Serum leptin levels in patients with primary hyperaldosteronism before and after treatment: relationships to insulin sensitivity

Secondary diabetes mellitus due to primary aldosteronism

Primary aldosteronism (PA) and diabetes mellitus (DM) are clinical conditions that increase cardiovascular risk. Approximately one in five patients with PA have DM. Nevertheless, the pathophysiology linking these two entities is not entirely understood. In addition, the majority of patients with PA have glucocorticoid co-secretion, which is associated with increased risk of impaired glucose homeostasis. In the present review, we aim to comprehensively discuss all the available research data concerning the interplay between mineralocorticoid excess and glucose metabolism, with separate analysis of the sequalae in muscle, adipose tissue, liver and pancreas. Aldosterone binds both mineralocorticoid and glucocorticoid receptors and amplifies tissue glucocorticoid activity, via 11-β-hydroxysteroid dehydrogenase type 1 stimulation. A clear classification of the molecular events as per specific receptor in insulin-sensitive tissues is impossible, while their synergistic interaction is plausible. Furthermore, aldosterone induces oxidative stress and inflammation, perturbs adipokine expression, thermogenesis and lipogenesis in adipose tissue, and increases hepatic steatosis. In pancreas, enhanced oxidative stress and inflammation of beta cells, predominantly upon glucocorticoid receptor activation, impair insulin secretion. No causality between hypokalemia and impaired insulin response is yet proven; in contrast, hypokalemia appears to be implicated with insulin resistance and hepatic steatosis. The superior efficacy of adrenalectomy in ameliorating glucose metabolism vs. mineralocorticoid receptor antagonists in clinical studies highlights the contribution of non-mineralocorticoid receptor-mediated mechanisms in the pathophysiologic process. The exact role of hypokalemia, the mechanisms linking mineralocorticoid excess with hepatic steatosis, and possible disease-modifying role of pioglitazone warrant further studies.

Mineralocorticoid receptors in the pathogenesis of insulin resistance and related disorders: from basic studies to clinical disease

Aldosterone is a steroid hormone that regulates blood pressure and cardiovascular function by acting on renal and vascular mineralocorticoid receptors (MRs) to promote sodium retention and modulate endothelial function. Indeed, MRs are expressed in endothelial cells, vascular smooth muscle cells, adipocytes, immune cells, skeletal muscle cells, and cardiomyocytes. Excessive aldosterone and associated MR activation impair insulin secretion, insulin metabolic signaling to promote development of diabetes, and the related cardiometabolic syndrome. These adverse effects of aldosterone are mediated, in part, via increased inflammation, oxidative stress, dyslipidemia, and ectopic fat deposition. Therefore, inhibition of MR activation may have a beneficial effect in prevention of impaired insulin metabolic signaling, type 2 diabetes, and cardiometabolic disorders. This review highlights findings from the recent surge in research regarding MR-related cardiometabolic disorders as well as our contemporary understanding of the detrimental effects of excess MR activation on insulin metabolic signaling.

Primary Aldosteronism and Obstructive Sleep Apnea: Casual Association or Pathophysiological Link?

The coexistence of aldosterone oversecretion and obstructive sleep apnea is frequently observed, especially in patients with resistant hypertension, obesity, and metabolic syndrome. Since aldosterone excess and sleep apnea are both independently associated with an increased risk of cardiovascular disease, to investigate whether their coexistence might be attributed to common predisposing conditions, such as metabolic disorders, or to an actual pathophysiological interconnection appears of great importance. Fluid overload and metabolic abnormalities relating to aldosterone oversecretion may be implicated in obstructive sleep apnea development. Nocturnal intermittent hypoxia may in turn exacerbate renin-angiotensin-aldosterone system activity, thus leading to hyperaldosteronism. Furthermore, fat tissue excess and adipocyte secretory products might predispose to both sleep apnea and aldosterone oversecretion in subjects with obesity. Consistent with these evidences, obstructive sleep apnea frequently affects patients with primary aldosteronism. Conversely, whether primary aldosteronism is more prevalent in individuals affected by obstructive sleep apnea compared to the general population remains controversial.

