Effects of Flaxseed Lignan Secoisolariciresinol Diglucosideon Preneoplastic Biomarkers of Cancer Progression in a Model of Simultaneous Breast and Ovarian Cancer Development

Abstract

Breast cancer prevention efforts are focused increasingly on potentially beneficial dietary modifications due to their ease of implementation and wide acceptance. Secoisolariciresinol diglucoside (SDG) is a lignan found in high concentration in flaxseed that may have selective estrogen receptor modulator-like effects resulting in antiestrogenic activity in a high estrogen environment. In parallel with a human phase II prevention trial, female ACI rats (n = 8-10/group) received 0, 10, or 100 ppm SDG in the feed. The 100 ppm SDG treatment produced similar blood lignan levels as those observed in our human pilot study. Mammary and ovarian cancer progression were induced using local ovarian DMBA treatment and subcutaneous sustained release 17β-estradiol administered starting at 7 weeks of age. Mammary gland and ovarian tissues were collected at 3 mo after initiation of treatment and examined for changes in epithelial cell proliferation (Ki-67, cell counts), histopathology, and dysplasia scores, as well as expression of selected genes involved in proliferation, estrogen signaling, and cell adhesion. Treatment with SDG normalized several biomarkers in mammary gland tissue (dysplasia, cell number, and expression of several genes) that had been altered by carcinogen. There is no indication that SDG promotes preneoplastic progression in the ovarian epithelium.

Figure 1

Serum concentrations of secoisolariciresinol (A), its major metabolites enterodiol (B) and enterolactone (C), and total lignans (D) after 3 weeks of administration of vehicle control, low dose SDG (10 ppm in feed) or high dose SDG (100 ppm, n=4 in each group. SDG administration elevated concentrations of secoisolariciresinol, enterodiol, enterolactone, and total lignans in a dose dependent fashion.

Figure 2

Serum concentrations of 17β-estradiol (A) and progesterone (B) at 3 months after initiation of carcinogen and treatment with vehicle control, 10 ppm SDG or 100 ppm SDG (n=6 each) in feed. All carcinogen and SDG groups received sustained release estradiol treatment. Median and full range values are shown; the dashed lines denote median hormone concentrations in the procedural controls. While the carcinogen treatment elevated estradiol and reduced progesterone, administration of SDG had no effect on concentrations of these ovarian steroids.

Figure 3

Histology (Carmine, 5×) of whole mount mammary tissue obtained at 3 months from a procedural naïve control (no carcinogen) rat, a rat treated with carcinogen (sustained release E₂/ovarian DMBA) and vehicle control, and carcinogen-treated rats that received 10 or 100 ppm SDG. Rats receiving carcinogen alone had confluent mammary epithelia obscuring the ductal tree. Both SDG groups had fewer epithelia, intermediate to carcinogen controls and naïve, age-matched controls.

Figure 4

Effects of SDG on epithelial dysplasia (A), epithelial cell number (B) and Ki-67 positive cells (C) in mammary glands after 3 months of carcinogen with and without SDG treatment (n=8–10/group). Median and full range values are shown; the dashed lines denote median hormone concentrations in the procedural controls The carcinogen treatment resulted in increases in dysplasia score, epithelial cell number, and a trend towards more Ki-67 positive cells. Administration of 10 ppm SDG normalized the epithelial cell number.

Figure 5

Effect of SDG on ovarian epithelial dysplasia after 3 months of carcinogen with and without SDG treatment (n=8–10/group). Median and full range values are shown; the dashed lines denote median hormone concentrations in the procedural controls.