Strengthening the link between air pollution and cardiovascular disease, new research suggests that people with high cholesterol are especially vulnerable to heart disease when they are exposed to diesel exhaust and other ultra-fine particles that are common pollutants in urban air.
Microscopic particles in diesel exhaust combine with cholesterol to activate genes that trigger hardening of the arteries, according to a study by UCLA scientists to be published today.
"Their combination creates a dangerous synergy that wreaks cardiovascular havoc far beyond what's caused by the diesel or cholesterol alone," said Dr. Andre Nel, chief of nanomedicine at the David Geffen School of Medicine at UCLA and a researcher at UCLA's California NanoSystems Institute. He led a team of 10 scientists who conducted the study, published in an online version of the journal Genome Biology.
Although diet, smoking and other factors contribute to the risk of cardiovascular disease -- the leading cause of death in the Western world -- scientists have long believed that air pollution, particularly tiny pieces of soot from trucks and factories, plays a major role, too.
For years, scientists around the world have reported that on days when fine-particle pollution increases, deaths from lung diseases, heart attacks and strokes rise substantially. Riverside County and the San Gabriel Valley have among the worst fine-particle pollution in the nation.
The scientists say their study, conducted on human cells as well as on mice, is the first to explain how particulates in the air activate genes that can cause heart attacks or strokes.
The researchers exposed human blood cells to a combination of diesel particles and oxidized fats, then extracted their DNA. Working together, the particles and fats switched on genes that cause inflammation of blood vessels, which leads to clogged arteries, or atherosclerosis.
The team then duplicated the findings in living animals by exposing mice to a high-fat diet and freeway exhaust in downtown Los Angeles. The same artery-clogging gene groups were activated in the mice.
The scientists reported that diesel particles may enter the body's circulatory system from the lungs, and then react with fats in the arteries to alter how genes are activated, triggering inflammation that causes heart disease.
Other research has shown similar inflammatory damage in lungs exposed to fine particles. Diesel exhaust has also been linked to lung cancer, asthma attacks and DNA damage.
