Comprehensive structural characterization of pectin, arabinan and galactan from Gentiana purpurea L. roots and their immunostimulatory effects

The roots of Gentiana purpurea L. have historically been an important herbal drug in Norwegian folk medicine. Due to its content of bitter compounds, it was used to treat digestive ailments, but it was also boiled in water for use against infections. Previous work has shown promising immunostimulatory effects of a polysaccharide enriched fraction from G. purpurea, and therefore the aim of this present study was to further isolate and characterize these polysaccharides and investigate their immunogenic properties. One acidic polysaccharide fraction (GP-AP) and one neutral (GP-NP) were isolated by anion-exchange chromatography from the ethanol precipitate of G. purpurea root water extract, and their structures were characterized by SEC-MALS, GC, GC-MS and NMR. GP-AP was shown to contain pectin type structures such as homogalacturonan and rhamnogalacturonan type I backbones, as well as neutral structures such as arabinogalactan type I and highly branched arabinans. GP-NP had similar neutral polysaccharides as GP-AP, with high amounts of highly branched arabinans. GP-AP was able to cause an immunostimulatory response in DS2C/1 cells, partly through interaction with TLR 4, whilst GP-NP was inactive.