The 11-ketosteroid 11-ketodexamethasone is a glucocorticoid receptor agonist

Development of novel liver-targeting glucocorticoid prodrugs

Background

Glucocorticoids (GCs) are widely used in the treatment of inflammatory liver diseases and sepsis, but GC's various side effects on extrahepatic tissues limit their clinical benefits. Liver-targeting GC therapy may have multiple advantages over systemic GC therapy. The purpose of this study was to develop novel liver-targeting GC prodrugs as improved treatment for inflammatory liver diseases and sepsis.

Methods

A hydrophilic linker or an ultra-hydrophilic zwitterionic linker carboxylic betaine (CB) was used to bridge cholic acid (CA) and dexamethasone (DEX) to generate transporter-dependent liver-targeting GC prodrugs CA-DEX and the highly hydrophilic CA-CB-DEX. The efficacy of liver-targeting DEX prodrugs and DEX were determined in primary human hepatocytes (PHH), macrophages, human whole blood, and/or mice with sepsis induced by cecal ligation and puncture.

Results

CA-DEX was moderately water soluble, whereas CA-CB-DEX was highly water soluble. CA-CB-DEX and CA-DEX displayed highly transporter-dependent activities in reporter assays. Data mining found marked dysregulation of many GR-target genes important for lipid catabolism, cytoprotection, and inflammation in patients with severe alcoholic hepatitis. These key GR-target genes were similarly and rapidly (within 6 h) induced or down-regulated by CA-CB-DEX and DEX in PHH. CA-CB-DEX had much weaker inhibitory effects than DEX on endotoxin-induced cytokines in mouse macrophages and human whole blood. In contrast, CA-CB-DEX exerted more potent anti-inflammatory effects than DEX in livers of septic mice.

Conclusions

CA-CB-DEX demonstrated good hepatocyte-selectivity in vitro and better anti-inflammatory effects in vivo. Further test of CA-CB-DEX as a novel liver-targeting GC prodrug for inflammatory liver diseases and sepsis is warranted.

Narrative Review: Glucocorticoids in Alcoholic Hepatitis—Benefits, Side Effects, and Mechanisms

Alcoholic hepatitis is a major health and economic burden worldwide. Glucocorticoids (GCs) are the only first-line drugs recommended to treat severe alcoholic hepatitis (sAH), with limited short-term efficacy and significant side effects. In this review, I summarize the major benefits and side effects of GC therapy in sAH and the potential underlying mechanisms. The review of the literature and data mining clearly indicate that the hepatic signaling of glucocorticoid receptor (GR) is markedly impaired in sAH patients. The impaired GR signaling causes hepatic down-regulation of genes essential for gluconeogenesis, lipid catabolism, cytoprotection, and anti-inflammation in sAH patients. The efficacy of GCs in sAH may be compromised by GC resistance and/or GC’s extrahepatic side effects, particularly the side effects of intestinal epithelial GR on gut permeability and inflammation in AH. Prednisolone, a major GC used for sAH, activates both the GR and mineralocorticoid receptor (MR). When GC non-responsiveness occurs in sAH patients, the activation of MR by prednisolone might increase the risk of alcohol abuse, liver fibrosis, and acute kidney injury. To improve the GC therapy of sAH, the effort should be focused on developing the biomarker(s) for GC responsiveness, liver-targeting GR agonists, and strategies to overcome GC non-responsiveness and prevent alcohol relapse in sAH patients.

Dexamethasone-Induced Adipose Tissue Redistribution and Metabolic Changes: Is Gene Expression the Main Factor? An Animal Model of Chronic Hypercortisolism

Chronic hypercortisolism has been associated with the development of several metabolic alterations, mostly caused by the effects of chronic glucocorticoid (GC) exposure over gene expression. The metabolic changes can be partially explained by the GC actions on different adipose tissues (ATs), leading to central obesity. In this regard, we aimed to characterize an experimental model of iatrogenic hypercortisolism in rats with significant AT redistribution. Male Wistar rats were distributed into control (CT) and GC-treated, which received dexamethasone sodium phosphate (0.5 mg/kg/day) by an osmotic minipump, for 4 weeks. GC-treated rats reproduced several characteristics observed in human hypercortisolism/Cushing’s syndrome, such as HPA axis inhibition, glucose intolerance, insulin resistance, dyslipidemia, hepatic lipid accumulation, and AT redistribution. There was an increase in the mesenteric (meWAT), perirenal (prWAT), and interscapular brown (BAT) ATs mass, but a reduction of the retroperitoneal (rpWAT) mass compared to CT rats. Overexpressed lipolytic and lipogenic gene profiles were observed in white adipose tissue (WAT) of GC rats as BAT dysfunction and whitening. The AT remodeling in response to GC excess showed more importance than the increase of AT mass per se, and it cannot be explained just by GC regulation of gene transcription.

Effects of HSD11B1 knockout and overexpression on local cortisol production and differentiation of mesenchymal stem cells

Exogenous glucocorticoids increase the risk for osteoporosis, but the role of endogenous glucocorticoids remains elusive. Here, we describe the generation and validation of a loss- and a gain-of-function model of the cortisol producing enzyme 11β-HSD1 (HSD11B1) to modulate the endogenous glucocorticoid conversion in SCP-1 cells — a model for human mesenchymal stem cells capable of adipogenic and osteogenic differentiation. CRISPR-Cas9 was successfully used to generate a cell line carrying a single base duplication and a 5 bp deletion in exon 5, leading to missense amino acid sequences after codon 146. These inactivating genomic alterations were validated by deep sequencing and by cloning with subsequent capillary sequencing. 11β-HSD1 protein levels were reduced by 70% in the knockout cells and cortisol production was not detectable. Targeted chromosomal integration was used to stably overexpress HSD11B1. Compared to wildtype cells, HSD11B1 overexpression resulted in a 7.9-fold increase in HSD11B1 mRNA expression, a 5-fold increase in 11β-HSD1 protein expression and 3.3-fold increase in extracellular cortisol levels under adipogenic differentiation. The generated cells were used to address the effects of 11β-HSD1 expression on adipogenic and osteogenic differentiation. Compared to the wildtype, HSD11B1 overexpression led to a 3.7-fold increase in mRNA expression of lipoprotein lipase (LPL) and 2.5-fold increase in lipid production under adipogenic differentiation. Under osteogenic differentiation, HSD11B1 knockout led to enhanced alkaline phosphatase (ALP) activity and mRNA expression, and HSD11B1 overexpression resulted in a 4.6-fold and 11.7-fold increase in mRNA expression of Dickkopf-related protein 1 (DKK1) and LPL, respectively. Here we describe a HSD11B1 loss- and gain-of-function model in SCP-1 cells at genetic, molecular and functional levels. We used these models to study the effects of endogenous cortisol production on mesenchymal stem cell differentiation and demonstrate an 11β-HSD1 dependent switch from osteogenic to adipogenic differentiation. These results might help to better understand the role of endogenous cortisol production in osteoporosis on a molecular and cellular level.

