Preparation Of Astragalus Polysaccharide Degradation Products And Their Anti-aging Effect

Aging and age-related health conditions are becoming increasingly serious,and thus how to slow aging has become a hot topic in biomedical field.Oxidative stress is closely associated with aging and related diseases,while increasing antioxidant capacity of aging body is considered an effective strategy to delay aging.Astragalus polysaccharide is previously shown to extend the lifespan of both wild-type and Huntington’s disease-like Caenorhabditis elegans models.Here we first attempted different methods to extract polysaccharides from Astragalus membranaceus and analyzed their physicochemical property and evaluated their antioxidant activity.Then hot water-extracted polysaccharide was used to prepare degradation products using different methods and reaction conditions,and the degradation products were separated by ultrafiltration based on molecular weights.The physicochemical properties of the degradation products and their ultrafiltration fractions were then analyzed,and their antioxidant and anti-aging activities were also investigated using C.elegans models.(1)Physicochemical properties and antioxidant activity of Astragalus polysaccharides obtained by different extraction methods.The polysaccharides were extracted from Astragalus membranaceus by hot water,acid(0.1 M HCl)-assisted and alkali(0.1 M Na OH)-assisted methods,and the yields were 2.0%,6.0% and 4.0%,respectively.Sugar content of the polysaccharide preparations was 51%,78% and 51%,respectively.The infrared characteristic absorption peaks of the polysaccharides were similar,and their monosaccharide compositions were arabinose,rhamnose,galacturonic acid,galactose and glucose but at different molar ratios.All the polysaccharides extracted by the three different methods showed DPPH and ABTS free radical scavenging ability,indicating their in vitro antioxidant activity.The polysaccharides were also shown to increase the survival rate of C.elegans under oxidative stress conditions induced by paraquat or tert-butyl hydroperoxide,demonstrating their in vivo antioxidant activity.(2)Preparation and physicochemical properties of Astragalus polysaccharide degradation products.Partial degradation of the hot water extracted Astragalus polysaccharide was attempted by enzymes and weak acids,and 0.5 M trifluoroacetic acid was used to degraded the polysaccharide at 95°C for 4 h.The polysaccharide degradation product obtained was then separated by ultrafiltration and fractions with molecular weights of <3 k Da,3-10 k Da and >10 k Da were collected,respectively.Similar infrared characteristic absorption peaks were found for all the ultrafiltration fractions,which were mainly composed of arabinose,rhamnose,galacturonic acid,galactose and glucose but at different molar ratios.(3)Antioxidant activity of Astragalus polysaccharide degradation products.The above degradation products and ultrafiltration fractions were shown to have in vitro antioxidant activity as demonstrated by DPPH and ABTS free radical scavenging assays.Further test using wild-type C.elegans revealed that the survival rate of C.elegans under oxidative stress was increased by the degradation products and ultrafiltration fractions,indicating their in vivo antioxidant activity.(4)Anti-aging effects of Astragalus polysaccharide degradation products.Further experiments using wild-type C.elegans showed that all the Astragalus polysaccharide degradation fractions were capable of extending lifespan and improving movement ability,including crawling speed,swimming speed and bending frequency,and feeding behavior of the nematodes was not affected by the degradation products.(5)Neuroprotective effect of Astragalus polysaccharide degradation products.Using chemo-avoidance assay in the Huntington’s disease-like polyglutamine C.elegans model HA759,the above Astragalus polysaccharide degradation fractions were found to improve the avoidance behavior of the nematodes in a hyperosmotic environment produced by glycerol,demonstrating their protection against polyglutamine-mediated neurotoxicity.In conclusion,the degradation products of Astragalus polysaccharides not only have in vitro as well as in vivo antioxidant activity but can also extend the lifespan of C.elegans.The degradation products are also shown to improve health indicators and have neuroprotective potential in the nematodes.These results provide an important basis for future studies on the structure-activity relationship of Astragalus polysaccharide and its bioactive oligosaccharide components.