Association Between Urinary Polycyclic Aromatic Hydrocarbon Metabolites And Lung Function Decline

Polycyclic aromatic hydrocarbons(PAHs)are considered as one kind of the most widespread organic environmental pollutants.Normally,PAHs are generated during incomplete burning of coal,oil,gas,garbage,or other organic materials containing carbon and hydrogen(substance like tobacco or charcoal broiled meat).Both natural(such as forest and prairie fires,volcanic eruptions)and anthropogenic(including fuels heating,refuse burning,coke production,industrial processes and motor vehicles)activities can develop a large amount of PAHs in environmental atmosphere.Inhalation and dietary intake are thought to the most common routes for PAH exposures.Currently,adverse health effects of PAHs exposure are a major environmental health problem worldwide.Previous studies demonstrated that PAHs exposure were associated with elevated risk of malignant tumors in the lung,bladder and skin.Both animal and epidemiologic studies reported that PAHs can cause damage to respiratory system(in particular the bronchi)after acute or chronic exposure.After breathing PAH though the respiratory tract,a fraction of the PAH compounds was deposited on the thin alveolar epithelium and retained in the pulmonary alveolar area because of the lipophilic properties of PAHs.Accumulation of PAHs in respiratory tract and alveolar thereby lead to direct damage to respiratory epithelium and observed inflammatory responses through oxidative stress and oxidative DNA damage.The latter is accompanied with a reaction of PAHs and mucus and its product of reactive oxygen or reactive nitrogen specie.Respiratory damage induced by PAHs has drawn much attention.Most of the studies are among occupational populations such as roofers,coke oven workers and even bus drivers.Elevated risk of mortality from obstructive lung diseases was reported among asphalt workers who were exposed to PAHs and coal tar.However,examining the association among the general population is important,because their PAH concentrations are known to be much lower.Moreover,the mechanisms for PAHs causing respiratory damages are unclear.Previous studies have found that PAH exposures can activate oxidative stress and inflammatory response by increasing reactive oxygen(ROS)and C-reactive protein,which have been implicated in the pathogenesis of lung diseases.Because these markers mainly reflect the level of systemic inflammation and are unspecific to lung injury,it is still insufficient to address how PAH exposures damage lung tissue.Clara cell secretory protein(CC16)is a 15.8-kDa protein secreted in abundance in airways by non-ciliated bronchiolar Clara cells,and recognized as a biomarker of integrity of lung epithelium.This protein increasingly appears to protect the respiratory tract against oxidative stress and inflammation.Cumulative evidence have demonstrated that low CC16 level was associated with lung function decline and development of respiratory diseases including asthma and COPD.Therefore,CC16 has emerged as a key biomarker to help confirm the diagnosis and define the prognosis in some respiratory disorders.Many noxious environmental pollutants such as wood smoke,cigarette smoke and air pollutants,can alter CC16 levels through damaging Clara cells.PAHs are very common components in these environmental pollutants.Several studies reported that Clara cells were more susceptible to PAHs than other airway epithelial cells due to highly expressed aryl hydrocarbon receptor(AhR),which is a ligand-activated transcription factor involved in PAH-induced immunotoxicity.However,only few studies focused on the association between PAHs and CC16.One vitro study in mice reported that PAH exposures could induce the reduction in both the number of Clara cell and the expression of CC16 mRNA and protein per cell.Furthermore,whether CC16 plays a potential role in lung function decline caused by PAH exposures has not been studied to date.Therefore,we conducted a study of 4,812 adults in two cities in China.The objectives of this study are:1)To investigate levels of urinary PAH metabolites among subjects from Wuhan and Zhuhai city,respectively.Meanwhile,to quantify the associations of urinary PAH metabolites with dietary PAH exposures,traffic exposure time and cigarette smoke in order to explore potential sources of PAH exposures;2)To quantify possible associations between urinary PAH metabolites and spirometric lung function changes,we measured lung functions and urinary PAH metabolites in this part of the study;3)The associations of CC16 concentration with urinary PAH metabolites and lung function parameters were quantified among 3,384 Chinese adults in a general population.We further investigated effect modification of CC16 on associations between urinary