Chenodeoxycholic acid and deoxycholic acid inhibit 11 beta-hydroxysteroid dehydrogenase type 2 and cause cortisol-induced transcriptional activation of the mineralocorticoid receptor

Deoxycholic Acid, a Secondary Bile Acid, Increases Cardiac Output and Blood Pressure in Rats

BACKGROUND

Deoxycholic acid (DCA) is a secondary bile acid produced by gut bacteria. Elevated serum concentrations of DCA are observed in cardiovascular disease (CVD). We hypothesized that DCA might influence hemodynamic parameters in rats.

METHODS

The concentration of DCA in systemic blood was measured with liquid chromatography coupled with mass spectrometry. Arterial blood pressure (BP), heart rate (HR) and echocardiographic parameters were evaluated in anesthetized, male, 3-4-month-old Sprague-Dawley rats administered intravenously (IV) or intracerebroventricularly (ICV) with investigated compounds. Mesenteric artery (MA) reactivity was tested ex vivo.

RESULTS

The baseline plasma concentration of DCA was 0.24 ± 0.03 mg/L. The oral antibiotic treatment produced a large decrease in the concentration. Administered IV, the compound increased BP and HR in a dose-dependent manner. DCA also increased heart contractility and cardiac output. None of the tested compounds-prazosin (an alpha-blocker), propranolol (beta-adrenolytic), atropine (muscarinic receptor antagonist), glibenclamide (K-ATP inhibitor) or DY 268 (FXR antagonist), glycyrrhetinic acid (11HSD2 inhibitor)-significantly diminished the DCA-induced pressor effect. ICV infusion did not exert significant HR or BP changes. DCA relaxed MAs. Systemic vascular resistance did not change significantly.

CONCLUSIONS

DCA elevates BP primarily by augmenting cardiac output. As a metabolite derived from gut bacteria, DCA potentially serves as a mediator in the interaction between the gut microbiota and the host's circulatory system.

Regulation of Immune Homeostasis, Inflammation, and HIV Persistence by the Microbiome, Short-Chain Fatty Acids, and Bile Acids

Despite antiretroviral therapy (ART), people living with human immunodeficiency virus (HIV) (PLWH) continue to experience chronic inflammation and immune dysfunction, which drives the persistence of latent HIV and prevalence of clinical comorbidities. Elucidating the mechanisms that lead to suboptimal immunity is necessary for developing therapeutics that improve the quality of life of PLWH. Although previous studies have found associations between gut dysbiosis and immune dysfunction, the cellular/molecular cascades implicated in the manifestation of aberrant immune responses downstream of microbial perturbations in PLWH are incompletely understood. Recent literature has highlighted that two abundant metabolite families, short-chain fatty acids (SCFAs) and bile acids (BAs), play a crucial role in shaping immunity. These metabolites can be produced and/or modified by bacterial species that make up the gut microbiota and may serve as the causal link between changes to the gut microbiome, chronic inflammation, and immune dysfunction in PLWH. In this review, we discuss our current understanding of the role of the microbiome on HIV acquisition and latent HIV persistence despite ART. Further, we describe cellular/molecular cascades downstream of SCFAs and BAs that drive innate or adaptive immune responses responsible for promoting latent HIV persistence in PLWH. This knowledge can be used to advance HIV cure efforts.

Acupuncture at Taichong and Zusanli points exerts hypotensive effect in spontaneously hypertensive rats by metabolomic analysis

BACKGROUND

The development of hypertension affects several target organs, the kidneys being one of them. Acupuncture has been used to treat hypertension for a long time. Several mechanisms of acupuncture on hypotensive effect have been reveled, while the effects of acupuncture on the alterations in renal cortex from a metabolomic perspective are still unclear.

METHODS

Twelve male Wistar rats served as the control group (Wistar Group). Twenty-four male spontaneously hypertensive rats (SHR) were randomly divided into two groups: the model group (SHR Group) and the acupuncture group (AC Group). In the AC Group, milli-needle acupuncture was used to puncture the bilateral Taichong (LR3) and Zusanli (ST36) points. Blood pressure values were measured weekly and the rats were euthanized after three weeks. Renal cortical tissues were collected for non-targeted and targeted metabolomic analyses.

RESULTS

Acupuncture reduced blood pressure values in rats (Compared with the SHR Group, P < 0.001). Thirteen metabolites with significant differences and three metabolic pathways were screened by untargeted metabolomics. The SHR Group was compared with the Wistar Group and AC Group both involving metabolites and pathways related to bile acid metabolism. Furthermore, targeted metabolomics quantification of four bile acids, Cholic acid (CA), Allocholic acid (ACA), Deoxycholic acid (DCA) and Chenodeoxycholic acid (CDCA), revealed that all bile acid concentrations were relatively high in the SHR Group, except for ACA.

CONCLUSION

This study indicate that abnormal bile acid metabolism may be an independent risk factor the development of hypertension. Acupuncture at Taichong and at Zusanli points effectively modulated bile acids metabolism in SHR renal cortex tissues to exert a hypotensive effect, and CA may be able to be a new target for the treatment of hypertension.

