The Idoma people are indigenous to the middle belt region in North Central Nigeria and they possess a rich history and tradition of using medicinal plants in the management of various ailments. Oral transmission is the primary method by which history is passed from one generation to another. The present study involved an ethnomedical survey done with the aid of questionnaires and it covered Otukpo Local Government Area of Benue State which is the headquarters of the Idoma speaking areas of the State. The information obtained showed that over a hundred species of plants from several families were identified and these were being used to manage a wide range of ailments from dysentery and gonorrhea to asthma and pneumonia. The scientific names and the part of the plant used together with their mode of preparation and dosage regimen were also reported. The importance of this kind of documentation was also discussed as it will help to preserve the rich cultural heritage of the tribe and could also serve as a basis for further research on the documented plants and aid in global bio-conservation efforts.
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.
Medicinal plants used against malaria in Mali have previously been tested for their antiplasmodial activities using their organic solvent and water extracts. As the healers mainly use the water extracts for their treatments of malaria-patients, our aim was to study the water-soluble components from Malian plants used for treatment of malaria. Argemone mexicana (aerial parts), Sarcocephalus latifolius (root bark), Vitex doniana (leaves), and Malarial-5 ® (an improved traditional medicine (ITM) in tea) were the objects of our studies. Water extracts of these plants contained primarily polysaccharides. Due to this, the studies focused on the determination of the monosaccharide composition of the polymers present as well as assessing the immunomodulatory properties of the polysaccharide fractions isolated from these plants. Each plant material was extracted sequentially with dichloromethane, 80% ethanol and water at 100°C. The polysaccharides were obtained using gel filtration of the aqueous extracts and their monosaccharide compositions were determined using gas chromatography. Immunomodulatory effects were assessed using the complement fixation test and macrophage stimulation. All aqueous extracts from the four samples contained polysaccharides. The monosaccharide compositions vary between the plants. Arabinose, rhamnose, galactose, glucose and galacturonic acid were present in all samples, glucose being the main monomer. These polysaccharides showed complement fixing activity and induced nitrite oxide release from macrophages in a dose dependent manner. The polysaccharide fractions of A. mexicana (Am1) and V. doniana (Vd1) showed the most potent activities. These two fractions had an ICH 50 of 2.4 and 6.3 μg/mL respectively in the complement fixation assay. The same two fractions induced a dose dependent release of nitrite oxide from macrophages. The results demonstrated that antimalarial plants contain polysaccharides with immunomodulatory properties. This preliminary work constitutes a new approach of antimalarial studies.
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