GSTP c C T SNP

GSTP1 c.341C > T SNP was genotyped in 90 patients tumor and 180 normal healthy individuals. The profile of GSTP1 c.341C > T Mitochondrial DNA Isolation Kit mg and genotypes is shown in Table 2. The profile of the genotypes was in agreement with Hardy-Weinberg equilibrium (χ2 = 2.11). Minor allele frequency (341T) among OSCC patients was 15.6%, which is about four times higher than its frequency in the control group (3.9%). The power of the study was 86.8%. The distribution of the GSTP1 c.341C > T alleles among case and control groups was compared by means of contingency table. The difference in the distribution profile of the minor allele was found to be statistically significant (P-value = 0.000004; Odds ratio = 4.5 [0.95 CI = 1.9–10.7]). We also found a statistically significant difference in the distribution of the genotypes (P-value = 0.00006). The distribution of the genotypes of GSTP1 c.341C > T SNP was also compared by considering dominant, recessive, additive and over-dominant genetic models (Table 3). Statistically significant difference was observed in all the four models. Of the four models, the best P-value was observed in the case of dominant genetic mode. The GST pi protein expression profile in the tumor samples was analysed by immunohistochemistry (IHC). Representative photomicrographs of IHC analysis are shown in Fig. 2. We noticed immunoreactivity for GST pi protein in the tumor cells and not in the surrounding normal squamous epithelium. Immunoreactivity of the tumor samples was assessed with respect to intensity of staining and the area of tumor tissue being stained. We evaluated the relationship between GST pi protein expression and the genotype of GSTP1 c.341C > T SNP. 5 tumor specimens from each of the 3 genotype groups viz., CC, CT and TT were chosen for IHC analysis. Expression levels in the 3 groups are summarised in Table 2. No statistically significant correlation was observed between the GSTP1 c.341C > T SNP and GST pi protein expression (P = 0.82) (Table 4).
Discussion Tobacco consumption and infection with high risk strains of human papilloma virus are the major environmental risk factors implicated in the development of oral cancers [15]. Our previous study with hospital based population which is predominantly rural in demography showed that tobacco consumption either in smokable or chewable form was the principal exogenous risk factors for oral carcinogenesis rather than infection with human papilloma virus [12]. This observation prompted us for examining the profile of genetic risk factors with particular emphasis on pathways that affect carcinogen detoxification. The practice of chewing tobacco is common to South and South East Asian region [16], [17]. It is consumed in as a co-ingredient with betel quid which is commonly known as “paan”. Betel quid involves wrapping of areca nut, lime, condiments, sweeteners, and sometimes with or without tobacco with fresh leaf of betel plant (Piper betle). The combinations of the ingredients are altered according to individual preferences. Tobacco was a common ingredient in betel quid consumed by the patient group in this study. The major carcinogenic constitutes of tobacco are nicotine, polycyclic aromatic hydrocarbons, nitrosamines, metals and aldehydes [18]. In addition, stable and unstable free radicals and reactive oxygen species (ROS) with the potential for biological oxidative damage are known to occur in the tobacco smoke [19]. Tobacco-specific nitrosamines, N-nitrosodiethylamine, N-nitrosoanabasine, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone, and N′-nitrosonornicotine have been detected in the saliva of betel quid chewers with tobacco [20]. Genetic polymorphisms associated with enzymes involved in carcinogen detoxification can lead to increased susceptibility to carcinogenesis [21]. The toxicological profile of tobacco guided us towards GST pi as it is an important enzyme involved in the detoxification of environmental carcinogens, xenobiotics and products of ROS induced oxidative damage; It is also the major subtype expressed in the oral mucosa. Toxicological importance of GST pi is also corroborated by animal studies. Epoxides of Polycyclic aromatic hydrocarbons (PAH) such as Benzo(a)pyrene [B(a)P] diolepoxide(BPDE), acrolein and other unsaturated carbonyls generated by oxidation of lipids and DNA can be used as substrates by GST pi [22].