Exhaust from cars and trucks is a significant source of outdoor air pollution. When we breathe in high levels of the particles present in exhaust, these particles can irritate the lungs and cause breathing disorders. Once in the bloodstream, fine particles (2.5 micrometers in diameter or less) may lead to inflammation throughout the body. Outdoor air pollution has been associated with heart attacks, strokes, and cancers.
Not much is known about how fine particles affect the body on a molecular level. However, breathing in fine particles has been associated with epigenetic changes that may increase the risk of disease. Epigenetic changes are alterations in the way genes are switched on and off without a change in the DNA sequence. The type of epigenetic change associated with air pollution is DNA methylation, the attachment of methyl groups to DNA.
An international team led by scientists at Columbia University set out to determine whether the fine particles in air pollution may alter DNA methylation in CD4+ T-helper cells, a type of circulating white blood cell involved in the inflammatory response. They also investigated whether a nutrient involved in DNA methylation, specifically a B vitamin supplement, might counteract the methylation changes. The study was supported by NIH’s National Institute of Environmental Health Sciences (NIEHS). Results appeared online on March 13, 2017, in Proceedings of the National Academy of Sciences.
Ten healthy volunteers, aged 19 to 49 years, took part in the 3-stage study. In the first stage, they were given an inactive placebo for 2 weeks before being exposed to filtered air for 2 hours. They then took the placebo for 4 weeks and were exposed to air containing fine particles from vehicle exhaust for 2 hours. The researchers obtained vehicle exhaust from a busy street in downtown Toronto and concentrated the fine particles before delivering them through an oxygen-type mask. In the final stage of the study, the participants took the vitamin B supplement for 4 weeks and were then exposed to fine particles for 2 hours.
At each stage, the scientists analyzed changes in the genes of CD4+ T-helper cells. They found that exposure to exhaust particles from outdoor air pollution was associated with DNA methylation changes. However, these changes were not observed when the participants took the daily B vitamin supplement before exposure to the particles.
Larger, longer-term studies are needed to validate the findings of this small study. A better understanding of how outdoor air pollution causes epigenetic changes could provide insights to guide the development of future prevention therapies.
“While emission control and regulation is the backbone of prevention, high exposures are, unfortunately, the rule still in many megacities throughout the world,” says senior author Dr. Andrea Baccarelli of Columbia University's Mailman School of Public Health. “As individuals, we have limited options to protect ourselves against air pollution. Future studies, especially in heavily polluted areas, are urgently needed to validate our findings and ultimately develop preventive interventions using B vitamins to contain the health effects of air pollution.”
B vitamins attenuate the epigenetic effects of ambient fine particles in a pilot human intervention trial. Zhong J, Karlsson O, Wang G, Li J, Guo Y, Lin X, Zemplenyi M, Sanchez-Guerra M, Trevisi L, Urch B, Speck M, Liang L, Coull BA, Koutrakis P, Silverman F, Gold DR, Wu T, Baccarelli AA. Proc Natl Acad Sci U S A. 2017 Mar 13. pii: 201618545. doi: 10.1073/pnas.1618545114. [Epub ahead of print]. PMID: 28289216.