Corticosteroid-binding globulin synthesis and distribution in rat white adipose tissue

Fabrication of an affordable and sensitive corticosteroid-binding globulin immunosensor based on electrodeposited gold nanoparticles modified glassy carbon electrode

Herein, we fabricated an ultrasensitive electrochemical immunosensor for the quantitative detection of corticosteroid-binding globulin (CBG). CBG is a protein that regulates glucocorticoid levels and is an important biomarker for inflammation. A decrease in CBG levels is a key biomarker for inflammatory diseases, such as septic shock. To enhance the electrochemical performance and provide a large surface area for anti-CBG immobilization, we functionalized the glassy carbon electrode surface with AuNPs. Electrochemical characterization methods including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to examine the construction of the fabricated immunosensor. The electrochemical signal demonstrated a remarkable sensitivity to the CBG antigen, with a detection range from 0.01 to 100 μg/mL and a limit of detection of 0.012 μg/mL, making it suitable for both clinical and research applications. This label-free immunosensor offers significant advantages, including high sensitivity, low detection limits and excellent selectivity, making it a promising tool for detecting CBG in complex biological samples. Its potential applications include early disease diagnosis, treatment monitoring and studying CBG-related physiological processes.

Coping with extreme free cortisol levels: Seasonal stress axis changes in sympatric North American flying squirrels

Most environments exhibit predictable yearly changes, permitting animals to anticipate them. The hypothalamic-pituitary-adrenal (HPA) axis is a key physiological pathway that enables animals to cope with such changes. Monitoring glucocorticoid (the end products of the HPA axis) levels in wild animals throughout the year can improve our understanding of how this pathway responds to different conditions. For this study, we collected 18 months of data on two species of North American flying squirrels (Glaucomys sabrinus and G. volans) living in a southern Ontario forest where temperature and food availability fluctuate dramatically throughout the year. These squirrels are active year-round, nest communally, and rely on scatter hoarded foods in the winter months. Flying squirrels have extremely high levels of free plasma cortisol relative to other mammals, but it is unknown how these levels are affected by environmental and reproductive factors. For both species, our goals were to (1) validate an enzyme immunoassay (EIA) to measure their fecal glucocorticoid metabolite (FGM) concentrations and (2) assess yearly differences, seasonal changes, and the influence of sex, reproduction, and ambient temperature on FGM concentrations in each species. In the lab, we successfully validated the use of antibody 5α-pregnane-3β, 11β, 21-triol-20-one EIA for FGM analysis in both species. In the field, neither sex nor reproductive status (breeding condition or not) were linked to FGM concentrations in either species. FGM concentrations were higher in autumn compared to the spring and summer. There were no other seasonal differences. We discuss possible explanations for the autumn peak in FGM concentrations (increased energy expenditure and social nesting changes), as well as outline possible avenues for future research. Understanding how individuals and populations respond to environmental change is a critical goal in evolutionary ecology, particularly in the context of a rapidly changing Anthropocene.

Corticosteroid-binding-globulin (CBG)-deficient mice show high pY216-GSK3β and phosphorylated-Tau levels in the hippocampus

Corticosteroid-binding globulin (CBG) is the specific carrier of circulating glucocorticoids, but evidence suggests that it also plays an active role in modulating tissue glucocorticoid activity. CBG polymorphisms affecting its expression or affinity for glucocorticoids are associated with chronic pain, chronic fatigue, headaches, depression, hypotension, and obesity with an altered hypothalamic pituitary adrenal axis. CBG has been localized in hippocampus of humans and rodents, a brain area where glucocorticoids have an important regulatory role. However, the specific CBG function in the hippocampus is yet to be established. The aim of this study was to investigate the effect of the absence of CBG on hippocampal glucocorticoid levels and determine whether pathways regulated by glucocorticoids would be altered. We used cbg^-/- mice, which display low total-corticosterone and high free-corticosterone blood levels at the nadir of corticosterone secretion (morning) and at rest to evaluate the hippocampus for total- and free-corticosterone levels; 11β-hydroxysteroid dehydrogenase expression and activity; the expression of key proteins involved in glucocorticoid activity and insulin signaling; microtubule-associated protein tau phosphorylation, and neuronal and synaptic function markers. Our results revealed that at the nadir of corticosterone secretion in the resting state the cbg^-/- mouse hippocampus exhibited slightly elevated levels of free-corticosterone, diminished FK506 binding protein 5 expression, increased corticosterone downstream effectors and altered MAPK and PI3K pathway with increased pY216-GSK3β and phosphorylated tau. Taken together, these results indicate that CBG deficiency triggers metabolic imbalance which could lead to damage and long-term neurological pathologies.

