Do Angiotensin Peptides Improve Memory? A Systematic Review of Animal Studies

What the researchers found

In this systematic review of 32 animal studies, angiotensin IV (Ang IV) improved cognitive performance in 7 of 11 studies in normal animals and 8 of 9 studies in cognitively impaired models. Ang IV and its analogs (including dihexa and Nle1-Ang IV) enhanced spatial working memory, passive avoidance, and object recognition. Angiotensin-(1-7) benefited memory in 2 of 3 studies and showed anti-dementia properties. The peptides were most effective when delivered directly into the brain (intracerebroventricularly) close to the time of learning or memory testing.

Why it matters

Dementia and cognitive decline affect tens of millions of people, and effective treatments remain elusive. This systematic review reveals that two peptides from the brain's own renin-angiotensin system can improve memory and learning in animal models — including models of cognitive impairment. The connection between blood pressure peptides and brain function is an underappreciated research area that could yield new treatments for Alzheimer's disease and other dementias.

How the study worked

The researchers conducted a systematic review of experimental (non-human) studies, searching databases and identifying 450 articles. Of these, 32 met inclusion criteria. Studies were categorized by peptide type (Ang IV or Ang-(1-7)), cognitive test (passive avoidance, spatial memory, object recognition), and whether animals were normal or cognitively impaired. Results were synthesized narratively.

Who was studied

32 experimental animal studies using rodent models of normal cognition and cognitive impairment

What this study cannot tell us

All 32 studies were in animals, primarily rodents, so translation to humans is uncertain. Most studies used intracerebroventricular delivery (directly into the brain), which isn't practical for human treatment. The review could not perform meta-analysis due to heterogeneity in study designs. Sample sizes of individual studies varied. Only acute (single-dose) administration was studied in most cases.

How to read the evidence

This is a systematic review of 32 preclinical (animal) studies. While the consistency of positive results across studies is encouraging, all evidence is from animal models with no human clinical trials included.

When this study was published

Published in 2018. Research on angiotensin peptides and cognition has continued, with growing interest in Ang IV analogs like dihexa as potential cognitive therapeutics.

The bigger picture

Most dementia research focuses on amyloid plaques, tau tangles, or neurotransmitter deficits. The finding that the brain's renin-angiotensin system directly influences memory opens a completely different therapeutic avenue. Dihexa, an Ang IV analog, has attracted particular interest as a potential cognitive enhancer. The connection also raises questions about whether common blood pressure medications (ACE inhibitors, ARBs) might affect cognition — positively or negatively.

Questions still open

• Can Ang IV analogs like dihexa be made orally bioavailable and brain-penetrant enough for human use?
• Do ACE inhibitors or ARBs affect cognitive outcomes in human patients through these same angiotensin pathways?
• Would chronic treatment with Ang IV analogs provide sustained cognitive benefits, or only acute effects?

Common questions

Read the original research

Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies.

Neuroscience and biobehavioral reviews, 92, 209-225

Citation

Ho, Jean K; Nation, Daniel A. (2018). Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies.. Neuroscience and biobehavioral reviews, 92, 209-225. https://doi.org/10.1016/j.neubiorev.2018.05.005