cancer risk. Future research should concentrate on profiles of estrogen metabolites, including 4OHE1, to gain a more complete picture of the relative importance of single metabolites for breast cancer.


References

Cavalieri, E. L. and E. G. Rogan (2011). "Unbalanced metabolism of endogenous estrogens in the etiology and prevention of human cancer." J Steroid Biochem Mol Biol 125(3-5): 169-80 PMID: 21397019

Mackey, R. H., T. J. Fanelli, et al. (2012). "Hormone therapy, estrogen metabolism, and risk of breast cancer in the Women's Health Initiative Hormone Therapy Trial." Cancer Epidemiol Biomarkers Prev 21(11): 2022-32 PMID: 22933427

Mense, S. M., J. Chhabra, et al. (2008). "Preferential induction of cytochrome P450 1A1 over cytochrome P450 1B1 in human breast epithelial cells following exposure to quercetin." J Steroid Biochem Mol Biol 110(1-2): 157-62 PMID: 18456490

Morimoto, Y., S. M. Conroy, et al. (2012). "Urinary estrogen metabolites during a randomized soy trial." Nutr Cancer 64(2): 307-14 PMID: 22293063

Obi, N., A. Vrieling, et al. (2011). "Estrogen metabolite ratio: Is the 2-hydroxyestrone to 16alpha-hydroxyestrone ratio predictive for breast cancer?" Int J Womens Health 3: 37-51 PMID: 21339936