Anne Kurrat

Dose-dependent effects of isoflavone exposure during early lifetime on the rat mammary gland: Studies on estrogen sensitivity, isoflavone metabolism, and DNA methylation

SCOPE Isoflavone (ISO) exposure during adolescence modulates 17β-estradiol (E2) sensitivity of the adult mammary gland. The present study investigated the dose dependency of these effects focusing on proliferation, estrogen receptor dependent and independent gene expression, as well as DNA methylation and ISO metabolism. METHODS AND RESULTS Female Wistar rats were lifelong exposed to an ISO-depleted diet or to diets enriched with a soy ISO extract (ISO-rich diet (IRD)) causing plasma concentrations as observed minimally (IRDlow) and maximally (IRDhigh) in Asian women. The extract was characterized by both phytochemical analysis and E-Screen. Rats were ovariectomized at postnatal day (PND) 80 and treated with E2 from PND94 to 97. In contrast to uterine response, body weight and visceral fat mass were affected by ISO. In the mammary gland, both E2-induced proliferation (proliferating cell nuclear antigen staining) and estrogen receptor activation (progesterone receptor staining) were significantly reduced by IRDhigh but not by IRDlow, which however attenuated Gdf15 mRNA expression. DNA methylation analysis revealed significant differences in the promoter regions of Aldhl1, Extl1, and WAP between IRDhigh and ISO-depleted diet. CONCLUSION Lifelong exposure to ISO results in dose-dependent differential effects on proliferation, gene expression, and DNA methylation in rat mammary glands. Yet, a decrease in estrogen responsiveness was only achieved by IRDhigh.

Lifelong exposure to dietary isoflavones reduces risk of obesity in ovariectomized Wistar rats.

SCOPE Traditional Asian diet rich in soy isoflavones (ISOs) is discussed to be linked to a lower obesity prevalence. In lifelong and short-term exposure scenarios we investigated effects of an ISO-rich diet on the body composition and development of obesity in female rats. METHODS AND RESULTS Female Wistar rats grew up on ISO-free or ISO-rich control diet (CON ISO: 467 mg/kg diet). Starting postnatal day 83, ovariectomized and intact animals received high calorie Western diet (WD) in the absence or presence of ISO (WD ISO: 431 mg/kg diet) for 12 weeks to induce obesity or maintained on respective control diet (CON). One group starting ISO exposure after ovariectomy mimics short-term ISO exposure in postmenopausal Western women. Lifelong but not short-term ISO exposure resulted in reduced body weight, visceral fat mass, serum leptin, and smaller adipocytes. ISO decreased hepatic SREBP-1c, ACC, FAS, and PPARγ mRNA expression in nonobese animals. Moreover, ovariectomy reduced skeletal muscle weight, which was antagonized by both short-term and lifelong ISO exposure. CONCLUSION Our results indicate that in female rats lifelong but not short-term ISO intake reduces the risk to develop obesity. Furthermore, lifelong and short-term ISO exposure may antagonize loss of skeletal muscle mass induced by ovariectomy.

Dose‐dependent effects of isoflavone exposure during early lifetime on development and androgen sensitivity in male Wistar rats

SCOPE The aim of our study was to investigate dose-dependent effects of isoflavone (ISO) exposure during adolescence on the androgen sensitivity of various physiological end points in male Wistar rats. METHODS AND RESULTS During embryogenesis and adolescence, rats were exposed to an ISO-depleted diet (IDD) or one of two diets enriched with different concentrations of a soy-based ISO extract causing plasma concentrations observed averagely (ISO-rich diet [IRD]low) and maximally (IRDhigh) in Asian men. Most of the rats were orchiectomized at postnatal day (PND) 81 and were treated with testosterone propionate (TP) or vehicle from PND 89 to 99. In intact rats (PND 99) body weight, food intake, and fat mass were not influenced by ISO, but serum triglycerides and hepatic fatty acid synthase expression were decreased. Trabecular bone mineral density (BMD) was reduced in IRDlow, but not in IRDhigh rats. Orchiectomy (ORX) induced loss of BMD, which was antagonized by IRDhigh. ISO increased androgen sensitivity of seminal vesicle and levator ani. Besides, ISO plasma levels were reduced by ORX compared to intact and TP-treated rats. CONCLUSION In summary, the results of this study indicate that exposure to ISO during adolescence affects bone homeostasis, lipid metabolism, and modulates androgen sensitivity in young adult male rats.

Neonatal isoflavone exposure interferes with the reproductive system of female Wistar rats.

There is increasing concern about possible adverse effects of soy based infant formulas (SBIF) due to their high amount of isoflavones (ISO). The aim of the present study was to investigate effects of neonatal exposure to ISO on reproductive system of female Wistar rats. Animals were exposed to an ISO depleted diet or a diet enriched with an ISO extract (IRD; 508mg ISO/kg) during embryogenesis and adolescence. Pups of each group were fed daily by pipette with ISO-suspension (ISO+; 32mg ISO/kg bw) or placebo from postnatal day (PND) 1 until PND23 resulting in plasma concentrations similar to levels reported in infants fed SBIF. The visceral fat mass was reduced by long-term IRD. Vaginal epithelial height was increased at PND23 and vaginal opening was precocious in ISO+ groups. Later in life, more often irregular estrus cycles were observed in rats of ISO+ groups. In addition, FSH levels and uterine epithelial heights were increased at PND80 in ISO+ groups. In summary, the results indicate that neonatal ISO intake, resulting in plasma concentrations achievable through SBIF, has an estrogenic effect on prepubertal rats and influences female reproductive tract later in life.