The effect of the leukotriene receptor antagonist zafirlukast on neurokinin A-induced bronchoconstriction in patients with asthma--A comparison with leukotriene D4 induced broncoconstriction

The bronchoconstriction caused by inhaled neurokinin A (NKA) in patients with asthma is indirect. The mediators involved in NKA-induced bronchoconstriction are unknown. Studies with various H1 receptor antagonists were negative, making an important contribution of histamine unlikely. To study the role of cysteinyl leukotrienes in neurokinin A-induced bronchoconstriction, we performed a randomised, double-blind, cross-over, placebo controlled trial in 12 patients with mild to moderate asthma. Zafirlukast and matching placebo were given orally, 40 mg the evening before and 40 mg the morning of assessment. In one period NKA was administered, in the other period leukotriene D4 (LTD4). Increasing concentrations of NKA and LTD4 were inhaled from a 30 L bag, after nebulization via a Mallinckrodt nebuliser. The difference between log10PC20LTD4 after treatment with placebo or zafirlukast was highly significant (p<0.0001). A trend was observed towards a difference between log10PC20 neurokinin A after treatment with placebo or zafirlukast (p=0.0741). The dose ratio for the neurokinin A provocation was 4.4 and for the LTD4 provocation 67.7. In conclusion, zafirlukast had a large inhibitory effect on LTD4-induced bronchoconstriction, but offered only limited protective effect against neurokinin A-induced bronchoconstriction. We suggest that leukotrienes play a limited role in the bronchoconstrictor effect of neurokinin A in patients with asthma.

Role of NK-1 and NK-2 tachykinin receptor antagonism on the growth of human breast carcinoma cell line MDA-MB-231

We demonstrate that neurokinin A (NKA) and substance P (SP) play a role in the proliferation of the estrogen receptor-negative (ER-) cell line MDA-MB-231, a human breast carcinoma expressing both NK-1 and NK-2 receptors. In vitro experiments showed that the specific receptor antagonists MEN 11,467 (NK-1) and nepadutant (MEN 11,420; NK-2) inhibited tumor cell proliferation, and blocked the stimulatory effect of SP and NKA. Anti-tumoral activity of NK-1 and NK-2 receptor antagonists was demonstrated in nude mice, measuring growth inhibition of MDA-MB-231 tumor cells xenografted s.c. and by using the hollow-fiber assay. In both systems a significant inhibition was found when compounds were administered at 5 mg/kg i.v. every day for 2 weeks. Results obtained from both these models suggest that the in vivo activity of NK-1 and NK-2 antagonists may be a result of a cytostatic effect rather than a cytotoxic effect. Our results suggest that the control of breast carcinoma (ER-) growth by tachykinin receptor antagonists may become a new form of targeted therapy for these human tumors.

Depressed contractile responses to neurokinin A in idiopathic but not neurogenic overactive human detrusor muscle

OBJECTIVE

The role of tachykinins such as neurokinin A in regulating bladder function is unclear, but NK2 receptors seem to mediate contraction in the human bladder and it has been suggested that these peptides may have a role in the pathophysiology of bladder dysfunction. The present study investigates neurokinin receptor-mediated contractility of detrusor muscle in the idiopathic overactive and neurogenic overactive bladder and investigates the neurokinin receptor subtypes involved.

METHODS

Human bladder was obtained from patients undergoing cystectomy (normal) or clam cystoplasty (idiopathic overactive) and from patients with spinal injuries (neurogenic overactive). Strips of isolated detrusor muscle were mounted in physiological Krebs-bicarbonate solution and cumulative concentration-response curves to 1 nM to 300 microM neurokinin A (NKA) were obtained in the absence and presence of neurokinin receptor antagonists, either the NK2 receptor-selective antagonist SR 48968 or the NK3 receptor-selective antagonist SB 223412.

RESULTS

NKA evoked concentration-dependent contraction of normal, idiopathic, and neurogenic overactive detrusor strips. In idiopathic overactive detrusor muscle, NKA-induced contraction was significantly reduced relative to normal detrusor (0.031 +/- 0.005 mg/g, n = 11 versus 0.193 +/- 0.039 mg/g, n = 7). Sensitivity to the peptide was also significantly (p < 0.01) reduced in idiopathic overactive detrusor, with mean pEC50 values (concentration producing 50% maximal response) of 6.62+/-0.16 (n = 11) compared to 7.47+/-0.19 (n = 7) in normal detrusor. In contrast, NKA-induced responses of neurogenic overactive detrusor were similar to those in normal detrusor, with a mean maximum contraction of 0.199 +/- 0.036 mg/g (n = 10) and mean pEC50 value of 7.85+/-0.16 (n = 10). NKA curves in all groups were shifted to the right by the NK2 receptor-selective antagonist SR 48968 with high affinity, pK(B) values being similar in normal, idiopathic, and neurogenic overactive detrusor (8.85 + 0.08, n = 14; 8.97 +/- 0.13, n = 12; 8.73 +/- 0.12, n = 8, respectively). In contrast the NK3 receptor-selective antagonist SB 223412 had a minimal effect on NKA responses and affinity values were low (pK(B) 5.81 +/- 0.11, n = 12 in normal; 5.75 +/- 0.08, n = 12 in idiopathic overactive, and 5.77 +/- 0.13, n = 11 in neurogenic overactive).

