Table 1. Studies carried out in rats investigating the effects of early life genistein/SPI/soy exposure on mammary gland morphology and tumorigenesis.
| Exposure time | Compound/diet, dose, route of administration | Effect on mammary gland morphology | Effect on carcinogen-induced mammary tumour growth | Reference |
|---|---|---|---|---|
| In utero and perinatal exposure | ||||
| GD 15–19 | Genistein 1.5 or 30 mg kg−1 per day, s.c. | PND 28: no changes in TEB number | MNU (50 mg kg−1 on PND 28): no changes in tumour latency and multiplicity by PND 182 | Pei et al (2003) |
| GD 15–20 | Genistein 20, 100, or 300 μg per rat per day (∼0.1, 0.5, 1.5 mg kg bw−1), s.c. | Not studied | DMBA (10 mg per rat ≈50 mg kg−1 on PND 45–50): increased tumour incidence. Follow-up until PND 170–200 | Hilakivi-Clarke et al (1999) |
| GD 0 – PND 0 | Genistein 15, 150, or 300 p.p.m. in AIN-93G diet (produces serum levels corresponding to Asians on high soy diet; Note 1) | PND 56: an increase in the number of TEBs, and a decrease in the number of lobules in the highest genistein group | DMBA (10 mg per rat ≈50 mg kg−1 on PND 47): no change in tumour latency, but increased tumour incidence on PND 119 in the high genistein group | Hilakivi-Clarke et al (2002) |
| GD 4 – PND 0 | Genistein 250 p.p.m. or SPI (gen 216 mg+daid 160 mg per kg) in AIN-93G diet (Note 1) | Not studied | MNU (50 mg kg−1 on PND 51): longer tumour latency in both groups, and lower tumour multiplicity and % high-grade tumours in SPI group on PND 149 | Su et al (2007a) |
| GD 0–21 | Genistein 250 p.p.m. in AIN-76A diet (Note 1) | Not studied | DMBA (80 mg kg−1 on PND 50): no effect on tumour multiplicity. Follow-up until PND 230 | Lamartiniere et al (2002) |
| PND 2–8 | Genistein 10 mg kg bw−1 per day, s.c. (pharmacological dose; Note 1) | PND 200: distended mammary glands with secretion and milk production, ductal hyperplasia, microcalcifications, fibrosis, and necrosis | Spontaneous: increased mammary atypical hyperplasias and in situ ductal carcinomas of comedo type on PND 200 | Foster et al (2004) |
| In utero and pre/peripubertal exposure | ||||
| GD 0 – PND 21 | Genistein 25 or 250 p.p.m. in AIN-76A diet (250 p.p.m. produced serum levels of ca. 700 and 1800 pmol ml−1 on PND 7 and 21, respectively) | PND 21 and 50: reduced number of TEBs. PND 50: lower number of lobules type I in the higher genistein group | DMBA (80 mg kg−1 on PND 50): a dose-dependent decrease in tumour multiplicity by PND 230 | Fritz et al (1998) |
| GD 1 – PND 22 | Genistein 300 or 800 p.p.m. in chow diet | PND 22: increased ductal branching in the higher genistein group in males | Not studied | You L, Sar M, Bartolucci EJ, McIntyre BS, Sriperumbudur R (2002) Modulation of mammary gland development in prepubertal male rats exposed to genistein and methoxychlor. Toxicol Sci 66: 216–225 |
| GD 4 – PND 21, 33 or 50 | 20% SPI in AIN-93G diet (Note 2) | PND 50: reduced number of TEBs | Not studied | Rowlands JC, Hakkak R, Ronis MJ, Badger TM (2002) Altered mammary gland differentiation and progesterone receptor expression in rats fed soy and whey proteins. Toxicol Sci 70: 40–45 |
| In utero → lifetime exposure | ||||
| GD 4→ PND 149 | SPI (gen 216 mg +daidzein 160 mg per kg) in AIN-93G diet | Not studied | MNU (50 mg kg−1 on PND 51): longer tumour latency, decreased tumour incidence and multiplicity by PND 149 | Su et al (2007a) |
