Serum regulates cortisol bioactivity by corticosteroid-binding globulin-dependent and independent mechanisms, as revealed by combined bioassay and physicochemical assay approaches.

CONTEXT: Corticosteroid-binding globulin (CBG) is the principal carrier of natural glucocorticoids in the circulation, and we hypothesized that it modulates glucocorticoid bioactivity (GBA). Alterations in CBG, the presence of noncortisol, naturally occurring glucocorticoids and the use of potent, synthetic glucocorticoids, all make it difficult to assess adrenal activity in-vivo; these problems can be addressed by a glucocorticoid bioassay. DESIGN AND SUBJECTS: A bioassay was developed for serum GBA and a physicochemical ultrafiltration-liquid chromatography-tandem mass spectrometry assay for free serum cortisol (FreeF). We studied individuals homozygous and heterozygous for a nonfunctioning CBG variant (CBG G237V) and healthy controls. RESULTS: FreeF concentrations were similar in healthy controls, and those with absent functional CBG, but surprisingly we found low GBA in CBG null individuals. This may suggest that CBG delivers cortisol to target cells. However, further experiments revealed that dilution of serum in the bioassay caused release of cortisol from CBG, resulting in elevated GBA measurements in all but the CBG G237V homozygotes. Furthermore, we identified a specific and potent inhibitory effect of high concentration serum on glucocorticoid sensitivity of the recipient cells used in the bioassay. Analysis of inflammatory synovial fluid, a filtrate of serum with lower CBG concentration, revealed elevated free cortisol compared to noninflammatory synovial fluid, a change not attributable to interconversion between cortisol and cortisone. CONCLUSIONS: Our findings reveal that dilution of CBG enhances cortisol release, and so bioactivity, and also that serum potently induces glucocorticoid resistance in target cells.

Corticosteroid-binding globulin regulates cortisol pharmacokinetics.

OBJECTIVE: 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. DESIGN AND SUBJECTS: 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. MEASUREMENTS: 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)). RESULTS: 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. CONCLUSIONS: 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.

Biochemical and clinical benefits of unilateral adrenalectomy in patients with subclinical hypercortisolism and bilateral adrenal incidentalomas.

OBJECTIVE: The treatment of subclinical hypercortisolism in patients with bilateral adrenal incidentalomas (AI) is debatable. We aimed to compare the biochemical and clinical outcome of unilateral adrenalectomy vs a conservative approach in these patients. DESIGN: Retrospective study. METHODS: The study included 33 patients with bilateral AI; 14 patients underwent unilateral adrenalectomy of the largest lesion (surgical group), whereas 19 patients were followed up (follow-up group). At baseline and at each follow-up visit, we measured 0800 h plasma ACTH, midnight serum cortisol (MSF), 24-h urinary-free cortisol (UFC) and serum cortisol following a standard 2-day low-dose-dexamethasone-suppression test (LDDST). We evaluated the following comorbidities: arterial hypertension, impaired glucose tolerance or diabetes mellitus, dyslipidemia and osteoporosis. RESULTS: Baseline demographic, clinical characteristics and the duration of follow-up (53.9±21.3 vs 51.8±20.1 months, for the surgical vs the follow-up group) were similar between groups. At the last follow-up visit the surgical group had a significant reduction in post-LDDST cortisol (2.4±1.6 vs 6.7±3.9 µg/dl, P=0.002), MSF (4.3±2 vs 8.8±4.6 µg/dl, P=0.006) and 24-h UFC (50.1±21.1 vs 117.9±42.4 µg/24 h, P=0.0007) and a significant rise in mean±s.d. morning plasma ACTH levels (22.2±9.6 vs 6.9±4.8 pg/ml, P=0.002). Improvement in co-morbidities was seen only in the surgical group, whereas no changes were noted in the follow-up group. CONCLUSIONS: Our early results show that removal of the largest lesion offers significant improvement both to cortisol excess and its metabolic consequences, without the debilitating effects of bilateral adrenalectomy. A larger number of patients, as well as a longer follow-up, are required before drawing solid conclusions.

Two different corticosteroid-binding globulin variants that lack cortisol-binding activity in a greek woman.

