Neuropeptides and the lung

[Role of the skin expression of neuropeptides, neurotrophins and their receptors in the pathogenesis of dermatoses]

OBJECTIVE

to define the role of neurotransmitters and their receptors in the development of itch and in the maintenance of a skin inflammatory response in patients with psoriasis and atopic dermatitis.

MATERIAL AND METHODS

Skin biopsy specimens from 30 patients with psoriasis and 30 patients with atopic dermatitis were investigated by histological, immunoperoxidase, and indirect immunofluorescence assays. The investigators determined the expression of protein gene product 9.5 (PGP9.5), amphiregulin, semaphorin 3A, calcitonin gene-related peptide (CGRP) and its receptor (CGRP-R), nerve growth factor (NGF) and its receptor TrkA, and substance P (SP) and its receptor SP-R. The indirect immunofluorescence assay was used for quantitative analysis. The findings were statistically analyzed using a Statistica 10 program.

RESULTS

Immunoperoxidase examination of the skin biopsy specimens from patients with atopic dermatitis and psoriasis revealed enhanced expression of amphiregulin, NGF, and PGP9.5, appearance of positively stained epidermal nerve fibers, and decreased expression of the nerve reduction factor semaphorin 3A in all cases. Some patients with atopic dermatitis and psoriasis showed increased expression of CGRP and CGRP-R, SP, SP-R, and TrkA. A pronounced inflammatory response was generally observed in these cases.

CONCLUSION

The investigation performed suggests that atopic dermatitis and psoriasis are characterized by a larger number of epidermal nerve fibers and by a direct correlation between this indicator, disease severity, and itch intensity. The production of neuropeptides and neurotrophins is closely related to the development of a skin inflammatory response irrespective of its cause and dysregulation of these processes is likely to favor the body's sensitization and the chronic pattern the course of diseases.

Neurotrophins and neuropeptides as inflammatory mediators in case of chronic dermatosis

This literature review examines the role of neurotrophins and neuropeptides for the development of skin inflammatory reactions in case of chronic inflammatory dermatoses. The article describes inflammatory effects of neurotrophin, a nerve growth factor, neuropeptide substance P and calcitonin gene-related peptide. Factors affecting the condition of skin innervation and development of inflammation - neurotrophin, a nerve growth factor, amphiregulin, an epidermal growth factor, and semaphorin 3A, a nerve repulsion factor - were examined. Searching for and administering antagonists of proinflammatory effects of neuropeptides, neurotrophins and epidermal growth factor can become new approaches to the treatment of chronic inflammatory dermatoses.

Involvement of enhanced neurokinin NK3 receptor expression in the severe asthma guinea pig model

In this study, we investigated the involvement of neurokinin NK3 receptors in a severe asthma model prepared by administering ovalbumin via inhalation three times to systemically sensitized guinea pigs. [3H]senktide, a neurokinin NK3 receptor ligand, showed significant specific binding to the lungs from the model animals, but not to those from negative control animals. The airway responsiveness to intravenous neurokinin B, a neurokinin NK3 receptor agonist, was increased in the model, indicating an increase in functional NK3 receptors. Furthermore, SB 223956 ((-)-3-methoxy-2-phenyl-N-[(1S)-phenylpropyl]quinoline-4-carboxamide), a selective neurokinin NK3 receptor antagonist, significantly inhibited the ovalbumin-induced airway hyperresponsiveness to inhaled methacholine, but it did not show significant effects on the ovalbumin-induced airway narrowing and eosinophil accumulation. These results suggest that the expressed neurokinin NK3 receptors in the severe asthma model are involved in the development of airway hyperresponsiveness.

Greater involvement of neurokinins found in Guinea pig models of severe asthma compared with mild asthma

BACKGROUND

Involvement of neurokinins in asthma has been previously pointed out by several reports. However, the relationship between neurokinins and the severity of asthma has remained unclear. We developed a model of mild asthma (model I) and severe asthma (model II) in guinea pigs, and investigated the function of neurokinins in both models.

METHODS

In models I and II, systemically sensitized guinea pigs were made to inhale ovalbumin once and three times, respectively. Substance P (SP) and neurokinin A (NKA) concentrations in the bronchoalveolar lavage fluid (BALF) were measured in models I and II. Then, the effects of a capsaicin pretreatment, which depletes neurokinins, in both animal models on airway narrowing induced by the last ovalbumin inhalation, airway hyperresponsiveness to inhaled methacholine, and eosinophil accumulation in BALF, were investigated.

