Abstract
Many electronic cigarettes (ECs) contain high concentrations of menthol. The effect of menthol on human embryos in pregnant women who vape is not well understood. Human embryonic stem cells (hESCs) (an epiblast model) were used to test the hypothesis that 6.4-640 nM and 19.2-192 µM menthol, which activates TRP (transient-receptor-potential) channels, alters calcium homeostasis in embryos and adversely affects processes that are critical to gastrulation. Micromolar concentrations of menthol inhibited mitochondrial reductase activity in hESCs, an effect that was blocked by TRPA1 and TRPM8 inhibitors. Pulsatile exposure to menthol elevated intracellular calcium primarily by activating TRPA1 channels at nanomolar concentrations and TRPM8 channels at µM concentrations. nM menthol significantly inhibited colony growth by activating TRPA1 channels, while both TRPA1 and TRPM8 were activated by µM menthol. Inhibition of colony growth was attributed to cell death induced by menthol activation of TRPA1 and TRPM8 channels. nM menthol altered colony phenotype by increasing the major/minor axis ratio via TRPA1 and TRPM8 channels. Both nM and µM menthol induced alterations in hESC colony motility, an effect that was blocked only by the TRPM8 inhibitor. The menthol-induced increase in intracellular calcium adversely influenced growth, death, and migration, processes that are critical in gastrulation. Menthol concentrations that reach embryos in women who vape are high enough to activate TRPA1 and TRPM8 channels and perturbed calcium homeostasis. Pregnant women who vape likely expose their embryos to menthol concentrations that are harmful. These data could help prevent birth defects or embryo/fetal death.