Placental transfer of the soy isoflavone genistein following dietary and gavage administration to Sprague Dawley rats
Introduction
Genistein, the principal soy isoflavone, has been the subject of numerous studies in experimental animals and humans because of possible beneficial [1] and adverse effects [2], [3] due to estrogenic activity. Genistein has been shown to prevent [4], [5] or to promote [6], [7] chemically induced mammary tumor formation in rodents, depending on the timing of exposure to genistein (prepubertal vs. in utero, respectively) and timing of chemical carcinogen exposure (either dimethylbenzanthracene or methylnitrosourea). Genistein and other isoflavones, primarily as the glucuronide conjugates, have been measured in umbilical cord plasma and amniotic from human pregnancies and the concentrations were comparable to those present in maternal plasma [8]. These reports suggested that human and experimental animal fetuses can be exposed to genistein through maternal consumption. However, Lamartiniere et al. concluded that prenatal exposure of rats to genistein through the maternal diet did not confer protection from chemically induced mammary cancer later in life because conjugated forms of genistein, the principal form in maternal blood, could not cross the placenta [9].
Estrogenic effects of genistein in the central nervous system have been reported in vitro and in vivo: an estrogen-dependent cell line derived from the anterior pituitary showed enhanced release of prolactin [10]; injection in neonatal rats altered neuroendocrine secretions (gonadotropin releasing hormone, luteinizing hormone) and produced developmental changes in the sexually dimorphic nucleus of the hypothalamus [11; Scallet, unpublished); and dietary administration to ovariectomized Sprague-Dawley rats increased prolactin secretion [12]. These findings are also consistent with the hypothesis that genistein can penetrate both the placental and blood brain barriers to a level sufficient to exert estrogenic effects. The exposure of the fetus to genistein is significant because the developing brain may be more susceptible than adult brain to chemically mediated events because of metabolic differences, incomplete formation of the blood-brain barrier, or the irreversibility of developmental effects [13], [14].
Consumption by animals and humans of soy isoflavones, which occur in the plant as glucosides, results in cleavage by microbial β-glucosidases in the gut, absorption of the aglycones, followed by conversion to glucuronide and sulfate conjugates through first pass metabolism in the intestine and liver and release into the circulation [1], [15]. The research described here relates concentrations of genistein, the aglycone and putative hormonally active form, and total genistein, which includes the conjugated forms (primarily glucuronides), in maternal and fetal serum and brain following oral administration of genistein. These determinations provide information during critical early developmental periods about genistein exposure derived from serum concentrations in pregnant female rats that are relevant to human exposures [16].
Section snippets
Reagents
Genistein, with purity greater than 99% determined using 1H- and 13C-NMR, EI/MS, melting point, and TLC analysis, was obtained from Toronto Research Chemicals (Ontario, Canada); crude glucuronidase/sulfatase from Helix pomatia containing 105 units/mL glucuronidase activity + 5 × 103 units/mL sulfatase activity was obtained from Sigma Chemical Co. (St. Louis, MO). Deuterated genistein (6,8,3′,5′-d4, 95%) was purchased from Cambridge Isotope Laboratories (Andover, MA) and characterized previously
Results
Initial studies used neonatal pups analyzed within two days after delivery from pregnant female rats that had been maintained on either soy-free or genistein-fortified feed from birth through adulthood as part of a multigeneration study. The results obtained from analysis of 18 individual pups in eight litters derived from dams consuming 500 μg/g genistein diet and two litters from dams consuming the control diet are shown in Table 1. The method detection limit was approximately 2 nM, which was
Discussion
These studies suggest that genistein crossed the placenta into blood, brain, and probably other organs of the developing rat fetus either by passive uptake of the aglycone or by placental hydrolysis of conjugated forms [20]. This conclusion is at odds with that of Lamartiniere et al. who reported low concentrations of genistein aglycone (ca. 3 nM) in fetal serum following administration through maternal diet [9]. Because LC/MS/MS methodology with similar sensitivity was used to quantify
Acknowledgements
The high level technical support of Connie Weis and Carrie Moland and helpful discussions with Daniel M. Sheehan and William Slikker, Jr., all from NCTR, are gratefully acknowledged. This research was supported in part by Interagency Agreement #224–93-0001 between NCTR/FDA and the National Institute for Environmental Health Sciences/National Toxicology Program. HCC acknowledges support of a fellowship from the Oak Ridge Institute for Science and Education, administered through an interagency
References (25)
- et al.
