Susceptibility Of Genetic Damage Among Workers Exposed To Vinyl Chloride Monomer

Vinyl chloride monomer(CH₂=CHCl,VCM) is a colorless gas and a synthetic chemical that does not naturally occur.At room temperature,it has a mild sweet odor, it burns easily,and it is not stable at high temperatures.VCM is one of the highest production volume chemicals is wildly used in the world.Approximately 95%of all VCM produced is used to manufacture polyvinyl chloride(PVC).With the fast development of petroleum industry,the total output of VCM in the world increased rapidly.In 1957,China began to produce PVC,and the annual output of PVC in China has jumped to the first place in the world with a total annual production of 9.72 millions ton in 2007.China as a leading producer of PVC in the world,thousands of workers could be exposed to VCM.It is necessary to pay more attention to the health of VCM-exposed workers in our country.VCM exposure has been associated with hepatic angiosarcoma(ASL) and hepatocellular cancer,and was classified as a group 1 carcinogen by IARC in 1987. Recent epidemiological studies have shown VCM is a multi-organ and multi-system carcinogen that induces a wide spectrum of tumors,including ASL and other tumors, brain tumors,and lung cancer.Since VCM is a known carcinogen,it has caused great concern to people who may be exposed to it.To avoid the potential health hazard, many countries have developed some techniques to make a great progress in reducing exposure concentration of VCM.At present,the permissible exposure limit(PEL) of VCM in developed countries is 1 ppm(2.79mg/m³),and the permissible concentration-time weighted average(PC-TWA) in China is 10mg/m³.So it is necessary to analyze occupational health effects in VCM-exposed workers whose exposure level was several times higher than the occupational health standard in developed countries.Under the same working environment and VCM-exposed level, only some VCM-exposed workers had got genetic damage,which indicated that there were genetic susceptible differences among the workers.A susceptible population will exhibit a different or enhanced response to VCM than will most persons exposed to the same level of VCM in the environment.Reasons may include age,gender,health and nutritional status,occupational and personal exposures(e.g.,alcohol drinking and cigarette smoking);moreover inherited metabolic and repaired traits may also explain the elevated risk in selected individuals.As we know,genetic polymorphisms related to VCM metabolism and DNA repair may increase the susceptibility of individuals to genotoxicity.Presently,many studies have been conducted to investigate the genotoxicity of VCM and the effect of genetic polymorphisms in genes coding for metabolic enzymes,but only a few studies paid attention to the DNA repair genes. Studies on relationship between genetic damage in VCM-exposed workers and susceptible genotypes of metabolic and/or DNA repair genes have been useful for revealing mechanism of toxicology and evaluation to health risk.This study evaluated the relationship between VCM exposure and occupational hazards based on calculated cumulative exposure dose of the VCM-exposed workers. In order to explore effect biomarkers under low level VCM exposure,this study investigated the health condition,potential oxidative injury,liver lesion,serum p53 protein and p53-Abs level,as well as genetic damage induced by VCM.Moreover, occupational epidemiological study were performed to study common variants in genes involved in metabolism pathways and DNA repair pathways,to elucidate the relationship between susceptible genotypes of metabolic and/or DNA repair genes and genetic damage in VCM-exposed workers,and to find biomarkers of susceptibility of genetic damage induced by VCM-exposure.This study investigated occupational health hazards among VCM-exposed workers whose exposure level was lower than the national occupational health standard.(1)Used ALT as an indicator of liver function and liver ultrasonography to detect liver morphological changes,we found VCM exposure was not associated with ALT level and liver morphological changes,so they could not be used as an sensitive index of VCM exposure;(2)The levels of superoxide dismutase(SOD), malondialchehyche(MDA) and glutathione S-transferases(GST) in serum were used as the effect biomarkers of VCM exposure.The findings of multiple-linear regression showed that the serum SOD activity of the VCM-exposed groups decreased significantly compared with the control group(P＜0.001),and the amount of MDA increased(P＜0.001).GST activity in the low and high exposure group was significantly higher than that of the control group(P＜0.05).Chi square-test showed that there was a dose-response relationship between serum levels of SOD/GST and the cumulative exposure dose of VCM.Furthermore,advanced age was the risk factor of the lower SOD activity and higher MDA level,and the males'MDA level was significantly elevated compared with females'.The activity of serum SOD,MDA and GST could be used as effect biomarkers when the exposure level is lower than the national occupational health standard of China;(3)Genetic damages of VCM-exposed workers were measured by the single cell gel electrophoresis(SCGE) and cytokinesis-block micronucleus(CBMN).In order to develop a normal reference value of CBMN and comet cells frequencies in cultured peripheral lymphocytes,a threshold of CBMN and comet cell frequency,such as the 95-percentile of the controls