Nitrated and oxidized plasma proteins in smokers and lung cancer patients

Cigarette smoking is a cause of lung cancer and other respiratory diseases. Oxidants either present in cigarette smoke and/or formed in the lung of smokers may trigger oxidative and nitrative damage to DNA and cellular components, contributing to carcinogenesis. We have used immunodot and Western blot analyses to measure nitrated (nitrotyrosine-containing) and oxidized (carbonyl-containing) proteins in plasma samples collected from 52 lung cancer patients and 43 control subjects (heavy and light smokers, nonsmokers with or without exposure to environmental tobacco smoke). The levels of nitrated proteins were significantly higher in lung cancer patients than in controls (P = 0.003). On the other hand, the levels of oxidized proteins were significantly higher in smokers than in nonsmokers (P < 0.001). Western-blot analyses showed the presence of two to five nitrated proteins and one oxidized protein. Using immunoprecipitation and Western-blot analyses with eight different antibodies against human plasma proteins, we identified fibrinogen, transferrin, plasminogen, and ceruloplasmin as nitrated proteins and fibrinogen as the only oxidized protein present in human plasma of lung cancer patients and smokers. Our results indicate that cigarette smoking increases oxidative stress and that during lung cancer development, formation of reactive nitrogen species results in nitration and oxidation of plasma proteins.