As the mitochondrial DNA copy number (mtDNAcn) had been reported to be a biomarker for mtDNA damage in honeybees when exposed to sublethal neonicotinoids, the feasibility of human mitochondria as a predictor upon neonicotinoid exposure remains elusive. This study investigated the association between the urinary neonicotinoid and the relative mtDNAcn (RmtDNAcn) of oral epithelial cells collected in a cross-sectional study with repeated measurements over six weeks. The molecular mechanism underlying neonicotinoid-caused mitochondrial damage was also examined by in vitro assay. Herein, the average integrated urinary neonicotinoids (IMI_RPF) concentration ranged from 8.01 to 13.70 μg/L (specific gravity-adjusted) during the sampling period. Concomitantly with an increase in urinary IMI_RPF, RmtDNAcn significantly increased from 1.20 (Low group) to 1.93 (High group), indicating potential dose-dependent mitochondrial damage. Furthermore, the linear regression analysis confirmed the significant correlation between IMI_RPF and RmtDNAcn. Results from in vitro assays demonstrated that neonicotinoid exposure led to the inhibition of genes encoding mitochondrial oxidative phosphorylation (OXPHOS) complex I and III (e.g., ND2, ND6, CytB, and CYC1), accompanied by increased reactive oxygen species (ROS) production in SH-SY5Y cells. Conjointly, neonicotinoid exposure led to mitochondrial dysfunction and the resulting increase in RmtDNAcn, which may serve as a plausible biomarker for humans.
 

Neonicotinoids,Mitochondrial DNA,Oral epithelial cells,Urine,Biomarker