Ability Of Vasoactive Intestinal Peptide Research Articles

VIP Modulates IL-22R1 Expression and Prevents the Contribution of Rheumatoid Synovial Fibroblasts to IL-22-Mediated Joint Destruction

Rheumatoid arthritis (RA) and osteoarthritis are two rheumatic diseases whose progression is associated with a chronic synovitis. Fibroblast-like synoviocytes (FLS) have been shown to play a pivotal role in initiating and perpetuating inflammatory and destructive processes in the rheumatoid joint. Recently, the stimulating role of IL-22 has been reported on RA-FLS contribution to joint destruction by means of the increase of proliferation and matrix-metalloproteinase-1 (MMP-1) and alarmin S100A8/A9 production. Besides, mediators potentially present in inflamed joints have been shown to increase the expression of IL-22/IL-22R1 axis, amplifying the capacity of FLS to respond to IL-22 signalling. Since targeting cytokines that govern FLS activation would allow controlling their contribution to synovial inflammation, the present study was designed to analyze the potential immunoregulatory capacity of vasoactive intestinal peptide (VIP) to counterbalance IL-22 effects on FLS behavior. Our results showed that VIP is able to downregulate the augmented expression of IL-22 specific receptor in FLS subjected to a proinflammatory milieu. Moreover, this study revealed the ability of VIP to inhibit the IL-22 stimulatory effects on proliferation as well as on expression of both MMP-1 and alarmins in RA-FLS. The present findings reinforce the potential of this neuroimmunopeptide as a therapeutic agent in rheumatic diseases.

Passage of vasoactive intestinal peptide across the blood–brain barrier

We investigated the ability of vasoactive intestinal peptide (VIP) to cross the blood–brain barrier (BBB), the interface between the peripheral circulation and central nervous system (CNS). VIP labeled with 131 I (I-VIP) and injected intravenously into mice was taken up by brain as determined by multiple-time regression analysis. Excess unlabeled VIP was unable to impede the entry of I-VIP, indicating that passage is by nonsaturable transmembrane diffusion. High pressure liquid chromatography (HPLC) showed the radioactivity entering the brain to be intact I-VIP. After intracerebroventricular (i.c.v.) injection, I-VIP was sequestered by brain, slowing its efflux from the CNS. In summary, VIP crosses the BBB unidirectionally from blood to brain by transmembrane diffusion.

Regulation of corticotropin-releasing factor receptor function in human Y-79 retinoblastoma cells: rapid and reversible homologous desensitization but prolonged recovery.

Homologous receptor desensitization is an important regulatory response to continuous activation by agonist that involves the uncoupling of a receptor from its G protein. When human retinoblastoma Y-79 cells expressing corticotropin-releasing factor (CRF) receptors were preincubated with CRF for 10 min-4 h, a time-dependent reduction in both the peak and sensitivity of CRF-stimulated intracellular cyclic AMP (cAMP) accumulation developed with a t1/2 of 38 min and an EC50 of 6-7 nM CRF. CRF receptor desensitization was slowly reversible after a 4-h CRF preincubation with a t1/2 of 13 h and a full restoration of cAMP responsiveness to CRF at 24 h following the removal of 10 nM CRF. Because the ability of vasoactive intestinal peptide, forskolin, or (-)-isoproterenol to stimulate cAMP accumulation was not diminished in Y-79 cells desensitized with 10 nM CRF, the observed desensitization was considered to be a specific homologous action of CRF. CRF receptor desensitization was markedly attenuated by CRF receptor antagonists, which alone did not produce any appreciable reduction in CRF-stimulated cAMP accumulation. Although recent reports have demonstrated a rapid decline in steady-state levels of CRF receptor type 1 (CRF-R1) mRNA in anterior pituitary cells during several hours of exposure to CRF, there was no observed reduction in CRF-R1 mRNA levels when Y-79 cells were preincubated with 10 nM CRF for 10 min-24 h despite a rapid time- and concentration-dependent loss of CRF receptors from the retinoblastoma cell surface.

Anterior pituitary release of prolactin is inhibited by exposure to short photoperiod.

