VIP (Vasoactive Intestinal Peptide) Research & Studies

The amygdaloid complex, also known as the amygdala, is a heterogeneous group of distinct nuclear and cortical pallial and subpallial structures. The amygdala plays an important role in several complex functions including emotional behavior and learning. The expression of calcium-binding proteins and peptides in GABAergic neurons located in the pallial and subpallial amygdala is not uniform and is sometimes restricted to specific groups of cells. Vasoactive intestinal polypeptide (VIP) is present in specific subpopulations of GABAergic cells in the amygdala. VIP immunoreactivity has been observed in somatodendritic and axonal profiles of the rat basolateral and central amygdala. However, a comprehensive analysis of the distribution of VIP immunoreactivity in the various pallial and subpallial structures is currently lacking. The present study used immunohistochemical and morphometric techniques to analyze the distribution and the neuronal localization of VIP immunoreactivity in the rat pallial and subpallial amygdala. In the pallial amygdala, VIP-IR neurons are local inhibitory interneurons that presumably directly and indirectly regulate the activity of excitatory pyramidal neurons. In the subpallial amygdala, VIP immunoreactivity is expressed in several inhibitory cell types, presumably acting as projection or local interneurons. The distribution of VIP immunoreactivity is non-homogeneous throughout the different areas of the amygdaloid complex, suggesting a distinct influence of this neuropeptide on local neuronal circuits and, consequently, on the cognitive, emotional, behavioral and endocrine activities mediated by the amygdala.

Polycystic ovary syndrome (PCOS) is a common multifactorial and polygenic disorder of the endocrine system, affecting up to 20% of women in reproductive age with a still unknown etiology. Follicular fluid (FF) represents an environment for the normal development of follicles rich in metabolites, hormones and neurotransmitters, but in some instances of PCOS the composition can be different. Vasoactive intestinal peptide (VIP) is an endogenous autonomic neuropeptide involved in follicular atresia, granulosa cell physiology and steroidogenesis.

We compared the effect of VIP on human blood monocytes infected with Salmonella typhimurium 4/74 or stimulated with LPS. VIP (10(-7)M) increased monocyte viability by 24% and 9% when cultured for 24h with 4/74 or Salmonella LPS (100ng/ml), respectively. Significantly increased (P<0.05) numbers of 4/74 were also recovered from monocytes co-cultured with VIP after 6h post-infection (pi) and this remained high after 24h pi. Both 4/74 and LPS increased (P<0.05) the concentration of TNF-α, IL-1β and IL-6 measured in monocyte supernatants. However, LPS induced this effect more rapidly while, with the exception of IL-6, 4/74 induced higher concentrations (P<0.05). VIP significantly decreased (P<0.05) TNF-α and IL-1β production by 4/74-infected monocytes after 6 pi, but only after 24h in LPS-cultured monocytes. This trend was reversed for IL-6 production. However, TNF-α and IL-1β production by 4/74-infected monocytes, cultured with VIP, still remained higher (P<0.05) than concentrations measured in supernatants cultured only with LPS. VIP also increased (P<0.05) production of anti-inflammatory IL-10 in both 4/74 and LPS cultures after 24h. We also show a differential effect of VIP on the expression of TNFα and IL-6 receptors, since VIP was only able to decreased expression in LPS-stimulated monocytes but not in 4/74-infected monocytes. In conclusion, we show a differential effect of VIP on human monocytes infected with virulent Salmonella or stimulated with LPS. Our study suggests that the use of VIP in bacteraemia and/or sepsis may be limited to an adjunctive therapy to antibiotic treatment.

