Vasoactive Intestinal Peptide (VIP) Research: VPAC Receptor Pharmacology, Neuroimmune Signaling, and Preclinical Anti-Inflammatory Evidence

Vasoactive intestinal peptide (VIP) is a 28-residue neuropeptide of the secretin-glucagon superfamily that signals through the VPAC1 and VPAC2 G protein-coupled receptors to raise cAMP, suppress NF-kappaB-driven cytokine production in macrophages and dendritic cells, and generate tolerogenic dendritic cells that induce regulatory T cells. Said and Mutt isolated it from hog small intestine in 1970 as a polypeptide with systemic vasodilator, hypotensive, cardiac, respiratory and hyperglycaemic actions (Said and Mutt, Science, 1970, 169:1217-1218), and vasoactive intestinal peptide (VIP) research has since made it one of the best-characterised endogenous immunomodulators, with receptor pharmacology formalised by the International Union of Basic and Clinical Pharmacology (Harmar et al., British Journal of Pharmacology, 2012, 166:4-17). This overview summarises the receptor biology and the preclinical evidence in inflammation, autoimmunity, lung injury and neurodegeneration, citing the primary paper for each finding.

Molecular Structure and Physicochemical Properties

VIP shares its N-terminal region with PACAP, secretin, glucagon, GIP, GHRH and the GLP peptides. Its sequence, His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Asn-Ser-Ile-Leu-Asn-NH2, matches the specification on our VIP product page, with a molecular weight of about 3326 Da and a net positive charge from its five basic residues against two acidic ones. Couvineau and Laburthe review the structure-function work: the N-terminal ectodomain of the VPAC1 receptor, folded as a Sushi domain, recognises the peptide’s C-terminal helix, while the peptide’s own N-terminal residues drive receptor activation (Couvineau and Laburthe, British Journal of Pharmacology, 2012, 166:42-50). The peptide is largely unstructured in water and becomes helical in membrane-mimetic environments, which is the conformation that docks into the receptor.

Proteolysis is the practical constraint on VIP research. Neutral endopeptidase and dipeptidyl peptidase-4 cleave the native peptide within minutes in circulation, which has driven work on stabilised analogues, and the sequence carries three residues that degrade in the vial as well: methionine 17 oxidises, and asparagine 9 and asparagine 24 can deamidate, with the Asn24-Ser25 site expected on sequence grounds to be the faster of the two. The degradation pathways post explains both reactions.

VPAC1 and VPAC2 Receptor Pharmacology

VIP acts through two class B receptors, VPAC1 and VPAC2, both of which respond to VIP and to PACAP with high affinity, whereas the PAC1 receptor is selective for PACAP (Harmar et al., 2012). In receptor-binding work on the human receptors, the wild-type VPAC1 receptor displayed a high-affinity VIP site near 1 nM and the wild-type VPAC2 receptor an EC50 of about 7 nM for cAMP production, with conserved tyrosines in the first transmembrane helix required to support the active conformation of both (Perret et al., British Journal of Pharmacology, 2002, 136:1042-1048). Both couple predominantly through Gs to adenylyl cyclase. VPAC1 is broadly expressed on macrophages, dendritic cells and T cells, in the gut mucosa, lung, liver and cortex; VPAC2 is concentrated in the suprachiasmatic nucleus, pancreatic islets, smooth muscle and particular immune subsets, and genetic studies implicate it in susceptibility to schizophrenia (Harmar et al., 2012).

Knockout mice have separated the two receptors’ immune roles. Tan and colleagues found that mice lacking the VPAC2 gene developed exacerbated MOG-induced experimental autoimmune encephalomyelitis, with more severe clinical and histopathological disease, higher TNF-alpha, IL-6, interferon-gamma and IL-17 and lower IL-10, TGF-beta and IL-4 in the central nervous system and lymph nodes, strikingly fewer CD4+CD25+FoxP3+ regulatory T cells in lymph node, thymus and CNS, and impaired suppressive activity in the Tregs that remained (Tan et al., Brain, Behavior, and Immunity, 2015, 44:167-175). That study is the source of the VPAC2 and Treg connection; earlier accounts placed it in the Proceedings of the National Academy of Sciences, which is incorrect.

