ABSTRACT
Aromatase is a member of the cytochrome P450 enzyme family and a product of the CYP 19A1 gene [1]. This membrane-bound protein (aromatase) is the rate limiting enzyme in the conversion of androstenedione to estrone (E1) and of testosterone to estradiol (E2) (Figure 1). Aromatase consists of two components: the hemoprotein aromatase cytochrome P450 encoded by the CYP19A1 gene and expressed only in steroidogenic cells, and the flavoprotein NADPH-cytochrome P450 reductase, expressed ubiquitously in many cell types [2-4]. The enzyme (aromatase) is localized in the endoplasmic reticulum of a cell, and catalyzes three hydroxylation reactions that convert androstenedione to E1 and testosterone to E2 [5,6]. The enzyme activity is increased by alcohol, age, obesity, insulin and
gonadotropins [7]. The CYP19A1 gene is highly expressed in the human placenta and in the granulosa cells of the ovarian follicles. However, many nonglandular tissues including liver, muscle, brain, bone, cartilage, blood vessels, breast (both normal and carcinogenic) and adipose tissues have lower level of CYP 19A1 expression under the control of tissue-specific promoters [8]. Inhibition of aromatase enzyme activity has been shown to reduce estrogen production throughout the body and aromatase inhibitors (AIs) are being used clinically to retard the development and progression of hormone-responsive breast cancer [6,7].
