Sex differences in the induction of angiotensin converting enzyme 2 (ACE-2) in mouse lungs after e-cigarette vapor exposure and its relevance to COVID-19.

The COVID-19 pandemic has affected over 114 million people and has resulted in >2.5 million deaths so far. Some people have greater susceptibility which influences both SARS-CoV-2 infectivity and COVID-19 severity. Smoking is associated with increased ACE-2, the receptor for SARS-CoV-2, which facilitates its entry through the lung. However, despite the widespread use of e-cigarettes, also known as 'vaping', little is known regarding the effects of vaping on ACE-2 expression and how this affects SARS-CoV-2 infection. In addition, the added effect of nicotine in the vapor is also unknown. Thus, we tested whether vaping induces ACE-2 expression in the mouse lung. BALB/c mice exposed to e-cigarette vapor (±nicotine) resulted in a significant increase in peribronchiolar inflammation and influx of immune cells into the airways. Vapor increased monocyte chemoattractant protein-1, interleukin 1β, and KC levels in bronchoalveolar lavage fluid in both sexes, which were further enhanced by nicotine (whereas increase in interleukin 6 was sex and nicotine independent). The reduction in basal inspiratory capacity with vapor exposure occurred independent of sex or nicotine. The increase in methacholine-induced airway hyper-responsiveness was independent of sex; however, in female mice it was only significant in the nicotine-exposed group. Lung ACE-2 expression was increased in male mice in a nicotine-dependent manner as compared with female mice. Collectively, while vaping (±nicotine) induced airway inflammation and impaired lung function, the induction of lung ACE-2 occurred to a significantly greater degree in males exposed to vapor containing nicotine as compared with females. Thus, via these effects on ACE-2 expression in the lungs and airways, vaping itself may facilitate SARS-CoV-2 entry into the airways.