KPV vs VIP.

KPV is a synthetic tripeptide composed of L-lysine, L-proline, and L-valine (Lys-Pro-Val), corresponding to the C-terminal residues 11-13 of alpha-melanocyte-stimulating hormone (alpha-MSH). It is the smallest fragment of alpha-MSH that retains the parent hormone's anti-inflammatory activity, and it is studied as a melanocortin-derived anti-inflammatory agent that lacks the pigmentary (melanogenic) action of the full hormone. It is a research compound, not an approved drug.

VIP (vasoactive intestinal peptide, also called vasoactive intestinal polypeptide) is a 28-amino-acid neuropeptide first isolated from porcine intestine in the early 1970s. It is highly conserved across mammals and belongs to the secretin/glucagon peptide superfamily, sharing close homology with PACAP (pituitary adenylate cyclase-activating polypeptide). It is widely distributed in the central and peripheral nervous systems and in the gut, and is notably enriched in lung tissue. The synthetic form used in human trials is known as aviptadil.

KPV's anti-inflammatory action appears to be largely receptor-independent: rather than signaling primarily through classical melanocortin receptors, it is taken up into intestinal epithelial and immune cells by the proton-coupled di/tripeptide transporter PepT1 (SLC15A1), which is normally restricted to the small intestine but is induced in the colon during inflammation. Once intracellular, KPV dampens canonical pro-inflammatory signaling, notably inhibiting NF-kB and MAP-kinase pathway activation and reducing secretion of pro-inflammatory cytokines. Work dissecting alpha-MSH fragments also implicates antagonism of IL-1beta-driven inflammatory functions as a contributor to its effect. This combination of mechanisms is the basis for its preclinical study in mucosal inflammation.

VIP signals through two class B G-protein-coupled receptors, VPAC1 and VPAC2, both of which bind VIP and PACAP with high affinity (a related receptor, PAC1, is PACAP-selective). Receptor activation couples primarily to adenylate cyclase, raising intracellular cAMP, with secondary coupling to phospholipase C in some contexts. Downstream effects include smooth-muscle relaxation and vasodilation, bronchodilation, stimulation of exocrine and electrolyte secretion, glucose-dependent insulin secretion (largely via VPAC2), and broad immunomodulatory/anti-inflammatory actions that shift cytokine balance away from pro-inflammatory mediators. In the lung, VIP receptors are concentrated on alveolar type II cells, which is part of the rationale for studying it in acute lung injury.

The evidence base for KPV is preclinical (cell culture and rodent models); there are no completed human clinical trials demonstrating efficacy or safety. Dalmasso and colleagues (Gastroenterology, 2008) showed that nanomolar KPV inhibited NF-kB and MAP-kinase activation in human intestinal epithelial (Caco2-BBE, HT29-Cl.19A) and Jurkat T cells via PepT1, and that oral KPV reduced DSS- and TNBS-induced colitis in mice. Kannengiesser et al. (Inflammatory Bowel Diseases, 2008) reported that KPV attenuated disease in DSS and CD45RB-transfer murine colitis models, with effects that did not require functional MC1R, supporting a non-melanocortin-receptor mechanism. Earlier mechanistic dissection by Getting, Schioth, and Perretti (J Pharmacol Exp Ther, 2003) compared core and C-terminal (KPV) alpha-MSH peptides and characterized their anti-inflammatory pharmacology. The broader pharmacology is summarized in a review by Brzoska et al. (Endocrine Reviews, 2008); the gap to human disease remains unbridged.

Human evidence is mixed and, for most systemic indications, limited. The strongest, most rigorous human data come from TESICO (ACTIV-3b), a randomized, placebo-controlled trial of intravenous aviptadil in COVID-19-associated hypoxaemic respiratory failure published in Lancet Respiratory Medicine (2023); it enrolled ~471 randomized participants and was stopped for futility, finding no improvement in clinical outcomes versus placebo. The earlier enthusiasm rested largely on small open-label series and preclinical/animal models of acute lung injury and cytokine suppression, which did not translate into proven benefit in the controlled setting. The best-established human use is local, not systemic: aviptadil combined with phentolamine (Invicorp) is an approved intracavernosal injection for erectile dysfunction in several countries. VIP has also held orphan-drug designations for pulmonary hypertension and sarcoidosis, but those indications lack confirmatory pivotal trial evidence.

Documented safety data come almost entirely from cell and rodent studies, where KPV has generally been reported as well tolerated at the doses tested; there is no established human safety profile, no characterized adverse-event spectrum in people, and no pharmacovigilance data. Long-term effects, immunogenicity, effects in pregnancy, and drug interactions are unknown. Because PepT1 expression and KPV uptake are upregulated specifically in inflamed tissue, the cellular pharmacology may differ between healthy and diseased states, which is not characterized in humans. Material sold for research or compounded use is not subject to pharmaceutical-grade quality control, introducing additional purity and identity risks.

As an endogenous vasodilator, systemic VIP/aviptadil can cause hypotension, flushing, and diarrhea, and intravenous infusion has been associated with these effects in trials. Excess endogenous VIP, as seen in VIPoma tumors, produces severe secretory (watery) diarrhea, hypokalemia, and dehydration, illustrating its potent secretory pharmacology. For intracavernosal use, the combination product is reported to carry low rates of penile pain and priapism relative to some other injectables. Long-term safety of systemic administration is not well characterized, and the controlled COVID-19 data did not establish a net clinical benefit; safety beyond the studied settings remains uncertain.

KPV is not approved by the FDA (or other major regulators) for any indication and has no marketed drug product; it is an investigational/research-use compound. It is not a recognized dietary supplement ingredient, and any human use occurs outside of established regulatory approval.

VIP itself is not an FDA-approved drug; intravenous aviptadil is investigational in the United States and was studied under FDA mechanisms including orphan-drug designations (pulmonary hypertension, sarcoidosis) and emergency COVID-19 trials. The aviptadil/phentolamine combination (Invicorp) is approved for erectile dysfunction in several countries including the UK, Denmark, and New Zealand, but not broadly in the US.