RESULTS

SP concentration tended to increase and the NKA concentration increased significantly in model II, but not in model I. Capsaicin pretreatment significantly inhibited the late bronchial response that was observed 2-6 h after the last ovalbumin inhalation, airway hyperresponsiveness and eosinophil accumulation in model II. On the other hand, it had no effects on the responses in model I.

CONCLUSION

It is suggested that the more severe the disease, the greater the involvement of neurokinins.

Glucagon-like peptide-1(7-36) amide stimulates surfactant secretion in human type II pneumocytes

To determine the influence of glucagon-like peptides on the secretion of human pulmonary surfactant, we used human type II pneumocytes. In these cells, GLP-1(7-36) amide and exendin-4 stimulated phosphatidylcholine secretion (PC) and cAMP formation in a concentration-dependent manner; these effects were reversed by exendin(9-39). No changes were observed with other related peptides. The mechanism by which GLP-1(7-36) amide exerts its stimulatory effect was investigated with various agents that are well known to be stimulators or inhibitors of PC secretion. Thus, 8-bromo-cAMP increased and both Rp-cAMPS and H-89, the latter an inhibitor of protein kinase A (PKA), reduced pulmonary surfactant secretion in type II pneumocytes. Also, GLP-1(7-36) amide and TPA exerted additive effects in stimulating PC secretion, and Calph C, a potent inhibitor of protein kinase C (PKC), blocked most of the effect of GLP-1(7-36) amide. By contrast, both the calcium ionophore A23187 and GLP-1(7-36) amide had additive effects in increasing PC secretion, and the specific inhibitor of Ca(2+)-calmodulin-dependent protein kinase (Ca-CM-PK), KN-62, inhibited the effect of A23187 but did not alter the stimulatory action of GLP-1(7-36) amide. Our findings suggest that both PKA and PKC are involved in the stimulatory effects of GLP-1(7-36) amide on PC secretion, whereas this peptide has no effect on PC secretion through a Ca-CM-PK mechanism.

Differential modulation of human immunoglobulin isotype production by the neuropeptides substance P, NKA and NKB

The modifying effects of tachykinins substance P, neurokinin A and neurokinin B on immunoglobulin production were analyzed in an in vitro culture system. Purified human T- and B-cells were stimulated with TGFbeta2 and IL-5 to induce preferential IgA production. Neuropeptides had the following effects. (1) The levels of IgA and IgG4 production were enhanced by IL-5 and TGFbeta2; IgA levels remained constant or were slightly augmented by neuropeptides, whereas IgG4 was further augmented. (2) IL-5 and TGFbeta2 did not alter IgG3 production, but neuropeptides stimulated secretion of this subclass. (3) IgG1 and IgM production were inhibited by IL-5 and TGFbeta2. This effect was prevented by neuropeptides. (4) Other isotypes including IgG2 and IgE remained unaffected. Except for IgM, these effects were blocked by specific receptor antagonists indicating specificity. The tachykinin receptor NK-1 mRNA was detected in B- and T-cells, whereas NK-3 mRNA was only present in T- and B-cell coculture following activation. Furthermore, neuropeptide effects depended on cytokine co-stimulation and the presence of T-cells. These results suggest that neuropeptides are potent modifiers of preferential IgA synthesis.

Role of substance P and neurokinin A in toluene diisocyanate-induced increased airway responsiveness in rabbits

The aim of the present study was to examine the role of neuropeptides, especially substance P (SP) and neurokinin A (NKA), in toluene diisocyanate (TDI)-induced airway hyperresponsiveness (AHR) to acetylcholine aerosols. Thirty parts per billion of TDI in air administered over 4 hours caused a significant increase in the airway constrictive response to acetylcholine (ACH) aerosols in rabbits (DeltaRI: 245 +/- 30%, p < 0.005) without altering basic values of respiratory, cardiovascular or blood gas parameters. Inhalation of the aerosolized neuropeptides SP and NKA resulted in a similar increase in airway responsiveness (AR) to ACH as exposure to 30 ppb TDI. To determine whether neuropeptides contribute to TDI-induced AHR, we studied their effects after systemic treatment with capsaicin as well as after infusion of specific synthetic antagonists for SP and NK2 (NKA) receptors. CAPS treatment performed on 4 consecutive days as well as antagonists' infusion only moderately (p > 0.05) decreased airway responses to ACH. CAPS application prevented the TDI-induced increase in AR to ACH in all rabbits. The increase in airway resistance to ACH did not significantly change after TDI exposure (98 +/- 22% of the control response before TDI, p > 0.05). Simultaneous infusion of specific synthetic SP and NK2 receptor antagonists also abolished the TDI-induced increase in airway responses to ACH in all animals investigated (p > 0.05). The results of this study demonstrate that neuropeptides, especially the tachykinins SP and NKA, are important mediators in TDI-induced AHR in rabbits.