Modulation of 11β-hydroxysteroid dehydrogenase functions by the cloud of endogenous metabolites in a local microenvironment: The glycyrrhetinic acid-like factor (GALF) hypothesis

11β-Hydroxysteroid dehydrogenase (11β-HSD)-dependent conversion of cortisol to cortisone and corticosterone to 11-dehydrocorticosterone are essential in regulating transcriptional activities of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Inhibition of 11β-HSD by glycyrrhetinic acid metabolites, bioactive components of licorice, causes sodium retention and potassium loss, with hypertension characterized by low renin and aldosterone. Essential hypertension is a major disease, mostly with unknown underlying mechanisms. Here, we discuss a putative mechanism for essential hypertension, the concept that endogenous steroidal compounds acting as glycyrrhetinic acid-like factors (GALFs) inhibit 11β-HSD dehydrogenase, and allow for glucocorticoid-induced MR and GR activation with resulting hypertension. Initially, several metabolites of adrenally produced glucocorticoids and mineralocorticoids were shown to be potent 11β-HSD inhibitors. Such GALFs include modifications in the A-ring and/or at positions 3, 7 and 21 of the steroid backbone. These metabolites may be formed in peripheral tissues or by gut microbiota. More recently, metabolites of 11β-hydroxy-Δ4androstene-3,17-dione and 7-oxygenated oxysterols have been identified as potent 11β-HSD inhibitors. In a living system, 11β-HSD isoforms are not exposed to a single substrate but to several substrates, cofactors, and various inhibitors simultaneously, all at different concentrations depending on physical state, tissue and cell type. We propose that this "cloud" of steroids and steroid-like substances in the microenvironment determines the 11β-HSD-dependent control of MR and GR activity. A dysregulated composition of this cloud of metabolites in the respective microenvironment needs to be taken into account when investigating disease mechanisms, for forms of low renin, low aldosterone hypertension.

Sepsis as a Pan-Endocrine Illness-Endocrine Disorders in Septic Patients

Sepsis is defined as "life-threatening organ dysfunction caused by a dysregulated host response to infection". One of the elements of dysregulated host response is an endocrine system disorder. Changes in its functioning in the course of sepsis affect almost all hormonal axes. In sepsis, a function disturbance of the hypothalamic-pituitary-adrenal axis has been described, in the range of which the most important seems to be hypercortisolemia in the acute phase. Imbalance in the hypothalamic-pituitary-thyroid axis is also described. The most typical manifestation is a triiodothyronine concentration decrease and reverse triiodothyronine concentration increase. In the somatotropic axis, a change in the secretion pattern of growth hormone and peripheral resistance to this hormone has been described. In the hypothalamic-pituitary-gonadal axis, the reduction in testosterone concentration in men and the stress-induced "hypothalamic amenorrhea" in women have been described. Catecholamine and β-adrenergic stimulation disorders have also been reported. Disorders in the endocrine system are part of the "dysregulated host response to infection". They may also affect other components of this dysregulated response, such as metabolism. Hormonal changes occurring in the course of sepsis require further research, not only in order to explore their potential significance in therapy, but also due to their promising prognostic value.

11β-hydroxysteroid dehydrogenases: A growing multi-tasking family

This review briefly addresses the history of the discovery and elucidation of the three cloned 11β-hydroxysteroid dehydrogenase (11βHSD) enzymes in the human, 11βHSD1, 11βHSD2 and 11βHSD3, an NADP⁺-dependent dehydrogenase also called the 11βHSD1-like dehydrogenase (11βHSD1L), as well as evidence for yet identified 11βHSDs. Attention is devoted to more recently described aspects of this multi-functional family. The importance of 11βHSD substrates other than glucocorticoids including bile acids, 7-keto sterols, neurosteroids, and xenobiotics is discussed, along with examples of pathology when functions of these multi-tasking enzymes are disrupted. 11βHSDs modulate the intracellular concentration of glucocorticoids, thereby regulating the activation of the glucocorticoid and mineralocorticoid receptors, and 7β-27-hydroxycholesterol, an agonist of the retinoid-related orphan receptor gamma (RORγ). Key functions of this nuclear transcription factor include regulation of immune cell differentiation, cytokine production and inflammation at the cell level. 11βHSD1 expression and/or glucocorticoid reductase activity are inappropriately increased with age and in obesity and metabolic syndrome (MetS). Potential causes for disappointing results of the clinical trials of selective inhibitors of 11βHSD1 in the treatment of these disorders are discussed, as well as the potential for more targeted use of inhibitors of 11βHSD1 and 11βHSD2.

Adrenal insufficiency in critical patients: New ethiopathogenic concepts and therapeutic implications

Recently, there have been advances in understanding of the changes that occur in the hypothalamic-pituitary-adrenal axis during the different stages of critical disease. Such advances have led to a paradigm change, so that the aforementioned adaptations are no longer considered the result of adrenal axis activation, but a consequence of decreased cortisol metabolism illness. Knowledge of this new pathophysiological bases should lead to reconsider the diagnosis and treatment of adrenal insufficiency in critically ill patients, a condition poorly understood to date.

