Nitric Oxide and Airway Reactivity

Nitric oxide (NO) has long been known as an atmospheric pollutant present in vehicle exhaust emissions and cigarette smoke. Its clinical importance as a biologic mediator in animals and humans has been recognized over the past decade. NO is present in virtually all mammalian organ systems and is present in the exhaled breath of humans. Patients with asthma have high levels of NO in their exhaled breath and high levels of nitric oxide synthase (NOS) II enzyme expression in the epithelial cells of their airways. Although these findings suggest a role for NO in asthma pathogenesis, the role of NO in asthma and airway reactivity remains elusive despite intense research. Whether NO is beneficial through its bronchodilator and antioxidant effects or harmful by inducing inflammation remains unclear. The use of exhaled NO in monitoring asthma is promising, but its clinical use awaits further developments in the field.