Vasoactive Intestinal Peptide (VIP)Mechanism, Evidence, and Clinical Research

Vasoactive intestinal peptide has the most misleading name in peptide pharmacology. It is neither primarily vasoactive nor primarily intestinal. What VIP actually does is orchestrate immune tolerance: programming dendritic cells to generate regulatory T cells, shifting macrophages from inflammatory to reparative states, and maintaining gut barrier integrity.

The receptor biology explains why this is not just another anti-inflammatory. VIP operates through two receptor subtypes (VPAC1 and VPAC2) that switch depending on immune activation state. VPAC1 on resting cells dampens acute inflammation. VPAC2 on activated T cells drives long-term tolerance programming. This is the difference between a fire extinguisher and an architect: VPAC1 puts out the fire; VPAC2 redesigns the building so it does not catch fire again.

VIP has accumulated more human trial data than most peptides in active research — including a 471-patient Phase 3 trial. That trial (IV delivery in COVID-19 ARDS) was stopped for futility, but Phase 2 data with inhaled and nebulized delivery showed positive results. VIP's plasma half-life is approximately one minute, making IV bolus dosing pharmacokinetically irrational. The Phase 3 "failure" is better understood as a delivery route problem than a drug problem.

What Is Vasoactive Intestinal Peptide?

Vasoactive intestinal peptide (VIP) is a 28-amino-acid neuropeptide whose name describes its least important modern function. It has accumulated more human trial data than most peptides in active research — including a 471-patient Phase 3 trial, multiple Phase 2 RCTs, and large observational cohorts — yet remains one of the least discussed outside specialist circles.

Discovered in 1970 as a vasodilator isolated from porcine gut, VIP is now understood as an immune tolerance orchestrator — binding two distinct receptor subtypes to regulate dendritic cell programming, regulatory T cell expansion, gut barrier integrity, and circadian clock synchronization across the central and peripheral nervous systems.

The misleading name persists because naming conventions in endocrinology freeze to the first observed function. VIP was isolated from intestinal extracts and it dilated blood vessels, so it became the vasodilator of gut physiology. But the molecule is neither primarily vasoactive nor primarily intestinal. VIP is expressed throughout the central nervous system, the enteric nervous system, the thymus, lung tissue, and immune organs. It belongs to the secretin-glucagon superfamily alongside PACAP (pituitary adenylate cyclase-activating peptide), sharing structural homology that hints at deep evolutionary conservation of its signaling architecture.

The receptor biology that emerged after 2005 — VPAC1 and VPAC2 differential expression, receptor switching during immune activation, tolerogenic dendritic cell generation — genuinely supersedes the vasodilator identity. What follows is a mechanism-first account of VIP's actual function, grounded in the receptor biology, immune programming, and clinical trial data that define its modern relevance.

VPAC1 and VPAC2: The Receptor Biology Behind VIP

VIP acts through two G-protein coupled receptors — cell-surface proteins that receive the VIP signal and translate it into intracellular action — with distinct immune roles. VPAC1, expressed constitutively on resting T cells, monocytes, and neutrophils, drives acute anti-inflammatory signaling.

VPAC2 is upregulated upon T cell activation while VPAC1 simultaneously downregulates — a receptor switching mechanism that shifts VIP's function from inflammation control to regulatory T cell expansion and long-term immune tolerance.¹ ²

This switching is the mechanistic proof that VIP is more than a generic anti-inflammatory signal. On resting immune cells, VPAC1 dominates. VIP binding to VPAC1 on macrophages and monocytes suppresses pro-inflammatory cytokine output — TNF-alpha, IL-6, IL-12 — through a signaling cascade where cAMP/PKA activation drives CREB to compete with NF-kB for the shared transcriptional coactivator CBP, while simultaneously stabilizing IkB/NF-kB complexes to prevent nuclear translocation.³ The net effect is rapid dampening of innate inflammatory responses.

When T cells activate — through antigen recognition, anti-CD3/CD28 stimulation, or inflammatory signaling — VPAC1 expression drops and VPAC2 expression rises.² This is not a passive shift. VPAC2 on activated T cells drives a fundamentally different program: expansion and maintenance of CD4+CD25+FoxP3+ regulatory T cells. VPAC2-knockout mice develop exacerbated experimental autoimmune encephalomyelitis (EAE) with strikingly reduced Treg abundance in lymph nodes, thymus, and CNS tissue, and their remaining Tregs show impaired suppressive function.¹ The loss of a single receptor subtype produces systemic autoimmune escalation.

