Estrogen Dosing in Turner Syndrome: Pharmacology and Metabolism

Overview

Estrogen is necessary for feminization during puberty and to decrease bone resorption, the latter critical for the achievement of peak bone mass and normal bone health in the female. The practicing pediatric endocrinologist often faces the dilemma of how to best feminize girls with hypogonadism (lack of estrogen), manifested as delayed or arrested puberty, due to disorders of the brain or the ovaries. We propose a series of studies to address which type, dose, and route of delivery of estrogen are suitable choices in feminizing and sustaining estrogen concentrations in adolescent girls with Turner syndrome. To accomplish this we will study girls/young woman between the ages of 13 to 20 with Turner Syndrome in 2 protocols. In Protocol # 1 we will study 24 girls with TS, they will receive 3 different estrogen preparations, either by mouth or via a patch for a total of 6 weeks. They will come to the clinical research center for blood draws after 2 wks of taking the estrogen. With this study, we hope to learn how the body responds to estrogen differently, depending on the form estrogen is given and how high, estrogen levels gets in the blood in these girls with Turner Syndrome. We will be comparing these patients estrogen levels to girls that menstruate normally and do not have Turner Syndrome. In Protocol #2, 40 patients with TS will be recruited; these patients will take estrogen for 1 year, either by mouth or via a patch. Patients will come to the lab for blood drawn in 7 occasions and we will measure estrogen levels as well as other hormones and lipid levels. We will also perform a Dual-energy X-ray absorptiometry (DXA) study (like an X ray) to assess body composition and bone mineralization. We will adjust doses based on the estrogen levels we find. With this study we hope to learn how estrogen affects body composition, i.e., the amount of fat vs. muscle, and how different forms of estrogen affect blood cholesterol and other hormones. This study will allow us to understand better how to best replace young woman with Turner Syndrome with estrogen.

Data on the specific effects and bioequivalency of the different forms of estrogen are lacking, and in the young adolescent age group in particular, virtually non-existent. This has been complicated further by the difficulty in accurately interpreting estradiol assay results as the conventional radioimmunoassays (RIA) for estradiol are inaccurate and insensitive measuring very small concentrations in plasma. There is wide variation in the types of estrogens used for estrogen replacement, as well as doses and route of administration. Girls with Turner syndrome (TS) represent an important case study for these issues as they have early primary gonadal insufficiency or failure many years before the achievement of peak bone mass. Hence, a study of the effects of different estrogen compounds in this patient population offers a unique model that eliminates the confounding effects of other products produced by the intact gonad. Since in this condition it is imperative that estrogen replacement is started during the adolescent years and continued for several decades, this issue becomes highly relevant to these young women's health.Our specific aims are to: 1. to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) and relative biological potency of different oral vs. transdermal preparations of estradiol using state-of-the-art tandem mass spectrometry assays and recombinant cell bioassays; 2. to investigate the differential, long term metabolic effects of oral vs. transdermal estrogen replacement, specifically the effects on lipid and protein metabolism as well as body composition in this patient population; 3. to determine feasibility of estrogen concentration-based dosing in puberty and 4. To characterize the metabolic profile of TS girls previously treated with GH. To accomplish this we will study girls/young woman between ages 13 to 20 with TS in 2 protocols. Protocol #1 will be a study of the pharmacokinetic/pharmacodynamic (PK/PD) of 3 different preparations of estrogen in different doses. Protocol #2 will be a one year longitudinal study of the effects of oral vs. transdermal (TD) estrogen on body composition, hormones and growth factors.