Regulation of Aldosterone Secretion

Real-World Application of a Quantitative Systems Pharmacology (QSP) Model to Predict Potassium Concentrations from Electronic Health Records: A Pilot Case towards Prescribing Monitoring of Spironolactone

Quantitative systems pharmacology (QSP) models are rarely applied prospectively for decision-making in clinical practice. We therefore aimed to operationalize a QSP model for potas-sium homeostasis to predict potassium trajectories based on spironolactone administrations. For this purpose, we proposed a general workflow that was applied to electronic health records (EHR) from patients treated in a German tertiary care hospital. The workflow steps included model exploration, local and global sensitivity analyses (SA), identifiability analysis (IA) of model parameters, and specification of their inter-individual variability (IIV). Patient covariates, selected parameters, and IIV then defined prior information for the Bayesian a posteriori prediction of individual potassium trajectories of the following day. Following these steps, the successfully operationalized QSP model was interactively explored via a Shiny app. SA and IA yielded five influential and estimable parameters (extracellular fluid volume, hyperaldosteronism, mineral corticoid receptor abundance, potassium intake, sodium intake) for Bayesian prediction. The operationalized model was validated in nine pilot patients and showed satisfactory performance based on the (absolute) average fold error. This provides proof-of-principle for a Prescribing Monitoring of potassium concentrations in a hospital system, which could suggest preemptive clinical measures and therefore potentially avoid dangerous hyperkalemia or hypokalemia.

Renal Hypokalemia: An Endocrine Perspective

The majority of disorders that cause renal potassium wasting present with abnormalities in adrenal hormone secretion. While these findings frequently lead patients to seek endocrine evaluation, clinicians often struggle to accurately diagnose these conditions, delaying treatment and adversely impacting patient care. At the same time, growing insight into the genetic and molecular basis of these disorders continues to improve their diagnosis and management. In this review, we outline a practical integrated approach to the evaluation of renal hypokalemia syndromes that are seen in endocrine practice while highlighting recent advances in understanding of the genetics and pathophysiology behind them.

MicroRNAs in aldosterone production and action

Aldosterone is a cardiovascular hormone with a key role in blood pressure regulation, among other processes, mediated through its targeting of the mineralocorticoid receptor in the renal tubule and selected other tissues. Its secretion from the adrenal gland is a highly controlled process subject to regulatory influence from the renin-angiotensin system and the hypothalamic-pituitary-adrenal axis. MicroRNAs are small endogenous non-coding RNA molecules capable of regulating gene expression post-transcriptionally through stimulation of mRNA degradation or suppression of translation. Several studies have now identified that microRNA levels are changed in cases of aldosterone dysregulation and that microRNAs are capable of regulating the expression of various genes involved in aldosterone production and action. In this article we summarise the major studies concerning this topic. We also discuss the potential role for circulating microRNAs as diagnostic biomarkers for primary aldosteronism, a highly treatable form of secondary hypertension, which would be highly desirable given the current underdiagnosis of this condition.

Renin-angiotensin-aldosterone system function in the pig-to-baboon kidney xenotransplantation model

After pig-to-baboon kidney transplantation, episodes of hypovolemia and hypotension from an unexplained mechanism have been reported. This study evaluated the renin-angiotensin-aldosterone system post-kidney xenotransplantation. Kidneys from genetically-engineered pigs were transplanted into 5 immunosuppressed baboons after the excision of the native kidneys. Immunosuppressive therapy was based on the blockade of the CD40/CD154 costimulation pathway. Plasma renin, angiotensinogen (AGT), angiotensin II (Ang II), aldosterone levels, and urine osmolality and electrolytes were measured in healthy pigs, healthy nonimmunosuppressed baboons, and immunosuppressed baboons with life-supporting pig kidney grafts. After pig kidney transplantation, plasma renin and Ang II levels were not significantly different, although Ang II trended lower, even though plasma AGT and potassium were increased. Plasma aldosterone levels were unchanged. Urine osmolality and sodium concentration were decreased. Even in the presence of increasing AGT and potassium levels, lower plasma Ang II concentrations may be because of reduced, albeit not absent, the reactivity of pig renin to cleave baboon AGT, suggesting an impaired response of the renin-angiotensin-aldosterone system to hypovolemic and hypotensive episodes. The maintenance of aldosterone may be protective. The reduced urine osmolality and sodium concentration reflect the decreased ability of the pig kidney to concentrate urine. These considerations should not prohibit successful clinical pig kidney xenotransplantation.

