Review

Authors: Anna L Goldman, Shalender Bhasin, Frederick C W Wu...

In the circulation, testosterone and other sex hormones are bound to binding proteins, which play an important role in regulating their transport, distribution, metabolism, and biological activity. According to the free hormone hypothesis, which has been debated extensively, only the unbound or free fraction is biologically active in target tissues. Consequently, accurate determination of the partitioning of testosterone between bound and free fractions is central to our understanding of how its delivery to the target tissues and biological activity are regulated and consequently to the diagnosis and treatment of androgen disorders in men and women. Here, we present a historical perspective on the evolution of our understanding of the binding of testosterone to circulating binding proteins. On the basis of an appraisal of the literature as well as experimental data, we show that the assumptions of stoichiometry, binding dynamics, and the affinity of the prevailing models of testosterone binding to sex hormone-binding globulin and human serum albumin are not supported by published experimental data and are most likely inaccurate. This review offers some guiding principles for the application of free testosterone measurements in the diagnosis and treatment of patients with androgen disorders. The growing number of testosterone prescriptions and widely recognized problems with the direct measurement as well as the computation of free testosterone concentrations render this critical review timely and clinically relevant.

Topics: Humans; Serum Albumin, Human; Sex Hormone-Binding Globulin; Testosterone; Transcortin

PubMed: 28673039
DOI: 10.1210/er.2017-00025

Review

Authors: A Chevais, M M Gadzhimuradova, D G Beltsevich...

Steroid hormones take an active part in a whole complex of physiological processes that are fundamental for the normal development and functioning of the human body. In the bloodstream steroid hormones are bind with specific transport proteins, in particular with transcortin. The matter of changes in hormone-protein complex in various conditions were actively studied in the second half of the twentieth century, but currently this issue has been taken a back seat by the development of high-precision diagnostic methods of steroid hormones determining. This literature review presents accumulated data on the physicochemical properties of transcortin, genetic factors affecting its synthesis and secretion. Published data on its physiological significance in the human body are analyzed in detail within the framework of not only the "free hormone" hypothesis, but also the reservoir hypothesis. Research results have shown that the synthesis of transcortin has been detected in some extrahepatic tissues, including the adrenal glands, however, its role is unknown.

Topics: Humans; Transcortin; Hormones; Adrenal Glands

PubMed: 39868445
DOI: 10.14341/probl13482

Review

Authors: Geoffrey L Hammond

Biologically active steroids are transported in the blood by albumin, sex hormone-binding globulin (SHBG), and corticosteroid-binding globulin (CBG). These plasma proteins also regulate the non-protein-bound or 'free' fractions of circulating steroid hormones that are considered to be biologically active; as such, they can be viewed as the 'primary gatekeepers of steroid action'. Albumin binds steroids with limited specificity and low affinity, but its high concentration in blood buffers major fluctuations in steroid concentrations and their free fractions. By contrast, SHBG and CBG play much more dynamic roles in controlling steroid access to target tissues and cells. They bind steroids with high (~nM) affinity and specificity, with SHBG binding androgens and estrogens and CBG binding glucocorticoids and progesterone. Both are glycoproteins that are structurally unrelated, and they function in different ways that extend beyond their transportation or buffering functions in the blood. Plasma SHBG and CBG production by the liver varies during development and different physiological or pathophysiological conditions, and abnormalities in the plasma levels of SHBG and CBG or their abilities to bind steroids are associated with a variety of pathologies. Understanding how the unique structures of SHBG and CBG determine their specialized functions, how changes in their plasma levels are controlled, and how they function outside the blood circulation provides insight into how they control the freedom of steroids to act in health and disease.

Topics: Animals; Estradiol; Glucocorticoids; Humans; Progesterone; Serum Albumin; Sex Hormone-Binding Globulin; Testosterone; Transcortin

PubMed: 27113851
DOI: 10.1530/JOE-16-0070

Review

Authors: Jessica H Lee, Emily J Meyer, Marne A Nenke...

