Nicotine affects human embryos at the level of individual stem cells.

Scientists have found that nicotine at the cellular level induces a number of common pathologies in human embryonic development. Single-cell RNA sequencing of human embryonic stem cell (hESC) suggests that the three-week exposure to nicotine disrupts intercellular communications, reduces the survival of the cells and changes the expression of genes that regulate important functions, such as, for example, contraction of the cardiac muscle.

The authors of the paper, published in Stem Cell Reports on February 28, report that their stem-cell model provides a new insight into the effects of nicotine on organs and individual stem cells of the developing fetus and can be used to optimize the drug and environmental toxicity screening.

“These results are especially important in that they provide a scientific basis for educating the public, especially young women, to keep away from smoking when they are pregnant or considering having a family”, – says senior author Joseph C. Wu of the Stanford University School of Medicine. “Nicotine found in products such as tobacco, e-cigarettes, and nicotine gums may have wide-ranging, harmful effects on different organs of a developing embryo during pregnancy.”

Maternal smoking during pregnancy is a known risk factor for the appearance of birth defects, such as growth retardation. It can also cause miscarriage and premature labor. It is known that smoking is closely associated with long-term adverse effects in the psycho-physiological, cardiovascular, respiratory, endocrine and metabolic areas of children’s development.

Nicotine, the main chemical component of tobacco smoking, is a major risk factor. Unfortunately, the creation and widespread use of new types of tobacco products containing nicotine, such as e-cigarettes, has negated recent progress in reducing tobacco consumption.

A large number of studies have revealed the harmful effect of nicotine on animal models, mainly in rodents. Experiments have shown that the effects of nicotine during pregnancy have a detrimental result on the development of the fetus. However, due to interspecies differences, doubts remain whether these results can be projected onto people.

Since nicotine toxicity studies were performed using human cells through bulk RNA-sequencing analysis, they did not allow scientists to study the negative effects at the level of a single cell. Therefore, the effect of nicotine on human embryonic development and the underlying molecular mechanisms remain poorly understood.

To investigate this process in detail, Wu and his colleagues used single-cell RNA sequencing. They analyzed the effects of 21 days of nicotine exposure on transcriptomes of a total of 12,500 cells obtained from embryoid bodies, which are 3-D aggregates of various types of pluripotent stem cells, which give rise to the development of the brain, heart, liver, blood vessels, muscles and other organs. Scientists have discovered that cell survival decreases, confirming the assumption that nicotine can affect embryo development as early as the preimplantation stage.

Exposure to nicotine also increased the level of aggressive molecules known as reactive oxygen species, leading to a decrease in the size of embryonic bodies, anomalies of their formation and differentiation. In addition, the effect of nicotine changed the cell cycle in populations of progenitor cells formed from embryonic stem cells, caused dysregulated cell-to-cell communication, another adverse effect that has not been well studied.

“This is important because we know that smoking and nicotine have been shown to increase the pathological risk in endocrine, reproductive, respiratory, cardiovascular, and neurologic systems that rely on intricate and dynamic interactions amongst multiple cell types for homeostasis and function”, – Wu says.

The researchers also found that nicotine exposure leads to changes in the expression of genes involved in mitochondrial function and in reactions to metal toxicity affecting brain malformations, mental retardation, muscle development and lung diseases, as well as genes associated with Ca2 +   arrhythmias that affect on the contractility of cardiac muscle cells.

“A major implication of our study is that we now have validated a new method for evaluating the effect of drugs and environmental toxicity on human embryonic development”, – Wu says. “But one major limitation is that we are not able to recapitulate the whole-body physiology of a pregnant woman using differentiation of hESCs into embryoid bodies. For example, the influence of exercise, stress, food, or hormonal changes are not captured in this model.”

In the future, researchers plan to continue studying the mechanisms of birth defects of the fetus caused by the effect of nicotine.

“We hope this will lead to the discovery of novel biomarkers that can help doctors better prevent, diagnose, and treat these diseases”, – Wu says. “In addition, we plan to utilize our hESC-derived embryoid body model and single-cell-sequencing technology to investigate the wider effects of other harmful conditions such as air pollution on human embryonic development.”