Association Of Polymorphisms In Genes AhR, CYP1A1, GSTM1 And GSTT1 With Levels Of DNA Damage In Peripheral Blood Lymphocytes Among Coke-oven Workers

Polycyclic aromatic hydrocarbons (PAHs) are a well-established group of chemical carcinogens. PAHs were formed and released during the coke process, resulting in direct exposure of coke-oven workers to PAHs by inhalation and dermal contact in the working hours. Epidemiological studies indicated that the risk of some cancers was higher in the workers with exposure to the coke process than those without. Lung cancer of coke-oven workers has been classified as one of the eight prescribed occupational cancers in China.The toxicity of PAHs, such as benzo(a)pyrene [B(a)P] and tetrachlorodibenzo-p-dioxin, is mediated by Ary1 hydrocarbon receptor (AhR), which is a ligand-activated transcriptional factor that plays an important role in the B(a)P-induced carcinogenesis. After binding with B(a)P, AhR translocates into the nuclear to interact with xenobiotic responsive elements, resulting in the upregulation of phase I and II enzymes, such as cytochrome P450 and glutathione S-transferase (GST) that are also involved in the metabolism of PAHs. It is thought that it is the DNA damage, caused by reactive oxygen species formed during the metabolism of PAHs, that plays a role in PAH-induced carcinogenesis. So AhR is indispensable in the carcinogenesis induced by B(a)P. Now it was reported that the level of AhR protein changed after the exposure of B(a)P, however, no studies have reported whether the level of the AhR mRNA changes after the exposure of B(a)P. Furthermore, the DNA damage caused by PAHs in the coke-oven workers could be detected in their peripheral primary lymphocytes by the alkaline comet assay and PAH-induced carcinogenesis may be modulated by genetic variation. Single nucleotide polymorphisms (SNPs) are widely used in the multi-gene diseases and environment-associated diseases. NCBI have listed 4,175,659 SNPs in the human genome of which 2,676,751 SNPs have been curated. The AhR gene encompasses about 47,000 nt at the genomic level, and is expected to contain about 50–80 SNPs. Thus far 20 have been identified and curated by NCBI. 16 are located within introns, three are located within the 3'-untranslated region and one is located within the open reading frame. One of the polymorphisms in human AhR, G1661A (Arg554Lys; rs2066853), was first discovered by Kawajiri et al., which is the most commonly studied polymorphism in the AhR gene since. However, no reported studies have investigated the effect of AhR polymorphisms on the levels of DNA damage among coke-oven workers.Cytochrome P450 1A1 (CYP1A1), a member of the phase I enzymes, is involved in the metabolic activation of PAHs, and an MspI restriction fragment length polymorphism in this gene was reportedly to be associated with risk of lung cancer. In the coke-oven workers, the effect of this polymorphism on PAH-induced DNA damage was unclear, because this polymorphism was also reportedly to be associated with the significant increase of urinary 1-hydroxypyrene concentrations but not with increased tail extent moment in lymphocytes in the coke-oven workers.GSTs are the members of the phase II enzymes, a multigene family. GST family includes five subgroups (i.e., alpha, pi, mu, theta, and zeta) and GSTM1 or GSTT1 alleles are lost in a subset of the general population. Previous studies indicated that the individuals null for GSTM1 or GSTT1 genes seemed to be susceptible to some cancers, especially lung and bladder cancers. However, the results to date are inconsistent for the effects of GST polymorphisms on exposure biomarkers in coke-oven workers. For instance, the GSTM1 null genotype was found to be associated with increased levels of benzo(a)pyrene diol epoxide (BPDE)-DNA adducts among the coke-oven worker, but this association was not confirmed by the other studies.Part I Association of polymorphisms in genes AhR, CYP1A1, GSTM1 and GSTT1 with levels of DNA damage in peripheral blood lymphocytes among coke-oven workersIn this part, a cross-sectional molecular epidemiological design was used to investigate the relationship between polymorphisms in genes AhR, CYP1A1, GSTM1 and GSTT1 and levels of DNA damage in peripheral blood lymphocytes among coke-oven workers. In this study of 240 coke-oven workers (the exposed group) and 123 non-coke-oven workers (the control group), we genotyped for the polymorphisms in the genes by the polymerase chain reaction (PCR) method and determined the levels of DNA damage in peripheral blood lymphocytes by the alkaline comet assay. We found that the ln-transformed Olive tail moment (Olive TM) values in the exposed group were significantly higher than those in the control group (P<0.01). Furthermore, in the exposed group, the Olive TM values in subjects with the AhR Lys554 variant genotype were higher than those with the AhR Arg554/Arg554 genotype (P=0.021). Similarly, the Olive TM values in the non-coke-oven workers with the CYP1A1 MspI CC+CT genotype were lower than that in those with the CYP1A1 MspI TT genotype (P=0.005). However, these differences were not evident for other genes. These results suggested that the polymorphism of AhR might modulate the effects of PAHs; however, the underlying molecular mechanisms by which this polymorphism may have affected the levels of PAH-induced DNA damage warrant further investigations.Part II Effects of BaP on the expression of the ary1 hydrocarbon receptorIn this part, we investigated the effects of BaP on ary1 hydrocarbon receptor expression. The real-time PCR was used to detect the expressions of the mRNA of the ary1 hydrocarbon receptor using cultured human adenocarcinoma A549 under different concentrations (0, 1, 5, 10, 50 and 100μMol/L) BaP respectively. The results showed that levels of the mRNA of ary1 hydrocarbon receptor decreased significantly in the range of 1-100μMol/L BaP compared with the control group. Ary1 hydrocarbon receptor may play a role in the BaP-induced carcinogenesis, though the precise mechanism is still unknown.