Physiologically Based Pharmacokinetic Modeling Involving Nonlinear Plasma and Tissue Binding: Application to Prednisolone and Prednisone in Rats

The pharmacokinetics (PK) of prednisolone (PNL) exhibit nonlinearity related to plasma protein binding, tissue binding, metabolic interconversion with prednisone (PN), and renal elimination. Blood and 11 tissues were collected from male Wistar rats after steady-state (SS) infusion and after subcutaneous boluses of 50 mg/kg of PNL. Concentrations of PNL and PN were measured by liquid chromatography-tandem mass spectrometry. Plasma and tissue profiles were described using a complex physiologically based pharmacokinetics (PBPK) model. Concentrations of PN and PNL were in rapid equilibrium in plasma and tissues. The tissue partition coefficients (K _p ) of PNL calculated from most subcutaneously dosed tissue and plasma areas were similar to SS infusion and in silico values. The blood-to-plasma ratio of PNL was 0.71 with similar red blood cell and unbound-plasma concentrations. Plasma protein binding (60%-90%) was related to corticosteroid-binding globulin (CBG) saturation. Tissue distribution was nonlinear. The equilibrium dissociation constant (K _d ) of PNL shared by all tissues was 3.01 ng/ml, with the highest binding in muscle, followed by liver, heart, intestine, and bone and the lowest binding in skin, spleen, fat, kidney, lung, and brain. Fat and bone distribution assumed access only to interstitial space. Brain PNL concentrations (K _p = 0.05) were low owing to presumed P-glycoprotein-mediated efflux. Clearances of CBG-free PNL were 1789 from liver and 191.2 ml/h from kidney. The PN/PNL ratio was nonlinear for plasma, spleen, heart, intestine, bone, fat, and linear for the remaining tissues. Our PBPK model with multiple complexities well described the PK profiles of PNL and PN in blood, plasma, and diverse tissues. SIGNIFICANCE STATEMENT: Because steroids, such as prednisolone and prednisone, have similar and complex pharmacokinetics properties in various species, receptors in most tissues, and multiple therapeutic and adverse actions, this physiologically based pharmacokinetics (PBPK) model may provide greater insights into the pharmacodynamic complexities of corticosteroids. The complex properties of these compounds require innovative PBPK modeling approaches that may be instructive for other therapeutic agents.

Corticosteroid-Binding Globulin is expressed in the adrenal gland and its absence impairs corticosterone synthesis and secretion in a sex-dependent manner

Corticosteroid-binding globulin (CBG) is synthesized by the liver and secreted into the bloodstream where binds to glucocorticoids. Thus CBG has the role of glucocorticoid transport and free hormone control. In addition, CBG has been detected in some extrahepatic tissues without a known role. CBG-deficient mice show decreased total corticosterone levels with missing of classical sexual dimorphism, increased free corticosterone, higher adrenal gland size and altered HPA axis response to stress. Our aim was to ascertain whether CBG deficiency could affect the endocrine synthetic activity of adrenal gland and if the adrenal gland produces CBG. We determined the expression in adrenal gland of proteins involved in the cholesterol uptake and its transport to mitochondria and the main enzymes involved in the corticosterone, aldosterone and catecholamine synthesis. The results showed that CBG is synthesized in the adrenal gland. CBG-deficiency reduced the expression of ACTH receptor, SRB1 and the main genes involved in the adrenal hormones synthesis, stronger in females resulting in the loss of sexual dimorphism in corticosteroid adrenal synthesis, despite corticosterone content in adrenal glands from CBG-deficient females was similar to wildtype ones. In conclusion, these results point to an unexplored and relevant role of CBG in the adrenal gland functionality related to corticosterone production and release.

