Modification Of Genetic Polymorphisms On Chromosomal Damage In Vinyl Chloride Monomer Exposed Workers

Vinyl chloride monomer(CH₂=CHCl,VCM) is widely used in industry,almost 95%in polymerization to polyvinyl chloride(PVC).China is one of the important PVC production countries,and its annual production accounts for about 10%of the global production,necessitating research regarding the health of VCM-exposed workers.VCM is a human carcinogen that has been proven to have multi-organ and multi-system effects.The mechanism of carcinogenesis was presumed to be related to the genetic damage induced by electrophilic metabolites of VCM.At present,the permissible exposure limit(PEL) of VCM in developed countries is 1 ppm (2.79mg/m³),and the STEL and TWA in China are 25mg/m³ and 10mg/m³, respectively.The permissible exposure limit is higher in China than that those in developed countries,indictating that more research is needed to investigate the health effect and genetic toxicity caused by VCM-exposure under this condition.Since genetic damage induced by toxic substances was related with individual susceptibility, especially with polymorphisms in genes encoding metabolic enzymes and DNA repair proteins.Studies on relationship between genetic damage in VCM workers and polymorphisms in metabolizing enzymes and/or repair genes have been useful for revealing mechanism of toxicology and evaluation to health risk.Routine health examination and cytokinesis-block micronucleus(CB-MN) assay were performed to investigate the health conditions of VCM-exposed workers.The CB-MN results showed that adverse effects in the exposed group were significantly higher than that of the control group,and that there is a dose-response relationship between VCM-exposure and the frequency of MN.Also,great age and female were risk factors for the frequency of MN.Therefore,the frequency of MN of peripheral blood lymphocyte can be used as an effect biomarker under low-level VCM exposure. According to the data of routine health examination,adverse effects in liver function and liver ultrasonography in the exposed group were not significantly higher than that of the control group.The relationship between cumulative exposed dose of VCM and chromosomal damage in VCM workers was analysed by BMDS soft,the result showing that BMDL of cumulative exposed dose of male and female were 3.35 and 2.43g,respectively.It means MN damage will occurr when cumulative exposed dose achieved to BMDL. This result can give reference to adjust the occupational standard of VCM in our country.Next,PCR-RFLP was used to detect polymorphisms of metabolizing enzymes and DNA repair genes.Using Poisson regression analysis,we investigated the relationship between polymorphisms in DNA repair genes and/or metabolizing enzyme genes and the frequency of MN.The PHASE 2.0.2 software was used to obtain maximum-likelihood estimates of the diplotype frequencies.In this study,we detected the 18 polymorphisms in 11 genes:ADH2,ALDH2,GSTT1,GSTM1,GSTP1, CYP2E1,and CYP2D6,which participate in the metabolism of VCM,and OGG1, MGMT,XRCC1,and P53,which participate in the process of DNA repair.A proper assay was developed for identifying SNP in 84 site of the MGMT gene, applying Creating Restriction Site and PCR-RFLP principle,and this assay is more economical than the old assasy.Also,a new assay was developed to detect the SNPs in sites 143,160,178 of MGMT gene using the same principle,and this assay can detect three SNPs by one PCR and three RFLP.The merit of this method include economy,speed and sample conservation.We additionally designed a new method to detect SNPs in site 194 and 399 of XRCC1 gene based on the principle of multiplex PCR and PCR-RFLP;this method is also effective.Poisson analyze showed that age,ADH2,OGG1 and MGMT84 were important factors in control group,while age,gender,ADH2,GSTT1,GSTP1,CYP2E1 and MGMT84 was impact factors in exposure group.There was no association between frequency of MN and other gene polymorphism,smoking,and alcohol consumption, nor interactions between these factors.This study showed that allele G of AHD2 gene was a protect factor,and the risk was 0.61(0.39-0.94) when one allele G increased in the site,in normal group.On the contrary,it was showed a risk factor in exposed group(FR=1.10[0.99-1.23]).Thereis a need for more study,as the mechanism was unknown.The polymorphism of ALDH2 had no relationship with changes in MN.The frequency of MN increased along with the increased prevalence of mutant allele C in CYP2E1 gene,in the exposed group(FR=1.75[1.28-2.33]).Also the result showed that GSTT1 null type had a protect effect,while allele G in GSTP1 had an opposite effect. The risk of OGG1(GC+GG) was 3.07(1.44-7.96) in control group compared with genotype CC and no same result in exposed group,a result need more studies. However,the risk of MGMT84CT was 0.53(0.25-0.98) in control group compared with CC genotype,while the value is 0.85(0.71-1.02) in exposure group.This result showed allele T in MGMT84 had a protect effect.The study showed that there is no relationship between MN frequency and diplotype of 194,280,399 sites of XRCC1 gene whether in the control and exposed group.Diplotype analysis of P53 intron3, exon4 and intron 6 demonstrated that the MN frequency in subjects with AAA/ABA(A:wild allele;B:variant allele) was significantly lower than that in subjects with AAA/AAA in control group(P=0.086).Results showed that frequency of MN increased accompany with age,especially at age≥40,with or without contact with chemical substances.Female gender was a susceptibility factor in the VCM group,while the fact that no similar result occurred in control group may due to limited samples.In conclusion,VCM can induce chromosomal damage even when the exposure level is lower than the national occupational health standard in China;some of the polymorphisms of DNA repair genes and metabolizing enzyme genes may be associated with chromosomal damage in VCM-exposed workers.