Chymase Activity in Plasma and Urine Extracellular Vesicles in Primary Hypertension.

BACKGROUND: Circulating extracellular vesicles (EVs) carry protected cargoes of nucleic acids, proteins, and metabolites. Here we identified and validated the surface proteins and enzymatic activity of chymase, angiotensin converting enzymes 1 (ACE) and 2 (ACE2), and neprilysin (NEP) in EVs isolated from the blood and urine of primary hypertensive patients. METHODS: Peripheral venous blood and spot urine from 34 hypertensive patients were processed to isolate plasma and urinary EVs. Immuno-gold labeling and transmission electron microscopy validated the presence of the exosomal marker protein CD63 on the surface of plasma and urinary EVs. Flow cytometry characterized plasma and urinary EVs for CD63, CD9, and CD81 surface markers. In addition, exosomal CD63, TSG101, and Alix were analyzed in urine by Western blotting. Urinary EVs did not express the endoplasmic reticulum protein calnexin and Golgi protein GM130. Chymase, ACE, ACE2, and NEP activities on 125I substrates ─ angiotensin-(1-12) [Ang-(1‒12)] and angiotensin II (Ang II) ─ [1 nmol/L each] were quantified by HPLC. Data were analyzed based on whether the patient's blood pressure was controlled (Group I: <140/80 mm Hg) or not controlled (Group II: ≥ 140/80 mm Hg). RESULTS: Chymase activity on Ang-(1‒12) was significantly higher in plasma and urinary EVs than in ACE, ACE2, and NEP. In addition, chymase activity in urine EVs was more than 3-fold higher than in plasma EVs. Chymase activity increased in plasma and urine EVs retrieved from Group II patients. No comparable differences were found in the enzymatic activities of ACE, ACE2, and NEP urinary EVs between Group I and Group II. CONCLUSION: These studies reveal a differential enzymatic activity of renin angiotensin system enzymes in plasma and urine EVs isolated from hypertensive patients. Demonstrating a comparatively high chymase enzymatic activity in EVs expands a previously documented finding of increased plasma Ang-(1‒12) in hypertensive patients.

Alternative Renin-Angiotensin System.

The renin-angiotensin system is the most important peptide hormone system in the regulation of cardiovascular homeostasis. Its classical arm consists of the enzymes, renin, and angiotensin-converting enzyme, generating angiotensin II from angiotensinogen, which activates its AT1 receptor, thereby increasing blood pressure, retaining salt and water, and inducing cardiovascular hypertrophy and fibrosis. However, angiotensin II can also activate a second receptor, the AT2 receptor. Moreover, the removal of the C-terminal phenylalanine from angiotensin II by ACE2 (angiotensin-converting enzyme 2) yields angiotensin-(1-7), and this peptide interacts with its receptor Mas. When the aminoterminal Asp of angiotensin-(1-7) is decarboxylated, alamandine is generated, which activates the Mas-related G-protein-coupled receptor D, MrgD (Mas-related G-protein-coupled receptor type D). Since Mas, MrgD, and the AT2 receptor have opposing effects to the classical AT1 receptor, they and the enzymes and peptides activating them are called the alternative or protective arm of the renin-angiotensin system. This review will cover the historical aspects and the current standing of this recent addition to the biology of the renin-angiotensin system.