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

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Anthracycline-induced cardiotoxicity and renin-angiotensin-aldosterone system-from molecular mechanisms to therapeutic applications

Few millions of new cancer cases are diagnosed worldwide every year. Due to significant progress in understanding cancer biology and developing new therapies, the mortality rates are decreasing with many of patients that can be completely cured. However, vast majority of them require chemotherapy which comes with high medical costs in terms of adverse events, of which cardiotoxicity is one of the most serious and challenging. Anthracyclines (doxorubicin, epirubicin) are a class of cytotoxic agents used in treatment of breast cancer, sarcomas, or hematological malignancies that are associated with high risk of cardiotoxicity that is observed in even up to 30% of patients and can be diagnosed years after the therapy. The mechanism, in which anthracyclines cause cardiotoxicity are not well known, but it is proposed that dysregulation of renin-angiotensin-aldosterone system (RAAS), one of main humoral regulators of cardiovascular system, may play a significant role. There is increasing evidence that drugs targeting this system can be effective in the prevention and treatment of anthracycline-induced cardiotoxicity what has recently found reflection in the recommendation of some scientific societies. In this review, we comprehensively describe possible mechanisms how anthracyclines affect RAAS and lead to cardiotoxicity. Moreover, we critically review available preclinical and clinical data on use of RAAS inhibitors in the primary and secondary prevention and treatment of cardiac adverse events associated with anthracycline-based chemotherapy.

Plasma Renin Measurements are Unrelated to Mineralocorticoid Replacement Dose in Patients With Primary Adrenal Insufficiency

CONTEXT

No consensus exists for optimization of mineralocorticoid therapy in patients with primary adrenal insufficiency.

OBJECTIVE

To explore the relationship between mineralocorticoid (MC) replacement dose, plasma renin concentration (PRC), and clinically important variables to determine which are most helpful in guiding MC dose titration in primary adrenal insufficiency.

DESIGN

Observational, retrospective, longitudinal analysis.

PATIENTS

A total of 280 patients (with 984 clinical visits and plasma renin measurements) with primary adrenal insufficiency were recruited from local databases and the international congenital adrenal hyperplasia (CAH) registry (www.i-cah.org). Thirty-seven patients were excluded from the final analysis due to incomplete assessment. Data from 204 patients with salt-wasting CAH (149 adults and 55 children) and 39 adult patients with Addison disease (AD) were analysed.

MAIN OUTCOME MEASURES

PRC, electrolytes, blood pressure (BP), and anthropometric parameters were used to predict their utility in optimizing MC replacement dose.

RESULTS

PRC was low, normal, or high in 19%, 36%, and 44% of patients, respectively, with wide variability in MC dose and PRC. Univariate analysis demonstrated a direct positive relationship between MC dose and PRC in adults and children. There was no relationship between MC dose and BP in adults, while BP increased with increasing MC dose in children. Using multiple regression modeling, sodium was the only measurement that predicted PRC in adults. Longitudinally, the change in MC dose was able to predict potassium, but not BP or PRC.

CONCLUSIONS

The relationship between MC dose and PRC is complex and this may reflect variability in sampling with respect to posture, timing of last MC dose, adherence, and concomitant medications. Our data suggest that MC titration should not primarily be based only on PRC normalization, but also on clinical parameters such as BP and electrolyte concentration.

Novel RAAS agonists and antagonists: clinical applications and controversies

The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure homeostasis and vascular injury and repair responses. The RAAS was originally thought to be an endocrine system critically important in regulating blood pressure homeostasis. Yet, important local forms of the RAAS have been described in many tissues, which are mostly independent of the systemic RAAS. These systems have been associated with diverse physiological functions, but also with inflammation, fibrosis and target-organ damage. Pharmacological modulation of the RAAS has brought about important advances in preventing morbidity and mortality associated with cardiovascular disease. Yet, traditional RAAS blockers such as angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) only reduce the risk of disease progression in patients with established cardiovascular or renal disease by ∼20% compared with other therapies. As more components of the RAAS are described, other potential therapeutic targets emerge, which could provide improved cardiovascular and renal protection beyond that provided by an ACE inhibitor or ARB. This Review summarizes the present and future pharmacological manipulation of this important system.