Human mast cells express only VPAC2. Resting monocytes and neutrophils express only VPAC1. This tissue-specific receptor distribution means VIP does not deliver a uniform signal — it delivers context-dependent instructions calibrated to the activation state of each immune cell population it encounters.

The receptor switching mechanism converts vasoactive intestinal peptide from an acute-phase anti-inflammatory molecule into a long-term tolerance programmer — the difference between a fire extinguisher and an architect. VPAC1 puts out the fire; VPAC2 redesigns the building so it does not catch fire again. This temporal regulation is what makes the "immune tolerance orchestrator" framing accurate rather than rhetorical.

Immune Tolerance Orchestration

VIP generates tolerogenic dendritic cells characterized by low costimulatory molecule expression (CD40, CD80, CD86), low pro-inflammatory cytokine output, and high IL-10 production. It induces both CD4+ and CD8+ regulatory T cells with a distinctive CD28-negative/CTLA4-positive phenotype, shifts macrophages from pro-inflammatory M1 to reparative M2 polarization, and downregulates toll-like receptor expression through transcription factor inhibition. This coordinated immune reprogramming — not simple inflammation suppression — defines VIP's functional identity.³ ⁴ ⁵

The distinction matters. Anti-inflammatory agents reduce inflammatory output. VIP reprograms the cells that generate and sustain immune responses.

Tolerogenic Dendritic Cell Generation

When VIP is present during the early differentiation of monocytes into dendritic cells, the resulting DCs acquire a tolerogenic profile. Surface expression of costimulatory molecules CD40, CD80, and CD86 remains low. Pro-inflammatory cytokine secretion drops. IL-10 output increases substantially.⁴ ⁵ These tolerogenic DCs do not simply fail to activate T cells — they actively generate regulatory T cells. Both CD4+ Tregs and, notably, CD8+ Tregs emerge from co-culture with VIP-conditioned dendritic cells. The CD8+ regulatory population displays a CD28-negative/CTLA4-positive surface phenotype and produces IL-10, suppressing allogeneic immune responses in functional assays.⁴

This tolerogenic DC pathway is VPAC1-mediated, driven by cAMP/PKA signaling that inhibits NF-kB activation at two levels: CREB competition for CBP cofactor binding, and stabilization of cytoplasmic IkB/NF-kB complexes.³

Macrophage Polarization

VIP biases macrophage differentiation from the classically activated M1 phenotype — high TNF-alpha, IL-1beta, IL-12, reactive oxygen species — toward the alternatively activated M2 phenotype associated with tissue repair, debris clearance, and resolution of inflammation. This is not suppression of macrophage function. It is redirection: the macrophage shifts from attack mode to repair mode while remaining functionally active.

TLR Downregulation

VIP reduces expression of toll-like receptors TLR-2 and TLR-4 on colonic tissue and mesenteric lymph node immune cells through inhibition of the PU.1 transcription factor.³ TLRs are pattern recognition receptors that detect microbial components and initiate inflammatory cascades. By reducing TLR density, VIP raises the activation threshold — the immune system becomes less reactive to commensal bacterial signals that would otherwise trigger inappropriate inflammation. This mechanism is particularly relevant at mucosal surfaces where the immune system must tolerate trillions of commensal organisms while remaining responsive to genuine pathogens.

The integration of these effects — tolerogenic DCs generating Tregs, macrophages redirected toward repair, TLR expression reduced at mucosal barriers — represents coordinated tolerance programming across multiple immune cell lineages. Calling VIP "anti-inflammatory" captures one consequence while missing the architecture. Thymosin Alpha-1 operates in a complementary register, supporting thymic T cell education and Treg homeostasis through distinct receptor systems.

