Effect of RU486 on hepatic and adipocyte gene expression improves diabetes control in obesity-type 2 diabetes

Mifepristone Improves Adipose Tissue Insulin Sensitivity in Insulin Resistant Individuals

BACKGROUND

Increased tissue cortisol availability has been implicated in abnormal glucose and fat metabolism in patients with obesity, metabolic syndrome, and type 2 diabetes (T2DM). Our objective was to evaluate whether blockade of glucocorticoid receptor (GR) with mifepristone ameliorates insulin resistance (IR) in overweight/obese subjects with glucose intolerance.

METHODS

We conducted a randomized, double-blinded, placebo-controlled, crossover study in overweight/obese individuals (n = 16, 44% female) with prediabetes or mild T2DM but not clinical hypercortisolism. Mifepristone (50 mg every 6 h) or placebo was administered for 9 days, followed by crossover to the other treatment arm after a washout period of 6 to 8weeks. At baseline and following each treatment, oral glucose tolerance test (OGTT) and frequently sampled intravenous glucose tolerance test (FSIVGTT) were performed. Insulin sensitivity was measured using FSIVGTT [primary outcome: insulin sensitivity index (SI)] and OGTT [Matsuda index (MI) and oral glucose insulin sensitivity index (OGIS)]. Hepatic and adipose insulin resistance were assessed using hepatic insulin resistance index (HIRI), and adipose tissue insulin sensitivity index (Adipo-SI) and adipo-IR, derived from the FSIVGTT.

RESULTS

Mifepristone administration did not alter whole-body glucose disposal indices of insulin sensitivity (SI, MI, and OGIS). GR blockade significantly improved Adipo-SI (61.7 ± 32.9 vs 42.8 ± 23.9; P = 0.002) and reduced adipo-IR (49.9 ± 45.9 vs 65.5 ± 43.8; P = 0.004), and HIRI (50.2 ± 38.7 vs 70.0 ± 44.3; P = 0.08). Mifepristone increased insulin clearance but did not affect insulin secretion or β-cell glucose sensitivity.

CONCLUSION

Short-term mifepristone administration improves adipose and hepatic insulin sensitivity among obese individuals with hyperglycemia without hypercortisolism.

FX5 as a non-steroidal GR antagonist improved glucose homeostasis in type 2 diabetic mice via GR/HNF4α/miR-122-5p pathway

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease characterized by glucose metabolic disorders, and gluconeogenesis inhibiting is a promisingly therapeutic strategy for T2DM. Glucocorticoid receptor (GR) is tightly implicated in the regulation of gluconeogenesis, although the underlying mechanism remains obscure. Here, we discovered that small molecule, 5-chloro-N-[4-chloro-3-(trifluoromethyl)phenyl]thiophene-2-sulfonamide (FX5) as a new non-steroidal GR antagonist efficiently ameliorated glucose homeostasis in db/db and HFD/STZ-induced T2DM mice. The mechanism underlying the suppression of FX5 against gluconeogenesis was highly investigated. FX5 suppressed gluconeogenetic genes G6Pase and PEPCK in mouse primary hepatocytes and liver tissues of T2DM mice. Results of mammalian one-hybrid and transactivation as well as nuclear translocation assays totally evaluated the antagonistic features of FX5 against GR. Moreover, siRNA and overexpression related assays verified that FX5 alleviated gluconeogenesis either directly by antagonizing GR or indirectly through GR/HNF4α/miR122-5p signaling pathway. Our work has presented a new mode for GR antagonist in the regulation of gluconeogenesis, which is expected to highlight the potential of FX5 in the treatment of T2DM.

Mifepristone for Treatment of Metabolic Syndrome: Beyond Cushing's Syndrome

A growing body of research indicates that cortisol, the glucocorticoid product of the activation of the hypothalamic-pituitary-adrenal axis, plays a role in the pathophysiology of metabolic syndrome. In this regard, chronic exposure to cortisol is associated with risk factors related to metabolic syndrome like weight gain, type 2 diabetes, hypertension, among others. Mifepristone is the only FDA-approved drug with antiglucocorticoids properties for improved the glycemic control in patients with type 2 patients secondary to endogenous Cushing’s syndrome. Mifepristone also have been shown positive effects in rodents models of diabetes and patients with obesity due to antipsychotic treatment. However, the underlying molecular mechanisms are not fully understood. In this perspective, we summarized the literature regarding the beneficial effects of mifepristone in metabolic syndrome from animal studies to clinical research. Also, we propose a potential mechanism for the beneficial effects in insulin sensitivity which involved the regulation of mitochondrial function in muscle cells.

