Electronic Cigarettes: Neurological Effects on Murine Offspring and the Response of Neuronal Cells

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Electronic cigarettes (e-cigarettes) are battery-powered devices that convert an oily-flavoured liquid into an aerosol. E-cigarette liquids contain propylene glycol, glycerin, flavouring and varying concentrations of nicotine. Due to aggressive marketing, e-cigarettes are attractive to a number of vulnerable groups such as young people and pregnant women. It is perceived within these populations that e-cigarettes are a safer alternative to smoking tobacco cigarettes although there is limited evidence proving this. In this thesis, Chapter 1 provides an extensive review on what is currently known about e-cigarettes within the literature. Chapter 2 describes a mouse pregnancy model of e-cigarette exposure and examines the offspring at three time-points; postnatal day 1 (right after birth), postnatal day 20 (right after weaning) and at week 13 (adulthood). Chapter 3 describes a pregnancy model of switching from tobacco cigarette to e-cigarette exposure during pregnancy. Behavioural assessments using the novel object recognition and the elevated plus maze tests were conducted in both Chapter 2 and 3 to determine changes to short-term memory, anxiety and exploration. In addition, epigenetic changes investigating DNA methylation and epigenetic gene expression on offspring brain were investigated. Finally, Chapter 4 investigated the effects of e-cigarette condensate on differentiated neuroblastoma cells (diff-SHSY5Y), microglial (BV2) cells and human brain endothelial cells (HBEC) in monoculture and in co-culture using a blood brain barrier (BBB) model. The results showed that offspring from mothers exposed to e-cigarette aerosols with and without nicotine had significant changes to memory, anxiety, hyperactivity, DNA methylation and epigenetic gene expression compared to normal offspring. Continuous tobacco cigarette exposure showed significant effects on offspring behaviour and epigenetics, however, switching to e-cigarettes during pregnancy reduced some of these changes but not all to normal levels. In the cell culture experiments, e-cigarette exposure on diff-SHSY5Y, BV2 and HBEC showed reduced cell-viability and an increase in oxidative stress in monoculture. In a co-culture model of the BBB, significant epigenetic gene changes were observed in diff-SHSY5Y cells after treatment with conditioned media from BV2 cells. All of these results are summarised in Chapter 5. In summary, the 𝘪𝘯 𝘷𝘪𝘷𝘰 experiments showed that neurological changes including behavioural and epigenetics occurred in the offspring after maternal e-cigarette exposure. The 𝘪𝘯 𝘷𝘪𝘵𝘳𝘰 experiments showed that this may be due to a direct effect of e-cigarette constituents on neuronal cells, or through an indirect inflammatory response involving microglia. Overall, this study concluded that e-cigarettes are not safe to be used during pregnancy.
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