In Primary Aldosteronism Acute Potassium Chloride Supplementation Suppresses Abundance and Phosphorylation of the Sodium-Chloride Cotransporter

ENaCγ in Urinary Extracellular Vesicles as an Indicator of MR Signaling in Primary Aldosteronism

BACKGROUND

Aldosterone and the MR (mineralocorticoid receptor) are important therapeutic targets for hypertension and cardiovascular diseases. However, biomarkers of tissue MR signaling are not fully established. Extracellular vesicles released from eukaryotic cells can provide information on tissue signaling. Using samples from patients with primary aldosteronism (PA), we explored the potential of urinary extracellular vesicles (uEVs) as a noninvasive indicator of MR signaling to guide treatment.

METHODS

We analyzed proteins contained in PA uEVs by liquid chromatography tandem mass spectrometry. We narrowed down candidate biomarkers by referring to an existing database of urinary exosomes. The results were validated through Western blot analysis involving 63 patients with PA and 11 healthy volunteers.

RESULTS

We identified a total of 1940 proteins in PA uEVs. Comparative analysis with the existing database narrowed down the pathways enriched in PA uEVs, which were related to diabetic complications, Rac1 signaling, and aldosterone-regulated sodium reabsorption. A closer look at the identified proteins revealed ENaCγ (epithelial Na+ channel γ) peptides near the proteolytic cleavage sites, and Western blot analysis confirmed the predominant presence of cleaved ENaCγ, a marker of aldosterone signaling in renal tubules. In PA uEVs, cleaved ENaCγ showed a 4.8-fold increase compared with healthy volunteers and was significantly correlated with the aldosterone-to-renin ratio, aldosterone levels, and fractional excretion of K+. Targeted treatment in PA reduced the abundance of cleaved ENaCγ, suggesting a causal role for MR in its induction.

CONCLUSIONS

This study provides a list of proteins contained in PA uEVs and suggests that ENaCγ in uEVs is a promising biomarker for renal MR signaling.

Sodium Chloride Cotransporter in Hypertension

The sodium chloride cotransporter (NCC) is essential for electrolyte balance, blood pressure regulation, and pathophysiology of hypertension as it mediates the reabsorption of ultrafiltered sodium in the renal distal convoluted tubule. Given its pivotal role in the maintenance of extracellular fluid volume, the NCC is regulated by a complex network of cellular pathways, which eventually results in either its phosphorylation, enhancing sodium and chloride ion absorption from urines, or dephosphorylation and ubiquitination, which conversely decrease NCC activity. Several factors could influence NCC function, including genetic alterations, hormonal stimuli, and pharmacological treatments. The NCC's central role is also highlighted by several abnormalities resulting from genetic mutations in its gene and consequently in its structure, leading to dysregulation of blood pressure control. In the last decade, among other improvements, the acquisition of knowledge on the NCC and other renal ion channels has been favored by studies on extracellular vesicles (EVs). Dietary sodium and potassium intake are also implicated in the tuning of NCC activity. In this narrative review, we present the main cornerstones and recent evidence related to NCC control, focusing on the context of blood pressure pathophysiology, and promising new therapeutical approaches.

Modifying Dietary Sodium and Potassium Intake: An End to the 'Salt Wars'?

Excessive salt intake raises blood pressure, but the implications of this observation for human health have remained contentious. It has also been recognized for many years that potassium intake may mitigate the effects of salt intake on blood pressure and possibly on outcomes such as stroke. Recent large randomized intervention trials have provided strong support for the benefits of replacing salt (NaCl) with salt substitute (75% NaCl, 25% KCl) on hard outcomes, including stroke. During the same period of time, major advances have been made in understanding how the body senses and tastes salt, and how these sensations drive intake. Additionally, new insights into the complex interactions between systems that control sodium and potassium excretion by the kidneys, and the brain have highlighted the existence of a potassium switch in the kidney distal nephron. This switch seems to contribute importantly to the blood pressure-lowering effects of potassium intake. In recognition of these evolving data, the United States Food and Drug Administration is moving to permit potassium-containing salt substitutes in food manufacturing. Given that previous attempts to reduce salt consumption have not been successful, this new approach has a chance of improving health and ending the 'Salt Wars'.