CONCLUSION

These data indicate that NKA-induced responses are impaired in detrusor muscle from idiopathic overactive human bladder, but not in detrusor muscle from neurogenic overactive bladder. The NK2 receptor subtype appears to mediate NKA responses in the normal, idiopathic overactive, and neurogenic overactive detrusor. This is important evidence suggesting a difference between the bladder pathophysiology observed in idiopathic versus neurogenic overactive detrusor.

The triple neurokinin-receptor antagonist CS-003 inhibits neurokinin A-induced bronchoconstriction in patients with asthma

Neurokinin A (NKA) causes bronchoconstriction in asthmatic patients. In vitro both NK1 and NK2 receptors can mediate airway contraction. Moreover in guinea pigs, NK3 receptors facilitate cholinergic neurotransmission. Dual tachykinin NK1/NK2 receptor antagonism results in prevention of NKA-induced bronchoconstriction. We have now examined the effect of a single dose of the triple tachykinin receptor antagonist CS-003 on NKA-induced bronchoconstriction in asthmatics. A double blind, crossover, placebo-controlled trial in 16 mild asthmatics was performed. One single dose of CS-003 (200 mg, solution in distilled water) or matched placebo was given orally on the assessment days. NKA-provocation tests were performed pre-dose and 1, 8 and 24 h after dosing. There was a significant shift to the right of the dose-response curve at 1 and 8 h after intake of CS-003. PC20 was not reached in 12/16 patients at 1h post-dose and in 5/16 patients at 8 h post-dose. This did not occur under placebo treatment. A single dose of 200 mg CS-003 protected significantly against NKA-induced bronchoconstriction at 1 and 8h post-dose in mild asthmatics.

Characterization of receptors for two Xenopus gastrointestinal tachykinin peptides in their species of origin

Two tachykinin peptides, bufokinin and Xenopus neurokinin A (X-NKA) were recently isolated from Xenopus laevis. In this study we investigated the tachykinin receptors in the Xenopus gastrointestinal tract. In functional studies using stomach circular muscle strips, all peptides had similar potencies (EC50 values 1-7 nM). The rank order of potency to contract the intestine was physalaemin (EC50 1 nM)> or =bufokinin (EC50 3 nM)>substance P (SP)> or =cod SP>NKA>>X-NKA (EC50 1,900 nM). No maximum response could be obtained for [Sar9,Met(O2)11]SP, eledoisin and kassinin. In stomach strips, the mammalian tachykinin receptor antagonists RP 67580 (NK1) and MEN 10376 (NK2) had agonistic effects but did not antagonize bufokinin or X-NKA. In intestinal strips, RP 67580 (1 microM) reduced the maximal response to X-NKA but not bufokinin, while MEN 10376 was ineffective. [125I]BH-bufokinin bound with high affinity to a single class of sites, of KD 213+/-35 (stomach) and 172+/-9.3 pM (intestine). Specific binding of [125I]BH-bufokinin was displaced by bufokinin> or =SP>NKA> or =eledoisin approximately kassinin>X-NKA, indicating binding to a tachykinin NK1-like receptor. Selective tachykinin receptor antagonists were weak or ineffective. Other iodinated tachykinins ([125I]NKA and [125I]BH-eledoisin) displayed biphasic competition profiles, with the majority of sites preferring bufokinin rather than X-NKA. In conclusion, there is evidence for two different tachykinin receptors in Xenopus gastrointestinal tract. Both receptors may exist in stomach, whereas the bufokinin-preferring NK1-like receptor predominates in longitudinal muscle of the small intestine. Antagonists appear to interact differently with amphibian receptors, compared with mammalian receptors.

Pemirolast potently attenuates paclitaxel hypersensitivity reactions through inhibition of the release of sensory neuropeptides in rats

The effects of anti-allergic agents on the hypersensitivity reactions to paclitaxel, an anti-cancer agent, were examined in rats. Intravenous injection of paclitaxel (15 mg/kg) caused a marked extravasation of plasma protein in lungs and a transient decrease in arterial partial oxygen pressure (PaO(2)). The paclitaxel-induced protein extravasation was inhibited by low doses (0.1-1 mg/kg) of pemirolast or high doses (30-100 mg/kg) of cromoglycate. However, ketotifen was not effective. The decrease in PaO(2) induced by paclitaxel was also significantly reversed by pemirolast. On the other hand, the paclitaxel-induced plasma extravasation was not attenuated by a histamine H(1) blocker diphenhydramine or an H(2) blocker famotidine, but was significantly reduced by a neurokinin NK(1) antagonist LY303870 (0.5 mg/kg) and an NK(2) antagonist SR48968 (1 mg/kg). The concentrations of proteins and sensory peptides such as substance P, neurokinin A and calcitonin gene-related peptide but not histamine in the rat bronchoalveolar lavage fluid were elevated by paclitaxel injection. Both cromoglycate and pemirolast reduced the paclitaxel-induced rise in proteins and sensory peptides. Therefore, we demonstrated for the first time that sensory nerve peptides are involved in paclitaxel hypersensitivity and that an anti-allergic agent pemirolast attenuates the paclitaxel response by inhibiting the release of sensory nerve peptides.

