Never deem lightly the “less harmful” low-molecular-weight PAH, NPAH, and OPAH - Disturbance of the immune response at real environmental levels

The upcoming energy structure optimization and the implementation of strict emissions control will effectively alleviated the pollution of high-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. Compared to HMW PAHs, the immune response to low-molecular-weight (LMW) PAHs is recognized as “less harmful”, despite the high proportions of these substances. The present study intends to investigate the effects of several of the most abundant LMW PAHs on macrophages RAW264.7 at environmentally relevant doses. The data assembled herein showed that Fluoranthene (Fluo, PAH) formed a π-π interaction with the Phe12 residue of AhR while inhibiting the transcription of CYP1A1 and CYP1B1, and ultimately induced the inflammatory cytokines in RAW264.7. The 1-Nitropyrene (1-Nitro, NPAH) formed both a π-π interaction and a hydrogen bond with AhR, stimulated CYP1A1transcription, while suppressed the cytokine levels. Additionally, the inflammation potency caused by TPAHs was highly correlated with the cytotoxic potency rather than the oxidative stress potency. When stimulated by LPS, the transcription of IL-6 was inhibited by Fluo, and 1-Nitro suppressed both IL-6 and TNFα transcription. Furthermore, only 1-Nitro gave a significant inhibition on phagocytosis. The effects of 9-Fluorenone (9-Fluo, OPAH) on macrophages remained insignificant throughout the study since the low affinity for AhR, which resulted in low cytotoxicity. Collectively, this study suggested that LMW PAHs tended to cause mild inflammation when they bind without activating AhR. During infection, AhR ligands caused immunosuppression and this potency for TPAHs may be higher in AhR activator than that in AhR inactivator.