Insights into the immunotoxicity of typical PPD and PPDQ compounds through integrating network toxicology and experimental validation

The rapid expansion of the automotive industry has led to increasing environmental release of N-(1,3-dimethylbutyl)- N ′-phenyl- p -phenylenediamine quinone (6PPDQ). Notably, N-isopropyl- N ′-phenyl-1,4-phenylenediamine quinone (IPPDQ) and N , N ′-Bis(1,4-dimethylpentyl)- p -phenylenediamine (77PD) have been detected at concentrations comparable to or higher than those of 6PPDQ and may exhibit greater toxicity. However, the potential immunotoxic risks of these compounds to humans remain poorly understood. In this study, in vitro experiments combined with network toxicology analysis were conducted to systematically evaluate the immunotoxic effects of 77PD, IPPDQ, and 6PPDQ. All three compounds exhibited dose- and time-dependent cytotoxicity in THP-1 cells. Exposure to 77PD and IPPDQ promoted macrophage apoptosis in a dose-dependent manner, whereas 6PPDQ exhibited a biphasic effect on apoptosis. In addition, all three compounds impaired macrophage immune functions and disrupted macrophage polarization profile. Mechanistically, these effects may be associated with dysregulation of the PI3K-AKT signaling pathway. Molecular docking and molecular dynamics simulations revealed stable interactions of these compounds with hub targets, maintained throughout simulation trajectories. Collectively, our findings demonstrate that 77PD, IPPDQ, and 6PPDQ disrupt macrophage homeostasis and induce immune dysfunction. This study advances understanding of the immunotoxicity of emerging tire-derived contaminants and highlights the urgent need for comprehensive health risk assessments of p -phenylenediamine (PPD) and PPD-derived quinones.