1. Effects on sister chromatid exchange frequency of polymorphisms in DNA repair gene XRCC1 in smokers; 2. Association of VCM exposure, plasma mutant oncoproteins, and genetic polymorphisms in polyvinyl chloride workers

• Main Authors: Lei Yu-Chen, 雷侑蓁
• Other Authors: Cheng Tsun-Jen
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/06309986527133903607

碩士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 90 === Part I The association between metabolic polymorphisms and cigarette smoking-induced cancers has been documented. However, the role of DNA repair polymorphism in carcinogenesis is less clear. To investigate if the polymorphisms of metabolic traits and DNA repair modulate smoking-related DNA damage, we used sister chromatid exchange (SCE) as a marker of genetic damage to explore the relationship of microsomal epoxide hydrolase (mEH), glutathione S-transferase M1 (GSTM1), and x-ray cross-complementing group 1 (XRCC1) and cigarette smoking-induced SCE. Sixty-one workers without significant exposure to mutagens were recruited. Questionnaires were completed to obtain detailed occupational, smoking, and medical histories. SCE frequency in peripheral lymphocytes was determined using a standard cytogenetic assay and GSTM1, mEH (exon 3, eoxn 4), XRCC1 (codon 399) genotypes were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR/RFLP). Smokers had higher SCE frequency than nonsmokers (8.4 vs. 7.1, p < 0.05). Among workers who had smoked equal to or greater than 10 cigarettes each day, those with XRCC1 Arg/Gln + Gln/Gln had higher SCE frequency than those with XRCC1 Arg/Arg after adjusting for potential confounders (9.0 vs. 7.9, p < 0.05). The interaction of XRCC1 and cigarettes smoked per day on SCE frequency was also observed (p = 0.02). There was no significant interaction between cigarettes smoked per day with GSTM1 and mEH on SCE frequency. Our results support previous epidemiological studies that XRCC1 may play a role in cigarette smoking-induced lung cancer. Part II The presence of mutant Asp13-K-ras protein, p53 overexpression and anti-p53 antibody have been reported to be associated with vinyl chloride monomer (VCM)-related cancers. The aim of this study was to compare the relationship between VCM-induced p53 and K-ras oncoproteins, and to further investigate the role of polymorphisms of metabolic and DNA repair genes on VCM-induced oncoprotein expression. We examined the plasma samples of 218 male workers occupationally exposed to VCM. Plasma mutant p53 protein and anti-p53 antibody were detected with enzyme-linked immunosorbent assay (ELISA), and Asp13-K-ras proteins were detected using enhanced chemiluminescence Western blotting. Genotypes of cytochrome P450 2E1 (CYP2E1), aldehyde dehydrogenase 2 (ALDH2), glutathione S-transferase T1 (GSTT1) and X-ray repair cross-complementing group 1 (XRCC1, exon 10) were identified using the polymerase chain reaction (PCR). The results revealed that the plasma mutant p53 protein was positive in 10.1% of workers, anti-p53 antibody was positive in 5% of workers and Asp13-K-ras protein was positive in 10.1% of workers. High VCM exposure group (>40 ppm-years) had significantly higher mutant oncoprotein (mutant p53 protein, anti-p53 antibody or Asp13-K-ras protein) expression as compared to low VCM exposure group (<40 ppm-years) (OR=2.0, 95%CI=1.0-3.8). Among high exposure workers, subjects with XRCC1 Gln/Gln genotypes demonstrated significantly higher risk of mutant oncoproteins expression as compared to those with XRCC1 Arg/Arg or Arg/Gln variants (OR=8.5, 95%CI=1.9-38.9) after adjusting for potential confounders. Moreover, there was an interaction between VCM exposure and XRCC1 polymorphisms on oncoprotein expression (p=0.06). In our further analysis, amongst low exposure workers, subjects with CYP2E1 c2c2 genotypes demonstrated greater risk than subjects with CYP2E1 c1c1 or c1c2 genotypes (OR=3.1, 95%CI=0.3-37.8). However, there was no interaction between VCM exposure and genotypes of CYP2E1, GSTM1, and ALDH2 on oncoproteins. We found that p53 overexprssion was significantly associated with VCM cumulative dose (OR=2.5, 95%CI=1.0-6.2). After adjusted for smoking, age, drinking, and hepatitis infection, amongst high exposure workers, subjects with XRCC1 Gln/Gln demonstrated significantly greater risk of p53 overexpression than subjects with Arg/Arg or Arg/Gln (OR=17.0, 95%CI=4.3-198.5). Amongst low exposure workers, subjects with CYP2E1 c2c2 genotypes have significantly higher risk than CYP2E1 c1c1 and c1c2 genotypes (OR=19.9, 95%CI=1.6-253.2). Mutant Asp13-K-ras oncoprotein was not associated with VCM cumulative exposure dose; however, it was significantly associated with current high exposure experience within 5 years of sample collection (OR=2.9, 95%CI=1.1-7.9). After further analysis, we found that subjects experiencing high exposure job within 5 years with XRCC1 Gln/Gln had greater risk of K-ras oncoprotein than those with XRCC1 Arg/Arg or Arg/Gln (OR=1.7, 95%CI=0.1-23.3) although didn’t reach statistical significance. Similarly, subjects with ALDH2 1-2 or 2-2 genotypes demonstrated greater risk than those with ALDH2 1-1 genotypes (OR=2.5, 95%CI=0.6-11.2). Further, subjects experiencing high exposure job within 5 years with GSTT1 non-null genotype revealed significantly higher risk than those GSTT1 null type. Our results suggest that mutant p53 protein and mutant K-ras oncoprotein revealed differential expression in VCM-exposed workers. Mutant K-ras oncoprotein was associated with current exposure, and it became undetected when exposure ends. However, mutant p53 protein was associated with cumulative dose. One possible explanation is mutant p53 gene provide selective growth advantage which making mutant p53 protein sustained in the cell persistently. In contratst, K-ras mutants may be demolished by p53 through the apoptosis. Furthermore, the relationship between p53 overexpression and DNA repair gene and metabolic genes was consistent with our previous study, but the association of mutant K-ras oncoprotein and DNA repair gene and metabolic traits are not clear in this study because of small sample size. Therefore, further studies are needed to elucidate the exact mechanism.