The potential regulatory sites responsible for the decrease of circulating prolactin (PRL) levels shown by many photoperiodic mammals following prolonged exposure to short days was investigated in Siberian hamsters that had been maintained under a stimulatory, long-day photoperiod, and in hamsters that had been shifted to a nonstimulatory, short-day photoperiod for 8-10 weeks. The ability of anterior pituitary fragments (AP) from each of these groups to release prolactin was evaluated in pituitary tissue cultured alone and also in pituitary tissue co-cultured with hypothalamic fragments (HF), using a perifusion tissue culture system. The perfusate from these cultures was collected every 1/2 h for 8 h, and was assayed for basal levels of prolactin using radioimmunoassay. For AP tissue cultured alone, there was a robust reduction in prolactin release by the fragments harvested from short-day housed animals. In AP tissue harvested from long-day exposed animals, co-culture with either long- or short-day HF did not induce significant changes in basal PRL release. Similarly, co-culture with short-day HF did not significantly alter PRL release in short-day APs. However, there was a significant increase in release when short-day APs were co-cultured with long-day HF. These results suggest a direct effect of photoperiod on PRL synthesis and/or release at the level of the pituitary. However, the altered responsiveness of short-day pituitaries could be the result of previous, chronic inhibitory hypothalamic input during short-day exposure. A follow-up study was conducted to investigate the ability of vasoactive intestinal peptide (VIP) to stimulate PRL release from long- and short-day APs. Results indicated that the ability of VIP to stimulate PRL release is both photoperiod and dose dependent.

Inhibition of nitric oxide synthase activity in dispersed gastric muscle cells by protein kinase C

The present study examined whether NO synthase (NOS) activity in gastric muscle cells was inhibited by protein kinase C (PKC). Vasoactive intestinal peptide (VIP) increased L-[3H]citrulline production (a coproduct and index of NO synthesis) in muscle strips (81.9 +/- 11.6%) and dispersed muscle cells (80.9 +/- 4.6%) of rabbit stomach. Cholecystokinin octapeptide (CCK-8), carbachol, and phorbol 12-myristate 13-acetate (PMA) inhibited VIP-induced L-[3H]citrulline production in muscle cells and muscle strips; the inhibition was reversed by pretreatment with the PKC inhibitor, calphostin C. The Ca(2+)-mobilizing agents, CCK-8, acetylcholine, ionomycin, and KCl, all of which increased PKC activity in dispersed muscle cells, did not increase L-[3H]citrulline production. After treatment of the cells with calphostin C, all four agents stimulated L-[3H]citrulline production, although to a lesser extent than VIP (approximately 50%). VIP-induced relaxation of basal but not carbachol-stimulated tension was accompanied by increase in L-[3H]citrulline production and was inhibited by the NOS inhibitor NG-nitro-L-arginine (L-NNA). Preincubation of carbachol-treated muscle strips with calphostin C restored the ability of VIP to stimulate L-[3H]citrulline production and the ability of L-NNA to inhibit VIP-induced relaxation. We conclude that 1) VIP-stimulated NOS activity is inhibited by agents that increase PKC activity in gastric smooth muscle cells, and 2) agents that increase both cytosolic free Ca2+ concentration and PKC activity stimulate NOS activity only when PKC activity is suppressed.

VIP restores natural killer cell activity depressed by hepatitis B surface antigen.

Vasoactive intestinal peptide (VIP) has recently been shown to bind to human lymphocytes and modulate immune functions. The ability of VIP in restoring natural killer (NK) cell activity depressed by hepatitis B surface antigen (HBsAg) has been investigated in the present research. Human lymphocytes were incubated with HBsAg and, after washing, a 4-hr cytotoxicity assay was performed. VIP was coincubated with lymphocytes during the preincubation with HBsAg or, alternatively, throughout the cytotoxicity assay. The study revealed that VIP, either preincubated or coincubated in the 4-hr assay, strongly restores NK cell activity depressed by viral antigen. This is noteworthy considering that a number of lymphocyte modulators such as interferons fail in restoring viral-dependent NK cell activity depression. In contrast with previous reports, even when coincubated in the 4-hr assay, VIP is a strong activator of NK cell activity. Further studies will be required to understand which mechanisms are involved in the interrelation between VIP and NK cells during viral infections.

A Mechanism Additional to Cyclic AMP Accumulation for Vasoactive Intestinal Peptide-Induced Prolactin Release

Vasoactive intestinal peptide (VIP) is a prolactin (PRL)-releasing factor which has been proposed to exert its secreting property by activating the adenylate cyclase enzyme. The present study shows that the omission of external Ca2+ did not affect the ability of VIP to induce PRL release while it completely abolished the VIP stimulatory effect on adenylate cyclase. We found that VIP (500 nM) stimulated PRL secretion in a time-dependent manner reaching a plateau at 3 min. This pattern was not changed when Ca2+ was omitted from the incubation medium. When tested at different concentrations, VIP stimulated PRL release with EC50 values of 1.3 nM in the presence of Ca2+ and 30 nM in the absence of Ca2+. On the other hand, Ca2+ removal completely suppressed the VIP-induced cAMP formation. VIP (200 nM) was also found to activate Ca2+ influx into pituitary cells. The increase in Ca2+ permeability showed a peak at 5 s and remained significantly higher than control values until 1 min. In conclusion, in an experimental condition where Ca2+ was omitted from the medium, VIP was found to induce PRL release without stimulating cAMP production. This cAMP-independent PRL release was blocked by preincubation of the cells with 1 microgram/ml pertussis toxin. An additional mechanism other than adenylate cyclase activation or Ca2+ entry is proposed to sustain VIP-induced PRL release.