Association of increased renal Cyp24a1 gene expression with low plasma 1,25-dihydroxyvitamin D levels in rats with streptozotocin-induced diabetes

Decreases in plasma vitamin D concentrations have been reported in diabetes, although the mechanism involved in this decrease is unclear. Here, we investigated the association between Cyp24a1, a vitamin D catabolic enzyme, and abnormalities in vitamin D metabolism in streptozotocin-induced diabetes rats, an animal model of type 1 diabetes. Plasma 1,25-dihydroxyvitamin D [1,25(OH)₂D] levels were significantly lower in streptozotocin-induced diabetes rats and renal Cyp24a1 mRNA expression levels were increased. Western blotting analysis of streptozotocin-induced diabetes rats kidney tissues with anti-CYP24A1 antibody showed a strong signal around 40 kDa, which differs from the predicted 50–55 kDa molecular weight for full-length Cyp24a1 and could represent the Cyp24a1-splicing variant that lacks exons 1 and 2. We observed high levels of renal Cyp24a1-splicing variant mRNA expression in streptozotocin-induced diabetes rats. We also confirmed transcriptional up-regulation of endogenous Cyp24a1 mRNA expression through glucocorticoid receptors by glucocorticoid in opossum kidney proximal cells. Taken together, our results indicated that high Cyp24a1 expression levels may play a role in the decrease of plasma 1,25(OH)₂D levels in streptozotocin-induced diabetes rats. High plasma corticosterone levels in diabetes may affect transcriptional regulation to promote increases in Cyp24a1 expression.

Effect of glucocorticoids on glyceroneogenesis in adipose tissue: A systematic review

Glyceroneogenesis is important for the maintenance of fat content in white adipose tissue (WAT). An increase in WAT, and especially the pattern of fat distribution, specifically in visceral depots, potentially contributes to cardiovascular and metabolic diseases, such as type 2 diabetes mellitus, myocardial infarction and hypertension. Recent studies have shown important differences in glyceroneogenesis of different fat sites under the administration of glucocorticoids (GCs). Such differences need to be analysed with criteria evidencing the parameter studied, the type of corticoid, the form of administration and also the tissue studied. PubMed, Scopus and Virtual Health Library were used to search for articles that analysed the effect of GCs on glyceroneogenesis in different sites of adipose tissue in mammals and primary cultures. GCs decrease the glyceroneogenesis in epididymal WAT (EWAT) and also decrease the expression of the mRNA, content and activity of phosphoenolpyruvate carboxykinase (PEPCK-C), key enzyme of glyceroneogenesis. However, in retroperitoneal WAT (RWAT), although there is no consensus about the effect of GCs on PEPCK mRNA, GCs increase PEPCK-C activity and glyceroneogenesis flux. In inguinal WAT (IWAT) an in vitro study showed an increase in the PEPCK mRNA induced by dexamethasone. However, prednisolone does not change glyceroneogenesis flux. In interscapular brown adipose tissue (IBAT) prednisolone or dexamethasone does not change PEPCK-C activity in control diet-fed rats but led to a decrease in PEPCK-C activity in fasted- or high-fat/low-carbohydrate diet-fed rats, as well as in suckling rats. Despite that fact that GCs have different potencies, the same dose of dexamethasone reduces PEPCK-C activity in EWAT, but not in RWAT and IBAT from control-diet fed rats. In summary, the data presented in this article show that GCs differentially regulate glyceroneogenesis in different sites of adipose tissue. Further experiments are needed to firmly establish our hypothesis and clarify the mechanisms involved.

Effects of combined glucocorticoid/mineralocorticoid receptor modulation (CORT118335) on energy balance, adiposity, and lipid metabolism in male rats

