Recent evidence suggests that nicotine may not only cause addiction but the compound and its derivatives could also promote cancer development and progression.
Scientists had until now assumed that the tar in cigarettes was the carcinogen, and that nicotine was responsible for the addiction. However, researchers in the US have reported that nicotine may be worse than originally thought.
Phillip Dennis and colleagues at the US National Cancer Institute in Bethesda studied the effect of nicotine and the nicotine-derived nitrosamine NKK on normal lung epithelial cells - those cells that are exposed to inhaled smoke and in which lung cancer starts.
The stimulation of lung epithelial cells with amounts of nicotine and NKK equivalent to those seen in smokers, resulted in the activation of a molecular pathway - the so-called Akt pathway - that 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 from smokers, according to the report in the 2 January issue of the Journal of Clinical Investigation.
This is significant because 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 host from propagation of abnormal cells that can, over time, form tumours. Virtually all cancers have found ways to undermine this defense mechanism, and activation of the Akt survival pathway is one of them.
Other recent research has also suggested that nicotine and its derivatives, in addition to their addictive properties, can directly promote cancer. In light of the mounting evidence, as Dennis and colleagues suggest, it might become necessary to re-evaluate the risk-benefit ratio of quitting-aids such as nicotine patches, chewing gum, or nasal sprays.