Protection of the Lung by Ascorbic Acid

The intracellular and extracellular ascorbic acid play an important role in protecting the lung against various oxidants. While ascorbic acts as a nonenzymatic antioxidant, its effectivity cannot be separated from that of the antioxidant enzymes. Together with these enzymes and other antioxidants such as glutathione and vitamin E, ascorbic acid is necessary to ensure optimal protection of the lung. 

Under aerobic conditions there are a variety of reactive species derived from oxygen that may potentially be involved in reactions with ascorbate. The reactions of the perhydroxyl (or hydroperoxyl, HO2) and superoxide anion (O2 ), in particular with ascorbic acid, have been studied (Cabelli and Bielski 1983 Nadezhdin and 

Dunford, 1979). These oxygen radicals are probably the most likely to be found in the lung under physiological conditions. The concentrations of HO2 and 02 depend on the equilibrium (p/Ta = 4.9) of the following reaction  

Ascorbic acid in the extracellular and intracellular fluid of the lung reacts with superoxide, releasing dehydroascorbic acid and hydrogen peroxide (H2O2). 

Hydrogen peroxide is also an oxidant with the potential to cause severe cell damage. It must therefore be rapidly removed by other antioxidants which occur intra-cellularly in the lung as well as in the bronchoalveolar fluid (Hefner and Repine, 1989), because ascorbic acid cannot react with hydrogen peroxide (Anderson and Lukey, 1987). 

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