Involvement of NK1 and NK2 receptors in pulmonary responses elicited by non-adrenergic, non-cholinergic vagal stimulation in guinea-pigs

Previous studies from our laboratory using exogenously administered neurokinin (NK) agonists have shown that both NK1- and NK2-receptor subtypes are involved in plasma extravasation in the guinea-pig airways. In the present study, we have extended these observations using antidromic vagal stimulation to stimulate sensory c-fibres as a means of eliciting the release of endogenous tachykinins in propranolol- and atropine-treated guinea-pigs. Antidromic vagal stimulation (5 ms, 30 s) induced frequency-dependent (1-10 Hz) bronchoconstriction that was completely abolished by co-administration of the NK1-selective antagonist CP-99,994 ((2s-methoxy-benzyl)-(2-phenyl-piperidin-3s-yl)-amine), and the NK2-selective antagonist SR-48,968 ((S)-N-methyl-N-[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl) butyl]benzamide), each at a dose sufficient to block NK1 and NK2 receptors, respectively (each at 0.3 mg kg-1, i.v.). In contrast, SR-48,968 when given alone only partially blocked the vagal stimulation-induced bronchospasm, whereas CP-99,994 had no effect. Significant increases (2-3-fold) in plasma extravasation of [125I]fibrinogen in the trachea, main bronchi, distal airways and oesophagus following vagal stimulation (5 Hz, 5 min, 10 V, 5 ms) were observed. Pretreatment with the neutral endopeptidase inhibitor, thiorphan (1 mg kg-1, i.v.), and the angiotensin-converting enzyme inhibitor, enalapril (1 mg kg-1, i.v.), potentiated both vagal stimulation-induced bronchoconstriction and plasma leakage in all tissues examined. This potentiation was due to reduced metabolism of endogenously released tachykinins since enhanced plasma overflow of immunoreactive substance P was observed following vagal stimulation in thiorphan- and enalapril-treated guinea-pigs. CP-99,994 substantially blocked plasma leakage in all parts of the airways and in the oesophagus. In comparison, SR-48,968 had no significant effect in the trachea and the oesophagus but partially inhibited plasma leakage in the main bronchi and distal airways. Co-administration of both CP-99,994 and SR-48,968 abolished the residual plasma leakage in these two regions. These results support the hypothesis that both NK1 and NK2 receptors are involved in tachykinin-induced pulmonary responses in the airways.

Galanin and somatostatin inhibition of neurokinin A and B induced airway mucus secretion in the rat

Neurokinin A and B are present in neurons situated in lung and NK-1 receptors have been described on tracheal submucosal gland cells. In the present study we compared the ability of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) to stimulate airway mucus secretion. Furthermore, we characterized the interaction of NKA and NKB with galanin and somatostatin. The rank order of the tachykinins to stimulate airway mucus secretion was SP > NKA > NKB suggesting that NK-1 receptors mediate these effects(EC50:SP: 50 nmol/l, NKA: 200 nmol/l, NKB: 400 nmol/l). Galanin and somatostatin were equally potent to inhibit NK-A and NK-B stimulated airway mucus release. These results suggest that NK-A and NK-B are potent stimulators of airway macromolecule secretion. Galanin and somatostatin potently inhibit these actions of the tachykinins. Therefore, airway mucus secretion is controlled by a complex network of several different mediators.

Galanin and somatostatin inhibition of substance P-induced airway mucus secretion in the rat

Substance P is present in several neurons innervating the lung. Tachykinin receptors are expressed on submucosal gland cells. Substance P is known to be a potent stimulator of airway mucus secretion. In the present study we characterized the effects of galanin and somatostatin on basal and substance P-induced mucus secretion. The stimulatory effect of substance P was concentration-dependent (100 pmol/l: 112%, 1 nmol/l: 120%, 10 nmol/l: 153%, 100 nmol/l: 223%, 1 mumol/l: 275%, 10 mumol/l: 172%) and was inhibited by galanin and somatostatin (1 mumol/l substance P: 277%; 1 mumol/l substance P + 1 mumol/l somatostatin: 190%, p < 0.01; 1 mumol/l substance P + 1 mumol/l galanin: 206%, p < 0.05). In the presence of lower concentrations of substance P 1 mumol/l somatostatin and 1 mumol/l galanin did not modify mucus secretion. Lower concentrations of galanin and somatostatin did not significantly change mucus secretion stimulated by 1 mumol/l substance P. Both, galanin and somatostatin at 1 mumol/l left basal airway mucus secretion unaltered. These data suggest that mucus secretion into airways is regulated by a complex network of peptidergic stimulators and inhibitors including substance P, somatostatin and galanin.

