Biphasic time course of the changes in aldosterone biosynthesis under high-salt conditions in Dahl salt-sensitive rats

OBJECTIVE

The comorbidity of excess salt and elevated plasma aldosterone has deleterious effects in cardiovascular disease. We evaluated the mechanisms behind the paradoxical increase in aldosterone biosynthesis in relation to dietary intake of salt.

METHODS AND RESULTS

Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats were fed a high-salt diet, and plasma and tissue levels of aldosterone in the adrenal gland and heart were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry. In Dahl-S rats, we found that the delayed and paradoxical increase in aldosterone biosynthesis after the initial and appropriate response to high salt. The late rise in aldosterone biosynthesis was accompanied by upregulation of CYP11B2 expression in the zona glomerulosa and increased adrenal angiotensin II levels and renin-angiotensin system components. It preceded the appearance of left ventricular systolic dysfunction and renal insufficiency. Blockade of angiotensin AT(1) receptors reversed the paradoxical increase in aldosterone biosynthesis. In contrast, Dahl-R rats maintained the initial suppression of aldosterone biosynthesis. Aldosterone levels in the heart closely paralleled those in the plasma and adrenal gland and disappeared after bilateral adrenalectomy.

CONCLUSIONS

Chronic salt overload in Dahl-S rats stimulates aberrant aldosterone production via activation of the local renin-angiotensin system in the adrenal gland, thereby creating the comorbidity of excess salt and elevated plasma aldosterone.

Diabetic lipoproteins and adrenal aldosterone synthesis--a possible pathophysiological link?

An increased prevalence of diabetes mellitus (DM) has been reported in patients with primary aldosteronism (PA). DM is associated with abnormal structure and metabolism of circulating lipoproteins, which normally serve as a major source of cholesterol for adrenocortical steroidogenesis. The present study has been designed to investigate the effect of diabetically modified lipoproteins on adrenocortical aldosterone synthesis. Lipoproteins (VLDL, LDL, HDL) isolated from healthy volunteers, were subjected to oxidation or glycoxidation in the presence of sodium hypochlorite (3 mmol/l) or glucose (200 mmol/l), and aldosterone synthesis in human adrenocortical cells (H295R) was examined. Native and glycoxidized VLDL had greatest stimulatory effect on aldosterone production by 15-fold and 14-fold, respectively. At the molecular level, these VLDL produced maximum increases in Cyp11B2 mRNA level up to 17-fold. Experiments with the highly selective scavenger receptor class B type I (SR-BI) inhibitor BLT-1 revealed that cholesterol uptake from native and glycoxidized HDL and VLDL for hormone production is considerably mediated by SR-BI. Western blot analysis of extracellular signal-regulated kinase (ERK 1/2) phosphorylation and experiments with the MEK inhibitor U0126 indicated a specific mechanistic role of the ERK cascade in lipoprotein-mediated steroid hormone release. In summary, diabetic dyslipidemia and modification of circulating lipoproteins may promote adrenocortical aldosterone synthesis.

Adrenal cell aldosterone production is stimulated by very-low-density lipoprotein (VLDL)

Very low-density lipoproteins (VLDL) are a class of large lipoprotein synthesized in the liver. The key function of VLDL, in vivo, is to carry triglyceride from the liver to adipose tissue. As a steroidogenic organ, the adrenal gland mainly uses lipoproteins as sources of cholesterol. Although VLDL receptors have been detected in the human adrenal, the function of VLDL in the adrenal gland remains unknown. Herein, we used primary cultures of human and bovine adrenal cells and the adrenocortical cell line H295R as models to determine the effects of VLDL on adrenal steroidogenesis. Our studies revealed that VLDL significantly increased aldosterone synthesis in all of the models tested. This increase was largely due to VLDL's stimulation of the expression of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2). VLDL increased CYP11B2 mRNA expression in a concentration-dependent manner. Effects of VLDL on CYP11B2 transcript levels were not additive with angiotensin II or potassium but were additive with the cAMP pathway agonists ACTH and forskolin. Nifedipine completely inhibited the effects of VLDL on CYP11B2 mRNA, suggesting that calcium is the main signal transduction pathway used by VLDL in adrenal cells. Indeed, VLDL increased cytosolic free calcium levels. An in vivo study conducted in sucrose-fed rats showed a positive correlation between elevated triglyceride (VLDL) levels in plasma and CYP11B2 expression in the adrenal. In conclusion, we have shown that VLDL can stimulate aldosterone synthesis in adrenocortical cells by increasing StAR and CYP11B2 expression, an event likely mediated by a calcium-initiated signaling cascade.

