Uncovering Mitochondrial Defects Induced by Chemicals: A Case Study of Low-Dose Medium-Chain Chlorinated Paraffin Exposure

Given the susceptibility of mitochondria to environmental pollutants, mitochondrial defects are critical end points for chemical safety evaluation. In this study, we present a comprehensive strategy for assessing mitochondrial toxicity, exemplified through a case study on medium-chain chlorinated paraffins (MCCPs, C_xH_2x+2-yCl_y with 14-17 carbon atoms), one of the most abundant organic pollutants in the human body. Our results demonstrate that MCCP exposure at levels commonly found in humans significantly reduces cellular ATP content by impairing mitochondrial respiration rather than glycolysis. Using an optimized mitochondrial metabolomics approach combined with dose-resolved proteomics, we elucidated the molecular mechanisms underlying MCCP-induced mitochondrial defects, including inhibition of the electron transport chain, mitochondrial membrane damage, accumulation of reactive oxygen species, and disruptions in nucleotide metabolism. Notably, over 80% of the MCCP-regulated mitochondrial proteins exhibited EC₅₀ values below the human internal levels of MCCPs, highlighting a significant threat to human health. This proposed strategy for mitochondrial toxicity assessment is expected to facilitate future research in mitochondrial toxicology.