Modulation of SHBG binding to testosterone and estradiol by sex and morbid obesity

OBJECTIVE

Sex hormone-binding globulin (SHBG) binds and transports testosterone and estradiol in plasma. The possibility that SHBG is a mixture of transporting proteins has been postulated. We analyzed in parallel the effects of obesity status on the levels and binding capacity of circulating SHBG and their relationship with testosterone and estradiol.

DESIGN

Anthropometric measures and plasma were obtained from apparently healthy young (i.e. 35 ± 7 years) premenopausal women (n = 32) and men (n = 30), with normal weight and obesity (BMI >30 kg/m²).

METHODS

SHBG protein (Western blot), as well as the plasma levels of testosterone, estradiol, cortisol and insulin (ELISA) were measured. Specific binding of estradiol and testosterone to plasma SHBG was analyzed using tritium-labeled hormones.

RESULTS

Significant differences in SHBG were observed within the obesity status and gender, with discordant patterns of change in testosterone and estradiol. In men, testosterone occupied most of the binding sites. Estrogen binding was much lower in all subjects. Lower SHBG of morbidly obese (BMI >40 kg/m²) subjects affected testosterone but not estradiol. The ratio of binding sites to SHBG protein levels was constant for testosterone, but not for estradiol. The influence of gender was maximal in morbid obesity, with men showing the highest binding/SHBG ratios.

CONCLUSIONS

The results reported here are compatible with SHBG being a mixture of at least two functionally different hormone-binding globulins, being affected by obesity and gender and showing different structure, affinities for testosterone and estradiol and also different immunoreactivity.

Altered lipid partitioning and glucocorticoid availability in CBG-deficient male mice with diet-induced obesity

OBJECTIVE

To evaluate how deficiency in corticosteroid-binding globulin (CBG), the specific carrier of glucocorticoids, affects glucocorticoid availability and adipose tissue in obesity.

METHODS

C57BL/6 (WT) and CBG-deficient (KO) male mice were fed during 12 weeks with standard or hyperlipidic diet (HL). Glucocorticoid availability and metabolic parameters were assessed.

RESULTS

Body weight and food intake were increased in KO compared with WT mice fed a standard diet and were similar when fed a HL diet. Expression of CBG was found in white adipose tissue by immunochemistry, real-time PCR, and Western blot. In obesity, the subcutaneous depot developed less in KO mice compared with WT, which was associated with a minor adipocyte area and peroxisome proliferator-activated receptor-γ expression. Conversely, the epididymal depot displayed higher weight and adipocyte area in KO than in WT mice. CBG deficiency caused a fall of hepatic 11β-hydroxysteroid dehydrogenase type 2 expression and an increase in epidymal adipose tissue, particularly in HL mice.

CONCLUSIONS

Deficiency in CBG drives lipid partitioning from subcutaneous to visceral adipose depot under a context of lipid excess and differentially modulates 11β-hydroxysteroid dehydrogenase type 2 expression.

New Roles for Corticosteroid Binding Globulin and Opposite Expression Profiles in Lung and Liver

Corticosteroid-binding globulin (CBG) is the specific plasma transport glycoprotein for glucocorticoids. Circulating CBG is mainly synthesized in liver but, its synthesis has been located also in other organs as placenta, kidney and adipose tissue with unknown role. Using an experimental model of acute pancreatitis in cbg^-/- mice we investigated whether changes in CBG affect the progression of the disease as well as the metabolism of glucocorticoids in the lung. Lack of CBG does not modify the progression of inflammation associated to pancreatitis but resulted in the loss of gender differences in corticosterone serum levels. In the lung, CBG expression and protein level were detected, and it is noteworthy that these showed a sexual dimorphism opposite to the liver, i.e. with higher levels in males. Reduced expression of 11β-HSD2, the enzyme involved in the deactivation of corticosterone, was also observed. Our results indicate that, in addition to glucocorticoids transporter, CBG is involved in the gender differences observed in corticosteroids circulating levels and plays a role in the local regulation of corticosteroids availability in organs like lung.