Psychological stress and excess glucocorticoids are associated with metabolic and cardiovascular diseases. Glucocorticoids act primarily through mineralocorticoid (MR) and glucocorticoid receptors (GR), and compounds modulating these receptors show promise in mitigating metabolic and cardiovascular-related phenotypes. CORT118335 (GR/MR modulator) prevents high-fat diet-induced weight gain and adiposity in mice, but the ability of this compound to reverse obesity-related symptoms is unknown. Adult male rats were subcutaneously administered CORT118335 (3, 10, or 30 mg/kg) or vehicle once daily. A 5-day treatment with CORT118335 at 30 mg/kg induced weight loss in rats fed a chow diet by decreasing food intake. However, lower doses of the compound attenuated body weight gain primarily because of decreased calorific efficiency, as there were no significant differences in food intake compared with vehicle. Notably, the body weight effects of CORT118335 persisted during a 2-wk treatment hiatus, suggesting prolonged effects of the compound. To our knowledge, we are the first to demonstrate a sustained effect of combined GR/MR modulation on body weight gain. These findings suggest that CORT118335 may have long-lasting effects, likely due to GR/MR-induced transcriptional changes. Prolonged (18 days) treatment of CORT118335 (10 mg/kg) reversed body weight gain and adiposity in animals fed a high-fat diet for 13 wk. Surprisingly, this occurred despite a worsening of the lipid profile and glucose homeostasis as well as a disrupted diurnal corticosterone rhythm, suggesting GR agonistic effects in the periphery. We conclude that species and tissue-specific targeting may result in promising leads for exploiting the metabolically beneficial aspects of GR/MR modulation.

A bile acid derivative with PPARγ-mediated anti-inflammatory activity

During our search for bioactive secondary metabolites in the jellyfish-derived fungus Penicillium chrysogenum J08NF-4, several bile acid derivatives (2-6) were isolated along with a new steroidal artifact (1). An in vitro anti-inflammatory assay showed that pretreatment with 1 suppressed NO production and the gene expressions of the pro-inflammatory mediators iNOS and TNF-α in LPS-induced RAW 264.7 macrophages. Docking analysis of 1 revealed that it might bind to the ligand binding domain (LBD) of PPARγ in a manner similar to that of the synthetic steroid mifepristone (7), which is used clinically to treat hypercortisolism and was recently reported to be a PPARγ agonist. Compound 1 activated PPARγ in murine Ac2F liver cells and suppressed the LPS-induced phosphorylation of the NF-κB p65 subunit leading to downregulation of pro-inflammatory mediators. Our findings suggest that 1 acts as a steroidal PPARγ activator that downregulates the expressions of pro-inflammatory mediators by suppressing the NF-κB signaling pathway.

Mifepristone enhances insulin-stimulated Akt phosphorylation and glucose uptake in skeletal muscle cells

Mifepristone is the only FDA-approved drug for glycaemia control in patients with Cushing's syndrome and type 2 diabetes. Mifepristone also has beneficial effects in animal models of diabetes and patients with antipsychotic treatment-induced obesity. However, the mechanisms through which Mifepristone produces its beneficial effects are not completely elucidated.

PURPOSE

To determine the effects of mifepristone on insulin-stimulated glucose uptake on a model of L6 rat-derived skeletal muscle cells.

RESULTS

Mifepristone enhanced insulin-dependent glucose uptake, GLUT4 translocation to the plasma membrane and Akt Ser⁴⁷³ phosphorylation in L6 myotubes. In addition, mifepristone reduced oxygen consumption and ATP levels and increased AMPK Thr¹⁷² phosphorylation. The knockdown of AMPK prevented the effects of mifepristone on insulin response.

CONCLUSIONS

Mifepristone enhanced insulin-stimulated glucose uptake through a mechanism that involves a decrease in mitochondrial function and AMPK activation in skeletal muscle cells.

In obese mice, exercise training increases 11β-HSD1 expression, contributing to glucocorticoid activation and suppression of pulmonary inflammation

