Evidence that nicotine stimulates new blood vessel growth in mice hints
that it could exacerbate cancer and heart disease. But harnessed, the same
quality might also help to treat Parkinson's and Alzheimer's disease
Smokers face increased risks of tumours and artery blockages - diseases that depend on new blood vessels. Whether components of smoke directly promote vessel growth is unknown.
Mice plied with doses of nicotine equivalent to those in smokers' blood sprout new blood vessels, John Cooke and his team at Stanford University, California, have now shown.
New vessels invaded oxygen-starved tissue after mice drank nicotine-laced water, the researchers showed. Cancerous tumours and fatty deposits in arteries also grew when their blood-supply was enhanced by the drug. The implication: "nicotine could be contributing to cancer," says Cooke.
The same receptors on nerve cells that make nicotine addictive in the brain are present on the endothelial cells that line blood vessels. Cells bathed in nicotine start to divide and form tubes, the group found.
"It's a provocative study," says Rakesh Jain, who works on blood vessel formation at Harvard Medical School in Boston, Massachusetts. The findings contrast with previous work in which animals exposed to nicotine showed no obvious blood vessel changes. Nicotine may only affect abnormally growing tissue, the researchers suggest.
But before pointing the finger at nicotine, "we need to be cautious", says Jain. The drug dose and time over which it is taken, may decide how potent a growth factor it is, he says.
Besides, nicotine is just one of the 4,000 chemicals in cigarette smoke. Other constituents, such as oxygen free-radicals, damage endothelial cells - this triggers a build up of artery deposits, says Michael Pittilo who studies cigarette smoking and heart disease at St Georges's Hospital Medical School in London. Compared with these, nicotine's effects are likely to be insignificant, he thinks. "In a nutshell [nicotine] is much less damaging that the effects of smoke," he says.
But nicotine alone is increasingly used in patches, gums and sprays to help smokers quit, and here the long-term effects of use are unknown. "The study raises issues that need to be explored," says Pittilo. "Some of it is quite concerning."
In fact, despite its villainous reputation, nicotine could be a potential hero. Stroke, Alzheimer's and Parkinson's disease can benefit from an increased blood supply. Therapeutic use of nicotine is a possible answer. It could be used locally to promote blood vessel growth, suggests Cooke. "If you can control it, it can be useful," he says, "but out of control it can be damaging."