Immunomodulating Effects of Flavonoids on Acute and Chronic Inflammatory Responses Caused by Tumor Necrosis Factor α

Flavonoids have beneficial activities which modulate oxidative stress, allergy, tumor growth and viral infection, and which stimulate apoptosis of tumor cells. In addition to these activities, dietary flavonoids are able to regulate acute and chronic inflammatory responses. Here we describe new aspects of regulatory mechanisms by which flavonoids suppress production of tumor necrosis factor-α (TNF-α) by macrophages, microglial cells and mast cells stimulated with lipopolysaccharide (LPS) and others via toll-like receptors (TLRs), and TNF-α-mediated acute and chronic inflammatory responses. Treatment with flavonoids such as luteolin, apigenin, quercetin, genistein, (-)-epigallocatechin gallate, and anthocyanidin resulted in significant downregulation of LPS-elicited TNF-α and nitric oxide (NO) production and diminished lethal shock. In chronic diseases, pathogenesis of collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis which is triggered by TNF-α, was improved by the oral administration of flavonoids after the onset of CIA. Here, we discuss that inhibitory effects of flavonoids on acute and chronic inflammation are due to regulation of signaling pathways, including the nuclear factor κB (NF-κB) activation and mitogen-activated protein (MAP) kinase family phosphorylation. FcεRI expression by NF-κB activation was also reduced by flavonoids; while accumulation of lipid rafts, which is the critical step for signaling, was blocked by flavonoids. The intake of dietary flavonoids reduces acute and chronic inflammation due to blocking receptor accumulation and signaling cascades, and would assist individuals at highrisk from life-style related diseases.