VIP

Background

Vasoactive intestinal peptide (VIP) is a 28–amino acid endogenous neuropeptide first isolated in 1970 by Said and Mutt from porcine small intestine based on its potent vasodilatory activity.[11] VIP belongs to the secretin/glucagon family of class B peptide hormones and is highly conserved across vertebrate species.[11][14] It is widely distributed in the central and peripheral nervous systems, gastrointestinal tract, pancreas, cardiovascular system, and immune organs.[11][14]

VIP functions as a neurotransmitter, neuromodulator, hormone, and immunomodulator. It is primarily synthesized and released by enteric neurons, parasympathetic and sympathetic nerve fibers, and multiple immune cell types, including T cells and macrophages.[11][15] Physiologically, VIP regulates smooth muscle relaxation, vasodilation, intestinal and pancreatic secretion, circadian rhythms, glucose homeostasis, and immune responses.[11][14][15]

As a therapeutic agent, native VIP has been limited by rapid enzymatic degradation, short plasma half‑life, and systemic vasodilatory effects, leading to development of more stable analogues and receptor‑selective ligands for potential treatment of inflammatory, autoimmune, infectious, and neurodegenerative diseases.[11][12][15]

Mechanism of action

Receptors and signaling

VIP exerts its effects mainly through three class B G protein‑coupled receptors (GPCRs):

• VPAC1 (VIP/PACAP receptor 1)
• VPAC2 (VIP/PACAP receptor 2)
• PAC1 (PACAP‑preferring receptor)

VIP has high affinity for VPAC1 and VPAC2 and lower affinity for PAC1, whereas the related peptide PACAP has high affinity for all three receptors.[5][11] VPAC1 is widely expressed in the gastrointestinal tract, exocrine glands, immune cells, and some tumors; VPAC2 is enriched in smooth muscle, lung, endocrine pancreas, and certain immune cell subsets.[1][11][15]

Binding of VIP to VPAC receptors primarily activates Gs proteins, stimulating adenylate cyclase, increasing intracellular cAMP, and activating protein kinase A (PKA) and exchange proteins activated by cAMP (EPAC).[11][15] Downstream pathways include CREB‑mediated transcription, modulation of NF‑κB signaling, and regulation of calcium and MAPK cascades.[11][15]

Immunomodulatory actions

VIP is a potent anti‑inflammatory and immunoregulatory peptide. In immune cells, VIP:

• Inhibits production of pro‑inflammatory cytokines (e.g., TNF, IL‑6, IL‑12) and chemokines via suppression of NF‑κB and AP‑1–dependent transcription.[15]
• Promotes anti‑inflammatory cytokines such as IL‑10 and favors differentiation of regulatory T cells (Tregs) over Th1/Th17 subsets.[15]
• Modulates antigen‑presenting cell function, reducing expression of MHC class II and co‑stimulatory molecules on dendritic cells and macrophages.[15]

These effects underlie interest in VIP and VIP analogues as candidates for autoimmune and inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease, and sepsis.[11][15]

Other physiological effects

In the gastrointestinal system, VIP promotes intestinal chloride and water secretion, relaxes smooth muscle, and modulates motility and sphincter function.[11][14] VIP also influences glycemic control by stimulating insulin and glucagon secretion and modulating islet blood flow.[11][14]

In the nervous system, VIP acts as a neuropeptide in circadian rhythm regulation, particularly in the suprachiasmatic nucleus, and has neuroprotective effects in multiple experimental models.[5][11] VIP and PACAP signaling in cranial autonomic pathways are implicated in migraine pathophysiology.[6]

Evidence summary

Preclinical evidence

1. Gastrointestinal and metabolic regulation
   Animal models with VIP or VPAC receptor deletion show impaired intestinal motility, altered mucosal secretion, disturbed circadian rhythms, and changes in glucose regulation, supporting a central physiological role for VIP signaling.[11][14]