VIP and the Gut-Brain-Immune Axis

VIP occupies a structurally unique position at the intersection of gut barrier integrity, vagal tone, and microbiome composition. VIP-deficient mice develop distorted crypt architecture, reduced goblet cell numbers, and restructured gut microbiota. Recent evidence shows feeding-triggered VIP release from enteric neurons activates innate lymphoid cells, linking nutritional status directly to mucosal immune surveillance — a mechanism with no parallel in other peptide systems studied to date.⁶ ⁷

Barrier Integrity

The enteric nervous system is the largest source of VIP in the body, with VIP-positive neurons densely distributed throughout the submucosal and myenteric plexuses. VIP-knockout mice demonstrate what happens when this signaling disappears: crypt architecture distorts, goblet cell populations decline, epithelial turnover becomes defective, and intestinal permeability increases.⁶ These animals develop more severe colitis when challenged with inflammatory stimuli, and exogenous VIP administration rescues the phenotype — preserving colonic structure and barrier function.⁸ ⁹

The mechanism involves both direct epithelial effects — enhanced tight junction assembly, stimulated mucus secretion — and indirect immune effects. VIP signaling recruits protective innate lymphoid cells to the gut mucosa and maintains the tolerogenic immune environment described above. Barrier integrity and immune tolerance are not separate functions in this context. They are two outputs of the same signaling axis.

BPC-157 operates on overlapping gut barrier targets through distinct receptor pathways, supporting epithelial restitution and angiogenesis at sites of mucosal injury.

The VIP-Microbiome Axis

VIP deficiency restructures gut microbiota composition. VIP-knockout mice show altered Firmicutes-to-Bacteroidetes ratios, reduced microbial biodiversity, and significant weight loss.⁶ This finding positions VIP not merely as a barrier maintenance signal but as a regulator of the microbial ecosystem itself — likely through its effects on mucus secretion, epithelial turnover, and the immune environment that determines which bacterial populations thrive at the mucosal surface.

Feeding-Responsive Immune Activation

A 2022 study in Mucosal Immunology demonstrated that enteric neurons release VIP in direct response to feeding, and this VIP release potentiates effector cytokine production by type 2 and type 3 innate lymphoid cells (ILC2 and ILC3).⁷ The functional consequence: feeding activates mucosal immune surveillance. Nutritional status couples directly to innate immune readiness through VIP as the intermediary signal. This mechanism increased resistance to both helminth and enterobacterial infection in experimental models, suggesting VIP links metabolic input to mucosal defense in real time.

How to Increase VIP Naturally

Feeding-triggered VIP release from enteric neurons represents the most directly supported endogenous stimulus.⁷ Regular circadian light exposure supports SCN VIP expression. Vagal tone exercises — controlled breathing, cold exposure protocols — activate parasympathetic pathways where VIP functions as a co-transmitter. These approaches support endogenous VIP signaling but cannot substitute for exogenous administration in states where VIP production or receptor responsiveness is fundamentally compromised. The distinction between supporting a functional system and replacing a deficient one is clinically meaningful.

Circadian Synchronization: VIP and the SCN Clock

VIP functions as the primary synchronizing neuropeptide in the suprachiasmatic nucleus (SCN), the brain's master circadian clock. VIP-expressing neurons coordinate firing patterns across SCN cell populations and align peripheral tissue clocks with the central light-dark cycle. Without VIP signaling, individual SCN neurons lose synchrony and circadian output fragments.

This positions VIP as a Tier 3 circadian intervention in research contexts — relevant after foundational behavioral strategies (light timing, meal timing, sleep hygiene) and sleep architecture support are established. The circadian reset protocol covers the full tiered framework for restoring circadian coherence, with VIP positioned in the clock-hardening tier. The circadian role is mechanistic and well-characterized in animal models, but human circadian intervention trials with exogenous VIP have not been conducted. The evidence supporting VIP's SCN function is strong; the evidence supporting its use as a circadian therapeutic in humans is extrapolated from that mechanism.

AM timing of VIP administration in research protocols reflects the rationale of reinforcing the morning cortisol peak and immune cycling that the SCN coordinates. NAD+ and the mitochondrial peptide stack operate in a complementary circadian register, providing the metabolic amplitude that sustains robust day-night oscillation.

Clinical Evidence: What the Human Trials Actually Show

Human evidence for vasoactive intestinal peptide spans respiratory failure trials, chronic lung disease studies, CIRS cohorts, and observational biomarker data — a broader clinical evidence base than most peptides in current research. The data tell a complex and editorially honest story: large trials that missed primary endpoints alongside smaller trials with clear positive signals, and route of administration emerging as a variable that may matter more than the molecule itself.

