Soy supplementation: Impact on gene expression in different tissues of ovariectomized rats and evaluation of the rat model to predict (post)menopausal health effect

Abstract

This toxicogenomic study was conducted to predict (post)menopausal human health effects of commercial soy supplementation using ovariectomized rats as a model. Different target tissues (i.e. breast, uterus and sternum) and non-target tissues (i.e. peripheral blood mononuclear cells (PBMC), adipose and liver) of ovariectomized F344 rats exposed to a commercially available soy supplement for eight weeks, were investigated. Changes in gene expression in these tissues were analysed using whole-genome microarray analysis. No correlation in changes in gene expression were observed among different tissues, indicating tissue specific effects of soy isoflavone supplementation. Out of 87 well-established estrogen responsive genes (ERGs), only 19 were found to be significantly regulated (p < 0.05) in different tissues, particularly in liver, adipose and uterus tissues. Surprisingly, no ERGs were significantly regulated in estrogen sensitive breast and sternum tissues. The changes in gene expression in PBMC and adipose tissue in rats were compared with those in (post)menopausal female volunteers who received the same supplement in a similar oral dose and exposure duration in human intervention studies. No correlation in changes in gene expression between rats and humans was observed. Although receiving a similar dose, in humans the plasma levels expressed as total free aglycones were several folds higher than in the rat. Therefore, the overall results in young ovariectomized female F344 rats indicated that using rat transcriptomic data does not provide a suitable model for human risk or benefit analysis of soy isoflavone supplementation.

Keywords: (Post)menopausal health effect; ERGs, estrogen responsive genes; ERα, estrogen receptor alpha; ERβ, estrogen receptor beta; Gene expression; Ovariectomized rat model; PBMC, peripheral blood mononuclear cells; Soy isoflavone supplementation.

Graphical abstract

Fig. 1

Flow chart of the microarray analysis indicating significantly changed genes and gene sets induced in different tissues of ovariectomizedF344 rats after oral gavage dosing (2 mg soy isoflavones/kg bw per day for 8 weeks) of a commercial soy supplement. The number of corresponding human homologue genes found in rats is also indicated (right hand column). AT, adipose tissue; BT, breast tissue; LT, liver tissue; PBMC, peripheral blood mononuclear cells; ST, sternum tissue and UT, uterus tissue.

Fig. 2

Rank-rank scattered plot for significantly changed common PBMC genes in the current long-term rat study (i.e. 8 week exposure) and from the group exposed to the same dose (i.e. 2 mg soy isoflavones/kg bw per day) in the short-term (2 days) rat study [18]. Each dot represents the t-value of a single gene and the highlighted dots (♦) indicate the highly correlated genes. The list of these 15 genes can be found in supplementary Fig. 3. Genes significantly changed in the same direction in both treatments are in Cartesian quadrants I and III, while genes significantly changed in opposite directions are in quadrants II and IV.

Fig. 3

Rank-rank scattered plot for significantly changed common PBMC genes in rat and (post)menopausal women (3a), and significantly changed common genes in adipose tissue of rats and (post)menopausal women (3b). Each dot represents the t-value of a single gene and the highlighted dots (♦) indicate the correlated genes. Corresponding human homologous genes were retrieved from the study with (post)menopausal women taking the same supplement, in a similar dose (about 1.5 mg soy isoflaone/kg bw per day) and time duration (i.e. 8 weeks) [4,19]. Genes significantly changed in the same direction in both treatments are in Cartesian quadrants I and III, while genes significantly changed in opposite directions are in quadrants II and IV.

Fig. 4

Comparison of the estimated in vivo concentration of total free aglycones with the concentration-response curve of daidzein in different in vitro cell models for estrogenicity. (Figure adapted from Islam et al. [36]). The solid lines indicate the expected effect of the total free aglycones present in the rat plasma, the dotted lines taking into account the higher estrogenic potency of equol compared to daidzein.