Neuropeptides are potentially valuable tools for clinical applications as they offer many distinct advantages over other bioactive molecules like proteins and monoclonal antibodies due to their reduced side effects and simple chemical modifications. Despite such advantages, the difficulty with neuropeptides often relies on their poor metabolic stability and reduced biological activity intervals. Among the neuropeptides, VIP has been identified as a potentially bioactive agent for inflammatory, neurodegenerative, and cancer-related diseases. However, the effective translation of preclinical studies related to VIP to clinical realities faces several major challenges, most of which are commonplace for other neuropeptides. Here, we present recent studies aimed at developing nanostructured organic and inorganic systems either for the appropriate delivery of VIP or for VIP targeting. These technologies stand as an alternative starting point for chemical manipulations of the neuropeptides in order to improve potency, selectivity, or pharmacokinetic parameters.

The parasympathetic transmitter vasoactive intestinal peptide (VIP) increases salivary gland blood flow and evokes protein secretion and, in some species, such as rats, a small fluid secretion. It interacts synergistically with muscarinics for protein and fluid output. Human salivary acini are supplied with VIP-containing nerves. We hypothesise that VIP and clozapine, acting together, evoke a volume of saliva greater than the sum of those induced by each drug given separately. It was further considered whether, in the current test situation, circulatory events influenced the magnitude of the secretory response.

Background and purpose The origin of migraine pain is still elusive, but increasingly researchers focus on the neuropeptides in the perivascular space of cranial vessels as important mediators of nociceptive input during migraine attacks. The parasympathetic neurotransmitters, pituitary adenylate cyclase activating peptide-38 (PACAP38) and vasoactive intestinal peptide (VIP) may be released from parasympathetic fibres and activate sensory nerve fibres during migraine attacks. Triptans are effective and well tolerated in acute migraine management but the exact mechanism of action is still debated. Triptans might reduce circulating neuropeptides. To examine this question, we examined the effect of sumatriptan on VIP and PACAP levels in vivo, under conditions without trigeminovascular system activation. Methods In 16 healthy volunteers we measured VIP and PACAP levels before and after administration of subcutaneous sumatriptan. We simultaneously collected blood samples from the internal and external jugular, the cubital veins and the radial artery, thereby covering both the cerebral and systemic circulation. VIP and PACAP determinations were assayed blindly with respect to timing and vascular compartments, but with all samples of a patient in the same assay, to minimize the influence of interassay variation. Results We found no difference in VIP and PACAP concentrations between the internal and external jugular, the cubital veins and the radial artery, (P>0.05), and the circulating levels of VIP and PACAP did not change over time (P>0.05). We found excellent agreement between neuropeptide levels in the internal and the external jugular system. Conclusion Sumatriptan did not change the levels of circulating VIP and PACAP in the intra or extra cerebral circulation in healthy volunteers. Under baseline conditions, without trigeminovascular activation, sumatriptan does not affect the release of neuropeptides VIP and PACAP. Implications Our results indicate no effect of 5-HT1B/D receptor activation on circulating levels of VIP and PACAP in humans without trigeminovascular activation. Given that neuropeptides play an important role for migraine it would be interesting to conduct a similar study in a migraine population.

Agonists of vasoactive intestinal peptide receptor 2 (VPAC2) stimulate glucose-dependent insulin secretion, making them attractive candidates for the treatment of hyperglycaemia and type-II diabetes. Vasoactive intestinal peptide (VIP) is an endogenous peptide hormone that potently agonizes VPAC2. However, VIP has a short serum half-life and poor pharmacokinetics in vivo and is susceptible to proteolytic degradation, making its development as a therapeutic agent challenging. Here, we investigated two peptide cyclization strategies, lactamisation and olefin-metathesis stapling, and their effects on VPAC2 agonism, peptide secondary structure, protease stability, and cell membrane permeability. VIP analogues showing significantly enhanced VPAC2 agonist potency, glucose-dependent insulin secretion activity, and increased helical content were discovered; however, neither cyclization strategy appeared to effect proteolytic stability or cell permeability of the resulting peptides.