COVID-19 and Respiratory Failure

The largest VIP trial to date — TESICO (NCT04843761) — enrolled 471 patients with COVID-19-associated respiratory failure and randomized them to intravenous aviptadil (the synthetic form of VIP) or placebo. The trial was stopped for futility. There was no significant difference in time to recovery or 90-day mortality.¹⁰

A separate Phase 2b/3 trial (NCT04311697) enrolled 196 patients. The primary endpoint — recovery from respiratory failure — did not reach statistical significance. However, a pre-specified subgroup analysis showed a statistically significant increase in 60-day survival with an odds ratio of 2.0, alongside reduced IL-6 levels.¹⁰

An 80-patient Phase 2 randomized controlled trial of inhaled aviptadil told a different story entirely. Inhaled VIP significantly reduced hospital stay (7.8 versus 10 days), improved blood oxygenation, and showed superior radiological scores compared to placebo.¹¹ A separate case series of 6 patients with severe viral ARDS (influenza and COVID-19) treated with intravenous aviptadil showed significant improvement in oxygenation (PaO2/FiO2 ratio) and radiological clearance within 3 days.¹⁸

The divergence between IV and inhaled routes is the most instructive finding across these trials. Intravenous VIP has a plasma half-life of approximately one minute — rapid enzymatic degradation limits systemic exposure. Inhaled delivery concentrates the molecule at the pulmonary epithelium, where VPAC receptors are densely expressed and where the anti-inflammatory and cytoprotective effects are most needed. The TESICO futility stop does not invalidate VIP's pulmonary biology. It may demonstrate that route of administration, timing, and patient selection determine whether a validated mechanism translates to clinical benefit.

The Long COVID context underscores this. Post-viral autonomic instability, persistent inflammation, and immune dysregulation — the hallmarks of Long COVID — map directly onto VIP's mechanism of action. Yale explored VIP nasal protocols specifically for these autonomic and inflammatory clusters. Meanwhile, parallel institutional work on NAD+ restoration (Mass General Brigham, NCT04809974) and Thymosin Alpha-1 immune reconstitution (University of Rome "Tor Vergata") addressed overlapping pathways in the same patient population — illustrating why systems biology interventions require multi-target approaches rather than single-molecule trials.

Sarcoidosis

A Phase II trial enrolled 20 patients with pulmonary sarcoidosis and administered nebulized VIP over 4 weeks. The intervention was safe, significantly reduced TNF-alpha production by bronchoalveolar lavage macrophages, and increased CD4+CD25+FoxP3+ regulatory T cells — the first demonstration of VIP's immunoregulatory effect in a controlled human trial.¹² This study directly validated the tolerogenic mechanism described above: VIP shifted the lung immune environment from inflammatory to regulatory.

Pulmonary Hypertension

In a study of 20 patients with pulmonary arterial hypertension, inhaled VIP produced significant temporary pulmonary vasodilation and decreased right heart load without systemic side effects. Extended treatment over 3-6 months reduced mean pulmonary artery pressure from 59 to 46 mmHg and increased cardiac output — hemodynamic improvements with direct functional significance.¹⁹

CIRS and Mold Illness

An 18-month open-label trial administered VIP nasal spray to 20 patients with chronic inflammatory response syndrome (CIRS) refractory to other interventions. Inflammatory markers — TGF-beta1, C4a, MMP-9 — normalized. NeuroQuant MRI showed structural brain improvements. Regulatory T cell levels increased.¹³

A larger observational cohort of over 10,000 patients treated with VIP nasal spray for CIRS has been reported with consistent inflammatory marker normalization and symptom improvement. This dataset comes from a single practitioner-researcher without independent replication or randomized controlled trial validation. The cohort size is notable; the methodological limitations are equally notable. Both facts belong in any honest assessment.

