Effects of flavoring compounds used in electronic cigarette refill liquids on endothelial and vascular function

Abstract

Electronic cigarette refill liquids are commercially provided with a wide variety of flavoring agents. A recent study suggested that several common flavors may scavenge nitric oxide (NO) and cause endothelial dysfunction. It was the aim of the present study to investigate the effects of these flavors on NO/cyclic GMP-mediated signaling and vascular relaxation. We tested the flavoring agents for effects on Ca2+-induced cGMP accumulation and NO synthase activation in cultured endothelial cells. NO scavenging was studied with NO-activated soluble guanylate cyclase and as NO release from a NO donor, measured with a NO electrode. Blood vessel function was studied with precontracted rat aortic rings in the absence and presence of acetylcholine or a NO donor. Cinnamaldehyde inhibited Ca2+-stimulated endothelial cGMP accumulation and NO synthase activation at ≥0.3 mM. Cinnamaldehyde and diacetyl inhibited NO-activated soluble guanylate cyclase with IC50 values of 0.56 (0.54–0.58) and 0.29 (0.24–0.36) mM, respectively, and caused moderate NO scavenging at 1 mM that was not mediated by superoxide anions. The other compounds did not scavenge NO at 1 mM. None of the flavorings interfered with acetylcholine-induced vascular relaxation, but they caused relaxation of pre-contracted aortas. The most potent compounds were eugenol and cinnamaldehyde with EC50 values of ~0.5 mM. Since the flavors did not affect endothelium-dependent vascular relaxation, NO scavenging by cinnamaldehyde and diacetyl does not result in impaired blood vessel function. Although not studied in vivo, the low potency of the compounds renders it unlikely that the observed effects are relevant to humans inhaling flavored vapor from electronic cigarettes.

Electronic Cigarette and Atherosclerosis: A Comprehensive Literature Review of Latest Evidences

“…Acetoin is the flavoring agent giving rise to the “buttery” taste of e-cigarettes, while the sweet taste is usually due to diacetyl in an exceedingly high concentration [ 50 , 51 ]. Several flavoring agents, such as acetylpyridine, vanillin, diacetyl, and menthol, were capable of inducing endothelial cell dysfunction in cell culture and act as oxidants and triggered the generation of ROS, ultimately leading to oxidative stress [ 52 ]. Flavorant such as acetoin and maltol were found to trigger IL-8 release by causing ROS release, shifting the immunity into a proinflammatory state [ 53 , 54 ].…”

Cardiorespiratory and Immunologic Effects of Electronic Cigarettes

“…Even though FMD changes in response to e-cigarettes are lower than those observed with combustible cigarettes [ 69 •], the observations that the use of e-cigarette is associated with an increase in oxidative stress [ 41 , 68 , 69 •] and decreased bioavailability of nitric oxide [ 69 •] and as well as diminished rates of nitric oxide production from endothelial cells [ 71 ] support the notion that e-cigarettes cause endothelial injury. Decreased nitric oxide production in endothelial cells has also been noted in endothelial cells exposed to flavoring agents used in e-cigarettes [ 72 – 74 ]. Acute exposure to e-cigarettes also increases the levels of circulating endothelial progenitor cells to levels similar in magnitude to that observed after smoking a combustible cigarette [ 75 ], and elevates the levels of circulating extracellular vesicles derived from the endothelium in healthy individuals [ 76 ], suggesting that using e-cigarettes could compromise vascular repair and incite vascular injury.…”

A Summary of In Vitro and In Vivo Studies Evaluating the Impact of E-Cigarette Exposure on Living Organisms and the Environment

“…Although none have been tested so far, viz. acetylpyridine, diacetyl, dimethylpyrazine, cinnamaldehyde, eucalyptol, eugenol, isoamylacetate, menthol and vanillin, have been found to cause cultured endothelial cell dysfunction (porcine aortic endothelial cells) [22]; studies on cellular models suggest that they may exert a toxic effect on respiratory cells based on oxidative stress and inflammatory processes [23][24][25][26][27][28]. Contact with such flavorant agents results in elevated level of ROS production and excessive IL-8 secretion in airway epithelium cells, with both mechanisms leading to cell cytotoxicity: oxidative stress is a cause of DNA damage [29].…”