Clear renal cell carcinoma (cRCC) is an aggressive and fatal neoplasm. The present work was undertaken to investigate the antiproliferative potential of vasoactive intestinal peptide (VIP) exposure on non-tumoral (HK2) and tumoral (A498, cRCC) human proximal tubular epithelial cell lines. Reverse transcription and semiquantitative PCR was used at the VIP mRNA level whereas enzyme immunoanalysis was performed at the protein level. Both renal cell lines expressed VIP as well as VIP/pituitary adenylate cyclase-activating peptide (VPAC) receptors whereas only HK2 cells expressed formyl peptide receptor-like 1 (FPRL-1). Receptors were functional, as shown by VIP stimulation of adenylyl cyclase activity. Treatment with 0.1μM VIP (24h) inhibited proliferation of A498 but not HK2 cells as based on a reduction in the incorporation of [(3)H]-thymidine and BrdU (5'-Br-2'-deoxyuridine), PCNA (proliferating-cell nuclear antigen) expression and STAT3 (signal transducer and activator of transcription 3) expression and activation. VPAC(1)-receptor participation was established using JV-1-53 antagonist and siRNA transfection. Growth-inhibitory response to VIP was related to the cyclic adenosine monophosphate (cAMP)/exchange protein directly activated by cAMP (EPAC)/phosphoinositide 3-kinase (PI3-K) signaling systems as shown by studies on adenylate cyclase stimulation, and using the EPAC-specific compound 8CPT-2Me-cAMP and specific kinase inhibitors such as H89, wortmannin and PD98059. The efficacy of VIP on the prevention of tumor progression was confirmed in vivo using xenografted athymic mouse. These actions support a potential role of this peptide and its agonists in new therapies for cRCC.

Vasoactive intestinal polypeptide (VIP) is derived from a 170 amino acid precursor which in addition is processed to preproVIP 22-79, PHI, preproVIP 111-122 and preproVIP 156-170. All preproVIP-derived peptides have been shown in normal tissue and VIP-producing cell lines and elevated quantities occur in plasma and tumour tissues from patients with VIP-producing tumours. In some tissues the dibasic cleavage site after PHI is uncleaved resulting in a C-terminally extended form, PHV. PHI and VIP are present in a 1:1 molar ratio in large dense core vesicles and released in roughly equimolar amounts. Carboxyamidation of VIP and PHI is not critical and glycine-extended forms of both peptides have been demonstrated. Pituitary adenylate cyclase activating polypeptide (PACAP) is derived from a 170 amino acid long precursor, which gives rise to PACAP 38, PACAP 27 and PACAP related peptide (PRP). All peptides are present in tissue, the dominating form being PACAP 38. Prohormone convertase (PC) 1 and 2 seem to be involved in the processing of PACAP, except in the testes and ovary, where the PACAP precursor is substrate for PC4.

Accelerated neuronal death brings about cognitive as well as motor and other dysfunctions. A major neuropeptide, vasoactive intestinal peptide (VIP), has been shown to be neuroprotective. However, VIP-based drug design is hampered by the instability of the peptide and its limited bioavailability. Two independent approaches were thus taken to exploit VIP as a lead drug candidate: (1) Potent neuroprotective lipophilic analogs of VIP were synthesized, e.g. [stearyl-norleucine-17] VIP (SNV); and (2) potent neuroprotective peptide derivatives were identified that mimic the activity of VIP-responsive neuroprotective glial proteins. VIP provides neuronal defense by inducing the synthesis and secretion of neuroprotective proteins from astrocytes; activity-dependent neuroprotective protein (ADNP) was discovered as such glial cell mediator of VIP- and SNV-induced neuroprotection. In subsequent studies, an eight-amino-acid peptide, NAP, was identified as the smallest active element of ADNP exhibiting potent neuroprotective activities. This paper summarizes the biological effects of SNV and NAP and further reports advances in NAP studies toward clinical development. An original finding described here shows that NAP, while protecting neurons, demonstrated no apparent effect on cell division in a multiplicity of cell lines, strengthening the notion that NAP is a specific neuroprotective drug candidate.