Effects of Neuropeptides on the Sumatriptan-Disturbed Circulation in the Optic Nerve Head of Rabbits

The purpose of this work was to study 'in vivo' the vascular responses of retinal vessels of New Zealand white rabbits to substance P (SP), neurokinin A (NKA), neurokinin B (NKB), senktide, capsaicin (CAPS), and calcitonin gene related peptide (CGRP) before and after selective antagonist administration. We examined the effects of these neuropeptides on the normal circulation in the optic nerve head of the rabbit. Drugs were injected via pars plana through a micropipette system. Ten minutes before perivascular injection of 10 nmol/l sumatriptan (to contract the vessel), a selective antagonist or its solvent was administered. Then, cumulative injection of the agonist was performed. The other eye was used as control. Direct measurement of retinal arteriole diameters was performed using digital angiography. The quantification of the relaxing effect is expressed as percentage related to the precontracted vascular diameter. Microinjection of SP (NK1 receptor agonist) up to 10 nmol/l induced a dose-dependent arteriolar dilating effect [E(max) (mean +/- SEM) 21.3 +/- 2.3%]. After the perivascular preinjection of 1 nmol/l L-668,169 or 1 nmol/l L-733,060 (NK1 receptor antagonists), the SP dose-response curve was shifted to the right. The same results were obtained with NKA (NK2 receptor agonist) which induced the most potent effect of all neuropeptides (E(max) 53.3+/-2.5%). The NK2 receptor antagonists L-659,877 and GR 159897 (1 nmol/l) strongly inhibited this arteriolar vasodilation. As for CGRP, doses up to 10 nmol/l induced a marked vasodilation (E(max) 41.1+/-0.4%) which decreased after microinjection of the selective antagonist CGRP8-37. The NK3 receptor agonists (senktide and NKB) showed a minor vasodilating effect (E(max) 5.1+/-1.2 and 8.0+/-0.9%, respectively). On the contrary, CAPS showed a marked dose-dependent vasodilating effect (E(max) 43.2+/-2.9%), antagonized by the tachykinin receptor antagonists and CGRP8-37. These results suggest, for the first time, the presence of NK1, NK2, and CGRP receptors on the retinal arteriolar wall of the rabbit.

Pharmacological properties of peptides derived from an antibody against the tachykinin NK1 receptor for the neuropeptide substance P

Two peptides were derived from the structural analysis of a previously described monoclonal antibody [Mol. Immunol. 37 (2000) 423] against the tachykinin NK(1) receptor for the neuropeptide substance P. Here we show that these two peptides were able to inhibit the inositol phosphate transduction pathway triggered both by substance P and neurokinin A, another high-affinity endogenous ligand for the tachykinin NK(1) receptor. They also reduced the cAMP production induced by substance P. By contrast, only one antagonist peptide was able to prevent substance P and neurokinin A from binding the receptor, as revealed both by biochemical and autoradiographic studies. First, these results illustrate the generality of the antibody-based strategy for developing new bioactive peptides. Second, they indicate that antagonists, even exhibiting very close amino acid composition, can interact with the tachykinin NK(1) receptor at different contact sites, some of them clearly distinct from the contact domains for endogenous agonists.

Inhibitory effect of a leukotriene receptor antagonist (montelukast) on neurokinin A-induced bronchoconstriction

BACKGROUND

Tachykinins are potent contractors of human airways producing a dose-related bronchoconstriction when administered by means of inhalation to asthmatic subjects.

OBJECTIVE

The aim of this study was to examine the effective role played by leukotrienes (LTs) in neurokinin A (NKA)-induced bronchoconstriction in asthmatic patients.

METHODS

To address this question, we investigated the protective effect of a selective cysteinyl LT receptor antagonist, montelukast, against inhaled NKA and determined LTE(4) excretion in the urine.