Glucocorticoids and gut bacteria: "The GALF Hypothesis" in the metagenomic era

A new concept is emerging in biomedical sciences: the gut microbiota is a virtual 'organ' with endocrine function. Here, we explore the literature pertaining to the role of gut microbial metabolism of endogenous adrenocorticosteroids as a contributing factor in the etiology of essential hypertension. A body of literature demonstrates that bacterial products of glucocorticoid metabolism are absorbed into the portal circulation, and pass through the kidney before excretion into urine. Apparent mineralocorticoid excess (AME) syndrome patients were found to have congenital mutations resulting in non-functional renal 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) and severe hypertension often lethal in childhood. 11β-HSD2 acts as a "guardian" enzyme protecting the mineralocorticoid receptor from excess cortisol, preventing sodium and water retention in the normotensive state. Licorice root, whose active ingredient, glycerrhetinic acid (GA), inhibits renal 11β-HSD2, and thereby causes hypertension in some individuals. Bacterially derived glucocorticoid metabolites may cause hypertension in some patients by a similar mechanism. Parallel observations in gut microbiology coupled with screening of endogenous steroids as inhibitors of 11β-HSD2 have implicated particular gut bacteria in essential hypertension through the production of glycerrhetinic acid-like factors (GALFs). A protective role of GALFs produced by gut bacteria in the etiology of colorectal cancer is also explored.

The HPA axis response to critical illness: New study results with diagnostic and therapeutic implications

For decades, elevated plasma cortisol concentrations in critically ill patients were exclusively ascribed to a stimulated hypothalamus-pituitary-adrenal axis with increased circulating adrenocorticotropic hormone (ACTH) inferred to several-fold increase adrenal cortisol synthesis. However, 'ACTH-cortisol dissociation' has been reported during critical illness, referring to low circulating ACTH coinciding with elevated circulating cortisol. It was recently shown that metabolism of cortisol is significantly reduced in critically ill patients explained by a suppression of the activity and expression of cortisol metabolizing enzymes in kidney and liver. This reduced cortisol breakdown determines hypercortisolemia, much more than increased cortisol production, in the critically ill. Although the low plasma ACTH concentrations, evoked by the elevated plasma cortisol via feedback inhibition, are part of this adaptation, they may negatively affect adrenocortical structure and function in the prolonged phase of critical illness. These new insights have implications for diagnosis and treatment of adrenal insufficiency in critically ill patients.

C21-steroids inactivation and glucocorticoid synthesis in the developing lung

Glucocorticoids (GCs) are important regulators of lung development. The genes normally involved in GC synthesis in adrenals are co-expressed with 20α-hydroxysteroid dehydrogenase (20α-HSD) in the developing lung. In this study, C21-steroid metabolism was investigated in fetal and postnatal mouse lungs. Incubation of [(3)H]-progesterone with lung explant cultures of different perinatal developmental time points revealed two different (antenatal vs. postnatal) complex metabolization patterns. Progesterone inactivation was predominant. 20αOH-derivatives were more abundant after birth and some metabolites were 5α-reduced. Using [(3)H]-progesterone as substrate, corticosterone synthesis was only observed in a fraction of lung explants from gestation day (GD) 15.5. Neither aldosterone synthase nor P450c17 activity was observed. With epithelial-enriched primary cell cultures, deoxycorticosterone synthesis from [(3)H]-progesterone was observed. With lung explants incubated with [(3)H]-corticosterone as substrate, [(3)H]-4-pregnen-21-ol-3,11,20-trione (11-dehydrocorticosterone), the product of 11β-HSD2, accumulated in higher proportion on GD 15.5 than at later developmental time points. The temporal correlation observed between levels of progesterone inactivation by 20α-HSD (higher after birth) and the sensitivity of lung development to GCs suggests a role for 20α-HSD in the modulation of GR occupancy through the control of 21-hydroxylase substrate and product levels. In conclusion, the developing lung is characterized by effective inactivation of c21-steroids by 20α-HSD. The formation of active GCs from the "adrenal"-like pathway was observed with some lung explants and primary epithelial cell cultures. Coexistence of this GC synthesis pathway with 20α-HSD activity strongly suggests local regulation of GC action and is compatible with intracrine/paracrine actions of GC.

Novel insights in the HPA-axis during critical illness

Critical illness represents a major challenge for the human body, implicating that an adequate stress response is indispensable for survival. Therefore, for a long time, activation of the hypothalamic pituitary adrenal axis was assumed to be increased to respond to this stressful situation. Recent novel insights, however, provided evidence that the HPA-axis is regulated differently during critical illness. Cortisol metabolism was shown to be reduced which contributed to hypercortisolism in an energy efficient way without increasing cortisol production dramatically. Yet, the concomitant low ACTH levels, explained by negative feedback inhibition, could lead to an understimulation of the adrenal gland and affect adrenal structure and function, given the crucial role of ACTH for adrenal gland maintenance. This side-effect could negatively affect outcome predominantly in the prolonged phase of critical illness and could explain the increased incidence of adrenal failure in these patients. Altogether, novel findings represent a paradigm shift in our current understanding of HPA-axis regulation during critical illness and redirect future research perspectives with an urgent need to well-designed clinical trials to further explore HPA-axis functioning during critical illness.