2. Immunomodulation and inflammatory disease
   Numerous rodent studies demonstrate that exogenous VIP or VPAC‑selective analogues attenuate experimental colitis, arthritis, sepsis, and autoimmune diabetes, primarily through suppression of pro‑inflammatory cytokines and promotion of regulatory immune phenotypes.[11][15] These studies typically involve small cohorts (n≈6–15 per group) and show reductions in histologic inflammation scores, cytokine levels, and mortality.[15]

3. Antimicrobial and anti‑infective analogues
   A 2014 study in Journal of Biological Chemistry evaluated two metabolically stabilized VIP analogues, VIP51 and VIP51(6–30), against multiple pathogens.[12][13] In vitro, these analogues exhibited improved antibacterial activity compared with native VIP, including against multidrug‑resistant bacteria, while VIP itself showed relatively weak antibacterial and no leishmanicidal activity.[12][13] In vivo mouse models (group sizes typically 5–10 per arm) showed enhanced survival and reduced pathogen burden with VIP analogues, suggesting potential for anti‑infective drug development.[12][13]

4. Pulmonary inflammation and inhaled derivatives
   A preclinical study developed an inhalable VIP derivative, [R15,20,21, L17]-VIP‑GRR, as a dry powder and tested it in cigarette smoke‑exposed rats (neutrophilic airway inflammation model).[2] Treatment attenuated airway neutrophilia and inflammatory markers compared with controls (group sizes around 6–10 animals), consistent with anti‑inflammatory actions in the lung.[2]

5. Neuroprotection and neurodegeneration
   PACAP and VIP have shown neuroprotective and neurotrophic effects in models of traumatic brain injury, Parkinsonism, and other neurodegenerative conditions, largely mediated via PAC1/VPAC receptors.[5] While this work focuses primarily on PACAP, VIP displays overlapping receptor activity and has promoted neuronal survival in several acute and chronic injury models.[5]

Human clinical evidence

There is limited direct clinical trial evidence for systemic therapeutic use of native VIP in humans. Short IV infusions of VIP or related peptides have been used predominantly as physiologic probes (e.g., for endocrine, vascular, or migraine studies) rather than as approved therapies.[6][11]

• In migraine research, infusion studies of PACAP‑38 and VIP have been used to dissect pathophysiology. PACAP‑38 reliably induces delayed migraine‑like attacks in a high proportion of patients; VIP primarily causes transient cranial vasodilation with less consistent migraine induction, suggesting differential receptor and circuit involvement.[6]
• Early exploratory studies (small sample sizes, generally <20 participants) investigated VIP effects on cardiac output, pulmonary vasodilation, or pancreatic secretion but did not proceed to late‑phase therapeutic development, largely due to short half‑life and systemic hemodynamic effects.[11]

Most current clinical development efforts focus on synthetic analogues or receptor‑selective ligands, rather than native VIP, and many are in preclinical or early clinical stages.[1][5][11]

Clinical and research uses

Approved uses

As of current evidence, native VIP is not approved as a therapeutic drug in the United States or European Union.[11][14] VIP is, however, widely employed as a research tool in physiology, immunology, and neuroscience.

Investigational and experimental contexts

• Inflammatory and autoimmune diseases: VIP and VPAC‑selective analogues are under investigation preclinically for rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, autoimmune diabetes, and sepsis, based on immunomodulatory actions.[11][15]
• Pulmonary disorders: Inhaled VIP derivatives, including [R15,20,21, L17]-VIP‑GRR, have been studied in animal models of COPD‑like neutrophilic inflammation and may have future relevance for chronic airway diseases.[2]
• Infectious diseases: Stable VIP analogues (VIP51, VIP51(6–30)) are being explored as host‑directed antimicrobial agents, particularly against multidrug‑resistant bacteria and protozoa.[12][13]
• Neurodegenerative and CNS disorders: PACAP/VIP analogues, including glycosylated brain‑penetrant variants, are in preclinical development for traumatic brain injury and Parkinsonism; although these efforts center on PACAP, the shared receptor systems maintain relevance for VIP‑mimetic therapeutics.[5]
• Migraine and headache research: VIP and PACAP infusions are used in experimental paradigms to probe autonomic and nociceptive circuitry in migraine; drug development is currently more advanced for PACAP and its receptors than for VIP itself.[6]

VIP is also implicated in cancer biology (e.g., VIP/VPAC1 signaling in gastrointestinal and other tumors), and VPAC‑targeted agents are under investigation for imaging and therapy, but these are largely at the preclinical or early translational stage.[11][14]

Dosing context

The following dosing information is descriptive of research use only and does not constitute a therapeutic recommendation.