RESULTS

Inhaled NKA in the absence of any drug treatment produced a concentration-related bronchospasm with a geometric mean provocative concentration required to produce a 15% decrease in FEV(1) from the postsaline baseline value (PC(15)) value of 290.9 microg/mL (+SE, 407.1 microg/mL; -SE, 207.84 microg/mL). Montelukast pretreatment significantly increased (P <.01) the PC(15) NKA value (708.8 microg/mL; +SE, 890.47 microg/mL; -SE, 564.15 microg/mL) in comparison with placebo (394.4 microg/mL; +SE, 491.88 microg/mL; -SE, 248.16 microg/mL) and produced a shift of the NKA concentration-response curve to the right in all the subjects studied. When compared with placebo, montelukast did not have a significant protective effect against methacholine challenge; the geometric mean PC(15) values obtained were 0.87 and 0.96 mg/mL with placebo and montelukast, respectively. Although we have not observed any increase in urinary LTE(4) excretion after NKA inhalation, we have shown that pretreatment of asthmatic subjects with montelukast elicits a significant protection against NKA-induced bronchoconstriction.

CONCLUSION

In asthmatic subjects NKA-induced bronchoconstriction is indirectly caused by the release of LTs, and this mechanism could explain some of the antiasthmatic and anti-inflammatory effects of LT antagonists.

Intrathecal histamine induces spinally mediated behavioral responses through tachykinin NK1 receptors

Intrathecal injection of histamine elicited a behavioral response consisting of scratching, biting and licking in conscious mice. Here, we have examined the involvement of substance P (SP) by using intrathecal injection of tachykinin neurokinin (NK)(1) receptor antagonists and SP antiserum. Histamine-induced behavioral response was evoked significantly 5-10 min after intrathecal injection and reached a maximum at 10-15 min. Dose-dependency of the induced response showed a bell-shaped pattern from 200 to 3200 pmol, and maximum effect was observed at 800-1000 pmol. The H(1) receptor antagonist, d-chlorpheniramine and pyrilamine but not the H(2) receptor antagonists, ranitidine and zolantidine, inhibited histamine-induced behavioral response. The NK(1) receptor antagonists, CP-99,994, RP-67580 and sendide, inhibited histamine-induced behavioral response in a dose-dependent manner. A significant antagonistic effect of [D-Phe(7), D-His(9)]SP (6-11), a selective antagonist for SP receptors, was observed against histamine-induced response. The NK(2) receptor antagonist, MEN-10376, had no effect on the response elicited by histamine. Pretreatment with SP antiserum resulted in a significant reduction of the response to histamine. No significant reduction of histamine-induced response was detected in mice pretreated with NK A antiserum. The present results suggest that elicitation of scratching, biting and licking behavior induced by intrathecal injection of histamine may be largely mediated by NK(1) receptors via H(1) receptors in the spinal cord.

Effect of monensin on the levels of tachykinins and their processing enzyme activity in rat dorsal root ganglia

Th effect of monensin, which inhibits trans-Golgi function, on the levels of tachykinins and their processing enzyme activity was examined in organ-cultured rat dorsal root ganglia (DRG). Using an enzyme immunoassay method, we measured neurokinin A and substance P immunoreactivity in the DRG cultured for 72 h with and without 0.1 microM monensin. Both tachykinins were reduced in the DRG treated with monensin. Treatment with monensin also reduced the activity of carboxypeptidase E, which is one of the proteolytic processing enzymes of neuropeptides. These data suggest that proteolytic processing enzymes may in part modulate the biological activity of neuropeptides within a trans-Golgi apparatus.

Tachykinin-stimulated small bowel myoelectric pattern: sensitization by NO inhibition, reversal by neurokinin receptor blockade

Tachykinins stimulate motility whereas NO inhibits motility in the gastrointestinal tract.

AIM

To investigate if inhibition of NO production sensitizes myoelectric activity to subthreshold doses of tachykinins in the small intestine of awake rats.

METHODS

Rats were supplied with a venous catheter and bipolar electrodes at 5, 15 and 25 cm distal to pylorus for electromyography of small intestine. The motor responses were evaluated using pattern recognition. Substance P and neurokinin A dose-dependently stimulated gut motility, with neurokinin A being more potent than substance P. Therefore, neurokinin A was chosen and administered under baseline conditions and 45-60 min after N(omega)-nitro-L-arginine (L-NNA) 1 mg kg(-1), with or without pretreatment with L-arginine 300 mg kg(-1). In addition, myoelectric activity effects of neurokinin A in conjunction with L-NNA were studied before and after administration of the tachykinin receptor antagonists, SR140333 (NK1), SR48968 (NK2) and SR142801 (NK3), each at 2.5 mg kg(-1).

RESULTS

Dose-finding studies verified 10 pmol kg(-1) min(-1) to be the threshold dose at which NKA caused phase II-like activity in a low percentage of experiments (12%, n=41). This dose was therefore used in combination with L-NNA for sensitization experiments of gut myoelectric activity. In experiments where NKA-induced no response, pretreatment with L-NNA led to phase II-like activity in 9 of 18 (50%, p<0.05) experiments. Co-administration of SR140333 and SR48968 abolished this effect.

CONCLUSION

NO counteracts the stimulatory effect of tachykinins on small bowel myoelectric activity in the rat. Inhibition of the L-arginine/NO pathway sensitizes the gut to tachykinin-stimulated motor activity.

