noun, plural: estrones
Estrone (E1) is one of the major endogenous estrogens of humans and other vertebrates. Other endogenous estrogens are estradiol (E2), estriol (E3), and estetrol (E4). Estrone is an estrogenic hormone with a chemical formula of C18H22O2.
Estrone is produced naturally in the gonads and adipose tissue. In females, the estrone is produced mainly in the ovarian follicles. It is also produced in the placental tissues during pregnancy. The biosynthesis of estrone begins with the use of cholesterol as the initial metabolite. Series of enzymatic steps lead to the production of androstenedione. The androstenedione is converted into estrone through the catalytic action of aromatase. Apart from this, estrone can also be formed by reversibly transforming estradiol into estrone through the action of the enzyme, 17β-hydroxysteroid dehydrogenase. The conversion of estradiol into estrone occurs in various tissues, e.g. in liver, mammary glands, and uterus.
Estrones that are released into the bloodstream are bound mainly to albumin. Some are bound to sex hormone-binding globulin whereas few of them remain free and unbound. When an estrone reaches its target cell, it diffuses readily into the cell across the cell membrane. It acts as an agonist of estrogen receptors (ERα and ERβ). However, estrones are relatively weak estrogen. They have less binding affinity to estrogen receptors than estradiol.
Estrones are hydroxylated by cytochrome P450 enzymes into catechol estrogens or into estriol in the liver. They may further serve as a precursor or metabolic intermediate of estradiol. Estrones are excreted from the body in the form of estrogen conjugates in the urine.
Estrone is also produced synthetically from urine of pregnant women or from ergosterol. In the commercial form, it is used as a medication to correct estrogen levels in patients with estrogen deficiency.