Corticosteroid-binding globulin (CBG) is a 50-60 kDa circulating glycoprotein with high affinity for cortisol. CBG is adapted for sepsis; its cortisol binding is reduced reversibly by pyrexia and acidaemia, and reduced irreversibly by neutrophil elastase (NE) cleavage, converting high cortisol-binding affinity CBG to a low affinity form. These characteristics allow for the targeted delivery of immunomodulatory cortisol to tissues at the time and body site where cortisol is required in sepsis and septic shock. In addition, high titer inflammatory cytokines in sepsis suppress CBG hepatic synthesis, increasing the serum free cortisol fraction. Recent clinical studies have highlighted the importance of CBG in septic shock, with CBG deficiency independently associated with mortality.

Topics: Humans; Hydrocortisone; Shock, Septic; Transcortin; Sepsis; Fever

PubMed: 36681594
DOI: 10.1016/j.tem.2023.01.002

Review

Authors: Kate C Verbeeten, Alexandra H Ahmet

Cortisol is a hydrophobic molecule that is largely bound to corticosteroid-binding globulin (CBG) in the circulation. In the assessment of adrenal insufficiency, many clinicians measure a total serum cortisol level, which assumes that CBG is present in normal concentrations and with a normal binding affinity for cortisol. CBG concentration and affinity are affected by a number of common factors including oral contraceptive pills (OCPs), fever and infection, as well as rare mutations in the serine protease inhibitor A6 (SERPINA6) gene, and as such, total cortisol levels might not be the ideal way to assess adrenal function in all clinical circumstances. This paper reviews the limitations of immunoassay and liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the measurement of total cortisol, the challenges of measuring free serum cortisol directly as well as the difficulties in calculating an estimated free cortisol from total cortisol, CBG and albumin concentrations. Newer approaches to the evaluation of adrenal insufficiency, including the measurement of cortisol and cortisone in the saliva, are discussed and a possible future role for these tests is proposed.

Topics: Adrenal Insufficiency; Algorithms; Child; Cortisone; Endocrinology; Humans; Hydrocortisone; Hydrophobic and Hydrophilic Interactions; Hypothalamo-Hypophyseal System; Mutation; Pediatrics; Pituitary-Adrenal System; Practice Guidelines as Topic; Reproducibility of Results; Saliva; Serum Albumin, Human; Transcortin

PubMed: 29194043
DOI: 10.1515/jpem-2017-0270

Observational Study

Authors: Eric L Wald, Carl L Backer, Joseph A Dearani...

BACKGROUND

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction may be partially responsible for the hemodynamic instability experienced by infants after cardiopulmonary bypass (CPB). We report the full spectrum of the HPA response surrounding CPB for infant congenital cardiac surgery.

METHODS

We enrolled 84 infants who received 1 mg/kg of dexamethasone before initiation of CPB. Total cortisol (TC), free cortisol (FC), adrenocorticotropic hormone (ACTH), and corticosteroid-binding globulin (CBG) were measured at 3 time points: immediately before CPB (TP1), on intensive care unit arrival (TP2), and at 24 hours after surgery (TP3). A 1-μg ACTH stimulation test was performed at each time point to evaluate adrenal responsiveness.

RESULTS

Sixty-eight infants completed all study procedures. Levels of TC, FC, CBG, and ACTH decreased significantly between the preoperative and 24-hour postoperative measurements. There were no significant associations between preoperative FC responses and clinical outcomes after adjusting for weight and Risk-Adjusted Scores for Congenital Heart Surgery. Infants with subnormal TC responses to ACTH stimulation (<9 μg/dL) at TP2 had greater fluid requirements (P < .001) and greater chest tube output (P < .001) during the first 24 hours, as well as longer length of stay (LOS) (P = .007). Except for LOS, these differences persisted for infants with subnormal stimulation tests at TP3.

CONCLUSIONS

We observed a significant decline in all aspects of the HPA axis throughout the first 24 hours after infant CPB. TC and FC levels were not associated with clinical outcomes. Subnormal (Δ <9 μg/dL) TC response to cosyntropin stimulation during the postoperative period was associated with increased fluid resuscitation and greater LOS.

