Table 5.

Studies in female animal models examining the effects of soy isoflavone exposure during early life.

Objective	Sample Size	Subjects	Intervention: Route of administration and dosage	Duration of Intervention	Reproductive Health Outcomes	Findings
		(age at time of intervention)
To determine if the orally administered genistin (GIN), the glycosylated form of genistein (GEN), causes adverse effects on the developing reproductive tract GIN is most predominant in soy isoflavone formulas, but infants consuming SBIF have high circulating levels of GEN [19]	n = 4–16 mice/group	CD-1 mice, PND 1	SC: genistein: 12.5, 20, 25 mg/kg body weight Oral genistin (GIN):6.25, 12.5, 25 or 37.5 mg/kg body weight Oral genistein (GEN): 25, 37.5, 75 mg/kg/day	PND 1–5	SC GEN, Oral GEN, Oral GIN Uterine wet weight gain Induction of estrogen-responsive gene, lactoferrin (LF) GIN Group only Vaginal opening Estrous cycling Fertility Morphologic alterations in ovary/reproductive tract	SC GEN, Oral GEN, Oral GIN 20–33% more oral GIN was needed to elicit uterine wet weight gain compared to SC GEN but similar response was observed Oral GEN uterine wet weight gain only observed at much higher doses of 75 mg genistein/kg body weight Induction of LF gene Oral GIN: Increased incidence of multioocyte follicles in the ovaries Delayed vaginal openingAltered estrous cycling Decreased fertility Delayed parturition
To develop a mouse model that more closely mimics the oral genistein exposure and total serum genistein concentrations. To assess reproductive and nonreproductive organs after dosing and during development [22]	Not determined	C57BL/6 mice, PND 1	Oral genistein-soy formula emulsion: 5, 20, 50, 100 mg/kg body weight	PND 1–5	Serum genistein concentration Thymic and uterine weights Follicle numbers Immunohistochemistry for progesterone receptor	5, 20, 100 mg genistein/kg body weight: below desired range of serum genistein 50 mg genistein/kg body weight Increased uterine weight Downregulation of progesterone receptor in uterine epithelia Increased incidence of multioocyte follicles Decrease in thymic weight Altered estrous cyclingNormal fertility
To determine the effects of oral exposure to genistein in order to assess human risk following oral ingestion of genistein [21]	Not determined	Alderley Park rat PND 1	PND 1–6 SC Genistein: 0.2 or 2 mg/kg body weight PND 7–21 Oral gavage Genistein: 4 or 40 mg/kg body weight Control: corn oil	PND 1–21	Serum LH, FSH, estradiol, progesterone Vaginal opening Estrous cycling Sex organ weights GnRH	40 mg genistein/kg body weight: Increased uterus weights at PND 22 Advanced mean day of vaginal opening Induced permanent estrus Decreased progesterone in mature females 4 mg genistein/kg body weight: No effects
To measure the estrogenic responses of several phytoestrogens including genistein, daidzein and compare them over a dose range and measuring the transcriptional activation of the estrogen receptor (ER) and an in vivo immature mouse uterotrophic assay [28]	Not determined	CD-1 mice, PND 17	SC Genistein and daidzein doses 0.00001 to 1000 mg/kg body weight Positive controls: Diethylstilbestrol (DES)17β-estradiol: 0.01 to 1,000,000 µg/kg body weight Negative control: corn oil	3 consecutive days (PND 17, 18,19)	Uterine wet weight Uterine epithelial height Uterine gland number	Daidzein treatment: Did not demonstrate any increase in uterine epithelial cell height; Increase in uterine gland number; Did not demonstrate an increase in uterine wet weight; Genistein treatment: Increase in uterine wet weight; Increase in uterine epithelial cell height; Increase in uterine gland number
To determine the biochemical effect of genistein as the induction of ectopic expression of ER in granulosa cells, a morphological effect as the induction of multioocyte follicles (MOFs) in the ovary, and a functional effect as the altered ovarian response to superovulation treatment [29]	n = 16/group	CD-1 mice, PND 1	SC Genistein: 1, 10, 100 µg/pup/day (approximately 0.5, 5 or 50 mg/kg body weight)	5 days PND 1–5	ER-ß and ER-α expression and distribution in ovarian tissues The impact of genistein on ER expression, ovulation and the development of multioocyte follicles	ER-β transcript expression predominated in the ovaries in all stages of life and over ER-α and increased with age Genistein did not change ER-β expression but ER-α expression increased on days 5 and 12 ER-β was immunolocalized to granulosa cells ER-α was immunolocalized in interstitial and thecal cells Genistein caused major increase in ER-α expression in granulosa cells Superovulated mice had an increase in the number of ovulated oocytes at the lowest dose Dose-related increase in multioocyte follicles (MOFs)