Genomic and Non-Genomic Actions of Glucocorticoids on Adipose Tissue Lipid Metabolism

Glucocorticoids (GCs) are hormones that aid the body under stress by regulating glucose and free fatty acids. GCs maintain energy homeostasis in multiple tissues, including those in the liver and skeletal muscle, white adipose tissue (WAT), and brown adipose tissue (BAT). WAT stores energy as triglycerides, while BAT uses fatty acids for heat generation. The multiple genomic and non-genomic pathways in GC signaling vary with exposure duration, location (adipose tissue depot), and species. Genomic effects occur directly through the cytosolic GC receptor (GR), regulating the expression of proteins related to lipid metabolism, such as ATGL and HSL. Non-genomic effects act through mechanisms often independent of the cytosolic GR and happen shortly after GC exposure. Studying the effects of GCs on adipose tissue breakdown and generation (lipolysis and adipogenesis) leads to insights for treatment of adipose-related diseases, such as obesity, coronary disease, and cancer, but has led to controversy among researchers, largely due to the complexity of the process. This paper reviews the recent literature on the genomic and non-genomic effects of GCs on WAT and BAT lipolysis and proposes research to address the many gaps in knowledge related to GC activity and its effects on disease.

Dexamethasone primes adipocyte precursor cells for differentiation by enhancing adipogenic competency

AIM

Dexamethasone (DXM) is a synthetic glucocorticoid whose effects in early and terminal adipogenesis have been addressed. In this study, we evaluated if DXM affects adipocyte precursor cells (APCs), priming them for further adipogenic differentiation. For this purpose, we analyzed APCs number and competency after DXM treatment.

MATERIALS AND METHODS

Adult male rats were injected for 2 or 7 days with either DXM (30 μg/kg of weight, sc.) or vehicle. Stromal vascular fraction (SVF) cells from retroperitoneal adipose tissue (RPAT) were isolated to quantify APCs by flow cytometry (CD34⁺/CD45^-/CD31^-). Also, expression of competency markers (PPARγ2 and Zfp423) was assessed. Additionally, SVF cells from control rats were incubated with DXM (0.25 μM) alone or combined with a mineralocorticoid receptor (MR) antagonist (Spironolactone 10 μM) and/or a glucocorticoid receptor (GR) antagonist (RU486 1 μM) to assess APCs competency and adipocyte differentiation.

KEY FINDINGS

APCs from 2 days DXM-treated rats showed increased expression of PPARγ2 and Zfp423 (competency markers), but did not affect APCs percentage by FACS analysis (CD34⁺/CD45^-/CD31^-). Additionally, we found that DXM treatment in SVF also increased APCs competency in vitro, predisposing APCs to further adipocyte differentiation. These effects on APCs were abrogated only when both, MR and GR, were blocked.

SIGNIFICANCE

Overall, our results suggest that DXM primes APCs for differentiation mainly by enhancing Zfp423 and PPARγ2 expressions. Also, we showed that the inhibition of MR and GR was necessary for the complete abolishment of DXM effects.

Beyond the heterodimer model for mineralocorticoid and glucocorticoid receptor interactions in nuclei and at DNA

Glucocorticoid (GR) and mineralocorticoid receptors (MR) are believed to classically bind DNA as homodimers or MR-GR heterodimers to influence gene regulation in response to pulsatile basal or stress-evoked glucocorticoid secretion. Pulsed corticosterone presentation reveals MR and GR co-occupy DNA only at the peaks of glucocorticoid oscillations, allowing interaction. GR DNA occupancy was pulsatile, while MR DNA occupancy was prolonged through the inter-pulse interval. In mouse mammary 3617 cells MR-GR interacted in the nucleus and at a chromatin-associated DNA binding site. Interactions occurred irrespective of ligand type and receptors formed complexes of higher order than heterodimers. We also detected MR-GR interactions ex-vivo in rat hippocampus. An expanded range of MR-GR interactions predicts structural allostery allowing a variety of transcriptional outcomes and is applicable to the multiple tissue types that co-express both receptors in the same cells whether activated by the same or different hormones.

Drug-induced endocrine blood pressure elevation

Patients with uncontrolled hypertension are at risk for cardiovascular complications. The majority of them suffers from unidentified forms of hypertension and a fraction has so-called secondary hypertension with an identifiable cause. The patient's medications, its use of certain herbal supplements and over-the-counter agents represent potential causal factors for secondary hypertension that are often overlooked. The current review focuses on drugs that are likely to elevate blood pressure by affecting the human endocrine system at the level of steroid synthesis or metabolism, mineralocorticoid receptor activity, or by affecting the catecholaminergic system. Drugs with known adverse effects but where benefits outweigh their risks, drug candidates and market withdrawals are reviewed. Finally, potential therapeutic strategies are discussed.

The Synergistic Effects of Gold Particles and Dexamethasone on the Electrochemical and Biological Performance of PEDOT Neural Interfaces

Although neural devices have shown efficacy in the treatment of neurodegenerative diseases, their functionality is limited by the inflammatory state and glial scar formation associated with chronic implantation. The aim of this study was to investigate neural electrode performance following functionalization with an anti-inflammatory coating derived from a conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) matrix doped with dexamethasone (Dex) and decorated with Au particles. Pristine PEDOT, PEDOT-Dex and their gold-decorated analogues (PEDOT/Au and PEDOT-Dex/Au) were formulated by electrochemical deposition and characterized with respect to electrode electrochemical properties, surface morphology and biocompatibility towards primary neural cells. Through a process of gold deposition, it was possible to eliminate the initial burst release observed in PEDOT-Dex and maintain a stable, stepwise increase in Dex elution over 7 days. The released amounts of Dex exceeded the concentrations considered as therapeutic for both PEDOT-Dex and PEDOT-Dex/Au. The results clearly indicated that the presence of either Dex or Au particles facilitated the outgrowth of neurites. Finally, it was shown that the application of composite materials, such as PEDOT-Dex/Au, is an efficient way to improve the efficacy of neural interfaces in vitro.

Inhibition of 11β-hydroxysteroid dehydrogenase 2 by the fungicides itraconazole and posaconazole

Impaired 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2)-dependent cortisol inactivation can lead to electrolyte dysbalance, hypertension and cardiometabolic disease. Furthermore, placental 11β-HSD2 essentially protects the fetus from high maternal glucocorticoid levels, and its impaired function has been associated with altered fetal growth and a higher risk for cardio-metabolic diseases in later life. Despite its important role, 11β-HSD2 is not included in current off-target screening approaches. To identify potential 11β-HSD inhibitors among approved drugs, a pharmacophore model was used for virtual screening, followed by biological assessment of selected hits. This led to the identification of several azole fungicides as 11β-HSD inhibitors, showing a significant structure-activity relationship between azole scaffold size, 11β-HSD enzyme selectivity and inhibitory potency. A hydrophobic linker connecting the azole ring to the other, more polar end of the molecule was observed to be favorable for 11β-HSD2 inhibition and selectivity over 11β-HSD1. The most potent 11β-HSD2 inhibition, using cell lysates expressing recombinant human 11β-HSD2, was obtained for itraconazole (IC₅₀ 139±14nM), its active metabolite hydroxyitraconazole (IC₅₀ 223±31nM) and posaconazole (IC₅₀ 460±98nM). Interestingly, experiments with mouse and rat kidney homogenates showed considerably lower inhibitory activity of these compounds towards 11β-HSD2, indicating important species-specific differences. Thus, 11β-HSD2 inhibition by these compounds is likely to be overlooked in preclinical rodent studies. Inhibition of placental 11β-HSD2 by these compounds, in addition to the known inhibition of cytochrome P450 enzymes and P-glycoprotein efflux transport, might contribute to elevated local cortisol levels, thereby affecting fetal programming.

