Measuring DNA Damage Among Smokers

To the Editors: Ellahueñe et al. (1) wrote in the abstract that ‘‘The objective of this study was to establish if the alkaline SCGE assay in whole blood cells gives similar results as the same method in isolated lymphocytes, because whole blood cells are simpler and more economical to use, specifically in human genotoxic biomonitoring.’’ It sounds strange because either isolated lymphocytes or whole blood is indicated as a source of human cells in the widely cited protocol of SCGE assay, implying that both options are equally suitable for biomonitoring (2). Successful application of whole blood cells in the comet assay was well documented—I randomly found some articles from Medline concerning both humans (3-5) and mice (6). The data concerning the influence of smoking on DNA damage of blood cells are very contradictory (7). Two recently published articles showed opposite results (8, 9). In both investigations the subjects smoked about 13 cigarettes per day, but in the first one the age of the subjects was 28.9 years (20 males), whereas in the other it was 36 years (5 males and 5 females). It is well known that the brand and the number of cigarettes consumed, diet, and geographic variation in smoking habit can be important variables in investigations on DNA damage in cells of smokers (7). The authors (1) studied only six smokers, but data on the number of cigarettes consumed per day and the gender are absent. Hence, very important data are not presented on these factors which should be considered in the study of DNA damage (7). The authors wrote that ‘‘the tail moment, expressed in arbitrary units, was calculated as: (tail length percentage of migrated DNA) / 100.’’ In Table 1 the data on three mentioned variables are presented. Calculations have shown that all data on ‘‘Tail moment’’ do not correspond to other data. For example, ‘‘0 sampling time’’ 0.15 (tail length) 0.03 (DNA%) = 0.0045. According to the authors’ definition, it should be divided by 100. However, the authors presented another figure as tail moment—0.54. I guess the sign (/ 100) is wrong and should be ( 100). But again in this case ‘‘Tail moment’’ is 0.45, and not 0.54. Another example: sampling time 16 hours, CP— 0.19 0.1 = 0.019 100 = 1.9. However, the authors indicated 3.37! It is extremely strange that all the digits on tail moment do not correspond to the calculations! In my opinion, the article has a lot of shortcomings that need to be clarified.