NEW YORK: A study by US researchers suggests that diesel fumes appear to raise the risk of heart disease in people with high cholesterol.

The researchers combined the pollutants and fats and cultured them with cells taken from the inner lining of human blood vessels. A few hours later, they extracted DNA from the cells for genetic analysis.

They showed that the genes that promote cellular inflammation had been activated, reported the online edition of the BBC news.

Next, they exposed mice with high cholesterol to the diesel particles and saw that some of the same genes were activated in the animals' tissue.

The scientists, however, said they could not understand exactly how air pollutants cause cardiovascular injury.

"But we do know that these particles are coated with chemicals that damage tissue and cause inflammation of the nose and lungs" University of California, Los Angeles researcher Andre Nel said.

"Vascular inflammation in turn leads to cholesterol deposits and clogged arteries, which can give rise to blood clots that trigger heart attack or stroke," Nel added.

Scientists said that the damaging particles in diesel fumes and the cholesterol act in combination to switch on genes that cause potentially dangerous inflammation of the blood vessels.

Their combination creates a dangerous synergy that wreaks cardiovascular havoc far beyond what's caused by the diesel or cholesterol alone.