Higher Blood Urea Nitrogen and Urinary Calcium: New Risk Factors for Diabetes Mellitus in Primary Aldosteronism Patients

Purpose: The aim of the study was to investigate the prevalence and risk factors of diabetes mellitus (DM) in primary aldosteronism (PA) patients. Methods: This case-control study enrolled 259 PA patients in West China Hospital, China from January 2016 to January 2019. Patients were divided into three groups: PA group, PA + impaired fasting glucose (IFG)/impaired glucose tolerance (IGT) group and PA + DM group. Clinical characteristics (like age and sex) and laboratory variables (like plasma aldosterone concentration and plasma renin activity) were compared between three groups. Univariate and multivariate logistic regression analyses were performed to determine risk factors for DM in PA patients. The association of random blood glucose with the above-mentioned factors were also investigated by Pearson correlation analyses. Nomogram model was developed to predict the probability of DM in PA patients. Results: 49 (18.9%) patients were diagnosed with DM and 22 (8.5%) with IFG/IGT in 259 PA patients. Apart from older age, male, higher body mass index, higher triglycerides and lower cholesterol, we found that higher blood urea nitrogen (BUN) and higher 24 h urinary calcium (Ca) might be potential new risk factors for dysglycemia. The nomogram model for DM in PA patients had a good predictive accuracy, with the area under the curve of receiver operating characteristic of 0.839 (95% CI 0.784-0.893). Conclusions: PA patients were more likely to have DM compared with general population. Apart from older age, overweight and dyslipidemia, higher BUN and excessive excretion of urinary Ca may also be the new potential risk factors for DM in PA patients.

The regulation of aldosterone secretion by leptin: implications in obesity-related cardiovascular disease

PURPOSE OF REVIEW

Although it has been known for some time that increases in body mass enhance aldosterone secretion, particularly in women, the origin of this elevation in aldosterone production is not well defined. Adipocyte-derived factors have emerged as potential candidates to increase aldosterone production in obesity.

RECENT FINDINGS

Emerging evidence suggests the presence of a mechanistic link in which the adipocyte-derived hormone leptin stimulates aldosterone production in obesity, thereby creating a positive feedback loop for obesity-associated cardiovascular disease. In addition, recent reports give credence to the concept that this leptin-aldosterone stimulation pathway in obesity is an underlying mechanism for sex-discrepancies in obesity-associated cardiovascular disease.

SUMMARY

Leptin appears as a new direct regulator of adrenal aldosterone production and leptin-mediated aldosterone production is a novel candidate mechanism underlying obesity-associated hypertension, particularly in females.

Impact of Adrenal Steroids on Regulation of Adipose Tissue

Corticosteroids are secreted by the adrenal glands and control the functions of adipose tissue via the activation of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). In turn, adipocytes release a large variety of adipokines into the bloodstream, regulating the function of several organs and tissues, including the adrenal glands, hereby controlling corticosteroid production. In adipose tissue, the activation of the MR by glucocorticoids (GC) and aldosterone affects important processes such as adipocyte differentiation, oxidative stress, autophagic flux, adipokine expression as well as local production of GC through upregulation of the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Notably, the proinflammatory responses induced by the MR are counteracted by activation of the GR, whose activity inhibits the expression of inflammatory adipokines. Both GR and MR are deeply involved in adipogenesis and adipose expansion; hence pharmacological blockade of these two receptors has proven effective against adipose tissue dysfunction in experimental models of obesity and metabolic syndrome (MetS), suggesting a potential use for MR and GR antagonists in these clinical settings. Importantly, obesity and Cushing's syndrome (CS) share metabolic similarities and are characterized by high levels of circulating corticosteroids, which in turn are able to deeply affect adipose tissue. In addition, pharmacological approaches aimed at reducing aldosterone and GC levels, by means of the inhibition of CYP11B2 (aldosterone synthase) or 11β-HSD1, represent alternative strategies to counter the detrimental effects of excessive levels of corticosteroids, which are often observed in obesity and, more general, in MetS. © 2017 American Physiological Society. Compr Physiol 7:1425-1447, 2017.

