Enhanced anti-inflammatory effects of DHA and quercetin in lipopolysaccharide-induced RAW264.7 macrophages by inhibiting NF-κB and MAPK activation

The aim of the present study was to investigate the anti-inflammatory effects of docosahexaenoic acid (DHA) + quercetin (QE) used in combination. DHA and QE are natural compounds derived from various foods and have been demonstrated to exert anti-inflammatory effects The protein mRNA expression involved in the nuclear factor (NF)-κB and mitogen-activated protein kinase (MAPK) signalling pathway was analyzed by western blot analysis and reverse transcription-polymerase chain reaction methods respectively, other cytokines were detected by an enzyme-linked immunosorbent assay kit. The results of the present study demonstrated that combined treatment of lipopolysaccharide (LPS)-stimulated RAW264.7 cells with DHA + QE decreased the levels of pro-inflammatory mediators to a greater extent than QE or DHA alone. Additionally, DHA + QE synergistically suppressed nitric oxide, pros-taglandin E2 and cyclooxygenase-2 levels. Molecular-level studies indicated that the DHA + QE combination can significantly inhibit the mRNA expression of NF-κB subunits p50 and p65, extracellular signal-regulated kinase (ERK) 1/2 and c-JUN N-terminal kinase (JNK) 1/2, which suggests that the NF-κB signalling pathway is involved in the synergistic effects observed. Furthermore, western blot analysis demonstrated that DHA + QE synergistically inhibit the phosphorylation of p50, p65, ERK1/2 and JNK1/2. This finding indicates that the enhanced anti-inflammatory effects of the combined compounds are achieved by suppressing NF-κB and MAPK signalling in LPS-stimulated RAW264.7 cells. The results of the present study suggest that DHA and QE in combination may be utilized as potent anti-inflammatory compounds, with potential preventative or palliative effects on obesity, atherosclerosis and cardiovascular diseases.