Regulation of 11β-hydroxysteroid dehydrogenase type 2 by microRNA

The enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) is selectively expressed in aldosterone target tissues, conferring aldosterone selectivity for the mineralocorticoid receptor. A diminished activity causes salt-sensitive hypertension. The mechanism of the variable and distinct 11β-hydroxysteroid dehydrogenase type 2 gene (HSD11B2) expression in the cortical collecting duct is poorly understood. Here, we analyzed for the first time whether the 11β-HSD2 expression is modulated by microRNAs (miRNAs). In silico analysis revealed 53 and 27 miRNAs with potential binding sites on human or rat HSD11B2 3'-untranslated region. A reporter assay demonstrated 3'-untranslated region-dependent regulation of human and rodent HSD11B2. miRNAs were profiled from cortical collecting ducts and proximal convoluted tubules. Bioinformatic analyses showed a distinct clustering for cortical collecting ducts and proximal convoluted tubules with 53 of 375 miRNAs, where 13 were predicted to bind to the rat HSD11B2 3'-untranslated region. To gain insight into potentially relevant miRNAs in vivo, we investigated 2 models with differential 11β-HSD2 activity linked with salt-sensitive hypertension. (1) Comparing Sprague-Dawley with low and Wistar rats with high 11β-HSD2 activity revealed rno-miR-20a-5p, rno-miR-19b-3p, and rno-miR-190a-5p to be differentially expressed. (2) Uninephrectomy lowered 11β-HSD2 activity in the residual kidney with differentially expressed rno-miR-19b-3p, rno-miR-29b-3p, and rno-miR-26-5p. In conclusion, miRNA-dependent mechanisms seem to modulate 11β-HSD2 dosage in health and disease states.

Cortisol metabolism in critical illness: implications for clinical care

PURPOSE OF REVIEW

Critical illness is uniformly characterized by elevated plasma cortisol concentrations, traditionally attributed exclusively to increased cortisol production driven by an activated hypothalamic pituitary adrenal axis. However, as plasma adrenocorticotropic hormone (ACTH) concentrations are often not elevated or even low during critical illness, alternative mechanisms must contribute.

RECENT FINDINGS

Recent investigations revealed that plasma clearance of cortisol is markedly reduced during critical illness, explained by suppressed expression and activity of the main cortisol metabolizing enzymes in liver and kidney. Furthermore, unlike previously inferred, cortisol production rate in critically ill patients was only moderately increased to less than double that of matched healthy subjects. In the face of low-plasma ACTH concentrations, these data suggest that other factors drive hypercortisolism during critical illness, which may suppress ACTH by feedback inhibition. These new insights add to the limitations of the current diagnostic tools to identify patients at risk of failing adrenal function during critical illness. They also urge to investigate the impact of lower hydrocortisone doses than those hitherto used.

SUMMARY

Recent novel insights reshape the current understanding of the hormonal stress response to critical illness and further underline the need for more studies to unravel the pathophysiology of adrenal (dys)functioning during critical illness.

Endocrine responses to critical illness: novel insights and therapeutic implications

CONTEXT

Critical illness, an extreme form of severe physical stress, is characterized by important endocrine and metabolic changes. Due to critical care medicine, survival from previously lethal conditions has become possible, but many patients now enter a chronic phase of critical illness. The role of the endocrine and metabolic responses to acute and prolonged critical illness in mediating or hampering recovery remains highly debated.

EVIDENCE ACQUISITION

The recent literature on changes within the hypothalamic-pituitary-thyroid axis and the hypothalamic-pituitary-adrenal axis and on hyperglycemia in relation to recovery from critical illness was critically appraised and interpreted against previous insights. Possible therapeutic implications of the novel insights were analyzed. Specific remaining questions were formulated.

EVIDENCE SYNTHESIS

In recent years, important novel insights in the pathophysiology and the consequences of some of these endocrine responses to acute and chronic critical illness were generated. Acute endocrine adaptations are directed toward providing energy and substrates for the vital fight-or-flight response in a context of exogenous substrate deprivation. Distinct endocrine and metabolic alterations characterize the chronic phase of critical illness, which seems to be no longer solely beneficial and could hamper recovery and rehabilitation.

CONCLUSIONS

Important novel insights reshape the current view on endocrine and metabolic responses to critical illness and further clarify underlying pathways. Although many issues remain unresolved, some therapeutic implications were already identified. More work is required to find better treatments, and the optimal timing for such treatments, to further prevent protracted critical illness, to enhance recovery thereof, and to optimize rehabilitation.

Farnesoid X receptor alpha: a molecular link between bile acids and steroid signaling?

