Long-term low-dose exposure to 9-chlorophenanthrene induces liver lipid accumulation via disrupting circadian rhythm

9-Chlorophenanthrene (9-ClPhe) is the most widely distributed chlorinated polycyclic aromatic hydrocarbons (ClPAHs) in environmental matrices such as the atmosphere, aquatic environments. However, the long-term low-dose toxicity of 9-ClPhe remains unclear. This study aimed to elucidate the effects and underlying mechanisms of 9-ClPhe on hepatic lipid accumulation and circadian rhythm disruption in C57BL/6 mice following a 90-day continuous exposure. Utilizing histopathological analyses and biochemical assays, we demonstrated that exposure to low-dose 9-ClPhe resulted in significant lipid accumulation in the liver. Peroxisome proliferator-activated receptor α (PPARα) activator (WY14643) was found to attenuate this hepatic lipid accumulation, indicating a critical role for PPARα in mitigating 9-ClPhe-induced effects. Moreover, our findings showed that 9-ClPhe reduced brain and muscle arnt-like protein 1 (BMAL1) protein expression, pivotal for PPARα activation, while melatonin administration restored BMAL1 levels, thereby alleviating lipid accumulation. Notably, co-immunoprecipitation assays revealed a binding interaction between aryl hydrocarbon receptor (AHR) and BMAL1, suggesting that 9-ClPhe activated AHR, leading to its interaction with BMAL1 and circadian disruption. Meanwhile, treatment with the AHR inhibitor (CH223191) mitigated 9-ClPhe-induced lipid accumulation and circadian disturbances. Collectively, our findings demonstrated that chronic low-dose 9-ClPhe exposure promoted hepatic lipid accumulation by activating the AHR-BMAL1 interaction, leading to circadian perturbation. These results highlighted the potential of low-dose 9-ClPhe to drive lipid accunmulation through circadian disruption.