Regulation of human CYP11B1 and CYP11B2 promoters by transposable elements and conserved cis elements

CYP11B1 and CYP11B2 responsible for the final steps of cortisol and aldosterone synthesis, respectively, are believed to be duplicate genes with distinctive promoters. Our sequence analysis uncovers that these two genes share great homology in the proximal upstream regions, but insertion of Alu and L1 elements drives promoters divergent. Each CYP11B promoter contains two Alu elements embedded in a truncated L1 element, breaking L1 into three disconnected fragments. Alu functions as an enhancer in both genes regardless of orientation and copy number. Insertion of Alu upstream of a SV40 promoter also elevates promoter activity. However, the effect of Alu on CYP11B1 is blocked by a second L1 element (CYP11B1-L1.2) inserted between the first one and the conserved proximal upstream region. Although CYP11B1-L1.2 is 5'-truncated and lacks a functional ORF, replacing it with a fluorescent gene demonstrates that the element can be transcribed from the CYP11B1 core promoter in an opposite direction and a smaller magnitude compared to CYP11B1. Deletion of CYP11B1-L1.2 greatly increases CYP11B1 promoter activity and restores the enhancing effect of Alu. The Ad5 and SF-1 binding elements conserved in the proximal core promoter play a role in basal expression of both genes. Mutation of the Ad5 site reduces promoter activity to the minimal level. ERRα is the transcription factor interacting with Ad5 during basal expression. The core promoters of both genes are also conserved in mouse and rat despite the fact that the sites corresponding to cre, Ad5, and SF-1 in rodent Cyp11b1 promoters deviate from consensus.

Differential effects of down-regulated steroidogenic factor-1 on basal and angiotensin II-induced aldosterone secretion

Aldosterone synthase (CYP11B2) is responsible for the final step in aldosterone synthesis and is importantly regulated by angiotensin-II (Ang II) through diverse pathways. However, under pathological conditions, such as in hyperaldosteronism, the regulation becomes disordered. The transcription factor steroidogenic factor-1 (SF-1) is important in regulating the endocrine system and is overexpressed in aldosterone-producing adenoma (APA), a common cause of hyperaldosteronism. Overexpression of SF-1 has been extensively studied, but little in-depth information is available regarding the effects of inhibitory SF-1 on CYP11B2 and Ang II. In this paper, we have investigated the roles of down-regulated SF-1 in basal and Ang II-induced CYP11B2 expression using SF-1-specific short hairpin RNA. Inhibitory SF-1 was found to decrease the sensitivity of CYP11B2 and aldosterone to Ang II stimulation, whereas a down-regulation of SF-1 enhanced basal CYP11B2 expression and aldosterone production in H295R cells. Considering these differential effects of SF-1 on aldosterone production, these results might provide a new insight into the understanding of hyperaldosteronism.

Endothelial progenitor cells in primary aldosteronism: a biomarker of severity for aldosterone vasculopathy and prognosis

CONTEXT

Primary aldosteronism (PA) is associated with a higher incidence of cardiovascular events, probably through mineralocorticoid receptor (MR)-dependent endothelial cell dysfunction, in comparison with essential hypertension (EH).

OBJECTIVE

Our objective was to investigate the number and function of endothelial progenitor cells (EPC) in PA and the relationship with arterial stiffness and disease progression.

DESIGN AND SETTING

We conducted a prospective study of the change of EPC number and outcome of PA patients after treatment at a tertiary medical center.