Influence of perinatal genistein exposure on the development of MNU-induced mammary carcinoma in female Sprague-Dawley rats
Cancer Lett
(2000) - et al.
Maternal and neonatal phytoestrogens in Japanese women during birth
Am J Obstet Gynecol
(1999) - et al.
Phytoestrogens act as estrogen agonists in an estrogen-responsive pituitary cell line
Toxicol Appl Pharmacol
(1998) - et al.
Dose-response characteristics of neonatal exposure to genistein on pituitary responsiveness to gonadotropin releasing hormone and volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in postpubertal castrated female rats
Reprod Toxicol
(1993) - et al.
Daidzein and genistein glucuronides in vitro are weakly estrogenic and activate human natural killer cells at nutritionally relevant concentrations
J Nutr
(1999) - et al.
Pharmacokinetics of 14C-genistein in the ratGender-related differences, potential mechanisms of biological action, and implications for human health
Toxicol Appl Pharmacol
(2000) Phytoestrogensthe biochemistry, physiology, and implications for human health of soy isoflavones
Am J Clin Nutr
(1998)- et al.
Estrogenic effects of genistein on the growth of estrogen receptor-positive human breast cancer (MCF-7) cells in vitro and in vivo
Cancer Res
(1998) - et al.
Maternal genistein exposure mimics the effects of estrogen on mammary gland development in female mouse offspring
Oncology Reports
(1998) - et al.
Dietary genisteinperinatal mammary cancer prevention, bioavailability and toxicity testing in the rat
Carcinogenesis
(1999)
Prepubertal exposure to zealeranone or genistein reduces mammary tumorigenesis
Br J Cancer
Maternal exposure to genistein during pregnancy increases carcinogen-induced mammary tumorigenesis in female rat offspring
Oncology Reports
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Endocrine disrupting chemicals (EDCs) and placental function: Impact on fetal brain development
2021, Advances in PharmacologyEarly postnatal genistein administration permanently affects nitrergic and vasopressinergic systems in a sex-specific way
2017, NeuroscienceCitation Excerpt :In addition, the experimental conditions are strongly different from our previous paper (Rodriguez-Gomez et al., 2014). In fact, in our first experiment the embryos were exposed to GEN during prenatal development (GEN easily crosses the placental barrier; Doerge et al., 2001), but the supply after birth was presumably reduced, because GEN is almost totally blocked by the mammary barrier in rodents (Doerge et al., 2006). In the present experiment (performed on both sexes) the pups were directly fed with GEN for 8 days, thus directly interfering with the organizational processes that take place in the course of the first post-natal week of life.
Urine and serum biomonitoring of exposure to environmental estrogens II: Soy isoflavones and zearalenone in pregnant women
2016, Food and Chemical ToxicologyCitation Excerpt :In contrast to endogenous estrogens, aglycones of the soy isoflavones are not tightly bound to serum proteins (e.g., SHBG), and can in addition be the principal (100% unconjugated) form present in target tissues such as brain, liver, and reproductive tissues (Milligan et al., 1998; Chang et al., 2000). Placental transfer results in similar blood concentrations of total isoflavones in the fetus and the mother but with a higher amount of aglycones, possibly due to immature conjugation metabolism (Doerge et al., 2001; Jarrell et al., 2012). The possibility for impacts by soy isoflavones on fetal development and reproductive health in later life has been hypothesized based on some support from studies in animals, if not in humans (NTP, 2008; Jefferson et al., 2012).