2-Aryl indole NK(1) antagonists: optimisation of the amide substituent

The in vivo properties of a series of 2-arylindole NK(1) antagonists have been improved, by modification of the amide substituent. The 1-(2-methoxyphenyl)piperazine amide was identified as a major area of metabolism in the lead compound 1. Replacement of this amine moiety by a 4-benzyl-4-hydroxypiperidine resulted in a compound 18 with reduced clearance and improved central duration of action.

Human colonic anti-secretory activity of the potent NK(1) antagonist, SR140333: assessment of potential anti-diarrhoeal activity in food allergy and inflammatory bowel disease

1. This in vitro study was designed to determine the potential use of the NK(1) antagonist, SR140333 as an anti-diarrhoeal treatment for food allergy or inflammatory bowel disease. The effect of various immune and neuronal stimuli on human colonic substance P (SP) release and the effect of SR140333 on subsequently stimulated mucosal ion transport was investigated. 2. Submucosal and sensory nerve fibre stimulation using electrical field stimulation (1 ms/7 Hz/7 V) and capsaicin (50 microM) respectively, mast cell activation by anti-IgE (1/250 dilution) and granulocyte stimulation using fMLP (50 microM) each released SP and evoked a secretory response. 3. SP and the NK(1) selective agonist, Sar-SP (0.1 - 1000 nM) stimulated an increase in colonic secretion which was antagonized by SR140333 (pD'(2)=6.7 and 7.25 versus SP and Sar-SP respectively). 4. SR140333, at a concentration that blocked NK(1)-mediated secretion (500 nM), also reduced the secretory response to both alphaIgE and capsaicin. This suggests a pathophysiologic role for NK(1) receptors. 5. Capsaicin evoked SP release was increased in tissue taken from Crohn's disease but not ulcerative colitis patients. The response to SP was however reduced by 70 and 89% respectively. 6. Mast cells and sensory afferents contribute to allergic diarrhoea. Since SR140333 reduced the secretory response to mast cell and afferent stimulation this compound may be particularly useful in reducing the symptoms of food allergy.

Differential role of neurokinin receptors in human lymphocyte and monocyte chemotaxis

The precise nature of neurokin receptor involvement in human immune cell chemotaxis is unclear. This study therefore sought to directly compare the chemotactic effects of neurokinins on human T lymphocytes and monocytes. Substance P was found to have a similar dose-dependent chemotactic action on T lymphocyte and monocyte populations. In contrast, T lymphocytes were found to be more responsive than monocytes both to the highly selective NK-1 agonist, [Sar(9)Met O(2)(11)]-substance P, and also to the NK-2 selective agonist, beta-alanine neurokinin A((4-10)). Consistent with these findings, substance P-induced chemotaxis of both T lymphocyte and monocytes was attenuated by the selective NK-1 antagonist LY303870. However, the selective NK-2 antagonist MEN 10,376 was only effective in inhibiting the T lymphocyte response. The study confirms that neurokinins have chemotactic actions on immune cells and indicates important functional differences between human T lymphocyte and monocyte responses. This provides a potential mechanism by which the nervous system can selectively influence cellular recruitment in inflammatory disease.

Bicyclic peptides as type I/type II beta-turn scaffolds

We recently reported the rational design, synthetics, and structural characterization of the most potent and selective peptide-based neurokinin A antagonist thus far described: cyclo(Met1-Asp2-Trp3-Phe4-Dap5-Leu6)cyclo(2 beta-5 beta). Its bicyclic structure is characterized by a type I and a type II two beta-turn around Trp3-Phe4 and Leu6-Met1, respectively. In order to understand whether the two different beta-turned structures are determined by the bicyclic structure or by the amino acid type at the corner positions, we have synthesized the pseudo-symmetrical analogue cyclo(Phe1-Asp2-Trp3-Phe4-Dap5-Trp6)cyclo(2 beta-5 beta). The structural characterization in the crystal state and in solution, here reported, gives an experimental evidence that the backbone of the bicyclic structure is a rigid scaffold that can be used to build both a type I and type II beta-turn independently from the amino acid composition.

Role of tachykinins in asthma

The sensory neuropeptides substance P (SP) and neurokinin A (NKA) are localized to sensory airway nerves, from which they can be released by a variety of stimuli, including allergen, ozone, or inflammatory mediators. Sensory nerves containing these peptides are relatively scarce in human airways, but it is becoming increasingly evident that inflammatory cells such as eosinophils, macrophages, lymphocytes, and dendritic cells can produce the tachykinins SP and NKA. Moreover, immune stimuli can boost the production and secretion of SP and NKA. SP and NKA have potent effects on bronchomotor tone, airway secretions, and bronchial circulation (vasodilation and microvascular leakage) and on inflammatory and immune cells. Following their release, tachykinins are degraded by neutral endopeptidase (NEP) and angiotensin-converting enzyme. The airway effects of the tachykinins are largely mediated by tachykinin NK1 and NK2 receptors. Tachykinins contract smooth muscle mainly by interaction with NK2 receptors, while the vascular and proinflammatory effects are mediated by the NK1 receptor. In view of their potent effects on the airways, tachykinins have been put forward as possible mediators of asthma, and tachykinin receptor antagonists are a potential new class of antiasthmatic medication.