Glucocorticoids and erythropoietin in chronic lung disease of prematurity: Proliferative potential in lung fibroblast and epithelial cells exposed to tracheal aspirates

BACKGROUND

We investigated the effects of glucocorticoids, erythropoietin (EPO) and spironolactone (SPL) n human fetal lung fibroblasts and human alveolar epithelial cells exposed to tracheal aspirate fluid (TAF) from extremely premature infants with chronic lung disease (CLD), characterized by fibrosis and changes in the alveolar epithelium.

METHODS

Fibroblasts and epithelial cells (FHs 738Lu and A549, respectively) were treated with different concentrations of hydrocortisone (HDC), dexamethasone (DEX), betamethasone (BET), SPL, and EPO in the absence or presence of TAF from infants with CLD (gestational age, 25.3 ± 0.8 weeks; birthweight, 658 ± 77 g; postnatal age, 0-28 days) and assayed for proliferation.

RESULTS

Exposure to TAF resulted in a concentration-dependent proliferation of fibroblasts and epithelial cells. Proliferation of TAF-exposed fibroblasts was suppressed most significantly by 100 μmol/L DEX (21%, P = 0.046) and 300 mIU/mL EPO (18%, P = 0.02) and promoted most significantly by 0.4 μmol/L HDC (10%, P = 0.04). Epithelial proliferation was promoted by 4 μmol/L HDC (15%, P = 0.04), 10 μmol/L DEX (53%, P < 0.01), 0.2 μmol/L BET (56%, P < 0.01), and 300 mIU/mL EPO (35%, P < 0.01) in the presence of TAF. Treatment with glucocorticoids alone did not significantly affect fibroblast proliferation.

CONCLUSIONS

Glucocorticoids and EPO reduced fibroproliferation while promoting epithelial cell growth in vitro within certain dose ranges. Appropriate doses of glucocorticoids and EPO may be useful in the prevention and resolution of CLD in extremely premature infants.

Adult nephron-specific MR-deficient mice develop a severe renal PHA-1 phenotype

Aldosterone is the main mineralocorticoid hormone controlling sodium balance, fluid homeostasis, and blood pressure by regulating sodium reabsorption in the aldosterone-sensitive distal nephron (ASDN). Germline loss-of-function mutations of the mineralocorticoid receptor (MR) in humans and in mice lead to the "renal" form of type 1 pseudohypoaldosteronism (PHA-1), a case of aldosterone resistance characterized by salt wasting, dehydration, failure to thrive, hyperkalemia, and metabolic acidosis. To investigate the importance of MR in adult epithelial cells, we generated nephron-specific MR knockout mice (MR(Pax8/LC1)) using a doxycycline-inducible system. Under standard diet, MR(Pax8/LC1) mice exhibit inability to gain weight and significant weight loss compared to control mice. Interestingly, despite failure to thrive, MR(Pax8/LC1) mice survive but develop a severe PHA-1 phenotype with higher urinary Na(+) levels, decreased plasma Na(+), hyperkalemia, and higher levels of plasma aldosterone. This phenotype further worsens and becomes lethal under a sodium-deficient diet. Na(+)/Cl(-) co-transporter (NCC) protein expression and its phosphorylated form are downregulated in the MR(Pax8/LC1) knockouts, as well as the αENaC protein expression level, whereas the expression of glucocorticoid receptor (GR) is increased. A diet rich in Na(+) and low in K(+) does not restore plasma aldosterone to control levels but is sufficient to restore body weight, plasma, and urinary electrolytes. In conclusion, MR deletion along the nephron fully recapitulates the features of severe human PHA-1. ENaC protein expression is dependent on MR activity. Suppression of NCC under hyperkalemia predominates in a hypovolemic state.

11β-Hydroxysteroid dehydrogenase 1: Regeneration of active glucocorticoids is only part of the story

11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1) is an endoplasmic reticulum membrane enzyme with its catalytic site facing the luminal space. It functions primarily as a reductase, driven by the supply of its cosubstrate NADPH by hexose-6-phosphate dehydrogenase (H6PDH). Extensive research has been performed on the role of 11β-HSD1 in the regeneration of active glucocorticoids and its role in inflammation and metabolic disease. Besides its important role in the fine-tuning of glucocorticoid action, 11β-HSD1 is a multi-functional carbonyl reductase converting several 11- and 7-oxosterols into the respective 7-hydroxylated forms. Moreover, 11β-HSD1 has a role in phase I biotransformation reactions and catalyzes the carbonyl reduction of several non-steroidal xenobiotics. Recent observations from experiments using selective inhibitors and studies with transgenic mice indicated a role for 11β-HSD1 in oxysterol metabolism and in bile acid homeostasis, with evidence for glucocorticoid-independent effects on gene expression. This review focuses on the promiscuity of 11β-HSD1 to accept structurally distinct substrates and discusses recent progress mainly on non-glucocorticoid substrates. This article is part of a Special Issue entitled 'Enzyme Promiscuity and Diversity'.

Switch of glycolysis to gluconeogenesis by dexamethasone for treatment of hepatocarcinoma

Gluconeogenesis is a fundamental feature of hepatocytes. Whether this gluconeogenic activity is also present in malignant hepatocytes remains unexplored. A better understanding of this biological process may lead to novel therapeutic strategies. Here we show that gluconeogenesis is not present in mouse or human malignant hepatocytes. We find that two critical enzymes 11β-HSD1 and 11β-HSD2 that regulate glucocorticoid activities are expressed inversely in malignant hepatocytes, resulting in the inactivation of endogenous glucocorticoids and the loss of gluconeogenesis. In patients' hepatocarcinoma, the expression of 11β-HSD1 and 11β-HSD2 is closely linked to prognosis and survival. Dexamethasone, an active form of synthesized glucocorticoids, is capable of restoring gluconeogenesis in malignant cells by bypassing the abnormal regulation of 11β-HSD enzymes, leading to therapeutic efficacy against hepatocarcinoma. These findings clarify the molecular basis of malignant hepatocyte loss of gluconeogenesis and suggest new therapeutic strategies.

Formation of threohydrobupropion from bupropion is dependent on 11β-hydroxysteroid dehydrogenase 1

Bupropion is widely used for treatment of depression and as a smoking-cessation drug. Despite more than 20 years of therapeutic use, its metabolism is not fully understood. While CYP2B6 is known to form hydroxybupropion, the enzyme(s) generating erythro- and threohydrobupropion have long remained unclear. Previous experiments using microsomal preparations and the nonspecific inhibitor glycyrrhetinic acid suggested a role for 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in the formation of both erythro- and threohydrobupropion. 11β-HSD1 catalyzes the conversion of inactive glucocorticoids (cortisone, prednisone) to their active forms (cortisol, prednisolone). Moreover, it accepts several other substrates. Here, we used for the first time recombinant 11β-HSD1 to assess its role in the carbonyl reduction of bupropion. Furthermore, we applied human, rat, and mouse liver microsomes and a selective inhibitor to characterize species-specific differences and to estimate the relative contribution of 11β-HSD1 to bupropion metabolism. The results revealed 11β-HSD1 as the major enzyme responsible for threohydrobupropion formation. The reaction was stereoselective and no erythrohydrobupropion was formed. Human liver microsomes showed 10 and 80 times higher activity than rat and mouse liver microsomes, respectively. The formation of erythrohydrobupropion was not altered in experiments with microsomes from 11β-HSD1-deficient mice or upon incubation with 11β-HSD1 inhibitor, indicating the existence of another carbonyl reductase that generates erythrohydrobupropion. Molecular docking supported the experimental findings and suggested that 11β-HSD1 selectively converts R-bupropion to threohydrobupropion. Enzyme inhibition experiments suggested that exposure to bupropion is not likely to impair 11β-HSD1-dependent glucocorticoid activation but that pharmacological administration of cortisone or prednisone may inhibit 11β-HSD1-dependent bupropion metabolism.

