Abstract | Objective: Sex hormone-binding globulin (SHBG) binds and transports testosterone and estradiol in plasma. The possibility that SHBG is a mixture of transporting proteins has been postulated. We analyzed in parallel the effects of obesity status on the levels and binding capacity of circulating SHBG and their relationship with testosterone and estradiol.

Design: Anthropometric measures and plasma were obtained from apparently healthy young (i.e. 35 ± 7 years) premenopausal women (n=32) and men (n=30), with normal weight and obesity (BMI>30 kg·m-2).

Methods: SHBG protein (Western blot), as well as the plasma levels of testosterone, estradiol, cortisol and insulin (ELISA) were measured. Specific binding of estradiol and testosterone to plasma SHBG was analyzed using tritium-labelled hormones.

Results: Significant differences in SHBG were observed within the obesity status and gender, with discordant patterns of change in testosterone and estradiol. In men, testosterone occupied most of the binding sites. Estrogen binding was much lower in all subjects. Lower SHBG of morbidly obese (BMI>40 kg·m-2) subjects affected testosterone but not estradiol. The ratio of binding sites to SHBG protein levels, was constant for testosterone, but not for estradiol. The impact of gender was maximal in morbid obesity, with men showing the highest binding / SHBG ratios.

Conclusions: The results reported here are compatible with SHBG being a mixture of at least two functionally different hormone-binding globulins, being affected by obesity and gender, and showing different structure, affinities for testosterone and estradiol, and also different immunoreactivity.

Maria del Mar Grasa, José Gulfo, Núria Camps, Rosa Alcalá, Laura Monserrat, José María Moreno-Navarrete, F Ortega, Montserrat Esteve, Xavier Remesar, José Antonio Fernández-López, José Manuel Fernández-Real and Marià Alemany⇑

– Author Affiliations

M Grasa, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
J Gulfo, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
N Camps, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
R Alcalá, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
L Monserrat, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
J Moreno-Navarrete, Endocrinology and Diabetes, Girona Institute of Biomedical Research and Hospital of Girona "Dr. Trueta", Girona, Spain
F Ortega, Endocrinology and Diabetes, Girona Institute of Biomedical Research and Hospital of Girona "Dr. Trueta", Girona, Spain
M Esteve, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
X Remesar, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
J Fernández-López, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain
J Fernández-Real, Endocrinology and Diabetes, Girona Institute of Biomedical Research and Hospital of Girona "Dr. Trueta", Girona, Spain
M Alemany, Department of Biochemistry and Molecular Biomedicine, University of Barcelona, Faculty of Biology, Barcelona, Spain

Correspondence: Marià Alemany, Email: malemany@ub.edu

Published online before print January 11, 2017, doi: 10.1530/EJE-16-0834
Eur J Endocrinol January 11, 2017 EJE-16-0834

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