Date of Award

5-2025

Document Type

Thesis

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Bournias-Vardiabasis, Nicole

Abstract

The prevalence of vaping has rapidly increased. ECs are often perceived as less harmful than tobacco cigarettes. A recent meta-analysis showed electronic cigarette (EC) aerosols adversely affected the respiratory system, similar to cigarette smoke, with some effects specific to EC use. Failure to prevent these alterations could lead to life-long comorbidities, and predisposition to respiratory diseases, including COPD and squamous cell carcinoma. While these effects are the result of active vaping, EC aerosols can also settle on indoor surfaces, be absorbed passively through the skin or orally, enter the blood stream, and subsequently expose internal organs, including the airway basal stem cells (ABSCs). Toddlers and children who often crawl and frequently mouth household objects are particularly vulnerable to this type of exposure. While prior reports have described the effects of thirdhand smoke (THS) on the respiratory system, no studies have examined how THS and EC chemicals in the blood effect development of the human tracheobronchial epithelium (hTET). In this study, we developed and used a 3D in vitro model derived from ABSCs to simulate hTET during development. We looked at the marker involucrin, which is associated with squamous metaplasia in epithelial tissue. Furthermore, we looked at the marker MUC5AC, a goblet cell marker and Acetylated Tubulin, a marker for cilia. Additionally, we measured tissue width to see if changes occurred in the epithelium associated with cigarette and EC use.

We hypothesized that ABSCs passively exposed to ECs form abnormal hTETs. To test this hypothesis, ABSCs were differentiated in vitro into 3D hTET. During the 4-week differentiation phase, the ABSCs were exposed on the basolateral surface to medium with dissolved Marlboro Red smoke or dissolved aerosol from FDA authorized ECs (Vuse Solo and NJOY) or a non-authorized EC (JUUL). Cigarette smoke was collected without impingers at 5 total puff equivalents. EC aerosol was collected using the impinger method at 6 total puff equivalents (TPE). Both cigarette smoke and EC aerosol stock concentrations were then diluted to 0.00001, 0.0001, and 0.001 TPE, which have nicotine concentrations similar to or below those in the blood of smokers and vapers. En-face immunofluorescence showed that involucrin, a marker of squamous metaplasia, was elevated in tissues exposed to all treatments (Marlboro Red, Vuse Solo, NJOY, and JUUL), and these markers were significantly increased in the highest concentrations. Western blots confirmed elevated expression of involucrin. Histology further confirmed elevated expression of involucrin and MUC5AC in treatments. Epithelial hyperplasia, thickening of the tissue, was also observed in histological sections of Marlboro Red and Vuse Solo exposed groups. These data show that passive exposure to chemicals in EC aerosols can negatively impact the developing respiratory epithelium when exposure occurs from the basal surface. Additionally, no safety advantages were observed with FDA authorized ECs compared non-FDA authorized ECs to cigarettes. Furthermore, all treatments had nicotine concentrations found in the blood of smokers. This information will be valuable to health care workers and may affect EC regulation and policymaking.

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