Relaxant effects of pituitary adenylate cyclase activating polypeptide (PACAP) on epithelium-intact and -denuded guinea-pig trachea: a comparison with vasoactive intestinal peptide (VIP)

Pituitary adenylate cyclase-activating polypeptide plays an anti-inflammatory role in endotoxin-induced airway inflammation: in vivo study with gene-deleted mice

The presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors in capsaicin-sensitive peptidergic sensory nerves, inflammatory and immune cells suggest its involvement in inflammation. However, data on its role in different inflammatory processes are contradictory and there is little known about its functions in the airways. Therefore, our aim was to examine intranasal endotoxin-induced subacute airway inflammation in PACAP gene-deficient (PACAP⁻/⁻) and wild-type (PACAP⁺/⁺) mice. Airway responsiveness to inhaled carbachol was determined in unrestrained mice with whole body plethysmography 6 h and 24 h after LPS. Myeloperoxidase (MPO) activity referring to the number of accumulated neutrophils and macrophages was measured with spectrophotometry and interleukin-1β (IL-1β) concentration with ELISA from the lung homogenates. Histological evaluation and semiquantitative scoring were also performed. Bronchial responsiveness, as well as IL-1β concentration and MPO activity markedly increased at both timepoints. Perivascular edema dominated the histological picture at 6 h, while remarkable peribronchial granulocyte accumulation, macrophage infiltration and goblet cell hyperplasia were seen at 24h. In PACAP⁻/⁻ mice, airway hyperreactivity was significantly higher 24 h after LPS and inflammatory histopathological changes were more severe at both timepoints. MPO increase was almost double in PACAP⁻/⁻ mice compared to the wild-types at 6 h. In contrast, there was no difference between the IL-1β concentrations of the PACAP⁺/⁺ and PACAP⁻/⁻ mice. These results provide evidence for a protective role for PACAP in endotoxin-induced airway inflammation and hyperreactivity.

Pulmonary Hypertension and Right Heart Failure in Pituitary Adenylate Cyclase–Activating Polypeptide Type I Receptor–Deficient Mice

Background— Pituitary adenylate cyclase–activating polypeptide (PACAP), acting via 3 different G protein–coupled receptors, has been implicated in the regulation of several homeostatic systems in the body, including cardiopulmonary control. To define the physiologic role of the PACAP-preferring type I receptor, PAC1, in cardiopulmonary function, we developed a mutant mouse strain lacking functional PAC1 receptors.

Methods and Results— When PAC1-deficient mice were crossed onto a C57BL/6 background, almost all mutants died during the second postnatal week. Whereas mutant mice were indistinguishable from their wild-type littermates at birth, they showed progressive weakness and died from rapidly developing heart failure. Right ventricles of PAC1 mutants were massively dilated and showed cardiac myocyte hypertrophy, whereas left ventricular structure was unaltered. On direct cardiac catheterization, right ventricular pressure was elevated by 45% in PAC1-deficient mice, indicating increased pulmonary artery pressure, as no malformations were detected in the valves or outflow tract of the right ventricle. Consistent with elevated pulmonary pressure, lung capillary density was decreased by 30% and small pulmonary arteries of mutant mice had significant vascular smooth muscle cell hypertrophy compared with wild-type mice.

Conclusions— Whereas PACAP induces vasodilation in isolated pulmonary vessels in wild-type mice, the absence of its specific receptor PAC1 causes pulmonary hypertension and right heart failure after birth. These in vivo findings demonstrate the crucial importance of PAC1-mediated signaling for the maintenance of normal pulmonary vascular tone during early postnatal life.

Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

Bronchodilation by an inhaled VPAC(2) receptor agonist in patients with stable asthma

BACKGROUND

The synthetic vasoactive intestinal peptide (VIP) analogue Ro 25-1553 is a selective VIP-PACAP type 2 (VPAC(2)) receptor agonist that causes a bronchodilatory effect in guinea pigs in vivo. The effect of Ro 25-1553 given by inhalation to patients with asthma was studied and compared with that of a long acting beta(2) adrenoceptor agonist.

METHODS

Twenty four patients with moderate stable asthma participated in a double blind, randomised, placebo controlled, crossover study. The primary variable was bronchodilatory effect (increase in forced expiratory volume in 1 second, FEV(1)) after inhalation of Ro 25-1553 (100 microg or 600 microg) and formoterol (4.5 microg), respectively. Putative side effects were characterised by monitoring sitting blood pressure, serum potassium, electrocardiography and echocardiography.

