Pulmonary, Gastrointestinal and Urogenital Pharmacology
ATP in the pathogenesis of lung emphysema

https://doi.org/10.1016/j.ejphar.2009.07.022Get rights and content

Abstract

Extracellular ATP is a signaling molecule that often serves as a danger signal to alert the immune system of tissue damage. This molecule activates P2 nucleotide receptors, that include the ionotropic P2X receptors and metabotropic P2Y receptors. Recently, it has been reported that ATP accumulates in the airways of both asthmatic patients and sensitized mice after allergen challenge. The role and function of ATP in the pathogenesis of chronic obstructive pulmonary diseases (COPD) are not well understood. In this study we investigated the effect of cigarette smoke on purinergic receptors and ATP release by neutrophils. Neutrophils and their mediators are key players in the pathogenesis of lung emphysema. Here we demonstrated that in an in vivo model of cigarette smoke-induced lung emphysema, the amount of ATP was increased in the bronchoalveolar lavage fluid. Moreover, activation of neutrophils with cigarette smoke extract induced ATP release. Treatment of neutrophils with apyrase (catalyses the hydrolysis of ATP to yield AMP) and suramin (P2-receptor antagonist) abrogated the release of CXCL8 and elastase induced by cigarette smoke extract and exogenous ATP. These observations indicate that activation of purinergic signaling by cigarette smoke may take part in the pathogenesis of lung emphysema.

Introduction

ATP, a molecule which belongs to the purine family, is an important signaling molecule. Extracellular ATP has recently gained attention as a mediator of intercellular communication via the activation of purinergic P2X and P2Y receptors (Fountain and Burnstock, 2009, Quintas et al., 2009). Extracellular ATP serves as a danger signal to alert the immune system of tissue damage (Kumar and Sharma, 2009). Extracellular nucleotides, primarily ATP, trigger various proinflammatory responses of neutrophils including arachidonic acid release, oxidative burst and phagocytosis (Bours et al., 2006). Neutrophils are primary phagocytic cells with important roles in host defense and tissue repair. However, activated neutrophils damage host tissues and contribute to chronic inflammatory diseases, including rheumatoid arthritis, chronic obstructive pulmonary diseases (COPD), and asthma (Chen et al., 2006). Recently, it has been reported that ATP accumulates in the airways of both the asthmatic patients and sensitized mice after allergen challenge. In addition, sensitization to an inhaled antigen was enhanced by endogenously released or exogenously added ATP (Idzko et al., 2007).

To our knowledge, the role of ATP in the disease COPD has not yet been investigated. COPD is a major and increasing global health problem and cigarette smoke has been considered a major player in the pathogenesis (Calverley and Walker, 2003, Yoshida and Tuder, 2007, Cosio et al., 2009). Neutrophils, neutrophil elastase, metalloproteases, and oxidants have all been shown to play a role in the pathogenesis of COPD (Pease and Sabroe, 2002). COPD has a complex underlying pathophysiology involving the inflammatory and structural cells, all of which have the capacity to release multiple inflammatory mediators, like chemokines and cytokines. Chemokines (mainly CXCL8) and proinflammatory cytokines recruit proinflammatory cells into the lungs (Pease and Sabroe, 2002, Cosio et al., 2009). Indirect evidence support the notion that ATP might be involved in the pathogenesis of COPD (Lazar et al., 2008, van der Toorn et al., 2009), since increased amounts of ATP induce chemotaxis of neutrophils (Kukulski et al., 2009). Chemotaxis allows neutrophils to rapidly reach infected and inflamed sites. Recent findings suggest that ATP and adenosine are involved in neutrophil chemotaxis through P2Y and adenosine A3 receptors (Chen et al., 2006, Kukulski et al., 2009). Therefore, these purinergic signaling processes may be targets for novel therapeutic approaches to ameliorate host tissue damage.

In this study, the effect of cigarette smoke on ATP release and signaling was investigated. The amount of ATP was significantly increased in the bronchoalveolar lavage fluid of cigarette smoke-exposed animals and was associated with lung emphysema. Activation of neutrophils with cigarette smoke extract induced ATP release. Furthermore, cigarette smoke extract and ATP increased the release of CXCL8 and elastase by human neutrophils, which were suppressed by suramin an apyrase. In conclusion, this study describes a new pathway for releasing proinflammatory mediators by cigarette smoke-stimulated neutrophils.

Section snippets

Animals

Five/six-week-old male Balb/c mice were obtained from Charles River (Maastricht, The Netherlands) and housed under controlled conditions in standard laboratory cages in the local animal facility. They were provided free access to water and food. All in vivo experimental protocols were approved by the Animal Care Committee of Utrecht University.

Smoke exposure

Cigarette smoke was generated by the burning of commercially available Lucky Strike cigarettes without filter (British-American Tobacco, Groningen, The

Increased ATP levels in bronchoalveolar lavage fluid of mice exposed to cigarette smoke

Mice were exposed to cigarette smoke for 3 months and 24 h after the last exposure, the concentration of ATP was significantly increased in the bronchoalveolar lavage fluid of the smoke-exposed mice compared to the control animals (Fig. 1A).

Airspace enlargement, as measured by the mean linear intercept (Lm), was significantly augmented in the cigarette smoke-exposed mice as compared to the control group (Fig. 1B).

Cigarette smoke extract increased the production of ATP by human neutrophils

It has been demonstrated that neutrophils have the capacity to release adenine

Discussion

Extracellular ATP liberated during hypoxia and inflammation can either signal directly on purinergic receptors or can activate adenosine receptors following phosphohydrolysis to adenosine. Given the association of neutrophils with adenine-nucleotide/nucleoside signaling in the inflammatory milieu and oxidative stress (Chen et al., 2006, Eltzschig et al., 2006, Eltzschig et al., 2008), we hypothesized a link between cigarette smoke and ATP release and signaling in the pathogenesis of COPD.

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    These authors contributed equally to this work.

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