VIP

Vasoactive Intestinal Peptide (VIP) is an endogenous 28-amino acid neuropeptide belonging to the secretin/glucagon superfamily, produced throughout the central and peripheral nervous systems, immune cells, and gastrointestinal tract. It was initially characterized as a vasodilator and gastrointestinal motility regulator but has since been established as a pleiotropic signaling molecule with potent immunomodulatory, neuroprotective, and autonomic regulatory functions.

VIP signals through three G protein-coupled receptors: VPAC1 (expressed in brain, lung, liver, lymphocytes), VPAC2 (expressed in brain, pancreas, smooth muscle, mast cells), and PAC1 (primarily targeted by PACAP). The wide distribution of these receptors explains VIP's diverse physiological and pathological roles. VIP is an investigational agent with no FDA approval for any therapeutic use; its short plasma half-life (~1-2 minutes) and broad receptor distribution have historically limited clinical development.

VIP exerts its anti-inflammatory effects primarily through VPAC1 receptor engagement in immune cells. Receptor activation stimulates adenylyl cyclase, raises intracellular cAMP, and activates protein kinase A, which inhibits NF-κB nuclear translocation — the master regulator of pro-inflammatory cytokine transcription. This results in suppressed production of TNF-α, IL-1β, IL-6, IL-12, and IL-17, while promoting IL-10 (anti-inflammatory) production. VIP simultaneously induces the generation of induced regulatory T cells (iTreg), suppressing autoimmune Th1 and Th17 responses.

In the nervous system, VIP acts as a neuroprotective neuromodulator. It reduces excitotoxicity, prevents neuronal apoptosis, supports microglial homeostasis, and modulates dopaminergic and cholinergic neurotransmission. Neuroprotective mechanisms involve both direct neuronal VPAC receptor signaling and indirect protection through suppression of neuroinflammatory glial activation.

In the gastrointestinal tract, VIP acts as an inhibitory neurotransmitter, relaxing smooth muscle, promoting secretion from intestinal crypts, and regulating gastrointestinal motility as part of the enteric nervous system.