| GD 0 → lifetime (for two generations) | SPI=430 mg total isoflavones, including 276 mg genistein and 132 mg daidzein per kg AIN-93G diet | Not studied | DMBA (80 mg kg−1 on PND 50: longer tumour latency, and a decline in tumour incidence in the second generation. No difference in tumour multiplicity or volumes by PND 175 | Hakkak et al (2000) |
| GD 7 → lifetime | Genistein 5, 25, 100, 250, 625, or 1250 p.p.m. in chow diet | PND 50: increased lobular differentiation, but ductal and alveolar hyperplasia in the higher genistein groups | Not studied | Delclos KB, Bucci TJ, Lomax LG, Latendresse JR, Warbritton A, Weis CC, Newbold RR (2001) Effects of dietary genistein exposure during development on male and female CD (Sprague–Dawley) rats. Reprod Toxicol 15: 647–663 |
| Prepubertal exposure | ||||
| PND 1–21 | Genistein: 250 p.p.m. in AIN-76A diet | PND 50: reduced number of TEBs and increased number of lobules | DMBA (80 mg kg−1 on PND 50): reduced tumour multiplicity by PND 230 | Lamartiniere et al (2002) |
| PND 7, 10, 14, 17, 20 | Genistein 20 μg per pup per day (ca.1 mg kg bw−1) s.c. | PND 183: increased lobular differentiation | DMBA (10 mg per rat ≈50 mg kg−1 on PND 45): reduced tumour multiplicity and number of proliferating tumours on PND 171 | Hilakivi-Clarke L, Onojafe I, Raygada M, Cho E, Skaar T, Russo I, Clarke R (1999) Prepubertal exposure to zearalenone or genistein reduces mammary tumorigenesis. Br J Cancer 80: 1682–1688 |
| PND 7–20 | Genistein 50 μg per pup per day (ca.3.3−1.25 mg kg−1 per day) or E2 10 μg per pup per day s.c. | PND 56: genistein reduced number of TEBs and epithelial density, increased number of lobuloalveolar structures | DMBA (studied only in prepubertally E2-exposed rats: a significant decrease in tumour incidence compared to control rats) | Cabanes et al (2004) |
| PNDs 16, 18, 20 | Genistein 500 mg kg−1 per day (in all studies) s.c. | PND 50: reduced number of TEBs, increased number of lobules | DMBA (80 mg kg−1 on PND 50): reduced mammary tumour multiplicity or incidence | Cotroneo MS, Wang J, Fritz WA, Eltoum IE, Lamartiniere CA (2002) Genistein action in the prepubertal mammary gland in a chemoprevention model. Carcinogenesis 23: 1467–1474 Brown NM, Wang J, Cotroneo MS, Zhao YX, Lamartiniere CA (1998) Prepubertal genistein treatment modulates TGF-alpha, EGF and EGF-receptor mRNAs and proteins in the rat mammary gland. Mol Cell Endocrinol 144: 149–165 Murrill WB, Brown NM, Zhang JX, Manzolillo PA, Barnes S, Lamartiniere CA (1996) Prepubertal genistein exposure suppresses mammary cancer and enhances gland differentiation in rats. Carcinogenesis 17: 1451–1457 |
| PND 15–19 | Genistein 1.5 or 30 mg kg bw−1 per day, s.c. | PND 28: no changes in TEB number | MNU (50 mg kg−1 on PND 28): decrease in tumour incidence through PND 182 (low-dose genistein) | Pei et al (2003) |
| PND 23,25,27,29 | Genistein 50 mg kg bw−1 per day, s.c. | PND 30: increase in mammary gland size, and the number of lobules I, but no effect on the TEBs | Not studied | Brown NM, Lamartiniere CA (1995) Xenoestrogens alter mammary gland differentiation and cell proliferation in the rat. Environ Health Perspect 103: 708–713 |
| Peripubertal exposure | ||||
| PND 31–45 | Genistein 375 or 750 p.p.m. in diet | PND 45: no effects on mammary ductal and lobuloalveolar development | Not studied | Santell RC, Chang YC, Nair MG, Helferich WG (1997) Dietary genistein exerts estrogeneic effects upon the uterus, mammary gland and the hypothalamic/pityuitary axis in rats. J Nutr 127: 263–269 |