The structurally related neuropeptides VIP and PACAP are released within the lymphoid organs following antigenic stimulation, and modulate the function of inflammatory cells through specific receptors. In activated macrophages, VIP and PACAP inhibit the production of pro-inflammatory agents (cytokines, chemokines, and nitric oxide), and stimulate the production of the anti-inflammatory cytokine IL-10. These events are mediated through the VIP/PACAP effects on de novo expression or nuclear translocation of several transcription factors, i.e., NFkappaB, CREB, c-Jun, JunB, and IRF-1. The in vivo administration of VIP/PACAP results in a similar pattern of cytokine and chemokine modulation, which presumably mediates the protective effect of VIP/PACAP in septic shock. In addition, VIP/PACAP reduce the expression of the co-stimulatory molecules B7.1/B7.2, and the subsequent stimulatory activity of macrophages for T-helper cells. In T-cells expressing specific VIP/PACAP receptors, VIP and PACAP inhibit the expression of FasL through effects on NFkappaB, NFAT, and Egr2/3. The reduction of FasL expression has several biological consequences: inhibition of antigen-induced cell death in CD4 T-cells, inhibition of the FasL-mediated cytotoxicity of CD8 and CD4 effectors against direct and bystander targets, and promotion of long-term memory Th2 cells, through a positive effect on the survival of Th2, but not Th1, effectors. The various biological effects of VIP and PACAP are discussed within the range of a general anti-inflammatory model.

Androgens play a major role in supporting normal growth and functional maintenance in the prostate. However, this gland contains an array of neuroendocrine peptides that can play a regulatory role in its physiopathology. Among these peptides, one of the best studied is vasoactive intestinal peptide (VIP), which is abundant in autonomic nerves surrounding both human and rat prostatic acini. This neuropeptide may act through interaction with two types of high-affinity receptors, named VPAC(1) and VPAC(2) receptors. Another regulatory peptide, the pituitary adenylate cyclase-activating peptide (PACAP), interacts with these receptors with the same affinity as VIP, but binds with higher affinity to PAC(1) receptors. Human prostate tumors and rat prostate show a major presence of VPAC(1) receptors, whereas various findings suggest a role for VIP in prostatic development. Here we studied the effects of VIP on the proliferation of rat prostatic epithelial cells in culture.

Vasoactive intestinal peptide (VIP) provides neuroprotection against beta-amyloid toxicity in models of Alzheimer's disease. A superactive analogue, stearyl-Nle17-VIP (SNV) is a 100-fold more potent than VIP. In primary neuronal cultures, VIP protective activity may be mediated by femtomolar-acting glial proteins such as activity-dependent neurotrophic factor (ADNF), activity-dependent neuroprotective protein (ADNP), peptide derivatives ADNF-9 (9aa) and NAP (8aa), respectively. It has been hypothesized that beta-amyloid induces oxidative stress leading to neuronal cell death. Similarly, dopamine and its oxidation products were suggested to trigger dopaminergic nigral cell death in Parkinson's disease. We now examined the possible protective effects of VIP against toxicity of dopamine, 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridinium ion (MPP+) in neuronal cultures [rat pheochromocytoma (PC12), human neuroblastoma (SH-SY5Y) and rat cerebellar granular cells]. Remarkably low concentrations of VIP (10(-16)-10(-8) M), ADNF-9 and NAP (10(-18)-10(-10) M) protected against dopamine and 6-OHDA toxicity in PC12 and neuroblastoma cells. VIP (10(-11)-10(-9) M) and SNV (10(-13)-10(-11) M), protected cerebellar granule neurons against 6-OHDA. In contrast, VIP did not rescue neurons from death associated with MPP+. Since dopamine toxicity is linked to the red/ ox state of the cellular glutathione, we investigated neuroprotection in cells depleted of reduced glutathione (GSH). Buthionine sulfoximine (BSO), a selective inhibitor of glutathione synthesis, caused a marked reduction in GSH in neuroblastoma cells and their viability decreased by 70-90%. VIP, SNV or NAP (over a wide concentration range) provided significant neuroprotection against BSO toxicity. These results show that the mechanism of neuroprotection by VIP/SNV/NAP may be mediated through raising cellular resistance against oxidative stress. Our data suggest these compounds as potential lead compounds for protective therapies against Parkinson's disease.

