In this study, five different kinds of polysaccharides (AAP1, AAP2, AAP3, AAP4, and AAP5) were extracted from different varieties of Auricularia auricula through an alkali extraction process. Furthermore, the crude polysaccharides were deproteinized by the Sevag method. Auricularia auricula produced in the Shanxi province had the highest content of polysaccharide, 53.02%. The monosaccharide composition was determined by the GC method. Their antioxidant capacities in vitro were assessed by radical-scavenging capacity (DPPH, superoxide, and hydroxyl radicals), metal chelating ability and reducing-power methods. In addition, the evaluation of their antioxidant effects in vivo was performed using the C. elegans model. The yield of crude polysaccharides, monosaccharide composition and antioxidant activity of Auricularia auricula polysaccharides (AAPs) were different among samples from various sources. Among them, the strongest antioxidant activity was shown for AAP1, consisting of arabinose, xylose, 2-deoxy-D-glucose, mannose, glucose, and N-acetyl-D-glucosamine with the molar ratio of 1 : 0.44 : 0.33 : 1.67 : 1 : 0.17. It could scavenge free radicals, up-regulate stress-resistance-related enzymes including superoxide dismutase (SOD) by 70.04 ± 8.75% and CAT by 117.32 ± 8.06% and reduce the level of reactive oxygen species (ROS) in C. elegans under oxidative stress. The present results suggested that variety was an important factor that affects the antioxidant activity of A. auricula polysaccharides.

Caenorhabditis elegans is an important model organism for studying stress response mechanisms and identifying genetic pathways that influence longevity. The present study was designed to explore the in vivo-antioxidant potential and the probable mechanism of acid hydrolysates prepared from A. auricula polysaccharides (AAPHs-F) with the optimal acid hydrolysis conditions using Box–Behnken design, and C. elegans was used as a model organism. The effects of AAPHs-F on the locomotory behavior, lifespan, activities of antioxidant-related enzymes and levels of antioxidants in C. elegans were studied. In addition, the potential of AAPHs-F in up-regulating the expression of antioxidant-related genes in C. elegans, such as daf-16, skn-1, sod-1, sod-2 and sir-2.1, and the inhibition of cell apoptosis of C. elegans were also discussed. The results indicated that AAPHs-F could significantly increase the U-Turn frequency of nematodes, extend their lifespan, enhance antioxidant systems including superoxide dismutase (SOD) by 70.60%, catalase (CAT) by 73.45% and glutathione reductase (GR) by 258.68% (p < 0.01), increase the level of glutathione (GSH) by 110.22% (p < 0.01), and decrease the level of reactive oxygen species (ROS) and malondialdehyde (MDA) by 31.86% and 46.16% (p < 0.01), respectively. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that AAPHs-F could up-regulate mRNA expression levels of daf-16, skn-1, sir, sod-1 and sod-2 in wild-type C. elegans (>1.3 fold) when treated at a concentration of 0.1 mg mL⁻¹ (p < 0.05 or p < 0.01). AAPHs-F was concluded to be heteropolysaccharides composed of mannose, glucose and galactose with a molar ratio of 12.7 : 3.25 : 1. The molecular weight of AAPHs-F was determined to be 885.37 Da. Furthermore, AAPHs-F is mainly formed of (1 → 3)-linked-α-D-glucopyranose, and carboxyl or acetamide is present in the molecule. In summary, our studies provide evidence that AAPHs-F helps improve the antioxidant defense system, and up-regulation of stress and longevity related genes suggests the possible involvement of these genes in the prevention of stress damage in C. elegans.