Role of nitric oxide and septide-insensitive NK(1) receptors in bronchoconstriction induced by aerosolised neurokinin A in guinea-pigs

The tachykinin, neurokinin A (NKA), contracts guinea-pig airways both in vitro and in vivo, preferentially activating smooth muscle NK(2) receptors, although smooth muscle NK(1) receptors may also contribute. In vitro evidence suggests that NKA activates epithelial NK(1) receptors, inducing the release of nitric oxide (NO) and subsequent smooth muscle relaxation. A number of selective NK(1) receptor agonists have been reported to activate both smooth muscle and epithelial NK(1) receptors, however septide appears only to activate smooth muscle NK(1) receptors. The aim of the present study was to investigate whether NKA-induced bronchoconstriction in guinea-pigs in vivo may be limited by NO release via NK(1) receptor activation, and whether selective NK(1) receptor agonists may activate this mechanism differently. Aerosolized NKA caused an increase in total pulmonary resistance (RL) that was markedly reduced by the NK(2) receptor antagonist, SR 48968, and abolished by the combination of SR 48968 and the NK(1) receptor antagonist, CP-99, 994. The increase in RL evoked by NKA was potentiated by pretreatment with the NO synthase (NOs) inhibitor, L-NAME, but not by the inactive enantiomer D-NAME. Potentiation by L-NAME of NKA-induced increase in RL was reversed by L-Arginine, but not by D-Arginine. Pretreatment with L-NAME did not affect the increase in RL induced by the selective NK(2) receptor agonist, [beta-Ala(8)]NKA(4-10), and by the selective NK(1) receptor agonist, septide, whereas it markedly potentiated the increase in RL caused by a different NK(1) selective agonist, [Sar(9),Met(O(2))(11)]SP. Dose-response curves showed that septide was a more potent bronchoconstrictor than [Sar(9),Met(O(2))(11)]SP to cause bronchoconstriction. Pretreatment with the NK(1) receptor antagonist, CP-96,994, abolished the ability of L-NAME to increase bronchoconstriction to aerosolized NKA. Bronchoconstriction to aerosolized NKA was increased by L-NAME, after pretreatment with the NK(3) receptor antagonist, SR 142801. The present study shows that in vivo bronchoconstriction in response to the aerosolized naturally occurring tachykinin, NKA, is limited by its own ability to release relaxant NO via NK(1) receptor activation. This receptor is apparently insensitive to septide, thus justifying, at least in part, the high potency of septide to cause bronchoconstriction in guinea-pigs.

Nociceptin-induced scratching, biting and licking in mice: involvement of spinal NK1 receptors

1. Intrathecal (i.t.) injection of nociceptin at small doses (fmol order) elicited a behavioural response consisting of scratching, biting and licking in conscious mice. Here we have examined the involvement of substance P-containing neurons by using i.t. injection of tachykinin neurokinin (NK)1 receptor antagonists and substance P (SP) antiserum. 2. Nociceptin-induced behavioural response was evoked significantly 5 - 10 min after i.t. injection and reached a maximum at 10 - 15 min. Dose-dependency of the induced response showed a bell-shaped pattern from 0.375 - 30.0 fmol, and the maximum effect was observed at 3.0 fmol. 3. The behavioural response elicited by nociceptin (3.0 fmol) was dose-dependently inhibited by intraperitoneal (i.p.) administration of morphine. 4. The NK1 receptor antagonists, CP-96,345, CP-99,994 and sendide, inhibited nociceptin-induced behavioural response in a dose-dependent manner. A significant antagonistic effect of [D-Phe7, D-His9]SP (6 - 11), a selective antagonist for SP receptors, was observed against nociceptin-induced response. The NK2 receptor antagonist, MEN-10376, had no effect on the response elicited by nociceptin. 5. Pretreatment with SP antiserum resulted in a significant reduction of the response to nociceptin. No significant reduction of nociceptin-induced response was detected in mice pretreated with NKA antiserum. 6. The N-methyl-D-aspartate (NMDA) receptor antagonists, dizocilpine (MK-801) and D(-)-2-amino-5-phosphonovaleric acid (APV) (D-APV), and L-NG-nitro arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, failed to inhibit nociceptin-induced behavioural response. 7. off present results suggest that SP-containing neurons in the mouse spinal cord may be involved in elicitation of scratching, biting and licking behaviour following i.t. injection of nociceptin.

