Structure characterization of one polysaccharide from Lepidium meyenii Walp., and its antioxidant activity and protective effect against H2O2-induced injury RAW264.7 cells

Lepidium meyeniiWalp. (Maca) belonging to the Brassicaceae is a perennial herbaceous plant native to South America, it grows under low temperature and high altitude varying between 3700 and 4450 m. Maca, as a food source, possesses high nutritive value and is rich in starches, proteins, minerals and sugars. Modern pharmacological research showed that maca had many pharmacological activities simultaneously, such as antifatigue, anti-inflammation, enhancing fertility, antioxidative, antiosteoporosis and antidepression. Polysaccharide, macaenes, macamides, alkaloid, flavonolignans and glucosinolates had been identified as major active ingredients. Studies on the structural characterization and antioxidant activity of polysaccharide obtained from maca roots or leaves have become a hotspot in recent years. Maca polysaccharide was a kind of heteropolysaccharide, mainly consisting of arabinose (Ara), glucose (Glc), galactose (Gal) and manose (Man) with different molar ratio, the molecular weights ranged from 6 × 103 to 1.1 × 106 Da, and the glycosyl patterns of maca polysaccharide were T-α-Glc, 1, 3-α-Glc, 1, 3-β-Glc, 1, 4-α-Glc, 1, 6-α-Glc, 1, 4, 6-α-Glc, T-β-Ara, 1, 5-α-Ara, T-α-Man, 1, 3-α-Man, 1, 2, 6-α-Man, 1, 3-β-GalpA and 1, 6-β-Gal. The antioxidant activities of maca polysaccharides were evaluated based on in vitro assays, such as the DPPH assay, superoxide radical assay, hydroxyl radical assay, reducing power assay and ferric-reducing antioxidant power assay. The in vivo experiments were carried out on forced swimming mice model and alcoholic liver oxidative injury mice model. Maca polysaccharide structure characterization was mainly focused on molecular weight, glycosyl pattern and monosaccharide composition, but a few studies have been reported on the maca polysaccharides glycosyl sequence. Antioxidant property of polysaccharides produced by maca was determined by several chemical based antioxidant activity assays which do not necessarily reflect the cellular physiological conditions, bioavailability and metabolism. Experiments with animal models are extremely expensive, time-consuming and inappropriate for initial antioxidant screening of food materials. Excess reactive oxygen species (ROS) will lead to oxidative damage to biomacromolecules and finally damage organ function. The process is especially obvious in the immune cells, which exert their biological functions by free radicals and sustain senescent deterioration that related to oxygen stress. The antioxidant activity of maca purified polysaccharide against oxidative stress-induced immune cell injury has not been reported.