Bile acids are cholesterol metabolites that have been extensively studied in recent decades. In addition to having ancestral roles in digestion and fat solubilization, bile acids have recently been described as signaling molecules involved in many physiological functions, such as glucose and energy metabolisms. These signaling pathways involve the activation of the nuclear receptor farnesoid X receptor (FXRα) or of the G protein-coupled receptor TGR5. In this review, we will focus on the emerging role of FXRα, suggesting important functions for the receptor in steroid metabolism. It has been described that FXRα is expressed in the adrenal glands and testes, where it seems to control steroid production. FXRα also participates in steroid catabolism in the liver and interferes with the steroid signaling pathways in target tissues via crosstalk with steroid receptors. In this review, we discuss the potential impacts of bile acid (BA), through its interactions with steroid metabolism, on glucose metabolism, sexual function, and prostate and breast cancers. Although several of the published reports rely on in vitro studies, they highlight the need to understand the interactions that may affect health. This effect is important because BA levels are increased in several pathophysiological conditions related to liver injuries. Additionally, BA receptors are targeted clinically using therapeutics to treat liver diseases, diabetes, and cancers.

Reduced cortisol metabolism during critical illness

BACKGROUND

Critical illness is often accompanied by hypercortisolemia, which has been attributed to stress-induced activation of the hypothalamic-pituitary-adrenal axis. However, low corticotropin levels have also been reported in critically ill patients, which may be due to reduced cortisol metabolism.

METHODS

In a total of 158 patients in the intensive care unit and 64 matched controls, we tested five aspects of cortisol metabolism: daily levels of corticotropin and cortisol; plasma cortisol clearance, metabolism, and production during infusion of deuterium-labeled steroid hormones as tracers; plasma clearance of 100 mg of hydrocortisone; levels of urinary cortisol metabolites; and levels of messenger RNA and protein in liver and adipose tissue, to assess major cortisol-metabolizing enzymes.

RESULTS

Total and free circulating cortisol levels were consistently higher in the patients than in controls, whereas corticotropin levels were lower (P<0.001 for both comparisons). Cortisol production was 83% higher in the patients (P=0.02). There was a reduction of more than 50% in cortisol clearance during tracer infusion and after the administration of 100 mg of hydrocortisone in the patients (P≤0.03 for both comparisons). All these factors accounted for an increase by a factor of 3.5 in plasma cortisol levels in the patients, as compared with controls (P<0.001). Impaired cortisol clearance also correlated with a lower cortisol response to corticotropin stimulation. Reduced cortisol metabolism was associated with reduced inactivation of cortisol in the liver and kidney, as suggested by urinary steroid ratios, tracer kinetics, and assessment of liver-biopsy samples (P≤0.004 for all comparisons).

CONCLUSIONS

During critical illness, reduced cortisol breakdown, related to suppressed expression and activity of cortisol-metabolizing enzymes, contributed to hypercortisolemia and hence corticotropin suppression. The diagnostic and therapeutic implications for critically ill patients are unknown. (Funded by the Belgian Fund for Scientific Research and others; ClinicalTrials.gov numbers, NCT00512122 and NCT00115479; and Current Controlled Trials numbers, ISRCTN49433936, ISRCTN49306926, and ISRCTN08083905.).

It takes two to tango: dimerisation of glucocorticoid receptor and its anti-inflammatory functions

For a number of years, there has been a widespread view that the adverse side-effects of prolonged glucocorticoid (GC) treatment are a result of glucocorticoid receptor (GR)-mediated gene activation, whilst the beneficial anti-inflammatory effects result from GR-mediated 'transrepression'. Since the introduction of the dimerisation-deficient GR mutant, GR(dim), was apparently unable to activate gene transcription, yet still able to repress pro-inflammatory gene transcription, the search for novel GR modulators has centred on the separation of gene activation from repression by prevention of GR dimerisation. However, recent work has questioned the conclusions drawn from these early GR(dim) studies, with evidence that GR(dim) mutants not only activate gene transcription, but that, in direct contradiction to the initial GR(dim) work, are also capable of forming dimers. This review of the current literature highlights the versatility of the GR in forming homodimer interactions, as well as the ability to bind to alternate nuclear receptors, and investigates the potential implications such varying GR dimer conformations may have for the design of GR ligands with a safer side effect profile.

Hepatic reduction of the secondary bile acid 7-oxolithocholic acid is mediated by 11β-hydroxysteroid dehydrogenase 1