Neuroimmune Signalling: The cAMP-PKA-CREB Axis

Receptor activation raises cAMP, activates protein kinase A and phosphorylates CREB, and in myeloid cells this cascade suppresses NF-kappaB. The founding experiment is Delgado and colleagues’ 1999 study: VIP and PACAP rapidly and specifically inhibited LPS-stimulated TNF-alpha production by murine peritoneal macrophages, acting through the VPAC1 receptor and adenylate cyclase and regulating TNF-alpha at the transcriptional level; the in vitro result was matched by inhibition of TNF-alpha expression and release in endotoxaemic mice, and LPS and the proinflammatory cytokines themselves raised VIP release into serum and peritoneal fluid, suggesting a physiological feedback loop (Delgado et al., Journal of Immunology, 1999, 162:2358-2367). The 2004 Pharmacological Reviews article by Delgado, Pozo and Ganea gathers this and the subsequent work into the argument that VIP functions as a type 2 cytokine (Delgado et al., Pharmacological Reviews, 2004, 56:249-290). Specific percentage reductions in TNF-alpha at stated nanomolar concentrations, previously attributed to that review, are not in its abstract and are not repeated here. Claims about EPAC-dependent effects on blood-brain barrier permeability attributed to a 2018 study in the Journal of Neuroinflammation could not be located and have been removed.

Regulatory T Cell Induction and Immune Tolerance

VIP’s best-documented immunological function is the generation of tolerogenic dendritic cells. In mouse bone marrow-derived cells, Delgado, Gonzalez-Rey and Ganea showed that VIP and PACAP produce dendritic cells that are CD11c-low and CD45RB-high, fail to upregulate CD80, CD86 and CD40 after LPS, and secrete large amounts of IL-10; the effect runs through VPAC1 and protein kinase A and correlates with inhibition of IkappaB phosphorylation and NF-kappaB p65 nuclear translocation. These cells induced functional regulatory T cells in vitro and in vivo that resembled Tr1 cells in phenotype and cytokine profile, suppressed Th1 responses including delayed-type hypersensitivity, and transferred suppression to naive hosts (Delgado et al., Journal of Immunology, 2005, 175:7311-7324). Gonzalez-Rey and colleagues then reproduced the finding with human monocyte-derived cells: VIP present during early differentiation generated IL-10-producing dendritic cells that could not fully mature after inflammatory stimulation and that induced both CD4 Tr1-like and CD8+CD28-CTLA4+ regulatory T cells from naive subsets, primarily suppressing antigen-specific Th1 responses (Gonzalez-Rey et al., Blood, 2006, 107:3632-3638). A 3.5-fold induction ratio and a 65 to 75 percent suppression figure previously attached to the Blood paper are not in its abstract.

The in vivo validation is Delgado’s collagen-induced arthritis study. VIP treatment significantly reduced the incidence and severity of arthritis in the mouse model, completely abrogating joint swelling and the destruction of cartilage and bone, and the effect was associated with downregulation of both the inflammatory and the autoimmune components of the disease (Delgado et al., Nature Medicine, 2001, 7:563-568). Percentage reductions in clinical score and the specific regimen described in earlier versions of this article are not stated in the abstract and are not repeated.

Pulmonary Research Applications

VIP is one of the most abundant neuropeptides in the lung, distributed in airway smooth muscle, vasculature, submucosal glands and epithelium. The classic protection experiment is Berisha and colleagues’ isolated perfused rat lung: adding xanthine and xanthine oxidase raised peak airway and perfusion pressure, produced oedema and increased protein in bronchoalveolar lavage fluid, and VIP at 1 to 10 µg/kg/min markedly reduced or totally prevented every sign of injury while diminishing or abolishing the associated generation of arachidonate products. Catalase gave similar protection; the related peptides secretin and glucagon and the vasodilator papaverine did not, and injured lungs released large amounts of endogenous VIP into the perfusate (Berisha et al., American Journal of Physiology, 1990, 259:L151-L155).

More recent work used lentiviral overexpression in mice. Sun and colleagues found that lentiviral VIP improved respiratory rate, compliance and tidal volume and lowered airway resistance in LPS-induced acute lung injury, reduced inflammatory cell infiltration, preserved alveolar septa, lowered total protein, neutrophil counts and lactate dehydrogenase in bronchoalveolar lavage, decreased TNF-alpha and increased IL-10, with the macrophage TNF-alpha effect running through protein kinase A and protein kinase C (Sun et al., Molecular Immunology, 2018, 97:8-15). Zhou and colleagues then showed that the same approach suppressed NLRP3 inflammasome priming and activation in lung and macrophages, preventing IkappaB degradation, TNF-alpha and IL-17A synthesis, caspase-1 autoproteolysis and IL-1beta and IL-18 secretion (Zhou et al., Biomedicine and Pharmacotherapy, 2020, 121:109596). Percentage figures for neutrophil infiltration and wet-to-dry ratio previously given for this model are not in either abstract.