Inflammatory Markers in Primary Aldosteronism

Primary aldosteronism (PA) is the most common cause of endocrine hypertension with a high frequency of cardiovascular complications. The unfavorable cardiometabolic profile may be due to aldosterone-mediated activation of inflammatory cells, circulatory cytokines and activation of collagen synthesis in the vessel wall. Aim of our study was to evaluate differences in the levels of hsCRP, IL-6, TNF-α and N-terminal propeptide of collagen I (PINP) in patients with PA and essential hypertension (EH) as a control group, and between the subtypes of PA (aldosterone producing adenoma – APA, idiopathic hyperaldosteronism – IHA). We studied 28 patients with PA (IHA – 10 patients, APA – 12 patients, 6 unclassified) and 28 matched patients with EH. There were no differences in the levels of inflammatory markers between the followed groups [EH vs. PA: TNF-α (5.09 [3.68-6.32] vs. 4.84 [3.62-6.50] pg/ml), IL-6 (0.94 [0.70-1.13] vs. 0.97 [0.71-1.28] pg/ml), hsCRP (0.53 [0.25-1.54] vs. 0.37 [0.31-0.61] mg/l), leukocytes (6.35±1.42 vs. 5.97±1.29 109 l); APA vs. IHA: TNF-α (4.54 [3.62-7.03] vs. 5.19 [4.23-5.27] pg/ml), IL-6 (0.96 [0.63-1.21] vs. 0.90 [0.65-1.06] pg/ml), hsCRP (0.34 [0.29-0.47] vs. 0.75 [0.36-1.11] mg/l), leukocytes (6.37±1.41 vs. 5.71±1.21 109 l)]. Significant differences in the levels of PINP between PA and EH group were observed (35.18 [28.46-41.16] vs. 45.21 [36.95-62.81] μg/l, p≤0.003). No differences in inflammatory markers were observed between the followed groups, we confirmed higher levels of PINP in patients with PA.

Aldosterone aggravates glucose intolerance induced by high fructose

We previously reported that aldosterone impaired vascular insulin signaling in vivo and in vitro. Fructose-enriched diet induces metabolic syndrome including hypertension, insulin resistance, hyperlipidemia and diabetes in animal. In the current study, we hypothesized that aldosterone aggravated fructose feeding-induced glucose intolerance in vivo. Rats were divided into five groups for six-week treatment; uninephrectomy (Unx, n=8), Unx+aldosterone (aldo, 0.75 µg/h, s.c., n=8), Unx+fructose (fruc, 10% in drinking water, n=8), Unx+aldo+fruc, (aldo+fruc, n=8), and Unx+aldo+fruc+spironolactone, a mineralocorticoid receptor antagonist (aldo+fruc+spiro, 20mg/kg/day, p.o., n=8). Aldo+fruc rats manifested the hypertension, and induced glucose intolerance compared to fruc intake rats assessed by oral glucose tolerance test, homeostasis model assessment of insulin resistance and hyperinsulinemic-euglycemic clamp study. Spironolactone, significantly improved the aldosterone-accelerated glucose intolerance. Along with improvement in insulin resistance, spironolactone suppressed upregulated mineralocorticoid receptor (MR) target gene, serum and glucocorticoid-regulated kinases-1 mRNA expression in skeletal muscle in aldo+fruc rats. In conclusion, these data suggested that aldosterone aggravates fructose feeding-induced glucose intolerance through MR activation.

Marine natural product des-O-methyllasiodiplodin effectively lowers the blood glucose level in db/db mice via ameliorating inflammation

AIM

des-O-methyllasiodiplodin (DML) from Cerbera manghas has shown antagonistic activity against mineralocorticoid receptor (MR). Considering the involvement of MR in the insulin tolerance, we attempted to investigate the potential of DML in the treatment of type 2 diabetes mellitus (T2DM).

METHODS

Surface plasmon resonance (SPR) technology and reporter gene-based assays were used to study protein-small molecule interactions. HepG2 and 3T3-L1 cells were treated with H2O2 (0.2 mmol/L) or aldosterone (10 nmol/L) for 24 h. The expression of MR in the cells was downregulated with siRNA. The anti-inflammatory effect of the compound was evaluated, respectively. db/db mice were administered DML (30 mg·kg(-1)·d(-1)) for 4 weeks. Serum biochemical parameters and insulin sensitivity were examined. The expression levels of pro-inflammatory cytokines (MCP-1, TNF-α and IL-6) and ROS-related genes (NADPH p47 subunit and transcriptional factor PU.1) in adipose tissues and livers were analyzed using real-time RT-PCR.

