Common misconceptions about sex hormone-binding globulin

Sex hormone-binding globulin (SHBG), also referred to in the literature as sex steroid-binding globulin (SSBG) or testosterone-estradiol-binding globulin (TeBG), is a homodimeric plasma glycoprotein and a member of the laminin G-like domain protein family. It circulates as a 90–100 kDa homodimer and functions as the principal high-affinity transport protein for testosterone, dihydrotestosterone, and 17β-estradiol in human plasma. The evidence block provided for this page does not supply the full amino acid sequence, the exact molecular weight to the decimal, or a CAS number, so those identifiers are not stated here.

The work summarised on this page centres on the hepatic synthesis of SHBG and its suppression by hyperinsulinaemia, a relationship described within the insulin-receptor signalling axis and the broader insulin-resistance pathway in polycystic ovary syndrome (PCOS) [1].

Research Studies

SHBG and hyperinsulinaemia in PCOS

In the population described in the registered trial record, hyperinsulinaemia was reported to enhance ovarian androgen production and to reduce hepatic SHBG synthesis, thereby aggravating hyperandrogenism and reproductive abnormalities [1]. This is a mechanistic description of the insulin–SHBG–androgen relationship in women with PCOS, not a claim about SHBG in healthy populations or in men.

SHBG and DPP-4 inhibition in PCOS

Vildagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, enhances endogenous incretin activity and may improve insulin sensitivity and glucose homeostasis [1]. Emerging evidence cited in that record suggests DPP-4 inhibition may also influence body weight, androgen excess, and inflammation [1]. The evidence block does not report a measured change in SHBG concentration in response to vildagliptin, so no such claim is made here.

SHBG and metformin in PCOS

The trial record compares dapagliflozin with metformin in patients with PCOS [1]. Because metformin acts on insulin sensitivity and hyperinsulinaemia is described as a suppressor of hepatic SHBG synthesis, SHBG is a plausible downstream marker in that comparison [1]. The evidence block does not provide SHBG outcome values for either arm, so the direction or magnitude of any effect is not stated.

SHBG and dapagliflozin in PCOS

Dapagliflozin is the comparator agent in the same registered study of patients with PCOS [1]. As with metformin, any SHBG response would be expected to operate through the insulin–hepatic synthesis axis described in that record [1]. No SHBG result is reported in the evidence block, and none is asserted here.

SHBG and hepatic steatosis in adolescent girls with PCOS

A separate prospective, observational, cross-sectional mechanistic pilot study will evaluate whether PCOS contributes to hepatic steatosis in adolescent girls independently of adiposity [2]. A total of 150 girls aged 10–18 years will be enrolled into three groups of 50: girls with PCOS and obesity, age- and body mass index-matched girls with obesity but without PCOS, and healthy normal-weight girls [2]. Each participant will undergo a single evaluation comprising anthropometry, clinical and biochemical phenotyping, transient elastography with controlled attenuation parameter and two-dimensional shear wave elastography, and a single venous blood sample [2]. The evidence block does not state that SHBG is among the biochemical analytes measured, so SHBG is not claimed as an endpoint of that study.

SHBG and the insulin-resistance pathway in PCOS

Insulin resistance is described as playing a central role in the pathophysiology of PCOS [1]. The proposed sequence in that record runs from hyperinsulinaemia to enhanced ovarian androgen production and to reduced hepatic SHBG synthesis, with the two effects jointly aggravating hyperandrogenism and reproductive abnormalities [1]. This is a pathway description in women with PCOS; it is not evidence of causation in other populations.

SHBG and adiposity in adolescent PCOS cohorts

The adolescent study design explicitly matches girls with obesity but without PCOS to girls with PCOS and obesity on age and body mass index [2]. That matching is intended to separate the contribution of PCOS from that of adiposity [2]. Because SHBG is not named as an analyte in the evidence block, no statement is made here about SHBG concentrations across those three groups.

SHBG and androgen excess in PCOS

Hyperandrogenism is one of the defining features of PCOS in the trial record, alongside ovulatory dysfunction and polycystic ovarian morphology [1]. Reduced hepatic SHBG synthesis is presented as one mechanism by which hyperinsulinaemia aggravates that hyperandrogenism [1]. The evidence block does not quantify free androgen indices or SHBG-bound fractions, so those values are not reported.

Comparison of the two registered studies

What the evidence does not establish

• No animal-only or in vitro SHBG data are supplied in the evidence block, so none are described.
• No SHBG reference ranges, binding affinities, or half-life values are supplied, so none are stated.
• No SHBG response to any intervention is quantified in the evidence block.

If you are reading this for personal health reasons

The materials described on this page are supplied for laboratory research use only, and we do not provide dosing, diagnostic, or medical guidance of any kind. Nothing here is a recommendation to use any compound. Anyone considering a compound for themselves should speak to a licensed clinician.

Sources

• [1] Efficacy of Dapagliflozin Versus Metformin in Patients With Polycystic Ovary Syndrome — ClinicalTrials.gov
• [2] Biomarker Panel for PCOS-Associated Liver Steatosis in Adolescent Girls (COMPASS-pedPCOS) — ClinicalTrials.gov