Electronic-Cigarette Vehicles and Flavoring Affect Lung Function and Immune Responses in a Murine Model

Abstract

The use of electronic nicotine delivery systems (ENDS), also known as electronic-cigarettes (e-cigs), has raised serious public health concerns, especially in light of the 2019 outbreak of e-cig or vaping product use-associated acute lung injury (EVALI). While these cases have mostly been linked to ENDS that contain vitamin E acetate, there is limited research that has focused on the chronic pulmonary effects of the delivery vehicles (i.e., without nicotine and flavoring). Thus, we investigated lung function and immune responses in a mouse model following exposure to the nearly ubiquitous e-cig delivery vehicles, vegetable glycerin (VG) and propylene glycol (PG), used with a specific 70%/30% ratio, with or without vanilla flavoring. We hypothesized that mice exposed sub-acutely to these e-cig aerosols would exhibit lung inflammation and altered lung function. Adult female C57BL/6 mice (n = 11–12 per group) were exposed to filtered air, 70%/30% VG/PG, or 70%/30% VG/PG with a French vanilla flavoring for 2 h a day for 6 weeks. Prior to sacrifice, lung function was assessed. At sacrifice, broncho-alveolar lavage fluid and lung tissue were collected for lipid mediator analysis, flow cytometry, histopathology, and gene expression analyses. Exposures to VG/PG + vanilla e-cig aerosol increased lung tidal and minute volumes and tissue damping. Immunophenotyping of lung immune cells revealed an increased number of dendritic cells, CD4+ T cells, and CD19+ B cells in the VG/PG-exposed group compared to air, irrespective of the presence of vanilla flavoring. Quantification of bioactive lung lipids demonstrated a >3-fold increase of 2-arachidonoylglycerol (2-AG), an anti-inflammatory mediator, and a 2-fold increase of 12-hydroxyeicosatetraenoic acid (12-HETE), another inflammatory mediator, following VG/PG exposure, with or without vanilla flavoring. This suggests that e-cig aerosol vehicles may affect immunoregulatory molecules. We also found that the two e-cig aerosols dysregulated the expression of lung genes. Ingenuity Pathway Analysis revealed that the gene networks that are dysregulated by the VG/PG e-cig aerosol are associated with metabolism of cellular proteins and lipids. Overall, our findings demonstrate that VG and PG, the main constituents of e-liquid formulations, when aerosolized through an e-cig device, are not harmless to the lungs, since they disrupt immune homeostasis.

Comparative Reactive Oxygen Species (ROS) Content among Various Flavored Disposable Vape Bars, including Cool (Iced) Flavored Bars

“…In general, cool (iced) flavors generated differential ROS than their counterpart non-cool (iced) flavors. However, further assays are needed to elucidate how both the flavor of a vape bar and its corresponding nicotine concentration affect ROS generation within vape bars, and immune-inflammatory responses in mouse model as seen previously [ 25 ]. Future studies can use Gas Chromatography–Mass Spectrometry (GC–MS) to analyze the compounds within flavoring agents within flavored vape bars.…”

Fundamentals of Vaping-Associated Pulmonary Injury Leading to Severe Respiratory Distress

“…Vape juice exposure provokes various biological responses including increased secretory activity (65), but the relative roles of the VG/PG vehicle versus minor component additives of flavorings and menthol cooling agents remains obscure and continues to be a focus of ongoing investigation. (24,25,47,82,83) Induction of inflammation and elevation of cytokine production (Figure 5) is commonly present in lung injury (25,(84)(85)(86), but cellular infiltrates in our VAPI model are present in focal areas rather than uniformly distributed throughout tissues, most prominently proximal to airways or vessels indicative of remodeling.…”

Fundamentals of vaping-associated pulmonary injury leading to severe respiratory distress

“…Elevation of mucin production and secretion represents a defensive mechanism within airways to facilitate clearance of inhaled foreign agents ( 55 , 56 ) and is clearly a feature of our VAPI model ( Fig 3 ). Vape juice exposure provokes various biological responses including increased secretory activity ( 56 ), but relative roles of the VG/PG vehicle versus minor component additives of flavorings and menthol cooling agents remains obscure and continues to be a focus of ongoing investigation ( 24 , 25 , 47 , 73 , 74 ). Induction of inflammation and elevation of cytokine production ( Fig 5 ) is commonly present in lung injury ( 25 , 75 , 76 , 77 ), but cellular infiltrates in our VAPI model are present in focal areas rather than uniformly distributed throughout tissues, most prominently proximal to airways or vessels indicative of remodeling.…”