Toll‐Like Receptors in the Mechanism of Hexabromocyclododecane‐Induced Production of Pro‐Inflammatory Cytokines

Hexabromocyclododecane (HBCD), a brominated flame retardant, has raised increasing health concerns due to its bioaccumulation in human tissues and its ability to induce proinflammatory cytokines. Interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) are major mediators of inflammation, and their chronic elevation contributes to autoimmune disorders, cardiovascular disease, and cancer. Previous studies have implicated mitogen-activated protein kinases (MAPKs) as mediators of HBCD-induced IL-1β and IL-6 production. Because MAPKs act downstream of Toll-like receptors (TLRs)-key inflammatory response regulators, identifying whether TLRs contribute to HBCD-driven inflammation is essential. This study examined the roles of TLR1/2, TLR2, TLR3, TLR4, and TLR8 in HBCD-induced IL-1β, IL-6, and TNF-α production in peripheral blood mononuclear cells (PBMCs). PBMCs were pretreated with selective inhibitors targeting TLR1/2 (CUCPT 22), TLR2 (C29), TLR3 (CUCPT 4a), TLR4 (TAK-242), TLR8 (CUCPT 9a), and MyD88 (TJ-M2010-5), followed by exposure to HBCD (1-5 μM). The results indicated that inhibition of TLR4 significantly reduced HBCD-induced production of all three cytokines, demonstrating its central roles in this response. Blocking TLR8 significantly reduced HBCD-induced IL-1β production. In contrast, inhibition of TLR1/2, TLR2, or TLR3 produced no consistent effects on HBCD-induced cytokine production. Inhibition of the TLR-associated adaptor protein MyD88 significantly attenuated HBCD-induced IL-1β and IL-6 production, whereas TNF-α production was not consistently affected. These results further elucidate the mechanism by which HBCD leads to elevation of pro-inflammatory cytokine production by human immune cells.