Vasoactive intestinal peptide (VIP) and the structurally related neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), produced and/or released in the lymphoid microenvironment act primarily as macrophage- and T cell-deactivating agents. In the present study we investigate the effect of VIP and PACAP on the production of TGF-beta1 in the macrophage cell line Raw 264.7 and in peritoneal macrophages. The two neuropeptides do not affect the baseline TGF-beta1 production by unstimulated macrophages, but reduce dramatically TGF-beta1 production by LPS-stimulated macrophages. The effects are mediated through the specific receptors VPAC1, VPAC2, and PAC1. The effect of VIP is mediated primarily through the cAMP pathway, whereas PACAP activates both the cAMP and the protein kinase C pathway. VIP reduces the TGF-beta1 steady-state mRNA levels in both peritoneal macrophages and Raw 264.7 cells treated with LPS. A similar effect is observed upon the in vivo administration of VIP. This report adds VIP and PACAP to the only other neuropeptide, substance P, known to regulate TGF-beta1 production in immune cells.

Vasoactive intestinal peptide (VIP) exhibits pronounced effects on the growth rate of cultured mouse embryonic day (E) 9.5 embryos and acts in tissue culture as a potent glial mitogen and neuron survival factor. However, previous studies using immunohistochemistry or in situ hybridization in the rat have not revealed the presence and location of VIP or VIP mRNA in the early developing embryo CNS. Using a sensitive in situ hybridization assay with a 33P-labeled riboprobe, we show here that the VIP gene is expressed at least as early as E11 in the mouse hindbrain. Northern blot analysis on RNA from brain dissected from mouse embryos beginning at E14 confirmed that a correct-size mRNA for VIP was present by E14 and at later time points. Expression of the VIP2 receptor gene was also detected by northern analysis in E14 mouse brains. These studies support the hypothesis that VIP produced by the embryo exerts important effects on embryonic nervous system development.

Nonadrenergic, noncholinergic (NANC) innervation, the third division of the autonomic nervous system, has both inhibitory and excitatory parts. The excitatory part received only limited attention. Substance P has been suggested to be the neurotransmitter of the excitatory part. The NANC-inhibitory innervation has recently been studied in detail. Although the neurotransmitter has not been conclusively identified, a substantial body of evidence exists to support vasoactive intestinal peptide (VIP) as the neurotransmitter. VIP is widely distributed in the body. Reports show that this innervation in animals and man plays a significant role in both health and disease. Pathological conditions could result from either an increase or decrease in VIP production. An absence of VIP-producing neurons has been identified to be responsible for Hirschsprung's disease in the alimentary system and hyperactive airways in the respiratory system. An increase in VIP production is associated with chronic water diarrhea syndrome in humans. Taking these factors into consideration, various therapeutic measures are suggested with the use of VIP or its antagonists.

VIP is a neuroregulator occurring in the central and peripheral nervous system which exhibits the function of neurotransmitter in the brain, neuroendocrine substance at the pituitary level, and neuroparacrine substance in peripheral organs. The structure and the specificity of the molecule as studied by antibody and receptor, and its location in brain and peripheral organs are summarized as well as its numerous biological effects. The method used to demonstrate the involvement of VIP in a physiological regulation is described and illustrated by two examples: the effect of VIP on gut epithelium and the neuroendocrine action of VIP in inducing prolactin release from pituitary cells. The consequence of this recent progress in the knowledge of VIP release and action in human physiology and disease is indicated.