To determine the the processes involved in altered mammary gland growth and development after neonatal genistein treatment [30]	n = 3–8/group	CD-1 mice, PND 1	SC Genistein 0.5, 5 or 50 mg/kg body weight	PND 1–5	Development of the mammary gland	4-week: No morphological differences were observed in development 5-week: Gen50 group had stunted development(less branching ) decreased numbers of terminal end buds 6-week: Gen50 had decreased number of terminal end buds, Gen 0.5 treated mice had advanced development with increased ductal elongationIncreased levels of progesterone receptor protein and estrogen receptor-β mRNA in Gen0.5-treated mice compared with controls ER-α expression decreased after all doses of Gen treatment Gen50 treated mice were unable to deliver live pups
To study the effects of neonatal genistein exposure on attainment of puberty and fertility [31]	Not determined	CD-1 mice 2, 4, 6 months of age	SC Genistein:0.5, 5 or 50 mg/kg body weight	PND 1–5	Vaginal opening Fertility Implantation and pregnancy Ovarian function (number of corpus luteum and ovarian capacity) Estrous cyclicity Serum hormone levels (estradiol and progesterone) before puberty	Genistein treated mice had prolonged estrous cycles that had a dose and age-related increase Pregnancy loss was attributed to fewer implantation sites and increased resorption Low dose genistein treated mice had increased numbers of corpora lutea compared to controls High dose genistein treated mice had fewer corpora lutea Similar levels of serum estrogen, progesterone and testosterone were observed before and during pregnancy Mice treated with Gen-50 did not deliver live pups
To evaluate whether early exposure of neonates to genistein has any effect on the development of sexual organs and/or reproductive performance [32]	n = 10–24/group	Sprague-Dawley rats PND 1	Oral gavage Genistein:12.5, 25, 50 or 100 mg/kg body weight Control: corn oil	PND 1–5	Fertility Vaginal Opening Estrous cycling Histopathological changes in the reproductive organs	Fertility was disrupted at 100 mg genistein/kg body weight Age at vaginal opening was not altered Estrous cycle: genistein-treated had cycle had variation in the amount of time spent in each phase and this was not dose responsive, cycle length was normal Histopathological changes in the uterus and ovary at 100 mg genistein/kg body weight
To study the formation of multioocyte follicles (MOFs) and potential disruption of the development of the ovary by genistein on ovarian differentiation [33]	n = 24–48/group	CD-1 mice, PND 1	SC Genistein 50 mg/kg body weight (~100 μg/pup/day)	PND 1–5	Ovarian differentiation	Genistein treatment: Fewer single oocytes Higher percentage of oocytes not enclosed in single follicles Oocytes nest breakdown was prolonged Fewer oocytes undergoing apoptosis on neonatal day 3
To determine the long-term carcinogenic potential in mice treated neonatally with genistein or DES with equal estrogenic dose [34]	n = minimum 8/group	CD-1 mice, PND 1	SC Genistein: 50 mg/kg body weight DES:0.001 mg/kg body weight Negative control: corn oil	5 days PND 1–5	Incidence of uterine adenocarcinoma Uterine weightCorpora lutea absence Abnormalities in the oviductOvarian tumor	Higher incidence of uterine adenocarcinoma at 18 months with genistein and DES; Higher uterine weight gain with genistein and DES; Higher absence of corpora lutea with genistein and DES
To elucidate the mechanism by which gensitein leads to infertility [35]	Not determined	CD-1 mice, PND 1	SC Genistein 50 mg/kg body weight Control: corn oil	PND 1–5	Oocyte developmental competence Timing of embryo loss	Genistein treatment: Females were not capable of supporting normal implantation of control embryos Oocytes were competent but the oviductal environment and the uterus have abnormalities that result in reproductive failure Complete infertility observed
To examine the effect of phytoestrogens on female sexual behavior and ovarian cyclicity [36]	n = 9–10/group	Wistar rats PND 1	SC Genistein 1 mg/day Daidzein 1 mg/day Control: sesame oil	PND 1–5	Estrous cycle Vaginal Opening Ovary histology Lordosis quotient (feminine sexual reflexes)	Genistein treatment: Prolonged estrous cycle Smaller ovaries and no corpora lutea compared to control or DZ group Low lordosis quoteint Daidzein treatment: Corpora lutea seen but ovaries were smaller compared to controls High lordosis quotient
To investigate the potential of genistein to protect against the development of breast cancer and to cause reproductive and developmental toxicity [37]	Not determined	Prepubertal female, suckling, Sprague-Dawley rats	SC Genistein 500 mg/kg body weight Oral gavage Carcinogen: Dimethylbenz[a]anthracene (DMBA) 80 mg/kg body weight	Genistein:3 days, every second dayPND 16, 18, 20 DMBA: PND 50	Mammary gland differentiation and cell proliferation in the presence of carcinogen DMBA; Offspring body weights; Anogential distance; Vaginal opening; Estrus cycle length; Follicular development	Genistein treatment: 50% reduction in chemically induced mammary tumorgenesis Increased mammary gland differentiation in immature rats leading to mammary gland less susceptible to mammary cancer No significant changes in fertility, number of male and female offspring, body weight, anogenital distance, vaginal opening, testes descent, estrus cycle, or follicular development among groups