A common vape flavoring may disrupt early embryo development

The findings, published on August 12 in Human Reproduction, offer a possible explanation for previously observed links between vaping, difficulty becoming pregnant, and miscarriage.

The study was conducted in the laboratory using human embryonic stem cells -- which are similar to cells found in human embryos at about three weeks of development -- rather than in pregnant women. The researchers emphasize that their results therefore cannot prove that the same effects occur in women or developing embryos.

Testing a Common Vape Flavoring

"There is little understanding of how vaping can affect developing embryos in pregnant women who use electronic cigarettes," said Prue Talbot, a professor of the graduate division in the Department of Molecular Cell & Systems Biology at UCR, who led the study. "We undertook this study to determine if vanillin, a flavor chemical often used in e-cigarettes at high concentrations, could adversely affect the development of young embryos in humans."

Talbot and her colleagues set out to investigate how chemicals found in vape aerosols might influence very early human development and what kinds of cellular damage could result.

"We focused on vanillin because it is frequently used in e-cigarette fluids, it is often used at high concentrations, and because we knew that embryonic cells had a channel called TRPV4 on their surfaces that would likely bind with vanillin," Talbot said.

Talbot and coauthor Shabnam Etemadi, a stem cell biologist and computational scientist at UCR, exposed human embryonic stem cells grown in laboratory dishes to several concentrations of vanillin. These included nanomolar (low) concentrations and micromolar (high) concentrations.

The researchers also tested the cells with a TRPV4 antagonist (a substance that inhibits vanillin binding to TRPV4), an antibody that blocks TRPV4 activity, and combinations of vanillin with either the antagonist or the antibody.

Vanillin Changed How Embryonic Cells Developed

Embryonic stem cells are pluripotent, meaning they can develop into virtually any type of cell in the body. During normal embryonic development, they give rise to three major cell types: endoderm, ectoderm, and mesoderm.

"We found that micromolar concentrations tended to kill the cells," Talbot said. "Nanomolar concentrations caused cells to lose pluripotency, which is the ability to develop into all cell types. Vanillin also caused the stem cells to differentiate into endoderm, rather than ectoderm or mesoderm. The endoderm is an embryonic tissue that gives rise to the lining of the gut and respiratory tissues. These changes are potentially very serious and could prevent normal development of embryos."

The team found that blocking TRPV4 with the antagonist prevented vanillin from producing these effects. That result pointed to the TRPV4 channel as the mechanism through which vanillin was affecting the cells.

"Our data predict that nanomolar concentrations of vanillin will reach the embryo in pregnant women who vape," Talbot said. "At nanomolar concentrations, vanillin binds to a channel called TRPV4 on the surface of embryonic cells, allowing a rapid influx of calcium, a signaling molecule. Calcium in turn activates downstream events that result in loss of pluripotency and differentiation of embryonic stem cells into endoderm."

Why Early Cell Development Matters

Talbot noted that healthy embryonic development depends on stem cells forming all three primary cell types: endoderm, ectoderm and mesoderm.

If an embryo failed to form ectoderm, the nervous system would not develop, she said. Without mesoderm, many other tissues, including muscle, would also fail to form properly.

"Women do not necessarily know the chemicals in vape products," Talbot said. "Our findings suggest they should be cautious and advised by physicians not to vape during pregnancy, especially if they are having trouble conceiving or experience miscarriages. "Regulatory policies are generally based on data derived from adults or adult cells. However, the prenatal stages of development are usually the most sensitive to environmental chemicals."

The researchers say regulators should consider requiring e-cigarette manufacturers to disclose ingredients on product packaging.

"When establishing policies for e-cigarette use and distribution, it would be advisable to consider if and how the products harm the unborn," Talbot said.

Researchers Are Testing Other Vape Chemicals

The team has previously studied menthol flavoring in e-cigarettes and found that it contributed to respiratory disease in humans.

Researchers are now investigating WS-23, a synthetic cooling chemical frequently used in e-cigarette products. They are also examining how both menthol and WS-23 affect the differentiation of embryonic cells.

The researchers caution that the current study does not estimate the effects of repeated or cumulative vanillin exposure over days, weeks, months, or years.

"The effect of long-term exposure could be higher," Talbot said.

The research was supported by grants from the Tobacco-Related Disease Research Program and the California Institute of Regenerative Medicine, along with UCR Yvonne Danielson Endowed Graduate and Dissertation Completion Fellowship Awards.

The title of the paper is "Nanomolar vanillin, an e-cigarette flavorant, appears to disrupt pluripotency and promote endodermal differentiation in human embryonic stem cells via TRPV4 activation."