Potential role of tachykinins in inflammatory diseases

Tachykinin Receptor-Selectivity of the Potential Glioblastoma-Targeted Therapy, DOTA-[Thi8,Met(O2)11]-Substance P

Radiopharmaceutical development hinges on the affinity and selectivity of the biological component for the intended target. An analogue of the neuropeptide Substance P (SP), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-[Thi8,Met(O2)11]-SP (DOTA-[Thi8,Met(O2)11]SP), in the theranostic pair [68Ga]Ga-/ [213Bi]Bi-DOTA-[Thi8,Met(O2)11]SP has shown promising clinical results in the treatment of inoperable glioblastoma. As the theranostic targeting component, modifications to SP that affect the selectivity of the resulting analogue for the intended target (neurokinin-1 receptor [NK1R]) could be detrimental to its therapeutic potential. In addition to other closely related tachykinin receptors (neurokinin-2 receptor [NK2R] and neurokinin-3 receptor [NK3R]), SP can activate a mast cell expressed receptor Mas-related G protein-coupled receptor subtype 2 (MRGPRX2), which has been implicated in allergic-type reactions. Therefore, activation of these receptors by SP analogues has severe implications for their therapeutic potential. Here, the receptor selectivity of DOTA-[Thi8,Met(O2)11]SP was examined using inositol phosphate accumulation assay in HEK293-T cells expressing NK1R, NK2R, NK3R or MRGPRX2. DOTA-[Thi8,Met(O2)11]SP had similar efficacy and potency as native SP at NK1R, but displayed greater NK1R selectivity. DOTA-[Thi8,Met(O2)11]SP was unable to elicit significant activation of the other tachykinin receptors nor MRGPRX2 at high concentrations nor did it display antagonistic behaviour at these receptors. DOTA-[Thi8,Met(O2)11]SP, therefore has high potency and selectivity for NK1R, supporting its potential for targeted theranostic use in glioblastoma multiforme and other conditions characterised by NK1R overexpression.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

Role of capsaicin-sensitive afferent nerves in different models of gastric inflammation in rats

Capsaicin-sensitive afferent nerves are described as being protective against gastric inflammation; their destruction leads to an exacerbation of inflammatory processes. However, these nerves have been shown to exert a pro-inflammatory action on stress-induced gastritis in rats. Our study aimed to investigate the role of capsaicin-sensitive afferent nerves in different experimental models of gastritis in rats. Functional ablation of sensory nerves was achieved by systemic capsaicin treatment (100 mg/kg). Gastritis was induced by mild (iodoacetamide, diquat, surgical duodeno-gastric reflux [DGR]) and strong (70% ethanol, indomethacin) inflammatory agents. Antagonists of the CGRP1 and NK1 receptors, hCGRP8-37 and SR140333, were administered in rats treated with iodoacetamide and ethanol. Macroscopic damage scores (MDS), myeloperoxidase (MPO) activity and malondialdehyde (MDA) concentration were evaluated after sacrifice. Macroscopic lesions appeared only in ethanol and indomethacin gastritis and were enhanced by capsaicin treatment. Gastric MPO activity was significantly increased by all agents compared to controls. Capsaicin treatment did not have any effect on MPO activity in indomethacin-treated rats or in rats submitted to surgery for duodeno-gastric reflux. However, it abolished the increase in MPO induced by iodoacetamide and diquat, and significantly enhanced that induced by ethanol. hCGRP8-37 and SR140333 abolished the increase in MPO activity and MDA concentration in iodoacetamide treated rats. In ethanol-treated rats, SR140333 diminished MPO activity. These results indicate that, depending upon the nature and duration of the experimental inflammation, capsaicin-sensitive afferent nerves may act differently to control gastric inflammatory processes, suggesting the involvement of a neurogenic component in some forms of gastric inflammation.

