Angiotensin IV
Also known as: Ang IV, angiotensin 3-8, Val-Tyr-Ile-His-Pro-Phe, AT4 receptor ligand
Endogenous hexapeptide / renin-angiotensin system metabolite / insulin-regulated aminopeptidase (IRAP) inhibitor
What it is
Researchers and neuroscience enthusiasts interested in memory, cognition, and Alzheimer's disease explore Angiotensin IV, a naturally occurring hexapeptide fragment of the renin-angiotensin system. It is studied primarily for its ability to enhance learning and memory in preclinical models by inhibiting the enzyme IRAP in the brain's hippocampus.
The scientific side
Angiotensin IV (Ang IV; sequence Val-Tyr-Ile-His-Pro-Phe) is a biologically active hexapeptide metabolite generated from Angiotensin II through sequential cleavage by aminopeptidases A and N within the brain renin-angiotensin system. Its primary confirmed molecular target is insulin-regulated aminopeptidase (IRAP; also called oxytocinase or the AT4 receptor), a zinc-dependent metalloenzyme of the M1 aminopeptidase family highly expressed in hippocampal neurons and cortical regions associated with cognitive function (PMIDs: 33178027, 34169156, 41280134). Ang IV binds competitively to the catalytic site of IRAP, causing inhibition of its peptidase activity (PMIDs: 40495656, 32154052). This inhibition is proposed to elevate levels of endogenous IRAP substrates — including oxytocin, vasopressin, somatostatin, and cholecystokinin-8 — thereby amplifying neuropeptide signalling cascades that modulate synaptic plasticity and memory consolidation. Quantum mechanics/molecular mechanics simulations have clarified why Ang IV inhibits rather than is cleaved by IRAP: bidentate coordination of the catalytic zinc ion by Ang IV's valine N-terminus distorts active-site geometry and raises the energy barrier for tetrahedral intermediate formation, preventing hydrolysis. At the cellular level, Ang IV and its analogs stimulate dendritic spine formation and increase expression of pro-cognitive markers drebrin and MAP2 in hippocampal cultures, changes associated with enhanced synaptic connectivity (PMIDs: 27501164, 39596085). Ang IV has also been shown to inhibit NMDA receptor currents in layer V pyramidal neurons of the prefrontal cortex, a mechanism that may modulate glutamatergic neurotransmission and executive cognitive function. In Alzheimer's disease mouse models, Ang IV restored hippocampal AT4R levels, increased subgranular zone neurogenesis, reduced oxidative stress, rescued neurovascular coupling and cerebrovascular dilatory responses, and normalized nitric oxide bioavailability — without altering blood pressure or amyloid-beta plaque burden (PMIDs: 31669735, 28476949). IRAP is also present in glucose transporter type 4 (GLUT4) vesicles and participates in GLUT4 trafficking to the plasma membrane; Ang IV-mediated IRAP inhibition is therefore proposed to modulate neuronal glucose uptake, a mechanism disrupted in Alzheimer's disease by excess 27-hydroxycholesterol. The Ang IV/AT4R axis acts on cerebral microvasculature in addition to its cognitive and neuropeptide-regulatory roles.
Class: Endogenous hexapeptide / renin-angiotensin system metabolite / insulin-regulated aminopeptidase (IRAP) inhibitor
Administration & storage
- Administration
- Intracerebroventricular (i.c.v.) injection — used in the majority of reviewed animal cognition studies (PMIDs: 2806943729733881)Intracerebroventricular continuous infusion via osmotic minipumps — used for chronic Alzheimer's disease model studies (~1.3 nmol/day for 1 month; PMID: 31669735)Subcutaneous injection — used in diabetic rat model (5 μg/kg; PMID: 34170263)Peripheral (systemic) injection — used to demonstrate peripheral pro-cognitive effects and IRAP modulation in novel object recognition studies (PMID: 31079845)
- Storage
- No peptide-specific storage conditions for Angiotensin IV are described in the reviewed abstracts. As an unprotected hexapeptide, standard peptide storage practices apply: lyophilized powder should be stored at −20°C or lower, protected from light and moisture, with reconstituted solutions used promptly or stored briefly at −20°C and used within one freeze-thaw cycle. The macrocyclic IRAP inhibitor HA08 is noted to be significantly more stable than endogenous Ang IV, but no formal stability data for Ang IV itself appears in reviewed literature.