BACKGROUND: Corticosteroid-binding globulin (CBG), encoded by SERPINA6, is the principal plasma binding protein for cortisol. Most nonsynonymous single-nucleotide polymorphisms that alter the production or function of CBG occur rarely, and their clinical significance remains obscure. METHODS: Serum and DNA were obtained from a Greek woman with low morning cortisol levels and from family members. SERPINA6 exons were sequenced, and serum CBG was measured by ELISA and cortisol-binding capacity assay. Recombinant CBG variants were produced for detailed functional studies. RESULTS: A novel heterozygous c.1282G>C transversion in exon 5 of SERPINA6, resulting in a p.Trp393Ser (W371S) substitution, was identified in the proband, who was also heterozygous for single-nucleotide polymorphisms encoding the CBG Lyon (D367N) and CBG A224S variants. The proband had no measurable plasma cortisol-binding activity despite a CBG level of 273 nm by ELISA. She inherited CBG W371S from her mother whose plasma cortisol-binding capacity was approximately 50% lower than the CBG measurements by ELISA (314 nm). The proband's father and four children were heterozygous for CBG D367N; their CBG levels by ELISA were normal, but corresponding cortisol-binding capacity measurements were 50% lower. Pedigree analysis revealed that W371S segregates with A224 and that D367N and W371S segregate separately. Recombinant CBG D367N and CBG W371S had no measureable cortisol-binding activity. CONCLUSION: A new CBG Athens (W371S) variant that lacks cortisol-binding activity has been identified in a carrier of the cortisol-binding deficient CBG Lyon (D367N) variant. Analyses of CBG levels in this pedigree illustrate how immunoassays fail to accurately reflect cortisol-binding activity.

Salivary cortisone is a potential biomarker for serum free cortisol.

CONTEXT: Salivary cortisol measurement is used as a practical surrogate for serum free cortisol. However, parotid tissue harbors 11ß-hydroxysteroid dehydrogenase (11ß-HSD2) activity converting cortisol to cortisone. OBJECTIVE: This study was designed to assess the impact of parotid 11ß-HSD2 activity on the measurement of salivary cortisol. PATIENTS, DESIGN, AND OUTCOME MEASURES: Study participants with changes in circulating corticosteroid-binding globulin (CBG) (±oral contraceptive, functionally CBG null) and controls were studied during adrenal stimulation by ACTH and postoral and iv hydrocortisone administration. Simultaneous serum and saliva samples were collected for the measurement of total serum cortisol (SerF) by immunoassay, and unbound cortisol and cortisone in serum (FreeF and FreeE) and saliva (SalF and SalE) by liquid chromatography-tandem mass spectrometry. RESULTS: ACTH stimulation increased SerF, FreeF, SalF, SalE, but not FreeE in all individuals. SerF significantly decreased after stopping oral contraceptive administration, but FreeF, SalF and SalE remained unchanged. In the hydrocortisone administration study, individual FreeF and SalE curves were nearly identical and SalE closely reflected FreeF in all participants, irrespective of CBG changes. The highest correlation in all (n = 537) matched serum-saliva samples was between SalE and FreeF (r = 0.95, P < 0.0001), and there was no evidence of 11ß-HSD2 saturation. CONCLUSION: Salivary cortisol is a useful surrogate for circulating free cortisol, but its concentration is determined both by serum free cortisol and parotid metabolism to cortisone. We have shown that salivary cortisone closely reflects free serum cortisol after adrenal stimulation and hydrocortisone administration and is unaffected by CBG changes. Salivary cortisone has potential as a useful surrogate for serum free cortisol in research and clinical assessment, and further research in states of chronic glucocorticoid excess is now needed.

Novel corticosteroid-binding globulin variant that lacks steroid binding activity.

BACKGROUND: Corticosteroid-binding globulin (CBG) is the principal carrier for glucocorticoids in the circulation and a regulator of their bioavailability. Inherited CBG deficiencies are rarely reported, and only three causative mutations in four families have been described. PATIENTS, METHODS, AND RESULTS: In a 26-yr-old female with hypotension, fatigue, and undetectable total serum cortisol at presentation, we have identified a novel homozygous c.776g>t transversion in exon 3 of the CBG (SERPINA6) gene. This results in a p.Gly237Val substitution that is predicted to influence the positioning of two ß-sheets that constitute part of the CBG steroid-binding site. Two siblings were also homozygous for the variant, whereas her mother and an unaffected sibling were heterozygous. No other symptomatic family members were identified apart from the proband. Individuals homozygous for the variant had serum CBG levels below the reference range when measured by RIA, but CBG was unmeasurable in cortisol-binding capacity assays. In the same individuals, we observed very low baseline and stimulated total serum cortisol levels but normal free serum and salivary cortisol and plasma ACTH. In a study of ultradian cortisol pulsatility, increased pulse frequency was only observed in the proband. CONCLUSION: We describe a novel CBG variant that lacks steroid binding activity. All mutant homozygotes have very low total serum cortisol, but normal free serum cortisol levels. The only biochemical feature to distinguish the symptomatic subject was increased cortisol pulsatility, and we suggest that this may influence glucocorticoid signaling and contribute to symptoms previously associated with CBG deficiency.