Structure, Phthaloyl Modification And Bioactivities Of A Polysaccharide From Lachnum

In this study, isolation, purification, structural characterization, antioxidant and moisture-preserving activities of an exopolysaccharide LEP-2a from Lachnum YM262 were investigated. Phthaloyl modification of LEP-2a was also performed, and the physicochemical and immunomodulatory properties before and after modification were also assessed.The crude exopolysaccharide (LEP) was isolated from Lachnum YM262 fermentation broth by ethanol precipitation, depigmentation and deproteinization. Then, LEP was separated and purified by DEAE-cellulose 52 and Sepharose CL-6B chromatographic column to obtain the single component, designated as LEP-2a. High performance gel permeation chromatography (HPGPC) analysis demonstrated that it was a homogeneous polysaccharide, with a molecular weight of 1.52×105 Da. The result of gas chromatography-mass spectrometry (GC-MS) indicated that it was composed of mannose and galactose in a molar ratio of 20.6:1.0. Its structural characteristics were investigated and elucidated by methylation analysis, periodate oxidation and Smith degradation, FT-IR and 1D/2D NMR spectroscopy (1H NMR,13C NMR, COSY, TCOSY, HSQC and HMBC). Based on obtained data, the backbone of LEP-2a consisted of 1,2-linked-α-D-mannose,1,3-linked-α-D-mannose,1,2,6-linked-α-D-mannose and 1,3-linked-β-D-galactose, and the side chains were attached to the backbone chain at O-6 position of 1,2,6-linked-a-D-mannose. Antioxidant activity assay proved that LEP-2a showed significant scavenging activities on superoxide, hydroxyl and DPPH radical. Furthermore, moisture absorption and retention assay showed that LEP-2a had strong in vitro moisture-absorption and -retention capacitiesThe phthaloyl polysaccharide (PHEP-2a) was prepared from a Lachnum exopolysaccharide (LEP-2a) by chemical modification, with a degree of substitution of 0.251. The results of UV, FT-IR and’H NMR analysis indicated that phthaloyl modification of polysaccharide was successful. Moreover, after phthaloyl modification, each elemental contents (C、 H、 N and S) and thermal properties of the polysaccharide were changed. Immunomodulatory activity evaluation revealed that compared with negative control group, LEP-2a and its derivative at high dose could remarkably increase the body weight, organ indexes, phagocytic index and half hemolysis value, promote splenocytes proliferation activity, improve the production of serum cytokines, such as interleukin-2 and tumor necrosis factor-alpha, and enhance the activities of acid phosphatase and lactate dehydrogenase in cyclophosphamide-treated mice. Meanwhile, they could also enhance the contents of T-SOD and GSH-Px while decrease MDA levels in model mice. Furthermore, PHEP-2a showed more significant effects than LEP-2a at the same dosage, indicating that phthaloyl modification was an effective way to enhance the immunomodulatory activity of the polysaccharide.