PRIMARY OUTCOMES

Changes in arterial stiffness and EPC number after treatment and the curability of hypertension were assessed.

PATIENTS

A total of 113 PA patients (87 patients diagnosed with aldosterone-producing adenoma, 26 with idiopathic hyperaldosteronism) and 55 patients with EH participated.

RESULTS

PA patients had higher arterial stiffness than EH patients (P = 0.006), with a lower numbers of circulating EPC and endothelial colony-forming units (P < 0.05). The differences were ameliorated at 6 months after unilateral adrenalectomy or treatment with spironolactone. Expression of MR was identified in the EPC. The number of circulating EPC was inversely correlated with the plasma aldosterone concentration (P = 0.021), arterial stiffness (P = 0.029) and serum high-sensitivity C-reactive protein (P = 0.03). High-dose aldosterone (10(-5) and 10(-6) m) attenuated EPC proliferation and angiogenesis in vitro. Among the 45 patients who underwent unilateral adrenalectomy, 32 (71%) were cured of hypertension. The preoperative number of EPC [log(EPC number percent) >-3.6] predicted the curability of hypertension after adrenalectomy (P = 0.003).

CONCLUSIONS

The relative deficiency of EPC in PA patients may contribute to aldosterone vasculopathy, which can be reversed by adrenalectomy and spironolactone. High aldosterone levels attenuated EPC proliferation and angiogenesis. Circulating EPC number may be a valuable biomarker to identify PA patients with a high incidence of arterial stiffness and to predict postoperative residual hypertension of aldosterone-producing adenoma.

The expression of genes encoding opioid precursors and the influence of opioid receptor agonists on steroidogenesis in porcine adrenocortical cells in vitro

Endogenous opioid peptides are involved in the regulation of the HPA-axis function and stress response mechanism. However, there is a scarcity of data on opioid involvement in the regulation of the adrenocortical endocrine function. This study was performed to: 1) establish the expression of proenkephalin, POMC and prodynorphin genes in the porcine adrenal cortex and test in vitro the influence of ACTH, angiotensin II, CRH and epinephrine on this expression, and 2) determine the effects of opioid receptor agonists on basal and ACTH- or angiotensin II-affected secretion of cortisol, aldosterone and progesterone by the cultured adrenocortical cells. Our experiment has demonstrated the presence of mRNAs for opioid precursors in cells isolated from the adrenal cortex and the significant effects of ACTH and angiotensin II, but not CRH or epinephrine, on adrenocortical transcription of the analyzed genes. Angiotensin II reduced the expression of the POMC gene but stimulated that of prodynorphin. In turn, ACTH decreased the transcription of prodynorphin. The study has also demonstrated the effects of selective opioid receptor agonists - DPLPE (delta), FK33-824 (mu) and U50,488 (kappa) - on adrenal steroidogenesis in pigs. Basal secretion of cortisol was enhanced after the activation of mu or kappa receptors, whereas ACTH-stimulated cortisol output was increased only by the mu receptor agonist. Angiotensin II-treated cells significantly decreased aldosterone secretion in the presence of the kappa receptor agonist. The present results suggest that opioid peptides are synthesized in the porcine adrenal cortex, indicating their involvement in the regulation of adrenal steroidogenesis through autocrine and/or paracrine interactions.

Peroxisome proliferator-activated receptor-{gamma} suppresses CYP11B2 expression and aldosterone production