Role of the hypothalamic-pituitary-adrenal axis in developmental programming of health and disease

Adverse environments during the fetal and neonatal development period may permanently program physiology and metabolism, and lead to increased risk of diseases in later life. Programming of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key mechanisms that contribute to altered metabolism and response to stress. Programming of the HPA axis often involves epigenetic modification of the glucocorticoid receptor (GR) gene promoter, which influences tissue-specific GR expression patterns and response to stimuli. This review summarizes the current state of research on the HPA axis and programming of health and disease in the adult, focusing on the epigenetic regulation of GR gene expression patterns in response to fetal and neonatal stress. Aberrant GR gene expression patterns in the developing brain may have a significant negative impact on protection of the immature brain against hypoxic-ischemic encephalopathy in the critical period of development during and immediately after birth.

Mineralocorticoid and glucocorticoid receptors differentially regulate NF-kappaB activity and pro-inflammatory cytokine production in murine BV-2 microglial cells

Background

Microglia, the resident macrophage-like cells in the brain, regulate innate immune responses in the CNS to protect neurons. However, excessive activation of microglia contributes to neurodegenerative diseases. Corticosteroids are potent modulators of inflammation and mediate their effects by binding to mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Here, the coordinated activities of GR and MR on the modulation of the nuclear factor-κB (NF-κB) pathway in murine BV-2 microglial cells were studied.

Methods

BV-2 cells were treated with different corticosteroids in the presence or absence of MR and GR antagonists. The impact of the glucocorticoid-activating enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) was determined by incubating cells with 11-dehydrocorticosterone, with or without selective inhibitors. Expression of interleukin-6 (IL-6), tumor necrosis factor receptor 2 (TNFR2), and 11β-HSD1 mRNA was analyzed by RT-PCR and IL-6 protein expression by ELISA. NF-κB activation and translocation upon treatment with various corticosteroids were visualized by western blotting, immunofluorescence microscopy, and translocation assays.

Results

GR and MR differentially regulate NF-κB activation and neuroinflammatory parameters in BV-2 cells. By converting inactive 11-dehydrocorticosterone to active corticosterone, 11β-HSD1 essentially modulates the coordinated action of GR and MR. Biphasic effects were observed for 11-dehydrocorticosterone and corticosterone, with an MR-dependent potentiation of IL-6 and tumor necrosis factor-α (TNF-α) expression and NF-κB activation at low/moderate concentrations and a GR-dependent suppression at high concentrations. The respective effects were confirmed using the MR ligand aldosterone and the antagonist spironolactone as well as the GR ligand dexamethasone and the antagonist RU-486. NF-κB activation could be blocked by spironolactone and the inhibitor of NF-κB translocation Cay-10512. Moreover, an increased expression of TNFR2 was observed upon treatment with 11-dehydrocorticosterone and aldosterone, which was reversed by 11β-HSD1 inhibitors and/or spironolactone and Cay-10512.

Conclusions

A tightly coordinated GR and MR activity regulates the NF-κB pathway and the control of inflammatory mediators in microglia cells. The balance of GR and MR activity is locally modulated by the action of 11β-HSD1, which is upregulated by pro-inflammatory mediators and may represent an important feedback mechanism involved in resolution of inflammation.

Suppression of the Nrf2-dependent antioxidant response by glucocorticoids and 11β-HSD1-mediated glucocorticoid activation in hepatic cells

Background

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a key transcription factor regulating a plethora of detoxifying enzymes and antioxidant genes involved in drug metabolism and defence against oxidative stress. The glucocorticoid receptor (GR) is a ligand-induced transcription factor involved in the regulation of energy supply for metabolic needs to cope with various stressors. GR activity is controlled by glucocorticoids, which are synthesized in the adrenal glands and regenerated mainly in the liver from inactive cortisone by 11β-hydroxysteroid dehydrogenase-1 (11β-HSD1).

Methods and Principal Findings

Using transfected HEK-293 cells and hepatic H4IIE cells we show that glucocorticoids, activated by 11β-HSD1 and acting through GR, suppress the Nrf2-dependent antioxidant response. The expression of the marker genes NQO1, HMOX1 and GST2A was suppressed upon treatment of 11β-HSD1 expressing cells with cortisone, an effect that was reversed by 11β-HSD1 inhibitors. Furthermore, our results demonstrate that elevated glucocorticoids lowered the ability of cells to detoxify H₂O₂. Moreover, a comparison of gene expression in male and female rats revealed an opposite sexual dimorphism with an inverse relationship between 11β-HSD1 and Nrf2 target gene expression.

Conclusions

The results demonstrate a suppression of the cellular antioxidant defence capacity by glucocorticoids and suggest that elevated 11β-HSD1 activity may lead to impaired Nrf2-dependent antioxidant response. The gender-specific differences in hepatic expression levels of 11β-HSD1 and Nrf2 target genes and the impact of pharmacological inhibition of 11β-HSD1 on improving cellular capacity to cope with oxidative stress warrants further studies in vivo.

Dexamethasone stimulates endothelin-1 gene expression in renal collecting duct cells

Aldosterone stimulates the endothelin-1 gene (Edn1) in renal collecting duct (CD) cells by a mechanism involving the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). The goal of the present study was to determine if the synthetic glucocorticoid dexamethasone affected Edn1 gene expression and to characterize GR binding patterns to an element in the Edn1 promoter. Dexamethasone (1μM) induced a 4-fold increase in Edn1 mRNA in mIMCD-3 inner medullary CD cells. Similar results were obtained from cortical collecting duct-derived mpkCCD(c14) cells. RU486 inhibition of GR completely blocked dexamethasone action on Edn1. Similarly, 24h transfection of siRNA against GR reduced Edn1 expression by approximately 50%. However, blockade of MR with either spironolactone or siRNA had little effect on dexamethasone induction of Edn1. Cotransfection of MR and GR siRNAs together had no additive effect compared to GR-siRNA alone. The results indicate that dexamethasone acts on Edn1 exclusively through GR and not MR. DNA affinity purification studies revealed that either dexamethasone or aldosterone resulted in GR binding to the same hormone response element in the Edn1Edn1 promoter. The Edn1 hormone response element contains three important sequence segments. Mutational analysis revealed that one of these segments is particularly important for modulating MR and GR binding to the Edn1 hormone response element.

Rational ligand-based virtual screening and structure-activity relationship studies in the ligand-binding domain of the glucocorticoid receptor-α

The interest in developing synthetic glucocorticoids (GCs) arises from the utility of endogenous steroids as potent anti-inflammatory and immunosuppressant agents. The first GCs to be discovered, such as cortisol or dexamethasone, still represent the main treatment for conditions of the inflammatory process, despite the fact that they carry a significant risk of side effects. Hence, there is a continuing need to find drugs that preserve the immune effects of GCs without the side effects, such as those on metabolism (diabetes), bone tissue (osteoporosis), muscles (myopathy), eyes and skin. In this review, we focus on the recent use of ligand-based computational approaches in glucocorticoid receptor (GR) drug-design efforts for the determination of novel GR ligands. We examine a number of ligand-based (similarity searches, pharmacophore screens and quantitative structure-activity relationships) approaches that have been implemented in recent years. A recent virtual high-throughput screening similarity search was successful in developing a novel series of nonsteroidal GR antagonists. Additionally, there has been considerable success in ligand-based structure-analysis relationship generation and lead optimization studies for the GR. Future trends toward integrated GR ligand design incorporating ligand- and structure-based methodologies are inevitable.

