| Polycyclic aromatic hydrocarbons(PAHs)are a group of pollutants that widely exist in living and production environments and can cause a variety of health damage and diseases.Coke oven workers are exposed to coke oven emissions containing high concentrations of PAHs.Growing evidence has shown that occupational PAHs exposure is associated with increased risks of occupational diseases such as lung cancer,melanosis,and other occupational related diseases such as chronic obstructive pulmonary disease and infertility.PAHs can generate a large number of reactive oxygen species(ROS)after metabolic activation.Mitochondria,important organelles for energy generation within cells,are the main target of ROS.Due to lack of protective histone and limited repair capacity,mitochondrial DNA is vulnerable to ROS-induced damage.It has been shown that cells attacked with ROS can synthesize more copies of mitochondrial DNA and increase the abundance of mitochondria to compensate for damage and meet the increased breathing needs required for ROS clearance.However,excessive oxidative stress may also result in reduced mitochondrial DNA copy number,mitochondrial dysfunction,and even cell necrosis and apoptosis.Therefore,it is likely PAHs can change the body’s oxidative stress state,ultimately contributing to DNA damage.And different levels of oxidative stress may affect the relationships between PAHs exposure and mitochondrial DNA copy number.In this study,we included 1385 coking plant workers,and measured 12 urinary PAHs metabolites and plasma anti-7,8,-dihydrodiol-9,10-epoxide benzo [a] pyrene-albumin(BPDE-Alb)adducts,as internal biomarkers for evaluating PAHs exposure levels of professional workers.Urinary concentrations of 8-hydroxy-2’-deoxyguanosine(8-OHd G)and 8-iso-prostaglandin-F2α(8-iso-PGF2α)and peripheral mitochondrial DNA copy number were also determined.We aimed to investigate the associations of PAHs internal biomarkers and oxidative stress levels with mitochondrial DNA copy number,and further explore the associations between PAHs exposure level and mitochondrial DNA copy number under different levels of oxidative stress and the interactive and combined effects of PAHs exposure and oxidative stress levels.The main contents are as follows:Part Ⅰ.Associations between polycyclic aromatic hydrocarbons exposure and peripheral blood mitochondrial DNA copy number among coke-oven workersObjective: To investigate the associations between PAHs exposure and mitochondrial DNA copy number,and further evaluate the modification effects of different characteristics and major lifestyles on the above relationships.Methods: In the wuhan coking population cohort established in 2010(n=1628),the coke oven workers with missing basic information(n=41)and insufficient blood samples(n=209)were excluded,finally we enrolled 1385 subjects with complete questionnaire information at baseline and urinary PAHs metabolites and plasma BPDE-Alb adducts concentrations and blood samples.The peripheral mitochondrial DNA copy number was measured by real-time quantitative polymerase chain reaction(RT-PCR).Meanwhile,urinary PAHs exposure levels and mitochondrial DNA copy number were normalized by natural logarithm(ln)transformation.Generalized linear models were conducted to examine the associations between PAHs exposure and peripheral mitochondrial DNA copy number,with adjustment for the covariates including age(years),gender,body mass index(BMI),current smoking(yes,no),current drinking(yes,no),exercise(yes,no)and workplace(the offices,adjunct areas,the bottom and side of coke oven and the top of coke oven).Results: The urinary levels of 1-hydroxyphenanthrene(1-OHPh)and 1-hydroxypyrene(1-OHP)showed inverse associations with mitochondrial DNA copy number(all P<0.050).We found that 1% increase in urinary concentration of 1-OHPh and 1-OHP were associated with 0.043% and 0.096% decrease in mitochondrial DNA copy number,respectively.We also found that the sum of hydroxyphenanthrene(ΣOH-Ph)and the sum of monohydroxy polycyclic aromatic hydrocarbons(ΣOH-PAHs)in urine showed the marginal associations with mitochondrial DNA copy number.Additionally,compared with subjects in the lowest quartile of 1-OHPh,1-OHP,ΣOH-Ph and ΣOH-PAHs,those in the highest quartile had significantly or marginal decreased mitochondrial DNA copy number,and the β and 95% confidence interval(95% CI)were-0.167(-0.292,-0.042),-0.164(-0.288,-0.039),-0.172(-0.297,-0.048),and-0.099(-0.226,0.028),respectively.The stratification analysis indicated that the association of 1-OHP and mitochondrial DNA copy number showed consistently significant in each subgroup of gender,BMI,smoking and drinking status.The significant association of 1-OHP and mitochondrial DNA copy number was also observed among participants with age>40 years old.While the associations between 1-OHPh,ΣOH-PAHs and mitochondrial DNA copy number were more robust in current drinkers [β(95% CI)were-0.085(-0.152,-0.018),-0.131(-0.249,-0.012),respectively].As for the association of ΣOH-Ph and mitochondrial DNA copy number,it is more evident in current smokers and current drinkers [β(95% CI)were-0.083(-0.161,-0.004),-0.118(-0.230,-0.006),respectively].We did not find any significant interactions between age,gender,BMI,smoking and drinking status and the above four urinary PAHs metabolites on mitochondrial DNA copy number(all P for interaction>0.050).Conclusions: Elevated urinary 1-OHPh and 1-OHP were associated with decreased mitochondrial DNA copy number in a dose-response manner.