Intralymphocyte free magnesium in patients with primary aldosteronism: aldosterone and lymphocyte magnesium homeostasis

TRPM7 deficiency exacerbates cardiovascular and renal damage induced by aldosterone-salt

Hyperaldosteronism causes cardiovascular disease as well as hypomagnesemia. Mechanisms are ill-defined but dysregulation of TRPM7, a Mg²⁺-permeable channel/α-kinase, may be important. We examined the role of TRPM7 in aldosterone-dependent cardiovascular and renal injury by studying aldosterone-salt treated TRPM7-deficient (TRPM7^+/Δkinase) mice. Plasma/tissue [Mg²⁺] and TRPM7 phosphorylation were reduced in vehicle-treated TRPM7^+/Δkinase mice, effects recapitulated in aldosterone-salt-treated wild-type mice. Aldosterone-salt treatment exaggerated vascular dysfunction and amplified cardiovascular and renal fibrosis, with associated increased blood pressure in TRPM7^+/Δkinase mice. Tissue expression of Mg²⁺-regulated phosphatases (PPM1A, PTEN) was downregulated and phosphorylation of Smad3, ERK1/2, and Stat1 was upregulated in aldosterone-salt TRPM7-deficient mice. Aldosterone-induced phosphorylation of pro-fibrotic signaling was increased in TRPM7^+/Δkinase fibroblasts, effects ameliorated by Mg²⁺ supplementation. TRPM7 deficiency amplifies aldosterone-salt-induced cardiovascular remodeling and damage. We identify TRPM7 downregulation and associated hypomagnesemia as putative molecular mechanisms underlying deleterious cardiovascular and renal effects of hyperaldosteronism.

Deficiency of the Mg2+-permeable channel/α-kinase TRPM7 in mice increases susceptibility to cardiovascular and renal fibrosis induced by aldosterone and salt.

Physiological magnesium concentrations increase fidelity of diverse reverse transcriptases from HIV-1, HIV-2, and foamy virus, but not MuLV or AMV

Reverse transcriptases (RTs) are typically assayed using optimized Mg²⁺ concentrations (~5-10 mM) several-fold higher than physiological cellular free Mg²⁺ (~0.5 mM). Recent analyses demonstrated that HIV-1, but not Moloney murine leukaemia (MuLV) or avain myeloblastosis (AMV) virus RTs has higher fidelity in low Mg²⁺. In the current report, lacZα-based α-complementation assays were used to measure the fidelity of several RTs including HIV-1 (subtype B and A/E), several drug-resistant HIV-1 derivatives, HIV-2, and prototype foamy virus (PFV), all which showed higher fidelity using physiological Mg²⁺, while MuLV and AMV RTs demonstrated equivalent fidelity in low and high Mg²⁺. In 0.5 mM Mg²⁺, all RTs demonstrated approximately equal fidelity, except for PFV which showed higher fidelity. A Next Generation Sequencing (NGS) approach that used barcoding to determine mutation profiles was used to examine the types of mutations made by HIV-1 RT (type B) in low (0.5 mM) and high (6 mM) Mg²⁺ on a lacZα template. Unlike α-complementation assays which are dependent on LacZα activity, the NGS assay scores mutations at all positions and of every type. Consistent with α-complementation assays, a ~four-fold increase in mutations was observed in high Mg²⁺. These findings help explain why HIV-1 RT displays lower fidelity in vitro (with high Mg²⁺ concentrations) than other RTs (e.g. MuLV and AMV), yet cellular fidelity for these viruses is comparable. Establishing in vitro conditions that accurately represent RT's activity in cells is pivotal to determining the contribution of RT and other factors to the mutation profile observed with HIV-1.

Does fludrocortisone treatment cause hypomagnesemia in children with primary adrenal insufficiency?

Background/aim

Aldosterone is a mineralocorticoid that secreted from adrenal glands and a known factor to increase magnesium excretion by direct and indirect effects on renal tubular cells. Although the frequency of hypomagnesemia was found to be approximately 5% in adult studies, there is no study in the literature investigating the frequency of hypomagnesemia in children by using fludrocortisone, which has a mineralocorticoid activity.

