Toxicological outcomes linked to e-cigarette consumption: evidence from an in vivo model

Background: Designed to deliver nicotine avoiding tobacco combustion, electronic cigarettes (e-cigs) are aggressively promoted as safer alternative to tobacco products and a putative approach to smoking cessation. However, to date the risk-benefit ratio remains largely unknown and recent investigations have questioned their safety. Here we presented our recent in vivo studies on the toxicological aspects associated to the electronic delivery systems. Methods: Male Sprague Dawley rats were whole-body exposed to the vapour generated by the devices. The e-cig was equipped with different coils (1.5 and 0.25 Ohm) and the Voltage applied ranged from 3.5 to 5.5 V in order to explore the role of these parameters on toxicological outcomes. The treatment was carried out loading the device with e-liquid containing or not 18 mg/mL (1 mL/day) of nicotine. E-cig treated animals were subjected to the procedure for 3 h/day for 28 days. The levels of O2, N2, and CO2 were monitored by GC/MS to establish safe O2/N2 and CO2/ O2 ratios in the cages. Furthermore, the experiments were repeated considering also “non-liquid devices” with alternative heating systems able to heat tobacco. Results: When e-cig was run at high voltage (5.5 V; 18 mg/mL nicotine) we recorded the release of hazardous carbonyl compounds (such as formaldehyde, acetaldehyde and acrolein). The animals showed a powerful booster effect on phase-I carcinogen-bioactivating enzymes, an impairment of the antioxidant and phase II catalysts, related to the increment of oxygen free radical (ROS) production, and DNA oxidation through 8-hydroxy-2′-deoxyguanosine yield in lung tissue. Insights into the genotoxicity also emerged from the extensive DNA damage in leukocytes measured by the comet assay, the increment in the percentage of immature micronucleated reticulocytes and the increased number of revertants in the urine. Lowering the voltage at 3.5 V and loading the device with a nicotine-free liquid, we still found aldehydes in the mainstream, and noteworthy, their amount enhanced moving form nicotine to nicotine-free liquids. Interestingly, the aldehydes increased as the resistance decreased from 1.5 to 0.25 Ohm, and the frames from electron microscope confirmed a disorganization of alveolar and bronchial epithelium more marked in the 0.25 Ohm group. Finally, since changes in liver parameters including ALT and hepatocellular vacuolization in rats exposed to the vapour from “non-liquid e-cigs” were reported, we added a breakthrough finding on treated animals showing a disruption of the redox homeostasis, with higher levels of ROS, and increased markers of oxidative injuries such as lipid peroxidation and protein carbonylation, combined with an impairment of the enzymatic and non-enzymatic antioxidant defence systems. Conclusion: As a whole, our studies show how electronic delivery devices can trigger detrimental phenomena typically induced by conventional cigarettes.