Effects of Pubertal Exposure to Dietary Soy on Estrogen Receptor Activity in the Breast of Cynomolgus Macaques

Abstract

Endogenous estrogens influence mammary gland development during puberty and breast cancer risk during adulthood. Early-life exposure to dietary or environmental estrogens may alter estrogen-mediated processes. Soy foods contain phytoestrogenic isoflavones (IFs), which have mixed estrogen agonist/antagonist properties. Here, we evaluated mammary gland responses over time in pubertal female cynomolgus macaques fed diets containing either casein/lactalbumin (n=12) or soy protein containing a human-equivalent dose of 120 mg IF/day (n=17) for ~4.5 years spanning menarche. We assessed estrogen receptor (ER) expression and activity, promoter methylation of ERs and their downstream targets, and markers of estrogen metabolism. Expression of ERα and classical ERα response genes (TFF1, PGR and GREB1) decreased with maturity, independent of diet. A significant inverse correlation was observed between TFF1 mRNA and methylation of CpG sites within the TFF1 promoter. Soy effects included lower ERβ expression before menarche and lower mRNA for ERα and GREB1 after menarche. Expression of GATA-3, an epithelial differentiation marker that regulates ERα-mediated transcription, was elevated before menarche and decreased after menarche in soy-fed animals. Soy did not significantly alter expression of other ER activity markers, estrogen-metabolizing enzymes, or promoter methylation for ERs or ER-regulated genes. Our results demonstrate greater ER expression and activity during the pubertal transition, supporting the idea that this life stage is a critical window for phenotypic modulation by estrogenic compounds. Pubertal soy exposure decreases mammary ERα expression after menarche and exerts subtle effects on receptor activity and mammary gland differentiation.

Exploratory analysis of the human breast DNA methylation profile upon soymilk exposure

“…age-independent) methylation differences in the adult female population due to soy consumption. However, whereas our analyses indicate no large, age-independent differences in breast methylation, recent literature links the possible positive or negative effect of soy consumption on breast cancer risk in adults to the period or age when soy consumption started 4 , 28 . Early-life exposure to soy may alter estrogen mediated processes and therefore, alter the effect of genistein, daidzein and other isoflavones, which are estrogen antagonists.…”

“…Early-life exposure to soy may alter estrogen mediated processes and therefore, alter the effect of genistein, daidzein and other isoflavones, which are estrogen antagonists. Whether this effect is sustained by DNA methylation remains largely unknown 28 . Note that also other sources of heterogeneity (e.g.…”

Investigation of the adolescent female breast transcriptome and the impact of obesity

“…Comparison of the 500 most highly expressed genes in breast tissue from ADOL and in post-pubertal/young adult mice [30] revealed that < 30% of genes overlapped. We expanded this comparative analysis to other existing genomic datasets: (1) RNA-seq data in GTEx from breast tissue samples in 52 adult women and (2) microarray data in GEO from mammary tissue in control or vehicle-treated post-pubertal macaques (7-12 months post-menarche) [31] and young adult rats (age 6-9 weeks) [32] (Additional File 1: Table S5). The adult women were 39.2 ± 8.6 years old (range 21-49), the majority (84.6%) were non-Hispanic Caucasian, and 34.6% were OB (mean BMI for cohort 26.4 ± 4.1 kg/m 2 , range 18.5-35.0), and the majority reported tobacco smoking and/or drinking.…”

Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation

“…However, in a study starting before menarche of pubertal female cynomolgus monkeys receiving a soy-protein enriched diet (corresponding to a human-equivalent dose of 120 mg isoflavones per day, expressed as aglycone equivalents) for approximately 4.5 years, only a subtle effect of the soy diet on breast differentiation and ER activity was observed. The authors discussed that even this modest change might dampen estrogen responsiveness in the breast tissue later in adulthood (Dewi et al 2013 , 2016 ). This decrease in estrogen responsiveness was also observed in the mammary gland of adult rats, which were exposed pre-/peripubertally or life-long to an isoflavone-rich diet (Blei et al 2015 ; Molzberger et al 2013 ).…”