Laser helps unblock arteries

LASER LIGHT can help prevent relapses after one of the most common treatments for blocked arteries. Stephen Bown of the U.K.'s National Medical Laser Centre in London described this new use of Photodynamic Therapy or `PDT' at the British Association for the Advancement of Science's annual festival.

PDT has been around in various guises for several years. The idea is simple enough. An innocuous substance is injected into or smeared onto the patient. Then light of the right colour and intensity, focused on the spot needing treatment, triggers chemical reactions that turn the innocuous substance into a potent drug in situ.

So, if you shine light onto a tumour, for instance, you can kill just those cells in the tumour and leave surrounding, unilluminated tissue intact. This is more precise, and hence less damaging, than surgery. "Theselectivity of destruction comes from where you put the light," says Bown.

Recent developments in laser technology and new drugs that react to the laser light much faster are bringing this technique within the reach of time - and cash - strapped health services. "Old- fashioned lasers took up a whole room and took a physicist an hour to start up," says Bown'scolleague, Chris Hopper. Modern `diode' lasers can be carried in a briefcase.

Having developed several promising therapies for cancer, Brown and his team are now seeing what PDT can do for other diseases. They have found, for instance, that PDT could make existing therapies for clogged arteries (atheroschlerosis) cheaper and more reliable.

Over half a million people in the U.S. alone suffer from atherosclerosis. Currently, when patients develop an occluded artery, doctors perform a `balloon angioplasty'. They thread a flaccid balloon into the artery and then gently inflate it to widen the vessel at the point where it has narrowed. When the balloon is removed, blood flows freely through the newly expanded artery.

In about a third of patients, the artery becomes clogged again within a few months. Many of these relapses happen because, in response to being stretched during an angioplasty, 'smooth muscle' cells in the wall of the artery proliferate more rapidly than usual, blocking the artery once more.

Now Bown's team has found that PDT can help. Used just after anangioplasty, PDT can kill smooth muscle cells in the offending area withoutdamaging the fibrous structure of the artery walls.

This leaves the artery essentially intact, but prevents the smooth muscle cells from proliferating into a new blockage. The cells grow back several weeks after the angioplasty, which is long enough to give them no reason to overgrow.

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Section  : Science & Tech
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