Materials and methods

A multi-center retrospective study was conducted, including children who were under fludrocortisone treatment for primary adrenal insufficiency and applied to participant pediatric endocrinology outpatient clinics.

Results

Forty-three patients (58.1% male, 41.9% prepubertal) included in the study, whose median age was 9.18 (0.61-19) years, and the most common diagnosis among the patients was a salt-wasting form of congenital adrenal hyperplasia (67.4%). Mean serum magnesium level was 2.05 (±0.13) mg/dL, and hypomagnesemia was not observed in any of the patients treated with fludrocortisone. None of the patients had increased urinary excretion of magnesium.

Conclusion

Unlike the studies performed in adults, we could not find any evidence of magnesium wasting effect of fludrocortisone treatment with normal or even high doses in children and adolescents.

Uncommon presentation of primary hyperaldosteronism with severe hypomagnesemia: a Gitelman syndrome mimic

Primary hyperaldosteronism (PA) usually presents with moderate to severe hypertension with or without hypokalemia in adults. However, PA is not commonly associated with severe hypomagnesemia. By contrast, Gitelman syndrome usually presents with clinical manifestations of hypokalemia and hypocalcemia due to hypomagnesemia. Here, we present the case of a 44-year-old woman who first presented with peripheral paresthesia. Her laboratory tests revealed severe hypokalemia, metabolic alkalosis, severe hypomagnesemia, hypocalcemia and secondary hyperparathyroidism. The patient took high dose KCL tablets and Mg tablets to maintain normal values. She took only low-dose hydralazine to maintain normal blood pressure. Further investigations revealed PA with a left adrenal tumor. After left adrenalectomy, she remained in a normotensive, normokalemic and normomagnesemic state without any medical supplements. Thus, PA should be considered in patients with severe hypomagnesemia without moderate to severe hypertension.

Non-nucleoside Reverse Transcriptase Inhibitors Inhibit Reverse Transcriptase through a Mutually Exclusive Interaction with Divalent Cation-dNTP Complexes

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are considered noncompetitive inhibitors that structurally alter reverse transcriptase (RT) and dramatically decrease catalysis. In this report, biochemical analysis with various divalent cations was used to demonstrate that NNRTIs and divalent cation-dNTP complexes are mutually exclusive, inhibiting each other's binding to RT/primer/template (RT-P/T) complexes. The binding of catalytically competent divalent cation-dNTP complexes to RT-P/T was measured with Mg²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺ using Ca²⁺, a noncatalytic cation, for displacement. Binding strength order was Mn²⁺ ≈ Zn²⁺ ≫ Co²⁺ > Mg²⁺ ≈ Ni²⁺. Consistent with but not exclusive to mutually exclusive binding, primer extension assays showed that stronger divalent cation-dNTP complexes were more resistant to NNRTIs (efavirenz (EFV), rilpivirine (RPV), and nevirapine (NVP)). Filtration assays demonstrated that divalent cation-dNTP complexes inhibited the binding of ¹⁴C-labeled EFV to RT-P/T with stronger binding complexes formed with Mn²⁺ inhibiting more potently than those with Mg²⁺. Conversely, filter binding assays demonstrated that EFV inhibited ³H-labeled dNTP binding to RT-P/T complexes with displacement of Mn²⁺-dNTP complexes requiring much greater concentrations of EFV than the more weakly bound Mg²⁺-dNTP complexes. EFV bound relatively weakly to the NNRTI resistant K103N RT; but, binding was modestly enhanced in the presence of P/T, and EFV was easily displaced by divalent cation-dNTP complexes. This suggests that K103N overcomes EFV inhibition mostly by binding more weakly to the drug and is in contrast to other reports that indicate K103N has little to no effect on drug or dNTP binding. Overall, this biochemical analysis supports recent biophysical analyses of NNRTI-RT interactions that indicate mutually exclusive binding.

Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis

Because serum magnesium does not reflect intracellular magnesium, the latter making up more than 99% of total body magnesium, most cases of magnesium deficiency are undiagnosed. Furthermore, because of chronic diseases, medications, decreases in food crop magnesium contents, and the availability of refined and processed foods, the vast majority of people in modern societies are at risk for magnesium deficiency. Certain individuals will need to supplement with magnesium in order to prevent suboptimal magnesium deficiency, especially if trying to obtain an optimal magnesium status to prevent chronic disease. Subclinical magnesium deficiency increases the risk of numerous types of cardiovascular disease, costs nations around the world an incalculable amount of healthcare costs and suffering, and should be considered a public health crisis. That an easy, cost-effective strategy exists to prevent and treat subclinical magnesium deficiency should provide an urgent call to action.

Toward a broader understanding of aldosterone in congestive heart failure

Discovered some 50 years ago, aldosterone (ALDO) has come to be recognised as a mineralocorticoid hormone with well-known endocrine properties in epithelial cells that contribute to the pathophysiology of congestive heart failure. This includes Na + resorption at the expense of K+ excretion in classic target tissues: kidneys, colon, sweat and salivary glands. Though less well known, Mg2+ excretion is likewise enhanced by ALDO, while adrenal ALDO secretion is regulated by extracellular Mg2+ ([Mg2+ ]o). An emerging body of information has and continues to identify other endocrine actions of ALDO receptor-ligand binding. They include: promoting an efflux of cytosolic free Mg2+, or [Mg2+]i, in exchange for Na+ in such non-epithelial cells as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions that involve regulation of cerebrospinal fluid composition produced by epithelial cells of the choroid plexus, activity of the hypothalamic paraventricular nucleus involved in Na+ appetite, Na+ and H2O excretion and sympathetic nerve activity, and the regulation of TNF-α production from central and/or peripheral sources. Extra-adrenal steroidogenesi and auto/paracrine properties of ALDO generated de novo in the cardiovasculature are now under investigation and preliminary findings suggest they contribute to tissue repair. The past decade has witnessed a revival of interest in this steroid molecule. In years to come, an even broader understanding of ALDO's contribution to the pathophysiology of congestive heart failure will undoubtedly emerge.

Magnesium in disease

Although the following text will focus on magnesium in disease, its role in healthy subjects during physical exercise when used as a supplement to enhance performance is also noteworthy. Low serum magnesium levels are associated with metabolic syndrome, Type 2 diabetes mellitus (T2DM) and hypertension; consequently, some individuals benefit from magnesium supplementation: increasing magnesium consumption appears to prevent high blood pressure, and higher serum magnesium levels are associated with a lower risk of developing a metabolic syndrome. There are, however, conflicting study results regarding magnesium administration with myocardial infarction with and without reperfusion therapy. There was a long controversy as to whether or not magnesium should be given as a first-line medication. As the most recent trials have not shown any difference in outcome, intravenous magnesium cannot be recommended in patients with myocardial infarction today. However, magnesium has its indication in patients with torsade de pointes and has been given successfully to patients with digoxin-induced arrhythmia or life-threatening ventricular arrhythmias. Magnesium sulphate as an intravenous infusion also has an important established therapeutic role in pregnant women with pre-eclampsia as it decreases the risk of eclamptic seizures by half compared with placebo.

Thrombotic microangiopathy: a role for magnesium?

Despite advances in more recent years, the pathophysiology and especially treatment modalities of thrombotic microangiopathy (TMA) largely remain enigmatic. Disruption of endothelial homeostasis plays an essential role in TMA. Considering the proven causal association between magnesium and both endothelial function and platelet aggregability, we speculate that a magnesium deficit could influence the course of TMA and the related haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura. A predisposition towards TMA is seen in many conditions with both extracellular and intracellular magnesium deficiency. We propose a rationale for magnesium supplementation in TMA, in analogy with its evidence-based therapeutic application in pre-eclampsia and suggest, based on theoretical grounds, that it might attenuate the development of TMA, minimise its severity and prevent its recurrence. This is based on several lines of evidence from both in vitro and in vivo data showing dose-dependent effects of magnesium supplementation on nitric oxide production, platelet aggregability and inflammation. Our hypothesis, which is further amenable to assessment in animal models before therapeutic applications in humans are implemented, could be explored both in vitro and in vivo to decipher the potential role of magnesium deficit in TMA and of the effects of its supplementation.

