LONDON (Reuters) - Premature aging caused by years of smoking could be due to tobacco smoke triggering an increase in a protein that breaks down the elasticity of the skin, British researchers said Friday.

Chemicals in tobacco have a damaging effect on the skin, causing it to appear older than it actually is. Scientists have been aware of the impact of tobacco on the skin but until now did not know how it occurred or why. But new research by doctors at Guy's, King's and St. Thomas's School of Medicine in London may help to explain it. Photobiologist Professor Antony Young and his team were studying the effects of ultraviolet (UV) light on the skin when they realized that smokers have high levels of a protein called matrix metalloproteinanse 1 (MMP-1) which breaks down collagen, an important element in maintaining the skin's elasticity. ``Smokers have higher expression of the gene for an enzyme MMP-1 that is known to degrade collagen, the major structural protein in the skin,'' Young said in a telephone interview. ``We're proposing that the reason smokers look older is the activation of this gene by some component of tobacco smoke.'' Young and his colleagues are not sure which of the thousands of chemicals in tobacco activate the gene but they suspect it could be the same as those that cause cancer because MMP-1 has also been linked to the disease. ``We know the sun has the same effect,'' Young explained. ``There is a maximum level of expression that can either be achieved by UVs or by smoking or a combination.'' The researchers discovered high levels of the protein in smokers while examining biopsies from 35 people during a research study. They were comparing levels of the gene in skin biopsies taken from people whose buttocks had been exposed to UV radiation and those who had not. They used skin from the buttocks because it is the area of the body least exposed to sunlight. When they noticed varying levels of the protein in people not exposed to UV rays they questioned them and discovered that smokers had much higher levels than non-smokers. ``We showed a significant association between smoking and expression of MMP-1 mRNA, which is a measure of gene activity,'' said Young. ``People who smoke are getting two things that may induce this protein, the smoking and the sun. It may be the combination of these two things that is important.''

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