| Yam(Dioscorea opposita) is an edible herbaceous plant and also served as a raw material for tranditional Chinese medicine. Yam has been attracted attention in the food science because it has a variety of biological activity. Many studies show that yam shows many biological activities. Among these biogical components of yam are yam polysaccharides. This study thus prepared the water-soluble yam polysaccharides and assessed their immunomodulatory and anti-cancer activities. The main results are listed as below.(1) The water-soluble yam polysaccharides had in vitro immunomodulatory activities.At the level of 50 μg/m L, the results showed that the water-soluble yam polysaccharides promoted T lymphocytes proliferation by 150%, enhanced macrophage phagocytosis and natural killer cell activity by 18% and 47%. The water-soluble yam polysaccharides could increase secretion levels of interleukin-2 and interferon-γ(from 41.4 and 24.6 to 48.8 and 91.5 pg/m L), but decrease secretion level of interleukin-4(from 38.9 to 27.9 pg/mL) in the splenocytes. At the same time, the water-soluble yam polysaccharides also stimulated nitric oxide synthase and lysozym in the macrophages, and enhanced secretion levels of interleukin-6, interleukin-1β and tumor necrosis factor-α(from 26.6, 73.4 and 39.6 to 60.2, 131.0 and 144.7 pg/mL). It is concluded that the water-soluble yam polysaccharides had immunoactivity, and are able to activate immune cells and regulate the secretion levels of immune molecules, as well as exhibite a dose-dependent manner on the evaluated immunological responses.(2) Both therml and stomach acid treatments had unclear effect on in vitro immunomodulatory activities water-soluble yam polysaccharides.The water-soluble yam polysaccharides at 50 μg/m L were heated or treated by acids and enzymes. The results indicated that the water-soluble yam polysaccharides heated at 100 oC for 30-60 min, or digested by simulated stomach acid for 1-2 h, or digested by two proteases and two amylases for 1-3 h showed unchanged immunomodulatory activities(P >0.05). However, treatment of the water-soluble yam polysaccharides by HCl solution of 3 mol/L for 3-6 h brought about lower immunomodulatory activities significantly(P <0.05). It is evidenced that the water-soluble yam polysaccharides could keep their immunomodulatory activities during thermal processing and body digestion, but 3 mol/L HCl solution was potential to destroy their immunomodulatory activities.(3) The water-soluble yam polysaccharides had in vivo immunomodulatory activities.The results indicated that the water-soluble yam polysaccharides showed clear activities towards the normal mice and immuno-suppressed mice treated by cyclophosphamide(CY), in a dose-dependent manner. For the normal mice, the water-soluble yam polysaccharides at 500 mg/kg increased spleen and thymus indices by 22-42%, macrophages phagocytosis, T lymphocytes proliferation and natural killer(NK) cell activity by 18-53%, IL-2 and IFN-γ levels in the splenocytes by 42-45%, or IL-1β, IL-6, TNF-α, i NOS and LZM levels in the macrophages by 40-219%, and increased serum Ig M, Ig A and Ig G by 44-51%. For the CY-treated mice, the water-soluble yam polysaccharides were observed able to restore the immune function of the treated mice. The water-soluble yam polysaccharides at 500 mg/kg enhanced spleen and thymus indices by 85-172%, three immune cell activity by 24-98%, IL-2 and IFN-γ levels in the splenocytes by 44-109%, or immune molecules levels in the macrophages by 53-287%, and increased serum Ig M, Ig A and Ig G by 24-69%. These results indicate that the water-soluble yam polysaccharides had in vivo immunomodulatory activities, and can improve the immune function of normal mice as well as restore the immune function of immuno-suppressed mice.(4) The water-soluble yam polysaccharides after stimulated colonic fermentation had anti-proliferation on colon cancer cells.The results indicated that the water-soluble yam polysaccharides itself had weaker inhibitory effect on the proliferation of colon cancer cells(HCT-116 cells). However, when the water-soluble yam polysaccharide was fermented by the fecal extract, the anti-proliferation of the fermentative products on HCT-116 cells was detected to be much stronger.,because the fermentative products generated more of the acetic acid, butyric acid and lactic acid especially butyric acid. These results indicate that the water-soluble yam polysaccharides after colonic fermentation had enhanced inhibition on the HCT-116 cells.It is evidenced that the water-soluble yam polysaccharides have immunomodulatory activities, can restore the immune status of the immuno-suppressed mices; moreever, the water-soluble yam polysaccharides after colonic fermentation have desired anticancer activity to the(HCT-116 cells. |
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