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor for the antidiabetic agent thiazolidinedione, which exerts various physiological activities, independent of lowering blood glucose. However, the role of PPARγ in aldosterone production has not been clarified. The objective of this study was to investigate the effect of PPARγ on aldosterone synthase gene (CYP11B2) expression and aldosterone production. Localization of PPARγ expression in normal adrenal cortex was determined by immunohistochemistry. Aldosterone production and CYP11B2 expression levels were determined using human adrenocortical carcinoma H295R cells. Pioglitazone suppressed angiotensin II-induced aldosterone secretion and CYP11B2 expression. PPARγ was expressed in zona glomerulosa in human normal adrenal gland. PPARγ overexpression enhanced pioglitazone-mediated CYP11B2 transrepression. The pioglitazone-mediated suppression of aldosterone secretion and CYP11B2 expression were canceled by PPARγ L466A/E469A mutant. Pioglitazone also suppressed potassium-mediated CYP11B2 induction, but not N6-2'-O-dibutyladenosine-3',5'-cyclic monophosphate stimulation. Rosiglitazone and GW1929 also suppressed CYP11B2 transactivation. Mutation analysis revealed that the Ad1/CRE element in CYP11B2 5'-flanking region was responsible for the pioglitazone-mediated transrepression. Pioglitazone suppressed ionomycin and a truncated constitutively active form Ca(2+)/calmodulin-dependent kinase I (CaMKI)-mediated CYP11B2 transcriptional activation. A CaMK inhibitor KN-93 attenuated pioglitazone-mediated CYP11B2 transrepression. PPARγ suppresses CYP11B2 expression and aldosterone secretion.

[Aldosterone exacerbates chronic renal insufficiency]

It is now clear that the synthesis of aldosterone (A) and the expression of the mineralocorticoid receptor also appear in the extra-adrenal tissues. Experimental studies have succeeded in showing the connection between A and the pathological mechanisms that appear in the development of chronic kidney diseases (CKD). Unfortunately, it is not currently possible to decide whether the effects of A are clinically relevant or not due to the lack of controlled trials.

CONCLUSION

A very likely has a role in the development of CKD, although considerably more clinical investigation is needed.

[Peculiarities of cardiac contractile function in patients with arterial hypertension depending on temperament and anxiety state]

The aim of the work was to elucidate the relationship between temperament and personal anxiety and between left ventricular myocardium hypertrophy, contractility and diastolic function in 671 men (mean age 54 +/- 1.8 yr) with newly diagnosed grade II arterial hypertension who took no antihypertensive drugs before the study. The tone of vegetative nervous system, serum levels of cortisol, aldosterone, thyroxin, and insulin were measured. EchoCG was used to determine left ventricular myocardium mass (LVMM), LVMM index, the ratio of transmitral blood flow at the beginning and end of diastole, left ventricular ejection and shortening fractions, end-systolic and diastolic size and volume. Phlegmatic and melancholic patients differed from cholerics and sanguinics in the predominance of parasympathetic influences, elevated blood aldosterone and insulin levels in combination with higher LVMM and LVMM index but lower left ventricular systolic and diastolic function. These characteristics were especially well apparent in anxious subjects comprising a risk group for cardiac insufficiency.

Role of genetic variation in regulation of aldosterone biosynthesis

Aldosterone biosynthesis is not only altered in rare mendelian disorders. Recent evidence suggests that common polymorphisms in the genes mediating the final stages of aldosterone and cortisol production (CYP11B1 and CYP11B2 respectively) are also associated with milder alterations in adrenal corticosteroid biosynthesis. These abnormalities consist of a decrease in adrenal 11β- hydroxylase activity and a subtle, life-long excess of aldosterone secretion which may lead to long-term cardiovascular risks. An interaction between the CYP11B1 and CYP11B2 genes may exist but is yet to be elucidated. This article describes the studies which highlight the importance of adrenal steroid synthesis in the development of hypertension and cardiovascular dysfunction as well as the role of common polymorphisms in adrenal synthetic genes in altering corticosteroid biosynthesis.

The role of TASK1 in aldosterone production and its expression in normal adrenal and aldosterone-producing adenomas

OBJECTIVES

Aldosterone production in the adrenal glomerulosa is mainly regulated by angiotensin II and K+. Adrenal glomerulosa cells are uniquely sensitive to extracellular K+. Genetic deletion of subunits of K+-selective leak-channels (KCNK), TASK1 and/or TASK3, in mice generates animals with hyperaldosteronism and histological changes in the adrenal cortex. Herein, we studied the expression of TASK1 in human adrenocortical cells, as well as its role in aldosterone production in H295R cells.

