Smoking Effects
The adverse effects of a smoking status on the clinical
outcome in terms of reliability of the fact and its reason remain very controversial, although tobacco-derived chemical compounds readily modulate cell function by altering genes and promoting various molecules. The most important considerations in the clinical study of the effects of smoking are the individual differences in susceptibility to these effects.
Recently, single nucleotide polymorphisms (SNPs)
have been clarifi ed for cytochrome 450P (CYP)1A170
which converts B(a)P to BPDE. The homozygosity of
the CYP1A1*2 allele is associated with an increased
risk of lung cancer in Asians, but this polymorphism is
never, or rarely, recognized in Caucasians. The polymorphisms of DNA repair genes must also be considered. The polymorphism of glutathione S-transferase (GST) M1, which plays an important role in the detoxification of BPDE and other PAH-metabolites, strongly affects DNA damage and the risk of lung cancer developing in smokers.71 The mean BPDE–DNA adduct level in persons with GSTM1*0 was 6.4 adducts, whereas it was 1.2 in those with GSTM1*1.72 Alexandrov et al.73 found that the combination of homozygosity of CYP1A1*2 and GSTM1*0 presents a high risk of PAH metabolites in DNA adducts. Oxoguanine glycosylase 1 (OGG1) is glycosylase involved in the excision of 7, 8- dihydro-8-oxoguanine, a common oxidized guanine induced through oxidative stress by smoking.74 Its gene also presents functional polymorphisms. The homozygous form of the ser326cys variant is found in about 10% of people and is responsible for decreased activity of OGG1.75 The XPD gene (also called ERCC2) encodes a helicase that is part of the TFIH complex.76 Several polymorphisms, including non-synonymous SNPs, at the 312 and 751 codons have been described and are associated with an impaired DNA repair capacity, thereby resulting in an increased risk of lung cancer.77 These SNPs of the genes encoding the critical enzymes contribute to the susceptibility of lung cancer, and may be involved in the biological modulation of established lung cancer in smokers. Ultimately, the patients with lung cancer are more likely to have the genetic features in the mentioned enzymes than healthy persons.
Another problem when investigating the clinical
effects of smoking is that there are no objective parameters or methods of brief evaluation of an individual’s exposure to smoking, other than the pack-year index or the term abstinence from smoking. Various metabolites of tobacco smoke-derived chemicals, such as PAH, aromatic amines, and tobacco-specifi c nitrosamines, form the DNA adduct,78 which is thought to be an essential early step in the development of cancers. A quantifi cation of the DNA adduct in the respiratory cells may be the proper measure for the DNA damage caused by smoking. The 32P-postlabeling assay is the classical method to measure DNA adducts of carcinogens.79 Using this method, Boysen and Hecht80 detected BPDE–DNA adducts in 45% of smokers, 33% of exsmokers, 52% of non-smokers, 39% of occupationally exposed individuals, and 34% of environmentally exposed individuals. Recently, Arif et al.81 attempted to measure PAH–DNA adducts by using a modified 32Ppostlabeling assay/thin layer chromatography, in which the adducts were eluted as diagonal radioactive zones from the purified lung DNA of patients with lung cancer, and chromatographed in urea-based solvent. However,although the method could quantify free radicals, aldehyde, and butadiene, it could not quantify polyaromatics. A novel alternative is required to achieve a precise quantification of the individual DNA adducts of smoking-related metabolites.