ERβ selective agonists and genistein mediate antiproliferative and proapoptotic effects in the digestive tract

Estrogens influence many physiological processes, including but not limited to reproduction, bone metabolism cardiovascular health, and homeostatic processes in different tissues. The estrogen receptor subtypes ERa and ERb have distinct tissue expression patterns and the amount of corepressors and coactivators varies within tissues responding to estrogens. ERb is the predominant ER in colon tissue and loss of ERb is associated with advanced stages of colon cancer and tumor cell differentiation, suggesting a protective role for ERb in colon tumorigenesis. To study ER subtype specific effects on intestinal homeostasis in an animal model, ovariectomized (OVX) female Wistar rats were either treated with 17b-estradiol (4µg/KG b.wt/d) (E2), the ERa specific agonist (ERA) 16a-LE2 (10µg/KG b.wt/d), the ERb specific agonist (ERB) 8b-VE2 (100µg/KG b.wt/d) or the phytoestrogen genistein (Gen) (10mg/KG b.wt/d) for 3 weeks. Vehicle treated OVX animals served as controls. The intestinal expression of the proliferation marker (PCNA) and the activity of caspase-3 were analyzed by immunohistochemistry and western blot analysis in small intestine and colon and correlated to uterine wet weights. A strong stimulation of uterine wet weights was detectable in E2 and ERA treated animals, whereas application of Gen resulted only in a faint but significant increase. In ERB treated animals no significant uterus stimulation was detectable. During 3 weeks Gen and ERB treatment, but not treatment with ERA and E2, significantly decreased cell proliferation of mucosa cells of both small intestine and colon. Investigation of apoptotic processes by using an antibody against active caspase-3 revealed that Gen and ERB treatment significantly stimulated the activation of caspase-3 of intestinal mucosa cells. In conclusion, these observations provide evidence that ERb and Gen inhibit intestinal cell proliferation and also have antiapoptotic properties in the digestive tract. These findings may indicate the value of Genistein and ERb selective agonists for the prevention and treatment of colon cancer.