DESIGN

TASK1 expression was investigated by comparative microarray analysis of aldosterone-producing adenomas (APA) and normal adrenals (NAs). The effects of TASK1 knockdown by siRNA transfection were investigated in H295R cells. Fluo-4 fluorescent measurements of intracellular Ca2+ and pharmacological inhibition of Ca2+ -dependent calmodulin kinases (CaMK) were performed to better define the effects of TASK1 on Ca2+ signalling pathways.

RESULTS

Microarray analysis of APA and NA showed similar expression of TASK1 between these two groups. However, in APA, NA and H295R cells the expression of TASK1 was predominant when compared with other KCNK family members. Knockdown of TASK1 (with siRNA) induced the expression of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2), and also stimulated pregnenolone and aldosterone production. Cells transfected with siTASK1 had increased intracellular Ca2+, leading to activation of CaMK and increased expression of CYP11B2.

CONCLUSIONS

Our study reveals the predominant expression of TASK1 over other KCNK family genes in the human adrenal cortex. Herein, we also described the role of TASK1 in the regulation of human aldosterone production through regulation of intracellular Ca2+ and CaMK signalling pathways.

Functional roles of protein kinase A (PKA) and exchange protein directly activated by 3',5'-cyclic adenosine 5'-monophosphate (cAMP) 2 (EPAC2) in cAMP-mediated actions in adrenocortical cells

In the adrenal cortex, the biosynthesis of steroid hormones is controlled by the pituitary-derived hormone ACTH. The functions of ACTH are principally relayed by activating cAMP-dependent signaling pathways leading to the induction of genes encoding enzymes involved in the conversion of cholesterol to steroid hormones. Previously, protein kinase A (PKA) was thought to be the only direct effector of cAMP. However, the discovery of the cAMP sensors, exchange proteins directly activated by cAMP (EPAC1 and 2), has led to a reevaluation of this assumption. In the present study, we demonstrate the occurrence of the EPAC2 splicing variant EPAC2B in adrenocortical cancer cells. Immunocytochemistry demonstrated that EPAC2B is localized predominantly in the nucleus. EPAC2B is functional because it activates Rap1 in these cells. Using the cAMP analogs 8-p-chlorophenylthio-2'-O-methyl-cAMP and N6-benzoyl-cAMP, which specifically activate EPAC1/2 and PKA, respectively, we evaluated the contribution of these factors in steroid hormone production, cell morphology, actin reorganization, and migration. We demonstrate that the expression of cAMP-inducible factors involved in steroidogenesis (steroidogenic acute regulatory protein, cytochrome P450 11A1 and 17, and nerve growth factor-induced clone B) and the cAMP-induced biosynthesis of steroid hormones (cortisol and aldosterone) are mediated by PKA and not by EPAC2B. In contrast, both PKA- and EPAC-specific cAMP analogs induced cell rounding, loss of stress fibers, and blocked migration. Taken together, the presented data confirm PKA as the central cAMP mediator in steroid hormone production and reveal the involvement of EPAC2B in cAMP-induced effects on cytoskeleton integrity and cell migration.

Aldosterone production and insulin resistance in healthy adults

CONTEXT

Aldosterone production is associated with insulin resistance in obese and hypertensive subjects. However, its effect on insulin sensitivity in healthy subjects is not clear.

OBJECTIVE

The objective of this study was to test the hypothesis that increased aldosterone production is associated with lower insulin sensitivity in healthy subjects.

DESIGN

This is an analysis of data previously collected during studies conducted as part of the International Hypertensive Pathotype Consortium.

PARTICIPANTS AND INTERVENTIONS

Eighty-four subjects free of any medical or psychiatric illness were included in this study. They were studied after 7 d of a standardized high-sodium diet confirmed by 24-h urine sodium above 200 mEq. Insulin sensitivity index (ISI) was calculated after a 75-g oral glucose load with glucose and insulin measurements at 0, 30, 60, and 120 min. Serum aldosterone levels were measured after 45 min of angiotensin II (3 ng/kg/min) infusion.

