Structure of an immunoactive polysaccharide isolated from Korean mulberry fruit (Morus alba L.)

A water-soluble polysaccharide (JS-MP-1) was isolated from the water extract of Korean white mulberry fruits (Morus alba L.) by ethanol precipitation and then purified by DEAE-cellulose ion exchange chromatography. Obtained final polysaccharide (1600 KDa) consisted of galactose, arabinose and rhamnose as major neutral sugars. JS-MP-1 also contains galacturonic and glucuronic acids (4:1). Sugar linkage, FTIR and correlation NMR analyses confirmed that it is a rhamnogalacturonan type I (RG I), which contains the alternating sequence of 1,4-alpha-D-GalAp and 1,2-alpha-L-Rhap units in the backbone. Neutral sugar side chains of JS-MP1 were identified as (1 -> 5)-alpha-L-arabinan and arabinogalactan type II (AG II) having the (1 -> 6)-beta-D-galactan core. The arabinan side chains are bound to the backbone at the O-4 position of some alpha-L-Rhap units, while the way of linkage between RG I and AG II chains is unclear. It was demonstrated that JS-MP-1 significantly stimulates murine macrophage RAW 264.7 cells to release chemokines (RANTES and MIP-1 alpha) and proinflammatory cytokines like INF-alpha and IL-6, and induce the iNOS and COX-2 gene expression, which are responsible for the production of NO and prostaglandin PGE2, respectively. These results suggest that JS-MP-1 can act as a potent immunomodulator and these observations may support the applicability of this polysaccharide or the water extracts of mulberry fruit can be used as an immunotherapeutic adjuvant or health beneficial food material