Mitochondrial dysfunction as a central mechanism of pentavalent antimony toxicity in embryos: Linking metabolic impairment to developmental outcomes

Pentavalent antimony [Sb(V)] contamination is an emerging threat in the human environment, yet its mechanistic basis for developmental toxicity remains poorly defined. This study investigates whether mitochondrial dysfunction mediates Sb(V)-induced developmental toxicity in human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and peripheral blood mononuclear cells (PBMCs), using an integrated suite of bioenergetic, imaging, ultrastructural, and proteomic endpoints. Cells exposed to Sb(V) at 0, 25, 50, 75, and 100 μmol/L for 72 h exhibited dose-dependent mitochondrial impairment. Seahorse extracellular flux analysis revealed significant reductions in basal oxygen consumption rate (p < 0.01 at ≥ 50 μmol/L), adenosine triphosphate (ATP)-linked respiration, and maximal respiratory capacity, alongside increased proton leak. Real-time ATP imaging with the FRET-based AT1.03 sensor showed progressive, compartment-specific energy depletion, most pronounced in cardiomyocytes (up to 33% reduction at 100 μmol/L; p < 0.01). Tetramethylrhodamine ethyl ester (TMRE) staining confirmed mitochondrial membrane depolarization, and MitoSOX staining demonstrated elevated mitochondrial superoxide generation. Electron transport chain (ETC) Complex I activity was reduced by 54.6% at 100 μmol/L (p < 0.01), with lesser but significant reductions in Complexes II, III, and IV. Transmission electron microscopy (TEM) revealed cristae disorganization, matrix swelling, and outer membrane disruption in a concentration-dependent pattern. Quantitative proteomics identified 286 differentially expressed proteins enriched in oxidative phosphorylation and tricarboxylic acid (TCA) cycle pathways. These mitochondrial perturbations correlated strongly with contractile dysfunction (Pearson r = 0.89-0.91, p < 0.001) and reduced cell viability/growth (r = 0.82-0.87, p < 0.001). The findings establish an adverse outcome pathway: Sb(V) exposure causes ETC inhibition, which drives ATP depletion and oxidative stress, leading to mitochondrial structural damage, cardiac cell dysfunction, and impaired cell growth. Mitochondrial endpoints such as basal oxygen consumption rate, ATP production capacity, and Complex I activity offer sensitive and quantifiable biomarkers for sublethal antimony monitoring in human health risk assessment, particularly for children in communities affected by mining, smelting, or antimony-contaminated drinking water.