Structural characterization of polysaccharides from Geranium sanguineum L. and their immunomodulatory effects in response to inflammatory agents

Abstract

Ethnopharmacological relevance: Geranium sanguineum L. is used for treatment of inflammations, anemia, malignant diseases of the blood-forming organs, diarrhea, respiratory infections, etc. Only flavonoids in root extracts have been elucidated as immunostimulating and anti-inflammatory compounds, and polysaccharides in the herb have not been examined.

Aim of the study: to compare the chemical features of polysaccharide complexes (PSCs) from leaves (GSL-PSC) and roots (GSR-PSC) of G. sanguineum, as well as their immunomodulatory activities on leukocytes after inflammation, and effects on the growth of different bacteria.

Materials and methods: The samples were isolated by water extraction and their structural features were studied by 2D NMR spectroscopy. The stimulatory effects of both PSCs on human leukocytes were analyzed with flow cytometry. Their suppressive activities on the oxidative burst in blood and derived neutrophils against opsonized zymosan and phorbol myristate acetate were investigated. The effects of the samples on viability, NO and interleukin 6 (IL-6) syntheses in RAW264.7 cells after inflammation with lipopolysaccharides (LPS) were tested. The prebiotic and anti-biofilm activities of the PSCs were evaluated.

Results: The total carbohydrate content in the samples was significant (73.6-76.8%). GSL-PSC contained pectins, which were rich in homogalacturonan (HG), and smaller amounts of rhamnogalacturonan (RG) type I, decorated by 1,5-α-L-Araf, 1,4- and 1,6-β-D-Galp chains. GSR-PSC contained starch, followed by pectins with lower HG content and more RG-I regions, substituted by 1 → 3,5-α-L-arabinans and 1 → 3,6-β-D-galactans. GSL-PSC and GSR-PSC (200 μg/mL) increased monocyte and granulocyte cell counts, but GSR-PSC also elevated T helper and B cell levels in a normal and activated state. GSR-PSC triggered a dose-dependent (50-200 μg/mL) oxidative burst in blood, but alleviated it after inflammation even in blood-derived neutrophils. It was free of LPS, and activated NO and IL-6 productions in RAW264.7 cells better than GSL-PSC, without affecting their viability. Both PSCs (2.0%, w/v) stimulated probiotic co-cultures between Clostridium beijerinckii strains and Lactobacillus sp. ZK9, and inhibited the growth and biofilm formation of Escherichia coli, Streptococcus mutans and Salmonella enterica.

Conclusions: The PSs in G. sanguineum could be involved in the stimulatory effects on blood-forming organs and anti-inflammatory action of aqueous root extracts in case of infections. These PSs should be included in synbiotic foods to support the treatment of inflammations and infections in the gut.

Keywords: Geranium sanguineum; Immunomodulatory activity; Inflammation; Interleukin 6; Lactose (PubChem CID: 6134); Lipopolysaccharide; Nitric oxide (PubChem CID: 145068); Pectic polysaccharide; Phorbol 12-myristate 13-acetate (PubChem CID: 27924); Polysaccharides; Probiotic bacteria; Starch; Structural analysis; Zymosan.