Transient receptor potential melastatin 7 (TRPM7) cation channels, magnesium and the vascular system in hypertension

Decreased Mg(2+) concentration has been implicated in altered vascular reactivity, endothelial dysfunction and structural remodeling, processes important in vascular changes and target organ damage associated with hypertension. Unlike our knowledge of other major cations, mechanisms regulating cellular Mg(2+) handling are poorly understood. Until recently little was known about protein transporters controlling transmembrane Mg(2+) influx. However, new research has uncovered a number of genes and proteins identified as transmembrane Mg(2+) transporters, particularly transient receptor potential melastatin (TRPM) cation channels, TRPM6 and TRPM7. Whereas TRPM6 is found primarily in epithelial cells, TRPM7 is ubiquitously expressed. Vascular TRPM7 has been implicated as a signaling kinase involved in vascular smooth muscle cell growth, apoptosis, adhesion, contraction, cytoskeletal organization and migration, and is modulated by vasoactive agents, pressure, stretch and osmotic changes. Emerging evidence suggests that vascular TRPM7 function might be altered in hypertension. The present review discusses the importance of Mg(2+) in vascular biology in hypertension and focuses on transport systems, mainly TRPM7, that might play a role in the control of vascular Mg(2+) homeostasis. Elucidation of the relationship between the complex systems responsible for regulation of Mg(2+) homeostasis, the role of TRPM7 in vascular signaling, and the cardiovascular impact will be important for understanding the clinical implications of hypomagnesemia in cardiovascular disease.

Efficacy of aldosterone receptor antagonism in heart failure: potential mechanisms

Results of the Randomized Aldactone Evaluation Study and the Eplerenone Post-acute Myocardial Infarction Heart Failure Efficacy and Survival Study indicate aldosterone receptor antagonism, together with angiotensin-converting enzyme inhibition and loop diuretics, is a most effective strategy in reducing risk for all-cause and cardiovascular-related mortality and morbidity in patients with symptomatic heart failure. Responsible mechanisms are likely multifactoral. As a circulating hormone, aldosterone has well-known endocrine properties that contribute to the pathophysiology of congestive heart failure. This includes Na+ resorption at the expense of K+ excretion in such tissues as kidneys, colon, sweat, and salivary glands. Mg2+ excretion at these sites is likewise enhanced by aldosterone, whereas adrenal aldosterone secretion is regulated by extracellular Mg2+. Other endocrine actions of aldosterone receptor-ligand binding include: a reduction in biologically active cytosolic-free Mg2+, with intracellular Ca2+ loading in nonepithelial cells such as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions, including the choroid plexus, activity of the hypothalamic paraventricular nucleus, and autonomic nervous system. De novo generation of aldosterone within the cardiovasculature is recognized and findings suggest its auto/paracrine properties contribute to tissue repair. Each of these actions is interrupted by aldosterone receptor antagonism and therefore may contribute to its salutary response in heart failure.

Responses in extracellular and intracellular calcium and magnesium in aldosteronism

