A study of mice exposed to tobacco smoke has offered scientists a new insight into the pathology of emphysema and chronic obstructive pulmonary disorder (COPD), and offers hope of a new treatment to reverse the lung damage underlying these conditions. Norbert Weissman of the University of Giessen Lung Center in Germany and colleagues found that changes to the pulmonary blood vessels and the development of high blood pressure precede the development of emphysema. Further investigation showed that this early pathology is caused by an inducible form of nitric oxide synthase (iNOS), an enzyme that catalyzes the formation of nitric oxide. Mice lacking the iNOS enzyme were protected from both emphysema and pulmonary hypertension. Importantly, drugs that can block iNOS activity are already available, and mice treated with one of these drugs were shown to be protected from COPD-like changes to their lungs. Moreover, treatment with the inhibitor also successfully reversed the course of the disease in the mice. Encouragingly, he iNOS inhibitor used in the study has already been used in clinical trials with no apparent major side effects. The researchers plan to pursue use of the drug as an inhaled therapy. COPD is expected to become the third-greatest cause of death worldwide by 2020.