Background: Chronic inflammation contributes to the development of lifestyle-related diseases, and dietary phytochemicals are recognized as important modulators of inflammatory responses. However, the synergistic anti-inflammatory effects of phytochemical combinations and their underlying mechanisms remain insufficiently understood. Methods: The anti-inflammatory activities of menthol (ME), 1,8-cineole (CI), β-eudesmol (EU), and capsaicin (CA) were evaluated in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Pro-inflammatory gene expression was quantified by quantitative PCR, intracellular Ca2+ signaling was assessed by calcium imaging, and the involvement of transient receptor potential (TRP) channels was examined using selective inhibitors. Synergistic effects were analyzed based on changes in half-maximal effective concentrations (EC50). Results: All compounds suppressed LPS-induced pro-inflammatory genes, including tumor necrosis factor-alpha (Tnf) and interleukin-6 (Il6), in a dose-dependent manner, with CA showing the lowest EC50 for Tnf expression (0.087 µM). Notably, combinations of CA with ME or CI exhibited strong synergy, reducing their EC50 values by 699-fold and 154-fold, respectively, without cytotoxicity. These effects likely resulted from the synergic interaction between ME/CI-induced TRP-mediated signaling and CA-activated, TRP-independent signaling. Conclusions: Specific combinations of plant-derived functional components can markedly enhance anti-inflammatory efficacy, supporting dietary strategies that harness multiple phytochemicals for inflammation control and disease prevention.
Terashita et al. (Fri,) studied this question.