MMP12 and chronic obstructive pulmonary disease: The present study revealed that YE blocked bronchiolar and alveolar inflammation and subsequent pulmonary emphysema in CS- and OVA-challenged COPD models, in which YE abrogated chronic inflammation, MMP-12 proteolytic activity, oxidative stress, and apoptosis of structural alveolar cells in the airways that might possibly be an important upstream event in the pathogenesis of COPD.