Native and chemically modified polysaccharides from Opuntia ficus-indica (l.) Mill. cladodes: Chemical characterization and complement fixating properties

Introduction: Opuntia ficus-indica (L.) Mill. is a cactus species rich in bioactive compounds, particularly pectic polysaccharides from cladode mucilage, with relevant biological activities. Objective: This study aimed to characterize native and chemically modified polysaccharide fractions (carboxy-reduced and sulfated) from O. ficus-indica cladodes and evaluate their in vitro effects on the classical pathway of the human complement system. Methodology: Chemical composition was determined by spectrophotometric assays (uronic acids, acetyl, and sulfate groups), gas chromatography (neutral monosaccharides), and HPAEC-PAD (uronic acids). Molecular weight and homogeneity were evaluated by HPSEC-RI-MALLS, and arabinogalactan-proteins (AGPs) were analyzed by radial gel diffusion. Structural characterization was performed using infrared spectroscopy and NMR. Complement activity was assessed by hemolytic microassay, determining IC50 values for inhibition of sensitized sheep erythrocyte lysis. Commercial pectic acid (CPA) and heparin were used as references. Results: The native fraction (NP-OFI) showed a highly branched pectin-like structure (Mw 8.6 × 106 g/mol), rich in arabinose, xylose, galactose, uronic acids, and AGPs, and activated the classical pathway (IC50 = 209 µg/mL). In contrast, the carboxy-reduced fraction (CP-OFI) and CPA were inactive, indicating that linear structures lacking side chains do not modulate complement activity. The sulfated fraction (SP-OFI) strongly inhibited complement activation (IC50 = 1.4–1.7 µg/mL), showing higher activity than heparin (IC50 = 23 µg/mL). Conclusion: Complement modulation by Opuntia polysaccharides depends on structural features. While branching and AGPs are associated with activation, sulfation is the key determinant of strong inhibitory activity, highlighting their potential for developing complement-targeting biomolecules.