Vanillin flavoring in e-cigarettes disrupt human embryonic stem cell development, lab study finds

Vanillin, a common flavoring chemical in e-cigarettes, may disrupt the normal development of embryos in pregnant women who vape, according to a study published in Human Reproduction. The finding explains how vaping may be linked to women having difficulty conceiving and to miscarriages.

As it is practically impossible and unethical to study the effects of chemicals on pregnant women and their developing embryos, researchers instead investigated human embryonic stem cells, which are similar to those in 3-week-old human embryos, in a series of laboratory tests. They warn that, as their findings are from a laboratory study, they cannot decisively establish that the same effects would be seen in women and their embryos.

Prue Talbot, a professor in the Graduate Division of the Molecular Cell & Systems Biology Department at the University of California, Riverside, U.S., who led the study, said, “There is little understanding of how vaping can affect developing embryos in pregnant women who use electronic cigarettes.

“So we undertook this study to determine if vanillin, a flavoring chemical often used in e-cigarettes at high concentrations, could adversely affect the development of young embryos in humans. We wanted to understand how chemicals in vape aerosols can affect young human embryos and identify the type of harm that may occur.”

Why vanillin drew scrutiny

“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 and Dr. Shabnam Etemadi, a stem cell biologist and computational scientist also at the University of California, Riverside, exposed human embryonic stem cells in laboratory dishes to either nanomolar (low) or micromolar (high) concentrations of vanillin.

They also exposed the stem cells to a TRPV4 antagonist (a substance that inhibits vanillin binding to TRPV4), an antibody that blocks the function of TRPV4, or vanillin combined with either the antagonist or the antibody.

Embryonic stem cells have the potential to differentiate into any type of cell. In normal embryonic development, they form three cell types: endoderm, ectoderm and mesoderm.

Talbot said, “We found that micromolar concentrations tended to kill the cells. 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.”

A calcium pathway to harm

The effect of vanillin on the stem cells was blocked by the TRPV4 antagonist, which identified the TRPV4 channel as the route by which vanillin adversely affected the cells.

“Our data predict that nanomolar concentrations of vanillin may reach the embryo in pregnant women who vape,” said Talbot. “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. In normal development, the embryonic stem cells would form three cell types: endoderm, ectoderm and mesoderm. In embryos lacking ectoderm, the nervous system would fail to develop. In embryos lacking mesoderm, many tissues, such as muscle, would fail to develop.

“Women do not necessarily know the chemicals in vape products. Our findings suggest they should be cautious and should be 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. When establishing policies for e-cigarette use and distribution, it would be advisable to consider if and how the products harm the unborn. Regulatory agencies should consider mandatory ingredient disclosure on packaging for e-cigarettes.”

Limits of the lab evidence

The researchers have already investigated menthol flavoring in e-cigarettes and found that it contributed to respiratory disease in humans. They are now studying WS-23, a synthetic coolant often used in e-cigarette products, and examining the effects of menthol and WS-23 on the differentiation of embryonic cells.

In addition to the lab study being unable to show definitively that the same effects would happen in human embryos, the researchers point out that their study does not predict the effect of cumulative exposure to vanillin over days, weeks, months or years. The effect of long-term exposure could be greater.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

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