Observational and Biomarker Data

In a study of 283 COPD patients, serum VIP levels were elevated during acute exacerbations — consistent with a counter-regulatory release pattern where the body upregulates VIP in response to inflammatory stress.¹⁶ In inflammatory bowel disease, rectal biopsies show increased VIP-containing nerve fibers, and plasma VIP correlates with disease activity, suggesting endogenous VIP signaling intensifies as a compensatory mechanism during gut inflammation.¹⁶

Despite strong preclinical data in TNBS colitis models — where VIP reduced clinical severity, downregulated TNF-alpha/IL-6, and promoted epithelial repair⁸ ⁹ — no human efficacy trials for VIP in IBD have been completed. The fundamental barrier is pharmacokinetic: free VIP degrades too rapidly for systemic dosing, and the dose-limiting hypotension associated with intravenous administration prevents dose escalation.

Nanomedicine approaches (VIP-SSM sterically stabilized micelles) have shown superior efficacy at lower doses in animal models while eliminating hypotensive toxicity,¹⁴ but these remain preclinical. KPV addresses mucosal inflammation through a complementary NF-kB inhibition pathway with more favorable oral bioavailability characteristics.

VIP Nasal Spray: Delivery, Dosing Context, and Safety

Vasoactive intestinal peptide is most commonly administered via intranasal spray in research contexts, typically at 50-100 mcg per dose. The VIP nasal spray route provides direct CNS access through the olfactory and trigeminal nerve pathways while avoiding the rapid systemic degradation that limits intravenous efficacy. Free vasoactive intestinal peptide has a plasma half-life of approximately one minute. Research dosing typically begins at the lower range with gradual titration. VIP is not FDA-approved for any clinical indication.

Route Rationale

The pharmacokinetic challenge defines VIP's delivery landscape. A one-minute plasma half-life makes oral and standard intravenous administration impractical for sustained effect. Intranasal delivery bypasses first-pass hepatic metabolism, concentrates the molecule at CNS-proximal tissue, and allows titration from low initial doses. Subcutaneous administration (25-50 mcg AM dosing in circadian research contexts) represents an alternative route studied in protocol settings.

Nanomedicine delivery systems are advancing. VIP-SSM (sterically stabilized phospholipid micelles) demonstrated superior efficacy at 0.25 nmol single doses compared to free peptide in colitis models, while eliminating hypotensive toxicity.¹⁴ An oral colonic capsule formulation has shown feasibility in preclinical studies.¹⁵ Neither is clinically available.

Safety Profile

The safety profile from published trials is generally favorable at intranasal doses. Mild transient flushing is the most commonly reported effect. At higher systemic doses (intravenous administration), dose-limiting hypotension and tachycardia occur — consistent with VIP's vasodilatory activity at supratherapeutic plasma concentrations. No dependency or withdrawal phenomena have been reported across published datasets. The sarcoidosis Phase II trial reported no serious adverse events with nebulized VIP over 4 weeks.¹²

VIP can increase susceptibility to intracellular pathogens through its immunomodulatory effects — a theoretical consideration documented in preclinical Salmonella models.³ This is mechanistically consistent: a molecule that biases immune responses toward tolerance necessarily reduces some aspects of pathogen-directed immunity.

VIP Blood Testing

Serum VIP testing is available through standard reference laboratories. Elevated VIP suggests VIPoma (a rare neuroendocrine tumor) or counter-regulatory release during active inflammation. Low VIP levels in the context of chronic inflammatory symptoms are observed in CIRS cohorts and form part of the Shoemaker diagnostic panel alongside MSH, C4a, TGF-beta1, MMP-9, and VEGF. Proper specimen handling requires plasma collection on ice with rapid processing — VIP degrades quickly ex vivo, and mishandled specimens produce falsely low results.

Regulatory status: VIP (aviptadil) is not FDA-approved for CIRS, mold illness, circadian rhythm disorders, immune modulation, IBD, pulmonary hypertension, or any clinical indication. All dosing ranges cited in this article reflect ranges reported in published literature and are illustrative, not prescriptive. Selank offers a complementary approach to autonomic rebalancing through distinct anxiolytic and immunomodulatory pathways with established safety data.

Evidence Hierarchy: What Is Proven, Plausible, and Speculative

Vasoactive intestinal peptide's evidence base spans a wider range of human data than most peptides in active research. Organizing that evidence by strength — rather than presenting it as uniformly promising or uniformly preliminary — is the only honest approach.