Characterization of activity and binding mode of glycyrrhetinic acid derivatives inhibiting 11β-hydroxysteroid dehydrogenase type 2

Modulation of intracellular glucocorticoid availability is considered as a promising strategy to treat glucocorticoid-dependent diseases. 18β-Glycyrrhetinic acid (GA), the biologically active triterpenoid metabolite of glycyrrhizin, which is contained in the roots and rhizomes of licorice (Glycyrrhiza spp.), represents a well-known but non-selective inhibitor of 11β-hydroxysteroid dehydrogenases (11β-HSDs). However, to assess the physiological functions of the respective enzymes and for potential therapeutic applications selective inhibitors are needed. In the present study, we applied bioassays and 3D-structure modeling to characterize nine 11β-HSD1 and fifteen 11β-HSD2 inhibiting GA derivatives. Comparison of the GA derivatives in assays using cell lysates revealed that modifications at the 3-hydroxyl and/or the carboxyl led to highly selective and potent 11β-HSD2 inhibitors. The data generated significantly extends our knowledge on structure-activity relationship of GA derivatives as 11β-HSD inhibitors. Using recombinant enzymes we found also potent inhibition of mouse 11β-HSD2, despite significant species-specific differences. The selected GA derivatives potently inhibited 11β-HSD2 in intact SW-620 colon cancer cells, although the rank order of inhibitory potential differed from that obtained in cell lysates. The biological activity of compounds was further demonstrated in glucocorticoid receptor (GR) transactivation assays in cells coexpressing GR and 11β-HSD1 or 11β-HSD2. 3D-structure modeling provides an explanation for the differences in the selectivity and activity of the GA derivatives investigated. The most potent and selective 11β-HSD2 inhibitors should prove useful as mechanistic tools for further anti-inflammatory and anti-cancer in vitro and in vivo studies. Article from the Special issue on Targeted Inhibitors.

Hypertension and other morbidities with Cushing's syndrome associated with corticosteroids: a review

Corticosteroids constitute an ideal treatment for various inflammatory and autoimmune disorders due to their anti-inflammatory and immunomodulatory actions. However, corticosteroids have a considerable number of side effects, including hypertension, diabetes, lipid disorders, sleep apnea, osteoporosis, myopathy, and disorders of coagulation and fibrinolysis, which are components of Cushing’s syndrome (CS). Corticosteroid-induced side effects are dependent on the formulation, route, dose, and time of exposure. However, the underlying pathogenetic mechanisms have not been clearly defined. A large body of evidence supports the role of an imbalance between vasoconstriction and vasodilation with possible links to nitric oxide, prostanoids, angiotensin II, arginine vasopressin, endothelins, catecholamines, neuropeptide Y, and atrial natriuretic peptide. Increased oxidative stress, renin–angiotensin system activation, increased pressor response, metabolic syndrome, and sleep apnea appear to be pathogenetically involved as well. The ideal treatment is the withdrawal of corticosteroids, which is most often impossible due to the exacerbation of the underlying disease. Alternatively, a careful plan, including the proper selection of the formulation, time, and route, should be made, and each side effect should be treated properly. The focus of the research should be to develop synthetic corticosteroids with anti-inflammatory effects but fewer metabolic effects, which so far has been unsuccessful.

Obesity and corticosteroids: 11beta-hydroxysteroid type 1 as a cause and therapeutic target in metabolic disease

The metabolic abnormalities found associated with high blood glucocorticoid levels (e.g. rare Cushing's syndrome) include insulin-resistance, visceral obesity, hypertension, dyslipidaemia and an increased risk of cardiovascular diseases. The same constellation of abnormalities is found in the highly prevalent idiopathic obesity/insulin-resistance (metabolic)-syndrome. It is now apparent that tissue-specific changes in cortisol metabolism explain these parallels rather than altered blood cortisol levels. Primary among these changes is increased intracellular glucocorticoid reactivation, catalysed by the enzyme 11beta-hydroxysteroid dehydrogenase type (HSD)-1 in obese adipose tissue. Liver, skeletal muscle, endocrine pancreas, blood vessels and leukocytes express 11beta-HSD1 and their potential role in metabolic disease is discussed. The weight of evidence, much of it gained from animal models, suggests that therapeutic inhibition of 11beta-HSD1 will be beneficial in most cellular contexts, with clinical trials supportive of this concept.

The glucocorticoid-activating enzyme 11beta-hydroxysteroid dehydrogenase type 1 has broad substrate specificity: Physiological and toxicological considerations

The primary function of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is to catalyze the conversion of inactive to active glucocorticoid hormones and to modulate local glucocorticoid-dependent gene expression. Thereby 11beta-HSD1 plays a key role in the regulation of metabolic functions and in the adaptation of the organism to energy requiring situations. Importantly, elevated 11beta-HSD1 activity has been associated with metabolic disorders, and recent investigations with rodent models of obesity and type 2 diabetes provided evidence for beneficial effects of 11beta-HSD1 inhibitors, making this enzyme a promising therapeutic target. Several earlier and recent studies, mainly performed in vitro, revealed a relatively broad substrate spectrum of 11beta-HSD1 and suggested that this enzyme has additional functions in the metabolism of some neurosteroids (7-oxy- and 11-oxyandrogens and -progestins) and 7-oxysterols, as well as in the detoxification of various xenobiotics that contain reactive carbonyl groups. While there are many studies on the effect of inhibitors on cortisone reduction and circulating glucocorticoid levels and on the transcriptional regulation of 11beta-HSD1 in obesity and diabetes, only few address the so-called alternative functions of this enzyme. We review recent progress on the biochemical characterization of 11beta-HSD1, with a focus on cofactor and substrate specificity and on possible alternative functions of this enzyme.

Retinoic acid reduces glucocorticoid sensitivity in C2C12 myotubes by decreasing 11beta-hydroxysteroid dehydrogenase type 1 and glucocorticoid receptor activities

Vitamin A is a nutrient with remarkable effects on adipose tissue and skeletal muscles, and plays a role in controlling energy balance. Retinoic acid (RA), the carboxylic form of vitamin A, has been associated with improved glucose tolerance and insulin sensitivity. In contrast, elevated glucocorticoids have been implicated in the development of insulin resistance and impaired glucose tolerance. Here, we investigated whether RA might counteract glucocorticoid effects in skeletal muscle cells by lowering 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1)-dependent local glucocorticoid activation and/or activation of glucocorticoid receptor (GR). We found a dose-dependent down-regulation of 11beta-HSD1 mRNA expression and activity upon incubation of fully differentiated mouse C2C12 myotubes with RA. In addition, RA inhibited GR transactivation by an 11beta-HSD1-independent mechanism. The presence of RA during myogenesis did not prevent myotube formation but resulted in relatively glucocorticoid-resistant myotubes, exhibiting very low 11beta-HSD1 expression and GR activity. The use of selective retinoic acid receptor (RAR) and retinoid X receptor ligands provided evidence that these effects were mediated through RARgamma. Importantly, short hairpin RNA against RARgamma abolished the effect of RA on 11beta-HSD1 and GR. In conclusion, we provide evidence for an important role of RA in the control of glucocorticoid activity during myogenesis and in myotubes. Disturbances of the nutrient and hormonal regulation of glucocorticoid action in skeletal muscles might be relevant for metabolic diseases.