RESULTS

There were significant negative correlations between ISI and age, body mass index (BMI), diastolic blood pressure, and angiotensin II-stimulated aldosterone level (P < 0.01). On multivariate regression analysis, stimulated aldosterone level was an independent predictor of ISI after adjusting for age, BMI, and diastolic blood pressure. Stimulated aldosterone level predicted 8% of the variance in ISI (P = 0.003) with age, BMI, and diastolic blood pressure together predicting 23% of the variance in ISI. Thus, the final regression model predicted 31% of the variance in ISI (P < 0.0001).

CONCLUSIONS

Aldosterone production is associated with insulin resistance in normotensive healthy subjects independent of traditional risk factors.

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

Neuropeptide Y modulates steroid production of human adrenal H295R cells through Y1 receptors

Neuropeptide Y (NPY) is abundantly expressed in the nervous system and acts on target cells through NPY receptors. The human adrenal cortex and adrenal tumors express NPY receptor subtype Y1, but its function is unknown. We studied Y1-mediated signaling, steroidogenesis and cell proliferation in human adrenal NCI-H295R cells. Radioactive ligand binding studies showed that H295R cells express Y1 receptor specifically. NPY treatment of H295R cells stimulated the MEK/ERK1/2 pathway, confirming that H295R cells express functional Y1 receptors. Studies of the effect of NPY and related peptide PYY on adrenal steroidogenesis revealed a decrease in 11-deoxycortisol production. RIA measurements of cortisol from cell culture medium confirmed this finding. Co-treatment with the Y1 antagonist BIBP2336 reversed the inhibitory effect of NPY on cortisol production proving specificity of this effect. At mRNA level, NPY decreased HSD3B2 and CYP21A2 expression. However NPY revealed no effect on cell proliferation. Our data show that NPY can directly regulate human adrenal cortisol production.

Effect of atorvastatin on aldosterone production induced by glucose, LDL or angiotensin II in human renal mesangial cells

Nephropathy is a major complication of diabetes mellitus, thus development of rational therapeutic means is critical for improving public health. It was previously reported that human mesangial cells locally produced aldosterone, a steroid hormone that plays an important role in the development of diabetic nephropathy. The present experiments clarified the effect of glucose, LDL and angiotensin II, the molecules frequently elevated in patients with diabetic nephropathy, on aldosterone production in human primary mesangial cells. These cells expressed the CYP11B2 mRNA, a rate-limiting enzyme in the aldosterone biosynthesis. LDL and angiotensin II stimulated CYP11B2 mRNA expression in these cells, while a high concentration of glucose, angiotensin II and/or LDL increased aldosterone production. Importantly, atorvastatin (CAS 134523-03-8), an HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) reductase inhibitor, strongly suppressed their effects on aldosterone production. Atorvastatin also suppressed positive effects of these compounds on the mRNA expression of the angiotensin II receptor type 1, thus atorvastatin exerted its negative effect in part through changing expression of this receptor. Since elevated levels of glucose and LDL, and increased action of the renin-angiotensin-aldosterone system is known to participate in the progression of diabetic nephropathy, it is speculated that the mesangial endocrine system that produces aldosterone locally is a promising therapeutic target for diabetic nephropathy where HMG-CoA reductase inhibitors provide a beneficial effect.

[A case of aldosterone-producing adenoma associated with end-stage renal disease]

A 53-year-old female had a history of long-term hemodialysis. Periodic follow-up abdominal ultrasonography revealed a tumor measuring 4 cm in diameter in an area adjacent to the upper pole of the right kidney. Abdominal computed tomography and magnetic resonance imaging confirmed a right adrenal tumor. Furthermore, adrenal scintigraphy after dexamethasone inhibition showed accumulation in the right adrenal gland. An endocrinological test revealed that the plasma renin activity (PRA) was normal, and that the plasma aldosterone (PAC) level was increased to 1,021.8 ng/dl. The PAC-to-PRA ratio (ARR) was 5,109. Under a diagnosis of aldosterone-producing adrenal tumor, laparoscopic right adrenalectomy was performed. After surgery, the PAC level was normalized. Pathological findings showed adrenal cortical adenoma. Primary aldosteronism causes hypertension, hypopotassiumemia, hyporeninemia, and hyperaldosteronemia via excessive secretion of aldosterone in the adrenal glands. However, the patient showed a high serum level of potassium due to anuria, and hypertension was not noted. Thus, some dialysis patients with primary aldosteronism do not show any typical clinical symptoms. A previous study also indicated the presence of hyperaldosteronemia in patients with end-stage renal disease. A diagnosis should be carefully made.