Tier 2 — Controlled human data with clear signals:

Pulmonary immune modulation holds the strongest position. The sarcoidosis Phase II trial demonstrated TNF-alpha reduction and Treg expansion in 20 patients with nebulized VIP.¹² Pulmonary hypertension studies showed significant hemodynamic improvement over 3-6 months.¹⁹ Inhaled aviptadil reduced hospital stay in an 80-patient COVID-19 RCT.¹¹ These represent replicated human signals across distinct pulmonary conditions, all using inhaled or nebulized delivery.

CIRS inflammatory marker normalization has Tier 2 observational data: an 18-month open-label trial with biomarker endpoints and a large cohort with consistent findings.¹³ The single-center, single-practitioner limitation must be stated directly. Independent replication with randomized controlled methodology has not occurred.

Tier 2 with important caveats — Large trials with mixed outcomes:

The COVID-19 IV aviptadil data occupy an unusual position. TESICO (471 patients) stopped for futility. The Phase 2b/3 (196 patients) missed its primary endpoint but showed a 60-day survival signal (OR 2.0). These are not failures of the molecule's biology — they may be failures of route selection and patient timing. The contrast with positive inhaled data supports this interpretation but does not confirm it.

Tier 3 — Strong mechanism, limited or no human efficacy data:

IBD application has one of the strongest preclinical rationales of any peptide studied in colitis models.⁸ ⁹ VIP reduced severity in TNBS-induced colitis, downregulated inflammatory cytokines, and promoted epithelial repair. No human efficacy trial has been completed. The pharmacokinetic barrier — rapid degradation, dose-limiting hypotension — is fundamental, not merely technical.

Circadian synchronization is mechanistically well-established in animal SCN physiology but untested in human circadian intervention trials. Gut barrier and microbiome effects derive from knockout mouse phenotyping and feeding-response studies — high-quality preclinical data that has not been evaluated in human subjects.

The translational lesson:

VIP illustrates why strong mechanism can fail to translate — and why the failure can be instructive rather than terminal. The TESICO result does not mean VIP lacks pulmonary anti-inflammatory activity. It may mean that intravenous delivery of a peptide with a one-minute half-life to critically ill patients was the wrong route, wrong timing, or wrong population. The positive inhaled data suggest the biology is sound when the delivery matches the target. This distinction — between mechanism failure and translational failure — is underappreciated in peptide research and deserves more rigorous study across every compound in this class. For how compounds with distinct mechanisms are combined across functional axes, see the peptide stacking guide.

Frequently Asked Questions

Related Topics

• Circadian Reset Protocol — VIP synchronises the master clock as the morning anchor
• Immune Peptide Protocol — VIP is the optional Phase 2 tolerance orchestrator
• Injury Recovery Protocol — VIP for disc and spinal degeneration recovery
• Selank Guide — Evening anxiolytic paired with VIP's morning clock role
• DSIP Guide — nighttime sleep architecture that follows VIP's daytime synchronisation

References

¹ VPAC2 and Treg expansion — VPAC2-knockout mice develop exacerbated autoimmune disease with reduced Treg abundance and impaired suppressive function: Tan YV, Abad C, Lopez R, et al. J Immunol. 2015;194(1):31-40. PubMed 25305591

² Receptor switching on T cell activation — Th lymphocyte activation alters VPAC1/VPAC2 expression pattern and cellular location: Juarranz Y, Gutierrez-Canas I, Carrion M, et al. Sci Rep. 2019;9(1):7016. PMC6517580

³ VIP immunomodulation of innate immunity — Comprehensive review of VIP's anti-inflammatory mechanisms including cAMP/PKA/CREB pathway, NF-kB inhibition, TLR downregulation, and Salmonella susceptibility: Smalley SG, Barrow PA, Foster N. Brain Behav Immun. 2009;23(6):1361-1370. PMC2730848

⁴ Tolerogenic DCs and CD4/CD8 Tregs — VIP generates human tolerogenic dendritic cells that induce both CD4+ and CD8+ regulatory T cells: Gonzalez-Rey E, Chorny A, Fernandez-Martin A, et al. Blood. 2006;107(9):3632-3638. PubMed 16397133

⁵ Regulatory DCs in autoimmune disorders — VIP induces regulatory dendritic cells with therapeutic effects on autoimmune disorders: Chorny A, Gonzalez-Rey E, Fernandez-Martin A, et al. J Immunol. 2005;175(11):7271-7280. PubMed 16301637

