Differential Effects of E-Cigarette on Microvascular Endothelial Function, Arterial Stiffness and Oxidative Stress: A Randomized Crossover Trial

Abstract

Propylene glycol and glycerol are electronic cigarettes vehicles allowing liquid vaporization and nicotine transport. The respective effects of these different constituents on the cardiovascular system are unknown. We assessed the differential effects of vehicles (propylene glycol and glycerol) and nicotine on microcirculatory function, arterial stiffness, hemodynamic parameters and oxidative stress. Twenty-five tobacco smokers were exposed to vaping with and without nicotine, and sham vaping, in a randomized, single blind, 3-period crossover design study. Neither sham-vaping nor vaping in the absence of nicotine resulted in modifications of cardiovascular parameters or oxidative stress. In contrast, vaping with nicotine: 1) impaired acetylcholine mediated vasodilation (mean ± standard error mean) (area under curve, perfusion unit (PU), 3385 ± 27PU to 2271 ± 27PU, p < 0.0001); 2) increased indices of arterial stiffness, namely augmentation index corrected for heart rhythm (-3.5 ± 1.5% to 1.9 ± 2.3%; p = 0.013) and pulse wave velocity (4.9 ± 0.1 m.s^-1 to 5.3 ± 0^.1 m.s^-1; p < 0.0001); 3) increased systolic and diastolic blood pressures as well as heart rate (all p < 0.0001) and finally; 4) raised plasma myeloperoxidase (median [interquartile range]) (13.6 ng.ml^-1 [10-17.7] to 18.9 ng.ml^-1 [12.2-54.4], p = 0.005). Our findings demonstrated that high temperature e-cigarette vehicle vaporization does not alter micro- and macro-vascular function, and oxidative stress, and that these effects are solely attributable to nicotine.

Figure 1

Endothelial microcirculatory function. Effect of (a) acetylcholine and (b) sodium nitroprusside iontophoresis after sham-vaping (open circle), nicotine free vaping (open square) and nicotine vaping (closed triangle). Effect of skin pretreatment by saline (continuous line) and L-N-arginine-methyl-ester (dotted line) iontophoresis on skin hyperemic response to local heating (c) after sham vaping, nicotine free vaping and nicotine vaping. Nicotine vaping decreased acetylcholine mediated vasodilation in comparison to sham-vaping (p < 0.0001) and vaping without nicotine (p < 0.0001). Sodium nitroprusside induced vasodilation was not affected by any of the three experimental sessions (ANOVA session effect; p > 0.8). Vasodilation induced by heat in presence of saline or L-N-arginine-methyl-ester were not affected by vaping with and without nicotine and sham-vaping (ANOVA session effect; p > 0.1). BSL indicates baseline; Scan 1 → 10 denotes the time from the first scan to the last scan (150 s per scan).

Figure 2

Hemodynamic parameters. Changes in (a) systolic blood pressure (SBP), (b) diastolic blood pressure (DBP) and (C) heart rate (HR) over time in the sham-vaping (open circle), nicotine free vaping (open square) and nicotine vaping (closed triangle) sessions. Nicotine vaping, compared to baseline (BSL), was associated with an increase in systolic and diastolic blood pressure as well as heart rate for 60 minutes, 120 minutes and 120 minutes post-exposure, respectively. In comparison to BSL, vaping without nicotine increased diastolic blood pressure and heart rate during the limited period of exposure. p-value for the time*session interaction effects for systolic and diastolic blood pressure as well as for heart rate were <0.001, <0.0001 and <0.0001, respectively. p-value for comparisons vs. BSL: *p < 0.05, **p < 0.01, ***p < 0.001. Data are the mean ± SEM.