Selective aldosterone synthase inhibitors reduce aldosterone formation in vitro and in vivo

Aldosterone plays a crucial role in salt and water homeostasis but in case of pathologically increased plasma aldosterone levels it is also involved in the development and the progression of severe cardiovascular diseases like heart failure and myocardial fibrosis. For the treatment of these diseases we propose inhibition of the aldosterone forming enzyme CYP11B2 as a new pharmacological strategy. We recently developed in vitro highly potent and selective inhibitors of human CYP11B2, but the evidence of their in vivo activity is still missing. For this purpose, rat aldosterone synthase gene was cloned and expressed in V79MZ cells to establish a new screening assay for the identification of "rat-active" substances. Compound 7 from the class of heteroaryl substituted 3,4-dihydro-1H-quinolin-2-ones showed a moderate inhibitory effect (65% at 2 microM) on rat CYP11B2 in vitro. Furthermore, it diminished the conversion of deoxycorticosterone to aldosterone in rat adrenals and significantly reduced plasma aldosterone levels in vivo.

Regulation of aldosterone and cortisol production by the transcriptional repressor neuron restrictive silencer factor

Aldosterone synthase (CYP11B2) and 11 beta-hydroxylase (CYP11B1) regulate aldosterone and cortisol production, respectively. The expression of these enzymes is promoted by calcium influx through Cav3.2, a T-type calcium channel. Neuron-restrictive silencer factor (NRSF) binds to neuron-restrictive silencer element (NRSE) to suppress the transcription of NRSE-containing genes. We found a NRSE-like sequence in human CYP11B2 and CYP11B1 genes as well as the CACNA1H gene of many mammalian species. The CACNA1H gene encodes the alpha-subunit of Cav3.2. Here we investigated how NRSF/NRSE regulates aldosterone and cortisol synthesis. Inhibition of endogenous NRSF by an adenovirus-expressing dominant-negative NRSF (AD/dnNRSF) increased human CYP11B2 and CYP11B1 mRNA expression, leading to aldosterone and cortisol secretion in human adrenocortical (H295R) cells. In reporter gene experiments, NRSE suppressed luciferase reporters driven by CYP11B2 and CYP11B1 promoters and dnNRSF enhanced them. Moreover, cotransfection of dnNRSF increased luciferase activity of reporter genes after deletion or mutation of NRSE, suggesting that NRSF/NRSE regulates transcription of CYP11B2 and CYP11B1 genes indirectly. AD/dnNRSF augmented mRNA expression of rat CYP11B2 and CYP11B1 genes, neither of which contains a NRSE-like sequence in rat adrenal cells. AD/dnNRSE also significantly increased CACNA1H mRNA in H295R and rat adrenal cells. Efonidipine, a T/L-type calcium channel blocker, significantly suppressed dnNRSF-mediated up-regulation of CYP11B2 and CYP11B1 expression. Moreover, NRSF/NRSE is also involved in angiotensin II- and K(+)-stimulated augmentation of CYP11B2 and CYP11B1 gene transcription. In conclusion, NRSF/NRSE controls aldosterone and cortisol synthesis by regulating CYP11B2 and CYP11B1 gene transcription mainly through NRSF/NRSE-mediated enhancement of the CACNA1H gene.

