Nitric Oxide (NO) and Peroxynitrite (ONNO-) Released by Alveolar Macrophages Play a Potential Role in Lung Injury of Cigarette Smokers
Cigarette smoking causes serious health problems according to undeniable evidence. Still uncertain are the mechanisms involved in causing these health problems. We have recently demonstrated that the exhaled cigarette smoke contains large amounts of •NO and ONNO-. Alveolar macrophages suffer oxidative stress when exposed to inhaled cigarette smoke. The causative stimuli for this macrophages stress are to a larger extent O and to a lesser extent CO. Oxidative stress of the macrophages activates the NO Synthase. This triggering mechanism results in NO release in a prolonged and amplified reaction. •NO inside the lungs is transformed into ONOO-, reacting with superoxide (O-2) released by alveolar macrophages. Oxidative stress also causes the production of hydrogen peroxide (H2O2). Both in vitro and in vivo measurements confirm all these findings. In vitro experiments were conducted with the aid of a special apparatus built in our lab, consisted of two chambers (A and B) separated by a tefflon membrane permeable to NO but not to ONOO and to NO-2. Mice lung macrophages placed in an HBSS solution were emptied into chamber A. An equal volume of Griess reagent was placed in the chamber B. The amount of NO released by the macrophages diffuses through the tefflon and was measured in chamber B. The amount of ONOO- and NO2 contained inside the chamber A by the impervious tefflon membrane is also measured Oxidative stress of macrophages and human erythrocytes both exposed to cigarette smoke was estimated. All findings prove conclusively that, (a) macrophages exposed to cigarette smoke produce a dramatic increase of NO, NOx, ONOO- and H2O2 inside the lung. These substances stimulate the macrophages and perhaps even the endothelium of the alveolar vessels. They may cause indirect damage by triggering the production of more nitrogen compounds inside the lung in a vicious circle.