Aldosterone deficiency in mice burdens respiration and accentuates diet-induced hyperinsulinemia and obesity.

Aldosterone synthase inhibitors (ASIs) should alleviate obesity-related cardiovascular and renal problems resulting partly from aldosterone excess, but their clinical use may have limitations. To improve knowledge for the use of ASIs, we investigated physiology in aldosterone synthase-knockout (ASKO) mice. On regular chow diet (CD), ASKO mice ate more and weighed less than WT mice, largely because they hyperventilated to eliminate acid as CO2. Replacing CD with high-fat diet (HFD) lessened the respiratory burden in ASKO mice, as did 12- to 15-hour fasting. The latter eliminated the genotype differences in respiratory workload and energy expenditure (EE). Thus, aldosterone deficiency burdened the organism more when the animals ate carbohydrate-rich chow than when they ate a HFD. Chronic HFD exposure further promoted hyperinsulinemia in ASKO mice that contributed to visceral fat accumulation accompanied by reduced lipolysis, thermogenic reprogramming, and the absence of weight-gain-related EE increases. Intracerebroventricular aldosterone supplementation in ASKO mice attenuated the HFD-induced hyperinsulinemia, but did not affect EE, suggesting that the presence of aldosterone increased the body's energetic efficiency, thus counteracting the EE-increasing effect of low insulin. ASIs may therefore cause acid-overload-induced respiratory burden and promote obesity. Their use in patients with preexisting renal and cardiopulmonary diseases might be contraindicated.

Involvement of renin-angiotensin-aldosterone system in calcium oxalate crystal induced activation of NADPH oxidase and renal cell injury.

INTRODUCTION AND OBJECTIVES: Reactive oxygen species (ROS) are produced during the interaction between oxalate/calcium oxalate monohydrate (COM) crystals and renal epithelial cells and are responsible for the various cellular responses through the activation of NADPH oxidase (Nox). Ox and COM also activate the renin-angiotensin-aldosterone system (RAAS). Aldosterone stimulates ROS production through activation of Nox with the involvement of mineralocorticoid receptor (MR), Rac1 and mitogen-activated protein kinases (MAPK). We investigated RAAS pathways in vivo in an animal model of hyperoxaluria and in vitro by exposing renal epithelial cells to COM crystals. METHODS: Hyperoxaluria was induced in male SD rats by administering ethylene glycol. One group of rats was additionally given spironolactone. Total RNA was extracted and subjected to genomic microarrays to obtain global transcriptome data. Normal rat kidney cell line (NRK-52E) was incubated with aldosterone(10(-7) M) and COM(67 µg/cm(2)) with or without spironolactone(10(-5) M), a selective inhibitor of SRC family of kinases; protein phosphatase 2(pp2) (10(-5) M) and Nox inhibitor; diphenylene iodonium (DPI) (10(-5) M). RESULTS: Relative expression of genes encoding for AGT, angiotensin receptors 1b and 2, Renin 1, Cyp11b, HSD11B2, Nr3c2, NOx4 and Rac1 was upregulated in the kidneys of rats with hyperoxaluria. Treatment with spironolactone reversed the effect of hyperoxaluria. Both aldosterone and COM crystals activated Nox and Rac1 expression in NRK52E, while spironolactone inhibited Nox and Rac1 expression. Increased Rac1 expression was significantly attenuated by treatment with PP2 and spironolactone. CONCLUSIONS: Results indicate that hyperoxaluria-induced production of ROS, injury and inflammation are in part associated with the activation of Nox through renin-angiotensin-aldosterone pathway.

Adrenal and Ovarian Phenotype of a Tissue-Specific Urocortin 2-Overexpressing Mouse Model.