Hepatic and visceral adipose tissue 11βHSD1 expressions are markers of body weight loss after bariatric surgery

OBJECTIVE

Cortisolemia and 11βHSD1 in liver and adipose tissue are altered in obesity. However, their participation in the development of obesity remains unclear. This study analyzed these parameters in the transition from morbid to type 1 obesity after bariatric surgery.

METHODS

A group of 34 patients with morbid obesity and 22 nonobese subjects were recruited. Initial hypothalamus-pituitary-adrenal (HPA) basal activity and 11βHSD1 mRNA expression in liver, subcutaneous (SAT), and visceral adipose tissue (VAT) were evaluated. A year after bariatric surgery (weight loss of 48 kg), these parameters were reappraised in plasma, SAT, and liver.

RESULTS

Body weight loss was accompanied by a downshift in basal HPA activity and 11βHSD1 expression in SAT. In patients with morbid obesity, 11βHSD1 expression correlated positively with BMI in VAT and negatively in liver at 6 and 12 months after surgery. In SAT, a correlation was observed with body weight only when patients showed type 1 obesity. Insulin, glucose, and HOMA correlated positively with all the HPA indicators and 11βHSD1 expression in SAT.

CONCLUSIONS

Body weight loss after bariatric surgery is accompanied by a downshift in basal HPA activity. Hepatic and VAT 11βHSD1 expressions in morbid obesity are predictors of body weight loss.

Adrenal steroids in the brain: role of the intrinsic expression of corticosteroid-binding globulin (CBG) in the stress response

The complex interaction between hypothalamus, pituitary and adrenal glands is a key component of the neuroendocrine stress response. The major stress hormones--glucocorticoids--have both central and peripheral effects. Among the factors regulating their availability to target tissues are levels of corticosteroid-binding globulin, as the major transport protein for glucocorticoids in systemic circulation. Our recent findings demonstrated expression of corticosteroid-binding globulin in various brain regions and in different cell populations (neurons and glial cells). We showed at the cellular level the presence of corticosteroid-binding globulin in the human hypothalamus, where it was co-localized with the classical neurohypophyseal neurohormones--vasopressin and oxytocin. For the first time we demonstrated in mouse that the same gene encodes brain and liver corticosteroid-binding globulin. The full-length sequencing of hypothalamic corticosteroid-binding globulin revealed a full homology with liver corticosteroid-binding globulin cDNA. Thus, we confirmed that corticosteroid-binding globulin mRNA is produced locally within various cerebral regions and thus not transported from blood. However, the amounts of mRNA encoding corticosteroid-binding globulin are in liver about 200 times higher than in brain. The wide distribution of corticosteroid-binding globulin, distinct from the localization of glucocorticoid receptors, observed in our comparative study in rodents, led us to propose two possibilities: (1) corticosteroid-binding globulin is made in certain neurons to deliver glucocorticoids into the cell and within the cell in the absence of cytoplasmic glucocorticoid receptors or (2) is internalized into neurons specifically to deliver glucocorticoids to classical glucocorticoid receptors. Brain corticosteroid-binding globulin may be involved in the response to changing systemic glucocorticoid levels either additionally to known nuclear and membrane corticosteroid receptors or in glucocorticoid responsive brain regions devoid of these receptors. Clearly the multiple locations of corticosteroid-binding globulin within the central nervous system of humans and rodents imply multiple functional properties in normal and/or pathological conditions, which are yet to be determined. Most likely, the importance of brain corticosteroid-binding globulin exceeds the function of a mere steroid transporter.

Modulation in Wistar rats of blood corticosterone compartmentation by sex and a cafeteria diet

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.

