Corticosteroid-binding globulin regulates cortisol pharmacokinetics
Corticosteroid-binding globulin (CBG) is the principal carrier for cortisol in the circulation. Variations in CBG-binding capacity are predicted to alter total serum cortisol disposition, but free serum cortisol is believed to be unaffected. Unbound cortisol pharmacokinetics (PK) have not been studied in the context of CBG changes. We aimed to assess the regulation of cortisol PK by CBG. Women on oestrogens [oral contraceptive pill, (OCP)], patients homozygous for a nonfunctioning CBG variant (CBG null) and healthy controls (HV) were studied before and after IV and oral administration of hydrocortisone 20 mg. PK parameters were studied for total serum cortisol (SerF), free serum cortisol (FreeF) and cortisone (FreeE), and salivary cortisol (SalF) and cortisone (SalE): area under the curve (AUC), clearance (CL), half-life and volume of distribution (V(d)). Following IV hydrocortisone, AUC and half-life of SerF were significantly higher in the OCP group and lower in the CBG null. SerF CL and V(d) were significantly lower in the OCP group and increased in the CBG null, compared to HV. PK parameters for FreeF and the salivary biomarkers were not different between the CBG null and HV, although OCP patients still had higher AUC compared to HV and prolonged half-life. These findings were confirmed following oral hydrocortisone, but concentration-time profiles were highly heterogeneous and SalF interpretation was problematic because of oral contamination. We have demonstrated that CBG has a distinct effect on cortisol PK. When CBG binding is disrupted, FreeF retains normal PK characteristics, although CBG null patients lack a CBG-bound pool of readily releasable cortisol. Women on oestrogens may have altered free serum cortisol kinetics and thus may be potentially overexposed to glucocorticoids.
[Show abstract] [Hide abstract] ABSTRACT: Corticosteroid-binding globulin (CBG) is the principal transport protein of glucocorticoids. Approximately 80-90% of serum cortisol binds to CBG with high affinity and only about 5% of cortisol remain unbound and is considered biologically active. CBG seems to modulate and influence the bioavailability of cortisol to local tissues. In this review, we will discuss physicochemical properties of CBG and structure of CBG in the mechanisms of binding and release of cortisol. This review describes several factors affecting CBG functions, such as genetic factors or temperature. Furthermore, clinical implications of CBG abnormalities and the measurement of CBG and its use for assessment of free cortisol levels are described in this review.0Comments 0Citations
- "The three equations to calculate free cortisol similarly perform rather poorly in this condition. Accordingly, for the accurate assessment measurement of unbound steroids by novel techniques such as ultra-filtration and LC-MS/MS are advocated . "
[Show abstract] [Hide abstract] ABSTRACT: Background Steroid profiling for diagnosis of endocrine disorders featuring disordered production of steroid hormones is now possible from advances in liquid chromatography with tandem mass spectrometry (LC–MS/MS). Adrenal venous (AV) measurements of aldosterone and cortisol are a standard practice in the clinical work-up of primary aldosteronism, but do not yet take advantage of steroid profiling. Methods A novel LC–MS/MS based method was developed for simultaneous measurement of 15 adrenal steroids: aldosterone, corticosterone, 11-deoxycorticosterone, progesterone, pregnenolone, cortisone, cortisol, 11-deoxycortisol, 17-hydroxyprogesterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone-sulfate, 21-deoxycortisol, 18-oxocortisol and 18-hydroxycortisol. These were compared in peripheral venous (pV) and AV plasma from 70 patients undergoing AV sampling with and without cosyntropin stimulation. Aldosterone and cortisol levels measured by LC–MS/MS were compared with those measured by immunoassay. Results Reproducibility of measurements with coefficients of variation ≤10% as well as analytical sensitivity sufficient to measure low pV levels particularly of aldosterone demonstrate the utility of the assay for profiling adrenal steroids in primary aldosteronism. Method comparisons indicated assay and concentration dependent differences of cortisol and aldosterone concentrations measured by immunoassay and LC–MS/MS. Median AV/pV ratios of 11-deoxycortisol (53.0), 17-hydroxyprogesterone (33.4), pregnenolone (62.4), androstenedione (40.6) and dehydroepiandrosterone (33.3) were 2.9- to, 5.4-fold larger than those for cortisol (11.6), with additionally generally larger increases than for cortisol with than without cosyntropin stimulation. Conclusion Our LC–MS/MS assay, in addition to improvements over existing immunoassay measurements of aldosterone and cortisol, offers profiling of 13 other adrenal steroids, providing a potentially useful method for the clinical work-up of patients with primary aldosteronism. In particular, the larger AV/pV ratios of several steroids compared to cortisol suggest more sensitive alternatives to the latter for assessing positioning of AV sampling catheters.0Comments 10Citations
- "Given that cortisol and DHEAS are the two most abundantly produced adrenal steroids, the small AV/pV ratios in their plasma concentrations compared to other adrenal steroids may seem contradictory, but are easily explained by differences in circulatory clearances. Protein binding of most circulating cortisol presumably contributes to relatively slow clearance of total plasma cortisol  . The much slower circulatory clearance of cortisol than of metanephrine, for example, means that this latter metabolite of adrenaline shows much larger AV/pV ratios than cortisol and consequently provides a superior analyte to assess selectivity of AVS . "
[Show abstract] [Hide abstract] ABSTRACT: In the metabolic syndrome, glucocorticoid activity is increased, but circulating levels show little change. Most of blood glucocorticoids are bound to corticosteroid-binding globulin (CBG), which liver expression and circulating levels are higher in females than in males. Since blood hormones are also bound to blood cells, and the size of this compartment is considerable for androgens and estrogens, we analyzed whether sex or eating a cafeteria diet altered the compartmentation of corticosterone in rat blood. The main corticosterone compartment in rat blood is that specifically bound to plasma proteins, with smaller compartments bound to blood cells or free. Cafeteria diet increased the expression of liver CBG gene, binding plasma capacity and the proportion of blood cell-bound corticosterone. There were marked sex differences in blood corticosterone compartmentation in rats, which were unrelated to testosterone. The use of a monoclonal antibody ELISA and a polyclonal Western blot for plasma CBG compared with both specific plasma binding of corticosterone and CBG gene expression suggested the existence of different forms of CBG, with varying affinities for corticosterone in males and females, since ELISA data showed higher plasma CBG for males, but binding and Western blot analyses (plus liver gene expression) and higher physiological effectiveness for females. Good cross- reactivity to the antigen for polyclonal CBG antibody suggests that in all cases we were measuring CBG.The different immunoreactivity and binding affinity may help explain the marked sex-related differences in plasma hormone binding as sex-linked different proportions of CBG forms.0Comments 1Citation
- "In obesity, CBG levels or their affinity for glucocorticoids are decreased ; insulin resistance and inflammation also contribute to decrease CBG levels [20,23]. CBG, in addition to transporting glucocorticoids in plasma  may control or facilitate their entry in the cell . CBG can bind to membrane proteins , and it has been found that, at least in adipose tissue, CBG may control glucocorticoid entry in the cells acting as a barrier . "