Study On Polymorphisms Of Drug-metabolizing Enzymes And Environmental Exposure Factors Of Colorectal Cancer Susceptibility

Colorectal cancer is one of the most common malignant tumors of digestive tract worldwide. Colorectal cancer has higher incidence rate in western countries. In China, its incidence and mortality rates rank fifth and sixth, respectively, among the most common malignant tumors, in 2002. Recently, with changes of diets and behavior habits, incidence rate of colorectal cancer has been increasing rapidly in China.Colorectal cancer is the result of both effect of environmental factors and genetic susceptibility. Most epidemiological studies have reported that 70 percent of colorectal cancer could be explained by the environmental factors especially diet factors and behavior habits. Metabolizing enzymes are responsible for activation or detoxification of foreign carcinogens or anti-carcinogens, some of which are derived from diet or tobacco smoke. Drug-metabolizing enzymes include phase I enzymes and phase II enzymes, and most of them have inheritance polymorphisms. Different allele combinations explain the different activities of metabolic enzymes with different expression.To explore the frequency distributions of genetic polymorphisms of drug-metabolizing enzyme genes, and their interaction with environmental factors in colorectal carcinogenesis, a population-based case-control study will be conducted in Jiashan County.Materials & Methods64,693 persons from 10 districts in Jiashan Country, Zhejiang Province, who took part in the colorectal cancer screening during 1989 to 1990, consisted of the cohort population of this study. 207 survival individuals (93 cases of colon cancer and 114 cases of rectal cancer), who had beendiagnosed with CRC during 1st May 1990 to 1st May 2005, composed the case group in this analysis;841 controls were random selected form cohort population. All of the controls alive never had neoplasm.A constructed questionnaire elicited information on the demographic condition, diet, and history of selected diseases, et al. The subjects were all given a face-to-face interview by trained interviewers. The sub-investigation of food intake was conducted by using uniform food models and questioning subjects the amount and frequency of each kind of food. With the subject's permission, 5ml blood was collected after interview.Genomic DNA was extracted using improved salting out procedure. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was applied to detect the genotypes of CYP1A1 Mspl, CYP1A2 C734A, CYP2E1 Rsa I , SULT1A1 G638A, UGT1A6 T181Aand Rl 84S. Di-allele-specific-amplification with artificially modified primer was used to detect the genotype of CYP1B1. Multiplex polymerase chain reaction method was used to detect the genotypes ofGSTMlandGSTTl.Basic variables of controls and cases were compared by Pearson's %2 tests. Odds ratio (OR) and its 95% confidence interval (95%C/) were estimated by unconditional logistic regression. The diet intake data in biased distributions were categorized into four groups based on the quartile of controls. The interactions of environmental exposures and genetic polymorphisms were evaluated by likelihood test, while case-only analyses were performed to estimate odds ratios for gene-gene interaction. All analyses were performed using SPSS for Windowsl3.0 and Excel 2003.Results1. Environment exposures and colorectal cancer Aged over 60, higher education, 20 cigarettes/day, consumed red meat more than 19.6 kg a year, intake of salted food, were significantly associated with an elevated risk of colorectal cancer. Both the higher intake of white meat and farming showed statistical significant associations with decreased risk of colon cancer. While aged over 60, consumed red meat more than 7.3 kg a year, intake of salted food were risk factors of rectal cancer, and the higher intake of white meat was significantly associated with a lower risk of rectal cancer.2. Polymorphisms of metabolic genes, interactions with environment exposures and colorectal cancerAmong the health population, the frequency of CYP1A1 Mspl TT, TC