Waterpipe Smoke Exposure and Arterial Plaque Formation: Effects and Mechanisms Related to Sex, Autonomic Nervous System Changes and Endothelial Permeability in a Mouse Model of Atherosclerosis

Chronic inhalation exposure to particulate matter (PM) has been well documented to increase the risk of developing and dying from cardiovascular disease (CVD). This risk, however, has been studied mostly in ambient PM and cigarette tobacco. Waterpipes have been used for centuries to smoke tobacco and have recently increased in popularity worldwide, but its cardiovascular toxicity has not been widely studied. Therefore, I aimed to begin to fill this gap by studying the effects of long-term waterpipe smoke (WPS) inhalation on disease progression in an atherosclerosis prone mouse model (ApoE-/- mice).Methods: Male and female ApoE-/- mice underwent nose-only exposure to WPS for 2 hours per day, 4 days per week for either 8 or 20 weeks. In the 8-week exposure, an additional group exposed to charcoal denuded WPS (dWPS) was included to study the importance of volatile and PM components on cardiovascular toxicity. Atherosclerosis progression was measured by histological assessment of intima-media thickness in the aortic arch, brachiocephalic, left carotid and left subclavian arteries. Inflammation and endothelial permeability were assessed in plasma, as well as tissue expression of biomarkers and extravasation of Evan’s blue dye (EBD), which was injected just prior to euthanasia. Heart rate variability (HRV) was assessed daily throughout the study as a proxy for autonomic nervous system perturbations associated with CVD. Results: Intima-media thickness was altered mainly in the aortic arch as increased thickness in male ApoE-/- mice but decreased in the female mice after 5 months of WPS exposure. EBD extravasation was increased after only 2 months of WPS exposure in male mice. Inflammation marker, C-reactive protein, was decreased in female mice after 2 months of WPS inhalation. No significant changes were found in other markers of permeability or inflammation. HRV indicated sex-dependent effects, where WPS induced dampening of vagally mediated responses in females. In males, WPS increased vagal stimulation of the heart in a transient manner, seen only on the days of exposure, and not on the non-exposure days of each week. Conclusions: In summary, despite differences from the initial hypotheses, this dissertation presents results that WPS exposure is able to induce cardiovascular toxicity as assessed by heart rate variability, and that WPS can influence the progression of atherosclerosis differently between male and female mice