PAH metabolites and lung function.This study included three parts as following:Part I.Potential sources and urinary PAH metabolite levels among the general population in the Wuhan-Zhuhai cohortObjective:To investigate levels of urinary PAH metabolites among subjects from Wuhan and Zhuhai city,and to explore potential sources of PAH exposures.Methods:We collected data on individual health and lifestyle by questionnaires covering information on demographic characteristics,occupational hazards exposure and habits including smoking,intake frequencies of foods and traffic exposure time.Urinary PAH metabolites were measured by using GC-MS.We also quantified the associations of urinary PAH metabolites with dietary PAH exposures,traffic exposure time and cigarette smoke by using multiple linear regression.Result:Participants who did not complete the questionnaire(N=676)were excluded in this part.A total of 4,136 residents are enrolled in this part of the study,including 2,780 and 1,356 from Wuhan and Zhuhai,respectively.The mean age of all the subjects is 53.1 and 32.5%of the subjects are males(N=1344).Compared to subjects from Zhuhai,those living in Wuhan present to have lower income,percentage of participating regular physical activity and cooking meals at home,and higher smoke amount,passive smoke amount,alcohol consumption and traffic exposure time.According to the results of distribution of urinary PAH metabolites,we found that 2-OHNa,9-OHFlu and 1-OHP were the main metabolites.We also observed that positive correlation between each bivariate among OHNa,OHFlu,OHPh and OHP(Spearman correlation coefficients r in the range from 0.41 to 0.63,all P<0.001).Subjects in Wuhan have a higher concentration of total urinary PAH metabolites(5.96 μg/mmol Cr)than those in Zhuhai(5.10 μg/mmol Cr).All the urinary PAH metabolites are higher in Wuhan than that in Zhuhai,except for 1-OHPh.Positive correlations were found between PM2.5-bound PAHs and total and specific urinary PAH metabolite(Spearman correlation coefficients r in the range from 0.08 to 0.53,all P<0.05).Significant associations of dietary PAH exposures and urinary PAH metabolites were observed in both Wuhan and Zhuhai city.The associations in Zhuhai present stronger than that in Wuhan.Traffic exposure time is associated with urinary PAH metabolites.The associations in Zhuhai are stronger than that in Wuhan.We also found significant associations between smoking amount and urinary PAH metabolites.The associations in Zhuhai are stronger than that in Wuhan.Conclusions:Subjects living in Wuhan exposed PAHs more than those in Zhuhai.Inhalation of PM2,5 may be an important source of PAH exposure.Dietary intake,traffic exhaust and smoking might be potential sources of PAH exposures in Chinese general population.Part II.Urinary polycyclic aromatic hydrocarbon metabolites and altered lung function among Chinese general populationObjective:To quantify possible associations between urinary PAH metabolites and lung function changes.Methods:We further measured lung function tests for all participants in this part of the study,in accordance with the American Thoracic Society recommendations.We also investigated whether any of several covariates(gender,age,BMI,smoking status,drinking status,physical activities)modified the association by using linear mixed models.Result:In this part,we further excluded 144 participants who failed to finish the lung function tests.Finally,there are 3,992 subjects enrolled in this study,including 1306 males and 2686 females.Older participants have higher level of ΣOH-PAHs.FVC and FEV1 decrease with increasing ΣOH-PAHs.With adjustment for confounders,urinary PAH metabolites are associated with FEV1 and FVC.In the continuous analyses,each one-unit increase in log-transformed values of 2-OHNa,2-OHFlu,4-OHPh,9-OHPh,3-OHPh,2-OHPh,1-OHP andΣOH-PAHs was associated with a 27.88,18.58,27.55,22.35,18.34,24.48 and 29.30 ml decrease in FVC,respectively.Additionally,each one-unit increase in log-transformed values of 1-OHNa,2-OHNa,9-OHFlu,2-OHFlu,4-OHPh,9-OHPh,3-OHPh,1-OHPh,2-OHPh,1-OHP and ΣOH-PAHs was associated with a 14.24,26.17,11.97,17.62,25.62,22.91,12.86,16.78,23.01,25.40 and 32.56 ml decrease in FEV1,respectively.The categorical analysis also showed significantly monotonic FVC decline for 4-OHPh and 1-OHP,and FEV1 decline for 9-OHFlu,4-OHPh,9-OHPh,1-OHP and ΣOH-PAHs.We found similar association between urinary PAH metabolites and lung function parameters among the subjects in both Wuhan and Zhuhai city.We analyzed the association between urinary PAH metabolites and FEV1,as well as FVC,among both smokers(including current and former smokers)and non-smokers(including passive and never smokers).Among smokers,we found a significant negative association between FVC and 2-OHNa,2-OHFlu,4-OHPh,3-OHPh,1-OHPh,1-OHP