Acute and chronic in vivo effects of exposure to nicotine and propylene glycol from an E-cigarette on mucociliary clearance in a murine model

Abstract

Objective: To determine the effect of an acute (1 week) and chronic (3 weeks) exposure to E-cigarette (E-cig) emissions on mucociliary clearance (MCC) in murine lungs.

Methods: C57BL/6 male mice (age 10.5 ± 2.4 weeks) were exposed for 20 min/day to E-cigarette aerosol generated by a Joyetech 510-T^® E-cig containing either 0% nicotine (N)/propylene glycol (PG) for 1 week (n = 6), or 3 weeks (n = 9), or 2.4% N/PG for one week (n = 6), or 3 weeks (n = 9), followed by measurement of MCC. Control mice (n = 15) were not exposed to PG alone, or N/PG. MCC was assessed by gamma camera following aspiration of ^99mtechnetium aerosol and was expressed as the amount of radioactivity removed from both lungs over 6 hours (MCC6hrs). Venous blood was assayed for cotinine levels in control mice and in mice exposed for 3-weeks to PG alone and N/PG.

Results: MCC6hrs in control mice and in mice acutely exposed to PG alone and N/PG was similar, averaging (±1 standard deviation) 8.6 ± 5.2%, 7.5 ± 2.8% and 11.2 ± 5.9%, respectively. In contrast, chronic exposure to PG alone stimulated MCC6hrs (17.2 ± 8.0)% and this stimulation was significantly blunted following chronic exposure to N/PG (8.7 ± 4.6)% (p < .05). Serum cotinine levels were <0.5 ng/ml in control mice and in mice exposed to PG alone, whereas, N/PG exposed mice averaged 14.6 ± 12.0 ng/ml.

Conclusions: In this murine model, a chronic, daily, 20 min-exposure to N/PG, but not an acute exposure, slowed MCC, compared to exposure to PG alone and led to systemic absorption of nicotine.

Keywords: E-cigarette emissions; acute exposure; chronic exposure; mucociliary clearance; murine model.

Figure 1

Photo of E-cigarette connected to MasterFlex Pump with tubing and Y-connector to two murine exposure chambers.

Figure 2

Schematic of the aerosol monitoring set-up showing E-cigarette connected to MasterFlex Pump, Y-tubing connected to one murine chamber and second tube unconnected, exit tubing connected to Scanning Mobility Particle Sizer (SMPS) and Aerodynamic Particle Sizer (APS).

Figure 3

Number-based plots (i.e. number of particles/cm³) for nano-sized airborne particles tested by SMPS and averaged over the 20 min aerosol generation period (error bars indicate standard errors).

Figure 4

Number-based plots (i.e. number of particles/cm³) for micron-sized airborne particles for the two solutions tested by APS and averaged over the 20 min aerosol generation period (error bars indicate standard errors).

Figure 5

2-D images showing lung retention of radioisotope at 0 and 6 hrs post aspiration. Right and left lungs are bordered in red. A portion of the radioactivity that was cleared from the lungs over 6 hours was swallowed and deposited in the stomach. This activity appears in the bottom right of the 6 hour image. In general, regions of the images with light blue/yellow-green coloration indicate areas with higher concentration of the radioisotope, whereas, regions with dark blue coloration indicate areas with lower concentration of the radioisotope.

Figure 6

MCC was not statistically different in mice that were acutely exposed (1 week) for 20min/day to emissions from a Joyetech E-cigarette containing 2.4% N/PG, or 0% N/PG (p > .05).

Figure 7

MCC was statistically significantly reduced in mice that were chronically exposed (3 weeks) for 20min/day to emissions from a Joyetech E-cigarette containing 2.4% N/PG, compared to mice that were chronically exposed to emissions containing 0% N/PG (p < .05).

Figure 8

Representative examples of tracheas exposed to three weeks of daily 0% N/PG, or 2.4% N/PG. (A) Trachea from mouse exposed to 0% N/PG (20×); (B) trachea from mouse exposed to 0% N/PG (40×); (C) trachea from mouse exposed to 2.4% N/PG (20×); (D) trachea from mouse exposed to 2.4% N/PG (40×). Arrows point to cilia from ciliated epithelium.