We hypothesized the hypercalciuria and hypermagnesuria that accompany aldosteronism could be pharmacologically attenuated to prevent shifts in extracellular and intracellular levels of these divalent cations and the adverse outcomes associated with them. Accordingly, rats administered aldosterone/salt treatment (ALDOST) were cotreated with either hydrochlorothiazide (Hctz), to selectively reabsorb urinary Ca2+, or with Hctz plus spironolactone (Hctz+Spi), where Spi retards the excretion of these cations in both urine and feces. We monitored urinary excretion and responses in extracellular and intracellular Ca2+ and Mg2+, together with indices of oxi/nitrosative stress in plasma and ventricular tissue. At 4 weeks ALDOST we found the following: (1) hypercalciuria was reduced by Hctz and normalized by Hctz+Spi, and this combination, unlike Hctz alone, also rescued hypermagnesuria; (2) the decrease in plasma-ionized [Ca2+]o was not seen with Hctz or Hctz+Spi, whereas Spi cotreatment protected against a decline in [Mg2+]o; (3) the Ca2+ loading of peripheral blood mononuclear cells and cardiac tissue was not seen with Hctz+Spi; and (4) the induction of oxi/nitrosative stress, expressed as reduced plasma alpha1-antiproteinase activity and activation of gp91(phox) subunit of NADPH oxidase in inflammatory cells invading intramural coronary arteries of the right and left ventricles, together with vascular fibrosis, was completely prevented by Spi cotreatment. In rats with aldosteronism, cotreatment with Hctz+Spi more effectively (vis-à-vis Hctz alone) protects against adverse iterations in extracellular and intracellular concentrations of Ca2+ and Mg2+, as well as the appearance of oxi/nitrosative stress to prevent the proinflammatory vascular phenotype.

Loss of bone minerals and strength in rats with aldosteronism

Congestive heart failure (CHF) is a clinical syndrome with origins rooted in a salt-avid state largely mediated by effector hormones of the circulating renin-angiotensin-aldosterone system. Other participating neurohormones include catecholamines, endothelin-1, and arginine vasopressin. CHF is accompanied by a systemic illness of uncertain causality. Features include the appearance of oxidative/nitrosative stress and a wasting of tissues including bone. Herein we hypothesized that inappropriate (relative to dietary Na+) elevations in plasma aldosterone (Aldo) contribute to an altered redox state, augmented excretion of divalent cations, and in turn, a loss of bone minerals and strength. In uninephrectomized rats that received chronic Aldo and 1% NaCl treatment for 4-6 wk, we monitored plasma alpha1-antiproteinase activity, which is an inverse correlate of oxidative/nitrosative stress; plasma concentrations of ionized Mg2+ and Ca2+; urinary Mg2+ and Ca2+ excretion; and bone mineral composition and strength to flexure stress. Compared with controls, we found reductions in plasma alpha1-antiproteinase activity and ionized Mg2+ and Ca2+ together with persistently elevated urinary Mg2+ and Ca2+ excretion, a progressive loss of bone mineral density and content with reduced Mg2+ and Ca2+ concentrations, and a reduction in cortical bone strength. Thus the hypermagnesuria and hypercalciuria that accompany chronic Aldo-1% NaCl treatment contribute to the systemic appearance of oxidative/nitrosative stress and a wasting of bone minerals and strength.

Catecholamine-induced Regulation in Vitro and ex Vivo of Intralymphocyte Ionized Magnesium

Despite the importance of the adrenergic activity and of the metabolism of magnesium in some important cardiovascular pathologies, very little is known about how intracellular ionized magnesium (Mgi2+) is regulated by catecholamines. We made an in-vitro study of the variations in the concentration of ionized magnesium in human lymphocytes using the fluorescent probe furaptra in response to different catecholamines. We also made an ex-vivo study of the changes in intracellular ionized magnesium in lymphocytes in 20 subjects with essential arterial hypertension, 10 treated with 120 mg/d of propranolol and 10 with placebo. Norepinephrine and isoproterenol significantly decrease Mgi2+ and this effect is blocked by beta-blockers but not by alpha-blockers. The EC50 of the effect of norepinephrine is within the range of concentrations physiologically present in plasma. The substitution of extracellular sodium with choline blocks the decrease in intracellular ionized magnesium induced by norepinephrine, which leads us to suppose that the magnesium-reducing effect of catecholamines is a result of the activation of a Na+-Mg2+ exchanger. We were not able to demonstrate any change in intracellular ionized magnesium after 1 and 17 days of active treatment in essential hypertensives. The impossibility of demonstrating ex vivo the mechanism of catecholamine-mediated regulation that is evident in vitro is perhaps due to our experimental conditions or to substances which in vivo inhibit the action of the catecholamines on magnesium, such as insulin and/or glucose.

