a1 Shanghai Key Laboratory of Formulated Chinese Medicines and MOE Key Laboratory for Standardization of Chinese Medicines, Institute of Chinese Materia Medica, Shanghai University of Traditional Chinese Medicine, Shanghai 201203, People's Republic of China
a2 Departments of Medicine and Genetics, Albert Einstein College of Medicine, New York 10461, USA
a3 Department of Pharmacognosy, China Pharmaceutical University, Nanjing 210038, People's Republic of China
a4 Shanghai R&D Center for Standardization of Traditional Chinese Medicine, Shanghai 201203, People's Republic of China
Naringenin, one of the most abundant flavonoids in citrus, grapefruits and tomatoes, has been used as a traditional anti-inflammatory agent for centuries. However, the molecular mechanism of naringenin in intestinal inflammation remains unknown so far. The present study investigated a molecular basis for the protective effect of naringenin in dextran sulphate sodium-induced murine colitis. Pre-administration of naringenin significantly reduced the severity of colitis and resulted in down-regulation of pro-inflammatory mediators (inducible NO synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1), cyclo-oxygenase-2 (Cox2), TNF-α and IL-6 mRNA) in the colon mucosa. The decline in the production of pro-inflammatory cytokines, specifically TNF-α and IL-6, correlated with a decrease in mucosal Toll-like receptor 4 (TLR4) mRNA and protein. Phospho-NF-κB p65 protein was significantly decreased, which correlated with a similar decrease in phospho-IκBα protein. Consistent with the in vivo results, naringenin exposure blocked lipopolysaccharide-stimulated nuclear translocation of NF-κB p65 in mouse macrophage RAW264.7 cells. In addition, in vitro NF-κB reporter assays performed on human colonic HT-29 cells exposed to naringenin demonstrated a significant inhibition of TNF-α-induced NF-κB luciferase expression. Thus, for the first time, the present study indicates that targeted inhibition of the TLR4/NF-κB signalling pathway might be an important mechanism for naringenin in abrogating experimental colitis.
(Received July 30 2012)
(Revised November 13 2012)
(Accepted November 14 2012)
(Online publication March 18 2013)
† Z.-T. Wang and S. Mani contributed equally to the paper.
Abbreviations: Cox2, cyclo-oxygenase-2; DSS, dextran sulphate sodium; iNOS, inducible NO synthase; IBD, inflammatory bowel disease; MCP-1, monocyte chemoattractant protein-1; TLR4, Toll-like receptor 4; UC, ulcerative disease