| Pre- or peripubertal → for lifetime exposure | ||||
| PND 21 →ca.218 | 0.35 or 0.7% soy extract (Soyselect™, contains 12% isoflavones) in AIN-76A diet | Not studied | DMBA (80 mg kg−1 on PND 50): longer tumour latency. No effect on the incidence, multiplicity, or median total tumour burden by PND 218 | Gallo et al (2001) |
| PND 25→158 | Genistein 800 or 1600 p.p.m. in AIN-76A diet | Not studied | MNU (50 mg kg−1 on PND 50): no significant effects by PND 158 | Kim H, Hall P, Smith M, Kirk M, Prasain JK, Barnes S, Grubbs C (2004) Chemoprevention by grape seed extract and genistein in carcinogen-induced mammary cancer in rats is diet dependent. J Nutr 134: 3445S–3452S |
| PND 36 → 127 | Isoflavones: 30 400 810 p.p.m. in SPI containing diet | Not studied | DMBA (10 mg per rat on PND 50): no significant effects by PND 127 | Appelt LC, Reicks MM (1999) Soy induces phase II enzymes but does not inhibit dimethylbenz[a]anthracene-induced carcinogenesis in female rats. J Nutr 129: 1820–1826 |
| PND 43 → ca.176 (F-344 rats) | 10 or 20% SPI, with and without isoflavones, in AIN-93G (Note 2) | Not studied | MNU (40 mg kg−1 on PND 50): no significant effects by PND 176 | Cohen LA, Zhao Z, Pittman BSJA (2000) Effect of intact and isoflavone-depleted soy protein on NMU-induced rat mammary tumorigenesis. Carcinogenesis 21: 929–935 |
| PND 43 → ca.163 | Genistein 200 p.p.m. or 16% SPI with and without isoflavones, in modified AIN-74A diet (Note 2) | Not studied | DMBA (15 mg per rat on PND 50): decreased tumour multiplicity with SPI, but not with genistein. Most significant effect on tumour multiplicity and latency in the SPI-without isoflavones group | Constantinou et al (2001) |
| PND 49 → 175 (CD/Crj rats) | 10% miso (fermented soybean product) in diet | Not studied | MNU (50 mg per rat on PND 49): significant decrease in incidence and multiplicity by PND 175 | Gotoh et al (1998) |
Abbreviations: bw=body weight; DMBA=dimethylbenz(a)anthracene; GD=gestational day; MNU=N-methyl-n-nitrosourea; PND=postnatal day; p.p.m.=parts per million (mg per kg); SPI=soy protein isolate; TEB=terminal end bud.
Note 1: Asian population on high soy diet consumes genistein ca. 1–30 mg per day=ca. 0.02–0.55 mg kg−1 per day. Native Japanese adults are reported typically to consume 30–40 mg (aglycone units) of isoflavones per day (Wakai et al J Nutr 1998; 128: 209–213), their plasma levels being ∼300 nmol l−1 (Adlercreutz et al Lancet 1993; 342: 1209–1210). Genistein intake in the Western Europe ca. 0.005 mg kg−1 per day. For extrapolation from human to rodent, small animals need ca. 10 times higher concentrations compared to humans, since they are less susceptible to drugs (Wuttke et al Ageing Res Rev 2007; 6(2): 150–88). Thus, genistein doses 0.1–1.5 mg kg−1 per day to rodents would be comparable to average daily intake in Asian countries. Doses >10 mg kg−1 per day are pharmacological.
Note 2: SPI contains the isoflavones genistein 216 mg kg−1, and daidzein 160 mg kg−1, and their β-glycosides (Hakkak et al Cancer Epidemiol Biomarkers Prev 2000; 9: 113–117). SPI (10 and 20%) is estimated to contain ca. 50 and 100 times the intake of an average Japanese adult (Cohen et al Carcinogenesis 2000; 21(5): 929–935).
Note 3: Sprague–Dawley rats were used unless otherwise stated in the first column, under the ‘exposure time’.