Aldosteronism and peripheral blood mononuclear cell activation: a neuroendocrine-immune interface

Aldosteronism eventuates in a proinflammatory/fibrogenic vascular phenotype of the heart and systemic organs. It remains uncertain whether peripheral blood mononuclear cells (PBMCs) are activated before tissue invasion by monocytes/macrophages and lymphocytes, as is the case for responsible pathogenic mechanisms. Uninephrectomized rats treated for 4 weeks with dietary 1% NaCl and aldosterone (ALDOST, 0.75 microg/h) with or without spironolactone (Spi, 100 mg/kg per daily gavage) were compared with unoperated/untreated and uninephrectomized/salt-treated controls. Before intramural coronary vascular lesions appeared at week 4 of ALDOST, we found (1) a reduction of PBMC cytosolic free [Mg2+]i, together with intracellular Mg2+ and Ca2+ loading, whereas plasma and cardiac tissue Mg2+ were no different from controls; (2) increased H2O2 production by monocytes and lymphocytes together with upregulated PBMC gene expression of oxidative stress-inducible tyrosine phosphatase and Mn2+-superoxide dismutase and the presence of 3-nitrotyrosine in CD4+ and ED-1-positive inflammatory cells that had invaded intramural coronary arteries; (3) B-cell activation, including transcription of immunoglobulins, intracellular adhesion molecule-1, and CC and CXC chemokines and their receptors; (4) expansion of B lymphocyte subset and myosin heavy chain class II-expressing lymphocytes; and (5) autoreactivity with gene expression for antibodies to acetylcholine receptors and a downregulation of RT-6.2, which is in keeping with cell activation and associated with autoimmunity. Spi cotreatment attenuated the rise in intracellular Ca2+, the appearance of oxidative/nitrosative stress in PBMCs and invading inflammatory cells, and alterations in PBMC transcriptome. Thus, aldosteronism is associated with an activation of circulating immune cells induced by iterations in PBMC divalent cations and transduced by oxidative/nitrosative stress. ALDO receptor antagonism modulates this neuroendocrine-immune interface. The full text of this article is available online at http://www.circresaha.org.

Aldosteronism: an immunostimulatory state precedes proinflammatory/fibrogenic cardiac phenotype

Chronic inappropriate (relative to dietary Na+ intake) elevations in circulating aldosterone (ALDO), termed aldosteronism, are associated with remodeling of intramural arteries of the right and left heart. Lesions appear at week 4 of treatment with ALDO and 1% dietary NaCl in uninephrectomized rats (ALDOST) and include invading monocytes, macrophages and lymphocytes with intracellular evidence of oxidative and nitrosative stress, myofibroblasts, and perivascular fibrosis. In this study, we tested the hypothesis that an immunostimulatory state with activated circulating peripheral blood mononuclear cells (PBMCs) precedes this proinflammatory and profibrogenic cardiac phenotype and is initiated by reduction in the cytosolic free Mg2+ concentration ([Mg2+]i). At 1 and 4 wk of ALDOST (preclinical and clinical stages, respectively), we monitored serum Mg2+, PBMC [Mg2+]i and cytosolic free [Ca2+] (via fluorimetry), and expressed genes (via microchip array) as well as markers of oxidative and nitrosative stress in plasma [alpha1-antiproteinase activity (alpha1-AP)] and cardiac tissue (immunohistochemical detection of gp91phox subunit of NADPH oxidase and 3-nitrotyrosine). Age- and gender-matched unoperated and untreated (UO) rats and uninephrectomized salt-treated (UN) rats served as controls. Serum [Mg2+] was unchanged by ALDOST. In contrast with UO and UN, [Mg2+]i and plasma alpha1-AP were each reduced (P < 0.05) at weeks 1 and 4. The decline in PBMC [Mg2+]i was accompanied by Ca2+ loading. Differential (twofold and higher) expression (up- and downregulation) in PBMC transcriptomes was present at week 1 and progressed at week 4. Involved were genes for the alpha1-isoform of Na+-K+-ATPase, the ATP-dependent Ca2+ pump, antioxidant reserves, inducible nitric oxide synthase, and PBMC activation with autoimmune responses. Expression of 3-nitrotyrosine and activation of gp91phox were seen in inflammatory cells that invaded intramural arteries. Thus early in aldosteronism (preclinical stage), an immunostimulatory state featuring activated circulating PBMCs with reduced ionized [Mg2+]i and oxidative and nitrosative stress precedes and may even predispose to coronary vascular lesions that first appear at week 4.

