Objective To isolate Astragalus polysaccharides-Ⅰ(APS-Ⅰ)(relative molecular mass>2×106)and APS-Ⅱ(relative molecular mass 1×104)from APS,and further clarify the efficacy of APS,APS-Ⅰ and APS-Ⅱ on dextran sulphate sodium(DSS)-induced ulcerative colitis in mice.Methods APS-Ⅰ and APS-Ⅱ were isolated and prepared,relative molecular mass,uronic acid content,monosaccharide composition and glycosidic linkage were determined.The BALB/c mice model of ulcerative colitis was established,APS,APS-Ⅰ and APS-Ⅱ were given.The disease activity index(DAI),colon length,spleen index and liver index of mice were measured;Hematoxylin-eosin(HE)staining was used to observe pathological changes in colon tissue;The activity of myeloperoxidase(MPO)and levels of Th1 related cytokines tumor necrosis factor-α(TNF-α),interferon-γ(IFN-γ),as well as Th2 related cytokines interleukin-4(IL-4)and IL-10 in colon tissue were measured;qRT-PCR was used to detect the mRNA expressions of TNF-α,IFN-γ,IL-4 and IL-10 in colon tissue;Immunohistochemical method was used to measure the expressions of T cell specific transcription factor T-bet(T-bet)and GATA binding protein 3(GATA-3)protein in colon tissue.The efficacy of APS,APS-Ⅰ and APS-Ⅱ was compared.Results APS was composed of two components APS-Ⅰ and APS-Ⅱ,with relative molecular weights>2×106 and 1×104,respectively;The mass fractions of uronic acid were 26.25％and 1.62％,respectively.The monosaccharide results showed that APS-Ⅰ and APS-Ⅱ were both composed of mannose,rhamnose,galacturonic acid,glucose,galactose and arabinose.The proportion of mannose,arabinose and galactose in APS-Ⅰ was higher than that in APS-Ⅱ.The glycosidic bond results showed that APS-Ⅰ was mainly composed of 1,4-linked glucose and 1,6-linked galactose,while APS-Ⅱ was mainly composed of 1,4-linked glucose.Compared with model group,APS-Ⅰ could significantly improve clinical symptoms such as decreased colon length,decreased body weight,increased DAI score,increased spleen and liver indexes(P<0.05,0.01,0.001),alleviate pathological damage to colon tissue,reduce MPO activity and levels of TNF-α,IFN-γ in colon tissue(P<0.01,0.001),increase IL-4 and IL-10 levels in colon tissue(P<0.05,0.01,0.001),down-regulate TNF-α,IFN-γ mRNA expressions and T-bet protein expression in colon tissue(P<0.05,0.001),up-regulate IL-4,IL-10 mRNA expressions and GATA-3 protein expression(P<0.05,0.01).However,APS-Ⅱ showed no significant differences compared to model group in terms of MPO activity,IFN-γ level,expressions of IL-4,IL-10 mRNA and T-bet,GATA-3 protein.The results indicated that APS-Ⅰ had a better therapeutic effect on ulcerative colitis than APS-Ⅱ.Conclusion APS-Ⅰ is the main component of APS in the treatment of ulcerative colitis,and its activity may be related to its uronic acid content,type of polysaccharide and glycosidic bond connection mode.APS-Ⅰ may treat ulcerative colitis by regulating Th1/Th2 immune balance.
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