A Study Of Genetic Polymorphisms And Chromosomal Damage Among1,3-butadiene Occupational Exposure Workers

BACKGROUND: As a major industrial chemical,1,3-butadiene(BD) is widely used inthe production of rubber and thermoplastic resins. It is also a common air pollutant found inhuman daily life such as auto emissions and cigarette smoke. In2008, the InternationalAgency for Research on Cancer (IARC) has raised the carcinogen classification of BD fromGroup2A (probably carcinogenic to humans) to Group1(known human carcinogen, by theIARC Working Group,2008) based on the carcinogenic evidence of rodent animals andhumans, especially a series of epidemiologic studies in North American BD workers whichfound BD exposure was associated positively with leukemia, lymphatic and hematopoieticcancer. BD is a high efficiency carcinogen in rodents and has been classified as a humancarcinogen, but its ability to induce genetic damage and the influence of metabolicpolymorphisms to such damage in humans are both controversial.In our previous study, we adopted HPRT by cloning assays to determine DNA damagein BD-exposed workers (Liu et al.2008). Our results showed that the BD-exposed workershad a higher mutation frequency (18.2±9.4×106) than the control subjects (12.7±7.3×106),but the difference was not significant.OBJECTIVE: The aim of the study was to investigate the impact of BD onchromosomal stability in workers as well as to evaluate polymorphism effects of metabolicgenes to this compound. We carried out a new study in the same petrochemical plant to seewhether the biomarkers in CBMN cytome assays (MNi, NPBs, NBUDs and NDI) could besensitive enough to evaluate the impact of occupational exposure to BD on geneticinstability in workers. Meanwhile, the polymorphisms of CYPs, mEH and GSTs as well asDNA repair related genes (XRCC1,MGMT,ADPRT,APE1and MTHFR) were studied todetermine whether they could influence the chromosomal damage among BD-exposed workers in the present study.METHODS: This study was conducted to investigate the relationships betweenexposure to BD, the polymorphisms of metabolic genes and the chromosomal damage in45pairs of occupationally exposed workers in a BD product workshop and mathched controlworkers in an administrative office and circulatory water workshop in China. Exposure toBD was evaluated by personal sampling and stationary sampling. Different DNA injury andchromosomal damage endpoints in peripheral blood lymphocytes were determined usingthe cytokinesis-blocked micronucleus (CBMN) cytome assay, EBC-MNT (exfoliated buccalcell micronucleus test) and SCGE (single cell gel electrophoresis, aka Comet assay);polymorphisms of metabolic genes (CYP2E1, GSTs and mEH) and DNA repair relatedgenes (XRCC1, MGMT, ADPRT, APE1and MTHFR) in BD-exposed group were detectedby PCR or PCR-RFLP analysis.RESULTS:1. The results showed that the average BD measurements of the exposedgroup were significantly higher than those for the control group (a personal sampling andstationary sampling, respectively). For personal sampling, the average BD measurement forthe exposed group (0.34±0.61p.p.m. or0.75±1.35mg/m3) was significantly higher (P<0.01)than that of the control group (0.04±0.01p.p.m. or0.09±0.02mg/m3). The personalsampling was not performed in our previous study. For stationary sampling, After excludingan outlier measurement (147.66p.p.m. or326.33mg/m3), the BD production plant had amean concentration of2.27±3.33p.p.m. or5.02±7.36mg/m3.2.Physic examinations were accompanied with sample collection, and the results ofblood routine tests showed that, although all of parameters in both of groups were withinreference ranges, the red cell counts (4.97±0.35×1012/L versus4.70±0.46×1012/L)(P<0.01)and hemoglobin content (154.07±11.21g/L versus147.56±18.70g/L)(P<0.05) ofBD-exposed workers were significantly higher than those of controls, respectively.3.Using LS-MS/MS methods, we identified urinary metabolites (M1and M2)concentrations of23pairs of subjects, and found that the M1median concentrations ofBD-exposed workers (122.54p.p.b.) was statistically higher than that of the controls(median,10.70p.p.b.)(P<0.01); no differences of M1concentrations or ration of M1/(M1+M2) existed between these two groups.4. The BD-exposed workers exhibited increased frequencies of micronuclei (MNi) (8.00±3.78‰versus5.62±2.41‰) and necleoplasmic bridges (NPBs)(2.58±2.79‰versus1.13±1.34‰), and a decreased nuclear division index (NDI)(2.20±0.14versus2.35±0.27)when compared subjects in the control group.5. No sensitive endpoints in Comet assay and EBC-MNT were found for genotoxicityinduced by BD exposure.6. Meanwhile, BD-exposed workers carrying cytochrome P450s (CYP2E1) c1c2/c2c2or microsomal epoxide hydrolase (mEH) intermediate (I)/high (H) group had asignificantly higher NPB frequency than those carrying CYP2E1pst1/rsa1c1c1(FR=2.60,95%CI1.72-3.93; P<0.0001) or the mEH low(S) group (FR=2.06, CI%1.17-3.62; P<0.05)respectively.7. For DNA repair related genes polymorphsims analysis, we did not find any singleSNP locus of XRCC1, MGMT, ADPRT or APE1genes could impact chromosomalinstability induced by BD exposure.8. When XRCC1diplotypes were taken as a categorical variables, after adjusted byage, gender, occupational length, smoking and drinking status in multivariate Poissonregression model, we found that the workers carring diplotypes TCGA-CCGG (FR=2.10,95%CI:1.03-4.28) and TCGG-TCGA(FR=2.75,95%CI:0.76-2.65) had a statisticallyhigher NBUDs frequencies than those who carried diplotype TCGG-TCGG in theBD-exposed workers.9. BD exposed workers carrying MTHFR677CC(2.00±2.00‰)(FR=0.36,95%CI:0.20-0.67, P <0.01) or MTHFR677CT (2.87±1.98‰)(FR=0.49,95%CI:0.32-0.77, P <0.01) genotypes had a significantly lower NBUD frequencies than those carrying genotypeMTHFR677TT(5.33±2.60‰), respectively.CONCLUSIONS: In conclusion, our group is the first to score NPBs and NBUDs inBD-exposed workers, and we found that the CBMN cytomeassay (especially NPBs) couldbe sensitive group biomarkers to use to monitor the genotoxicity of BD occupationalexposure. Polymorphism of metabolic genes and DNA repair related genes should beconsidered when evaluating human susceptibility to such exposure. Diplotypes could benext potential biomarkers for further polymorphism analysis concerning occupationalexposre induced genotoxicity. Since BD is classified as a human carcinogen, these resultsrepresent an important contribution to the biomonitoring of the potential health risks in BD-exposed workers. Nevertheless, the present findings in Chinese workers should beconfirmed by prospective studies under different exposure conditions and with occupationalpopulations.