E-Cigarette Exposure in Zebrafish Leads to Defects in Neurogenesis Similar to Those Found Following Exposure to Traditional Tobacco Cigarettes

Nicotine has been shown to have neuroteratogenic effects on the developing fetus. In recent years, nicotinecontaining electronic cigarettes (e-cigarettes) have become a popular alternative to traditional tobacco cigarettes, especially among pregnant women who may believe that e-cigarettes are comparably less harmful. The health effects of e-cigarette smoke exposure during prenatal life, however, are currently not well known. This study compared the neuroteratogenic effects of embryonic exposure to nicotine-containing e-cigarette smoke condensate (e-CSC) and cigarette smoke condensate (CSC) on retinal ganglion cell (RGC) development in a zebrafish (Danio rerio) model. Embryos of the transgenic zebrafish, Tg(-17.6 is l2b:GFP)zc7, were dechorionated at 24 hours post-fertilization (hpf) and exposed to varying concentrations of e-CSC or CSC for 46 hours. The number of surviving embryos was counted at 72 hpf. The median lethal dose (LD50) for CSC and e-CSC was calculated from the proportion of non-surviving fish to the total number of fish exposed. Fluorescent images were subsequently taken of all surviving embryos and used to measure gross eye size and differentiated RGC layer size along the dorsal-ventral and nasal-temporal axes, and to measure width of the optic nerve. The LD50 of e-CSC was determined at 5.06x, compared to an LD50 of CSC at 0.035x. Exposure to both e-CSC and CSC resulted in significant reductions in gross eye size and optic nerve width. While e-cigarettes were comparably less toxic than cigarettes, the similar morphological eye changes and RGC developmental perturbations observed following exposure to e-CSC and CSC suggest that nicotine containing e-cigarettes are as harmful to developing neurons as cigarettes.