Role of angiotensin II-induced rapid response genes in the regulation of enzymes needed for aldosterone synthesis

Aldosterone is principally synthesized in the zona glomerulosa of the adrenal by a series of enzymatic reactions leading to the conversion of cholesterol to aldosterone. Angiotensin II (Ang II) is the major physiological regulator of aldosterone production acting acutely to stimulate aldosterone biosynthesis and chronically to increase the capacity of the adrenals to produce aldosterone. We previously defined eight transcription factors that are rapidly induced following Ang II treatment using three in vitro adrenocortical cell models. Herein, we investigated the function of these transcription factors in the regulation of the enzymes needed for aldosterone production. H295R adrenal cells were co-transfected with expression vectors for each transcription factor and promoter/reporter constructs prepared for genes encoding the enzymes needed for aldosterone production. NGFI-B family members induced promoter activity of 3-beta-hydroxysteroid-dehydrogenase type 2 (HSD3B2), 21-hydroxylase (CYP21A2), and aldosterone synthase (CYP11B2). The importance of NGFI-B in the regulation of CYP11B2 was also demonstrated by reduced CYP11B2 transcription in the presence of a dominant-negative-NGFI-B. A pharmacological approach was used to characterize the Ang II pathways regulating transcription of NGFI-B family genes. Transcription of NGFI-B members were decreased following inhibition of Ang II type 1 receptor (AT1R), protein kinase C (PKC), calcium/calmodulin-dependent kinases (CaMK), and Src tyrosine kinase (SRC). Taken together, these results suggest that Ang II binding to the AT1R increases activity of PKC, CaMK, and SRC, which act to increase expression of the family of NGFI-B genes as well as CYP11B2. Ang II induction of the NGFI-B family members represents an important pathway to increase the capacity of adrenal cells to produce aldosterone.

Protein kinase A activity controls the regulation of T-type CaV3.2 channels by Gbetagamma dimers

Low voltage-activated (LVA), T-type, calcium channels mediate diverse biological functions and are inhibited by Gbetagamma dimers, yet the molecular events required for channel inhibition remain unknown. Here, we identify protein kinase A (PKA) as a molecular switch that allows Gbeta(2)gammax dimers to effect voltage-independent inhibition of Ca(v)3.2 channels. Inhibition requires phosphorylation of Ser(1107), a critical serine residue on the II-III loop of the channel pore protein. S1107A prevents inhibition of unitary currents by recombinant Gbeta(2)gamma(2) dimers but does not disrupt dimer binding nor change its specificity. Gbetagamma dimers released upon receptor activation also require PKA activity for their inhibitory actions. Hence, dopamine inhibition of Ca(v)3.2 whole cell current is precluded by Gbetagamma-scavenger proteins or a peptide that blocks PKA catalytic activity. Fittingly, when used alone at receptor-selective concentrations, D(1) or D(2) agonists do not elicit channel inhibition yet together synergize to inhibit Ca(v)3.2 channel currents. We propose that a dual-receptor regulatory mechanism is used by dopamine to control Ca(v)3.2 channel activity. This mechanism, for example, would be important in aldosterone producing adrenal glomerulosa cells where channel dysregulation would lead to overproduction of aldosterone and consequent cardiac, renal, and brain target organ damage.

Altered corticosteroid biosynthesis in essential hypertension: A digenic phenomenon

Aldosterone plays an important role in electrolyte and blood pressure homeostasis. Our studies have focused on the role of aldosterone in essential hypertension. We have shown that plasma aldosterone and ARR are heritable characteristics and that aldosterone concentrations in older subjects are inversely correlated with birthweight and positively correlated with blood pressure. Aldosterone levels are also associated with polymorphic variation in the CYP11B2 gene, which encodes aldosterone synthase, the enzyme responsible for aldosterone production. Interestingly, CYP11B2 polymorphisms are also associated with less efficient activity of 11beta-hydroxylase, encoded by the neighbouring, highly homologous CYP11B1 gene. We propose that a digenic effect leads to increased aldosterone production, with inefficient 11beta-hydroxylation causing a long-term increase in ACTH drive to the adrenal gland and enhanced expression of CYP11B2, thereby resulting in chronically raised aldosterone secretion in response to factors such as angiotensin II and potassium. In susceptible subjects this is likely, over many years, to result in hypertension with relative aldosterone excess.