and CC genotype was 36.9°/(k 48.3% and 14.8%, respectively. Individuals with genotype of CYP1A1 Mspl CC had a significantly lower risk of colon cancer. There was an interaction existed between CYP1 AlMspl and red meat, and individuals with CYPlAlMspI wild homogeneity that also consumed red meat more than 19.6 kg a year had an significantly elevated risk of colon cancer (OR: 8.04, 95%C7: 2.16-29.92).The frequency of CYP1A2 C743A CC, CA and A A genotype was 14.2%, 43.6% and 42.2%, respectively. There was a significant combined effect of smoking duration more than 30 years and CYP1A2 C743 genotype in colon cancer, while interaction between intake of fried fish and CYP1A2 C743 was risk factor of rectal cancer.The frequency of CYP1B1 C1294G CC, CG and GG genotype was 73.0%, 25.9% and 1.1%, respectively. Individuals with CYP1B1 1294G allele had a significantly higher risk of colon and rectal cancer (OR: 1.65, 95%C7: 1.03-2.65 and OR: 1.55, 95%C7: 1.02-2.36, respectively), and which combined with fried fish significantly increased risk of colon cancer.Among the health population, the frequency of CYP2E1 Rsal CC, CT and TT genotype was 55.5%, 40.3% and 4.2%. Subjects with the genotype of CYP2E1 Rsal TT had significantly increased risk of colon and rectal cancer. When analyzing the combined effect, some significant associations between red meat and CYP2E1 Rsal T allele were also showed in colon and rectal cancer. Individuals with CYP2Elifaal T allele and consumed salted food more than 1 kg a year had a significantly higher risk of colorectal cancer (Pinteractio/0.05).The frequency of null genotype of GSTM1 and GSTT1 was 54.5% and 26.3% in the health population, respectively. There has a significantly interaction between GSTT1-deleted genotype and fried fish in recta) cancer.About 86.1% of the health population has the genotype of SULT1A1 638 GG, while 13.4% and 0.5% have the genotype of GA and AA, respectively. The allele of SULT1A1 638A associated with fish braised in soy sauce was a risk factor of rectal cancer CPinteraction<0.05).Among the health population, the frequency of UGT1A6 A541G (T181A) AA, AG and GG genotype was 57.3%, 37.0% and 5.7%, while the frequency of A552C (R184S) AA, AC and CCgenotype was 60.8%, 34.2% and 4.9%, respectively. There was no obvious evidence of any significantly increased or decrease risk of UGT1A6 genotypes alone and combined of environmental exposures in colon and rectal cancer.3. Gene-gene interaction and colorectal cancer In combinative analysis on phase I and phase II metabolic genes, there was an interaction existed between CYP1A1 Msp\ and UGT1A6, and individuals with CYPlAlMspI C allele and UGT1A6 variant had an significantly lower risk (COR: 2.39, 95%C/: 0.17-0.97). Interaction also existed between CYP1B1 1294G allele and SULT1A1 variant (COR: 3.65, 95%C/: 1.25-10.63).ConclusionsWe can conclude from the results of the population-based case-control study as followed. The risk factors of colon cancer in Jia-shan county include aged over 60, higher education, 20 cigarettes/day, consumed red meat more than 19.6 kg a year, intake of salted food, CYP1B1 1294G, C YP2E1 Rsa I TT genotype, interaction of red meat and C YP1A1 Msp I or C YP2E1 Rsa I polymorphism, interaction of CYP1B1 1294G polymorphism and fried fish, interaction of smoking duration and CYP1A2 C734 polymorphisms. And as well, intake of white meat, engaged in farming and CYP1A1 Msp I homozygous of variant are the protective factors of colon cancer.Individuals aged over 60, consumed red meat more than 7.3 kg a year, intake of salted food, CYP1B1 1294G, CYP2E1 Rsa I TT genotype, association between intake of fried fish and CYP1A2 C734A, interaction of CYP2E1 Rsa I polymorphism and red meat, interaction of fish braised in soy sauce and SULT1A1 G638A, interaction of CYP1B1 1294G and SULT1A1 G638A are risk factors of rectal cancer, while intake of white meat and interaction between CYP1A1 Msp I and UGT1A6 showed statistical significant associations with decreased risk of rectal cancer. There also has a significantly interaction between GSTTl-deleted genotype and fried fish in rectal cancer.