Half a pack of cigarettes a day more than doubles DNA breaks in circulating leukocytes

A comparative quantification of single-stranded DNA breaks was performed by comet assay analysis in the circulating leukocytes of ten healthy smokers (average smoking rate: half a pack a day, range: 9-12 cigarettes a day) and ten age and sex matched healthy non-smokers. DNA breaks lead to smaller pieces of DNA, which migrate out of the nucleus forming a tail during gel-electrophoresis. Damage of an individual cell was quantified by the parameters tail moment and olive moment.Smoking had a clear effect on both study parameters (tail and olive moment). Smokers had more than double the amount of ss-DNA breaks in their circulating leukocytes than non-smokers [tail moment: 0·75 AU [smokers] compared to 0·2 AU [non-smokers]; olive moment: 0·85 AU [smokers] compared to 0·3 AU [non-smokers]; both p < 0·001].Smoking half a pack a day interferes with DNA integrity. One potential explanation for the enhanced DNA breaks in smokers is oxidative stress.Little doubt exists that smoking is an important risk factor for variousDiseases [1]. Extrapolating from the tobacco-attributed mortality rates in 1995, and taking into account population growth, approximately 3·4 million deaths in developed countries from tobacco is anticipated in 2025 [2]. The exact mechanism by which smoking contributes to the pathogenesis of diseases, like cataracts and age-related macular degeneration, has not yet been identified in detail. One plausible cause is oxidative stress. The term oxidative stress is widely used in the literature but not very well defined. Oxidative stress occurs when the amount of ROS generated in cells exceeds the capacity of normal detoxification systems [3]. It leads to cellular damage, including DNA damage, in particular DNA breaks.Under physiological conditions, DNA can undergo spontaneous breaks. DNA damage can occur as double-strand (ds) breaks or as single-strand (ss) breaks [4]. The number of DNA breaks depends on different factors. For example, it increases with age. Fortun