Long-term Exposure To Carbon Black Induces Genomic Instability Of Peripheral Blood Lymphocytes In Occupational Population

Objective Carbon black(CB)as virtually pure elemental carbon could be inhaled and deposited deeply in the lung due to size.The previous studies suggested that long-term CB exposure could cause lung function decreased and a variety of respiratory diseases.CB occupational exposure risk assessment had received widespread attention,a large number of occupational groups engaged in the production and use of CB in worldwide.The research of CB causing cancer(especially lung cancer)mainly focuses on animal level,but insufficient epidemiological evidence of CB to human carcinogenicity,CB was classified as a Class 2B carcinogen by the International Agency for Research on Cancer(IARC).At present,there was no effective genotoxicity biomarker evaluation indicator for CB exposure and cancer risk.This research mainly used the Cytokinesis-block micronucleus test(CBMNT)as a biomarker to detect the carcinogenicity of CB exposure for occupational populations,and discussed the long-term CB exposure on the genomic instability of peripheral blood lymphocytes in occupational population.Further analyzed the potential carcinogenic risk of CB exposure and provided a reasonable scientific basis for the occupational exposure risk assessment of CB.Methods In 2012,our research group selected 85 carbon black packers(CBPs)in a CB production workshop and 106 local water plant workers(non-CBPs)who had never been exposed to CB as the research group to establish CBP cohort.Subsequently,127 CBPs and 105 non-CBPs were followed up in 2018(53 CBPs and 55 non-CBPs included in2012).During molecular epidemiological studies,we counted the incidence of micronucleus(MN)、nuclear bridge(NPB)and nuclear bud(NBUD)by CBMNT,and assessed the instability of the genomic instability of peripheral blood lymphocytes in occupational population.Carbon content in airway macrophage(CCAM)quantified in induced sputum was used as a biomarker to assess the elemental carbon exposure.Luminex multi-cytokines quantitative analysis was used to detect circulating inflammatory factors in the serum of the research groups.Mediation effect analysis was applied to determine the role of circulating pro-inflammatory factors in the effect of CB exposure on the genomic instability of occupational workers.We selected non-smokinghealthy adults to establish lymphocyte in vitro model,and added physiologically relevant doses of TNF-α(1.44 ng/mL)after 24 hours for CBMN measurement to assess the effect of TNF-α on genomic instability.Generalized linear models and poisson regression were used to assess the correlation between CB exposure and genomic instability of peripheral blood lymphocytes in occupational population.Results The results of 85 CBPs and 106 non-CBPs studied in 2012 found that the MN rate,NPB rate,NBUD rate,and CBMN frequency of the CB exposure groups(the sum of the MN rate,NPB rate,and NBUD rate,also called genome instability Index)were significantly higher than that of the non-CBPs control group,and the frequency ratio(FR)was about 1.78-3.09.The results of 127 CBPs and 105 non-CBPs studied in 2018 also found that the MN and NBUD rate of the current carbon black packers(CBP-Cs)groups were significantly higher than that of the non-CBPs control group,and the FR was about1.24-1.59.Moreover,CCAM was associated with CBMN endpoints in a dose-dependent manner.CB aerosol and diesel engine exhaust shared the same potency of inducing genomic instability of peripheral blood lymphocytes in occupational workers.Circulating inflammation factor test results showed that the serum levels of TNF-α、IL-1β and IL-6 in CBPs increased by 10.2 、10.6 and 7.0-fold compared with the non-CBPs controls,in addition,MIP-1β and CRP were added 3.3 and 2.7-fold respectively.The results of the mediation effect analysis proved that the circulating inflammatory factors such as TNF-α、IL-6、IL-1β、MIP-1β and CRP were the intermediary factors between CB exposure and the endpoint of CBMN.TNF-α had a mediation effect for all three CBMN endpoints.At last,in vitro functional validation supported the role of TNF-α in inducing the genomic instability.Conclusions Long-term CB exposure could increase genomic instability of peripheral blood lymphocytes in the occupational population,which confirmed the dose-response relationship between the internal exposure dose of CB exposed occupational population and the micronucleus rate,nuclear bud rate and genomic instability index of peripheral blood lymphocytes.It’s helpful to screen biomarkers for biological detection of CB exposed population and provide scientific theoretical basis for better protection of CB exposed population.Long-term CB aerosol and DEE(class 1 carcinogen)exposure were very similar to their ability to induce genomic instability in occupational populations.In summary,this study provided a new population epidemiological evidence for the possiblecarcinogenesis of CB,which would help the IARC to reassess the carcinogenic grade of CB.