| Porphyra haitanensis, distributes naturally in intertidal zone of Fujian,Guangdong and Zhejiang provinces coast areas. Porphyra is not only an important economic alga, but also has been used traditionally to treat nephritic and urinary diseases etc. The previous work carried out in our lab showed that the water-soluble polysaccharide from Porphyra haitanensis (porphyran) has a favorable effect on antiaging. Molecular weight is reported to be an important factor to the bioactivity of polysaccharide. In this dissertation, studies were concentrated on degradation of seaweed polysaccharide, and its influences on antiaging activities of different molecular weight porphyran.Porphyran (P) was degraded by ascorbate and hydrogen peroxide, imitated the scissions of polysaccharides undergo in the walls of living plant cells. The reaction is mainly affected by the ratios and concentrations of the two reagents. Different molecular weight porphyrans in terms of P1, P2, P3, P4 and P5 were achieved by the degradation method, and their molecular size are 50, 30, 13, 8.2, 2.7 kD, respectively. P1, P2 and P3 are coincident with P in infrared absorptions which indicated that the structural units composing the polysaccharide were not modified in the degradation. However, carboxylic absorption was observed in P4 and P5.The five porphyrans were investigated about their effect on eliminating free radical, T/B-cell proliferation, antifatigue, prolonging lifespan and anti-Alzheimer disease to examine the influence of molecular weight on antiaging effect of porphyrans.The antioxidant activities of five degraded porphyrans and natural porphyran in vitro were investigated by chemical spectrometric methods. The results proved that they have different antioxidant activity. Degraded products are less effective on scavenging superoxide anion than natural porphyran and almost lose the chelating effect. Degraded products are similar with natural porphyran on scavenging hydroxyl radical. But they are more effective on scavenging 1, 1-diphenyl-2-picrylhydrazyl (DPPH·) radicals and reducing power and the effects are increased with decreasing the molecular weight. Among them, P4 is the most effective on scavenging 1, 1-diphenyl-2-picrylhydrazyl (DPPH·) radicals and P5 possesses the most pronounced reducing power.The immunoregulatory effects on T/B-cell proliferation of five degraded products and natural porphyrans proved that they can evidently facilitate T-cell proliferation and inhibit B-cell proliferation. The effects of P2 and P4 activated stronger than other products and P.The antifatigue effects of P1, P2, P4 and P were evaluated on mice. Degraded products were more effective than P. P1, P2 and P4 can improve the content of liver glycogen and prolong the time to fatigue.The effects of P1, P2, P4 and P on the lifespan and vitality were evaluated in Drosophila melanogaster. Molecular weights influence the effect of porphyran on lifespan and vitality favorably. It seems that P1 and P2 are more effective in the normal metabolism; they had significant prolonging effects on lifespans of both genders and vitality than P. And in the heat stress station, P4 treatment showed pronouncedly longer survival time.The effects of P1 on Aβ1-40 induced cognitive deficits were evaluated in mice. P1 treatment significantly ameliorated the cognitive deficits; moreover, the choline acetyltransferas (ChAT) was significantly higher in P1 supplement groups than in the only Aβ-injection groups. Aβtoxicity is viewed as a pathogeny of AD. Thus the effect of P1 on neurotoxicty induced by aged Aβ25-35 was evaluated. In SHSY-5Y cells, treatment with 20μM of aged Aβ25-35 resulted in a significant inhibition of MTT reduction. Incubation with the mixture of Aβ25-35 and 10 mM P1 remarkably attenuated Aβ-induced inhibition of MTT reduction. However, the toxicity effect of Aβ25-35 was significantly reinforced when the concentration of P1 was increased to 80μM.Consequently, molecular weight affects the bioactivities significantly. In vitro, lower molecular weight polysaccharides are more effective in antioxidant and immunoregulaory effect. However, in vivo, P1 treatment is more effective in antifatigue, prolonging lifespan, improving vitality and ameliorated the cognitive deficits. The difference of activities in vitro and in vivo needs further research. |
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