Urocortin 2 (UCN2) is a neuropeptide of the CRH family, involved in homeostatic mechanisms, the stress response, and control of anxiety. To elucidate the effects of UCN2 on steroidogenesis, we developed a mouse model that allows a Cre recombinase-determined conditional overexpression of UCN2 (UCN2-COE). In these mice SF1-Cre-driven overexpression of UCN2 was restricted to the adrenal glands, gonads, and parts of the hypothalamus. UCN2-COE animals of both sexes revealed significantly higher plasma UCN2 levels and significantly higher UCN2 expression levels in the adrenals and ovaries. In contrast, the baseline expression of UCN2 was already high in the testes of control mice with no further increase achievable in UCN2-COE animals. Adrenal steroidogenesis of UCN2-COE animals was investigated under baseline conditions, upon an ACTH stimulation test, and following a restraint stress test. A tendency toward lower expression of steroidogenic enzymes was detectable in UCN2-COE animals of both sexes with slight differences between males and females. A similar reduction in the expression levels of the final steps of ovarian steroidogenesis, accompanied by reduced plasma estradiol levels, was observed in female UCN2-COE animals. Thus, adrenal UCN2 overexpression resulted in down-regulation of adrenal steroidogenesis, suggesting a reduction in the stress response in the mouse (stress coping behavior). Similarly, UCN2 overexpression in the ovaries caused a decrease in steroidogenesis and reduction of follicles that had undergone ovulation. Nevertheless, this finding was not associated with reduced fertility.

Role of Ca(2+)/calmodulin-dependent protein kinase kinase in adrenal aldosterone production.

There is considerable evidence supporting the role of calcium signaling in adrenal regulation of both aldosterone synthase (CYP11B2) and aldosterone production. However, there have been no studies that investigated the role played by the Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK) in adrenal cells. In this study we investigated the role of CaMKK in adrenal cell aldosterone production. To determine the role of CaMKK, we used a selective CaMKK inhibitor (STO-609) in the HAC15 human adrenal cell line. Cells were treated with angiotensin II (Ang II) or K+ and evaluated for the expression of steroidogenic acute regulatory protein and CYP11B2 (mRNA/protein) as well as aldosterone production. We also transduced HAC15 cells with lentiviral short hairpin RNAs of CaMKK1 and CaMKK2 to determine which CaMKK plays a more important role in adrenal cell regulation of the calcium signaling cascade. The CaMKK inhibitor, STO-609, decreased aldosterone production in cells treated with Ang II or K+ in a dose-dependent manner. STO-609 (20 µM) also inhibited steroidogenic acute regulatory protein and CYP11B2 mRNA/protein induction. CaMKK2 knockdown cells showed significant reduction of CYP11B2 mRNA induction and aldosterone production in cells treated with Ang II, although there was no obvious effect in CaMKK1 knockdown cells. In immunohistochemical analysis, CaMKK2 protein was highly expressed in human adrenal zona glomerulosa with lower expression in the zona fasciculata. In conclusion, the present study suggests that CaMKK2 plays a pivotal role in the calcium signaling cascade regulating adrenal aldosterone 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.

Azelnidipine inhibits aldosterone synthesis and secretion in human adrenocortical cell line NCI-H295R.

Blockade of a mineralocorticoid receptor is a clinically useful approach to the prevention of cardiovascular disease. The present study was designed to evaluate the effect of azelnidipine, a unique dihydropyridine Ca(2+) channel blocker, on aldosterone production in the human adrenocortical cell line NCI-H295R. Azelnidipine inhibited angiotensin II- and KCl-induced expression of steroid 11beta-hydroxylase, steroid 18-hydroxylase, and the alpha1H subunit of the T-type Ca(2+) channel, and suppressed steroid biosynthesis in H295R cells by the same amount as efonidipine. On the basis of these findings, azelnidipine appears to suppress steroid biosynthesis in H295R cells beyond the blockade of L-type calcium channels.

Modulation of steroidogenic gene expression and hormone production of H295R cells by pharmaceuticals and other environmentally active compounds.