Exercise training is advocated for treating chronic inflammation and obesity-related metabolic syndromes. Glucocorticoids (GCs), the anti-inflammatory hormones, are synthesized or metabolized in extra-adrenal organs. This study aims to examine whether exercise training affects obesity-associated pulmonary inflammation by regulating local GC synthesis or metabolism. We found that sedentary obese (ob/ob) mice exhibited increased levels of interleukin (IL)-1β, IL-18, monocyte chemotactic protein (MCP)-1, and leukocyte infiltration in lung tissues compared with lean mice, which was alleviated by 6 wk of exercise training. Pulmonary corticosterone levels were decreased in ob/ob mice. Exercise training increased pulmonary corticosterone levels in both lean and ob/ob mice. Pulmonary corticosterone levels were negatively correlated with IL-1β, IL-18, and MCP-1. Immunohistochemical staining of the adult mouse lung sections revealed positive immunoreactivities for the steroidogenic acute regulatory protein, the cholesterol side-chain cleavage enzyme (CYP11A1), the steroid 21-hydroxylase (CYP21), 3β-hydroxysteroid dehydrogenase (3β-HSD), and type 1 and type 2 11β-hydroxysteroid dehydrogenase (11β-HSD) but not for 11β-hydroxylase (CYP11B1). Exercise training significantly increased pulmonary 11β-HSD1 expression in both lean and ob/ob mice. In contrast, exercise training per se had no effect on pulmonary 11β-HSD2 expression, although pulmonary 11β-HSD2 levels in ob/ob mice were significantly higher than in lean mice. RU486, a glucocorticoid receptor antagonist, blocked the anti-inflammatory effects of exercise training in lung tissues of obese mice and increased inflammatory cytokines in lean exercised mice. These findings indicate that exercise training increases pulmonary expression of 11β-HSD1, thus contributing to local GC activation and suppression of pulmonary inflammation in obese mice.NEW & NOTEWORTHY Treadmill training leads to a significant increase in pulmonary corticosterone levels in ob/ob mice, which is in parallel with the favorable effects of exercise on obesity-associated pulmonary inflammation. Exercise training increases pulmonary 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expression but has no significant effect on 11β-HSD2 expression in both lean and ob/ob mice. These findings indicate that exercise training increases pulmonary expression of 11β-HSD1, thus contributing to local glucocorticoid activation and suppression of pulmonary inflammation in obese mice.

Glucocorticoids and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the global obesity and metabolic disease epidemic and is rapidly becoming the leading cause of liver cirrhosis and indication for liver transplantation worldwide. The hallmark pathological finding in NAFLD is excess lipid accumulation within hepatocytes, but it is a spectrum of disease ranging from benign hepatic steatosis to steatohepatitis through to fibrosis, cirrhosis and risk of hepatocellular carcinoma. The exact pathophysiology remains unclear with a multi-hit hypothesis generally accepted as being required for inflammation and fibrosis to develop after initial steatosis. Glucocorticoids have been implicated in the pathogenesis of NAFLD across all stages. They have a diverse array of metabolic functions that have the potential to drive NAFLD acting on both liver and adipose tissue. In the fasting state, they are able to mobilize lipid, increasing fatty acid delivery and in the fed state can promote lipid accumulation. Their action is controlled at multiple levels and in this review will outline the evidence base for the role of GCs in the pathogenesis of NAFLD from cell systems, rodent models and clinical studies and describe interventional strategies that have been employed to modulate glucocorticoid action as a potential therapeutic strategy.

Pertussis toxin administered spinally induces a hypoglycemic effect on normal and diabetic mice

BACKGROUND/AIMS

To show whether intrathecal (i.t.) treatment with pertussis toxin (PTX) produces a hypoglycemic effect in ICR, db/db and streptozotocin-treated mice.

METHODS

The blood glucose level (BGL) was measured after i.t. treatment with PTX, AB5 toxins and PTX subunits. Insulin or leptin levels were measured after PTX injection. The effect of PTX on the BGL was examined in adrenalectomized (ADX) mice. Glucose transporter (GLUT) levels were determined by Western blotting.

RESULTS

PTX attenuated the elevated BGL in the D-glucose-fed model in a long-term manner. Heat-labile toxin (HLT), HLT subunit B or Shiga toxin, which belong to the AB5 toxins, administered i.t. did not affect the BGL. PTX A protomer (PTX-A) or PTX B oligomers (PTX-B) injected i.t. did not have an effect on the BGL as well. However, combined treatment with PTX-A and PTX-B subunits caused a hypoglycemic effect. The leptin level was gradually reduced by PTX for up to 6 days, without affecting the insulin level. PTX administered i.t. significantly decreased the BGL further in ADX mice. Moreover, GLUT-2 (hypothalamus and pituitary gland), GLUT-4 (muscle) and GLUT-3 (adrenal gland) expression levels were increased, whereas GLUT-1 (brain cortex, liver, muscle and spinal cord), GLUT-2 (liver) and GLUT-3 (brain cortex and pituitary gland) expression levels were decreased.

DISCUSSION

Our data suggest that PTX administered spinally produces a hypoglycemic effect in a long-term manner, and PTX-induced hypoglycemia appears to be mediated by the reduction in activity of the glucocorticoid system. Furthermore, PTX may modulate the insulin level during hypoglycemia. Among GLUTs, GLUT-4 in muscle, GLUT-2 in the liver, hypothalamus and pituitary gland as well as GLUT-1 in the adrenal gland may be responsible for PTX-induced hypoglycemia.