Defects of tyrosine289phenylalanine mutation on binding and functional properties of the human tachykinin NK2 receptor stably expressed in chinese hamster ovary cells

A point mutation was made at position 289 in the transmembrane segment 7 of the human tachykinin NK2 receptor to yield a tyrosine/phenylalanine (Tyr/Phe) substitution. Chinese hamster ovary cells stably transfected with the wild-type or Tyr289Phe mutant NK2 receptor both bound neurokinin A (NKA) and the synthetic NK2 receptor-selective agonists, GR 64349 and [betaAla8]NKA(4-10), with high and even affinities. Neurokinin B (NKB) and substance P (SP) also displayed sizeable binding affinities, albeit with lower affinity as compared to NKA. In a functional assay (production of inositol-1,4,5-trisphosphate, IP3), NKA, GR 64349, and [betaAla8]INKA(4-10) stimulated IP3 accumulation via the wild-type and mutant receptors with similar potencies. On the other hand, NKB and SP exhibited a dramatic reduction in their agonist efficacies at the mutant receptor, NKB acting as a partial agonist (maximum effect = 50% of the response to NKA) and SP being totally inactive. The results obtained with phenoxybenzamine inactivation experiments indicated that a large and similar receptor reserve existed for both the wild-type and the mutant receptor. SP, which displayed sizeable binding affinity for the mutant receptor but did not stimulate IP3 accumulation, antagonized the agonist effect of NKA. The antagonist action of SP at the mutant NK2 receptor cannot be ascribed to receptor internalization. The Tyr/Phe replacement at position 289 markedly reduced the binding affinity and antagonist potency of the non-peptide ligand, SR 48968, without affecting the binding affinity and antagonist potency of the bicyclic peptide antagonist MEN 11420. The results indicate that the hydroxyl radical function of Tyr289 in transmembrane segment 7 of the human NK2 receptor is, directly or indirectly, involved in stimulus transduction when the NK2 receptor is occupied by NKB or SP, but not when using NKA or NK2 receptor-selective agonists.

Antagonists of sensory neuropeptides inhibit the secondary phase of increased circulation following thermally induced inflammation

A model of thermally induced inflammation in the anesthetized rat was used to measure acute microcirculatory reactions after heat exposure. The thermal injury was inflicted by dipping the right hindpaw into hot water at 60 degrees for 20 s. Local blood flow was recorded simultaneously in both hindpaws and continuously by laser Doppler flowmetry before, during and for 2 h after the thermal injury and the mean arterial blood pressure (MAP) was displayed on a chart recorder. To assess the contribution of the nervous system to the vascular changes seen, neuropeptide antagonists directed toward substance P (SP), neurokinin A (NKA), and calcitonin gene-related peptide (CGRP) were administered. The neurokinin antagonists (NK1, NK2) and the CGRP antagonist (CGRP8-37) were injected via a catheter into the jugular vein. During the first few minutes after thermal injury to the controls, an immediate increase in blood perfusion of about 351% was recorded, followed by a slow decrease of circulation. At 30 min after thermal injury, there was a secondary phase of increased microcirculation of approximately 329%. A slow decline of cutaneous circulation then followed and, after another 30 min, the value stabilized at a level about 100% above the level before injury. Pretreatment with intravenous injections of the NK1 antagonist, NK2 antagonist, and CGRP8-37 attenuated the first phase and almost abolished the secondary phase. No significant change of perfusion was observed on the unscalded paw. The MAP remained at a stable level throughout the experiment and was not affected by the thermal injury or by the administration of the antagonists as compared to controls. Our results show that sensory neuropeptides play a significant role in the blood flow increase seen following thermal injury.

The peripheral NK-1/NK-2 receptor antagonist MDL 105,172A inhibits tachykinin-mediated respiratory effects in guinea-pigs

1. Stimulation of sensory nerves causes release of tachykinins, including substance P (SP) and neurokinin A (NKA), which produce a variety of respiratory effects via NK-1 and NK-2 receptors, respectively. Hence, development of a compound which could potently and equivalently antagonize both receptors was pursued. 2. MDL 105,172A ((R)-1-[3-(3,4-dicholorophenyl)-1-(3,4,5-trimethoxybenzoyl)- 3-pyrrolidinyl]-4- phenyl-piperidine-4-morpholinecarboxamide) exhibited high affinity for NK-1 (4.34 nM) and NK-2 (2.05 nM) receptors. In vitro, the compound antagonized SP (pA2 = 8.36) or NKA (pA2 = 8.61)-induced inositol phosphate accumulation in tachykinin monoreceptor cell lines. 3. In anaesthetized guinea-pigs, MDL 105,172A inhibited SP-induced plasma protein extravasation (ED50 = 1 mg kg-1, i.v.) and [beta-Ala8]NKA 4-10-induced bronchoconstriction (ED50 = 0.5 mg kg-1, i.v.) indicating NK-1 and NK-2 antagonism, respectively. 4. Capsaicin was used to elicit respiratory effects in anaesthetized and conscious guinea-pigs; the latter were inhibited by MDL 105,172A following i.v. (ED50 = 1 mg kg-1) or oral (ED50 = 20 mg kg-1) administration. Hence, MDL 105,172A can inhibit pulmonary responses to tachykinins released endogenously in the airways. 5. At doses up to 200 mg kg-1, p.o., MDL 105,172A failed to inhibit repetitive hind paw tapping induced by i.c.v GR 73632, and NK-1 selective agonist, in gerbils, whereas CP-99,994 (0.87 mg kg-1, s.c.) completely ablated the effect. These data suggest that MDL 105,172A does not penetrate the central nervous system (CNS) and its tachykinin antagonism is restricted to the periphery. 6. MDL 105,172A is a non-peptide, potent, equivalent antagonist of NK-1 and NK-2 receptors. Its ability to inhibit both exogenously administered as well as endogenously released tachykinins support its use in examining the role of sensory neuropeptides in diseases associated with neurogenic inflammation including asthma.