Conditional transgenic mice for studying the role of the glucocorticoid receptor in the renal collecting duct

The mineralocorticoid receptor (MR) is a major regulator of renal sodium reabsorption and body fluid homeostasis. However, little is known about glucocorticoid receptor (GR)-dependent renal effects. Glucocorticoids may activate both receptors, so it is difficult to distinguish between MR- and GR-mediated effects in vivo. To overcome this complexity, we used a transgenic mouse model allowing conditional GR overexpression (doxycycline inducible TetON system, Hoxb7 promoter) in the renal collecting duct (CD) to identify GR-regulated genes involved in sodium transport in the CD. In microdissected cortical CD, induction of GR expression led (after 2 d of doxycycline) to increased alpha-epithelial sodium channel and glucocorticoid-induced leucine zipper and decreased abundance of with-no-lysine kinase 4 transcripts, without modification of Na,K-ATPase, serum- and glucocorticoid-kinase-1, or MR expression. No changes occurred in the upstream distal and connecting tubules [distal convoluted tubule (DCT), connecting tubule (CNT)]. Sodium excretion was unaltered, but the urinary aldosterone concentration was reduced, suggesting compensation of transitory extracellular volume expansion that subsequently disappeared. At steady state, i.e. after 15 d of doxycycline administration, transcript abundance remained altered in the CD, whereas mirror changes appeared in the DCT and CNT. Plasma aldosterone or glucocorticoids and blood pressure were all unaffected. These experiments show that: 1) GR, in addition to MR, controls epithelial sodium channel- and glucocorticoid-induced leucine zipper expression in vivo in the CD; 2) with-no-lysine kinase 4 is negatively controlled by GR; and 3) the DCT and CNT compensate for these alterations to maintain normal sodium reabsorption and blood pressure. These results suggest that enhanced GR expression may contribute to enhanced sodium retention in some pathological situations.

Dibutyltin disrupts glucocorticoid receptor function and impairs glucocorticoid-induced suppression of cytokine production

Background

Organotins are highly toxic and widely distributed environmental chemicals. Dibutyltin (DBT) is used as stabilizer in the production of polyvinyl chloride plastics, and it is also the major metabolite formed from tributyltin (TBT) in vivo. DBT is immunotoxic, however, the responsible targets remain to be defined. Due to the importance of glucocorticoids in immune-modulation, we investigated whether DBT could interfere with glucocorticoid receptor (GR) function.

Methodology

We used HEK-293 cells transiently transfected with human GR as well as rat H4IIE hepatoma cells and native human macrophages and human THP-1 macrophages expressing endogenous receptor to study organotin effects on GR function. Docking of organotins was used to investigate the binding mechanism.

Principal Findings

We found that nanomolar concentrations of DBT, but not other organotins tested, inhibit ligand binding to GR and its transcriptional activity. Docking analysis indicated that DBT inhibits GR activation allosterically by inserting into a site close to the steroid-binding pocket, which disrupts a key interaction between the A-ring of the glucocorticoid and the GR. DBT inhibited glucocorticoid-induced expression of phosphoenolpyruvate carboxykinase (PEPCK) and tyrosine-aminotransferase (TAT) and abolished the glucocorticoid-mediated transrepression of TNF-α-induced NF-κB activity. Moreover, DBT abrogated the glucocorticoid-mediated suppression of interleukin-6 (IL-6) and TNF-α production in lipopolysaccharide (LPS)-stimulated native human macrophages and human THP-1 macrophages.

Conclusions

DBT inhibits ligand binding to GR and subsequent activation of the receptor. By blocking GR activation, DBT may disturb metabolic functions and modulation of the immune system, providing an explanation for some of the toxic effects of this organotin.

Dexamethasone suppresses the expression of multiple rat carboxylesterases through transcriptional repression: evidence for an involvement of the glucocorticoid receptor

Carboxylesterases play important roles in the metabolism of xenobiotics and detoxication of insecticides. Without exception, all mammalian species studied express multiple forms of carboxylesterases. Several rat carboxylesterases are well-characterized including hydrolase A, B and S, and the expression of these enzymes is significantly suppressed by glucocorticoid dexamethasone. In this study, we used multiple experimental systems and presented a molecular mechanism for the suppression. Rats receiving one or more daily injections of dexamethasone consistently expressed lower HA, HB and HS. The suppression occurred at the levels of mRNA, protein and hydrolytic activity. In hepatoma cell line H4-II-E-C3, nanomolar dexamethasone caused significant decreases in HA, HB and HS mRNA, and the decreases were abolished by antiglucocorticoid RU486. Additionally, dexamethasone at nanomolar concentrations repressed the promoters of carboxylesterases, and the repression was reduced by glucocorticoid receptor-beta, a dominant negative regulator of the glucocorticoid receptor (GR). In contrast, co-transfection of the pregnane X receptor (PXR) increased the reporter activities, but the increase occurred only at micromolar concentrations of dexamethasone. These findings establish that both GR and PXR are involved in the regulated expression of rat carboxylesterases by dexamethasone but their involvement depends on the concentrations.

Impaired protein stability of 11beta-hydroxysteroid dehydrogenase type 2: a novel mechanism of apparent mineralocorticoid excess

Apparent mineralocorticoid excess (AME) is a severe form of hypertension that is caused by impaired activity of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), which converts biologically active cortisol into inactive cortisone. Mutations in HSD11B2 result in cortisol-induced activation of mineralocorticoid receptors and cause hypertension with hypokalemia, metabolic alkalosis, and suppressed circulating renin and aldosterone concentrations. This study uncovered the first patient with AME who was described in the literature, identified the genetic defect in HSD11B2, and provided evidence for a novel mechanism of reduced 11beta-HSD2 activity. This study identified a cluster of amino acids (335 to 339) in the C-terminus of 11beta-HSD2 that are essential for protein stability. The cluster includes Tyr(338), which is mutated in the index patient, and Arg(335) and Arg(337), previously reported to be mutated in hypertensive patients. It was found that wild-type 11beta-HSD2 is a relatively stable enzyme with a half-life of 21 h, whereas that of Tyr(338)His and Arg(337)His was 3 and 4 h, respectively. Enzymatic activity of Tyr(338)His was partially retained at 26 degrees C or in the presence of the chemical chaperones glycerol and dexamethasone, indicating thermodynamic instability and misfolding. The results provide evidence that the degradation of both misfolded mutant Tyr(338)His and wild-type 11beta-HSD2 occurs through the proteasome pathway. Therefore, impaired 11beta-HSD2 protein stability rather than reduced gene expression or loss of catalytic activity seems to be responsible for the development of hypertension in some individuals with AME.

Disruption of glucocorticoid action by environmental chemicals: potential mechanisms and relevance

Glucocorticoids play an essential role in the regulation of key physiological processes, including immunomodulation, brain function, energy metabolism, electrolyte balance and blood pressure. Exposure to naturally occurring compounds or industrial chemicals that impair glucocorticoid action may contribute to the increasing incidence of cognitive deficits, immune disorders and metabolic diseases. Potentially, "glucocorticoid disruptors" can interfere with various steps of hormone action, e.g. hormone synthesis, binding to plasma proteins, delivery to target cells, pre-receptor regulation of the ratio of active versus inactive hormones, glucocorticoid receptor (GR) function, or export and degradation of glucocorticoids. Several recent studies indicate that such chemicals exist and that some of them can cause multiple toxic effects by interfering with different steps of hormone action. For example, increasing evidence suggests that organotins disturb glucocorticoid action by altering the function of factors that regulate the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) pre-receptor enzymes, by direct inhibition of 11beta-HSD2-dependent inactivation of glucocorticoids, and by blocking GR activation. These observations emphasize on the complexity of the toxic effects caused by such compounds and on the need of suitable test systems to assess their effects on each relevant step.

