Structural characterization of three acidic polysaccharides from Opuntia dillenii Haw. fruits and their protective effect against hydrogen peroxide-induced oxidative stress in Huh-7 cells

Three novel acidic polysaccharide fractions (OFPP-1, OFPP-2, OFPP-3) with different molecular weights (803.7, 555.1 and 414.5 kDa) were isolated from the peeled Opuntia dillenii Haw . fruits by alkali-extraction, graded alcohol precipitation and column chromatography. Structural analysis indicated that OFPPs were pectic polysaccharides consisting of rhamnose, arabinose and galactose residues. The backbone of OFPP-1 consisted of a repeating unit →6- α - D -Gal p A-(1→2)- α - L -Rha p -(1→ with T- α - D -Gal p A-(1→6)- α - D -Gal p A-(1→4)- α - D -Glc p- (1→, T- β - D -Xyl p -(1→6)- α - D -Gal p A-(1→4)- α - D -Glc p- (1→ or T- α - D -Gal p A-(1→3)- α - L -Ara f -(1→ as the side chains. The backbone of OFPP-2 consisted of a disaccharide repeating unit →2)- α - L -Rha p- (1→4)- β - D -Gal p A-(1→ with T- β - L -Ara f -(1→ as the branches substituted at the O-4 position of →2,4)- α - L -Rha p -(1→. Whereas the backbone of OFPP-3 was →2,4)- α - L -Rha p -(1→2)- α - L -Rha p -(1→3)- β - L -Ara f -(1→ or →2,4)- α - L -Rha p -(1→2)- α - L -Rha p -(1→4)- β - D -Gal p A-(1→, which was branched at the O-4 position of →2,4)- α - L -Rha p -(1→. Moreover, these 3 polysaccharide fractions could protect Huh-7 cells against H 2 O 2 -induced oxidative stress to different extents by decreasing the MDA content and increasing the SOD, CAT, GSH-Px activities and the GSH level in the Huh-7 cells. These results suggest that OFPPs have the potential to be used as natural antioxidants.