Topics: Adrenal Cortex; Adrenal Cortex Function Tests; Adrenocorticotropic Hormone; Age Factors; Biomarkers; Cardiac Surgical Procedures; Cardiopulmonary Bypass; Child, Preschool; Cosyntropin; Dexamethasone; Female; Heart Defects, Congenital; Humans; Hydrocortisone; Hypothalamo-Hypophyseal System; Infant; Infant, Newborn; Male; Pituitary-Adrenal System; Prospective Studies; Time Factors; Transcortin; Treatment Outcome; United States

PubMed: 28024808
DOI: 10.1016/j.jtcvs.2016.11.030

Authors: Eric Rozenveld, Nieko Punt, Martijn van Faassen...

BACKGROUND

Patients with adrenal insufficiency are treated with oral hydrocortisone (HC) to compensate for the loss of endogenous cortisol production. Intrinsic imperfections of cortisol replacement strategies in mimicking normal cortisol secretion are the underlying cause of the increased morbidity and mortality of patients suffering from secondary adrenal insufficiency (SAI). To improve oral hydrocortisone substitution therapy, a better understanding of its pharmacokinetics (PK) is necessary. The previous PK model did not include protein binding. It is known that protein binding can impact hydrocortisone pharmacokinetics. The aim of this study is to describe HC pharmacokinetics including the protein-binding state using Edsim++ (Mediware, Prague) pharmacokinetic modeling software, paving the way for an in-silico tool suitable for drug delivery design.

METHODS

A total of 46 patients with SAI participated in a randomized double-blind crossover study Patients randomly received a low dose of HC (0.2-0.3 mg/kg body weight/day) for 10 weeks, followed by a high dose (0.4-0.6 mg/kg body weight/day) for another 10 weeks, or vice versa. Plasma samples were obtained and analyzed for free and total hydrocortisone. Single compartment population pharmacokinetic analysis was performed using an extended Werumeus-Buning model built in Edsim++. This model includes a mathematical approach for estimating free cortisol by Nguyen et al., taking the protein binding of HC to albumin and hydrocortisone-binding globulin (CBG, transcortin) into consideration, as well as different states of CBG which affect binding kinetics to HC. The goodness of fit for observed versus predicted values was calculated.

RESULTS AND CONCLUSIONS

Nguyen's formula for free cortisol estimation was successfully implemented in a pharmacokinetic model. The model shows high Spearman's correlation for observed versus predicted hydrocortisone concentrations. Significantly higher correlations (Spearman's r, 0.901 vs. 0.836) between total and free hydrocortisone AUC (area-under the curve over 24 h) are found when comparing new and old models. This new model was used to simulate the plasma concentration-time behavior of a more suitable hydrocortisone formulation.

PubMed: 35745734
DOI: 10.3390/pharmaceutics14061161

Authors: Marc Simard, Caroline Underhill, Geoffrey L Hammond...

Corticosteroid-binding globulin (CBG) is a plasma carrier of glucocorticoids. Human and rat CBGs have six -glycosylation sites. Glycosylation of human CBG influences its steroid-binding activity, and there are -glycosylation sites in the reactive center loops (RCLs) of human and rat CBGs. Proteolysis of the RCL of human CBG causes a structural change that disrupts steroid binding. We now show that mutations of conserved -glycosylation sites at N238 in human CBG and N230 in rat CBG disrupt steroid binding. Inhibiting glycosylation by tunicamycin also markedly reduced human and rat CBG steroid-binding activities. Deglycosylation of fully glycosylated human CBG or human CBG with only one -glycan at N238 with Endo H-reduced steroid-binding affinity, while PNGase F-mediated deglycosylation does not, indicating that steroid binding is preserved by deamidation of N238 when its -glycan is removed. When expressed in -acetylglucosaminyltransferase-I-deficient Lec1 cells, human and rat CBGs, and a human CBG mutant with only one glycosylation site at N238, have higher (2-4 fold) steroid-binding affinities than when produced by sialylation-deficient Lec2 cells or glycosylation-competent CHO-S cells. Thus, the presence and composition of an -glycan in this conserved position both appear to influence the steroid binding of CBG. We also demonstrate that neutrophil elastase cleaves the RCL of human CBG and reduces its steroid-binding capacity more efficiently than does chymotrypsin or the protease LasB. Moreover, while glycosylation of N347 in the RCL limits these activities, -glycans at other sites also appear to protect CBG from neutrophil elastase or chymotrypsin.