Somatostatin release from isolated ganglia of the myenteric plexus

Somatostatin neurons of the myenteric plexus project caudad exclusively within the plexus synapsing with neurons in the same or other ganglia. Isolated ganglia offer a unique opportunity to examine peptide transmitter release from these interneurons. Ganglia were isolated from the myenteric plexus by sequential enzymatic digestion, centrifugation, and filtration. Single ganglia were harvested by suction and dispersed in polyacrylamide gel. The ganglia were placed in chambers (200 ganglia/chamber) and perfused with Krebs medium at the rate of 1 ml/min. Addition of the nicotinic agonist, dimethylphenylpiperazinium (DMPP), caused a concomitant increase in somatostatin (152%; P less than 0.001) and vasoactive intestinal peptide (VIP) (79%; P less than 0.05) release above basal level that was abolished by hexamethonium. Addition of the VIP antagonist, VIP-(10-28), (5 microM), to the perfusate augmented significantly DMPP-induced somatostatin release (440%; P less than 0.05), implying that the concomitant release of VIP attenuates somatostatin release. Addition of VIP (1 microM) to the perfusate abolished somatostatin release, confirming the ability of VIP to inhibit somatostatin release. The study shows that VIP interneurons exert a regulatory feedback control over somatostatin interneurons in the myenteric plexus.

Attenuation of hen granulosa cell steroidogenesis by a phorbol ester and 1-oleoyl-2-acetylglycerol.

A series of studies was conducted to evaluate the effects of phorbol esters and a diacylglycerol analog on basal and hormone-stimulated steroidogenesis in granulosa cells from the largest preovulatory follicle of the domestic hen. Agents that previously have been shown to activate protein kinase C, such as the tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), and the synthetic diacylglycerol analog, 1-oleoyl-2-acetylglycerol (OAG), suppressed luteinizing hormone (LH)-induced progesterone (PMA at levels of 10 and 100 ng/tube; OAG at levels of 10 and 25 micrograms/tube), and androgen (10 and 100 ng PMA; 25 micrograms OAG) production, but had no effect on basal levels of either steroid. Furthermore, PMA decreased the ability of vasoactive intestinal peptide to induce steroidogenesis, suggesting that protein kinase C activation may generally modulate the activity of hormones that act via the adenylyl cyclase/cyclic 3',5'-adenosine monophosphate (cAMP) second messenger system. In further support of this proposal was the finding that PMA and OAG decreased the production of cAMP in response to LH, and attenuated the steroidogenic response in granulosa cells exposed to 10 mM 8-bromo-cAMP. By contrast, the induction of calcium mobilization using a calcium ionophore (A23187; 0.5-2.0 microM) stimulated progesterone and androgen production without increasing intracellular levels of cAMP, and this stimulatory effect on steroidogenesis was not inhibited by the presence of 100 ng PMA/tube. From these data, we suggest that the activation of protein kinase C in granulosa cells of the hen may provide a physiological mechanism by which receptor-mediated steroidogenesis, involving the adenylyl cyclase second messenger system, is modulated.

Gastrointestinal Regulatory Peptides Modulate Mouse Lymphocyte Functions Under Serum-Free ConditionsIn Vitro

Conditions are described for performing mitogen (Concanavalin A, Con A; lipopolysaccharide, LPS) and mixed lymphocyte reaction (MLR) cultures using serum-free medium. The effects of exogenously adding several gastrointestinal regulatory peptides (beta-endorphin, substance P, met-enkephalin, vasoactive intestinal peptide, bombesin and somatostatin) on the incorporation of 3H-methyl-thymidine was determined. It was observed that mitogen stimulation of lymph node cells with Con A was inhibited (70% of control) by vasoactive intestinal peptide (VIP) but spleen cells stimulated by LPS were insensitive to immunomodulation (98% of control). The ability of VIP to inhibit Con A induced thymidine incorporation was concentration dependent (10(-6) to 10(-18) M) and was not attributable to kinetic shifts or cell toxicity. None of the other tested neuropeptides affected Con A or LPS induced blastogenesis. MLR cultures were inhibited by VIP, beta-endorphin and somatostatin in a biphasic manner with maximal inhibition observed at 10(-8) to 10(-12) M. Both substance P and bombesin exhibited slight immunoenhancing properties at 10(-14) to 10(-18) M. Met-enkephalin was ineffective as an immunomodulator of MLR cultures. The utility of using serum-free medium in identifying neuropeptides with immunomodulatory properties are discussed.

