Effects of pubertal exposure to dietary soy on estrogen receptor pathway in the breast of cynomolgus macaques

We evaluated mammary gland responses over time in pubertal female cynomolgus macaques fed diets containing either casein/lactalbumin or soy protein that contained a human-equivalent dose of 120 mg isoflavones/day for ~4.5 years spanning menarche. We assessed estrogen receptors (ERs) expression, and markers of ER activity and estrogen metabolism. Promoter methylation of ERs and their downstream targets was also evaluated. As we found that pubertal soy exposure resulted in transient effects on mammary ER-a transcription after menarche with subtle effects on differentiation and ER activity, a gene expression microarray was performed on a subset of samples as an exploratory approach to investigate potential pathways and gene sets that may be of importance during this post-menarchal breast development. Gene expression profiles were assessed from breast biopsy samples from a subset of soy-fed and casein/lactalbumin-fed cynomolgus monkeys (n=4/diet group) from two timepoints, which are 7-12 months and 19-24 months after menarche.