Mitochondrial complex I and II inhibiting pesticides activate DELE1-HRI integrated stress signaling but engage distinct cell death programs in human neuronal cells.

Several pesticides exert lethal actions by inhibiting the mitochondrial respiratory chain, yet the determinants of their differential cytotoxicity remain poorly characterized. We provide the first systematic comparison of fenpyroximate (FEN, Complex I inhibitor) and fluxapyroxad (FXX, Complex II inhibitor) in human SH-SY5Y neuronal cells. Both induced concentration-dependent cytotoxicity, with FEN displaying greater potency than FXX (IC₅₀ ≈ 10 vs. 40 μM; confirmed by MTT and trypan blue assays). The two pesticides produced qualitatively distinct bioenergetic injuries: FEN drove mitochondrial membrane potential collapse and a robust superoxide burst, while FXX caused marked ATP depletion without significant oxidative bursting. FEN triggered ROS accumulation, lipid peroxidation, DNA strand breakage and G2/M arrest, whereas FXX produced modest oxidative and genotoxic stress with G0/G1 arrest. N-acetylcysteine attenuated cytotoxicity of both, more effectively for FEN. FEN drove classical intrinsic apoptosis with full Bax translocation, cytochrome c release and caspase-3 activation. FXX engaged the upstream apoptotic machinery only partially-with substantial Bax and cytochrome c events but no caspase-3 activation-revealing an abortive apoptotic signal. Chloroquine co-treatment significantly rescued viability in both treatments, demonstrating a pro-toxic autophagic program operating in parallel with apoptosis for FEN and as a principal death effector for FXX. Both pesticides converged on the DELE1-HRI-eIF2α-ATF4-CHOP integrated stress response, more pronounced for FXX. Early cytoskeletal disorganization was detectable at 6 h, preceding biochemical death markers. Mitochondrial respiratory chain-inhibiting pesticides thus engage divergent yet mechanistically interconnected cell death programs in human neurons, underscoring the value of mechanistic characterization for neurotoxic risk assessment.