Antioxidant and anti-diabetic effects of Auricularia auricular polysaccharides and their degradation by artificial gastrointestinal digestion - Bioactivity of Auricularia auricular polysaccharides and their hydrolysates.

BACKGROUND: Auricularia auricular polysaccharides (AAPs) derived from the dried fruit body of A. auricular are valuable compounds with many bioactivities. This research aimed to investigate the antioxidant and anti- diabetic activities of these polysaccharides and their artificial gastrointestinal fluid hydrolysates (AAPHs).

METHODS: Artificially simulated gastrointestinal fluid was used to obtain polysaccharide-de- rived fragments, and a rat model of type 2 diabetes mellitus (T2DM) using a high-fat diet and low-dose streptozotocin (STZ) was established to assess their antioxidant and anti-diabetic effects.

RESULTS: It was found that AAPs and AAPHs were both heteropolysaccharides and were comprised of arab- inose, xylose, mannose, 2-deoxy-glucose, glucose and glucosamine, but at different mole ratios. AAPHs was purified by Sephadex G-100 chromatography to produce three fractions, namely, AAPHs1, AAPHs2, and AAPHs3. The molecular weights of these three fractions were 320, 169, and 62 kDa respectively. Both AAPs and AAPHs exhibited the evident ability to enhance the activities of antioxidant enzymes and the level of GSH, while increasing the content of liver glycogen and plasma C-peptide compared with the diabetic model group (p < 0.05). Furthermore, AAPHs could cause a marked improvement in glucose-stimulated GLP-1 secretion from 0 min to 30 min (p < 0.05).

CONCLUSIONS: The possible mechanism was that AAPHs could partly restore the STZ-induced impairment of GLP-1 secretion, and inhibit the oxidative stress pathway, and thereby alleviate the progression of diabetes. This data demonstrated that the molecular mole ratio and molecular weight had a definite effect on antioxi- dant and anti-diabetic activities.