Exposure To Thallium And Its Interactions With Smoking And Genetic Variants In Apoptotic Pathway On Lung Function Decline Among Coke-oven Workers: An Occupational Cohort Study

The metal thallium(T1)is considered as a highly toxic heavy metal to humans.T1 can be easily found in pyrites and sphalerite ore,but it is usually present at very low levels which are generally below 1 ?g/g in natural environments,thus,seldom public concern was focused on the T1 toxicity on human health.During many manufacturing processes,emissions from coal combustion,cement plants,and smelting of nonferrous metals could result in a high concentration and accumulation of T1 in the atmosphere.Researchers have reported that exposure to high T1 could cause damage to the nervous system,kidneys,heart,and liver,and what's worse,it had caused death.Furthermore,exposure to high T1 could cause damage to some pathological changes in lungs of people.However,no significant association between urinary T1 and lung function levels was found in cross-sectional studies.Lung function,an important severity indicator of chronic obstructive pulmonary disease(COPD),is a critical measurement and early severity predictor for indicating respiratory health.It is essential to explore the association between T1 exposure and longitudinal lung function decline in prospective cohort studies.It was estimated that approximately 70%?90%of lung disease was likely to be attributable to environmental factors.With the completion of the Human Genome Project and the Human Genome Haplotype Project,it is now well believed that most complex and chronic diseases are caused by the interactions of environmental and genetic factors.As we all know,smoking has been considered as the major important environmental factor that impaired lung function and consequently developed COPD.More and more studies reported that metal pollutants were significantly associated with lung function decline,and smoking could enhance the relationships between metals and lung function decline.However,only 13.7%of the smokers developed COPD in China.It was indicated that the genetic polymorphisms could contribute to the susceptibility to many chronic diseases.Therefore,it is essential to explore the interactions of T1 with smoking and genetic variants on lung function decline,in order to reveal the mechanism for the toxic effect of T1 exposure on lung injury.In this study,we carried out a prospective cohort study involving 1243 workers with a follow-up period from 2010 to 2014.The baseline and follow-up lung function levels among these subjects were measured,which included the real values of forced vital capacity(FVC),forced expiratory volume in 1 second(FEVi),and their secondary outcomes:the percentage of predicted FVC(ppFVC)and FEVi(ppFEVi).For each participant,the baseline urinary level of T1 was measured.Furthermore,DNA from peripheral blood were genotyped through whole genomic gene chips.We conducted the following studies:(1)We evaluated the associations between baseline urinary T1 and the 4-year's declines in lung function measurements among the study participants.Baseline plasma C-reactive protein(CRP)levels,a biomarker of inflammatory response,were further tested in a subcohort of 474 subjects randomly selected from 1185 workers who met the criteria from 1243 workers.The correlations between urinary T1 and plasma CRP was also evaluated in the subcohort.(2)We further stratified the participants by their baseline smoking status and smoking intensity,and analyzed the interactive and combine effects of T1 and tobacco smoke on lung function declines.We also compared the plasma CRP levels in different T1 and smoking exposure subgroups.(3)We extracted 540 genetic variants in 80 apoptotic genes,and evaluated their interactions with T1 exposure on FEVi decline.In order to explore the biological function of the positive SNPs with interaction,their effects on the corresponding gene expression levels in normal lung tissues were evaluated through a public database of genotype-tissue expression(GTEx).Furthermore,we analyzed the interactive and combine effects of T1 and SNP genotypes on lung function declines.Part ?.Effect of thallium exposure on lung function decline among coke-oven workers:an occupational prospective cohort studyObjectives:This study aimed to evaluate the effect of T1 exposure on 4-year's lung function decline among the coke-oven workers.Methods:A total of 1682 coke-oven workers were enrolled in October 2010,and 1243 of those subjects were successfully followed up in October 2014.Their demographic information,smoking and drinking status,and disease history were obtained through standardized questionnaires at both baseline(in 2010)and follow-up(in 2014)visits.Urinary and blood samples were collected during their health examinations.The baseline and follow-up