Exposure to metal mixtures and micronuclei frequency among occupational populations: Association analysis, benchmark dose estimation, and network toxicology.

BACKGROUND

Few studies have investigated the associations between mixed metal exposure and genetic damage, and determining the benchmark dose for metals in urine based on micronuclei (MN) frequency.

OBJECTIVE

To analyze the associations between metal mixtures in urine and micronuclei frequency, estimate the benchmark dose (BMD) and lower confidence limit (BMDL), and explore potential biological pathways using network toxicology.

METHODS

A total of 578 participants were recruited from a large lead smelting plant. The concentrations of 16 metals in urine were measured using inductively coupled plasma mass spectrometry (ICP-MS). Cytokinesis-block micronuclei (CBMN) assay was performed to detect the frequency of micronuclei (MN). Negative binomial regression (NBR), weighted quantile sum (WQS) regression, and Bayesian kernel machine regression (BKMR) were used to analyze the associations between urinary metals and MN frequency, pinpoint key contributors, as well as interactions among metals. Three BMD software were utilized to estimate the BMD and BMDL for metals in urine. Additionally, network toxicology analysis was carried out employing CTD, GeneCards, STRING, Cytoscape, along with GO and KEGG enrichment analyses to predict potential pathways linking lead (Pb), cadmium (Cd) and arsenic (As) exposure with MN frequency.

RESULTS

The distribution of urinary metals concentrations was skewed, with medians (P25, P75) being 9.53 (4.67, 19.48) for Pb, 1.64 (0.92, 2.98) for Cd, 31.36 (19.54, 50.03) for As, and 2.55 (0.77, 4.71) μg/g creatinine for Ba. The average level of MN frequency was (1.22 ± 1.41)‰ for all participants, with values of (3.60 ± 1.01)‰ for the elevated MN group and (0.67 ± 0.76)‰ for the normal MN group (t = -33.658, P < 0.001). Both the NBR and WQS models indicated that Pb, Cd, As and Ba were significant contributors to MN frequency. The BKMR model revealed positive associations between the mixtures of urinary metals and the MN frequency, highlighting potential interactions among Pb and Cd, As and Cd, as well as Ba and Cd that could elevate the micronuclei rate. The BMDs and BMDLs were 1.425 and 0.485 for Pb, 0.199 and 0.041 for Cd, 7.661 and 3.678 for As, and 0.435 and 0.003 μg/g creatinine for Ba. Network toxicology analysis identified 315 candidate target genes, and GO and KEGG enrichment analyses identified potential pathways related to oxidative stress, inflammatory responses, apoptosis, and cellular senescence.

CONCLUSION

The metal mixtures in urine were positively associated with the frequency of micronuclei, with Pb, Cd, As, and Ba being the key contributing factors. The BMD and BMDL for these urinary metals could serve as a preliminary reference for genetic damage risk assessment. Exploratory network toxicology indicated that genetic damage associated with Pb, Cd and As exposure may involve pathways related to oxidative stress, inflammation, apoptosis, and aging.