Comparison between electronic cigarette refill liquid and nicotine on metabolic parameters in rats

Nicotine is known to promote body weight loss and to disturb glucose homeostasis and lipoprotein metabolism. Electronic cigarettes, as a substitute to nicotine, are becoming increasingly popular, although there is no evidence regarding their safety. Considering the dearth of information about e-cigarette toxicity, the present study was designed to compare nicotine alone to e-liquid with or without nicotine on metabolic parameters in Wistar rats. For this purpose, e-liquid with or without nicotine and nicotine alone (0.5mg/kg of body weight) were administered intra-peritoneally during 28days. Our results show a significant decrease in food and energy intake after nicotine or e-liquid with nicotine exposure, when compared to control or e-liquid without nicotine. Analysis of lipid status identified a significant decrease in cholesterol and LDL levels in e-cigarette groups, suggesting an improvement in lipid profile. Interestingly, e-liquid without nicotine induced hyperglycemia which is negatively correlated to hepatic glycogen level, acting like nicotine alone. Furthermore, an increase in liver biomarkers was observed in all treated groups. qRT-PCR analysis showed GSK3β up-regulation in e-liquid with nicotine as well as, surprisingly, in e-liquid without nicotine exposure. In contrast, PEPCK genes were only up-regulated in e-liquid with nicotine. While some features observed in rats may not be observed in human smokers, most of our data are consistent with, e-liquid per se i.e. without nicotine, not being neutral from a metabolic stand point since disrupting glucose homeostasis in rats.