MMP9 and chronic obstructive pulmonary disease: Oxidative stress can participate in the induction of an inflammatory reaction together with other pathogenic factors, and can damage the pulmonary structures (through non-enzymatic modification of macromolecules such as oxidation of α1-antitrypsin and lipids that compose cell membranes, or by favoring the release of neutrophilic elastase, and ny hyperexpression of MMP-9), which can contribute to pathology of COPD through other mechanisms.