Exposure Assessment And Susceptibility Of Chromosomal Damage In1,3-Butadiene Exposed Workers

1,3-butadiene (BD) is a known human carcinogen widely used in chemical production, and is also considered as a ubiquitous environmental pollutant found in automobile exhausts, tobacco smoke et al. China is one of the important BD production and assumption countries in the world, and its annual production has reached2.5million ton in2011. So the health of BD exposed workers should be paid more attention.As one known human carcinogen, BD has been proved to be one of the multi-organ and multi-system carcinogen. The mechanism of carcinogenesis was presumed to be related to the genetic damage induced by electrophilic metabolites of BD. At present, the permissible exposure limit (PEL) of BD in developed countries is1ppm (2.22mg/m3), while the PC-TWA in China is5mg/m3. The study analyzed occupational health effects especially genotoxicity effect in BD exposed workers whose exposure levels were lower than the national occupational health standard. In the same environment, the majority of BD exposed workers did not develop neoplasm, suggesting the susceptibility was modulated, at least in part, by polymorphisms in genes encoding metabolic enzymes, and DNA repair proteins. Some studies have been done to investigate the effect of genetic polymorphisms of enzymes involved in BD metabolism, otherwise there was rare report about the series of enzymes polymorphisms in the BD metabolic pathway. The individual susceptibility on chromosomal damage was one important factor for the difference of xenobiotics detoxified in bodies. We might find the susceptible individual to detect metabolic enzyme polymorphisms in BD exposed workers and protected the workers’health.In the study, we established the method to detect the concentrations of DHBMA and MHBMA with UPLC-MS/MS and try to find more sensible expose biomarkers through discussing the relation between the air BD concentration and in-end-of-shift urine DHBMA and MHBMA level. Exploring the influence of BD exposure on health effect and chromosomal damage, we try to find the major effect biomarker in BD exposed workers. Occupational epidemiological study was performed to investigate the relation between chromosome damage induced by BD and polymorphisms of metabolic genes, in order to provide scientific evidence to screen the susceptible workers.The subjects in the study from a Synthetic Rubber Factory were including200individuals with the mean age40.94years as exposure group:male154and female46.179individuals as control groups with the mean age42.75years (male66and female23) of this factory as well as health groups (90individuals with the mean age39.92years:male56and female34).UPLC-MS/MS method was to determine DHBMA and MHBMA concentrations with isotope as inner standards. GC-FID method was to detect air BD levels in the workplace. Employing multiple line regression, the influence factors of urine DHBMA were analyzed to acquire the meaningful equation about DHBMA concentration (y) and air BD levels (x):y=2.417+0.520*x, and adjusted R2of the model is0.262, correlation coefficient was0.503. So in-end-of urine DHBMA might be inner biomarker in BD exposed workers.The abnormal parameters found in the clinic health examination of workers (200BD exposed individuals,89control individuals) were analyzed, we found hemoglobin levels were higher in exposed group than in control group, and the difference was evident (P<0.001). Currently, we didn’t explain the phenomenon. We found BD exposure was not associated with liver lesion, kidney lesion, heart damage etc. We did not also find that BD exposure affected the WBC, RBC and PLT counting.Concentrations of p53protein and p53antibody which were well known biomarkers of p53gene mutant in plasma, were also detected in parts of workers (90indivuals:male63and female27) and controls (90indivuals:male56and female34) using an enzyme-linked immunosorbent assay (ELISA) to determine the relation between BD exposure and plasma p53biomarkers. These results suggested that workers with BD exposure below the current permissible exposure limit (PEL) had a risk for the occurrence of seropositive for both of the p53biomarkers which was significantly greater than unexposed controls, the presence of plasma p53antibody was greatly elevated in exposure group compared with that in the normal controls. Plasma p53antibody might represent suitable biomarker in assessing the lesion of BD occupational exposure. But no difference was observed for p53protein between exposure and control individuals (P>0.05). This substance in plasma was not available to be a sensitive biomarker for BD exposed in this study.Cytokinesis block micronucleus assay (CBMN), sister chromatid exchange assay (SCE) and chromosomal aberration assay (CA) were conducted to detect chromosome damage and DNA damage of the peripheral blood lymphocytes in BD exposed workers. The results exhibited that the frequency of CA or SCE between the exposure and control group was not observed significant difference (SCE:FR1.14,95%CI:0.81-1.61; CA:FR1.25,95%CI:0.88-1.78). The frequency of CBMN in BD exposed group was significantly higher than which in the controls (FR1.48,95%CI:1.14-1.91, P<0.01). BD exposed workers were categorized into high and low exposure groups with the median24.80mg/m of individual cumulative exposure levels. Employing multifactorial poisson regression analysis, MN frequency was ascending in the higher level of BD exposed workers compared to which in the controls (FR1.59,95%CI:1.18-2.15, P<0.05), otherwise, there was no significant difference for MN frequency between the lower level of BD exposed workers and controls (FR1.31,95%CI:0.95-1.80, P>0.05). So, MN frequency of peripheral blood lymphocytes could be used as an effect biomarker to assess the BD exposure.Then, PCR-RFLP and multiple PCR were used to detect polymorphisms of metabolic enzymes. In this study, we examined the6sites polymorphisms in5genes: CYP2E1, GSTT1, GSTM1, GSTP1, mEH113and mEH139, which participate in the metabolism of BD in body. Occupational epidemiological study was performed to investigate the relation between DNA damage induced by BD and gene polymorphisms of metabolic enzymes. Using poisson regression analysis, when the confounding factors such as age, gender, BD exposure levels, drinking and smoking habits were adjusted, compared with workers carrying GSTT1(+), GSTM1(+) or mEH low (L) genotypes, that individuals carrying GSTT1(-), GSTM1(-) or mEH high (H) polymorphisms had a significantly higher MN frequency (GSTT1:FR1.33,95%CI:1.01-1.75; GSTM1:FR1.37,95%CI:1.03-1.83; mEH:FR1.85,95%CI:1.08-3.17), respectively. CYP2E1and GSTP1polymorphisms did not affect MN frequency. So GSTT1(-), GSTM1(-), mEH (L) might be sensible genotype in the heritage damage induced by BD, and individuals with those genotypes might be susceptible.Adjusted confounding factors, analyzing gene-gene, gene-environment combination effects on MN frequency, GSTT1-GSTM1interaction was found to affect heritage damage. The analysis on combination between BD exposure levels and GSTT1or GSTM1displayed BD exposure levels interacted with GSTT1or GSTM1on chromosomal damage.In conclusion, BD could induce genetic damage of workers whose exposure levels were lower than the national occupational health threshold limit value (PC-TWA5mg/m3). The occurrence of seropositive p53could be used as a valuable indicator in the regular health surveillance and examination of BD exposed workers. The CBMN frequency could be supposed to be an effect biomarker for BD exposure to detect early gene damage. We should pay attention to the genotoxic effect from the aspects such as hereditary factors, nutrition condition, lifestyles and BD exposure etc. The polymorphisms of metabolic enzyme genes were associated with chromosomal damage induced by BD exposure, which could help us to understand the carcinogenesis mechanisms of BD and to find susceptible individuals, which was useful for us to recognize the susceptible individuals in the course of the primary prevention of BD-caused damage.