∑OH-Ph and ∑OH-PAHs showed marginal associations with mitochondrial DNA copy number.Part Ⅱ.Oxidative stress levels and their combined effects with PAHs exposure on peripheral blood mitochondrial DNA copy numberObjective: We aimed to explore the associations between urinary 8-OHd G and 8-iso-PGF2α levels and peripheral mitochondrial DNA copy number,and to evaluate the associations between PAHs exposure and peripheral DNA copy number under different levels of oxidative stress,as well as the interactive and combined effects of oxidative stress indices and the above four PAHs metabolites.Methods: Based on the population of the first part,1179 coke oven workers with indicators of oxidative stress were included in this part.8-OHd G and 8-iso-PGF2α were normalized by ln transformation.We then assessed the associations of the above two oxidative stress indicators(as independent variables)with mitochondrial DNA copy number(as dependent variables)by generalized linear models.Meanwhile,based on the above results,PAHs metabolites and oxidative stress indicators were all divided into high and low groups by the 75 th quantile.We further investigated the relationships between urinary 1-OHPh,1-OHP,ΣOH-Ph and ΣOH-PAHs and mitochondrial DNA copy number under different levels of oxidative stress,and their interactive and combined effects on mitochondrial DNA copy number were testified.Results: There was an inverse association between urinary 8-OHd G and mitochondrial DNA copy number.We found 1% increase in urinary concentration of 8-OHd G level was associated with 0.051% decrease in mitochondrial DNA copy number [β(95% CI)=-0.051(-0.092,-0.011)].The association remained significant when further adjusting for urinary ΣOH-PAHs and plasma BPDE-Alb adducts(P=0.048).Compared with subjects in the lowest quartile of 8-OHd G,those in the highest quartile had significantly decreased mitochondrial DNA copy number [β(95% CI)=-0.160(-0.311,-0.009),P for trend=0.046).The above association was more evident in current drinkers [β(95% CI)=-0.082(-0.163,-0.002)].However,no such association existed between urinary 8-iso-PGF2α and mitochondrial DNA copy number [β(95% CI)=0.031(-0.036,0.097)].We further investigated the associations between PAHs exposure and mitochondrial DNA copy number under different levels of oxidative stress.We found that in the subjects with higher level of urinary 8-OHd G,compared with the low 1-OHPh,1-OHP,∑OH-Ph,∑OH-PAHs level,mitochondrial DNA copy numbers of individuals with high 1-OHPh,1-OHP,∑OH-Ph,∑OH-PAHs were significantly reduced,[β(95% CI)were-0.356(-0.706,-0.006),-0.277(-0.466,-0.089),-0.418(-0.800,-0.037),-0.225(-0.410,-0.039),respectively].While in the subjects with lower level of urinary 8-OHd G,higher 1-OHPh,1-OHP,∑OH-Ph,∑OH-PAHs concentrations are not significantly related to mitochondrial DNA copy number.Similarly,such associations also existed in different levels of urinary 8-iso-PGF2α.Additionally,there was a significant interaction between 1-OHP and 8-iso-PGF2α on mitochondrial DNA copy number(P for interaction=0.036).When 8-OHd G and 1-OHP were combined,compared with low 8-OHd G and low 1-OHP level group(referent group),the variation trend of mitochondrial DNA copy number in the high 8-OHd G and low 1-OHP group,low 8-OHd G and high 1-OHP group,high 8-OHd G and high 1-OHP group was statistically significant [β(95% CI)were 0.057(-0.098,0.212),-0.036(-0.192,0.119),-0.201(-0.338,-0.064),respectively],and P for trend=0.011.Meanwhile,8-OHd G and ∑OH-PAHs have similar joint effects(P for trend=0.022).In addition,joint effect of 8-iso-PGF2α with 1-OHP on mitochondrial DNA copy number was also observed(P for trend=0.034).Conclusions: 8-OHd G was inversely associated with mitochondrial DNA copy number.The relationships between 1-OHPh,1-OHP,∑OH-Ph and ∑OH-PAHs and the reduction of mitochondrial DNA copy number were more pronounced in subjects with higher levels of oxidative stress,and combined effects of 1-OHP or ∑OH-PAHs with 8-OHd G or 8-iso-PGF2α,respectively,on the reduction of mitochondrial DNA copy number were observed. |
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