Effects of selective and non-selective glucocorticoid receptor II antagonists on rapid-onset diabetes in young rats

The blockade of glucocorticoid (GC) action through antagonism of the glucocorticoid receptor II (GRII) has been used to minimize the undesirable effects of chronically elevated GC levels. Mifepristone (RU486) is known to competitively block GRII action, but not exclusively, as it antagonizes the progesterone receptor. A number of new selective GRII antagonists have been developed, but limited testing has been completed in animal models of overt type 2 diabetes mellitus. Therefore, two selective GRII antagonists (C113176 and C108297) were tested to determine their effects in our model of GC-induced rapid-onset diabetes (ROD). Male Sprague-Dawley rats (∼ six weeks of age) were placed on a high-fat diet (60%), surgically implanted with pellets containing corticosterone (CORT) or wax (control) and divided into five treatment groups. Each group was treated with either a GRII antagonist or vehicle for 14 days after surgery: CORT pellets (400 mg/rat) + antagonists (80 mg/kg/day); CORT pellets + drug vehicle; and wax pellets (control) + drug vehicle. After 10 days of CORT treatment, body mass gain was increased with RU486 (by ∼20% from baseline) and maintained with C113176 administration, whereas rats given C108297 had similar body mass loss (∼15%) to ROD animals. Fasting glycemia was elevated in the ROD animals (>20 mM), normalized completely in animals treated with RU486 (6.2±0.1 mM, p<0.05) and improved in animals treated with C108297 and C113176 (14.0±1.6 and 8.8±1.6 mM, p<0.05 respectively). Glucose intolerance was normalized with RU486 treatment, whereas acute insulin response was improved with RU486 and C113176 treatment. Also, peripheral insulin resistance was attenuated with C113176 treatment along with improved levels of β-cell function while C108297 antagonism only provided modest improvements. In summary, C113176 is an effective agent that minimized some GC-induced detrimental metabolic effects and may provide an alternative to the effective, but non-selective, GRII antagonist RU486.

Mifepristone promotes adiponectin production and improves insulin sensitivity in a mouse model of diet-induced-obesity

The steroid receptor antagonist mifepristone is used as an anti-cancer agent, eliciting both cytostatic and cytotoxic effects on malignant cells. However, the metabolic effects of long-term treatment with mifepristone have remained unclear. The effects of mifepristone on insulin sensitivity and adiponectin secretion were evaluated both in in vivo and in vitro. First, we explored the effects of mifepristone, on metabolic functions in obese mice receiving a high-fat diet. When these mice were fed mifepristone, they exhibited a marked improvement in insulin sensitivity, attenuated hepatic injury, and decreased adipocyte size, compared with mice that received only the high-fat diet. Intriguingly, mifepristone-treated mice showed significantly elevated plasma adiponectin levels. Second, we tested the effects of mifepristone on differentiated 3T3-L1 adipocytes in vitro. When differentiated adipocytes were treated with mifepristone for 48 h, adiponectin was upregulated at both mRNA and protein levels. Collectively, these results reveal novel actions of mifepristone on metabolic functions, in vivo and in vitro, in which the drug exerts antidiabetic effects associated with an upregulation in adiponectin-secretion.

Chronic treatment with the glucocorticoid receptor antagonist RU486 inhibits diabetes-induced enhancement of experimental periodontitis

BACKGROUND AND OBJECTIVE

Chronic hypothalamic-pituitary-adrenal (HPA) axis hyperactivity and excessive glucocorticoid hormone release have been associated with diabetes, altered immune responses and increased susceptibility to periodontitis. In the present study we tested the impact of streptozotocin (STZ)-induced diabetes on ligature-induced periodontitis and the effect of subsequent treatment with the glucocorticoid receptor (GR) antagonist, RU486.

MATERIAL AND METHODS

A single dose of STZ [45 mg/kg, intraperitoneally (i.p.)] or vehicle was given 10 d before induction of ligature-induced periodontitis and implantation subcutaneously of a drug pellet containing the GR antagonist, RU486, or a placebo pellet. Periodontitis was assessed when the ligatures had been in place for 21 d. Two hours before decapitation all rats received gram-negative bacterial lipopolysaccharide (LPS) (150 μg/kg, i.p.) to induce a robust immune and stress response.

