Identification of New Biomarkers for the Classification and Monitoring of Difficult-to-treat Arterial Hypertension: Prospective Observational Study

Background:

Difficult-to-treat hypertension is characterized by uncontrolled blood pressure despite 2 or more antihypertensive drugs. In many cases, abnormal renal Na and volume handling plays a central role. Arterial vasoconstriction and renal function are regulated by the renin-angiotensin-aldosterone system (RAAS) and its effector hormones angiotensin II and aldosterone. Both control renal tubular function and Na excretion. Blocking the renin-angiotensin-system pharmacologically is therefore a current standard approach to treat hypertension. However, there is great clinical need to improve the classification of hypertensive patients and to predict patient sensitivity to different therapeutic strategies more precisely by new biomarkers that take into account tubular function and the various bioactive angiotensin fragments.

Ang fragments generated by non-canonical enzymatic pathways such as Ang III co-exist with Ang I and Ang II in plasma. Their profile could help classify hypertensive patients with greater precision than plasma renin and aldosterone alone. Furthermore, urinary exosomes are small membrane vesicles (<0.1 μm) shed into the urine by tubular epithelial cells. They contain tubular Na channels known as targets of furosemide and thiazide drugs used to treat volume overload and arterial hypertension. Na channel concentrations in the tubules are regulated by Ang II and aldosterone. Exosomal Na channel abundance could thus give valuable extra information on the actual tubular functional status not provided by standard laboratory tests of plasma renin and aldosterone or urinary electrolytes alone. Plasma Ang peptide profiles and urinary exosomal Na channels could improve the classification of patients with difficult-to-control hypertension and inform antihypertensive treatment decisions. The usual concentrations and variabilities of these biomarkers are a prerequisite for the planning of future validation studies. However, data are still lacking in this population.

Study aim:

This study aims to determine the concentration and interindividual variability of urinary exosomal sodium channels and of plasma angiotensins (candidate biomarkers) in patients with difficult-to-treat arterial hypertension and to determine their dependency on sampling conditions, dietary salt intake, and plasma renin and aldosterone concentrations.