Two-week dietary soy supplementation has an estrogenic effect on normal premenopausal breast.

An association has been reported between consumption of a high soy diet and a low incidence of breast cancer within populations of Southeast Asia. Phytoestrogens present in soy act as partial estrogen agonists or antagonists and can inhibit breast cancer cell proliferation in vitro. The effect of 14-day dietary soy supplementation with 60 g (45 mg isoflavones) on the normal breast of 84 premenopausal patients was determined. Serum concentrations of the isoflavanoids, genistein, daidzein, and equol, were raised in patients after soy supplementation (P < or = 0.025). Nipple aspirate (NA) levels of genistein and daidzein were higher than paired serum levels, both before (P < 0.001 and P = 0.001, respectively) and after soy supplementation (P < 0.001 and P = 0.049, respectively); however, there was no significant increase in NA isoflavone levels in response to soy. NA levels of apolipoprotein D were significantly lowered and pS2 levels raised in response to soy supplementation (P < or = 0.002), indicative of an estrogenic stimulus. No effect of soy supplementation on breast epithelial cell proliferation, estrogen and progesterone receptor status, apoptosis, mitosis, or Bcl-2 expression was detected. In conclusion, short term dietary soy has a weak estrogenic response on the breast, as measured by nipple aspirate apolipoprotein D and pS2 expression. No antiestrogenic effect of soy on the breast was detected.

In vivo administration of genistein has no effect on small intestinal epithelial proliferation and apoptosis, but a modest effect on clonogen survival.

The soya metabolite genistein possesses anti-proliferative, pro-apoptotic activities in intestinal epithelial cells in vitro and may reduce epithelial cancer incidence. This could involve cell cycle arrest/apoptosis in the proliferative or clonogenic cells. We investigated the effects of genistein on the small intestinal epithelium in vivo. No effect on the number or distribution of proliferative cells in the crypts was detected. Similarly, no change in spontaneous apoptotic cell incidence or the characteristic stem cell apoptotic response following low dose irradiation was observed. Genistein afforded a modest decrease in clonogen radiosensitivity. Hence, using a range of dosing protocols, sub-cutaneous administration of genistein for periods of up to 1 week did not alter intestinal epithelial homeostasis.

Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro.

There have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high levels of isoflavones derived from the soya bean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have both oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6, IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Responses were compared to those elicited by oestradiol, the anti-oestrogen tamoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamoxifen were potent inhibitors of cell proliferation. Of seven novel isoflavones tested, none were more potent inhibitors than genistein, and all displayed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed when the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour development (reducing the risk) and may reduce colonic tumour growth.

Epithelial proliferation and hormone receptor status in the normal post-menopausal breast and the effects of hormone replacement therapy.

The proliferation rate (as assessed by Ki67 expression) and expression of oestrogen-regulated progesterone receptor (PR) was studied in normal post-menopausal breast epithelium. Normal breast epithelium from patients receiving hormone replacement therapy (HRT) at the time of surgery containing either oestrogen alone (E2) or oestrogen and progesterone combined activities (E2 + P) was also studied, as HRT has been linked to an increased breast cancer risk. Samples of breast tissue, containing normal epithelium, from 185 patients undergoing surgery for benign or malignant disease were immunocytochemically stained for PR and Ki67. The percentage of labelled cells was expressed as the labelling index (LI). The median Ki67 LI in normal post-menopausal breast epithelium was 0.19 and median PR LI was 4.75, and both were unaffected by patient age, duration of menopause or if the tissue sample originated from a breast with benign or malignant disease. Proliferation did not alter significantly in patients taking HRT (P = 0.61); however, PR expression was up-regulated in both E2 and E2 + P users (P = 0.01). The dose and duration of HRT had no effect on either parameter. A possible attenuation of sensitivity to oestradiol-induced proliferation but not to PR expression occurs in the post-menopausal breast.