Identification of both NK1 and NK2 receptors in guinea-pig airways

1. NK1 and NK2 receptors have been characterized in guinea-pig lung membrane preparations by use of [125I-Tyr8]-substance P and [125I]-neurokinin A binding assays in conjunction with tachykinin-receptor selective agonists ([Sar9Met(O2)11]substance P for NK1 and [beta Ala8]neurokinin A (4-10) for NK2) and antagonists (CP-99,994 for NK1 and SR48968 for NK2). 2. The presence of high affinity, G-protein-coupled NK1 receptors in guinea-pig lung parenchymal membranes has been confirmed. The rank order of affinity for competing tachykinins was as predicted for an NK1 receptor: substance P = [Sar9Met(O2)11]substance P > substance P-methyl ester = physalaemin > neurokinin A = neurokinin B >> [beta Ala8]neurokinin A (4-10). The novel NK1 antagonist CP-99,994 has a Ki of 0.4 nM at this NK1 site. 3. In order to characterize [125I]-neurokinin A binding to guinea-pig lung, the number of [125I]-neurokinin A specific binding sites was increased 3-4 fold by purification of the parenchymal membranes over discontinuous sucrose gradients. The rank order of affinity determined for NK1- and NK2-receptor agonists and antagonists in competition for these sites showed that the majority (80%) of [125I]-neurokinin A specific binding was also to the NK1 receptor. 4. Under conditions where the guinea-pig lung parenchymal NK1 receptor was fully occupied by a saturating concentration of either [Sar9Met(O2)11]substance P (1 microM) or CP-99,994 (2.7 microM), residual [125I]-neurokinin A specific binding was inhibited in a concentration-dependent manner by both [beta Ala8]neurokinin A and SR48968. This result shows that the NK2 receptor is also present in these preparations. 5. Similar studies using guinea-pig tracheal membranes demonstrated that [125I]-neurokinin A specific binding was composed of a NK1-receptor component (60%), inhibited by both [Sar9Met(02)11]substance P and CP-99,994, and a significant NK2-receptor component, inhibited by both [beta Ala 8]neurokinin A andSR48968.6. In summary, these data demonstrate that guinea-pig lung parenchyma and guinea-pig trachea express both NK1 and NK2 receptors.

Tachykinin-mediated respiratory effects in conscious guinea pigs: modulation by NK1 and NK2 receptor antagonists

Tachykinins, in particular neurokinin A and substance P, produce a number of airway effects which may contribute to respiratory diseases such as asthma. We examined the ability of aerosolized substance P, neurokinin A or capsaicin to produce respiratory alterations in conscious guinea pigs using modified whole body plethysmography. Substance P-mediated dyspnea and significant respiratory events were inhibited by the NK1 receptor antagonist, CP-96,345. Neurokinin A-mediated respiratory effects were ablated by the NK2 receptor antagonists: MEN 10207, MDL 29,913 and SR 48,968, the latter being the most potent. The peptide-based antagonist, MEN 10207, produced respiratory effects itself suggesting partial agonist activity. The cyclic hexapeptide, MDL 29,913, relaxed airway smooth muscle via mechanisms other than tachykinin antagonism. NK2 but not NK1 receptor antagonists were able to delay the onset of capsaicin-induced dyspnea, although alone they did not usually (in approximately 10% of the animals) eliminate the response. However, when NK2 receptor antagonists were combined with CP-96,345, the incidence of dyspnea induced by capsaicin decreased significantly (40%) suggesting that both tachykinins contribute to dyspnea in this system.

The effect of Ca2+ channel modulators on vagally induced bronchoconstriction in the guinea-pig

The effects of N- and L-type voltage operated calcium channel (VOCC) antagonists were examined on the bronchoconstriction induced by vagal stimulation in artificially respired guinea-pigs. Vagal stimulation produced a reproducible and consistent bronchoconstrictor response which corresponded to an increase in pulmonary inflation pressure equivalent to (10.4 +/- 1.0%) of the maximum. This vagally induced rise in pulmonary inflation pressure was reduced (54% P less than 0.001) by pretreatment with atropine (1 mg/kg i.v.) and almost completely blocked by pretreatment with capsaicin (54.5 mg/kg s.c.) and atropine. omega-Conotoxin GVIA (CgTx) (5-20 micrograms/kg i.v.) caused a dose and time-related inhibition of the vagal response but did not affect either methacholine or substance P (SP)-induced bronchoconstriction. Combination studies with CgTx, atropine and capsaicin pretreatment revealed that CgTx effectively blocked both the atropine-sensitive cholinergic component and the capsaicin-sensitive non-adrenergic non-cholinergic (NANC) component of the vagal response. Selective L-type VOCC antagonists nicardipine, diltiazem and verapamil, at doses which had significant cardiovascular effects, did not reduce the rise in pulmonary inflation pressure to vagal stimulation. This study indicates that N-type VOCCs are important in controlling the release of neurotransmitters from both the cholinergic and NANC neurones within the airways of guinea-pigs.