RESULTS

Compared with control rats, STZ-treated rats developed significantly more periodontal bone loss, and RU486 treatment of STZ -treated rats significantly inhibited this effect. STZ-treated rats also showed significantly higher levels of the HPA axis-derived hormone, corticosterone, as well as of the proinflammatory cytokine, tumor necrosis factor-alpha (TNF-α), but lower levels of the anti-inflammatory cytokines interleukin-10 (IL-10) and transforming growth factor-1beta (TGF-1β) after LPS stimulation. GR blockade had no statistically significant effects on these measurements in diabetic rats, but tended to enhance the levels of TNF-α and TGF-1β, and reduce the levels of IL-10 and blood glucose.

CONCLUSION

In diabetic subjects, excessive GR activation as a result of chronic high levels of glucocorticoid hormones may alter immune-system responses in a manner that may increase the susceptibility to periodontitis.

Alteration of 11β-hydroxysteroid dehydrogenase type 1 and glucocorticoid receptor by ethanol in rat liver and mouse hepatoma cells

Alcohol is a potential risk factor of type 2 diabetes, but its underlying mechanism is unclear. To explore this issue, Wistar rats and mouse hepatoma cells (Hepa 1-6) were exposed to ethanol, 8 g·kg(-1) ·d(-1) for 3 months and 100 mM for 48 h, respectively. Glucose and insulin tolerance tests in vivo were performed, and protein levels of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) and glucocorticoid receptor (GR) in liver and Hepa 1-6 cells were measured. Alterations of key enzymes of gluconeogenesis phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6 phosphatase (G6Pase), as well as glycogen synthase kinase 3a (GSK3 α ), were also examined. The results revealed that glucose levels were increased, and insulin sensitivity was impaired accompanied with liver injury in rats exposed to ethanol compared with controls. The 11β-HSD1, GR, PEPCK, G6Pase, and GSK3 α proteins were increased in the liver of rats treated with ethanol compared with controls. Ethanol-exposed Hepa 1-6 cells also showed higher expression of 11β-HSD1, GR, PEPCK, G6Pase, and GSK3 α proteins than control cells. After treatment of Hepa 1-6 cells exposed to ethanol with the GR inhibitor RU486, the expression of 11β-HSD1 and GR was significantly decreased. At the same time the increases in PEPCK, G6Pase, and GSK3 α levels induced by ethanol in Hepa 1-6 cells were also attenuated by RU486. The results indicate that ethanol causes glucose intolerance by increasing hepatic expression of 11β-HSD1 and GR, which leads to increased expression of gluconeogenic and glycogenolytic enzymes.

Regulation of triglyceride metabolism by glucocorticoid receptor

Glucocorticoids are steroid hormones that play critical and complex roles in the regulation of triglyceride (TG) homeostasis. Depending on physiological states, glucocorticoids can modulate both TG synthesis and hydrolysis. More intriguingly, glucocorticoids can concurrently affect these two processes in adipocytes. The metabolic effects of glucocorticoids are conferred by intracellular glucocorticoid receptors (GR). GR is a transcription factor that, upon binding to glucocorticoids, regulates the transcriptional rate of specific genes. These GR primary target genes further initiate the physiological and pathological responses of glucocorticoids. In this article, we overview glucocorticoid-regulated genes, especially those potential GR primary target genes, involved in glucocorticoid-regulated TG metabolism. We also discuss transcriptional regulators that could act with GR to participate in these processes. This knowledge is not only important for the fundamental understanding of steroid hormone actions, but also are essential for future therapeutic interventions against metabolic diseases associated with aberrant glucocorticoid signaling, such as insulin resistance, dyslipidemia, central obesity and hepatic steatosis.

Revealing a steroid receptor ligand as a unique PPARγ agonist

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates metabolic homeostasis and is a molecular target for anti-diabetic drugs. We report here the identification of a steroid receptor ligand, RU-486, as an unexpected PPARγ agonist, thereby uncovering a novel signaling route for this steroid drug. Similar to rosiglitazone, RU-486 modulates the expression of key PPARγ target genes and promotes adipocyte differentiation, but with a lower adipogenic activity. Structural and functional studies of receptor-ligand interactions reveal the molecular basis for a unique binding mode for RU-486 in the PPARγ ligand-binding pocket with distinctive properties and epitopes, providing the molecular mechanisms for the discrimination of RU-486 from thiazolidinediones (TZDs) drugs. Our findings together indicate that steroid compounds may represent an alternative approach for designing non-TZD PPARγ ligands in the treatment of insulin resistance.

