17alpha-estriol

17alpha-Estriol is a naturally occurring steroid hormone belonging to the estrogen family. It is the 17-alpha epimer of estriol and considered a minor hydroxylated metabolite of estradiol. Functionally it acts as a relatively weak estrogen due to its low affinity for the estrogen receptor alpha (ERα), but it is a selective agonist for the estrogen receptor beta (ERβ). Notably, in vitro studies have shown that it can be approximately 400-fold more potent than estradiol in inhibiting TNF-alpha-induced VCAM-1 expression. Its primary mechanism involves binding to and activating estrogen receptors—mainly ERβ—leading to modulation of gene transcription and downstream physiological effects[2][4]. There are no widely recognized brand names or pharmaceutical products containing this specific epimer; most clinical use and research focus on other estrogens such as estradiol or standard estriol.

Other names

17alpha-Estriol17α-Epiestriol16α-hydroxy-17α-estradiolestra-1,3,5(10)-triene-3,16α,17α-triol