The oxidized bile acid 7-oxoLCA (7-oxolithocholic acid), formed primarily by gut micro-organisms, is reduced in human liver to CDCA (chenodeoxycholic acid) and, to a lesser extent, UDCA (ursodeoxycholic acid). The enzyme(s) responsible remained unknown. Using human liver microsomes, we observed enhanced 7-oxoLCA reduction in the presence of detergent. The reaction was dependent on NADPH and stimulated by glucose 6-phosphate, suggesting localization of the enzyme in the ER (endoplasmic reticulum) and dependence on NADPH-generating H6PDH (hexose-6-phosphate dehydrogenase). Using recombinant human 11β-HSD1 (11β-hydroxysteroid dehydrogenase 1), we demonstrate efficient conversion of 7-oxoLCA into CDCA and, to a lesser extent, UDCA. Unlike the reversible metabolism of glucocorticoids, 11β-HSD1 mediated solely 7-oxo reduction of 7-oxoLCA and its taurine and glycine conjugates. Furthermore, we investigated the interference of bile acids with 11β-HSD1-dependent interconversion of glucocorticoids. 7-OxoLCA and its conjugates preferentially inhibited cortisone reduction, and CDCA and its conjugates inhibited cortisol oxidation. Three-dimensional modelling provided an explanation for the binding mode and selectivity of the bile acids studied. The results reveal that 11β-HSD1 is responsible for 7-oxoLCA reduction in humans, providing a further link between hepatic glucocorticoid activation and bile acid metabolism. These findings also suggest the need for animal and clinical studies to explore whether inhibition of 11β-HSD1 to reduce cortisol levels would also lead to an accumulation of 7-oxoLCA, thereby potentially affecting bile acid-mediated functions.

Important clinical syndromes associated with liver disease

Several clinical syndromes can develop in many different liver diseases. They are important to understanding the clinical manifestations of hepatobiliary diseases. The signs, diagnostic procedures, and specific diseases associated with these syndromes are discussed.

DHEA induces 11 -HSD2 by acting on CCAAT/enhancer-binding proteins

11beta-Hydroxysteroid dehydrogenase (11beta-HSD) type 1 and type 2 catalyze the interconversion of inactive and active glucocorticoids. Impaired regulation of these enzymes has been associated with obesity, diabetes, hypertension, and cardiovascular disease. Previous studies in animals and humans suggested that dehydroepiandrosterone (DHEA) has antiglucocorticoid effects, but the underlying mechanisms are unknown. In this study, DHEA treatment markedly increased mRNA expression and activity of 11beta-HSD2 in a rat cortical collecting duct cell line and in kidneys of C57BL/6J mice and Sprague-Dawley rats. DHEA-treated rats tended to have reduced urinary corticosterone to 11-dehydrocorticosterone ratios. It was found that CCAAT/enhancer-binding protein-alpha (C/EBP-alpha) and C/EBP-beta regulated HSD11B2 transcription and that DHEA likely modulated the transcription of 11beta-HSD2 in a phosphatidylinositol-3 kinase/Akt-dependent manner by increasing C/EBP-beta mRNA and protein expression. Moreover, it is shown that C/EBP-alpha and C/EBP-beta differentially regulate the expression of 11beta-HSD1 and 11beta-HSD2. In conclusion, DHEA induces a shift from 11beta-HSD1 to 11beta-HSD2 expression, increasing conversion from active to inactive glucocorticoids. This provides a possible explanation for the antiglucocorticoid effects of DHEA.

Sodium retention and ascites formation in a cholestatic mice model: role of aldosterone and mineralocorticoid receptor?

Renal sodium retention in experimental liver cirrhosis originates from the distal nephron sensitive to aldosterone. The aims of this study were to (1) determine the exact site of sodium retention along the aldosterone-sensitive distal nephron, and (2) to evaluate the role of aldosterone and mineralocorticoid receptor activation in this process. Liver cirrhosis was induced by bile duct ligation in either adrenal-intact or corticosteroid-clamped mice. Corticosteroid-clamp was achieved through adrenalectomy and corticosteroid supplementation with aldosterone and dexamethasone via osmotic minipumps. 24-hours renal sodium balance was evaluated in metabolic cages. Activity and expression of sodium- and potassium-dependent adenosine triphosphatase were determined in microdissected segments of nephron. Within 4-5 weeks, cirrhosis induced sodium retention in adrenal-intact mice and formation of ascites in 50% of mice. At that time, sodium- and potassium-dependent adenosine triphosphatase activity increased specifically in cortical collecting ducts. Hyperaldosteronemia was indicated by increases in urinary aldosterone excretion and in sgk1 (serum- and glucocorticoid-regulated kinase 1) mRNA expression in collecting ducts. Corticosteroid-clamp prevented induction of sgk1 but not cirrhosis-induced sodium retention, formation of ascites and stimulation of sodium- and potassium-dependent adenosine triphosphatase activity and expression (mRNA and protein) in collecting duct. These findings demonstrate that sodium retention in cirrhosis is independent of hyperaldosteronemia and of the activation of mineralocorticoid receptor.

CONCLUSION

Bile duct ligation in mice induces cirrhosis which, within 4-5 weeks, leads to the induction of sodium- and potassium-dependent adenosine triphosphatase in cortical collecting ducts, to renal sodium retention and to the formation of ascites. Sodium retention, ascites formation and induction of sodium- and potassium-dependent adenosine triphosphatase are independent of the activation of mineralocorticoid receptors by either aldosterone or glucocorticoids.

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.

