Abstract
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 IκB kinase alpha (IKKα), IκB kinase beta (IKKβ), inhibitor of kappa B alpha (IκBα), nuclear factor kappa B (NF-κB) and activations of inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Cyclo(L-Pro-L-Val) (5) significantly suppressed phosphorylations of IKKα, IKKβ, IκBα, and NF-κB 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.
Highlights
Inflammation is a complex physiological response to foreign harmful stimuli including particles, toxic compounds, bacteria, and viruses
The fruits of mulberry tree (Morus alba L.) belonging to the family of Moraceae are known as white mulberry, which is popularly consumed in various forms, including tea, beverages, and desserts, worldwide [3]
Phytochemical analysis of the CH2 Cl2 fraction was carried out using repeated column chromatography and preparative/semipreparative high-performance liquid chromatography (HPLC), which afforded 22 compounds (1–22) (Figure 1)
Summary
Inflammation is a complex physiological response to foreign harmful stimuli including particles, toxic compounds, bacteria, and viruses. In the host defense system of macrophages, the regulation of inflammation is involved in immune function [1]. In response to lipopolysaccharide (LPS), macrophages overproduce proinflammatory mediator nitric oxide (NO) and cyclooxygenase (COX-2) to upregulate inflammatory states. NO is synthesized by inducible nitric oxide synthase (iNOS) via the NF-kB signaling pathway. Inhibition of LPS production and related mechanisms are considered useful targets in research to discover potential anti-inflammatory compounds [2]. The fruits of mulberry tree (Morus alba L.) belonging to the family of Moraceae are known as white mulberry, which is popularly consumed in various forms, including tea, beverages, and desserts, worldwide [3].
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