Raspberry Polyphenol Extract Decreases NF-kB and IL-6 Expression in Lipopolysaccharide (LPS)-Induced RAW 264.7 Macrophages

Abstract

Abstract Objectives To investigate whether raspberry polyphenol extract attenuates the inflammatory response induced by lipopolysaccharide (LPS) in RAW 264.7 macrophages. Methods Raspberry polyphenol extract was prepared using methanolic extraction, followed by solvent evaporation and freeze-drying. RAW 264.7 macrophages were treated with 0, 50, 100, 200 and 400 μg/ml of raspberry polyphenol extract in six-well plates. After 2 h, cells were then treated with 100 ng/ml of LPS for 6 h. Cells were collected for protein expression analysis of the transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) and inflammatory cytokines, i.e., interleukin (IL)-6 and IL-1β, via western blot. Results were analyzed using ANOVA followed by Tukey-Kramer post-hoc test. Results As expected, LPS significantly increased NF-kB compared to control (P < 0.0001). Pre-treatment with 400 μg/ml raspberry polyphenol extract significantly decreased phosphorylation of NF-kB in LPS stimulated cells (0.71 ± 0.03 vs. 1.00 ± 0.00-fold, P = 0.005) compared to LPS alone. LPS treatment significantly increased the expression of IL-6 compared to the control group (P < 0.0001). IL-6 expression was significantly reduced in LPS stimulated macrophages by pre-treatment with 200 and 400 µg/ml of raspberry polyphenol extract (0.49 ± 0.03-fold, P < 0.0001 and 0.33 ± 0.04-fold, P < 0.0001 respectively) compared to LPS alone (1.00 ± 0.00-fold). The expression of the inflammatory cytokine IL-1β was significantly greater than control in LPS-only treated cells (P < 0.0001). However, treatment with 400 μg/ml raspberry polyphenol was able to significantly prevent this effect (0.59 ± 0.1 vs. 1.00 ± 0.00-fold, P = 0.007). Conclusions Results indicate that raspberry polyphenols possess anti-inflammatory properties suggesting a possible role as a complementary and alternative therapy to prevent inflammation. However, in vivo and human studies are needed to confirm this. Funding Sources None.