Aldosterone, mineralocorticoid receptors, and vascular inflammation

The aldosterone-mineralocorticoid receptor pathway exerts anti-inflammatory effects in endotoxin-induced uveitis

We have previously shown that the eye is a mineralocorticoid-sensitive organ and we now question the role of mineralocorticoid receptor (MR) in ocular inflammation. The endotoxin-induced uveitis (EIU), a rat model of human intraocular inflammation, was induced by systemic administration of lipopolysaccharide (LPS). Evaluations were made 6 and 24 hours after intraocular injection of aldosterone (simultaneous to LPS injection). Three hours after onset of EIU, the MR and the glucocorticoid metabolizing enzyme 11-beta hydroxysteroid dehydrogenase type 2 (11β-HSD2) expression were down-regulated in iris/ciliary body and the corticosterone concentration was increased in aqueous humor, altering the normal MR/glucocorticoid receptor (GR) balance. At 24 hours, the GR expression was also decreased. In EIU, aldosterone reduced the intensity of clinical inflammation in a dose-dependent manner. The clinical benefit of aldosterone was abrogated in the presence of the MR antagonist (RU26752) and only partially with the GR antagonist (RU38486). Aldosterone reduced the release of inflammatory mediators (6 and 24 hours: TNF-α, IFN-γ, MIP-1α) in aqueous humor and the number of activated microglia/macrophages. Aldosterone partly prevented the uveitis-induced MR down-regulation. These results suggest that MR expression and activation in iris/ciliary body could protect the ocular structures against damages induced by EIU.

An emerging concept of vascular salt sensitivity

Excessive amounts of salt in food, as usually consumed worldwide, affect the vascular system, leading to high blood pressure and premature disabilities. Salt entering the vascular bed after a salty meal is transiently bound to the endothelial glycocalyx, a negatively charged biopolymer lining the inner surface of the blood vessels. This barrier protects the endothelium against salt overload. A poorly-developed glycocalyx increases the salt permeability of the vascular system and the amount of salt being deposited in the body, which affects organ function. A simple test system is now available that evaluates vascular salt sensitivity in humans and identifies individuals who are at risk of salt-induced hypertension. This short review aims to discuss how the underlying basic research can be translated into medical practice and, thus, meaningful health outcomes.

Eplerenone inhibits aldosterone-induced renal expression of cyclooxygenase

INTRODUCTION

The upregulation of cyclooxygenase (COX) expression by aldosterone (ALDO) or high salt diet intake is very interesting and complex in the light of what is known about the role of COX in renal function. Thus, in this study, we hypothesize that apocynin (APC) and/or eplerenone (EPL) inhibit ALDO/salt-induced kidney damage by preventing the production of prostaglandin E₂ (PGE₂).

METHODS

Dahl salt-sensitive rats on either a low-salt or high-salt diet were treated with ALDO (0.2 mg pellet) in the presence of EPL (100 mg/kg/day) or APC (1.5 mM). Indirect blood pressure, prostaglandins and ALDO levels and histological changes were measured.

RESULTS

Cyclooxygenase-2 (COX-2) levels were upregulated in the renal tubules and peritubular vessels after high-salt intake, and APC attenuated renal tubular COX-2 protein expression induced by ALDO. Plasma PGE₂ levels were significantly reduced by ALDO in the rats fed a low-salt diet when compared to rats fed a high-salt diet. PGE₂ was blocked by EPL but increased in the presence of APC.

CONCLUSIONS

The beneficial effects of EPL may be associated with an inhibition of PGE₂. The mechanism underlying the protective effects of EPL is clearly distinct from that of APC and suggests that these agents can have differential roles in cardiovascular disease.

The involvement of prostaglandins in the contractile function of the aorta by aldosterone

Background

Aldosterone, one of the major culprits associated with the renin-angiotensin-aldosterone system (RAAS), is significantly elevated following high salt administration in Dahl rats. Since we have previously demonstrated that aldosterone (ALDO) upregulates cyclooxygenase (COX) expression in the kidney, the present study was design to assess whether prostaglandin release is involved in the effects of chronic aldosterone treatment on vascular function of the aorta from nonhypertensive Dahl salt-sensitive rats.

Findings

The effects of aldosterone on arachidonic acid metabolism and on the expression of cyclooxygenase (COX)-2 were evaluated in the Dahl salt sensitive (DS) rat aorta, renal, femoral and carotid arteries. DS rats on a low salt (0.3% NaCl) diet were treated with or without ALDO for four weeks. Indirect blood pressure (BP), the release of prostacyclin (PGI₂) and prostaglandin E₂, and the expression of COX-2 were measured to assess the vascular remodelling by aldosterone. Vascular function was also assessed by contractile responsiveness in the aorta to phenylephrine. ALDO increased BP (17 ± 1%) and inhibited the basal release of PGE₂. ALDO enhanced vascular reactivity to phenylephrine and up regulated the expression of COX-2 in both aorta and renal vessels but reduced COX-2 expression in the femoral artery.