Sodium Homeostasis, a Balance Necessary for Life

Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this solute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, paraventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin-angiotensin-aldosterone system, cardiac natriuretic peptides, antidiuretic hormone, and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis.

Phosphorylation of CaMK and CREB-Mediated Cardiac Aldosterone Synthesis Induced by Arginine Vasopressin in Rats with Myocardial Infarction

Both aldosterone and arginine vasopressin (AVP) are produced in the heart and may participate in cardiac fibrosis. However, their relationship remains unknown. This study aims to demonstrate the regulation and role of AVP in aldosterone synthesis in the heart. Rats were subjected to a sham operation or myocardial infarction (MI) by ligating the coronary artery. Cardiac function and fibrosis were assessed using echocardiography and immunohistochemical staining, respectively. In addition, the effects of AVP stimulation on cardiac microvascular endothelial cells (CMECs) were studied using ELISA, real-time PCR, and Western blotting. Compared with the rats having undergone a sham operation, the MI rats had an increased LVMI, type I collagen composition, and concentrations of aldosterone and AVP in the heart but decreased cardiac function. As the MI rats aged, the LVMI, type I collagen, aldosterone, and AVP increased, while the LVMI decreased. Furthermore, AVP time-dependently induced aldosterone secretion and CYP11B2 mRNA expression in CMECs. The p-CREB levels were significantly increased by AVP. Nevertheless, these effects were completely blocked by SR49059 or partially inhibited by KN93. This study demonstrated that AVP could induce the secretion of local cardiac aldosterone, which may involve CaMK and CREB phosphorylation and CYP11B2 upregulation through V1 receptor activation.

A quantitative systems pharmacology model of plasma potassium regulation by the kidney and aldosterone

Plasma potassium regulation within a narrow range is vital for life. The risk for hyperkalemia increases when kidney function is impaired and with therapeutic interventions such as mineralocorticoid receptor antagonists (MRAs). The kidney maintains potassium homeostasis by matching potassium intake and excretion, in part through the action of aldosterone. A mechanistic mathematical model was developed and used to investigate the effect of renal impairment and MRAs on plasma potassium levels. The model describes renal potassium filtration, reabsorption, and secretion along the nephron; potassium-aldosterone regulatory feedbacks; whole body potassium balance; and the pharmacologic effects of MRAs. The model was calibrated by fitting (1) the plasma potassium and aldosterone response to potassium infusion in humans on high/low potassium diets, and (2) the acute potassium excretion response to spironolactone. The model was validated by predicting steady-state plasma potassium with sustained spironolactone treatment in hyperaldosteronism patients. The model was then used to demonstrate that (1) declining renal function alone has a small effect on plasma potassium for GFR > 30 ml/min, but an increasing effect as GFR approaches end stage renal disease (GFR ~ 15 ml/min) (2) the effect of increasing potassium intake has minimal effect at normal GFRs but increasing effect on plasma potassium as GFR declines, and 3) MRAs have a minor effect on plasma potassium when GFR is normal, but cause larger increases as GFR falls below 60 ml/min. This model provides a quantitative framework for investigating integrated impacts of diseases and therapies in this complex system.

Progesterone in gender-affirming therapy of trans women

Progesterone is an endogenous steroid hormone with an important role for the physiology of the female reproductive system and the mammary gland. It has additional significant actions in other tissues, such as the cardiovascular system, the central nervous system, and bones. The present article explores potential clinical implications from the addition of bioidentical progesterone to gender-affirming treatment of trans women. For this purpose, it provides an overview of the physiological action of progesterone in target tissues and speculates on possible benefits for gender transitioning. Progesterone is expected to exert moderate anti-androgen action through suppression of the hypothalamic-pituitary-gonadal axis and inhibition of the conversion of testosterone to dihydrotestosterone. It may also contribute to breast maturation. In the long-term, progesterone could prevent bone loss and protect cardiovascular health. The potential benefits are mainly inferred by extrapolating evidence from biological actions in cisgender women and medical assumptions and hence, clinicians need to be cautious when applying these data into practice. Further research is needed to ascertain the efficacy and safety of progesterone in current hormonal regimens.