Adenylate cyclase from rabbit small intestine: Activation by cholera toxin and interaction with calcium

The stimulation of adenylate cyclase in various fractions of plasma membranes from rabbit small intestinal epithelium has been studied. In crude plasma membranes cholera toxin activated 5-fold at 10 μg/ml; vasoactive intestinal peptide (VIP) activated at concentration from 10 −8 to 10 −7 m, the maximal stimulation being 6-fold. Fluoride activated 10-fold at 10 m m. VIP-stimulated enzyme was inhibited by Ca 2+ concentrations in the micromolar range. In the presence of calmodulin a biphasic response was obtained. At low Ca 2+ concentration (4 × 10 −9−6 × 10 −8 m) the enzyme was activated. As the Ca 2+ concentration was increased the enzyme was concomitantly inhibited. We have investigated the mechanism by which cholera toxin activates intestinal adenylate cyclase. We have found that cholera toxin catalyzed incorporation of 32P into proteins located in the brush-border membrane whose molecular weights are in the range of 40–45kDa. These membranes bind [ 3H ]GTP with a K d of 1.8 × 10 −8 m. In contrast, basal lateral membranes do not contain any protein which becomes labeled in a toxin-dependent manner when incubated with cholera toxin and [ 32P ]NAD. The modification of brush-border membrane protein occurred in spite of the absence of adenylate cyclase in these membranes. Adenylate cyclase in basal lateral membranes was poorly activated by cholera toxin as compared to crude plasma membranes. On the other hand, the ability of VIP and fluoride to activate the enzyme was enhanced in basal lateral membranes with respect to crude membranes. The results are discussed in relation to the mechanism by which cholera toxin activates adenylate cyclase in intact intestinal cells.

Effects of HIS 1 modifications on the ability of vasoactive intestinal peptide to stimulate adenylate cyclase from rat and human tissues

The importance of the N-terminal His residue of VIP for stimulating adenylate cyclase was appreciated by estimating the intrinsic activity and EC 50 of four VIP analogues on membranes from rat lung, liver, brain, anterior pituitary, and pancreas, and on human heart membranes. In all tissue preparations tested except one, the order of efficacy (and often potency) was: VIP > (AC-His 1)VIP > (Phe 1)VIP = (3-Me-His 1)VIP > (D-His 1)VIP. In rat heart membranes, the order of efficacy was somewhat different: VIP > (Ac-His 1)VIP = (Phe 1)VIP > (D-His 1)VIP > (3-Me-His 1)VIP. These data demonstrated the key role of His 1 in VIP in activating adenylate cyclase. They suggest that a given VIP analogue might act as full agonist in tightly coupled adenylate cyclase systems (such as those of rat lung and liver membranes) whereas the same analogue could not promote full activity in poorly coupled systems (such as that present in rat brain synaptic membranes).

In vivo bronchodilator activity of vasoactive intestinal peptide in the cat.

Vasoactive intestinal peptide (VIP) is an octacosapeptide that occurs widely in the animal kingdom, is distributed in many organs and tissues, and has a broad range of biologic actions. We evaluated the ability of VIP to produce bronchodilation in anesthetized, mechanically ventilated, atropinized, closed chest cats. Boluses of VIP injected intravenously (0.1 to 10 micrograms X kg-1) reversed in a dose-dependent manner the increase in lung resistance (RL) and the decrease in dynamic lung compliance (Cdyn) induced by an intravenously administered infusion of 5-hydroxytryptamine (5HT) (5 to 30 micrograms X kg-1 X min-1). Distribution of bronchodilator activity was assessed by using RL as an index of central airways caliber and dynamic elastance (Edyn; the inverse of Cdyn) as an index of tone in peripheral airways and lung parenchyma. Although all levels of the tracheobronchial tree responded to VIP, the predominant site of action appeared to be in central airways. A similar distribution and magnitude of relaxant effects were observed after the intravenous administration of prostaglandin E2 (PGE2) (0.1 to 10 micrograms X kg-1). Prostaglandin E2 also was effective in reversing 5HT-induced bronchoconstriction when given by ultrasonic nebulization, whereas VIP was not. Bronchodilation mediated by VIP persisted after pretreatment with indomethacin or propranolol. We conclude that VIP is a potent relaxant of feline airways smooth muscle in vivo and that this effect of the peptide occurs independent of prostaglandin production or beta adrenergic receptor activation.