Comparative activity of pulsed or continuous estradiol exposure on gene expression and proliferation of normal and tumoral human breast cells

Abstract

Intranasal administration of hormone replacement therapy presents an original plasma kinetic profile with transient estrogen levels giving rise to the concept of pulsed therapy. To further understand the molecular effects of this new therapy, we have compared the effects of pulsed and continuous estradiol treatments on two critical aspects of estradiol action: gene expression and cell proliferation. Cells were stimulated with estradiol as 1-h pulsed or 24-h continuous treatments at concentrations such that the 24-h exposure (concentration×time) was identical in both conditions. In MCF7 cells, the transcriptional activity of estrogen receptors (ER) on a transiently transfected responsive estrogen response element-luciferase reporter construct was shown to be drastically (∼10-fold) and similarly stimulated after both treatments. Moreover, the increased mRNA expression of three representative estradiol-sensitive genes (pS2, cathepsin D, progesterone receptor), evaluated by Northern blot, was identical after 1-h pulse with 7 nM estradiol or continuous treatment with 0·29 nM estradiol with the same kinetic profile over 48 h. Proliferation was quantified by a histomorphometric method on primary cultures of human normal breast cells from reduction mammoplasties and using a fluorescence DNA assay in six human breast cancer cell lines which were ER positive or negative. After a 7-day treatment period, estradiol had no effect on the proliferation of the three ER negative cell lines (BT20, MDA MB231, SK BR3) but significantly stimulated the proliferation of the normal cells and of the three tumoral hormone-sensitive cell lines (MCF7, T47D, ZR 75-1); both hormone treatments producing the same increases in cell growth. In conclusion, we have shown that the genomic or proliferative effects of estradiol were identical with pulsed or continuous treatments, thus indicating that estrogenic effects are not strictly related to concentrations but rather to total hormone exposure.

Differing transcriptional responses to pulsed or continuous estradiol exposure in human umbilical vein endothelial cells

“…Here, we focus on the roles of some genes that are actively involved in tumorigenesis, proliferation and apoptosis. It has been reported that pulsed and continuous E2 administration exerted the same effect on gene expression and cell proliferation in normal and in cancerous breast cells [7], but our results showed that continuous E2 (10 −9 M) treatment did not induce proliferation in HUVECs, and that pulsed treatment elicited, surprisingly, an inhibitory effect on cell proliferation at the same dosage of exposure. This anti-proliferative effect might be important therapeutically.…”

“…This suggests a possible differential effect of pulsed E2 administration on vascular biology such that the development of capillary congestion and edema is less in endometrial and breast tissues during pulsed E2 therapy. It also has been demonstrated that pulsed exposure is as efficient as continuous exposures on the expression of endogenous or transfected estrogen-regulated genes and proliferation in normal and malignant human breast cells [7]. As the pulsed administration (nasal spray of estradiol) and continuous administration (oral or patches) lead to different pharmacokinetics profiles and subsequent E2 plasma levels in postmenopausal women, it is important to compare both routes of administration with regard to the modulation of carcinogenesis.…”

Glucocorticoid receptor activity discriminates between progesterone and medroxyprogesterone acetate effects in breast cells

“…Control cells were treated with ethanol as vehicle (1:1000). Treatments were carried out in a phenol red-free medium containing 5% dextran-charcoal-stripped serum for a period of 48 h in breast cancer cells and 96 h in HBE cells due to difference in doubling time and optimal conditions as previously reported [16][17][18][19]. Steroid concentrations were chosen according to two criteria.…”

Estrogen replacement regimen and brain infusion of lipopolysaccharide differentially alter steroid receptor expression in the uterus and hypothalamus

“…Estrogen receptor quantification Hippocampal ERs were quantified by [2,4,6, H(N)]-17b-estradiol radioligand binding (1 nM; specific activity, 95 Ci/mmol; displaced by 1 lM diethylstilbestrol [18,70,71]). The entire right hippocampus was assayed to ensure consistency between samples, as the density and subtype of the estrogen receptor varies between dorsal and ventral aspects of the hippocampus [72,73].…”

“…The regimen of estrogen replacement also appears to play a role and studies have begun to address whether pulsed administration of estrogens may be more efficacious [6][7][8]. Quality of life in women is improved by pulsed, but not constant estrogen therapy [9].…”