Data on oxidants and antioxidants.

The monovalent reduction of O2 gives rise to highly reactive O2 intermediates, such as superoxide radical (O2-.), hydrogen peroxide (H2O2), and hydroxyl radical (OH.), as well as to singlet O2 (1O2). These O2 metabolites are capable of acting on several groups of substances: enzymes to inactivate them, polyunsaturated fatty acids to form lipid peroxides and DNA to cause single strand breaks and mutations. There are, however, several lines of antioxidant defences, which can be enzymatic (superoxide dismutase, catalase, glutathione peroxidase) or non-enzymatic (glutathione, vitamins C and E, beta-carotene, etc.). These defences are necessary to protect the cell against the intracellular or extracellular generation of O2 metabolites. Since O2 intermediates can affect the general cellular metabolism and inhibit cell replication or reduce protein synthesis, all the biological effects of O2 and its metabolites should therefore be considered in the pathogenesis of emphysematous lesions in the lung.