Polychlorinated Biphenyls (PCBS)-induced oxidative stress and inflammation in human thyrocytes: involvement of AhR and NRF-2/HO-1 pathway

Purpose: In this in vitro study, we investigated the effects of polychlorinated biphenyls (PCBs) on human thyrocytes, with a focus on the involvement of AhR, a key player in xenobiotic response, and the anti-oxidant Nrf-2/HO-1 pathway. Methods: Primary cultured thyrocytes were exposed to the dioxin-like congeners PCB118 and PCB126 at 2.5 and 5 µM concentrations. mRNA expression was assessed by real-time PCR, and protein expression by Western Blot and ELISA, while protein quantification was assessed by densitometric analysis. Results: In cultured thyrocytes, PCB118 and PCB126 induced a significant (P< 0.01) increase of mRNA and protein levels of the pro-inflammatory cytokines IL-1beta and IL-6, while reducing those of thyroglobulin (TG) and NIS (p< 0.05), indicating down-regulation of these thyroid-specific genes in PCB-induced inflammation. ROS production also increased (p< 0.001). mRNA levels of AhR and the downstream molecules cytochrome P4501A, Nrf-2/HO-1 increased (p< 0.001), as well as related protein levels (p< 0.01), suggesting the activation of AhR and Nrf-2 pathways in response to PCBs exposure. AhR silencing decreased AhR-related gene expression and restored NIS and TG expression, while reducing inflammatory cytokines and oxidative stress markers (p< 0.05). Conclusions: Dioxin-like PCBs (PCB118 and PCB126) may promote inflammation and oxidative stress in thyrocytes, impairing the expression of genes that are key players of thyroid function. These effects can be partially attributed to the activation of the AhR and Nrf-2 pathways. These data may contribute to explain the mechanisms underlying thyroid toxicity of PCBs, highlighting the potential role of these pollutants as a trigger of autoimmune thyroid inflammation and damage.