• Intravenous infusion in human physiologic studies: VIP has typically been administered as short IV infusions in the range of approximately 4–8 pmol/kg/min for 20–30 minutes in older endocrine and vascular studies, producing marked vasodilation and changes in cardiac output and intestinal secretion.[11] Exact regimens vary by protocol.
• Preclinical systemic dosing: In rodent inflammatory models, VIP or its analogues are commonly administered intraperitoneally or intravenously at doses on the order of 1–25 nmol/kg, given once or repeatedly over several days, depending on the disease model.[11][15]
• Inhaled VIP derivative in rats: The [R15,20,21, L17]-VIP‑GRR dry powder was delivered via inhalation, with doses calculated to achieve pharmacologically active airway concentrations; specific µg/kg ranges are reported in the original preclinical study but are not directly translatable to humans.[2]
• Antimicrobial VIP analogues: VIP51 and VIP51(6–30) were administered systemically in mouse infection models at doses sufficient to achieve effective antimicrobial exposure (e.g., in the low mg/kg range), but detailed dose‑response relationships remain investigational.[12][13]

Pharmacokinetic limitations of native VIP (rapid clearance, enzymatic degradation) are a primary driver for the development of more stable analogues, depot formulations, and receptor‑selective ligands.[11][12][13]

Safety profile

Common and dose‑limiting effects (from human infusion and preclinical data)

• Vasodilation and cardiovascular effects: Transient flushing, hypotension, tachycardia, and increased cardiac output are prominent during IV infusion in humans, reflecting potent vasodilatory properties.[11]
• Gastrointestinal effects: VIP stimulates intestinal secretion and motility; high levels or VIP‑secreting tumors (VIPomas) cause watery diarrhea, hypokalemia, and achlorhydria (WDHA syndrome), illustrating potential adverse effects of sustained VIP receptor activation.[11][14]

Immunological and infectious considerations

While VIP is broadly anti‑inflammatory, excessive systemic immunosuppression is a theoretical concern for chronic use, given its ability to down‑regulate pro‑inflammatory cytokines and promote regulatory T‑cell responses.[15] Conversely, VIP analogues designed as antimicrobial agents have been engineered to retain or augment direct microbicidal activity without excessive immunosuppression.[12][13]

Preclinical toxicity

Studies of VIP analogues (e.g., VIP51, VIP51(6–30), [R15,20,21, L17]-VIP‑GRR) report acceptable tolerability in rodents at therapeutically active doses, without major organ toxicity on histology, though comprehensive GLP toxicology and long‑term safety data are limited.[2][12][13]

Overall, the safety database in humans for therapeutic‑intent VIP administration is sparse, and most information derives from short‑term physiologic studies rather than chronic disease treatment trials.[11]

Regulatory status

• United States (FDA): Native VIP is not approved as a drug product by the U.S. Food and Drug Administration for any indication. VIP is used in research settings and as a biochemical reagent but has no marketed therapeutic formulation.[11][14]
• European Union (EMA): Similarly, there is no centrally authorized medicinal product containing VIP as an active substance within the European Medicines Agency framework.[11][14]

Several VIP‑related or VPAC‑targeted compounds (including stabilized analogues and receptor‑selective ligands) are at preclinical or early clinical development stages, but these remain investigational and have not received marketing authorization.[1][5][11] The regulatory landscape is currently more advanced for targeted agents against PACAP or its receptors (e.g., in migraine) than for VIP itself.[6]