Tobacco Smoke Induced Cough: Mechanisms Driving Acute and Chronic Cough Pathology

Abstract

Cough is an important protective mechanism that clears foreign material from the airway and aids in immune defence. However, chronic excessive cough of various aetiologies is a common presentation to specialist respiratory clinics, and is reported as a troublesome symptom by a significant proportion of the population (Ford et al., 2006). In extreme situations chronic cough can persist for several years, and is not only socially embarrassing, but can be painful and debilitating. Chronic cough is often associated with an underlying respiratory disease, several of which can be caused or exacerbated by exposure to tobacco smoke or environmental pollution, for example chronic obstructive pulmonary disease (COPD), emphysema, bronchitis, lung cancer and asthma. In addition, chronic cough can be of unknown cause (idiopathic) (Morice et al., 2007). Recently, the label chronic ‘cough hypersensitivity syndrome’ (CCHS) was proposed as a means of focussing the cough community and general practitioners on the symptomology of cough and understanding of the mechanisms behind cough sensation, with the ultimate goal of developing effective antitussive treatments (Millqvist et al., 1998; Chung, 2011). At present, little is known about the mechanisms that drive the cough reflex, and even less about how these mechanisms are altered to lead to chronic cough. Numerous environmental irritants are known to induce coughing such as air pollution, tobacco smoke, smoke from burning vegetation, and vehicle exhaust. This chapter focuses on tobacco smoke (TS), which is one of the most common inhaled irritants (both as an active smoker, and as a secondary environmental pollutant), and is known to contain thousands of noxious chemicals (U.S. Department of Health and Human Services, 2010). Exposure to acute TS readily evokes coughing in both animals and human non-smokers (Andre et al., 2009; Lee et al., 1993; Lee et al., 2007), and prolonged exposure to TS can lead to an altered sensitivity to a range of tussive stimuli (Karlsson et al., 1991; Doherty et al., 2000; Bergren, 2001; Dicpinigaitis, 2003; Lewis et al., 2007). It is believed that if the mechanisms behind acute or chronic cough associated with TS exposure can be revealed it would lead to the development of truly effective cough therapies. The aim of this chapter is to discuss the current understanding of how exposure to TS can cause/alter the cough response and we will consider some of the most promising new therapeutic targets for the treatment of cough.