Associations Of Genetic Variations In Metabolism Enzymes Genes And DNA Damage In Coke Oven Workers

Polycyclic aromatic hydrocarbons (PAHs) may cause DNA damage, which is the main cause for lung cancer of coke oven workers. Epidemiological studies have showed that coke oven workers had different DNA damage levels with a similar environmental PAHs exposure levels, suggesting that genetic variations may play an important role in the individual's genetic toxicity. PAHs are regulated by aryl hydrocarbon receptor (AhR). Upon ligand activation, the AhR translocates into nucleus, induce xenobiotics metabolic enzymes synthesis, including cytochrome P4501A1 (CYP1A1), cytochrome P4501B1 (CYP1B1), cytochrome P4502B6 (CYP2B6) and cytochrome P4502E1 (CYP2E1).Although urinary 1-hyrdroxyprene (1-OHP) was used as PAHs exposure markers in numerous studies, there are limitations because urinary 1-OHP is used to assess recent exposure to PAHs only. Plasma BPDE-Alb adducts may be considered as PAHs exposure markers in coke oven workers because of its longer half-life. Therefore, we attempted to discuss the feasibility about using plasma BPDE-Alb adducts as PAHs exposure markers and hypothesized that the single nucleotide polymorphisms (SNPs) which exist in the CYP1A1 gene, CYP1B1 gene, CYP2B6 gene and CYP2E1 gene may affect the DNA damage in coke oven workers. This study aimed to identify the associations between genetic variants of CYP1A1, CYP1B1, CYP2B6 and CYP2E1 genes and plasma BPDE-Alb adducts, and DNA damage levels of coke oven workers, which would identify exposure markers and find the cancer risk potential sensitive factors for occupational exposure risk prevention.PartⅠEpidemiology study of research subjectsA total of 298 male subjects were recruited from a steel plant in Taiyuan, northern China, of whom 202 coke oven workers were defined as exposure groups, the other 96 non coke oven workers from the same plant were used as control groups. We detected the plasma BPDE-Alb adducts levels using reverse phase-high performance liquid chromatography (RP-HPLC), and measured Olive Tail Moment (OTM) by alkaline single cell gel electrophoresis experiment. The results showed that there were no significant difference of age, length of work, smoking and drinking between the exposure and control groups (P>0.05). The in-transformed plasma BPDE-Alb adducts concentration (median, 25-75 percentile) in coke oven workers (3.55(2.37-4.11)) was significantly higher than control groups (3.06(1.47-2.85)) (P<0.01). The in-transformed Olive Tail Moment value in coke oven workers (1.25±1.09) was higher than control groups (0.55±0.93) (P<0.01). These results demonstrated that there were significant differences of plasma BPDE-Alb adduct levels and OTM values between coke oven workers and control groups. PartⅡAssociations of genetic variations in metabolism enzymes genes and plasma BPDE-Alb adducts in coke oven workersThere are many factors including PAHs environmental exposure levels, metabolic enzyme function, smoking and drinking may influence plasma BPDE-Alb adducts levels. In this part, we discussed the feasibility of using plasma BPDE-Alb adducts as PAHs exposure markers in coke oven workers. According to the Han Chinese Beijing data in the HapMap project, we selected 12 tagSNPs in metabolic enzymes gene. We genotyped the selected tagSNPs in 298 study subjects by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) techniques. Our results indicated in exposed groups CYP2B6 gene rs3760657 loci GA+AA genotype carriers had significantly lower plasma BPDE-Alb adducts (3.31(2.01-4.07)) compared with GG genotype carriers (3.59(2.67-4.27)) (P<0.05). The diplotype analysis revealed that the CYP2E1 GC/GT diplotype carriers had the lowest plasma BPDE-Alb adducts levels (3.00(0.96-3.73)) compared with that of the most widely distributed CG/CG diplotype carriers (3.63(2.97-4.25)) (P<0.05) in control groups. The results of this part suggested that the main factor affect plasma BPDE-Alb adducts levels was the genetic variations of CYP2B6 gene. The results of this part warrant validation by larger populations. PartⅢAssociations of genetic variations in metabolism enzymes genes and DNA damage in coke oven workersCarcinogens PAHs are oxidated, reducted, hydrolyzed and changed toxic function first commonly by I phase metabolic enzymes CYPs. DNA damage is induced by the end products BPDE of PAHs through direct DNA and/or protein binding. Therefore, we hypothesized that the genetic variations in CYPs genes play an important role in DNA damage in coke oven workers, and explored the associations of genetic variations in CYPs genes and DNA damage. We divided the sujects into three groups according to plasma BPDE-Alb adducts. The results showed that CYP2B6 gene rs1042389 loci TC genotype carriers DNA damage levels (1.04±1.06) was lower than TT genotype carriers (1.51±1.05) in high exposure groups (P<0.05). However, there were no associations between the other genes (CYP1A1 gene, CYP1B1 gene and CYP2E1 gene) and DNA damage levels in the three groups. The results of this part suggested that genetic variations in CYP2B6 gene may prevent coke oven workers from DNA damage.In summary, we selected 12 tagSNPs in the CYP1A1, CYP1B1, CYP2B6 and CYP2E1 genes and detected their associations with plasma BPDE-Alb adducts levels and DNA damage. There are some advantages in this study, to our knowledge, it was the first study using plasma BPDE-Alb adducts as PAHs exposure markers; Our study provided the first evidence that genetic variations in CYP2B6 gene were associated with plasma BPDE-Alb adducts and DNA damage.There were several limitations in our study that need to be addressed. First, it was insufficient only discussed the association among CYP1A1, CYP1B1, CYP2B6 and CYP2E1 genes and DNA damage, for the complex process of PAHs metabolism. Second, the association between SNPs in the CYP2B6 gene and plasma BPDE-Alb adducts and DNA damage should be validated by larger population studies. Finally, there were no functional investigations of positive SNPs sites in this study.