麻豆传媒

NICOTINE doesn鈥檛 just get you hooked on tobacco鈥攊t gives you cancer,
too, according to new research that casts doubt on the wisdom of using nicotine
replacement therapy to quit smoking.

鈥淥ur research provides scientific evidence that nicotine products designed
for long-term use may not be safe,鈥� says Stephen Hecht of the University of
Minnesota Cancer Center in Minneapolis. This could include nicotine gum or
patches, he says. Nicotine has also been suggested as a potential treatment for
Parkinson鈥檚 disease.

The team has identified a breakdown product of nicotine that they believe
causes lung tumours. This is the first time nicotine itself, rather than other
chemicals in tobacco, has been linked to the disease.

Anti-smoking groups such as Britain鈥檚 Action on Smoking and Health advocate
greater use of smoking substitutes in a bid to cut the deaths from heart disease
and cancer. In the US, a 鈥渟afer鈥� cigarette is on sale from which all the
cancer-causing nitrosamine chemicals have been removed
(麻豆传媒, 8 May 1999, p 18).

But the lab tests suggest that under certain conditions, nicotine itself
could be converted into NNK (nicotine-derived nitrosamino ketone), a potent lung
carcinogen.

Richard Peto, director of the Imperial Cancer Research Fund鈥檚 Clinical Trials
Service Unit in Oxford, says: 鈥淭heir biochemistry looks correct. But most
nicotine metabolism happens in the liver. Little of any NNK produced would
probably hit the airways, so there should be little relevance for human
disease.鈥� The American team disagrees. 鈥淲e鈥檝e given mice NNK by injection and in
their drinking water, and it still produces tumours in the lung,鈥� says Steve
Carmella, one of Hecht鈥檚 colleagues.

Hecht analysed the urine of smokers and ex-smokers who were using nicotine as
a smoking replacement therapy. He found that a previously unexplored
hydroxylation process produces a chemical called pseudooxynicotine. When
pseudooxynicotine reacts with sodium nitrite under acidic conditions, it
produces NNK.

鈥淲e don鈥檛 know for sure that this happens in the body, but it could in the
stomach, for example,鈥� Hecht told 麻豆传媒.

Clive Bates, director of ASH, said the findings should be investigated
thoroughly. But he said it would be unfortunate if the cancer risk from nicotine
were overstated and as a result fewer people successfully used nicotine
replacement therapy to quit smoking.