Leptin and its relationship with magnesium biomarkers in women with obesity

Some studies have demonstrated the participation of leptin in magnesium metabolism. On the other hand, there is evidence of the role of magnesium in the leptin intracellular signaling pathway. Therefore, the aim of this study was to investigate the existence of a relationship between serum leptin concentrations and magnesium biomarkers in women with obesity. Case-control study involving 108 women aged between 20 and 50 years, divided into two groups: obese (n = 52) and control (n = 56). Body weight, height and waist circumference, body mass index, dietary magnesium intake, magnesium biomarkers and serum leptin concentrations were measured. Serum leptin concentrations showed a statistically significant difference between groups (p < 0.001). Mean values of magnesium intake were lower than intake recommended, and with no statistically significant difference between two groups (p > 0.05). Women with obesity had lower plasma and erythrocyte magnesium concentrations than control group did (p < 0.001). Magnesium concentrations found in the urine of women with obesity were higher than the control group was, with a statistically significant difference (p < 0.001). There was a correlation between serum leptin and magnesium biomarkers (p < 0.001). Women with obesity show an inadequate magnesium nutritional status characterized by low plasma and erythrocyte concentrations and high concentrations in urine, and they also have high serum leptin concentrations. Thus, it was possible to observe a correlation between hyperleptinemia and magnesium biomarkers, requiring further studies to determine whether the dysfunction of this hormone can influence the compartmentalization of the mineral in obese organisms.

Primary Aldosteronism and Resistant Hypertension: A Pathophysiological Insight

Primary aldosteronism (PA) is a pathological condition characterized by an excessive aldosterone secretion; once thought to be rare, PA is now recognized as the most common cause of secondary hypertension. Its prevalence increases with the severity of hypertension, reaching up to 29.1% in patients with resistant hypertension (RH). Both PA and RH are "high-risk phenotypes", associated with increased cardiovascular morbidity and mortality compared to non-PA and non-RH patients. Aldosterone excess, as occurs in PA, can contribute to the development of a RH phenotype through several mechanisms. First, inappropriate aldosterone levels with respect to the hydro-electrolytic status of the individual can cause salt retention and volume expansion by inducing sodium and water reabsorption in the kidney. Moreover, a growing body of evidence has highlighted the detrimental consequences of "non-classical" effects of aldosterone in several target tissues. Aldosterone-induced vascular remodeling, sympathetic overactivity, insulin resistance, and adipose tissue dysfunction can further contribute to the worsening of arterial hypertension and to the development of drug-resistance. In addition, the pro-oxidative, pro-fibrotic, and pro-inflammatory effects of aldosterone may aggravate end-organ damage, thereby perpetuating a vicious cycle that eventually leads to a more severe hypertensive phenotype. Finally, neither the pathophysiological mechanisms mediating aldosterone-driven blood pressure rise, nor those mediating aldosterone-driven end-organ damage, are specifically blocked by standard first-line anti-hypertensive drugs, which might further account for the drug-resistant phenotype that frequently characterizes PA patients.

The invention of aldosterone, how the past resurfaces in pediatric endocrinology

Sodium and water homeostasis are drastically modified at birth, in mammals, by the transition from aquatic life to terrestrial life. Accumulating evidence during the past ten years underscores the central role for the mineralocorticoid signaling pathway, in the fine regulation of this equilibrium, at this critical period of development. Interestingly, regarding evolution, while the mineralocorticoid receptor is expressed in fish, the appearance of its related ligand, aldosterone, coincides with terrestrial life, as it is first detected in lungfish and amphibian. Thus, aldosterone is likely one of the main hormones regulating the transition from an aquatic environment to an air environment. This review will focus on the different actors of the mineralocorticoid signaling pathway from aldosterone secretion in the adrenal gland, to mineralocorticoid receptor expression in the kidney, summarizing their regulation and roles throughout fetal and neonatal development, in the light of evolution.

Sexual Dimorphism of Corticosteroid Signaling during Kidney Development

Sexual dimorphism involves differences between biological sexes that go beyond sexual characteristics. In mammals, differences between sexes have been demonstrated regarding various biological processes, including blood pressure and predisposition to develop hypertension early in adulthood, which may rely on early events during development and in the neonatal period. Recent studies suggest that corticosteroid signaling pathways (comprising glucocorticoid and mineralocorticoid signaling pathways) have distinct tissue-specific expression and regulation during this specific temporal window in a sex-dependent manner, most notably in the kidney. This review outlines the evidence for a gender differential expression and activation of renal corticosteroid signaling pathways in the mammalian fetus and neonate, from mouse to human, that may favor mineralocorticoid signaling in females and glucocorticoid signaling in males. Determining the effects of such differences may shed light on short term and long term pathophysiological consequences, markedly for males.

