Airborne Particulate and Heart Disease

Air Pollution May Cause Heart Disease

Patients prone to heart disease may one day be told by physicians to avoid not only fatty foods and smoking but air pollution too.

A new academic study led by UCLA researchers has revealed that the smallest particles from vehicle emissions may be the most damaging components of air pollution in triggering plaque buildup in the arteries, which can lead to heart attack and stroke. The findings appear in the Jan. 17 online edition of the journal Circulation Research.

The scientists identified a way in which pollutant particles may promote hardening of the arteries—by inactivating the protective qualities of high density lipoprotein (HDL) cholesterol, known as "good" cholesterol.

A multicampus team from UCLA, USC, the University of California, Irvine, and Michigan State University contributed to the research, which was led by Dr. Andre Nel, UCLA's chief of nanomedicine. The study was primarily funded by the National Institute of Environmental Health Sciences and the EPA.

"It appears that the smallest air pollutant particles, which are the most abundant in an urban environment, are the most toxic," said first author Dr. Jesus Araujo, assistant professor of medicine and director of environmental cardiology at the David Geffen School of Medicine at UCLA. "This is the first study that demonstrates the ability of nano-sized air pollutants to promote atherosclerosis in an animal model."

Nanoparticles are the size of a virus or molecule—less than 0.18 micrometers, or about one-thousandth the size of a human hair. The EPA currently regulates fine particles, which are the next size up, at 2.5 micrometers, but doesn't monitor particles in the nano or ultrafine range.

These particles are too small to capture in a filter, so new technology must be developed to track their contribution to adverse health effects.

"We hope our findings offer insight into the impact of nano-sized air pollutant particles and help explore ways for stricter air quality regulatory guidelines," said Nel, principal investigator and a researcher at UCLA's California NanoSystems Institute.

Nel added that the consequences of air pollution on cardiovascular health may be similar to the hazards of secondhand smoke.

Pollution particles emitted by vehicles and other combustion sources contain a high concentration of organic chemicals that could be released deep into the lungs or even spill over into the systemic circulation.

The UCLA research team previously reported that diesel exhaust particles interact with artery-clogging fats in low-density lipoprotein (LDL) cholesterol to activate genes that cause the blood-vessel inflammation that can lead to heart disease.

In the current study, researchers found that mice exposed to ultrafine particles exhibited 55% greater atherosclerotic-plaque development than animals breathing filtered air and 25% greater plaque development than mice exposed to fine-sized particles.

"This suggests that ultrafine particles are the more toxic air pollutants in promoting events leading to cardiovascular disease," Araujo said.

Scientists also identified a key mechanism behind how these air pollutants are able to affect the atherosclerotic process. Using a test developed by Dr. Mohamad Navab, study co-author and a UCLA professor of medicine, researchers found that exposure to air pollutant particles reduced the anti-inflammatory protective properties of HDL cholesterol.

"HDL normally helps reduce the vascular inflammation that is part of the atherosclerotic process," said Dr. Jake Lusis, study co-author and a UCLA professor of cardiology, human genetics and microbiology, immunology and molecular genetics. "Surprisingly, we found that exposure to air pollutant particles, and especially the ultrafine size, significantly decreased the positive effects of HDL."

Researchers added that previous studies assessing the cardiovascular impact of air pollution have taken place over longer periods of exposure time, such as five to six months. The current study demonstrated that ill effects can occur more quickly, in just five weeks.

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