andΣOH-PAHs,while a significant negative association between FEV1 and each urinary PAH metabolite.Among non-smokers,FVC was negatively associated with 2-OHNa,2-OHFlu,4-OHPh,9-OHPh,3-OHPh,2-OHPh,1-OHP and ΣOH-PAHs,while FEV1 was negatively associated with 2-OHNa,4-OHPh,9-OHPh,2-OHPh,1-OHP and ΣOH-PAHs.The associations were stronger among smokers than that among non-smokers.Subgroup analyses showed that alcohol consumption,but not age,sex,smoking status,BMI,physical activity,or city significantly modified the negative associations ofΣOH-PAHs with FVC and FEV1.Conclusions:We found that total and specific urinary PAH metabolites were associated with lung function reduction in a general Chinese population.The associations were stronger among smokers than that among non-smokers.Part III.Urinary polycyclic aromatic hydrocarbons metabolites,Clara cell secretory protein,and lung function alterationObjective:To quantify the associations of CC16 concentration with urinary PAH metabolites and lung function parameters.Methods:We measured the plasma CC16 concentration by using Elisa kits.We used urinary PAH metabolites as the biomarkers to assess internal dose of PAH exposures and investigated effect modification of CC16 in associations between urinary PAH metabolites and lung function among 3,384 Chinese adults in a general population,by using linear mixed models.We also repeated the measurements of CC16 concentration and lung function after 3 years to quantify the longitudinal association of CC16 concentration and risk of lung function decline.Result:After excluded 608 subjects who were not collected whole blood in this part of the study,a total of 3,384 subjects were included finally.Mean age of subjects was 53.3 years old,and one third were males(32.1%).Among subjects attending the baseline,the median of total urinary PAH metabolites and CC16 concentration was 5.70 μg/mmol Cr and 17.36 ng/ml respectively.Higher urinary PAH metabolites were found among older subjects and those having a higher percentage of cooking meals at home,higher CC16 concentration,and lower height,weight,FEV1 and FVC.In continuous analysis,both ΣHMW OH-PAH and ΣLMW OH-PAHs were negatively associated with a 22.59 ml and 25.25 ml FEV1 decline respectively,while onlyΣHMW OH-PAH was significantly associated with FVC[-30.38(-48.17,-12.60)].No significant association was observed between ΣLMW OH-PAHs and FVC.In categorical analysis,we found significantly monotonic FEV1 and FVC declines for both ΣHMW OH-PAH and ΣLMW OH-PAHs.The association of urinary PAH metabolites and lung function alteration were quantified across CC16 tertiles(Table 3).We observed that these associations were only significantly negative among subjects with low plasma CC16 level,and tended to be weaker or absent among those with higher CC16 levels.Compared with the first quartile of ΣHMW OH-PAH,we observed significantly decreased CC16 concentration for subjects with highest quartile of ΣHMW OH-PAH[-0.10(-0.18,-0.02)];while we did not observed any significant association betweenΣLMW OH-PAH and CC16 concentration(all P>0.05).We found similar results using the urinary PAH metabolite level as a natural cubic spline function in linear mixed model.Significant nonlinear dose-response associations between ΣHMW OH-PAH and CC16 concentration(P values for nonlinear trend=0.03)was observed,and the plasma CC16 concentration monotonically decreased when log-transformed ΣHMW OH-PAH was more than-0.40(i.e.original concentration of ΣHMW OH-PAH=0.67 μg/mmol Cr).There was no significant nonlinear association between ΣLMW OH-PAHs and CC16 concentration(P values for nonlinear trend=0.15).Lower baseline lung function parameters were significantly associated with decreased baseline CC16 levels(for FEV1:P trend=0.02;for FVC:P trend=0.004).After repeated the data analyses at follow-up,similar associations were observed between 3-year follow-up CC16 levels and follow-up FEV1 and FVC(P trend<0.001 and 0.04 respectively).In longitudinal analyses,we investigated the estimated changes of follow-up FEV1 and FVC across baseline CC16 levels.The results shows that CC16 concentration at baseline predicts reduction in FEV1(P trend=0.006)rather than FVC(P trend=0.21).There is significance in the relationship between baseline CC16 concentration and the risk of lung function decline(FEV1/F V C<0.7).Overall,we observed an inversed U-shaped exposure-response relationship between CC16 concentration and risk ratio of lung function decline.The risk ratio monotonically decreased with increasing CC16 at concentrations from 11 to 40.Conclusions:We found that total and specific urinary PAH metabolites were associated with lung function reduction in a general Chinese population.The associations were stronger among smokers than that among non-smokers.