Effect of E‐liquid Base Solution (Vegetable Glycerin or Propylene Glycol) on Aortic Function in Mice

Abstract

The effects of vaping with electronic cigarettes (e-cigs) on cardiovascular health are still under investigation. An important question that still remains unknown is the role of individual constituents within the e-liquid used for vaping. In this study, we examine the sole effect of either vegetable glycerin (VG) or propylene glycol (PG), without the presence of any flavors or nicotine, on aortic reactivity. Healthy C57BL/6J mice were exposed to e-cig vapor for 4 weeks (5d/wk, 1-hour/day, 60 puffs/day) to e-cig aerosol from either 100% VG or 100% PG e-liquid using a whole-body chamber exposure system (SCIREQ InExpose). Control mice were exposed to ambient air. E-cig aerosol was produced by a Joyetech eGRIP OLED device at 17.5 watts, with 5-second puff duration. Mice were sacrificed >24 hours after their final exposure, and thoracic aortas were excised, cleaned of perivascular adipose tissue, and were cut into 2mm ring segments. Aortic rings were mounted on wire myograph system (DMT, AD Instruments) containing warm aerated Krebs-Henseleit buffer solution. The vessels were pre-constricted with 50 µL of U46619 [7.5e-9 M], and then exposed to a serial dilution of methacholine [MCh 10-9 to 10-5 M] to assess endothelial-dependent (EDD) vasodilation, and separately to serial dilutions of sodium nitroprusside [SNP 10-9 to 10-5 M] to assess endothelium-independent (EID) vasodilation. In PG-exposed mice, max aortic EDD was reduced by 18±2% (P<0.05) compared to controls, and reduced by 14±2% (P<0.05) compared to VG-exposed mice. VG-exposed mice were not significantly different compared to controls. Maximal aortic EID was slightly impaired in PG- mice compared to control (8±2% P<0.05) and VG (5±1% P<0.05) groups. In summary, chronic exposure to e-cig aerosol from PG in the base solution resulted in aortic EDD and EID dysfunction, however VG-exposed mice were not affected. These data suggest that both endothelial-dependent and -independent mechanisms are adversely affected by PG, and therefore vaping with PG in the base solution alone poses a significant risk for adverse cardiovascular health effects.