RESULTS

In HepG2 and 3T3-L1 cells, both H2O2 and aldosterone markedly stimulates the expression of MCP-1, TNFα, IL-6, p47 and PU.1 genes. Co-treatment with DML (10 μmol/L) significantly reduced the H2O2- or aldosterone-induced expression of these genes. SPR-based assay confirmed the antagonistic activity of DML against the interaction between SRC-1 and MR-LBD. Furthermore, DML decreased aldosterone-induced MR transcriptional activity in a dose-dependent manner. Downregulation of MR with siRNA in the cells prevented or significantly attenuated aldosterone-stimulated expression of these genes, whereas DML did no longer affect the expression of these genes except that of IL-6. Oral administration of DML effectively reduced the levels of blood glucose and glycosylated hemoglobin (HbA1c) in db/db mice. The treatment also rectified the expression of pro-inflammatory factor and ROS-related genes in db/db mice.

CONCLUSION

DML effectively lowers the blood glucose level in db/db mice possibly via ameliorating the expression of obesity-related pro-inflammatory cytokines, highlighting the potential of the marine natural product as a drug lead for the treatment of metabolic disorders.

Aldosterone excess impairs first phase insulin secretion in primary aldosteronism

CONTEXT

Primary aldosteronism (PA) represents the most frequent cause of secondary arterial hypertension. Conflicting data have been published regarding the effect of aldosterone excess on glucose metabolism.

OBJECTIVE

Our aim was to analyze insulin sensitivity and β-cell function in a cohort of PA patients. Prospective follow-up investigations were performed in a subgroup of patients before and after adrenalectomy to assess the metabolic outcome.

DESIGN

Oral glucose tolerance test, combined intravenous glucose tolerance test, hyperinsulinemic-euglycemic glucose clamp test, and arginine test were carried out after a 12-hour fasting period.

PATIENTS

Twenty-two consecutive patients with both unilateral aldosterone-producing adenoma and bilateral idiopathic adrenal hyperplasia were recruited through the Munich center of the German Conn's Registry. The control group of patients with essential hypertension (n = 11) of corresponding age and body mass index was recruited from our hypertension unit. A normotensive cohort (n = 11) served as a further control group.

RESULTS

At baseline, first-phase insulin reaction in intravenous glucose tolerance test was significantly reduced in patients with PA as compared to normal controls (36.0 [24.0; 58.7] vs 90.1 [52.6; 143.8] μU/mL, P = .031) and lower in comparison to essential hypertension without reaching statistical significance (53.2 [30.8; 73.3] μU/mL, P = .123). The study was repeated 6 months after unilateral adrenalectomy in 9 consecutive patients with aldosterone-producing adenoma. At this time point, blood pressure had been normalized in most of the patients while body mass index remained unchanged (26.9 [25.5; 37.6] vs 27.5 [25.1; 35.6] kg/m(2), P = .401). First-phase insulin reaction in response to glucose significantly increased at follow-up (from 36.0 [25.5; 58.7] to 48.5 [40.4; 95.2] μU/mL, P = .038, n = 9). In contrast, insulin sensitivity and response to iv arginine did not differ before and after adrenalectomy.

CONCLUSION

Aldosterone excess has a direct negative effect on β-cell function in patients with PA. After adrenalectomy, glucose-induced first-phase insulin secretion improves significantly in the patients.

Visceral adipose tissue: emerging role of gluco- and mineralocorticoid hormones in the setting of cardiometabolic alterations

Several clinical and experimental lines of evidence have highlighted the detrimental effects of visceral adipose tissue excess on cardiometabolic parameters. Besides, recent findings have shown the effects of gluco-and mineralocorticoid hormones on adipose tissue and have also underscored the interplay existing between such adrenal steroids and their respective receptors in the modulation of adipose tissue biology. While the fundamental role played by glucocorticoids on adipocyte differentiation and storage was already well known, the relevance of the mineralocorticoids in the physiology of the adipose organ is of recent acquisition. The local and systemic renin–angiotensin–aldosterone system (RAAS) acting on adipose tissue seems to contribute to the development of the cardiometabolic phenotype so that its modulation can have deep impact on human health. A better understanding of the pathophysiology of the adipose organ is of crucial importance in order to identify possible therapeutic approaches that can avoid the development of such cardiovascular and metabolic sequelae.

Effects of auricular acupressure combined with low-calorie diet on the leptin hormone in obese and overweight Iranian individuals

BACKGROUND

Human leptin is a peptide hormone that is released from white adipocytes. The absence of leptin or its receptor leads to uncontrolled food intake, leading to obesity. In the present work, the effects of auricular acupressure combined with low-calorie diet on the leptin hormone level were investigated.

