Metformin protects against PM2.5-induced lung injury and cardiac dysfunction independent of AMP-activated protein kinase α2

Fine particulate matter (PM2.5) airborne pollution increases the risk of respiratory and cardiovascular diseases. Although metformin is a well-known antidiabetic drug, it also confers protection against a series of diseases through the activation of AMP-activated protein kinase (AMPK). However, whether metformin affects PM2.5-induced adverse health effects has not been investigated. In this study, we exposed wild-type (WT) and AMPK alpha 2(-/-) mice to PM2.5 every other day via intratracheal instillation for 4 weeks. After PM2.5 exposure, the AMPK alpha 2(-/-) mice developed more severe lung injury and cardiac dysfunction than were developed in the WT mice; however the administration of metformin was effective in attenuating PM2.5-induced lung injury and cardiac dysfunction in both the WT and AMPK alpha 2(-/-) mice. In the PM2.5-exposed mice, metformin treatment resulted in reduced systemic and pulmonary inflammation, preserved left ventricular ejection fraction, suppressed induction of pulmonary and myocardial fibrosis and oxidative stress, and increased levels of mitochondrial antioxidant enzymes. Moreover, pretreatment with metformin significantly attenuated PM2.5-induced cell death and oxidative stress in control and AMPK alpha 2-depleted BEAS-2B and H9C2 cells, and was associated with preserved expression of mitochondrial antioxidant enzymes. These data support the notion that metformin protects against PM2.5-induced adverse health effects through a pathway that appears independent of AMPK alpha 2. Our findings suggest that metformin may also be a novel drug for therapies that treat air pollution associated disease.