lung functions were measured by using Chestgraph HI-101,and the measurements including forced vital capacity(FVC),forced expiratory volume in one second(FEV1),the percentage of predicted FVC(ppFVC),and the percentage of predicted FEV1(ppFEV1),were recorded for each participant.Among all 1628 subjects who had ever admitted in the baseline study,the associations between baseline levels of urinary T1 and baseline values of four lung function measurements were evaluated.In particularly,the associations between baseline urinary T1 levels and 4-year's declines in above four lung function measurements were further analyzed.Both associations were evaluated by using multivariate regression models,with adjustment for sex,age,body mass index(BMI),waist-hip-ratio,smoking status,drinking status,exercise status,and the sum of ten urinary monohydroxy polycyclic aromatic hydrocarbons(?OH-PAHs).We also measured the urinary levels of T1 at both baseline and follow-up visits in a randomly selected 50 healthy subjects,in order to evaluate the stability of urinary T1 levels between these two time points.Furthermore,we determined the baseline plasma levels of C-reactive protein(CRP)among 474 randomly selected workers by using ELISA method,and the correlations of urinary T1 and plasma CRP levels were tested in this population.Results:The levels of FVC,ppFVC,FEVi,and ppFEVi in follow-up study were all significantly lower than their corresponding levels in the baseline visit(all P<0.001).We found no significant cross-sectional associations between baseline T1 and baseline levels of above four lung function measurements.The results from prospective cohort study showed that a 2-fold increase in urinary T1 was associated with 29.81 mL(95%CI:3.83?55.80)increased decline in FEV1.We further classified workers by the quartiles of urinary T1 levels into 4 subgroups(Q1,Q2,Q3,and Q4).Subjects within the high T1 exposure(>0.073 ?g/mmol creatinine;Q4 subgroup)had significant increased decline in FEV1 than those with low T1 exposure(<0.073 ?g/mmol creatinine;combining Q1,Q2,and Q3 subgroups)[?(95%CI)=71.08 mL(13.12?129.04),P=0.016].The intraclass correlation coefficient(ICC)and 95%CI was 0.444(0.192?0.641,P=0.001)for urinary T1 level,which were tested in both baseline and follow-up visits among 50 healthy subjects.Furthermore,the plasma levels of CRP in workers with high T1 exposure(>0.073 ?g/mmol creatinine)were obviously higher than the levels in workers with low T1 exposure(<0.073 ?g/mmol creatinine)(P=0.006).Conclusions:Our prospective cohort study identified that exposure to high T1 had a deleterious effect on lung function measurement FEV1.Subjects with high exposure to T1 had increased level of plasma CRP,suggesting that increased inflammation may partly explain the associations of T1 exposure with lung function decline.These results provide epidemiological evidence for the toxic effect of T1 on respiratory health,but the underlying biological mechanisms need further explorations.Part ?.The interaction effects of thallium exposure and smoking on lung function decline among the coke-oven workersObjectives:This study aimed to investigate the interaction effects of T1 exposure and smoking on lung function decline among the coke-oven workers.Methods:We stratified the 1243 workers into never smokers and smokers(including current smokers and ever smokers).We then analyzed the interactive and combine effects of T1 exposure and smoking status on declines in lung function measurements by using multivariable linear regression models with adjustment for potential confounders.In addition,we stratified smokers into light smokers(<15 pack-years)and heavy smokers(>15 pack-years),and evaluated the interactive and combine effects of T1 exposure and smoking intensity on lung function declines.The comparisons of plasma CRP levels among subgroups stratified by smoking status and high/low T1 exposure were also evaluated.Results:Among the never smokers and smokers,the FVC,ppFVC,FEVi,and ppFEVi levels in the follow up study were significantly decreased than their corresponding levels in the baseline(all P<0.05);moreover,FVC and FEVi declines among heavy smokers(>15 pack-years)were obviously higher than the declines in corresponding lung function measurements among never smokers,respectively(all P<0.05).There was significant interaction between urinary T1 levels and smoking status and smoking intensity on ppFEV1 decline(Pint=0.039 and 0.034,respectively).Among smokers,a 2-fold increase in urinary T1 was associated with 31.91 mL(95%CI:5.31?70.52)elevated decline in FEV1.The association of urinary T1 with FEV1 decline was more pronounced among the heavy smokers[?