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WORLD / Health
Air pollution triggers blood clots
(Agencies)
Updated: 2007-09-21 16:49
CHICAGO - Tiny particles of air pollution - less than one tenth the width
of a human hair - can trigger clotting in the blood, US researchers said
on Thursday in a finding that helps explain how air pollution causes
heart attacks and strokes.
Large population studies have shown pollution from the exhaust of trucks,
buses and coal-burning factories increases the risk of fatal heart
attacks and strokes.
But researchers have not understood how these microscopic particles
actually kill people.
"We now know how the inflammation in the lungs caused by air pollutants
leads to death from cardiovascular disease," said Dr. Gokhan Mutlu of
Northwestern University in Chicago, who studied the effects of air
pollution in mice.
Lungs inflamed by pollution secrete interleukin-6, an immune system
compound that sparks inflammation and has been shown to make blood more
likely to clot.
The research appears in the Journal of Clinical Investigation. It follows
a study last week in the New England Journal of Medicine that found
breathing diesel fumes interfered with heart attack survivors' ability to
break down blood clots.
Mutlu got a clue about the clotting issue two years ago when he was
studying the effects of air pollution on heart failure in mice. Mice who
had been exposed to pollution bled significantly less.
"They were forming blood clots," he said in a telephone interview.
In the latest study, he and colleagues exposed mice to particles of air
pollution collected by the US Environmental Protection Agency. These were
mixed with a saline solution and injected into the lungs of mice.
Mice exposed to pollution showed a 15-fold increase in interleukin-6 just
24 hours later. That time frame is important because some studies have
shown a spike in air pollution can boost heart attacks with 24 hours.
Mutlu and colleague Dr. Scott Budinger said they were able to prevent
this clotting by suppressing immune cells in the lungs called macrophages
that attack foreign substances and secrete interleukin-6.
Mice with suppressed immune responses did not show increased blood
clotting. "This suggested that interleukin-6 was the driving force,"
Mutlu said.
He said most people understand that high levels of air pollution can make
lung diseases such as asthma worse.
"The same thing is not known for patients with coronary artery disease or
congestive heart failure," Mutlu said. "I think we need to increase the
awareness of this link among those individuals."
The researchers now plan to study whether aspirin can counteract the
clotting effect in mice. Low-dose aspirin helps thin the blood and is
already recommended for people with heart problems.
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