Impact of theophylline/corticosteroid

combination therapy on sputum hydrogen sulfide levels in patients with COPD To the Editor: Hydrogen sulfide (H2S) has emerged as a new and important endogenous regulator of inflammation in recent years [1] and may also protect from emphysema induced by cigarette smoke exposure [2]. We have also recently shown that H2S can inhibit airway smooth muscle cell proliferation and inflammatory mediator release in vitro [3]. Serum levels of H2S positively correlate with the decline in lung function in chronic obstructive pulmonary disease (COPD) and were significantly lower in Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage III patients compared with those in GOLD I [4]. Existing therapies for COPD, such as corticosteroids or long-acting anticholinergic agents, may reduce the exacerbation rate but do not significantly slow disease progression. A previous study has shown that theophylline alone had no impact on serum H2S levels and is of limited value in the management of stable COPD [5]. Interestingly, sputum H2S measured in patients with asthma correlated with sputum neutrophil counts and the degree of airflow obstruction measured by forced expiratory volume in 1 s (FEV1) % predicted [6]. Moreover, combination therapy of an inhaled glucocorticoid with low-dose theophylline has been shown to attenuat