Cinnamon and Derivatives as Modulators of Toll-like Receptors

Toll-like receptors (TLRs) are critical components of the innate immune system, acting as pattern recognition receptors and interacting with oxidative stress. TLR2, TLR4, and TLR7 play distinct yet overlapping roles in immune regulation, contributing to both physiological processes and disease progression. Therefore, modulation of TLR signaling pathways represents a promising therapeutic strategy for a wide range of diseases. Natural antioxidants have attracted considerable interest as modulators of TLRs, with cinnamon-derived phytochemicals, particularly cinnamaldehyde, emerging as promising candidates for the treatment of TLR-mediated diseases. Experimental evidence, supported by molecular docking studies, demonstrates that cinnamaldehyde directly interacts with TLR2 and TLR4. Specifically, it inhibits ligand-induced heterodimerization of TLR2 with TLR1 and TLR6, while binding to MD-2 to prevent TLR4 oligomerization and subsequent receptor activation. Furthermore, emerging evidence suggests that cinnamaldehyde may also interact with TLR7 and suppress its downstream signaling. To improve the pharmacokinetic properties, bioavailability, and targeted delivery of cinnamon-derived compounds, nanoformulations and semi-synthetic derivatives have been developed and have shown potential to modulate TLR signaling pathways. However, despite the strong biological plausibility and experimental evidence supporting the parent cinnamaldehyde scaffold as a direct TLR modulator, direct interactions between TLRs and these advanced formulations or semi-synthetic derivatives remain insufficiently documented.