Reflex mechanisms in gastroesophageal reflux disease and asthma

This article presents a brief description of the reflex mechanisms responsible for cough and bronchospasm, and identifies several potential mechanisms by which gastroesophageal reflux (GER) may precipitate these reflexes. Airway and esophageal reflexes related to various mechanoreceptors and chemoreceptors have been elucidated, primarily in animal studies. Central nervous system (CNS) reflex pathways as well as local axon reflexes may each contribute to the pathogenesis of both asthma and GER disease (GERD). When activated, airway nociceptors precipitate defensive reflexes such as cough, bronchospasm, and mucus secretion. Nociceptors innervating both the airways and the esophagus respond to similar stimuli with defensive manuevers. The pathways of some esophageal and airway sensory nerves terminate in the same regions of the CNS. It appears possible that synergistic interactions between esophageal nociceptors and airway sensory nerves may precipitate the asthma-like symptoms associated with GERD.

Role of nerves in asthmatic inflammation and potential influence of gastroesophageal reflux disease

Inflammation of the lower airways is a defining characteristic of asthma. Microaspiration of refluxate may initiate an inflammatory response in the airways of patients with gastroesophageal reflux disease (GERD), thereby precipitating asthma. Airway nerves are likely to play a role in the pathogenesis of asthma and could potentially mediate airway inflammation initiated by GERD through axonal reflexes. Alternatively, refluxate may initiate airway reflexes from the esophagus that are markedly exaggerated by inflammation-induced enhancement of airway neuronal excitability. The characteristic features of inflammation in asthma are defined, and the potential role of nerves in inflammation is discussed. Mechanisms by which GERD may initiate airway inflammation or act synergistically with airway inflammation to produce asthma also are discussed.

Neural regulation of airway smooth muscle tone

Airway smooth muscle is innervated by sympathetic and parasympathetic nerves. When activated, airway nerves can markedly constrict bronchi either in vivo or in vitro, or can completely dilate a precontracted airway. The nervous system therefore plays a primary role in regulating airway caliber and its dysfunction is likely to contribute to the pathogenesis of airways diseases. The predominant contractile innervation of airway smooth muscle is parasympathetic and cholinergic in nature, while the primary relaxant innervation of the airways is comprised of noncholinergic (nitric oxide synthase- and vasoactive intestinal peptide-containing) parasympathetic nerves. These parasympathetic nerves are anatomically and physiologically distinct from one another and differentially regulated by reflexes. Sympathetic-adrenergic nerves play little if any role in directly regulating smooth muscle tone in the human airways. Activation of airway afferent nerves (rapidly adapting receptors, C-fibers) can evoke increases in airway smooth muscle parasympathetic nerve activity, or decreases in parasympathetic nerve activity (through activation of slowly adapting receptors). Extrapulmonary afferents can also modulate nerve mediated regulation of airway smooth muscle tone. In guinea pigs and rats, peripheral activation of tachykinin-containing airway afferent nerves evokes bronchospasm via release of substance P and neurokinin A. This effect of airway afferent nerve activation appears to be unique to guinea pigs and rats. The actions and interactions between the components of airway innervation are discussed.

Regulation of baseline cholinergic tone in guinea-pig airway smooth muscle

1. We quantified baseline cholinergic tone in the trachealis of mechanically ventilated guinea-pigs and determined the influence of vagal afferent nerve activity on this parasympathetic tone. 2. There was a substantial amount of baseline cholinergic tone in the guinea-pig trachea, eliciting contractions of the trachealis that averaged 24.6 +/- 3.5 % (mean +/- s.e.m.) of the maximum attainable contraction. This tone was essentially abolished by vagotomy or ganglionic blockade, suggesting that it was dependent upon on-going pre-ganglionic input arising from the central nervous system. 3. Cholinergic tone in the trachealis could be markedly and rapidly altered (either increased or decreased) by changes in ventilation (e. g. cessation of ventilation; hyperpnoea; slow, deep breathing) and by lung distention (via positive end-expiratory pressure). These effects were not accompanied by marked alterations in blood gases and were abolished by vagotomy or atropine. By contrast, tachykinin receptor antagonists, which abolished capsaicin-induced bronchospasm, were without effect on baseline cholinergic tone. This and other evidence suggests that capsaicin-sensitive nerves have little if any influence on baseline parasympathetic tone. Likewise, while activation of afferent nerves innervating the larynx can alter airway parasympathetic nerve activity, transection of the superior laryngeal nerves was without effect on baseline cholinergic tone. 4. Cutting the vagus nerves caudal to the recurrent laryngeal nerves, thus leaving the preganglionic parasympathetic innervation of the trachealis intact but disrupting all afferent nerves innervating the lungs and intrapulmonary airways, abolished baseline cholinergic tone in the trachea. Sham vagotomy or cutting the vagi caudal to the lungs did not reduce baseline cholinergic tone. 5. The results indicate that baseline airway cholinergic nerve activity is necessarily dependent upon afferent nerve activity arising from the intrapulmonary airways and lungs. More specifically, the data are consistent with the hypothesis that on-going activity arising from the nerve terminals of intrapulmonary rapidly adapting receptors determines the level of baseline airway cholinergic tone.