The H295R cell bioassay was used to evaluate the potential endocrine disrupting effects of 18 of the most commonly used pharmaceuticals in the United States. Exposures for 48 h with single pharmaceuticals and binary mixtures were conducted; the expression of five steroidogenic genes, 3betaHSD2, CYP11beta1, CYP11beta2, CYP17 and CYP19, was quantified by Q-RT-PCR. Production of the steroid hormones estradiol (E2), testosterone (T) and progesterone (P) was also evaluated. Antibiotics were shown to modulate gene expression and hormone production. Amoxicillin up-regulated the expression of CYP11beta2 and CYP19 by more than 2-fold and induced estradiol production up to almost 3-fold. Erythromycin significantly increased CYP11beta2 expression and the production of P and E2 by 3.5- and 2.4-fold, respectively, while production of T was significantly decreased. The beta-blocker salbutamol caused the greatest induction of CYP17, more than 13-fold, and significantly decreased E2 production. The binary mixture of cyproterone and salbutamol significantly down-regulated expression of CYP19, while a mixture of ethynylestradiol and trenbolone, increased E2 production 3.7-fold. Estradiol production was significantly affected by changes in concentrations of trenbolone, cyproterone, and ethynylestradiol. Exposures with individual pharmaceuticals showed the possible secondary effects that drugs may exert on steroid production. Results from binary mixture exposures suggested the possible type of interactions that may occur between drugs and the joint effects product of such interactions. Dose-response results indicated that although two chemicals may share a common mechanism of action the concentration effects observed may be significantly different.

Can the dextroenantiomer of the aromatase inhibitor fadrozole be useful for clinical investigation of aldosterone-synthase inhibition?

The beneficial effects of spironolactone, eplerenone, amiloride and potassium in preventing cardiovascular damage in various experimental models of salt-induced hypertension can be dissociated from blood pressure effects, and have drawn attention to the direct genomic and non-genomic actions of aldosterone at the level of the vessels, the heart and the kidneys. Exposure to endogenous aldosterone could be decreased by direct and specific aldosterone-synthase inhibition. FAD 286A, the dextroenantiomer of the aromatase inhibitor fadrozole, might be a first candidate to investigate in humans, the physiological impact and therapeutic properties of aldosterone-synthase inhibition, especially in various forms of primary aldosteronism.

The orphan nuclear receptors NURR1 and NGFIB regulate adrenal aldosterone production.

Aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex is regulated by transcription of CYP11B2 (encoding aldosterone synthase). The effects of nerve growth factor-induced clone B (NGFIB) (NR4A1), Nur-related factor 1 (NURR1) (NR4A2), and steroidogenic factor-1 (SF-1) (NR5A1) on transcription of human CYP11B2 (hCYP11B2) and hCYP11B1 (11 beta-hydroxylase) were compared in human H295R adrenocortical cells. hCYP11B2 expression was increased by NGFIB and NURR1. Although hCYP11B1 was activated by SF-1, cotransfection with SF-1 inhibited activation of hCYP11B2 by NGFIB and NURR1. NGFIB and NURR1 transcript and protein levels were strongly induced by angiotensin (Ang) II, the major regulator of hCYP11B2 expression in vivo. Sequential deletion and mutagenesis of the hCYP11B2 promoter identified two functional NGFIB response elements (NBREs), one located at -766/-759 (NBRE-1) and the previously studied Ad5 element at -129/-114. EMSAs suggested that both elements bound NGFIB and NURR1. In human adrenals, NURR1 immunoreactivity was preferentially localized in the zona glomerulosa and to a lesser degree in the zona fasciculata, whereas NGFIB was detected in both zones. The calmodulin kinase inhibitor KN93 partially blocked K(+)-stimulated transcription of NGFIB and NURR1. KN93 partially inhibited the effect of Ang II on NURR1 mRNA levels but did not modify the effect on expression of NGFIB. Mutation of the NBRE-1, Ad5, and Ad1/cAMP response element (CRE) cis-elements reduced both basal and Ang II-induced levels of hCYP11B2, demonstrating that all three elements are important for maximal transcriptional activity. Our results suggest that NGFIB and NURR1 are key regulators of hCYP11B2 expression and may partially mediate the regulation of hCYP11B2 by Ang II.

-344C/T polymorphism of CYP11B2 gene in Italian patients with idiopathic low renin hypertension.