⁶ VIP deficiency and gut microbiota — VIP-knockout mice show altered microbiota communities, distorted crypt architecture, and reduced goblet cells: Bains M, Laney C, Wolfe AE, et al. Front Microbiol. 2019;10:2689. PMC6900961

⁷ Feeding-dependent VIP-ILC circuit — Enteric neuron VIP release in response to feeding activates ILC3 and regulates intestinal barrier: Talbot J, Hahn P, Kroehling L, et al. Mucosal Immunol. 2022;15(6):1111-1120. PubMed 35501356

⁸ VIP in TNBS colitis (Crohn's model) — Therapeutic effects of VIP in trinitrobenzene sulfonic acid mouse model of Crohn's disease: Abad C, Martinez C, Juarranz MG, et al. Gastroenterology. 2003;124(4):961-971. PubMed 12671893

⁹ TNBS colitis cytokine analysis — cDNA array analysis of cytokines and receptors in TNBS-induced colitis; homeostatic role of VIP: Abad C, Juarranz Y, Martinez C, et al. Inflamm Bowel Dis. 2005;11(7):674-684. PubMed 18667799

¹⁰ TESICO and Phase 2b/3 COVID-19 trials — TESICO (NCT04843761): 471-patient Phase 3, IV aviptadil, stopped for futility: Youssef JG, et al. NIH/ACTIV-3b trial. PubMed 37348524. Phase 2b/3 (NCT04311697): 196 patients, primary endpoint not met, pre-specified 60-day survival signal OR 2.0: Youssef JG, et al. PubMed 35142163

¹¹ Inhaled aviptadil COVID-19 RCT — 80-patient Phase 2 RCT of inhaled aviptadil; reduced hospital stay 7.8 vs 10 days, improved oxygenation and radiological scores vs placebo. NeuroRx/Relief Therapeutics data.

¹² Sarcoidosis Phase II — Inhaled VIP exerts immunoregulatory effects in sarcoidosis; 20 patients, reduced TNF-alpha, increased Tregs: Prasse A, Zissel G, Lutzen N, et al. Am J Respir Crit Care Med. 2010;182(4):540-548. PubMed 20442436

¹³ CIRS open-label trial — VIP nasal spray corrects CIRS biomarkers in 20 patients over 18 months; TGF-beta1, C4a, MMP-9 normalization: Shoemaker RC, House D, Ryan JC. Health. 2013;5(3):396-401.

¹⁴ VIP nanomedicine for IBD — VIP-SSM sterically stabilized micelles; superior efficacy at lower doses, eliminates hypotensive toxicity: Jayawardena D, Anbazhagan AN, Guzman G, et al. Mol Pharm. 2017;14(11):3698-3708. PubMed 28991483

¹⁵ Oral colonic VIP delivery — Colonic delivery of VIP nanomedicine alleviates colitis with enhanced bioadhesion: Vu TT, Ilio KY, Bhatt H, et al. J Control Release. 2020;328:278-291. PMC7713900

¹⁶ VIP pleiotropic immune functions — Comprehensive review covering VIP in COPD, IBD biomarker data, and immune regulation: Delgado M, Ganea D. Amino Acids. 2013;45(1):25-39. PMC3883350

¹⁷ VIP in allergic diseases — Role of VIP in allergic disease contexts and immune modulation: Verma AK, Manohar M, Mishra A. Cytokine Growth Factor Rev. 2017;38:37-48. PMC5705463

¹⁸ Viral ARDS case series — 6 patients with severe viral ARDS treated with IV aviptadil; significant oxygenation improvement and radiological clearance within 3 days. Data incorporated into the Phase 2b/3 trial from early expanded access protocols: Youssef JG, et al. VIP (Aviptadil) improves survival in patients with critical COVID-19 and respiratory failure. PubMed 35142163

¹⁹ Pulmonary hypertension — 20 patients with PAH; inhaled VIP produced pulmonary vasodilation without systemic effects; 3-6 month treatment reduced mean PA pressure from 59 to 46 mmHg: Petkov V, et al. J Clin Invest. 2003;111(9):1339-1346. PubMed 12727926