Novel mechanistic targets for the treatment of sub-acute and chronic bronchitis

Sub-acute and chronic bronchitis (SACB) are among the least well studied major medical problems that exist today. While much research and novel drug discovery have focused on asthma, comparatively little has been performed on chronic bronchitis, the fourth or fifth most frequent disease (4 to 6% of the population over 45 years of age), or on sub-acute bronchitis, the persistent symptoms of a respiratory infection which is the major reason Americans visit a physician (20%). This lack of attention is largely due to difficulties associated with modeling the pathophysiology of SACB in vitro, in situ, in organs or in animals as well as the presumption that drugs developed for asthma would also be effective in SACB. Data with bronchodilators (anti-cholinergics versus beta2-adrenergic agonist) and corticosteroids have strongly dismissed that premise. In this review of potential novel mechanistic targets directed specifically at SACB, an emphasis is given to recent data, gathered most convincingly from tissues and patients with cystic fibrosis, that have led to an appreciation of the critical role respiratory epithelial dysfunction plays in the pathophysiology and symptoms of these diseases. Mechanistic targets that restore (normalize or accelerate) airway 'cleansing' (enhance host defense) by accelerating mucociliary clearance are described and given preference over anti-inflammatory mechanisms that could further impair host defense.