METHODS

Volunteers (n=86) with body mass indices (BMI) between 25 and 45 kg/m² were randomised into a case (n=43) or a control (n=43) group. Participants in each group received a low-calorie diet for 6 weeks. The case group was treated with auricular acupressure and the control group received a sham procedure. Plasma leptin levels, body fat mass, body weight and BMI were measured before and after treatment.

RESULTS

Participants who received auricular acupressure showed significant reductions in their plasma leptin levels (18.57%, p<0.01) as well as in their body fat mass (4%, p<0.05). These changes were not observed in the control group. The reduction in leptin was significantly greater in the acupressure group than the controls.

CONCLUSIONS

Auricular acupressure combined with a low-calorie diet significantly reduced plasma levels of leptin. However, the mechanism of this reduction is not clear.

Adipokines and cardiometabolic profile in primary hyperaldosteronism

CONTEXT

Primary aldosteronism (PA) has been recently associated with an unfavorable cardiometabolic profile. However, whether pro- and antiinflammatory adipokines levels can vary in PA is unknown.

OBJECTIVE

We evaluated the circulating levels of resistin, leptin, and adiponectin, echocardiographic left ventricle (LV) parameters, and the prevalence of metabolic syndrome (SM) in subjects with PA.

PATIENTS

Seventy-five subjects with established diagnosis of PA and 232 consecutive individuals with known or suspected hypertension were enrolled.

MAIN OUTCOME MEASURES

Plasma adipokine levels and echocardiographic parameters were calculated. Prevalence of SM was also estimated.

RESULTS

Among the 75 PA subjects, 37 patients were affected by aldosterone-producing adenoma and 38 by idiopathic hyperaldosteronism; 40 subjects were affected by essential hypertension (EH) and SM (EH SM+); 152 subjects were affected by EH without SM (EH SM-); and 40 subjects were normotensive (NT). Subjects with PA had the highest plasma resistin levels among the four groups (P < 0.01). Plasma resistin concentration was significantly higher in PA subjects when compared with EH SM+ individuals (P < 0.01) and EH SM- subjects (P < 0.01). PA subjects showed the higher LV mass and left atrium than EH individuals, irrespectively of the presence of SM (P < 0.01 for both). Plasma resistin levels was significantly correlated with ejection fraction and LV end-diastolic volume. The prevalence of SM was higher in PA subjects than in those with EH (25.4 vs. 20.3%).

CONCLUSIONS

Our data suggest that elevated aldosterone levels is associated with elevated circulating resistin levels and cardiac morphological changes independently of the presence of SM.

Aldosterone: a forgotten mediator of the relationship between psychological stress and heart disease

Numerous studies support the notion that cumulative exposure to chronic stress is a risk factor for cardiovascular disease (CVD). Various stress-related hormones have been proposed as potential mediators of the relationship between psychological stress and CVD, including catecholamines and more indirectly, cortisol. Somewhat surprisingly, although aldosterone is also released in response to hypothalamic-pituitary-adrenal (HPA) axis activation, it has not been considered as relevant for this relationship. In the present review we will consider aldosterone as a potentially important mediator of the relationship between negative affective states and CVD. First, we will briefly review the known functions and roles of aldosterone, and then consider its actions in both the brain and the periphery. We will then review the available literature on the role of aldosterone in CVD, and also consider links between aldosterone and various forms of chronic psychological stress. Finally we will present an integrated model of how aldosterone may mediate effects of chronic stress on CVD, recommend new directions for research, and identify important methodological and design issues for this work.

Mineralocorticoid receptors in the metabolic syndrome

The mineralocorticoid receptor (MR) mediates aldosterone effects on salt homeostasis and blood pressure regulation. MR activation also promotes inflammation, cardiovascular remodelling and endothelial dysfunction, and affects adipose tissue differentiation and function. Some of these effects derive from MR activation by glucocorticoids. Recent epidemiological studies show that the incidence of metabolic syndrome increases across quartiles of aldosterone, implicating the MR as a central player in metabolic homeostasis, involving electrolyte, water and energy balance. This review summarizes the current understanding of MR-mediated effects in diverse tissues and the role of aldosterone as a cardiometabolic risk factor, and discusses the possible relationship between inappropriate MR activation (by both mineralocorticoids and glucocorticoids) and the development of metabolic syndrome.

