Abstract 078: Angiotensin Converting Enzyme type 2 shedding in the central nervous system of hypertensive patients

Abstract

ACE2 (Angiotensin Converting Enzyme type 2) is involved in the conversion of the vasoconstrictor peptide Angiotensin (Ang)-II into its vasodilatory metabolite Ang-(1-7), thereby offering a new perspective for the treatment of cardiovascular diseases associated with over-activity of the renin-angiotensin system. Our group recently reported that ACE2 shedding, a process by which ACE2 is cleaved from the plasma membrane and secreted into the surrounding milieu, contributes to the loss of the enzyme’s compensatory activity in the central nervous system (CNS) during the development of experimental hypertension. The objective of this study was to determine whether ACE2 shedding is taking place in the CNS of patients during hypertension. Unused cerebrospinal fluid, collected from patients (17 males and 27 females, aged 22-66) for diagnostic purposes, was divided in 3 groups: normotensive (n=23), hypertensive (n=9), and hypertensive controlled with medication (n=12). In addition, blood pressure values and current medications were recorded. While ELISA lacked sensitivity, soluble levels of hACE2 (sACE2) could be detected by Mass spectrometry-based RAS-Fingerprint™ in all patients. Validation experiments (n=16) indicated that pre-treatment with MLN4760 (ACE2 inhibitor) abolished the conversion of Ang-II to Ang-(1-7) by 76 ±3 %, suggesting that ACE2 is the main enzyme converting Ang-II to Ang-(1-7) in human CSF. In hypertensive patients not taking blood pressure medications, (Systolic: 157 ±10, Diastolic: 95 ±7 mmHg; n=6) CSF sACE2 activity was significantly higher (21.7 ±8.3 AU; P<0.05) than in normotensive (Systolic: 114 ±4, Diastolic: 75 ±4 mmHg; n=15) patients (6.6 ±0.9 AU). However, in patients with controlled hypertension (Systolic: 129 ±6, Diastolic: 86 ±5 mmHg; n=5), CSF sACE2 levels were normalized (6.9 ±1.9 AU). Comparison of systolic or diastolic blood pressure vs. sACE2 activity levels showed no significant correlation. These data suggest that ACE2 shedding is taking place in the CNS of hypertensive patients. Soluble ACE2 activity in the CSF is correlated with high blood pressure and could be used as a biomarker of neurogenic hypertension. AU: arbitrary unit.