Abstract
background
Tobacco smoke contains over 4000 different chemicals, many of which increase the risk for cerebrovascular diseases associated with the blood-brain barrier (BBB) disruption. The BBB is formed by brain endothelial cells (BECs) and its barrier property is characterized by the presence of tight junctions (TJs) between BECs. Several studies showed that nicotine and other substances derived from combustion of tobacco induced severe impairment of endothelial barrier by opening TJs. Therefore, heat-not-burn (HNB) tobacco products, which allow inhalation of nicotine without burning, are expected to have less harmful chemicals induced by combustion than traditional cigarettes. The purpose of this study is to evaluate whether the substances extracted from HNB tobacco products induce BBB disruption and to compare its effect with that of nicotine alone.
methods
One of the HNB tobacco products distributed in Japan, Ploom TECH® was used. It heats a non-nicotine liquid, which passes through granulated tobacco leaves, to produce nicotine-containing vapor. To mimic the vapor, we extracted granulated tobacco leaves in Ploom TECH® tobacco capsule with water or glycerol at 60°C (Ploom TECH® tobacco extract; PTE). Primary cultures of the rat brain endothelial cells (RBECs) were isolated from Wistar rats (3-week-old) to prepare the in vitro BBB models (RBEC monolayer). RBEC monolayers were treated with water and glycerol PTE and nicotine. The viability of RBECs was assessed using LDH assay. To evaluate BBB integrity, transendothelial electrical resistance (TEER) and transendothelial transport of sodium fluorescein (Na-F) were measured. The protein levels of TJs in RBECs were determined by Western blot.
results
In RBEC monolayers, treatment with nicotine alone had no effect on the TEER and the permeability coefficients for Na-F. On the other hand, water and glycerol PTE induced lowered TEER and elevated permeability to Na-F. Exposure of the water and glycerol PTE decreased the protein levels of claudin-5 in RBECs. However, there were no changes in the expression of occludin and ZO-1. The water and glycerol PTE had no effects on the release of LDH.
conclusion
These data suggest that the substances extracted from HNB tobacco products impair BBB integrity.