Aldosteronism revisited: perspectives on less well-recognized actions of aldosterone

Aldosterone is a mineralocorticoid with protean actions in both epithelial and nonepithelial cells. These include endocrine properties of circulating aldosterone that promote Na(+) resorption at the expense of well-recognized K(+) excretion and less well-recognized Mg(2+) excretion in classic target tissues: kidneys, colon, and sweat and salivary glands. The regulation of adrenal aldosterone secretion by [Mg(2+)](o) is also less well appreciated. More recently recognized endocrine actions of aldosterone include induction of Mg(2+) efflux in exchange for Na(+) in such nonepithelial cells as peripheral-blood mononuclear cells and influence on epithelial cells of the choroid plexus, where aldosterone alters the composition of cerebrospinal fluid that contributes to blood-pressure regulation. An association between primary aldosteronism and idiopathic intracranial hypertension has recently been reported. Extraadrenal steroidogenesis with de novo aldosterone production by the cardiovasculature, where its auto-/paracrine properties may contribute to tissue repair at sites of injury, has been observed. These less well-recognized actions of aldosterone have led to a revival of interest in how this steroid molecule contributes to the pathophysiology of various clinical disorders.

Aldosterone-induced inflammation in the rat heart : role of oxidative stress

Heart failure and hypertension have each been linked to an induction of oxidative stress transduced by neurohormones, such as angiotensin II and catecholamines. Herein, we hypothesized that aldosterone (ALDO) likewise induces oxidative stress and accounts for a proinflammatory/fibrogenic phenotype that appears at vascular and nonvascular sites of injury found in both right and left ventricles in response to ALDO/salt treatment and that would be sustained with chronic treatment. Uninephrectomized rats received ALDO (0.75 micro g/hour) together with 1% dietary NaCl, for 3, 4, or 5 weeks. Other groups received this regimen in combination with an ALDO receptor antagonist, spironolactone (200 mg/kg p.o. daily), or an antioxidant, either pyrrolidine dithiocarbamate (PDTC) (200 mg/kg s.c. daily) or N-acetylcysteine (NAC) (200 mg/kg i.p. daily). Unoperated and untreated age- and gender-matched rats served as controls. We monitored spatial and temporal responses in molecular and cellular events using serial, coronal sections of right and left ventricles. Our studies included: assessment of systolic blood pressure; immunohistochemical detection of NADPH oxidase expression and activity; analysis of redox-sensitive nuclear factor-kappaB activation; in situ localization of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha mRNA expression; monitoring cell growth and infiltration of macrophages and T cells; and analysis of the appearance and quantity of fibrous tissue accumulation. At week 3 of ALDO/salt treatment and comparable to controls, there was no evidence of oxidative stress or pathological findings in the heart. However, at weeks 4 and 5 of treatment, increased gp91(phox) and 3-nitrotyrosine expression and persistent activation of RelA were found in endothelial cells and inflammatory cells that appeared in the perivascular space of intramural coronary arteries and at sites of lost cardiomyocytes in both ventricles. Coincident in time and space with these events was increased mRNA expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha. Macrophages, lymphocytes, and proliferating endothelial and vascular smooth muscle cells and fibroblast-like cells were seen at each of these sites, together with an accumulation of fibrillar collagen, or fibrosis, as evidenced by a significant increase in ventricular collagen volume fraction. Co-treatment with spironolactone, PDTC, or NAC attenuated these molecular and cellular responses as well as the appearance of fibrosis at vascular and nonvascular sites of injury. Furthermore, elevated systolic blood pressure in ALDO-treated rats was partially suppressed by spironolactone or either antioxidant. Thus, chronic ALDO/salt treatment is accompanied by a time-dependent sustained activation of NADPH oxidase with 3-nitrotyrosine generation and nuclear factor-kappaB activation expressed by endothelial cells and inflammatory cells. This leads to a proinflammatory/fibrogenic phenotype involving vascular and nonvascular sites of injury found, respectively, in both normotensive and hypertensive right and left ventricles. Spionolactone, PDTC, and NAC each attenuated these responses suggesting ALDO/salt induction of oxidative/nitrosative stress is responsible for the appearance of this proinflammatory phenotype.