Conclusions

These data reveal that the effect of ALDO in the vasculature is tissue specific and may involve the inhibition of PGE₂ release. Thus, suggesting a role for prostaglandins in the vasculopathic aspects of aldosterone.

Involvement of Depressive Catecholamines as Thrombosis Risk/Inflammatory Markers in Non-Smoker, Non-Obese Congestive Heart Failure, Linked to Increased Epidermal Growth Factor-Receptor (EGF-R) Production

The EGF-R, also known as HER-1 or erbB-1 (EGF-R/HER-1/erbB-1), is a member of the human epithelial receptor tyrosine kinase family. sEGF-R is considered to play a role in cardiac (patho)physiology. We aimed to investigate whether soluble EGF-R is increased in congestive heart failure (CHF) patients and if related to disease severity. Soluble EGF-R, vitamin D, parathyroid hormone (PTH) was studied, and being evaluated in relation to Ca(2+), lipids, hsCRP, fibrinogen, serotonin, norepinepherine (NE). The study compared non-smoker, non-obese male CHF patients (n = 50) with age and gender-matched essential hypertension (HTN) patients (n = 20). Moreover, comparison with healthy control volunteers (n = 20) were employed. EGF-R/HER-1/erbB-1 was higher (P = 0.013) in 50 CHF male patients mean 12 ± 0.7 fmol/ml, than in 20 HTN, 9.25 ± 0.6 fmol/ml or in 20 controls, 6.25 ± 1 fmol/ml. Serum EGF-R levels correlated positively with hsCRP and NE, and were highest among CVD patients (n = 70) as well as negatively with vitamin D and HDL-C. EGF-R/HER-1/erbB-1 levels are increased in HTN and more in CHF patients. This study confirms a strong association between catecholamines as well as EGF-R/HER-1/erbB-1 levels with PTH and low vitamin D levels, being related to hyperlipidemia and inflammation (hsCRP and fibrinogen) in CVD. Moreover, contributing to the complex process of the inflammatory component of atherosclerosis in hypertensive patients that leads eventually to CHF.

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.

Aldosterone blockade in chronic kidney disease: can it improve outcome?

PURPOSE OF THIS REVIEW

The purpose of this review is to explain the rationale and limitations for use of mineralocorticoid receptor blockers (MRBs) for the treatment of chronic kidney disease (CKD) and its complications.

RECENT FINDINGS

Recent studies in animal models of CKD demonstrate that blockade of the mineralocorticoid receptor using spironolactone or eplerenone decreases inflammation, oxidative stress, proteinuria and glomerular and tubular injury. Patients with CKD are at very high risk for progression of kidney disease and major cardiovascular events. Recent studies in patients with CKD demonstrate that administration of low doses of MRBs added onto an angiotensin-converting enzyme inhibitor-based regimen reduces proteinuria--a risk marker for both progressive kidney disease and cardiovascular events. However, incident hyperkalemia, an unwanted side effect, dampened enthusiasm for this approach. There are no large-scale, long-term outcome trials examining whether MRB can slow progression of kidney disease or prevent cardiovascular events.

SUMMARY

At this time it is unknown whether mineralocorticoid receptor blockade can improve outcomes in patients with CKD. To move this field forward and determine whether these agents can improve the lives of patients with kidney disease, novel strategies to prevent or ameliorate hyperkalemia are needed.

Aldosterone activates endothelial exocytosis

Although elevated levels of aldosterone are associated with vascular inflammation, the proinflammatory pathways of aldosterone are not completely defined. We now show that aldosterone triggers endothelial cell exocytosis, the first step in leukocyte trafficking. Exogenous aldosterone stimulates endothelial exocytosis of Weibel-Palade bodies, externalizing P-selectin and releasing von Willebrand factor. Spironolactone, a nonselective mineralocorticoid receptor (MR) blocker, antagonizes aldosterone-induced endothelial exocytosis. Knockdown of the MR also decreases exocytosis, suggesting that the MR mediates exocytosis. Aldosterone triggers exocytosis within minutes, and this effect is not inhibited by actinomycin D, suggesting a nongenomic effect of aldosterone. Aldosterone treatment of endothelial cells increases leukocyte adherence to endothelial cells in culture. Taken together, our data suggest that aldosterone activates vascular inflammation in part through nongenomic, MR-mediated pathways. Aldosterone antagonism may decrease vascular inflammation and cardiac fibrosis in part by blocking endothelial exocytosis.