Pharmacological evaluation of insulin mimetic novel suppressors of PEPCK gene transcription from Paeoniae Rubra Radix

ETHNOPHARMACOLOGICAL RELEVANCE

Paeoniae Rubra Radix (root of Paeonia lactiflora) has been frequently employed in Traditional Chinese Medicine (TCM) as and anti-diabetic therapy to enhance blood circulation and dissipate stasis.

AIM OF THE STUDY

Previously, we identified a novel hypoglycemic action of a crude extract from Paeoniae Rubra Radix, which also suppressed phosphoenolpyruvate carboxykinase (PEPCK) gene transcription. Therefore, the current investigation intended to elucidate potential active bio-constituents of this herb and mechanisms of action.

MATERIALS AND METHODS

Glucocorticoid receptor (GR) nuclear localization, the PEPCK messenger (m)RNA level, pregnane X receptor (PXR) mRNA expression, cAMP-responsive element-binding protein (CREB) serine phosphorylation and DNA binding were evaluated in dexamethasone (Dex) and 8-bromo-cAMP (CA)-stimulated H4IIE cells, while efficacy of agents was assessed in a stable cell line containing a green fluorescent protein (GFP) reporter driven by the PEPCK promoter. HPLC profiling, colorimetric assays, and NMR analysis were employed for chemical characterization purpose.

RESULTS

An extract of Paeoniae Rubra Radix lacking the insulin mimetic compound, 1,2,3,4,6-penta-O-galloyl-beta-d-glucose (PGG), and termed the non-PGG fraction (NPF), consisting of tannin polymers, suppressed PEPCK expression in the presence of an insulin receptor antagonist (HNMPA-AM(3)), suggesting the action of this fraction is independent of the insulin receptor. Furthermore, Dex-stimulated GR nuclear localization and transactivation were prevented by the NPF. Similarly, CA-stimulated CREB serine phosphorylation and DNA binding were also inhibited by the NPF in H4IIE cells. Hence NPF antagonizes both signaling pathways that induce PEPCK gene transcription.

CONCLUSION

In conclusion, the current study proposes that the potent suppressive activity on PEPCK gene transcription observed with Paeoniae Rubra Radix extract, can be attributed to at least two distinct components, namely PGG and NPF.

Tissue-specific dysregulation of hexose-6-phosphate dehydrogenase and glucose-6-phosphate transporter production in db/db mice as a model of type 2 diabetes

AIMS/HYPOTHESIS

Tissue-specific amplification of glucocorticoid action through 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) affects the development of the metabolic syndrome. Hexose-6-phosphate dehydrogenase (H6PDH) mediates intracellular NADPH availability for 11β-HSD1 and depends on the glucose-6-phosphate transporter (G6PT). Little is known about the tissue-specific alterations of H6PDH and G6PT and their contributions to local glucocorticoid action in db/db mice.

METHODS

We characterised the role of H6PDH and G6PT in pre-receptor metabolism of glucocorticoids by examining the production of the hepatic 11β-HSD1-H6PDH-G6PT system in db/db mice.

RESULTS

We observed that increased production of hepatic H6PDH in db/db mice was paralleled by upregulation of hepatic G6PT production and responded to elevated circulating levels of corticosterone. Treatment of db/db mice with the glucocorticoid antagonist RU486 markedly reduced production of both H6PDH and 11β-HSD1 and improved hyperglycaemia and insulin resistance. The reduction of H6PDH and 11β-HSD1 production by RU486 was accompanied by RU486-induced suppression of hepatic G6pt (also known as Slc37a4) mRNA. Incubation of mouse primary hepatocytes with corticosterone enhanced G6PT and H6PDH production with corresponding activation of 11β-HSD1 and PEPCK: effects that were blocked by RU486. Knockdown of H6pd by small interfering RNA showed effects comparable with those of RU486 for attenuating the corticosterone-induced H6PDH production and 11ß-HSD1 reductase activity in these intact cells. Addition of the G6PT inhibitor chlorogenic acid to primary hepatocytes suppressed H6PDH production.

CONCLUSIONS/INTERPRETATION

These findings suggest that increased hepatic H6PDH and G6PT production contribute to 11β-HSD1 upregulation of local glucocorticoid action that may be related to the development of type 2 diabetes.