Childhood asthma has reached epidemic proportions across the globe for unknown reasons. Maternal smoking is associated with childhood asthma, but a study published in 2005 suggested that if your grandmother smoked, you were at greater risk of developing asthma than if your mother smoked. How could this happen?
Your genes determine the traits you have, and changing a gene’s DNA sequence can affect the trait. However, a trait can also be altered by changing how the cell reads the DNA sequence. This is called “epigenetic changes.” We hypothesized that nicotine—the primary chemical in cigarette smoke that affects fetal lung development—altered genes in this way and conducted several studies to test our hypothesis.
In our research, we saw that rats given nicotine while in the womb developed asthma. What was interesting, however, was that their offspring also developed asthma, even though those offspring weren’t directly exposed to nicotine. This effect lasted at least three generations. We think the reason is because nicotine caused epigenetic changes in the egg and sperm cells, cells that are inherited by the next generation. These changes made the next generation’s developing lung hyper-reactive, which is characteristic of asthma.
We also saw that repeated environmental exposure to nicotine amplified the asthma symptoms. Nicotine dissolves in fat and can be stored in fat tissue in the body. When it crosses the placenta, we think it can accumulate in the fetus because the fetus is rich in fat.
The news coverage on neonicotinoid pesticides harming the honey bee population has been catching our attention. Neonicotinoids are chemically similar to nicotine and have similar biological effects. Although neonicotinoid pesticides are supposed to be far less toxic to mammals, such as humans, than they are to bees, our studies show that nicotine has serious transgenerational effects on lung health and that repeated exposure worsens the impact. In light of the increasing incidence of childhood asthma, we wonder if stopping cigarette smoking and the use of neonicotinoid pesticides could reduce the occurrence of asthma.
John S. Torday, PhD, is a professor of pediatrics at Harbor-UCLA Medical Center, Torrance, Calif.
Virender K. Rehan, MD, is a professor of pediatrics at Harbor-UCLA Medical Center, Torrance, Calif.