Mineralocorticoid receptor blockade reverses obesity-related changes in expression of adiponectin, peroxisome proliferator-activated receptor-gamma, and proinflammatory adipokines

BACKGROUND

In obesity, decreases in adiponectin and increases in proinflammatory adipokines are associated with heart disease. Because adipocytes express mineralocorticoid receptor (MR) and MR blockade reduces cardiovascular inflammation and injury, we tested the hypothesis that MR blockade reduces inflammation and expression of proinflammatory cytokines in adipose tissue and increases adiponectin expression in adipose tissue and hearts of obese mice.

METHODS AND RESULTS

We determined the effect of MR blockade (eplerenone, 100 mg/kg per day for 16 weeks) on gene expression in retroperitoneal adipose and heart tissue from obese, diabetic db/db mice (n=8) compared with untreated obese, diabetic db/db mice (n=10) and lean, nondiabetic db/+ littermates (n=11). Expression of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, plasminogen activator inhibitor type 1, and macrophage protein CD68 increased, and expression of adiponectin and peroxisome proliferator-activated receptor-gamma decreased in retroperitoneal adipose tissue from obese versus lean mice. In addition, adiponectin expression in heart was reduced in obese versus lean mice. MR blockade prevented these obesity-related changes in gene expression. Furthermore, treatment of undifferentiated preadipocytes with aldosterone (10(-8) mol/L for 24 hours) increased mRNA levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1 and reduced mRNA and protein levels of peroxisome proliferator-activated receptor-gamma and adiponectin, supporting a direct aldosterone effect on gene expression.

CONCLUSIONS

MR blockade reduced expression of proinflammatory and prothrombotic factors in adipose tissue and increased expression of adiponectin in heart and adipose tissue of obese, diabetic mice. These effects on adiponectin and adipokine gene expression may represent a novel mechanism for the cardioprotective effects of MR blockade.

The metabolic syndrome in primary aldosteronism

Patients with hypertension have a high prevalence of concurrent metabolic abnormalities (eg, obesity, dyslipidemia, and hyperglycemia). Clustering of these risk factors, defined as the metabolic syndrome, is associated with a high cardiovascular risk profile. This review summarizes current knowledge about the prevalence and characteristics of the metabolic syndrome in primary aldosteronism, and discusses the possible pathophysiological link between aldosterone and individual components of the metabolic syndrome, other than hypertension. Impaired glucose metabolism due to insulin resistance appears to be the major contributor to metabolic dysfunction in primary aldosteronism. Experimental observations support the possibility that aldosterone could act directly on insulin receptor function. The potential proadipogenic role of aldosterone and its negative effect on insulin sensitivity through production of cytokines remains to be investigated. Higher rates of cardiovascular events reported in primary aldosteronism could be due in part to the increased prevalence of the metabolic syndrome in this disorder.

Aldosterone Suppresses Insulin Signaling Via the Downregulation of Insulin Receptor Substrate-1 in Vascular Smooth Muscle Cells

Clinical reports indicate that patients with primary aldosteronism commonly have impaired glucose tolerance; however, the relationship between aldosterone and insulin signaling pathway has not been clarified. In this study, we examined the effects of aldosterone treatment on insulin receptor substrate-1 expression and insulin signaling pathway including Akt phosphorylation and glucose uptake in rat vascular smooth muscle cells. Insulin receptor substrate-1 protein expression and Akt phosphorylation were determined by Western blot analysis with anti-insulin receptor substrate-1 and phosphorylated-Akt antibodies, respectively. Glucose metabolism was evaluated using (3)H-labeled 2-deoxy-d-glucose uptake. Aldosterone (1-100 nmol/L) dose-dependently decreased insulin receptor substrate-1 protein expression with a peak at 18 hours (n=4). Aldosterone-induced degradation of insulin receptor substrate-1 was markedly attenuated by treatment with the selective mineralocorticoid receptor antagonist eplerenone (10 micromol/L; n=4). Furthermore, degradation was blocked by the Src inhibitor PP1 (20 micromol/L; n=4). Treatment with antioxidants, N-acetylcysteine (10 mmol/L), or ebselen (40 micromol/L) also attenuated aldosterone-induced insulin receptor substrate-1 degradation (n=4). In addition, proteasome inhibitor MG132 (1 micromol/L) prevented insulin receptor substrate-1 degradation (n=4). Aldosterone treatment abolished insulin-induced Akt phosphorylation (100 nmol/L; 5 minutes; n=4). Furthermore, aldosterone pretreatment decreased insulin-stimulated (100 nmol/L; 60 minutes; n=4) glucose uptake by 50%, which was reversed by eplerenone (10 micromol/L; n=4). These data indicate that aldosterone decreases insulin receptor substrate-1 expression via Src and reactive oxygen species stimulation by proteasome-dependent degradation in vascular smooth muscle cells; thus, aldosterone may be involved in the pathogenesis of vascular insulin resistance via oxidative stress.

