Structural characterization of a polysaccharide from Coreopsis tinctoria Nutt. and its function to modify myeloid derived suppressor cells

Coreopsis tinctoria Nutt. (C. tinctoria) is a natural plant with many health benefits, such as clearing heat and toxic materials. In this study, we investigate the effect of a polysaccharide from C. tinctoria, aiming at improving the tumor microenvironment, which is associated with non-resolving inflammation. Through combining ion-exchange and gel permeation chromatography, a polysaccharide named CTAP-3 is purified from the crude polysaccharides of C. tinctoria. The structure of CTAP-3 is characterized through high-performance gel permeation chromatography, chemical derivative analyses, GC-MS, FT-IR, and NMR. Results reveal that CTAP-3 consists of predominant amounts (87.2%) of galacturonic acid (GalA) residues, small amounts of arabinose (Ara) and rhamnose (Rham), and trace amounts of galactose (Gal). CTAP-3 is deduced to be native pectin-type polysaccharide containing a homo-galacturanan backbone consisting of α-(1 → 4)-linked GalAp and methyl-esterified α-(1 → 4)-linked GalAp residues in the ratio of 4:1. When myeloid-derived suppressor cells (MDSCs) are treated by CTAP-3, its suppressive effect on T cell proliferation is impaired. This result indicates that CTAP-3 is a candidate drug for improving the tumor microenvironment.