Structural Analogs TOCP and TPHP Induce Immunotoxicity in Zebrafish through Divergent Disruption of Energy Metabolism

Aryl organophosphate flame retardants (aryl-OPFRs), such as triphenyl phosphate (TPHP) and tris(2-methylphenyl) phosphate (TOCP), have been identified as ubiquitous environmental contaminants, but their immunotoxicity and underlying mechanisms in aquatic organisms remain largely unclear. This study investigated the immunomodulatory effects of two structurally analogous aryl-OPFRs using zebrafish larvae during the window of exclusively innate immunity, prior to the maturation of the adaptive immune system. Strikingly, they induced opposite immune responses: TOCP increased macrophage numbers and provoked inflammation, whereas TPHP decreased neutrophil and macrophage counts and suppressed inflammation. This divergence challenges the conventional structure-activity relationship paradigm. Both compounds ultimately compromised antibacterial capacity. To elucidate the mechanism, integrated transcriptomic and metabolomic analyses were performed, revealing that the opposing phenotypes were linked to differential regulation of energy-related pathways, including glycolysis and purine metabolism. Molecular docking predicted AMPK as a potential common target, while subsequent molecular dynamics simulations provided a critical dynamic perspective: TPHP rapidly dissociated from AMPK, whereas TOCP maintained a more persistent interaction. This differential binding stability offers a plausible mechanistic basis for their distinct immunometabolic reprogramming. Overall, these findings demonstrate that the structural analogs TOCP and TPHP induce divergent immunotoxicity in zebrafish, potentially mediated through a differential disruption of host energy metabolism during the early innate immune phase.