Reduction of glucocorticoid receptor ligand binding by the 11-beta hydroxysteroid dehydrogenase type 2 inhibitor, Thiram

Endogenous and synthetic glucocorticoids (GCs), such as cortisol and dexamethasone (Dex), modulate airway inflammation, regulate the production of surfactant by lung epithelial cells, and influence fetal lung maturation. The 11-beta hydroxysteroid dehydrogenase type 2 (HSD2) enzyme catalyzes the oxidation of bioactive cortisol and Dex to their 11-keto metabolites. Thiram (tetramethylthiuram disulfide) specifically inhibits HSD2 activity by oxidizing cysteine residues located in the cofactor binding domain of the enzyme. During studies performed to define a potential role for HSD2 in modulating GC action in human lung epithelial cells, we observed that exposure of intact human lung epithelial cells (NCI-H441) to 50 microM Thiram significantly attenuated the down-stream effects of Dex (100 nM) on the expression of two GC-sensitive genes, pulmonary surfactant proteins A and B. This observation appeared to be inconsistent with simple inhibition of HSD2 activity. Although Thiram inhibited HSD2 oxidase activity in a dose-dependent manner without affecting HSD2 protein expression, Thiram also reduced specific binding of [3H]-Dex to the glucocorticoid receptor (GR). Pre-treatment of cells with 1 mM dithiothreitol (DTT), a thiol-reducing agent, completely blocked the inhibitory effect of Thiram on ligand binding. These results are suggestive that Thiram may alter the ligand-binding domain of the GR by oxidizing critical thiol-containing amino acid residues. Taken collectively, these data demonstrate that attenuated down-stream GC signaling, via decreased binding of ligand to the GR, is a novel cellular effect of Thiram exposure in human lung epithelial cells.

11Beta-hydroxysteroid dehydrogenase type 2 and the regulation of surfactant protein A by dexamethasone metabolites

Glucocorticoid (GC) metabolism by the 11beta-hydroxysteroid dehydrogenase (HSD) system is an important prereceptor regulator of GC action. The HSD enzymes catalyze the interconversion of the endogenous, biologically active GC cortisol and its inactive 11-dehydro metabolite cortisone. The role of the HSD enzymes in the metabolism of synthetic GCs, such as dexamethasone (Dex), is more complex. The human lung is a classic GC-sensitive organ; however, the roles of the HSD enzymes (HSD1 and HSD2) in the human lung are poorly understood. In the present study, we examined the expression of the HSD enzymes in human adult and fetal lung tissues and the human lung epithelial cell line NCI-H441. We observed that human adult and fetal lung tissues, as well as H441 cells, express HSD2 protein and that it is upregulated by Dex (10(-7) M). By contrast, HSD1 protein was undetectable. We also show that the Dex-mediated regulation of surfactant protein A is attenuated by inhibition of HSD2 activity. Furthermore, we demonstrate that unlike the inactive, 11-dehydro metabolite of cortisol (i.e., cortisone), the 11-dehydro metabolite of Dex, 11-dehydro-Dex, competes for binding to the GC receptor (GR) in human lung epithelial cells and retains GR agonist activity. Together, these data suggest that differences exist in the biological activities of the metabolites of cortisol and Dex.

Glucocorticoid Metabolism in the Human Fetal Lung: Implications for Lung Development and the Pulmonary Surfactant System

It has been nearly 35 years since Liggins and Howie first reported the benefits of antenatal glucocorticoid (GC) treatment to promote the maturation of the human fetal lung, and nearly that long since Pasqualini and colleagues demonstrated that the human fetal lung actively metabolizes GCs. Since that time, our understanding of the effects of GCs on fetal lung maturation and pulmonary surfactant production has increased dramatically. Similarly, characterization of the enzymes involved in GC metabolism has greatly expanded our understanding of GC signaling in target tissues. In man, the biologically active GC (cortisol) and the biologically inactive GC (cortisone) are interconverted by the tissue-specific expression of the type 1 and type 2 11beta-hydroxysteroid dehydrogenase enzymes (HSD1 and HSD2). Much of the research on GC metabolism in peripheral target tissues has focused on the role of HSD1 in amplifying the effects of GCs in liver and adipose tissue or on the role of HSD2 in blocking the effects of GCs in the kidney and placenta. In contrast, the role of GC metabolism in modulating the effects of GCs on fetal lung maturation and the pulmonary surfactant system in humans is less understood. The goal of this review article is to present a brief overview of the role of GCs in human fetal lung maturation and pulmonary surfactant production, and to familiarize the reader with the biochemistry of the metabolism of natural and synthetic GCs by the HSD enzymes. In addition, we will review data concerning the expression and activity of the HSD enzymes in the human fetal lung and contrast this to what is known about the HSD enzymes in the fetal rodent lung. Although rodents, rabbits, sheep, and several primates have been invaluable model systems for the study of fetal lung development, we have chosen to largely focus this review on human lung, since there are significant differences in GC metabolism between humans and other species.

A genetically encoded indicator for assaying bioactive chemicals that induce nuclear transport of glucocorticoid receptor

Glucocorticoids, the adrenal steroid hormones secreted during stress, are essential to homeostasis and metabolism in the human body. An impaired glucocorticoid signaling due to dysfunction of the glucocorticoid receptor (GR) by synthetic chemicals can cause diseases and disruptions of the homeostasis and metabolism. Here we demonstrate the development of a method for screening endocrine-disrupting chemicals and potent risk factors of human diseases based on the nuclear trafficking of the GR. We constructed a new assay using a pair of genetic indicators with the full length of the GR, split Renilla luciferase (RLuc), and split DnaE (a protein splicing element). The GR-containing fusion protein with C-terminal halves of DnaE and RLuc is localized in cytosol due to the cytosolic character of the GR, whereas the fusion protein with N-terminal halves of DnaE and RLuc stays in the nucleus due to the cofused nucleus localization signal. On being stimulated with a ligand, the GR is translocated into the cellular nucleus. Thus, a protein splicing occurs in the nucleus by an interaction between the splicing junctions of each DnaE fragment. The enzymatic activities from the reconstituted RLuc allow the ligand-dependent luminescence intensities. The feasibility of the method was evaluated by quantifying the hormonal activities of 20 different kinds of steroids and synthetic chemicals using the NIH 3T3 cells carrying the pair of indicators. The hormonal activities of tested ligands are discussed based on the chemical structure-activity relationship. We found that androgens, testosterone, and 19-nortestosterone weakly induce the nuclear transport of the GR. The current assay allows high-throughput screening of risk chemicals and drug candidates influential to a signal transduction pathway of the GR.