Diuretic Effect and Metabolomics Analysis of Crude and Salt-Processed Plantaginis Semen

Plantaginis Semen (PS) is well recognized in traditional Chinese medicine (TCM) and health products. Crude PS (CPS) and salt-processed CPS (SPS) are the two most commonly used decoction pieces of PS, and are included in the 2020 edition of Chinese Pharmacopoeia. Although they all have multiple effects, the mechanisms for treating diseases are different and remain unclear, the processing mechanism of SPS is also indeterminate, which hinders their clinical application to a certain extent. In order to solve these problems and further develop PS in the clinical application. Here, we used saline-loaded model rats for experiments, and utilized an integrated approach consisting of pharmacological methods and metabolomics, which could assess the diuretic impact of CPS and SPS ethanol extracts on saline-loaded rats and elucidate the underlying mechanism. The results showed that CPS and SPS both produced increased urine volume excretion and urine electrolyte excretion, but the levels of aldosterone (ALD) and aquaporin 2 (AQP2) were decreased. And 30 differential metabolites such as linoleic acid, lysoPC(O-18:0), sphingosine-1-phosphate, lysoPC(18:0) were found, mainly involving three metabolic pathways. In conclusion, CPS and SPS both have a diuretic effect, and that of SPS is better. This work investigated the possible diuretic mechanisms of CPS and SPS which may also be the mechanism of PS for anti-hypertension. In addition, a holistic approach provided novel and helpful insights into the underlying processing mechanisms of TCM.

Regulation of ion channels in the microcirculation by mineralocorticoid receptor activation

The mineralocorticoid receptor (MR) has classically been studied in the renal epithelium for its role in regulating sodium and water balance and, subsequently, blood pressure. However, the MR also plays a critical role in the microvasculature by regulating ion channel expression and function. Activation of the MR by its endogenous agonist aldosterone results in translocation of the MR into the nucleus, where it can act as a transcription factor. Although most of the actions of the aldosterone can be attributed to its genomic activity though MR activation, it can also act by nongenomic mechanisms. Activation of this ubiquitous receptor increases the expression of epithelial sodium channels (ENaC) in both the endothelium and smooth muscle cells of peripheral and cerebral vessels. MR activation also regulates activity of calcium channels, calcium-activated potassium channels, and various transient receptor potential (TRP) channels. Modification of these ion channels results in a myriad of negative consequences, including impaired endothelium-dependent vasodilation, alterations in generation of myogenic tone, and increased inflammation and oxidative stress. Taken together, these studies demonstrate the importance of studying the impact of the MR on ion channel function in the vasculature. While research in this area has made advances in recent years, there are still many large gaps in knowledge that need to be filled. Crucial future directions of study include defining the molecular mechanisms involved in this interaction, as well as elucidating the potential sex differences that may exist, as these areas of understanding are currently lacking.

Prenatal metyrapone treatment modulates neonatal cerebrovascular structure, function, and vulnerability to mild hypoxic-ischemic injury

This study explored the hypothesis that late gestational reduction of corticosteroids transforms the cerebrovasculature and modulates postnatal vulnerability to mild hypoxic-ischemic (HI) injury. Four groups of Sprague-Dawley neonates were studied: 1) Sham-Control, 2) Sham-MET, 3) HI-Control, and 4) HI-MET. Metyrapone (MET), a corticosteroid synthesis inhibitor, was administered via drinking water from gestational day 11 to term. In Shams, MET administration 1) decreased reactivity of the hypothalamic-pituitary-adrenal (HPA) axis to surgical trauma in postnatal day 9 (P9) pups by 37%, 2) promoted cerebrovascular contractile differentiation in middle cerebral arteries (MCAs), 3) decreased compliance ≤46% and increased depolarization-induced calcium mobilization in MCAs by 28%, 4) mildly increased hemispheric cerebral edema by 5%, decreased neuronal degeneration by 66%, and increased astroglial and microglial activation by 10- and 4-fold, respectively, and 5) increased righting reflex times by 29%. Regarding HI, metyrapone-induced fetal transformation 1) diminished reactivity of the HPA axis to HI-induced stress in P9/P10 pups, 2) enhanced HI-induced contractile dedifferentiation in MCAs, 3) lessened the effects of HI on MCA compliance and calcium mobilization, 4) decreased HI-induced neuronal injury but unmasked regional HI-induced depression of microglial activation, and 5) attenuated the negative effects of HI on open-field exploration but enhanced the detrimental effects of HI on negative geotaxis responses by 79%. Overall, corticosteroids during gestation appear essential for normal cerebrovascular development and glial quiescence but induce persistent changes that in neonates manifest beneficially as preservation of postischemic contractile differentiation but detrimentally as worsened ischemic cerebrovascular compliance, increased ischemic neuronal injury, and compromised neurobehavior.