Pharmacotherapy of childhood asthma. An inflammatory disease

The recognition that asthma constitutes 2 kinds of physiopathological reactions, namely bronchospasms (immediate reactions) and inflammatory responses (late reactions), suggests that the treatment should be focused against these events. Furthermore, the allergen provocation model, showing the existence of immediate and late asthmatic reactions, can be used to study the effects of different antiasthmatic drugs. Recently, the importance of inflammation in the pathogenesis of asthma in adults has led to the development of therapeutic regimens in which anti-inflammatory treatments are used frequently as a first-line step in the management of asthma. Although at the moment the hard data showing inflammation in childhood asthma are scarce, it is assumed that childhood asthma constitutes the same kind of chronic inflammatory processes as in adult asthma and that its treatment should also include anti-inflammatory drugs.

Inflammation and the allergic response

The atopic diseases--allergic rhinitis, asthma, and atopic dermatitis--are chronic inflammatory diseases characterized by an exacerbating and remitting course and can only rarely be associated causally with allergen exposure. The challenge to ascribe an allergic basis to these diseases is derived from the apparent inability to reconcile these chronic inflammatory features with a process thought to be initiated by the rapid release of mediators after the interaction of allergen with IgE-coated mast cells. The traditional understanding has been that mast cell activation results in the release of a series of preformed and rapidly synthesized substances that mediate the immediate onset of vasodilatation, vascular leakage, smooth muscle contraction, and irritant nerve receptor stimulation. These mediators, however, are rapidly degraded and are not thought to be associated with a significant inflammatory component. Recent studies, however, have established that the interaction of allergen with the immune system is, in fact, far more complex (Fig. 4). In addition to mast cell activation, allergen can interact with and activate T-lymphocytes and mononuclear phagocytic cells, leading to the secretion of cytokines and other inflammatory substances. Furthermore, the interaction of allergen with the mast cell may be far more complex, with the potential to stimulate the delayed release of newly synthesized cytokines. The interaction of allergen with the immune system also promotes the secondary release of inflammatory neuropeptides. Thus, the known spectrum of mediators released after allergen exposure has vastly been expanded. These include numerous still uncharacterized chemotactic and activating peptides; eicosanoids such as 5-HETE, 12-HETE, and leukotriene B4; platelet-activating factor; several proteases; neuropeptides and, most importantly, the cytokines. These mediators recruit and activate neutrophils, monocytes, basophils, and eosinophils, attract additional lymphocytes and mononuclear phagocytic cells, and induce mast cell proliferation with further mast cell degranulation. A vicious cycle subsequently develops, with further inflammation and tissue destruction. Thus, the interaction of allergen with the immune system has become a complex cascade capable of producing the chronic inflammatory changes characteristic of allergic diseases.

Relaxant effect of pituitary adenylate cyclase-activating polypeptide on guinea-pig tracheal smooth muscle

We investigated the relaxant effect of the pituitary adenylate cyclase-activating polypeptide with 27 residues (PACAP27) and with 38 residues (PACAP38) on guinea-pig tracheal smooth muscle. Both forms of PACAP showed dose-dependent relaxant effects. The EC50 of PACAP27 was 8.7 +/- 1.9 x 10(-8) M and that of PACAP38 was 6.8 +/- 1.0 x 10(-8) M. Both increased cyclic AMP levels dose dependently and the elevation of cyclic AMP preceded the relaxation of tracheal smooth muscle. There was a marked difference in the duration of action of the two peptides. PACAP38 showed a longer-lasting relaxation compared to PACAP27. Furthermore PACAP38 maintained significantly higher levels of cyclic AMP, with cyclic AMP levels at 60 min after a 5-min exposure to PACAPs (10(-6) M) being 14.0 +/- 1.4 pM/mg protein for PACAP27 and 35.9 +/- 2.4 pM/mg protein for PACAP38. These results suggest that PACAP27 and PACAP38 may be novel potent relaxants in tracheal smooth muscle and their relaxant effect might be mediated by cyclic AMP. However PACAP38 had a longer-lasting action on relaxation of tracheal smooth muscle and production of tissue cyclic AMP than PACAP27.