E‐Cigar Vapor Alters Lung Fibroblast Viability via Alpha 7 Nicotine Acetylcholine Receptor
Authors: Nho Richard 
Published: April 2020

Rationale

Idiopathic Pulmonary Fibrosis (IPF) is the most lethal fibrotic lung disease characterized by the presence of apoptosis‐resistant lung fibroblasts and relentless production of a collagen‐rich extracellular matrix. Recently, e‐cigars become popular in young adults due to their easy availability, various e‐liquid flavors, and belief that e‐cigars are safer than tobacco products. However, there is a growing concern that the exposure to e‐cigar vapors can increase the risk of developing lung diseases including lung fibrosis. However, the patho‐biological effect of e‐cigar vapor on lung fibroblasts has not been understood.

Study objective

The objective of this study is to examine the pathological effect of e‐cig vapor on fibrotic and non‐fibrotic lung fibroblasts and to elucidate the underlying mechanism that alters fibroblast viability.

Methods

Primary lung fibroblasts from IPF and non‐IPF patients (n=7, each) were treated with Aroma E‐juice Dark Honey e‐cig aerosol extracts (EAEs) and Marlboro Gold smoke extracts that contain 10 ng/ml of nicotine. Fibroblast viability and proliferation were measured on 3 D collagen matrices. Fibroblasts were then treated with various does of nicotine and nicotine‐free e‐liquid (NicVape Retro Fruit Twist flavor), and their viability and proliferation were measured under the same condition. Molecular assays were carried out to elucidate the cellular mechanism that alters fibroblast viability.

Results

When non‐IPF lung fibroblasts were treated with EAEs, their viability was significantly increased compared to that of smoke extract‐treated fibroblasts. Likewise, EAE‐treated IPF fibroblast viability was also highly increased. However, smoke extract treatment had minor effects on their viability. Similar to this finding, non‐IPF and IPF fibroblast proliferation was not changed in response to EAEs. Our study further showed that nicotine in EAEs predominantly alters control and IPF fibroblast viability. In contrast, nicotine free e‐liquid did not affect their viability. Our molecular assays further revealed that α7 nicotine acetylcholine receptor (α7nAChR) expression was up‐regulated in nicotine and EAE‐treated lung fibroblasts. However, the utilization of a selective α7nAChR inhibitor, methyllycaconitine and siRNA significantly sensitized non‐IPF and IPF fibroblasts to collagen matrix‐induced cell death by inhibiting a fibroblast survival pathway.

Conclusions

Our results suggest that exposure to e‐cig vapor alters fibroblast viability and nicotine in e‐cigs plays a crucial role in altering a fibroblast phenotype via the α7nAChR‐dependent apoptosis‐resistant pathway. These results show a possibility that the inhalation of e‐cigar vapor is a risk factor to promote lung fibrosis and that the selective inhibition of α7‐dependent cellular pathway may be an effective approach to reduce e‐cig vapor‐induced lung fibrosis.

Support or Funding Information

This study was supported by the University of Minnesota Medical School Faculty Research Award and Center for Lung Science and Health grant.