Most patients with low renin essential hypertension are not qualitatively different from patients with idiopathic hyperaldosteronism, as in both conditions aldosterone secretion is not appropriately reduced. The aim of the study was to investigate allele and genotype frequencies of the -344C/T polymorphism, located in the promoter region of the aldosterone synthase gene, in 83 patients with idiopathic low renin hypertension characterized by an increased aldosterone to renin ratio, including both patients with low renin essential hypertension (n=53) and subjects with idiopathic hyperaldosteronism (n=30), compared with 78 patients with normal to high renin essential hypertension and 126 normotensive control subjects. The relationship of -344C/T genotypes to basal and postcaptopril plasma aldosterone/plasma renin activity ratio was also examined in the entire hypertensive population. An increased frequency of the T allele and a relative excess of TT homozygosity over CC homozygosity were found in patients with idiopathic low renin hypertension in comparison with both normal to high renin hypertensives and normotensive controls. A higher post-captopril aldosterone to renin ratio was found in the hypertensives with TT genotype than in those with CC genotype, and TT+TC genotypes were associated with a smaller decrease in the aldosterone-to-renin ratio elicited by captopril administration. The present study suggests that the -344C/T polymorphism, or a functional variant in linkage disequilibrium with it, may play a role in the abnormal regulation of aldosterone secretion in idiopathic low renin hypertension.

Mechanism for the stabilization in vivo of the aziridine precursor --(4-acetoxyphenyl)-2-chloro-N-methyl-ethylammonium chloride by serum proteins.

Oral and intraperitoneal administration of 2-(4-acetoxyphenyl)-2-chloro-N-methyl-ethylammonium chloride (Compound A), an analogue of phenyl aziridine precursors that occur in the shrub Salsola tuberculatiformis Botsch, had a contraceptive effect on female Wistar rats with a concomitant decrease in total body, uterus, and every mass and an increase in abronal mass. Compound A elicited a Type II difference spectrum and inhibited the Type I deoxycorticosterone (DOC) induced difference spectrum of sheep adrenal cytochrome P450c11 in a manner similar to that of S2, a biologically active fraction isolated from S. tuberculatiformis. The effects of Compound A on the spectral properties of P450c11 were diminished with time in PBS. Electrospray mass spectrometry (ES-MS) indicated that the rate of cyclization of Compound A to the corresponding aziridine followed a time course similar to the attenuation of cytochrome P450c11 inhibition. It was concluded that the aziridine precursor. Compound A, rather than aziridine itself, was the inhibiting agent of sheep adrenal P450c11. Addition of sheep and rat plasma prevented the attenuation of the effect of Compound A on the spectral properties of cytochrome P450c11. Subsequent ES-MS analysis indicated that Compound A was stabilized in plasma by sex hormone binding globulin and corticosteroid binding globulin. These results suggest a mechanism whereby natural plant products, which are highly reactive and unstable in vitro, can be stabilized by binding to plasma proteins, and so remain biologically active in vivo.

Expression of aldosterone synthase cytochrome P450 (P450aldo) mRNA in rat adrenal glomerulosa cells by angiotensin II type 1 receptor.

Changes in the mRNA levels for aldosterone synthase cytochrome P450 (P450aldo or CYP11B2) in rat adrenal glands were studied in response to angiotensin II type 1 (AT1) and type 2 (AT2) receptor antagonists. Since 11 beta hydroxylase P450 (P45011 beta or CYP11B1), which shows high homology (88.5%) with P450aldo in their nucleotide sequences of the amino acid coding regions, is also expressed in the adrenal gland, RT-PCR was performed with specific primers for each P450. Upon sodium restriction (5 mmol Na+/kg of diet) of the rats for 14 days, the amount of the P450aldo mRNA in the adrenal glands increased 8.5 fold above from the rats fed on a normal diet (225 mmol Na+/kg of diet), whereas no significant change of the P45011 beta mRNA was observed after the dietary sodium restriction. As shown by an immunoblot analysis, the adrenal capsule portions (mainly zona glomerulosa) of the rats kept on the low Na diet for 14 days expressed significantly higher level of P450aldo than those from the rats fed the normal diet. In concert with the alteration, plasma aldosterone concentration increased. However, when a specific AT1 antagonist E4177 was given to the rats kept on a low Na diet, the amount and activity of P450aldo as well as the plasma aldosterone concentration was suppressed. On the other hand, the increase of P450aldo induced by the low Na diet was not affected by an AT2-specific antagonist, PD123177.