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Particulate Matter Exposure with High-Fat Diet Accelerates Hardening of Arteries

Section of abdominal aorta.

Researchers at the Mount Sinai School of Medicine and the New York University School of Medicine have shown a direct cause-and-effect link between exposure to fine particle (PM) air pollution and the development of atherosclerosis, commonly known as hardening of the arteries.

In the study, funded by the National Institute of Environmental Health Sciences (NIEHS) and the EPA, mice that were fed a high-fat diet and exposed to air with fine particles (PM2.5) had 1.5 times more plaque production than mice fed the same diet and exposed to clean filtered air.

Plaque, a fatty deposit on the inner lining of the blood vessels, can predispose individuals to conditions such as heart attacks and strokes. The fine particle exposure also led to increased inflammation of the artery walls and reduced function of the artery wall’s inner lining.

Particulate matter in the ambient air comes from a variety of sources including diesel exhaust and other fuel combustion.

The study showed that the combination of fine particle pollution and high-fat diet can promote the development of atherosclerosis, and may explain why people who live in highly polluted areas have a higher risk of heart disease. The findings are also important because the fine particle concentrations used in the study were well within the range of concentrations found in the air around major metropolitan areas.

The researchers did not observe significant differences in plaque production and artery wall inflammation in fine particle-exposed mice given the normal diet. However, among mice given clean air, those on the high-fat diet had greater plaque production and artery wall inflammation than those given the normal diet. These results suggest that both diet and fine particle pollution contributed to the development of atherosclerosis in the mice.

This is one of the first studies to demonstrate measurable changes in plaque production and artery inflammation following exposure to fine particle matter. These findings have important implications for the long-term impact of fine particle air pollution on urban populations.

—NIEHS Director David A. Schwartz, M.D.

For six months, researchers fed mice with normal chow or high-fat chow and exposed them to concentrated ambient particles of less than 2.5 µm (PM2.5) or filtered air (FA) for 6 hours per day, 5 days per week.

The exposure concentrations were relatively low—average particle exposure over the course of the study was 15 µm/m3, well below the current federal air quality 24-hour standard of 65 µm/m3 in a 24-hour period.

Following the exposures, the researchers measured plaque concentration in the aorta, the largest artery in the body. They found that among mice fed the high-fat diet, those exposed to fine particles had plaque concentrations more than 1.5 times higher than those exposed to clean air.

These results suggest that the fine particle exposure is actually accelerating the development of atherosclerosis in the high-fat group.

—Sanjay Rajagopalan, M.D., senior author

Further comparison of the high-fat groups showed that the artery walls of the mice exposed to fine particle pollution were significantly more inflamed than their clean-air counterparts. In addition, the fine particles had a measurable effect on the ability of the arteries to dilate, an important indicator of artery wall function.

The study results are published in the 21 December 2005 issue of the Journal of the American Medical Association.

Another recent study, published in Circulation, the journal of the American Heart Association, also found that PM exposure affects the ability of blood vessels to dilate. (Earlier post.)



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