Structural characterization of three acidic polysaccharides from <i>Opuntia dillenii</i> Haw. fruits and their protective effect against hydrogen peroxide-induced oxidative stress in Huh-7 cells
Rui Liu, F.-F. Chu, Yan Zheng, Han-Qing Chen
Abstract
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 <em>Opuntia dillenii </em>Haw<em>. </em>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-<em>α</em>-<em>D</em>-Gal<em>p</em>A-(1→2)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→ with T-<em>α</em>-<em>D</em>-Gal<em>p</em>A-(1→6)-<em>α</em>-<em>D</em>-Gal<em>p</em>A-(1→4)-<em>α</em>-<em>D</em>-Glc<em>p-</em>(1→, T-<em>β</em>-<em>D</em>-Xyl<em>p</em>-(1→6)-<em>α</em>-<em>D</em>-Gal<em>p</em>A-(1→4)-<em>α</em>-<em>D</em>-Glc<em>p-</em>(1→ or T-<em>α</em>-<em>D</em>-Gal<em>p</em>A-(1→3)-<em>α</em>-<em>L</em>-Ara<em>f</em>-(1→ as the side chains. The backbone of OFPP-2 consisted of a disaccharide repeating unit →2)-<em>α</em>-<em>L</em>-Rha<em>p-</em>(1→4)-<em>β</em>-<em>D</em>-Gal<em>p</em>A-(1→ with T-<em>β</em>-<em>L</em>-Ara<em>f</em>-(1→ as the branches substituted at the <em>O</em>-4 position of →2,4)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→. Whereas the backbone of OFPP-3 was →2,4)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→2)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→3)-<em>β</em>-<em>L</em>-Ara<em>f</em>-(1→ or →2,4)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→2)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→4)-<em>β</em>-<em>D</em>-Gal<em>p</em>A-(1→, which was branched at the <em>O</em>-4 position of →2,4)-<em>α</em>-<em>L</em>-Rha<em>p</em>-(1→. Moreover, these three polysaccharide fractions could protect Huh-7 cells against H<sub>2</sub>O<sub>2</sub>-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.