Differences in colocalization of corticosteroid-binding globulin and glucocorticoid receptor immunoreactivity in the rat brain

Endocrine regulation of central and systemic stress response as well as learning and memory are in part controlled by systemic glucocorticoid levels. So far steroids have been thought to act on the brain predominantly through nuclear receptors. However, some brain systems known to respond to glucocorticoids seem to be devoid of the respective receptor proteins (GR). It is likely that known central actions of adrenal steroids may also be mediated by non-genomic actions involving intrinsic binding globulins. In recent studies we described the intrinsic expression of corticosteroid-binding globulin (CBG) in rat, mouse and human brains. Here we report an immunohistochemical mapping study on the colocalization of CBG and of GR in the rat brain. In the nucleus accumbens, septum, hippocampus, globus pallidus, medial and basolateral amygdale nuclei, magnocellular preoptic nuclei, diagonal band of Broca high intensity of CBG immunoreactivity was accompanied by weak or moderate GR staining, and vice versa. In the caudate putamen, bed nucleus of stria terminalis, septohypothalamic nucleus and parvocellular subdivision of the paraventricular nucleus strong GR immunoreactivity was observed, but CBG was almost undetectable. In contrast, throughout the supraoptic nucleus and magnocellular subdivision of the paraventricular nucleus numerous strongly CBG-positive cells were observed, devoid of specific GR immunoreactivity. It is most likely that CBG in the brain may be involved in the response to changing systemic glucocorticoid levels in addition to known nuclear and membrane corticosteroid receptors, or in glucocorticoid responsive regions devoid of these receptors.

The role of receptor-interacting protein 140 in the accumulation of fat in ovariectomised rats

BACKGROUND

Receptor-interacting protein 140 (RIP140) is a corepressor for nuclear receptors with an important role in the inhibition of energy expenditure. Postmenopausal women have increased white adipose tissue (WAT), and excessive accumulation of adipose tissue (obesity) implies a health risk. The aim of the present work was to investigate the time course of RIP140 expression in WAT during the development of ovariectomy (OVX)-induced obesity in rats.

METHODS

OVX was performed in female Sprague-Dawley (SD) rats 8 weeks old. Body weight and food intake were determined once a week. WAT of sham-operated, OVX and OVX plus 17β-estradiol therapy (OVX/E2) female SD rats was weighed and used to analyse RIP140 and uncoupling protein 1 (UCP-1) expression by Western blot.

RESULTS

Food intake and body weight were significantly increased during the 2-8 weeks after OVX. Even though body weight increased until killing, food intake progressively decreased from 9 to 16 weeks after OVX in rats. Meanwhile, increased WAT mass and decreased RIP140 expression in WAT were observed in OVX rats. In contrast, the expression of UCP-1, a key target gene of RIP140, in WAT of OVX rats was significantly higher than in sham-operated rats. All of these alterations caused by OVX were mostly reversed by the replacement of 17β-estradiol.

CONCLUSIONS

The down-regulation of RIP140 in WAT may play a compensatory role in OVX-induced obesity in rat.

Intrinsic expression of transcortin in neural cells of the mouse brain: a histochemical and molecular study

Corticosteroid binding globulin (CBG, transcortin) has been shown to be expressed in the brain of rat and human species. In this study we examined the CBG brain expression and cDNA structure in mice, comparing wild-type (Cbg+/+) and Cbg knockout mice (Cbg-/-, obtained by genetic disruption of the SerpinA6 alias Cbg gene). We used double immunofluorescence labelling with specific neuronal and glial markers to analyze the cellular localization of CBG in various regions of the mouse brain. In wild-type (Cbg+/+) mice we found CBG immunoreactivity in neuronal perikarya of the magnocellular hypothalamic nuclei, amygdala, hippocampus, cerebral cortex, cerebellum and pituitary. A portion of glial cells (astrocytes, oligodendrocytes) contained CBG immunoreactivity, including some of the ependymal cells and choroid plexus cells. No CBG immunoreactivity was detected in Cbg-/- brain tissues. We showed by RT-PCR that the full-length Cbg mRNA is present in those regions, indicating an intrinsic expression of the steroid-binding globulin. Furthermore, we found by sequencing analysis that Cbg cDNA obtained from the mouse hypothalamus was homologous to Cbg cDNA obtained from the liver. Finally, we have evaluated the relative levels of CBG expression by quantitative PCR in various brain regions and in the liver. We found that brain levels of Cbg mRNA are low compared to the liver but significantly higher than in CBG-deficient mice. Although derived from the same gene than liver CBG, brain CBG protein may play a specific or complementary role that requires the production and analysis of brain-specific Cbg knockout models.