Angiotensin II type I receptor modulates intracellular free Mg2+ in renally derived cells via Na+-dependent Ca2+-independent mechanisms

Treatment of Madin-Darby canine kidney (MDCK) cells with the peptide hormone angiotensin II (Ang II) results in an increase in the concentrations of cytosolic free calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) with a concomitant decrease in cytosolic free Mg(2+) concentration ([Mg(2+)](i)). In the present study we demonstrate that this hormone-induced decrease in [Mg(2+)](i) is independent of [Ca(2+)](i) but dependent on extracellular Na(+). [Mg(2+)](i), [Ca(2+)](i), and [Na(+)](i) were measured in Ang II-stimulated MDCK cells by fluorescence digital imaging using the selective fluoroprobes mag-fura-2AM, fura-2AM, and sodium-binding benzofuran isophthalate (acetoxymethyl ester), respectively. Ang II decreased [Mg(2+)](i) and increased [Na(+)](i) in a dose-dependent manner. These effects were inhibited by irbesartan (selective AT(1) receptor blocker) but not by PD123319 (selective AT(2) receptor blocker). Imipramine and quinidine (putative inhibitors of the Na(+)/Mg(2+) exchanger) and removal of extracellular Na(+) abrogated Ang II-mediated [Mg(2+)](i) effects. In cells pretreated with thapsigargin (reticular Ca(2+)-ATPase inhibitor), Ang II-stimulated [Ca(2+)](i) transients were attenuated (p < 0.01), whereas agonist-induced [Mg(2+)](i) responses were unchanged. Clamping the [Ca(2+)](i) near 50 nmol/liter with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) inhibited Ang II-induced [Ca(2+)](i) increases but failed to alter Ang II-induced [Mg(2+)](i) responses. Benzamil, a selective blocker of the Na(+)/Ca(2+) exchanger, inhibited [Na(+)](i) but not [Mg(2+)](i) responses. Our data demonstrate that in MDCK cells, AT(1) receptors modulate [Mg(2+)](i) via a Na(+)-dependent Mg(2+) transporter that is not directly related to [Ca(2+)](i). These data support the notion that rapid modulation of [Mg(2+)](i) is not simply a result of Mg(2+) redistribution from intracellular buffering sites by Ca(2+) and provide evidence for the existence of a Na(+)-dependent, hormonally regulated transporter for Mg(2+) in renally derived cells.

Physiological and pathophysiological role of magnesium in the cardiovascular system: implications in hypertension

Attention is growing for a potential role of magnesium in the pathoetiology of cardiovascular disease. Magnesium modulates mechanical, electrical and structural functions of cardiac and vascular cells, and small changes in extracellular magnesium levels and/or intracellular free magnesium concentration may have significant effects on cardiac excitability and on vascular tone, contractility and reactivity. Thus, magnesium may be important in the physiological regulation of blood pressure whereas alterations in cellular magnesium metabolism could contribute to the pathogenesis of blood pressure elevation. Although most epidemiological and experimental studies support a pathological role for magnesium in the etiology and development of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of essential hypertension is unclear. The present review discusses the molecular, biochemical, physiological and pharmacological roles of magnesium in the regulation of vascular function and blood pressure and introduces novel concepts relating to magnesium as a second messenger in intracellular signaling in cardiovascular cells. In addition, alterations in magnesium regulation in experimental and clinical hypertension and the potential antihypertensive therapeutic effects of magnesium are addressed.