[Mechanisms of tolerance to sulfur dioxide and sodium metabisulfite]

Inhalation of sulphur dioxide (250 ppm), (SO2) or sodium metabisulfite (80 mM) (MBS) aerosol or perfusion with MBS (3 mM) induced a reduction in compliance and conductance in the isolated, perfused and ventilated guinea pig lung. Pretreatment of the lung with sodium sulfite (3 mM), a dissolution product of SO2 and MBS, reduced the bronchoconstriction induced by SO2 and MBS. Bronchoconstriction induced by SO2 and MBS in associated to increased levels of Calcitonin gene-Related Peptide (CGRP) in the perfusate effinent, indicating activation of sensory nerves. The release of CGRP induced by SO2 and MBS was not affected by sodium sulfite. Sulfite treatment did not modify lung reactivity towards acethylcholine, bradykinin, serotonin, histamine and substance P (fragment 5-11). An inhibitory effect by sulfite was observed on bronchoconstriction induced by neurokinin A (fragment 4-10). Since bronchoconstriction induced by SO2 and MBS appears to be mediated by neurokinin A release and action, sulfite may act by affecting its signal transduction pathway. In conclusion, the results indicate that during exposure to some environmental and occupational pollutants, e.g. SO2 and MBS, critical modifications of sulfhydryl groups on smooth muscle receptors may occur. We hypothesise this as a possible step in the development of tolerance and hyperreactivity.

Experimental treatments for asthma

There has been increased recognition of the importance of inflammatory cells and their products in the pathogenesis of asthma. From this recognition has evolved a number of new approaches to treat the various components of the asthmatic inflammatory response. Nonselective anti-inflammatory agents such as cyclosporine and gold appear to decrease symptoms and allow a steroid-sparing effect in many cases, though side effects from cyclosporine often necessitate dose reduction. Novel oral compounds as the 5-lipoxygenase inhibitors have been effective in controlling asthma symptoms triggered by various stimuli, and the cysteinyl leukotriene receptor antagonists have shown promise in this regard as well. Neurokinin antagonists, inhaled loop diuretics, and lidocaine may play significant roles in asthma therapy through inhibition of neurogenic inflammation and possibly mast cell function. Inhibition of mast cell products by existing drugs such as heparin or the development of specific inhibitors of mast cell tryptase may also be effective agents, as are selective phosphodiesterase inhibitors, which appear to have anti-inflammatory properties. Finally, specific cytokine antagonists, agonists, inhibitors of T-cell function, selective inducible nitric oxide synthase inhibitors, and even gene-directed strategies may provide not only insights into the pathogenesis of asthma but also novel therapeutic approaches to treat the inflammation in this disease.

Role of sensory neuropeptides in post-allergic propranolol-induced bronchoconstriction in guinea pigs in vivo

BACKGROUND

Administration of propranolol can provoke bronchoconstriction in asthmatic patients. We hypothesized that such bronchoconstriction may result from the inflammatory mediators released by an allergic reaction. We recently developed a guinea pig model for propranolol-induced bronchoconstriction (PIB). Neuropeptides which are released from C-fibre nerve endings have been postulated to induce bronchial hyperresponsiveness through neurogenic inflammation.

OBJECTIVE

The purpose of this study was to examine whether sensory neuropeptides are involved in the development of PIB after allergic reaction.

METHODS

Propranolol at a concentration of 10 mg/ml was inhaled 20 min after antigen challenge in passively sensitized, anaesthetized and artificially ventilated guinea pigs. The animals were treated intravenously with a NK1 and NK2 dual antagonist, FK224, in a dose of 1 or 10 mg/kg or vehicle or a selective NK1 antagonist, FK888, in a dose of 1 or 10 mg/kg or vehicle 10 min before or 15 min after antigen challenge.

RESULTS

Propranolol inhaled 20 min after antigen challenge caused bronchoconstriction. FK224 or FK888 administered 15 min after antigen challenge as well as 10 min before antigen challenge did not reduce the PIB.

CONCLUSION

We conclude that neuropeptides such as neurokinin A and substance P do not directly contribute to the development of PIB after allergic reaction.