Oleoyl-estrone

Oleoyl-estrone (OE) is a powerful slimming agent that is also present in plasma and adipose tissue, where it is synthesized. It acts through the formation of a derivative W. OE effects (and W levels) are proportional to the dose. OE reduces food intake but maintains energy expenditure (thermogenesis). The energy gap is fulfilled with adipose tissue fat, sparing body protein and maintaining glycemia (and glycogen) with lower insulin and leptin levels. OE (in fact W) acts through specific receptors, different from those of estrogen. OE increases cholesterol catabolism, reducing hypercholesterolemia in obese rats. The main metabolic effect on adipose tissue is lowering of lipid synthesis, maintaining unchanged the intracellular lipolytic processes; the imbalance favors the progressive loss of fat, which is largely used by the muscle. OE administration induces additive effects with other antiobesity agents, such as β(3)-adrenergic agonists, forcing a massive loss of lipid. Corticosteroids markedly limit OE action by altering the liver control of lipogenesis. OE also inhibits the action of 17β-hydroxysteroid dehydrogenase, decreasing the synthesis of β-estradiol and testosterone. Discontinuous treatment allows for maximal efficacy both in rats and humans. OE has the advantage that the loss of fat is maintained and does not require additional dietary limitations.

Genotype-phenotype associations in understanding the role of corticosteroid-binding globulin in health and disease animal models

Corticosteroid-binding globulin (CBG) is a plasma glycoprotein discovered more than 60 years ago for its high-affinity for glucocorticoids. Although its molecular structure and its biochemical properties have been described, its various biological roles and its importance are not yet fully understood. This review focuses first on studies that have used no-hypothesis-driven genetic approaches in animal models to reveal the higher than expected importance of CBG in particular in glucocorticoid stress responses. Then the dissection of some CBG physiological roles in an animal model of genetic CBG deficiency is reported. Finally, studies on the role of CBG genetic variability in human obesity traits are reviewed and discussed.

Corticosterone inhibits the lipid-mobilizing effects of oleoyl-estrone in adrenalectomized rats

Oleoyl-estrone (OE) is an adipose-derived signal that decreases energy intake and body lipid, maintaining energy expenditure and glycemic homeostasis. Glucocorticoids protect body lipid and the metabolic status quo. We studied the combined effects of OE and corticosterone in adrenalectomized female rats: daily OE gavages (0 or 10 nmol/g) and slow-release corticosterone pellets at four doses (0, 0.5, 1.7, and 4.8 mg/d). Intact and sham-operated controls were also included. After 8 d, body composition and plasma metabolites and hormones were measured. OE induced a massive lipid mobilization (in parallel with decreased food intake and maintained energy expenditure). Corticosterone increased fat deposition and inhibited the OE-elicited mobilization of body energy, even at the lowest dose. OE enhanced the corticosterone-induced rise in plasma triacylglycerols, and corticosterone blocked the OE-induced decrease in leptin. High corticosterone and OE increased insulin resistance beyond the effects of corticosterone alone. The presence of corticosterone dramatically affected OE effects, reversing its decrease of body energy (lipid) content, with little or no change on food intake or energy expenditure. The maintenance of glycemia and increasing insulin in parallel to the dose of corticosterone indicate a decrease in insulin sensitivity, which is enhanced by OE. The reversal of OE effects on lipid handling, insulin resistance, can be the consequence of a corticosterone-induced OE resistance. Nevertheless, OE effects on cholesterol were largely unaffected. In conclusion, corticosterone administration effectively blocked OE effects on body lipid and energy balance as well as insulin sensitivity and glycemia.