The metabolic syndrome in primary aldosteronism

Patients with hypertension have a high prevalence of concurrent metabolic abnormalities (eg, obesity, dyslipidemia, and hyperglycemia). Clustering of these risk factors, defined as the metabolic syndrome, is associated with a high cardiovascular risk profile. This review summarizes current knowledge about the prevalence and characteristics of the metabolic syndrome in primary aldosteronism, and discusses the possible pathophysiological link between aldosterone and individual components of the metabolic syndrome, other than hypertension. Impaired glucose metabolism due to insulin resistance appears to be the major contributor to metabolic dysfunction in primary aldosteronism. Experimental observations support the possibility that aldosterone could act directly on insulin receptor function. The potential proadipogenic role of aldosterone and its negative effect on insulin sensitivity through production of cytokines remains to be investigated. Higher rates of cardiovascular events reported in primary aldosteronism could be due in part to the increased prevalence of the metabolic syndrome in this disorder.

Aldosterone as a key mediator of the cardiometabolic syndrome in primary aldosteronism: an observational study

OBJECTIVE

Primary aldosteronism (PA) is characterized by the onset of both cardiac and gluco-metabolic alterations. The aim of this study was to evaluate the impact of aldosterone excess on the development of such complications, and the effects of surgical and pharmacological treatment on their long-term outcome.

METHODS

We prospectively re-examined 61 patients: 25 with aldosterone-producing adenoma (APA), after surgery, and 36 patients with idiopathic hyperaldosteronism (IHA) on pharmacological treatment. The lipid, fasting and dynamic glucose profiles and the echocardiographic parameters were evaluated at diagnosis and at follow-up.

RESULTS

After adrenalectomy all patients had normalization of aldosterone levels and were cured of hypokalaemia, and a resolution of hypertension was achieved in 12 of 25 patients. APA patients showed a significant reduction of both plasma glucose (P=0.017) and insulin levels (P=0.001) after 75 g oral glucose tolerance test. Stabilization of glucose metabolism complications was observed in IHA patients. Multiple regression analysis at diagnosis showed a positive correlation between homeostasis model assessment (HOMA) insulin resistance index and HOMA beta cell and serum aldosterone levels in both APA and IHA. Echocardiographic parameters were improved in both APA and IHA at follow-up and the difference was statistically significant for left ventricular mass index (P=0.017) and interventricular septum thickness (P=0.007) in APA patients.

CONCLUSIONS

The removal of aldosterone excess in APA patients induces the regression of both cardiac and gluco-metabolic complications, indicating aldosterone as a main determinant of such alterations. In IHA patients the medical treatment seems to avoid the possible progression of the these alterations that appear to be stable.

Leptin and the regulation of the hypothalamic-pituitary-adrenal axis

Leptin, the product of the obesity gene (ob) predominantly secreted from adipocytes, plays a major role in the negative control of feeding and acts via a specific receptor (Ob-R), six isoforms of which are known at present. Evidence has been accumulated that leptin, like other peptides involved in the central regulation of food intake, controls the function of the hypothalamic-pituitary-adrenal (HPA) axis, acting on both its central and peripheral branches. Leptin, along with Ob-R, is expressed in the hypothalamus and pituitary gland, where it modulates corticotropin-releasing hormone and ACTH secretion, probably acting in an autocrine-paracrine manner. Only Ob-R is expressed in the adrenal gland, thereby making it likely that leptin affects it by acting as a circulating hormone. Although in vitro and in vivo findings could suggest a glucocorticoid secretagogue action in the rat, the bulk of evidence indicates that leptin inhibits steroid-hormone secretion from the adrenal cortex. In keeping with this, leptin was found to dampen the HPA axis response to many kinds of stress. In contrast, leptin enhances catecolamine release from the adrenal medulla. This observation suggests that leptin activates the sympathoadrenal axis and does not appear to agree with its above-mentioned antistress action. Leptin and/or Ob-R are also expressed in pituitary and adrenal tumors, but little is known about the role of this cytokine in the pathophysiology.

