Biomarkers

The renin-angiotensin system (RAS) has been proposed as a potential modifier of the development of Alzheimer's disease (AD). However, prospective studies are sparse. We aimed to determine whether plasma ACE-1, ACE-2, angiotensin II (ANG-II), and angiotensin 1-7 (ANG1-7) a) change over time, b) differ by cognitive status, c) differ by race.

We performed a secondary data analysis of the Action for Health in Diabetes (Look AHEAD) study among community-dwelling, dementia free participants with overweight/obesity and T2DM, aged 45-76 years at baseline and observed over 12 years. Of 5,145 participants, we included 310 who were not using medications affecting the RAS system, had blood available at follow-up years 1, 4, and 10, and underwent cognitive adjudication. Plasma ACE and angiotensin were measured using ELISA (R&D systems), and ACE activity was measured using an immunocapture fluorogenic peptide assay. T-tests were used to test the association between log-converted ACE-1 and ACE-2 at years 1, 4, and 10 and ANGII and ANGII levels at years 1 and 4. We then stratified groups by cognitive status at mean year 11 (cognitively impaired or unimpaired) and race (White and Non-White [Black and Hispanic)].

ACE-2 activity between increased significantly between years 1 (1,542  ±  873 rfu and 10 (1,727.05  ±  1,116 rfu) (Figure 1). Similarly, ANG 1-7 levels increased significantly between years 1 (253.4  ±  80 pg/ml) and 4 (298.4  ±  112 pg/ml) (Figure 2). Cognitively impaired participants (adjudicated between years 8-12) had significantly lower ANG1-7 levels (221.0  ±  46 pg/ml) than unimpaired participants (285.8 + 114 pg/ml) in year 1. ANGII levels were significantly lower (61.8  ±  69 pg/ml) in year 1 among Non-White (mainly Black) compared to White participants (74.8  ±  93 pg/ml).

In this sample of older adults with T2DM and dementia-free at baseline, we found increased ACE-2 enzyme over time. We further found lower levels of some of the enzymes in those of non-white race and those with cognitive impairment. ACE-2 enzyme is involved in the production of ANG1-7; thus, the findings of increased ACE-2 activity associated with increased ACE1-7 levels are biologically plausible. These findings warrant further evaluation.