Abstract: Enzymatic hydrolysis and ultrasonic method were used for polysaccharides extraction from Dendrobium officinale. The optimum extraction conditions of polysaccharides from Dendrobium officinale were determined by single factor and orthogonal experiments with material-liquid ratio, ultrasonic time, and enzyme concentration. High performance liquid chromatography (HPLC) was used for analyzing the composition of Dendrobium officinale polysaccharides. Coumarin-3-carboxylic acid (CCA) fluorescence method was employed for the antioxidant activity determination of Dendrobium officinale polysaccharides. Methyl thiazolyl tetrazolium (MTT) and cell flow cytometry experiments were employed for investigating the inhibition effect of polysaccharides for SH-SY5Y apoptosis which induced by hydroxyl radical. The results showed that the optimum extraction conditions were as follows: the ratio of material to liquid was 1:100, the ultrasonic time was 2 hours, the amount of complex enzymes (cellulase and pectinase mixed equally) was 50 %, and the yield of polysaccharides was 25.69 %. The main monosaccharide composition of Dendrobium officinale polysaccharides is mannose and glucose. At the concentration rang of Dendrobium officinale polysaccharides was from 20 to 80 ug/mL, they can effectively scavenge the hydroxyl radicals produced by Cu2+ catalyzing hydrogen peroxide and effectively inhibit the apoptosis of SH-SY5Y cells (the apoptotic rate decreased from 56.95 % to 17.97 %). The cell apoptosis inhibition effect of the polysaccharides is concentration-dependent. Therefore, Dendrobium officinale polysaccharides can inhibit SH-SY5Y cell apoptosis induced by hydroxyl radicals, which produced by Cu2+ catalyzed hydrogen peroxide reaction.

Key words: dendrobium officinale polysaccharide, extraction, hydroxyl radical, SH-SY5Y cell