Neutrophil recruitment by interleukin-17 into rat airways in vivo. Role of tachykinins

We determined whether neutrophil recruitment induced by the T-lymphocyte cytokine, interleukin-17 (IL-17) is modulated by tachykinins in airways in vivo. Cell recruitment into airways was induced by either human (h) IL-17 (1 microgram) or rat (r) IL-1beta (2. 5 ng), instilled intratracheally in rats (n = 5 to 7). Six hours after instillation, hIL-17 (3.1 +/- 1.2 x 10(6) cells/ml) and rIL-1beta (4.1 +/- 0.5 x 10(6) cells/ml), respectively, induced a significant and selective increase in neutrophil count in bronchoalveolar lavage fluid (BAL) when compared with vehicle (0.6 +/- 0.2 x 10(6) cells/ml). For hIL-17, this effect was dose-dependent. Inhalation of peptidase inhibitors (phosphoramidon plus captopril) potentiated the effect of both hIL-17 and rIL-1beta. Inhalation of a neutral endopeptidase inhibitor (phosphoramidon) alone also increased the neutrophil count for hIL-17, whereas an angiotensin-converting enzyme inhibitor (captopril) alone did not. A selective neurokinin (NK)-1 receptor antagonist (SR 140333) reduced the neutrophil count, both with and without phosphoramidon pretreatment. In conclusion, IL-17 selectively recruits neutrophils into rat airways in vivo and this effect is modulated by endogenous tachykinins acting via NK-1 receptors.

A method to measure dual NK1/NK2-antagonist activity in dogs

The major pulmonary effects of tachykinins are produced by activation of both NK1- and NK2-receptors. A variety of animal models have been used to profile activity of the tachykinins, particularly rodents and guinea pigs, but little information exists regarding methods to evaluate NK1- and NK2-receptor antagonist activity in dogs. This study describes a simple method in dogs to measure NK1- and NK2-receptor agonist and antagonist activity of drugs in the same preparation. We measured pulmonary resistance (RL), dynamic lung compliance (CDyn), minute volume (MV), and mean arterial blood pressure (MAP) before and after challenge with aerosolized NKA (1%) and i.v. SP (100 ng/kg) to quantify responses to the tachykinin challenge. Challenge with NKA produced an increase in RL and a decrease in CDyn, and this bronchospasm was inhibited by the NK2-antagonist SR 48968 (ID50 RL=1.3 mg/kg and ID50 CDyn=1.3 mg/kg, p.o.). The NK1-antagonist, CP 99994 was inactive against NKA-induced bronchospasm at doses up to 10 mg/kg, p.o. When the dogs were challenged with SP, there was a fall in MAP and an increase in MV and both responses were inhibited by CP 99994 (ID50 MV=2.3 mg/kg and ID50 BP=4.5 mg/kg, p.o.), but not by SR 48968 at doses up to 3 mg/kg, p.o. These results identify that NK2-receptors mediate the bronchoconstrictor effect of NKA, and NK1-receptors mediate the hypotension and respiratory stimulation due to SP in dogs. This method offers many advantages for evaluating the effects of tachykinin antagonists including the fact that it is relatively simple to perform and has the capacity to assess both NK1 and NK2 antagonist activity in the same preparation.