Renal sodium retention in cirrhotic rats depends on glucocorticoid-mediated activation of mineralocorticoid receptor due to decreased renal 11β-HSD-2 activity

Downregulation of the renal glucocorticoid-metabolizing enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD-2) during liver cirrhosis may allow activation of the mineralocorticoid receptor (MR) by glucocorticoids and contribute to sodium retention. We tested this hypothesis in male Wistar rats with decompensated liver cirrhosis and ascites 7 wk after bile duct ligation (BDL). Renal 11β-HSD-2 mRNA, protein, and activity were significantly decreased in decompensated rats. The urinary Na+/K+ ratio was reduced by 40%. Renal epithelial sodium channel (ENaC) mRNA and immunostaining were only slightly affected. Complete metabolic studies, including fecal excretion, showed that the BDL rats had avid renal sodium retention. Treatment of the BDL rats with dexamethasone suppressed endogenous glucocorticoid production, normalized total sodium balance and renal sodium excretion, and reduced ascites formation to the same degree as direct inhibition of MR with K-canrenoate. Total potassium balance was negative in the BDL rats, whereas renal potassium excretion was unchanged. In the distal colon, expression of ENaC was increased in BDL rats. Fecal potassium excretion was increased in cirrhotic rats, and this was corrected by treatment with K-canrenoate but not dexamethasone. We conclude that development of sodium retention and decompensation in cirrhotic rats is associated with downregulation of renal 11β-HSD-2 activity and inappropriate activation of renal sodium reabsorption by endogenous glucocorticoids. In addition, the overall potassium loss in the BDL model is due to increased fecal potassium excretion, which is associated with upregulation of ENaC in distal colon.

Functional genome analysis indicates loss of 17beta-hydroxysteroid dehydrogenase type 2 enzyme in the zebrafish

Among the family of 17beta-hydroxysteroid dehydrogenases, the type 2 (17beta-HSD 2) is the main enzyme responsible for inactivation of estrogens and androgens, catalyzing the oxidation of the C17 hydroxyl group. 17beta-HSD 2 has been studied only in mammals, its occurrence and function in other vertebrates hardly known. We investigated the presence of homologs in non-mammalian species and found sequences of 17beta-HSD 2 and its closest homolog 11beta-HSD 2 in zebrafish (Danio rerio), Takifugu rubripes, Tetraodon nigroviridis, Xenopus tropicalis and chicken databases. Furthermore, we cloned zebrafish 17beta-HSD 2 from ovarian tissue and found high expression also in the testis of adult fish and throughout embryogenesis. The enzyme, though, is inactive likely due to a non-sense N-terminal region including a dysfunctional cofactor binding motif. Replacement of the affected part by the corresponding human 17beta-HSD 2 sequence fully restored enzymatic activity. Comparison of all retrieved 17beta-HSD 2 sequences indicates that this functional loss may have occurred only in zebrafish, where steroid inactivation at position C17 seems to pursue without the protein studied. The closely related 11beta-HSD 2 is unlikely to substitute for 17beta-HSD 2 since in our hands it did not catalyze the respective oxidation of testosterone or estradiol.

Impaired 11 beta-hydroxysteroid dehydrogenase contributes to renal sodium avidity in cirrhosis: hypothesis or fact?

Exaggerated renal sodium retention with concomitant potassium loss is a hallmark of cirrhosis and contributes to the accumulation of fluid as ascites, pleural effusion, or edema. This apparent mineralocorticoid effect is only partially explained by increased aldosterone concentrations. I present evidence supporting the hypothesis that cortisol confers mineralocorticoid action in cirrhosis. The underlying molecular pathology for this mineralocorticoid receptor (MR) activation by cortisol is a reduced activity of the 11 beta-hydroxysteroid dehydrogenase type 2, an enzyme protecting the MR from promiscuous activation by cortisol in healthy mammalians.

The discovery of new 11beta-hydroxysteroid dehydrogenase type 1 inhibitors by common feature pharmacophore modeling and virtual screening

11beta-Hydroxysteroid dehydrogenase (11beta-HSD) enzymes catalyze the conversion of biologically inactive 11-ketosteroids into their active 11beta-hydroxy derivatives and vice versa. Inhibition of 11beta-HSD1 has considerable therapeutic potential for glucocorticoid-associated diseases including obesity, diabetes, wound healing, and muscle atrophy. Because inhibition of related enzymes such as 11beta-HSD2 and 17beta-HSDs causes sodium retention and hypertension or interferes with sex steroid hormone metabolism, respectively, highly selective 11beta-HSD1 inhibitors are required for successful therapy. Here, we employed the software package Catalyst to develop ligand-based multifeature pharmacophore models for 11beta-HSD1 inhibitors. Virtual screening experiments and subsequent in vitro evaluation of promising hits revealed several selective inhibitors. Efficient inhibition of recombinant human 11beta-HSD1 in intact transfected cells as well as endogenous enzyme in mouse 3T3-L1 adipocytes and C2C12 myotubes was demonstrated for compound 27, which was able to block subsequent cortisol-dependent activation of glucocorticoid receptors with only minor direct effects on the receptor itself. Our results suggest that inhibitor-based pharmacophore models for 11beta-HSD1 in combination with suitable cell-based activity assays, including such for related enzymes, can be used for the identification of selective and potent inhibitors.

