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Nicotine implicated as a cancer promoter
Source: (cancerfacts.com)
Friday, January 03, 2003
BETHESDA, MD. -- Jan. 4, 2003 -- Once thought to be only the addictive agent in tobacco, a new study shows that nicotine itself may promote cancer.
The finding could change the view of smoking cessation treatments such as nicotine patches, gums and nasal sprays as themselves carrying a risk of cancer that people may need to take into consideration.
The study by Dr. Phillip Dennis and colleagues at the US National Cancer Institute in Bethesda, Md. showed that the lung cells, called epithelial cells, that come into contact with smoke, become unresponsive to a signal to self-destruct when exposed to nicotine in the laboratory and in mice.
That finding together with an another group's earlier finding that nicotine or its derivative stimulates the growth of blood vessels in tumors, a process called angiogenesis, implicates nicotine as promoting both development and progression of cancer. The report appears in the Jan. 1 issue of the Journal of Clinical Investigation.
"In addition to increasing epithelial cell survival as described in this report," the researchers wrote, "nicotine can stimulate endothelial cell growth and angiogenesis."
Programmed cell death, or apoptosis, is one of the body's most effective defense mechanisms against cancer. Cells are constantly checking their "normal status," and are poised to commit suicide at the first sign of irregularities, thus protecting the body from production of abnormal cells that can, over time, form tumors. Virtually all cancers have found ways to undermine this defense mechanism, and activation of a molecular circuit called the Akt pathway is one of them.
In the study, the researchers found that lung epithelial cells exposed to nicotine and a derivative of nicotine called, nicotine-derived nitrosamine (NKK), in amounts equivalent to those seen in smokers, resulted in the activation the Akt pathway, which promotes cell growth and survival. They also found that the Akt pathway was active in the lungs of mice treated with NKK and in lung cancer tissue taken smokers.
Scientists have long thought that of the two "active ingredients" in tobacco, nicotine was the addictive agent, and tar contained the carcinogen. In this new study and a handful of others, scientists are beginning to unravel the mechanisms of how tobacco consumption causes cancer. While that information may one day lead to more effective treatments for cell damage caused by tobacco, this new information may also require that people weigh the risks and benefits of current stop-smoking aids.
More than 4 million deaths worldwide are attributed annually to tobacco use and more than 400,000 people in the United States die each year from tobacco-related causes according to the American Cancer Society.
SOURCE: J. Clin. Invest. 111:81-90 (2003)
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