Isolation, characterisation and complement fixation activity of acidic polysaccharides from Argemone mexicana used as antimalarials in Mali

Abstract

Context Global studies on Argemone mexicana L. (Papaveraceae) traditionally used against malaria in Mali are limited to its low-mass compounds activities, and little information on its bioactive polysaccharides is available. Objective This study determines the structure and the immunomodulatory activity of polysaccharides from aerial parts of A. mexicana . Materials and methods Acidic polysaccharides from this plant material named HMAmA1 and HMAmA2 were isolated from water extracts. Their monosaccharide composition was determined by gas chromatography. Glycosidic linkages were determined using GC-MS. NMR was also applied. The polymers were tested for effects on the human complement system in vitro at different doses. Results The monosaccharide composition showed that the two polysaccharides contained in different amounts the following monomers: arabinose, rhamnose, galactose, and galacturonic acid. Overall structural analysis showed the presence of a low ratio of 1,2-linked rhamnose compared to 1,4-linked galacturonic acid with arabinogalactans substituted on position 4 of rhamnose. NMR data showed the presence of galacturonans alternated by rhamnogalacturonans bearing arabinose and galactose units. α-Linkages were found for l -arabinose, l -rhamnose and d -galacturonic acid, while β-linkages were found for d -galactose. The two polysaccharides exhibited strong complement fixation activities, with HMAmA1 being the highest potent fraction. ICH 50 value of HMAmA1 was 5 µg/mL, compared to the control BPII being 15.9 µg/mL. Discussion and conclusions Polysaccharides form A. mexicana presented a complement fixation effect. The complement system is an important part of the immune defense, and compounds acting on the cascade are of interest. Therefore, these polymers may be useful as immunodulatory agents.

Bioactive polysaccharides in different plant parts of Aconitum carmichaelii

“…It was noticed that the first SEC fractions showed the highest complement fixation activity, and they are mainly composed of T‐, 1,5‐ and 1,3,5‐linked Ara f , and/or T‐, 1,3‐ and 1,3,6‐linked Gal p in addition to a HG linear chain. This is consistent with previous conclusions for pectic polysaccharides from various medicinal plants, that arabinans and AG‐II moieties are important to attach to human complement 43‐45 . Earlier studies also concluded that pectic polysaccharides with higher Mw had much more potent complement fixation activity, 46 which matched with our primary finding that the second SEC fractions with lower Mw (41.6–105 kDa) were shown to be inactive (Fig.…”

“…This is consistent with previous conclusions for pectic polysaccharides from various medicinal plants, that arabinans and AG-II moieties are important to attach to human complement. [43][44][45] Earlier studies also concluded that pectic polysaccharides with higher Mw had much more potent complement fixation activity, 46 which matched with our primary finding that the second SEC fractions with lower Mw (41.6-105 kDa) were shown to be inactive (Fig. 5).…”