title: Effects of sex hormone-binding globulin (SHBG) on androgen bioactivity in vitro.
abstract: Biochemical assessments of androgen status (hyper- or hypoandrogenism) are usually based on serum testosterone concentrations. According to the free hormone hypothesis, sex hormone-binding globulin (SHBG) determines free and bioavailable testosterone concentrations. Previous studies have suggested that in vitro androgen bioassay results may also be influenced by SHBG and correlate with free or bioavailable testosterone concentrations. To test this hypothesis, we established a stable HEK293 cell line with high expression of the human androgen receptor (AR) and a luciferase reporter downstream of a classical androgen response element. Importantly, we demonstrate that bioassay results are sensitive to dilution effects which increase apparent bioactivity in an SHBG-dependent manner. We therefore adopted a method using undiluted serum, which reduced cell proliferation but did not significantly affect the luciferase signal, cell viability or cytotoxicity. To correct for serum matrix effects, we applied signal correction based on internal controls with AR agonists or antagonists. Using this method, we provide direct evidence that in vitro androgen bioactivity reflects the inhibitory effects of SHBG, and correlates with free or bioavailable testosterone concentrations in adult hypogonadal men receiving androgen replacement therapy. In men receiving anti-androgens, serum bioactivity decreased tenfold while serum testosterone concentrations decreased only four-fold. Further pilot results in prostate cancer patients showed that androgen synthesis inhibitors result in more complete inhibition of androgen bioactivity than gonadorelin-based androgen deprivation therapy, even in patients whose testosterone concentrations were undetectable by mass spectrometry. We conclude that in vitro androgen reporter bioassays are useful tools to study how androgen bioactivity in serum is determined by androgens, anti-androgens as well as SHBG, provided that dilution and matrix effects are accounted for.
authors: Laboratory of Molecular Endocrinology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49 PO Box 901, 3000, Leuven, Belgium; Gerontology and Geriatrics, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49 PO Box 7003, 3000, Leuven, Belgium.
authors: Michaël R
authors: MR
authors: Laurent
authors: Laboratory of Molecular Endocrinology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49 PO Box 901, 3000, Leuven, Belgium.
authors: Christine
authors: C
authors: Helsen
authors: Laboratory of Molecular Endocrinology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49 PO Box 901, 3000, Leuven, Belgium; Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49 PO Box 902, 3000, Leuven, Belgium.
authors: Leen
authors: L
authors: Antonio
authors: Laboratory of Molecular Endocrinology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49 PO Box 901, 3000, Leuven, Belgium.
authors: Dieter
authors: D
authors: Schollaert
authors: Laboratory for Experimental Urology, Organ Systems, Department of Development and Regeneration, KU Leuven, Herestraat 49 PO Box 7003-41, 3000, Leuven, Belgium.
authors: Steven
authors: S
authors: Joniau
authors: Laboratory Medicine, University Medical Centre Groningen, Hanzeplein 1 PO Box 30001, 9700 RB, Groningen, The Netherlands.
authors: Michel J
authors: MJ
authors: Vos
authors: Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49 PO Box 902, 3000, Leuven, Belgium.
authors: Brigitte
authors: B
authors: Decallonne
authors: Department of Cellular and Physiological Sciences, University of British Columbia, 2350 Health Sciences Mall, V6T 1Z3, Vancouver, B.C., Canada.
authors: Geoffrey L
authors: GL
authors: Hammond
authors: Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49 PO Box 902, 3000, Leuven, Belgium.
authors: Dirk
authors: D
authors: Vanderschueren
authors: Laboratory of Molecular Endocrinology, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49 PO Box 901, 3000, Leuven, Belgium. Electronic address: frank.claessens@med.kuleuven.be.
authors: Frank
authors: F
authors: Claessens
mesh_terms: D000328:Adult; D000368:Aged; D000728:Androgens / Q000494:pharmacology*; D000818:Animals; D001681:Biological Assay; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008822:Mice, Transgenic; D008875:Middle Aged; D050505:Mutant Proteins / Q000378:metabolism; D010865:Pilot Projects; D011471:Prostatic Neoplasms / Q000473:pathology; D017208:Rats, Wistar; D044967:Serum / Q000378:metabolism; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D055815:Young Adult
chemical_list: D000728:Androgens; D050505:Mutant Proteins; D012738:Sex Hormone-Binding Globulin
keywords: Androgen receptor; Androgens; Bioassay; Luciferase; Sex hormone-binding globulin