Bioactive Phytochemicals from Mulberry: Potential Anti-Inflammatory Effects in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

The fruits of the mulberry tree (Morus alba L.), known as white mulberry, have been consumed in various forms, including tea, beverages, and desserts, worldwide. As part of an ongoing study to discover bioactive compounds from M. alba fruits, the anti-inflammatory effect of compounds from M. alba were evaluated in lipopolysaccharide (LPS)-stimulated mouse RAW 264.7 macrophages. Phytochemical analysis of the ethanol extract of the M. alba fruits led to the isolation of 22 compounds. Among the isolated compounds, to the best of our knowledge, compounds 1, 3, 5, 7, 11, 12, and 14-22 were identified from M. alba fruits for the first time in this study. Inhibitory effects of 22 compounds on the production of the nitric oxide (NO) known as a proinflammatory mediator in LPS-stimulated RAW 264.7 macrophages were evaluated using NO assays. Western blot analysis was performed to evaluate the anti-inflammatory effects of cyclo(L-Pro-L-Val) (5). We evaluated whether the anti-inflammatory effects of cyclo(L-Pro-L-Val) (5) following LPS stimulation in RAW 264.7 macrophages occurred because of phosphorylation of I kappa B kinase alpha (IKK alpha), I kappa B kinase beta (IKK beta), inhibitor of kappa B alpha (I kappa B alpha), nuclear factor kappa B (NF-kappa B) and activations of inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Cyclo(L-Pro-L-Val) (5) significantly suppressed phosphorylations of IKK alpha, IKK beta, I kappa B alpha, and NF-kappa B and activations of iNOS and COX-2 in a concentration-dependent manner. Taken together, these results indicate that cyclo(L-Pro-L-Val) (5) can be considered a potential therapeutic agent for the treatment of inflammation-associated disorders.