Acute and chronic regulation of aldosterone production

Aldosterone is the major mineralocorticoid synthesized by the adrenal and plays an important role in the regulation of systemic blood pressure through the absorption of sodium and water. Aldosterone production is regulated tightly by selective expression of aldosterone synthase (CYP11B2) in the adrenal outermost zone, the zona glomerulosa. Angiotensin II (Ang II), potassium (K(+)) and adrenocorticotropin (ACTH) are the main physiological agonists which regulate aldosterone secretion. Aldosterone production is regulated within minutes of stimulation (acutely) through increased expression and phosphorylation of the steroidogenic acute regulatory (StAR) protein and over hours to days (chronically) by increased expression of the enzymes involved in the synthesis of aldosterone, particularly CYP11B2. Imbalance in any of these processes may lead to several disorders of aldosterone excess. In this review we attempt to summarize the key molecular events involved in the acute and chronic phases of aldosterone secretion.

The regulation of aldosterone synthase expression

Aldosterone, the primary human mineralocorticoid, is a major regulator of intravascular volume and blood pressure. The capacity of the adrenal gland to produce aldosterone is controlled, in large part, by the regulated transcription of CYP11B2, the gene encoding aldosterone synthase. Aldosterone synthase is responsible for the conversion of 11-deoxycorticosterone to aldosterone and is expressed only within the zona glomerulosa of the adrenal cortex. The development of new systems for in vitro studies of expression has helped define molecular mechanisms that regulate this enzyme and thus the capacity of the adrenal gland to produce aldosterone. Both potassium and angiotensin II (ANG II) increase intracellular calcium levels, which regulate expression of CYP11B2 through transcription factors that interact with defined sites in the 5'-flanking region of the gene.

Adrenal zonation: clues from 11beta-hydroxylase and aldosterone synthase

Aldosterone and cortisol are the major mineralocorticoid and glucocorticoid produced by the human adrenal. Circulating levels of angiotensin II and potassium control the adrenal production of aldosterone, while the production of cortisol is controlled mainly by adrenocorticotropin. The capacity of the adrenal cortex to differentially produce aldosterone and cortisol relies to a large degree on the expression of aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1). CYP11B2 catalyzes the final steps in the biosynthesis of aldosterone and is expressed solely in the glomerulosa of the adrenal cortex, while CYP11B1 catalyzes the final steps in the biosynthesis of cortisol and is expressed in the fasciculata/reticularis. The zonal expression of these two isozymes appears to result from transcriptional regulation of the two genes. Herein, the recent progress in defining the cellular mechanisms that regulate transcription of these two isozymes and thus the capacity of the adrenal gland to differentially produce aldosterone and cortisol is discussed.

Transcription-modulating drugs: a new frontier in the treatment of essential hypertension

While the promises of gene therapy may be years away from realization, the therapeutic use of drugs that act by modifying gene transcription is a well-established practice in clinical medicine. Although transcription-modulating drugs are frequently used in many different specialties, the deliberate development and use of these agents in cardiovascular medicine has been comparatively limited. However, research advances in the area of gene transcription and in the molecular genetic regulation of blood pressure, insulin resistance, lipid metabolism, and cell growth are providing new opportunities for controlling the expression of genes that are relevant to the pathogenesis of cardiovascular disease and essential hypertension. These research advances are beginning to converge in the development of transcription-modulating drugs with the potential to attack genetically determined risk factors that often cluster in patients with essential hypertension. Ligand-activated transcription factors that serve as receptors for small lipophilic compounds such as the thiazolidinediones and retinoids represent examples of potential therapeutic targets with direct effects on the expression of genes relevant to the pathogenesis of essential hypertension and its complications. Mounting evidence suggesting that the superior cardiorenal protective properties of converting enzyme inhibitors are related in part to their ability to indirectly modify the expression of genes in the heart and vasculature provides provisional support for the clinical value of this therapeutic approach. Given the success of transcription-modulating drugs in the treatment of type II diabetes and many other clinical disorders, it is anticipated that these agents will be developed as tools for the prevention and treatment of hypertension and cardiovascular disease in the not too distant future.