(95%CI)=56.42(9.66?103.19)].Compared to the never smokers with low urinary T1,the heavy smokers with high T1 had a separate 158.44 mL(95%CI:54.88?262.00,P=0.003)and 4.58%(95%CI:1.40?7.76,P=0.005)elevated declines in FEV1 and ppFEV1,respectively.Furthermore,compared to the never smokers with low urinary T1,the heavy smokers with high urinary T1 had the highest plasma CRP level(2.18 mg/L vs.1.01 mg/L,P=0.008).Conclusions:Our prospective cohort study identified that the effects of T1 exposure on 4-year's decline in FEVi could be enhanced by tobacco smoking,especially by heavy smoking with pack-years>15 during their lifetime.Increased inflammation was seen among heavy smokers with high T1 exposure.The findings give a hint that increased inflammation might be a biological explanation for the combination effect of T1 exposure and smoking on lung function decline.Part ?.The interaction effects of thallium exposure and genetic variants in apoptotic pathway on lung function declineObjectives:In the first part of the prospective cohort study,we found that workers with an elevated exposure of T1 had a significantly increased decline in FEVi.According to the information from CTD database,16 of 56 genes were enriched in the apoptotic pathway.In this part,we aimed to further explore the interaction effect of T1 exposure and genetic variants in apoptotic pathway on FEVi decline among the coke-oven workers.Methods:The DNA samples were extracted from the peripheral blood of the study participants.We then did a genome-wide genotyping by using the Illumina Global Screening Array-24 Multi-Disease BeadChip Array(GSA-MD).A total 80 genes of the apoptotic pathway were selected according to the KEGG database.Then,we extracted the tagging single nucleotide polymorphisms(SNPs)those located from 5 kb upstream to 5 kb downstream of these genes.Samples with genotype call rate<90%,and SNPs with genotype call rate<95%,Hardy-Weinberg equilibrium P<1.0 × 10-6,or minor allele frequency(MAF)?0.05 were excluded.A total of 540 tagging SNPs was selected.The interactive effects between these SNPs and urinary T1 on decline in FEV1 were further evaluated by using the multivariate regression models,with adjustment for sex,age,BMI,waist-hip-ratio,smoking status,drinking status,exercise status,baseline FEV1 levels and urinary ?OH-PAHs.In order to explore the correlations between positive SNPs and the expression levels of corresponding genes in normal lung tissues,we further made the expression quantitative trait loci(eQTL)analysis by using data from the public database of genotype-tissue expression(GTEx).Furthermore,we analyzed the association between T1 exposure and FEV1 decline among workers stratified by SNP genotypes.Results:The results revealed that 12 SNPs in 8 apoptotic genes showed significant interactions with urinary T1 on FEV1 decline 0.01).The rs7373858 A allele,which located in the intron region of IRAK2 gene,was associated with significantly increased expression of IRAK2 gene in normal lung tissues than rs7373858 G allele(Ptrend=0.035).The rs1 13420705 C allele,which located in the 5' untranslated region(UTR)of CASP3 gene,was associated with significantly increased expression of CASP3 gene in normal lung tissues than rs113420705 T allele(Atrend=1.30×10-4).Among the IRAK2-rs7373858 GA+AA genotype carriers and CASP3-rs113420705 CC genotype carriers,a 2-fold increase in urinary T1 was associated with 45.36 mL(95%CI:18.20?72.54,P=0.001)and 74.35 mL(95%CI:24.78?123.91,P=0.003)increased decline in FEV1,respectively.However,the effects of T1 on FEVi decline were not seen among rs7373858 GG genotype carriers,rs1 13420705 TT,or rs1 13420705 TC carriers(all P>0.05).The rs4647601 A allele,which located in the intron region of CASP3 gene,was associated with significantly decreased expression of CASP3 gene in normal lung tissues than rs4647601 C allele(Ptrend=5.50×10-7).The effects of T1 on FEVi decline were not seen among rs4647601 CC carriers,rs4647601 CA carriers,or rs4647601 AA carriers(all P>0.05).Compared to the rs7373858 GG genotype carriers with low urinary T1,the rs7373858 GA+AA genotype carriers with high urinary T1 had a 90.00 mL(95%CI:1.60?182.40,P=0.046)increased 4-year's decline in FEVi.Compared to the rs113420705 TT genotype carriers with low urinary T1,the rs113420705 CC genotype carriers with high urinary T1 had a 117.82 mL(95%CI:-8.00?243.65,P-0.067)increased 4-year's decline in FEV1.Conclusions:There was significant interactive and combine effects of IRAK2-rs7373858,CASP3-rs113420705 and T1 exposure on increasing 4-year's FEVi decline.The elevated expression of IRAK1 and CASP3 caused by rs7373858 A allele and rs113420705 C allele,respectively,may contribute to the above effects.These findings also suggested that IRAK1 and CASP3 may take important part in the biological process of lung function impairment caused by T1 exposure.Further molecular studies were warranted to uncover the underlying biological mechanisms for the toxic effect of T1 exposure on lung injury.