Effect of e-cigarette flavoring agents on the neural retina of chick embryo: histological and gene expression study

An electronic cigarette (e-cigarette) is initially marketed as an assistant product to quit smoking or limit its use. However, recent studies suggest the opposite, describing it as a product that lacks adequate quality and user safety. The present study aimed to investigate the effect of e-cigarette flavoring agent (cinnamon flavor) on the neural retina development of chick embryos and apoptosis induction after the early and late apoptosis stages by quantitative detection of gene expression CASP-3 at both embryonic days E9 and E17.

Fertilized chicken eggs were divided into two groups: control and treatment, and each group included two embryonic days; E9 and E17. For each treatment stage, two dosages of the treatment were applied, 2% and 5%. The neural retinas were dissected from the sclera and retinal pigment epithelium for subsequent RNA extraction and histological examination.

This study indicated that aerosol of the subtle cinnamon flavor e-liquid causes downregulated expression of CASP3 in neural retina development. In addition, the hematoxylin and eosin (H&E)-stained sections showed multiple structural changes in the retinal layers and evidence of apoptotic cell death.

Cell death was visible and abundant in E9, and E17 concludes that flavor vapor condensate treatment caused neuronal cell death. CASP-3 was downregulated, which indicates that cell death occurred independently of CASP-3.