Cell-based assay for screening 11beta-hydroxysteroid dehydrogenase inhibitors using liquid chromatography/tandem mass spectrometry detection

Cortisol is an important glucocorticoid that regulates many physiological pathways by activating various intracellular receptors. The type 1 isozyme of 11beta-hydroxysteroid dehydrogenase (11beta-HSD1) functions in vivo predominantly as a reductase by converting cortisone into cortisol. A high-throughput liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed to screen for inhibitors of 11beta-HSD1 by monitoring cortisol and cortisone simultaneously. The injection cycle time can be as fast as 1 min/sample, making it amenable to the analysis of large numbers of the cell-assay samples in the screening of 11beta-HSD inhibitors. The reductase and dehydrogenase activities of 11beta-HSD1 are assessed separately.

11β-Hydroxysteroid dehydrogenase Type 1 as a novel therapeutic target in metabolic and neurodegenerative disease

11beta-hydroxysteroid dehydrogenase Type 1 (11HSD1) catalyses regeneration of active 11-hydroxy glucocorticoids from inactive 11-keto metabolites within target tissues. Inhibition of 11HSD1 has been proposed as a novel strategy to lower intracellular glucocorticoid concentrations, without affecting circulating glucocorticoid levels and their responsiveness to stress. Increased 11HSD1 activity may be pathogenic, for example, in adipose tissue in obesity. Experiments in transgenic mice and using prototype inhibitors in humans show benefits of 11HSD1 inhibition in liver, adipose and brain tissue in treating features of the metabolic syndrome and cognitive dysfunction with ageing. The clinical development of potent selective 11HSD1 inhibitors is now a high priority.

The role of glucocorticoid action in the pathophysiology of the Metabolic Syndrome

Glucocorticoids are stress hormones that modulate a large number of physiological actions involved in metabolic, inflammatory, cardiovascular and behavioral processes. The molecular mechanisms and the physiological effects of glucocorticoids have been extensively studied. However, the involvement of glucocorticoid action in the etiology of the Metabolic Syndrome has not been well appreciated. Recently, accumulating clinical evidence and animal genetics studies have attracted growing interest in the role of glucocorticoid action in obesity and insulin resistance. This review will discuss the metabolic effects in the context of glucocorticoid metabolism and establish the association of glucocorticoid action with the features of the Metabolic Syndrome, especially obesity and insulin resistance. Special discussions will be focused on corticosteroid-binding globulin and 11beta-hydroxysteroid dehydrogenase type 1, two proteins that mediate glucocorticoid action and have been implicated in the Metabolic Syndrome. Due to the complexities of the glucocorticoid biology and the Metabolic Syndrome and limited space, this review is only intended to provide a general link between the two areas with broad rather than in-depth discussions of clinical, pharmacological and genetic findings.

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.

Effect of chenodeoxycholic acid on 11beta-hydroxysteroid dehydrogenase in various target tissues

Glucocorticoids are metabolized by isoforms of the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD). There is some controversy concerning the bile acid, chenodeoxycholic acid (CDCA), as a potential endogenously produced inhibitor of 11beta-HSD. The present experiments were designed to determine the relative specificity of CDCA for both isoforms of 11beta-HSD and to assess the biological relevance of inhibition in vascular tissue. IC(50) values (concentrations which inhibit 50% of the enzyme reaction) were calculated using rat liver microsomes as a source of 11beta-HSD1 dehydrogenase, Leydig cells for 11beta-HSD1 dehydrogenase and reductase, aorta for 11beta-HSD1 dehydrogenase and reductase, and sheep kidney for 11beta-HSD2 dehydrogenase. In each case, CDCA functioned as a potent inhibitor of 11beta-HSD1 dehydrogenase with IC(50) values of ranging from 0.2 to 7 micromol/L in contrast to 37 to 200 micromol/L for 11beta-HSD1 reductase. CDCA exhibited relatively weak inhibitory activity against 11beta-HSD2 from sheep kidney with an IC(50) of 70 micromol/L. The effect of CDCA on vascular contraction was studied in aortic rings isolated from Spague-Dawley rats incubated in medium containing corticosterone 10 nmol/L +/- CDCA (1 micromol/L) for 24 hours. Rings were stimulated with graded concentrations of phenylephrine (PE) (10 nmol/L, 100 nmol/L, and 1 micromol/L). Rings exposed to corticosterone and CDCA consistently demonstrated a greater contractile response at lower doses of PE (63% at PE 10 nmol/L, P <.001; 20% at PE 100 nmol/L, P <.025; and 10% at PE 1 micromol/L, not significant [NS]) compared to control preparations incubated with cortiosterone alone. These studies demonstrate (1) that CDCA preferentially affects 11beta-HSD1 dehydrogenase; (2) CDCA does inhibit 11beta-HSD2 dehydrogenase and 11beta-HSD1 reductase but only at high(er) concentrations exceeding 70 micromol/L and 37 micromol/L, respectively; and (3) inhibition of 11beta-HSD1 dehydrogenase in aortic rings by CDCA (1 micromol/L) enhances the contractile response of corticosterone plus PE.