Organotins disrupt the 11beta-hydroxysteroid dehydrogenase type 2-dependent local inactivation of glucocorticoids

Organotins, important environmental pollutants widely used in agricultural and industrial applications, accumulate in the food chain and induce imposex in several marine species as well as neurotoxic and immunotoxic effects in higher animals. Reduced birth weight and thymus involution, observed upon exposure to organotins, can also be caused by excessive glucocorticoid levels. We now demonstrate that organotins efficiently inhibit 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), converting active 11beta-hydroxyglucocorticoids into inactive 11-ketoglucocorticoids, but not 11beta-HSD1, which catalyzes the reverse reaction. Di- and tributyltin as well as di- and triphenyltin inhibited recombinant and endogenous 11beta-HSD2 in lysates and intact cells with IC50 values between 500 nM and 3 microM. Dithiothreitol protected 11beta-HSD2 from organotin-dependent inhibition, indicating that organotins act by binding to one or more cysteines. Mutational analysis and 3-D structural modeling revealed several important interactions of cysteines in 11beta-HSD2. Cys90, Cys228, and Cys264 were essential for enzymatic stability and catalytic activity, suggesting that disruption of such interactions by organotins leads to inhibition of 11beta-HSD2. Enhanced glucocorticoid concentrations due to disruption of 11beta-HSD2 function may contribute to the observed organotin-dependent toxicity in some glucocorticoid-sensitive tissues such as thymus and placenta.

Glucocorticoid programming of adult disease

Fetal exposure to elevated levels of glucocorticoids can occur naturally when maternal glucocorticoids are elevated in times of stress or when exogenous glucocorticoids are administered. Epidemiological studies and animal models have shown that, whereas short-term benefits may be associated with fetal glucocorticoid exposure, long-term deleterious effects may arise. This review compares the effects of exposure to natural versus synthetic glucocorticoids and considers the ways in which the timing of the exposure and the sex of the fetus may influence outcomes. Some of the long-term effects of glucocorticoid exposure may be explained by epigenetic mechanisms.

MineralocorticoidversusGlucocorticoid Receptor Occupancy Mediating Aldosterone-Stimulated Sodium Transport in a Novel Renal Cell Line

Aldosterone controls sodium balance by regulating an epithelial sodium channel (ENaC)-mediated sodium transport along the aldosterone-sensitive distal nephron, which expresses both mineralocorticoid (MR) and glucocorticoid receptors (GR). Mineralocorticoid specificity is ensured by 11beta-hydroxysteroid dehydrogenase type 2, which metabolizes cortisol or corticosterone into inactive metabolites that are unable to bind MR and/or GR. The fractional occupancy of MR and GR by aldosterone mediating the sodium transport response in the aldosterone-sensitive distal nephron cannot be studied in vivo. For answering this question, a novel mouse cortical collecting duct cell line (mCCD(cl1)), which expresses significant levels of MR and GR and a robust aldosterone sodium transport response, was used. Aldosterone elicited a biphasic response: Low doses (K(1/2) = approximately 0.5 nM) induced a transient and early increase of sodium transport (peaking at 3 h), whereas high doses (K(1/2) = approximately 90 nM) entailed an approximately threefold larger, long-lasting response. At 3 h, the corticosterone dose-response curve was shifted to the right compared with that of aldosterone by more than two log concentrations, an effect that was fully reverted in the presence of the 11beta-hydroxysteroid dehydrogenase type 2 inhibitor carbenoxolone. Low doses of dexamethasone (0.1 to 1 nM) failed to induce an early response, but high doses elicited a long-lasting response (K(1/2) = approximately 8 nM), similar to that observed for high aldosterone concentrations. Equilibrium binding assays showed that both aldosterone and corticosterone bind to a high-affinity, low-capacity site, whereas dexamethasone binds to one site. Within the physiologic range of aldosterone concentrations, sodium transport is predicted to be controlled by MR occupancy during circadian cycles and by MR and GR occupancy during salt restriction or acute stress.

Epigenetic regulation of 11 beta-hydroxysteroid dehydrogenase type 2 expression

The enzyme 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta HSD2) is selectively expressed in aldosterone target tissues, where it confers aldosterone selectivity for the mineralocorticoid receptor by inactivating 11 beta-hydroxyglucocorticoids. Variable activity of 11 beta HSD2 is relevant for blood pressure control and hypertension. The present investigation aimed to elucidate whether an epigenetic mechanism, DNA methylation, accounts for the rigorous control of expression of the gene encoding 11 beta HSD2, HSD11B2. CpG islands covering the promoter and exon 1 of HSD11B2 were found to be densely methylated in tissues and cell lines with low expression but not those with high expression of HSD11B2. Demethylation induced by 5-aza-2'-deoxycytidine and procainamide enhanced the transcription and activity of the 11 beta HSD2 enzyme in human cells in vitro and in rats in vivo. Methylation of HSD11B2 promoter-luciferase constructs decreased transcriptional activity. Methylation of recognition sequences of transcription factors, including those for Sp1/Sp3, Arnt, and nuclear factor 1 (NF1) diminished their DNA-binding activity. Herein NF1 was identified as a strong HSD11B2 stimulatory factor. The effect of NF1 was dependent on the position of CpGs and the combination of CpGs methylated. A methylated-CpG-binding protein complex 1 transcriptional repression interacted directly with the methylated HSD11B2 promoter. These results indicate a role for DNA methylation in HSD11B2 gene repression and suggest an epigenetic mechanism affecting this gene causally linked with hypertension.

Glucocorticoid-mediated mineralocorticoid receptor activation and hypertension

PURPOSE OF REVIEW

Traditionally, the mineralocorticoid receptor was thought to be activated by the mineralocorticoid hormone aldosterone, and to exhibit its main action on epithelia by promoting renal sodium retention, potassium excretion and inducing hypertension upon excessive activation. Recently, evidence appeared that mineralocorticoid receptors are expressed in nonepithelial cells and activated by endogenous glucocorticoids including cortisol. Therefore, the prereceptor regulation of cortisol access to the mineralocorticoid receptors by 11beta-hydroxysteroid dehydrogenase enzymes (11beta-HSDs), a mechanism absent in most nonepithelial cells, appears to be relevant for disease states with cortisol-induced mineralocorticoid action. The present review focuses on direct and indirect effects attributable to mineralocorticoid receptor activation by glucocorticoids.

RECENT FINDINGS

The determination of the intracellular topology of 11beta-HSD1, facing the endoplasmic reticulum lumen, and 11beta-HSD2, facing the cytoplasm, suggests that 11beta-HSD1 acts as a prereceptor mechanism in the local activation of glucocorticoid receptors, whereas 11beta-HSD2 controls mineralocorticoid receptors by interacting with the receptor in the absence of aldosterone. Downregulation of 11beta-HSD2 was observed with various stimuli including hypoxia, shear stress, angiotensin II and tumor necrosis factor alpha. The corresponding signal transcription pathways and some relevant transcription factors have been identified. Renal sodium retention in liver cirrhosis, nephrotic syndrome and hypoxia have been linked to 11beta-HSD2 reduced activity. Overexpression of 11beta-HSD1 specifically in adipose tissue in mice caused central obesity, a metabolic syndrome and hypertension due to increased intracellular cortisol concentrations. Peroxisome proliferator-activated receptor gamma agonists reduce 11beta-HSD1 activity and diminish the intracellular availability of cortisol, an effect accompanied by a decline in blood pressure. Three individuals with loss-of-function mutations of peroxisome proliferator-activated receptor gamma developed early hypertension. A potential mechanism might be glucocorticoid dependent mineralocorticoid receptor-mediated downregulation of endothelial nitric oxide synthase.

SUMMARY

Recently, mineralocorticoid receptor antagonists have been used in the randomized aldactone evaluation study (RALES) with spironolactone, the eplerenone post-AMI heart failure efficacy and survival study (EPHESUS), and in severe and postmyocardial infarct heart failure, respectively. These investigations cannot be understood on the basis of the present physiological knowledge and underscore the relevance of focusing on mineralocorticoid receptor activation by ligands other than aldosterone.