Neuropeptide Y
NPY, NPY(1-36), pancreatic polypeptide family member
Neuropeptide Y is a 36-residue peptide and one of the most abundant neuropeptides in the mammalian brain, also present throughout sympathetic nerves. It governs appetite, anxiety, stress resilience, circadian rhythm and vascular tone through a family of Y receptors. Despite a compelling physiological case, therapeutic attempts have so far produced only small early-phase human data, one of which missed its primary endpoint.
Mechanism
NPY belongs to the pancreatic polypeptide family alongside peptide YY and pancreatic polypeptide, sharing the compact PP-fold. In humans it signals through Y1, Y2, Y4 and Y5 receptors, all Gi/Go-coupled, inhibiting adenylate cyclase and reducing calcium conductance. Y1 and Y5 are largely postsynaptic and mediate the powerful orexigenic and anxiolytic effects; Y2 is chiefly a presynaptic autoreceptor restraining further NPY and glutamate release. Selectivity is set enzymatically: DPP-4 trimming to NPY(3-36) abolishes Y1 activity and produces a Y2/Y5-preferring agonist, so the same peptide has opposite net effects depending on local peptidase activity.
In the arcuate nucleus NPY is co-expressed with agouti-related peptide in the neurons that oppose POMC signalling, making it a core component of hypothalamic energy balance. In the amygdala, hippocampus and locus coeruleus it dampens noradrenergic and corticotropin-releasing factor signalling, which is the basis of its reputation as an endogenous stress-resilience peptide. Peripherally it is co-released with noradrenaline from sympathetic terminals and produces slow, long-lasting vasoconstriction.
What the research shows
Two placebo-controlled intranasal studies from a single centre form nearly all the human therapeutic evidence, and both must be read carefully. A crossover single-ascending-dose study randomised 26 people with PTSD, of whom 24 completed both treatment days; NPY was tolerated up to 9.6 mg and there was a significant treatment-by-dose interaction favouring NPY on the Beck Anxiety Inventory, but no significant effect on the State-Trait Anxiety Inventory. A separate trial randomised 30 patients with major depression to a single 6.8 mg intranasal dose or placebo. It did not meet its primary endpoint, which was the change in depression score at 48 hours; the differences reported in its favour were at the secondary 5-hour and 24-hour timepoints. Describing that trial as positive, as it is often described, misstates what happened.
The most informative negative data come from the obesity programme. Velneperit, an oral Y5 antagonist, was taken through phase 2 in obesity and produced only modest weight loss, leading to discontinuation. This is a useful corrective: NPY's dominance in rodent feeding models did not transfer to clinically meaningful human weight change through a single receptor.
Evidence assessment
Limited evidence
Human therapeutic data amount to two small single-centre randomised trials of intranasal NPY totalling 56 participants with very short follow-up. The PTSD study was a single-dose tolerability study with anxiety as a secondary efficacy measure, and the depression study did not meet its primary endpoint. The largest test of the pathway, a Y5 antagonist in obesity, was disappointing and has no located primary publication.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Neuropeptide Y - a novel brain peptide with structural similarities to peptide YY and pancreatic polypeptide Preclinical only
Original identification of NPY using the C-terminal amide detection method, establishing the 36-residue sequence and family relationship.
A Randomized Dose-Ranging Study of Neuropeptide Y in Patients with Posttraumatic Stress Disorder Preclinical only
Intranasal NPY up to 9.6 mg was well tolerated. A significant treatment-by-dose interaction favoured NPY on the Beck Anxiety Inventory (P=.038), but there was no significant effect on the State-Trait Anxiety Inventory. The primary outcome was tolerability, not efficacy.
A Randomized Controlled Trial of Intranasal Neuropeptide Y in Patients With Major Depressive Disorder Preclinical only
The trial did NOT meet its primary endpoint, which was change in MADRS at 48 hours. Differences favouring NPY were seen only at the secondary 5-hour and 24-hour timepoints. Small, single-centre and unreplicated.
Velneperit (S-2367), an oral neuropeptide Y Y5 receptor antagonist, in obesity Preclinical only
Only modest weight loss when combined with a reduced- or low-calorie diet. Development discontinued. Treated here as a substantive but unpublished negative result for the Y5 hypothesis.
Safety
Intranasal NPY was tolerated at the single doses tested with no serious adverse events reported, though sample sizes were far too small to characterise risk and no repeated-dosing data exist. Systemic NPY is a vasoconstrictor and would be expected to raise blood pressure. Nothing is known about long-term exposure in humans.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No UK marketing authorisation. NPY is an unlicensed substance with no legitimate route of supply for human consumption. |
| United States | No FDA-approved product. Intranasal NPY has been studied only under investigational new drug applications. Material sold online is a research chemical, not for human use. |
| WADA (sport) | Not named on the WADA Prohibited List. As an unapproved substance it falls under section S0 and is prohibited at all times, in and out of competition. |
Questions
In rodents, injecting NPY into the hypothalamus triggers dramatic feeding. In humans the picture is far more redundant, which is why blocking a single Y receptor in a phase 2 obesity programme produced only modest weight loss and was discontinued.
No. One small crossover study found intranasal NPY was tolerated with an anxiety signal on one of two scales. A separate depression trial in 30 people missed its primary endpoint. No regulator has approved NPY for anything.