CBMN(i.e.3‰) and comet cell(i.e.4%) distribution,maybe used to define chromosomal damage and DNA damage caused by VCM-exposure,above which the CBMN or comet cell frequency may indicate an aberration from being normal,hence indicating chromosomal or DNA damage.Statistics results indicate that mean CBMN frequencies and levels of DNA damage were significantly elevated for the low, intermediate and high VCM-exposure groups compared with that of the controls(P＜0.001).Moreover,multiple Poisson regression analysis showed that a significant increase of micronuclei occurred with age and in females,when occupationally exposed.So the results of CBMN and comet assay of peripheral blood lymphocyte can be used as an early and sensitive biomarker under low level VCM exposure;(4)To determine the relation between VCM exposure and serum p53 biomarkers,this study examined serum samples for the levels of p53 protein and p53 antibodies,using an enzyme-linked immunosorbent assay(ELISA).These biomarkers results suggest that workers with VCM exposure below the current permissible exposure limit have a risk for the occurrence of seropositive for both of the p53 biomarkers is significantly greater than unexposed controls,the presence of both serum p53 biomarkers were greatly elevated in high exposure group compared with that of the normal controls. Serum p53 protein and antibodies may represent suitable biomarkers in assessing the level of occupationally exposure.Then,PCR-RFLP,CRS-RFLP and multiplex PCR was used to detect polymorphisms of metabolizing enzymes and DNA repair genes.In this study,we detected the 15 polymorphisms in 11 genes:GSTT1,GSTM1,GSTP1,CYP2E1,ADH2 and ALDH2,which participate in the metabolism of VCM;OGG1,MGMT,XRCC1,p53 and TDG,which participate in the process of DNA repair.Occupational epidemiological study was performed to investigate the relationship between DNA damage induced by VCM and polymorphisms of metabolizing enzymes and DNA damage repair genes.Logistic regression analysis was employed to model the relationship between DNA damages and genotypes of xenobiotic metabolizing and DNA repair genes and related indicator among VCM-exposed workers.A prominent risk increasing of DNA damage was observed for those individuals possessing the GSTP1 GA/GG,CYP2E1 clc2/c2c2,ADH2 AG/ GG and MGMT 84 CC genotypes when compared with other genotypes,these genotypes may jointly contribute to the susceptibility of DNA damage.There was no association between DNA damage and other genotypes and gender,age,drinking,smoking.PHASE software(version 2.0.2) was used to obtain maximum-likelihood estimates of the XRCC1 and p53 haplotype frequencies.Diplotype analysis showed that risk of DNA damage increased in the subjects carrying the WGG/WCG diplotype compared with those with the WGG/WGG diplotype of p53 intron 3,exon 4,and intron 6 genes(OR=2.33,95%CI: 1.88-2.89,P＜0.001),the risk of DNA damage for individuals with the WCG/WGG diplotype was 0.42-fold(OR=0.42,95%CI:0.35-0.50,P＜0.001) compared with those with the WGG/WGG diplotype.These implied that WGG/WCG diplotype of p53 is potentially one of the risk factors for DNA damage,and WCG/WGG diplotype of p53 may contribute to resist against DNA damage in VCM-exposed workers.Moreover,we studied common variants in genes involved in metabolism pathways(phaseâ… and phaseâ…¡enzymes) and DNA repair pathways,in order to elucidate the relationship between genetic polymorphisms and chromosomal damage in workers exposure to VCM.Poisson analyze showed that five factors that significantly altered CBMN frequencies:GSTP1,CYP2E1,ALDH2,XRCC1 Arg280His genotypes and age.This analysis confirmed the increase in CBMN frequency with age,mean CBMN frequencies were significantly elevated for the older workers compared with yonger workers(P＜0.001).Specifically,subjects with CYP2E1 and XRCC1 Arg280His variance showed higher mean CBMN frequencies compared with their wild-type homozygous counterparts(P＜0.05);those with GSTP1 GG genotype and ALDH2 GG genotype showed higher mean CBMN frequencies than those with other genotypes(P＜0.01).Our findings consider that age and GSTP1,CYP2E1, ALDH2 andXRCC1 Arg280His genotypes are the major factors that modulate CBMN induction in VCM-exposed workers.Diplotype analysis of XRCC1 194,280 and 399 demonstrated that the CBMN frequency in subjects with CGA/CAG diplotype was significantly higher than that in subjects with CGG/CGG(P＜0.001),and CGA/CAG diplotype is potentially one of the risk factors for chromosomal damage in VCM-exposed workers.In conclusion,VCM can induce some occupational health hazards of workers whose exposure level was lower than the national occupational health standard.The activity of serum SOD,MDA,GST and occurrence of seropositive p53 could be used as effect biomarkers for estimation of in vivo dose of VCM exposure.The CBMN and comet assay seems to be a valuable indicator in the regular health surveillance of VCM-exposed workers.We should pay attention to the genotoxic effect from the aspects such as hereditary factors,lifestyles and VCM performance.The health care of VCM-exposed workers should be given full consideration.Further study to investigate the relationship of individual characteristics and genetic susceptibility with VCM-caused DNA and chromosome damage is warranted,it could help us to understand the mechanism of VCM metabolism and find the biomarkers of susceptibility,which is useful for us to recognize the susceptible individuals in the primary prevention of VCM-caused damage.