RESULTS

Inhalation of 600 microg Ro 25-1553 caused a rapid bronchodilatory effect (geometric mean increase in FEV(1) compared with placebo) within 3 minutes of 6% (95% CI 4 to 9), as did inhalation of formoterol (8% (95% CI 5 to 10)). The corresponding maximum bronchodilatory effect during 24 hours was similar for 600 microg Ro 25-1553 (7% (95% CI 4 to 10)) and the reference bronchodilator formoterol (10% (95% CI 7 to 12)). However, for both doses of Ro 25-1553 the bronchodilatory effect was attenuated 5 hours after inhalation whereas formoterol still had a bronchodilatory effect 12 hours after inhalation. Neither Ro 25-1553 nor formoterol produced any clinically relevant side effects. No drug related difference in adverse events was observed.

CONCLUSION

Inhalation of a synthetic selective VPAC(2) receptor agonist constitutes a promising approach for bronchodilation in patients with asthma.

Pituitary adenylate cyclase-activating peptide and lung-liquid reabsorption in vitro by lungs from fetal guinea-pigs

Pituitary adenylate cyclase-activating peptide (PACAP) is present in the lungs, notably in their internal neuroendocrine system; however, its use is not clear. It was investigated for its possible ability to cause lung-liquid reabsorption around birth. Lungs from 31 late-term fetal guinea-pigs (at 60 ± 2 days of gestation) were supported in vitro for 3 h; lung-liquid movements were monitored by a dye-dilution method. Untreated control preparations (n = 9) produced fluid at 1.85 ± 0.40 mL·kg–1 body mass·h–1 (mean ± SD), with no significant change (ANOVA, regression analysis). Those given 10–8 M PACAP in the middle hour turned to reabsorption (n = 3) or reduced production markedly (n = 3) (average fall 84.4 ± 5.4%; significant at P < 0.001–0.0005); effects continued and increased after the PACAP was removed. Preparations given 10–9 M PACAP reacted similarly, but there was partial recovery after treatment (five reabsorbed, four reduced production; average fall 91.4 ± 14.3%; significant at P < 0.01–0.0005). Preparations given 10–10 M PACAP all reduced production, with partial recovery (average fall 43.5 ± 8.2%; significant at P < 0.005–0.0005). Preparations given 10–11 M PACAP showed little or no effect. The linear log dose–response curve became maximal at 10–9 M (r2 = 0.98; theoretical threshold 10–13 M). The results increase the likelihood that the neuroendocrine system is important in lung-liquid reabsorption, and suggest that PACAP could combine its relaxation of airways with lung-liquid removal, and therefore aid the first attempts of the newborn to breathe.

Pituitary adenylate cyclase-activating peptide inhibits neutrophil chemotaxis

Pituitary adenylate cyclase-activating peptide 38 (PACAP 38) is a neuropeptide that displays several biological effects of interest in the context of airway diseases such as asthma and chronic obstructive pulmonary disease. These effects include inhibition of airway and vascular smooth muscle tone as well as modulation of inflammatory cell activity. However, little is known about the effect of PACAP on granulocytes. The present study was designed to investigate if PACAP and the closely related peptide vasoactive intestinal peptide (VIP) could affect neutrophil migration. A standard 48 well chemotaxis chamber was used to assess the effects of PACAP on N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced neutrophil chemotaxis and spontaneous random migration. PACAP 38 and VIP inhibited fMLP-induced human neutrophil chemotaxis. Furthermore, both peptides also exhibited a dose-related trend toward inhibiting the spontaneous, unstimulated migration of neutrophils. Since enhanced cell migration in cell chamber systems is reported to correlate with increased invasive properties in vivo, the presented inhibitory effects of PACAP 38 on neutrophil chemotaxis, supports the idea of an anti-inflammatory role for PACAP. This together with the well documented bronchodilatory capacity of PACAP might indicate a role for PACAP-agonists in future treatment of asthma and other inflammatory airway diseases.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Pituitary adenylate cyclase activating peptide mediates inhibitory nonadrenergic noncholinergic relaxation

We investigated the contribution of pituitary adenylate cyclase activating peptide (PACAP) to inhibitory nonadrenergic noncholinergic (inhibitory-NANC) relaxation of tracheal smooth muscle in cats. We also investigated the roles of vasoactive intestinal peptide (VIP) and nitric oxide (NO) on this function. Smooth muscle strips prepared from feline trachea were precontracted with 1 microM serotonin, and inhibitory-NANC relaxation was induced by electrical-field stimulation in the presence of atropine and propranolol. PACAP-(6-38) (a selective antagonist of PACAP; 1, 3 and 10 microM), VIP-(10-28) (a selective antagonist of VIP; 1, 3 and 10 microM) and N(omega)-nitro-L-arginine methyl ester (L-NAME, a selective NO synthase inhibitor; 3, 10 and 30 microM) each partially but significantly attenuated the amplitude of inhibitory-NANC relaxation. The effects of PACAP-(6-38) and VIP-(10-28) were additive. Addition of PACAP-(6-38) and/or VIP-(10-28) further attenuated relaxation in the presence of L-NAME. These results suggest that PACAP, VIP and NO contribute to the relaxation induced by inhibitory-NANC in tracheal smooth muscle in cats, and that they mediate this relaxation via different pathways.

