UC Riverside

Electronic cigarettes (ECs) are popular alternatives to combustible tobacco cigarettes, particularly among women of reproductive age. This trend is partly driven by the perception that ECs are less harmful than traditional cigarettes and by the widespread availability of appealing flavor and synthetic coolants such as menthol, WS-23, and vanillin. However, these bioactive compounds are capable of activating transient receptor potential (TRP) channels, which regulate calcium signaling-a process critical for early embryonic development. This Dissertation investigated how representative flavor and synthetic chemicals used in EC liquids affect human embryonic stem cells (hESCs), which model the epiblast cells during early development. As the epiblast stage is tightly linked to early patterning and germ layer specification, disruptions at this stage may interfere with pathways relevant to gastrulation and downstream developmental events. Menthol exposure at nanomolar to micromolar concentrations induced robust calcium influx primarily via TRPA1 and TRPM8 channels, resulting in inhibition of mitochondrial reductase activity, increased cell death, reduced colony expansion, altered colony morphology, and impaired migration. Similarly, WS-23, a synthetic coolant commonly used in EC products, triggered TRPM8-mediated calcium entry. WS-23 exposure induced cell death, reduced proliferation, inhibited mitochondrial function, and disrupted colony morphology and integrity. It further downregulated OCT4 and induced early SOX17 expression, indicative of aberrant endodermal differentiation. Vanillin, another popular EC flavor chemical, activated TRPV4 channels and elevated intracellular calcium. This exposure produced concentration-dependent toxicity characterized by reduced viability and proliferation, decreased colony area, colony detachment, and impaired mitochondrial function. It also diminished EpCAM and OCT4 expression while inducing SOX17, suggesting loss of pluripotency and early differentiation of endoderm. In all cases, pharmacological inhibition of the relevant TRP channels mitigated these adverse effects, confirming that dysregulation of calcium homeostasis is a central mechanism underlying the observed toxicity. This Dissertation demonstrated that menthol, WS-23, and vanillin present in EC aerosols can compromise embryonic cell survival, adhesion, phenotype, migration, and lineage commitment by activating distinct TRP channels. Taken together, these findings reveal the potential developmental hazards associated with maternal EC use and reinforce the need for regulatory scrutiny and public health interventions to limit prenatal exposure to bioactive EC chemicals.