Search

Background: The tachykinins, substance P and neurokinin A, present in sensory nerves and inflammatory cells such as macrophages and dendritic cells, are considered as pro-inflammatory agents. Inflammation of the airways and lung parenchyma plays a major role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and increased tachykinin levels are recovered from the airways of COPD patients. The aim of our study was to clarify the involvement of the tachykinin NK1 receptor, the preferential receptor for substance P, in cigarette smoke (CS)-induced pulmonary inflammation and emphysema in a mouse model of COPD.Methods: Tachykinin NK1 receptor knockout (NK1-R-/-) mice and their wild type controls (all in a mixed 129/sv-C57BL/6 background) were subjected to sub acute (4 weeks) or chronic (24 weeks) exposure to air or CS. 24 hours after the last exposure, pulmonary inflammation and development of emphysema were evaluated.Results: Sub acute and chronic exposure to CS resulted in a substantial accumulation of inflammatory cells in the airways of both WT and NK1-R-/- mice. However, the CS-induced increase in macrophages and dendritic cells was significantly impaired in NK1-R-/- mice, compared to WT controls, and correlated with an attenuated release of MIP-3alpha/CCL20 and TGF-beta1. Chronic exposure to CS resulted in development of pulmonary emphysema in WT mice. NK1-R-/- mice showed already enlarged airspaces upon air-exposure. Upon CS-exposure, the NK1-R-/- mice did not develop additional destruction of the lung parenchyma. Moreover, an impaired production of MMP-12 by alveolar macrophages upon CS-exposure was observed in these KO mice. In a pharmacological validation experiment using the NK1 receptor antagonist RP 67580, we confirmed the protective effect of absence of the NK1 receptor on CS-induced pulmonary inflammation.Conclusion: These data suggest that the tachykinin NK1 receptor is involved in the accumulation of macrophages and dendritic cells in the airways upon CS-exposure and in the development of smoking-induced emphysema. As both inflammation of the airways and parenchymal destruction are important characteristics of COPD, these findings may have implications in the future treatment of this devastating disease. [ABSTRACT FROM AUTHOR]

The role of the NK1 receptor in airway contraction induced by electrical field stimulation (EFS) was evaluated by comparing the response in NK1 receptor knockout mice (NK1R-/-) with that of NK1 receptor wild-type controls (WT). A frequency/response curve on tracheas from NK1R-/- mice and NK1R WT littermates was constructed. After incubation with [3H]choline, [3H]acetylcholine release upon EFS was measured by high-performance liquid chromatography and liquid scintillation counting. The effects of atropine (1 x 10(-6) M), tetrodotoxin (1 x 10(-6) M) and a specific NK1R antagonist (SR140333, 1 x 10(-8) M) were studied, as well as the effects of substance P (1 x 10(-5) M) on precontracted tracheas. Upon EFS, NK1R-/- mice had a significant lower trachea contractility than the NK1R WT animals, accompanied with less [3H]acetylcholine release. Pretreatment with atropine or tetrodotoxin abolished the EFS-induced contraction in both strains. Pretreatment with the NK1R antagonist SR140333 significantly reduced the contractility in the NK1R WT but not in the NK1R-/- mice. Substance P caused a small contraction in both NK1R WT and NK1R-/- mice. Substance P induced a relaxation in precontracted tracheas in NK1R WT but not in NK1R-/- mice. The data presented here provide direct evidence that the NK1 receptor augments cholinergic neurotransmission in mouse trachea.