Neuroprotective Mechanisms and CNS Research

The neuroprotection evidence is the MPTP mouse model, not a 6-hydroxydopamine rat model. Delgado and Ganea reported that VIP treatment significantly decreased MPTP-induced dopaminergic neuronal loss in the substantia nigra pars compacta and nigrostriatal fibre loss, and prevented MPTP-induced microglial activation and the expression of the cytotoxic mediators iNOS, IL-1beta and TNF-alpha in the substantia nigra and striatum (Delgado and Ganea, FASEB Journal, 2003, 17:944-946). The mechanism is microglial deactivation rather than direct neuronal rescue, which is the conceptual basis for later VPAC2-selective analogue work. The percentage preservation of tyrosine hydroxylase-positive neurons, the intracerebroventricular regimen and the rat 6-OHDA design that earlier versions of this article attributed to this literature do not correspond to the published study.

Research Considerations: Stability, Storage and Handling

VIP’s proteolytic sensitivity and its methionine and asparagine content set the handling rules. Store lyophilized VIP at -20 °C or below, protected from light and moisture, and minimise headspace oxygen. Once reconstituted, aliquot into single-use volumes and freeze once rather than reopening a vial. As a cationic peptide, VIP dissolves readily in water or dilute acetic acid; if it must be held in a neutral buffer for an assay, prepare that dilution at the time of use. The storage and handling post covers the general chemistry.

The certificate matters more for VIP than for a short stable peptide, because a methionine sulfoxide or a deamidated asparagine can be present at the point of sale and will change receptor affinity. HPLC should show the measured purity of the specific batch with degradation peaks resolved, and mass spectrometry should confirm the expected mass near 3326 Da. At Maple Research Labs, independent third-party laboratory reports for tested batches are published in full on the Certificates of Analysis page, which also lists the compounds still awaiting a certificate, so a researcher can check the measured HPLC-UV purity of a specific lot before ordering.

Connections to the Broader Research Peptide Landscape

VIP’s receptor-mediated immunosuppression contrasts with the cytoprotective mechanisms of BPC-157, which acts through nitric oxide modulation and VEGFR2-dependent angiogenesis rather than cAMP-PKA signalling, and its neuroimmune profile intersects with work on Selank, a tuftsin-derived peptide with documented anxiolytic activity in preclinical models. In the pancreas, VIP’s stimulation of insulin secretion connects conceptually to the incretin mechanisms studied for semaglutide and tirzepatide, though through a different receptor family within the same class B superfamily.

Summary of Key Research Findings

VIP is a 28-residue amidated peptide acting at VPAC1 and VPAC2 receptors with nanomolar affinity to raise cAMP. It inhibits LPS-induced TNF-alpha transcription in macrophages through VPAC1 in vitro and in endotoxaemic mice (Delgado 1999), generates IL-10-producing tolerogenic dendritic cells that induce Tr1-like CD4 and CD8 regulatory T cells in mouse and human systems (Delgado 2005; Gonzalez-Rey 2006), prevents collagen-induced arthritis with abrogation of joint destruction (Delgado 2001), protects isolated rat lungs from oxidant injury (Berisha 1990), attenuates LPS-induced acute lung injury and NLRP3 inflammasome activation when overexpressed in mice (Sun 2018; Zhou 2020), and reduces MPTP-induced dopaminergic loss by blocking microglial activation (Delgado and Ganea 2003). VPAC2 deletion exacerbates EAE and depletes regulatory T cells (Tan 2015). Canadian researchers can access VIP and related immunomodulatory peptides through Maple Research Labs, with same-day processing from our Canadian facility and independent batch reports published on the Certificates of Analysis page where testing is complete.

Vasodilatory signalling and antifibrotic signalling frequently appear in the same disease models. Relaxin-2 and RXFP1 receptor research examines a peptide studied for both, with preclinical endpoints in vascular tone and in collagen turnover.

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For peer-reviewed research on this topic, visit PubMed.