- Cautions
- All preclinical data — no human safety data exists for Ang IV administered exogenously; no clinical trials have been conducted,CNS delivery required for reliable cognitive effects — the blood-brain barrier severely limits peripheral bioavailability; attempts at peripheral administration produce inconsistent or attenuated effects compared to i.c.v. routes,Rapid degradation by peripheral aminopeptidases (aminopeptidase N) limits circulating half-life; elevated aminopeptidase N (induced by 27-hydroxycholesterol) can completely oppose Ang IV's CNS actions,Sex differences observed — pro-cognitive effects of peripheral Ang IV were demonstrated only in male mice; no effect in females; prenatal alcohol exposure abolished the effect in males (PMIDs: 31079845, 28457883),Ang IV analog Dihexa (PNB-0408) failed to protect against Huntington's disease-like symptoms in a 3-NP rat model, highlighting that not all neurodegenerative models respond to AT4R/IRAP targeting,NMDA receptor inhibition in prefrontal cortex pyramidal neurons observed at 1 nM–1 μM — potential modulation of excitatory neurotransmission warrants characterization of dose-response and circuit-level effects before therapeutic extrapolation
Legal & regulatory status
Not approved by the US FDA for any therapeutic indication. Angiotensin IV is an endogenous hexapeptide studied exclusively in preclinical and mechanistic research contexts; no completed Phase I, II, or III clinical…
Not explicitly listed on the WADA Prohibited List in reviewed literature. Angiotensin IV and its synthetic analogs (e.g., Dihexa/PNB-0408) are not currently named as prohibited substances in the reviewed abstracts…
Not stated in reviewed literature — requires manual verification. No Health Canada Drug Product Database listing identified for Angiotensin IV as a therapeutic agent.
What it's studied for
- Cognitive enhancement and memory consolidation in healthy animals Animal studies only
- Alzheimer's disease — cognitive and cerebrovascular deficit rescue Animal studies only
- Diabetes-associated cognitive impairment and oxidative stress Animal studies only
- IRAP inhibition as a target for cognitive disorder drug development Mechanistic only
- Neuronal glucose uptake and metabolic cognitive protection (IRAP-GLUT4 pathway) Mechanistic only
- Huntington's disease analog therapy (Dihexa/PNB-0408 — Ang IV analog) Animal studies only
- Alzheimer's disease — Ang IV analog Dihexa via PI3K/AKT pathway (APP/PS1 model) Animal studies only
- Prefrontal cortex glutamatergic modulation (NMDA receptor inhibition) Mechanistic only
Safety signals
- No dedicated toxicology or formal safety studies identified in reviewed literature — all evidence is from mechanistic/efficacy animal studies without systematic adverse event reporting
- Null efficacy in Huntington's disease model — Dihexa (Ang IV analog, PNB-0408) failed to attenuate 3-nitropropionic acid-induced motor dysfunction, spatial memory impairment, or weight loss; histopathology showed persistent neurotoxic damage
- Sex-dependent response — peripheral Ang IV improves memory consolidation in male but not female mice; prenatal alcohol exposure abolishes the effect in males; IRAP activity modulation similarly sex-specific
- Interaction with voltage-gated calcium channels — both L-type (nimodipine) and T-type (mibefradil) VGCC blockers at behaviorally inactive doses completely prevented Ang IV's memory-enhancing effects in rats, indicating calcium channel dependence of its procognitive mechanism
- Aminopeptidase N upregulation by 27-hydroxycholesterol can degrade Ang IV and oppose its IRAP-mediated glucose uptake facilitation — elevated cholesterol metabolites may pharmacologically nullify Ang IV action
- No effect on blood pressure — chronic Ang IV i.c.v. infusion in APP transgenic mice (~1.3 nmol/day, 1 month) did not alter arterial blood pressure, distinguishing it from cardiovascular renin-angiotensin system peptides
- No effect on amyloid-beta pathology or neuroinflammation — Ang IV rescued cognition and cerebrovascular function in APP mice without reducing Aβ plaque load or altering neuroinflammatory markers, indicating disease-modifying mechanism is independent of amyloid clearance
All studies (13)
Frequently asked
Can I take Angiotensin IV to improve my memory or protect against Alzheimer's disease?
Angiotensin IV has shown memory-enhancing and cognitive-protective effects in numerous animal models, including Alzheimer's disease mouse models. However, all evidence to date is preclinical — no human clinical trials have been conducted. The peptide also has significant pharmacokinetic barriers: it is rapidly degraded by plasma enzymes and does not reliably cross the blood-brain barrier after peripheral injection. The strongest effects in studies required direct injection into brain ventricles (intracerebroventricular delivery), which is not feasible outside a research or neurosurgical setting. There is no established safe or effective human dosing protocol.
Is Angiotensin IV the same as Dihexa?
Dihexa (also called PNB-0408 or N-hexanoic-Tyr-Ile-(6)-amino hexanoic amide) is a synthetic analog of Angiotensin IV designed to share its IRAP-inhibiting mechanism while offering improved stability and potential oral bioavailability. Dihexa has been studied separately in Alzheimer's and Parkinson's disease animal models and showed procognitive effects in some — but not all — neurodegenerative disease contexts; it failed to protect against Huntington's disease-like symptoms in one preclinical study. Angiotensin IV is the endogenous parent peptide; Dihexa is a designed derivative. They are related but distinct compounds.
What does AT4 receptor mean, and what does it have to do with Angiotensin IV?
The AT4 receptor was the original name given to the high-affinity brain binding site for Angiotensin IV. In 2001, research established that this 'receptor' is actually IRAP — insulin-regulated aminopeptidase — a zinc metalloenzyme expressed in hippocampal neurons and other brain regions. Angiotensin IV binds to IRAP's catalytic site and inhibits its enzyme activity rather than activating a classic G-protein-coupled receptor cascade. This discovery reframed Angiotensin IV from a receptor agonist into an enzyme inhibitor, and shifted drug development toward designing small-molecule IRAP inhibitors as cognitive enhancers.