Chemical characterization and complement modulating activities of an arabinogalactan-protein-rich fraction from an aqueous extract of avocado leaves.

The aim of this study was to chemically characterize an arabinogalactan-protein-rich fraction (FRAGP) obtained from an aqueous extract of avocado leaves and investigate its effects on the classical pathway of the complement system. The FRAGP contained 4.6% ± 1.8%, 22.5% ± 4.9%, and 76.7% ± 8.8% of total protein, arabinogalactan-protein, and carbohydrates, respectively. Arabinose and galactose were the main monosaccharide constituents. FT-IR and NMR data, together with linkage analyses, indicated the presence of a structure that included a (1 → 3)-linked β-D-Galp main chain, mainly substituted at O-6 by Gal and Ara residues, which was characteristic of a type II arabinogalactan. The effect of FRAGP on the classical pathway of complement system was examined by a hemolytic fixation test and comparing with heparin, which was used as a control for inhibition. With pre-incubation, the IC50 of FRAGP was 1.90 ± 1.1 μg/mL, which was similar to that of heparin (IC50 = 2.90 ± 0.3 μg/mL). Without pre-incubation, the IC50 values were 18.6 ± 3.7 and 8.0 ± 4.1 μg/mL for FRAGP and heparin, respectively. Collectively, these results suggested that FRAGP has an inhibitory effect on the classical pathway of the complement system.