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2-Hydroxyestrone

2-Hydroxyestrone (2-OHE1), also known as estra-1,3,5(10)-trien-2,3-diol-17-one, is an endogenous, naturally occurring catechol estrogen and a major metabolite of estrone and estradiol. 2-Hydroxyestrone belongs to the class of organic compounds known as estrogens and derivatives. These are steroids with a structure containing a 3-hydroxylated estrane. Thus, 2-Hydroxyestrone is considered to be a steroid molecule. It is formed irreversibly from estrone in the liver and to a lesser extent in other tissues via 2-hydroxylation mediated by cytochrome P450 enzymes, mainly the CYP3A and CYP1A subfamilies. 2-OHE1 is the most abundant catechol estrogen in the body. 2-Hydroxyestrone is found in all vertebrates. Vertebrates, especially mammals, metabolizes estrogen into two major pathways and one minor. The two major pathways lead to 2-hydroxyestrone and 16a-hydroxyestrone (2-OHE1 and 16a OHE1, respectively). The minor pathway leads to 4-hydroxyestrone (4-OHE1). 2a-hydroxyestrone is considered to be the good steroid metabolite (PMID: 8943806) as 2-hydroxyestrone does not stimulate cell growth and it blocks the action of stronger estrogens that may be carcinogenic. 2-hydroxyestrone is not significantly uterotrophic, whereas other hydroxylated estrogen metabolites including 2-hydroxyestradiol, 16a-hydroxyestrone, estriol, 4-hydroxyestradiol, and 4-hydroxyestrone all are. A low urinary ratio of 2-hydroxyestrone to 16-alpha-hydroxyestrone is a strong predictor of breast cancer risk among women (PMID: 19502596).