Insulin sensitivity in patients with primary aldosteronism: a follow-up study

CONTEXT

The relationship between aldosterone and glucose metabolism is poorly understood, and there is substantial disparity among findings of studies that have examined glucose tolerance and insulin sensitivity in patients with primary aldosteronism.

OBJECTIVE

The objective of the study was to determine the outcome of glucose tolerance and insulin sensitivity in patients with primary aldosteronism after treatment.

DESIGN

This was a prospective study of patients who received a diagnosis of primary aldosteronism and were followed up for an average period of 5.7 yr (range, 3-9 yr).

SETTING

The study was conducted at a university referral center.

PATIENTS

A consecutive sample of 47 patients with tumoral or idiopathic aldosteronism was followed up after either surgical or medical treatment. Patients with primary aldosteronism were compared with 247 patients with essential hypertension with the same severity and duration of disease and 102 normotensive subjects.

MAIN OUTCOME MEASURES

Short- and long-term changes in glucose tolerance and insulin sensitivity were measured.

RESULTS

After adjustment for age, gender, and body mass index, patients with primary aldosteronism had greater homeostasis model assessment index (P < 0.05) and plasma insulin response to an oral glucose load (P < 0.05) and lower quantitative insulin sensitivity check index (P < 0.01) than normotensive controls. Changes in insulin sensitivity were significantly greater in essential hypertension than primary aldosteronism, and this difference was confirmed by assessment with the hyperinsulinemic-euglycemic clamp (P < 0.01). Treatment of primary aldosteronism decreased blood pressure significantly, and during the initial 6 months of follow-up, parameters of insulin sensitivity were restored to normal. Analysis of subsequent follow-up showed nonsignificant changes in glucose metabolism parameters in both adrenalectomized and spironolactone-treated patients.

CONCLUSIONS

Insulin resistance is present in patients with tumoral and idiopathic aldosteronism, but the defect appears less severe than in patients with essential hypertension. Treatment with surgery or aldosterone antagonists restores rapidly and persistently normal sensitivity to insulin.

Neurohumoral stimulation in type-2-diabetes as an emerging disease concept

Neurohumoral stimulation comprising both autonomic-nervous-system dysfunction and activation of hormonal systems including the renin-angiotensin-aldosterone system (RAAS) was found to be associated with Type-2-diabetes (T2D). Therapeutic strategies such as RAAS interference proved to be beneficial in both T2D treatment and prevention. In addition to an activated RAAS, hyperleptinemia in obesity, hyperinsulinemia in conditions of peripheral insulin resistance and overall oxidative stress in T2D represent known activators of the sympathetic component of the autonomic nervous system. Here, we hypothesize that sympathetic activation may cause peripheral insulin resistance defined as partial blocking of insulin effects on glucose uptake. Resulting hyperinsulinemia or hyperglycemia-related oxidative stress may further aggravate sympatho-excitation. This notion leads to a secondary hypothesis: sympathetic activation worsens from obesity towards insulin resistance, and further towards T2D. In this review, existing evidence relating to neurohumoral stimulation in T2D and consequences thereof, such as oxidative stress and inflammation, are discussed. The aim of this review is to provide a rationale for therapies, which are able to intercept neuroendocrine pathways in T2D and precursor states such as obesity.

The effect of aldosterone on glucose metabolism

There is an association of glucose intolerance and diabetes with primary aldosteronism, but the frequency and mechanisms are not clear. This paper reviews the possible mechanisms of impaired glucose metabolism in primary aldosteronism. Patients with primary aldosteronism can have impaired pancreatic insulin release and reduction in insulin sensitivity. These effects may be due to hypokalemia, but the evidence suggests other factors such as a direct impact of excess aldosterone on insulin action in contributing to the metabolic dysfunction. In general adrenal surgery in cases of aldosterone-producing adenoma will correct the metabolic abnormalities, but it is less sure if treatment with spironolactone in cases of idiopathic hyperplasia will correct impaired glucose tolerance.