Topics: Animals; CHO Cells; Cricetinae; Cricetulus; Glycosylation; Humans; Polysaccharides; Proteolysis; Rats; Steroids; Transcortin

PubMed: 29273683
DOI: 10.1530/JME-17-0234

Authors: Richard I Dorin, Clifford R Qualls, David J Torpy...

OBJECTIVE

Cortisol clearance is reduced in sepsis and may contribute to the development of impaired adrenocortical function that is thought to contribute to the pathophysiology of critical illness-related corticosteroid insufficiency. We sought to assess adrenocortical function using computer-assisted numerical modeling methodology to characterize and compare maximal cortisol secretion rate and free cortisol half-life in septic shock, sepsis, and healthy control subjects.

DESIGN

Post hoc analysis of previously published total cortisol, free cortisol, corticosteroid-binding globulin, and albumin concentration data.

SETTING

Single academic medical center.

PATIENTS

Subjects included septic shock (n = 45), sepsis (n = 25), and healthy controls (n = 10).

INTERVENTIONS

I.v. cosyntropin (250 μg).

MEASUREMENTS AND MAIN RESULTS

Solutions for maximal cortisol secretion rate and free cortisol half-life were obtained by least squares solution of simultaneous, nonlinear differential equations that account for free cortisol appearance and elimination as well as reversible binding to corticosteroid-binding globulin and albumin. Maximal cortisol secretion rate was significantly greater in septic shock (0.83 nM/s [0.44, 1.58 nM/s] reported as median [lower quartile, upper quartile]) compared with sepsis (0.51 nM/s [0.36, 0.62 nM/s]; p = 0.007) and controls (0.49 nM/s [0.42, 0.62 nM/s]; p = 0.04). The variance of maximal cortisol secretion rate in septic shock was also greater than that of sepsis or control groups (F test, p < 0.001). Free cortisol half-life was significantly increased in septic shock (4.6 min [2.2, 6.3 min]) and sepsis (3.0 min [2.3, 4.8 min] when compared with controls (2.0 min [1.2, 2.6 min]) (both p < 0.004).

CONCLUSIONS

Results obtained by numerical modeling are consistent with comparable measures obtained by the gold standard stable isotope dilution method. Septic shock is associated with generally not only higher levels but also greater variance of maximal cortisol secretion rate when compared with control and sepsis groups. Additional studies would be needed to determine whether assessment of cortisol kinetic parameters such as maximal cortisol secretion rate and free cortisol half-life is useful in the diagnosis or management of critical illness-related corticosteroid insufficiency.

Topics: Academic Medical Centers; Adrenal Cortex; Adult; Aged; Aged, 80 and over; Cosyntropin; Critical Illness; Female; Humans; Hydrocortisone; Male; Middle Aged; Sepsis; Serum Albumin; Shock, Septic; Transcortin

PubMed: 25365720
DOI: 10.1097/CCM.0000000000000721

Review

Authors: Michelle A Rensel, Barney A Schlinger

Songbirds exhibit significant adult neuroplasticity that, together with other neural specializations, makes them an important model system for neurobiological studies. A large body of work also points to the songbird brain as a significant target of steroid hormones, including corticosterone (CORT), the primary avian glucocorticoid. Whereas CORT positively signals the brain for many functions, excess CORT may interfere with natural neuroplasticity. Consequently, mechanisms may exist to locally regulate CORT levels in brain to ensure optimal concentrations. However, most studies in songbirds measure plasma CORT as a proxy for levels at target tissues. In this paper, we review literature concerning circulating CORT and its effects on behavior in songbirds, and discuss recent work suggesting that brain CORT levels are regulated independently of changes in adrenal secretion. We review possible mechanisms for CORT regulation in the avian brain, including corticosteroid-binding globulins, p-glycoprotein activity in the blood-brain barrier and CORT metabolism by the 11ß hydroxysteroid dehydrogenases. Data supporting a role for CORT regulation within the songbird brain have only recently begun to emerge, suggesting that this is an avenue for important future research.

Topics: Animals; Blood-Brain Barrier; Brain; Corticosterone; Humans; Songbirds; Transcortin

PubMed: 26141145
DOI: 10.1016/j.ygcen.2015.06.010