Immunohistochemical localization and distribution of VIP/PACAP receptors in human lung

VIP and PACAP are distributed in nerve fibers throughout the respiratory tract acting as potent bronchodilators and secretory agents. By using RT-PCR and immunoblotting techniques, we have previously shown the expression of common VIP/PACAP (VPAC(1) and VPAC(2)) and specific PACAP (PAC(1)) receptors in human lung. Here we extend our aims to investigate by immunohistochemistry their localization and distribution at this level. A clear immunopositive reaction was obtained in human lung sections by using either anti-VPAC(1) or -VPAC(2) receptor antibodies but not with anti-PAC(1) receptor antibody. However, PAC(1) receptor (and VPAC(1) and VPAC(2) receptors) could be identified in lung membranes by immunoblotting which supports that the PAC(1) receptor is expressed at a low density. Both VPAC(1) and VPAC(2) receptors showed similar immunohistochemical patterns appearing in smooth muscle cells in the wall of blood vessels and in white blood cells (mainly in areas with inflammatory responses). The results agree with previous evidence on the importance of both peptides in the immune system and support their anti-inflammatory and protective roles in lung.

Effect of vasoactive intestinal peptide (VIP)-related peptides on cholinergic neurogenic and direct mucus secretion in ferret trachea in vitro

1 We investigated whether vasoactive intestinal peptide (VIP) and its related peptides, pituitary adenylate cyclase activating peptide (PACAP) and secretin, regulate cholinergic neural mucus secretion in ferret trachea in vitro, using 35SO4 as a mucus marker. We also studied the interaction between VIP and secretin on cholinergic mucus output. 2 VIP (1 and 10 microM) increased secretion, whereas neither PACAP1 - 27, PACAP1 - 38 nor secretin (up to 10 microM) increased mucus output. In contrast, VIP, PACAP1 - 27 and PACAP1 - 38 concentration-dependently inhibited cholinergic neural secretion, with an order of potency of VIP>PACAP 1 - 38>PACAP1 - 27. Neither PACAP1 - 27 nor PACAP1 - 38 altered the secretion induced by acetylcholine (ACh). 3 Secretin increased cholinergic neural secretion with a maximal increase of 190% at 1 microM. This potentiation was blocked by VIP or atropine. Similarly, secretin (1 microM) potentiated VIP (1 microM)-induced mucus output by 160%. Secretin did not alter exogenous ACh-induced secretion. VIP vs secretin competition curves suggested these two peptides were competing reversibly for the same receptor. 4 We conclude that, in ferret trachea in vitro, VIP and PACAPs inhibit cholinergic neural secretion via pre-junctional modulation of cholinergic neurotransmission. VIP and secretin compete for the same receptor, possibly a VIP1 receptor, at which secretin may be a receptor antagonist.

Expression, pharmacological, and functional evidence for PACAP/VIP receptors in human lung

Pituitary adenylate cyclase-activating peptide (PACAP) type 1 (PAC(1)) and common PACAP/vasoactive intestinal peptide (VIP) type 1 and 2 (VPAC(1) and VPAC(2), respectively) receptors were detected in the human lung by RT-PCR. The proteins were identified by immunoblotting at 72, 67, and 68 kDa, respectively. One class of PACAP receptors was defined from (125)I-labeled PACAP-27 binding experiments (dissociation constant = 5.2 nM; maximum binding capacity = 5.2 pmol/mg protein) with a specificity: PACAP-27 approximately VIP > helodermin approximately peptide histidine-methionine (PHM) >> secretin. Two classes of VIP receptors were established with (125)I-VIP (dissociation constants of 5.4 and 197 nM) with a specificity: VIP approximately helodermin approximately PACAP-27 >> PHM >> secretin. PACAP-27 and VIP were equipotent on adenylyl cyclase stimulation (EC(50) = 1.6 nM), whereas other peptides showed lower potency (helodermin > PHM >> secretin). PACAP/VIP antagonists supported that PACAP-27 acts in the human lung through either specific receptors or common PACAP/VIP receptors. The present results are the first demonstration of the presence of PAC(1) receptors and extend our knowledge of common PACAP/VIP receptors in the human lung.

A novel long-acting VIP analog in the guinea pig trachea in vitro

The relaxant effect of a novel VIP analog, [Arg15,20,21Leu17]-VIP-Gly-Lys-Arg-NH2 was compared with that of the original VIP in the same guinea pig trachea precontracted by carbachol in vitro. The VIP analog caused significantly and concentration-dependent relaxation similarly to the original VIP. In contrast to the original VIP, the VIP analog demonstrated a slow onset and offset of action, with more than 90% of its maximum relaxation remaining 6 h after administration. Peptidase inhibition by captopril and phosphoramidon increased the relaxant effect and duration of action for original VIP but not for the VIP analog.