Structure and bioactivities of a glycan isolated from Fritillaria unibracteata.

Fritillaria unibracteata (F. unibracteata) has been used to treat respiratory diseases in traditional Chinese medicine. However, the therapeutic components of this treatment remain unclear due to the functions of polysaccharides have not been fully characterized. This study aimed to identify the bioactive polysaccharides in F. unibracteata (FUP). A notable characteristic of FUP is its high starch content. Therefore, crude polysaccharide FUP-C was hydrolyzed using amylase after hot water extraction and ethanol precipitation. Subsequently, liquid chromatographic purification yielded five polysaccharide fractions (FUP-1 to FUP-5). The active components were screened using in vitro antioxidant and macrophage inflammatory models. FUP-1 showed greater antioxidative and anti-inflammatory activities. Further characterization revealed that FUP-1 was predominantly composed of glucose (90.69%) and had a molecular weight of 7.1 kDa. Its structure consists of →4)-α-Glcp-(1 → as the backbone, whereas the →4,6)-α-Glcp-(1 → and →3,6)-β-Glcp-(1 → form the branches. The anti-inflammatory effects of FUP-1, as evidenced by its suppression of NO, TNF-α, and IL-6, were further supported by findings from the zebrafish model, which demonstrated that FUP-1 dose-dependently suppressed ROS generation, mitigated oxidative damage, and attenuated inflammatory responses. Furthermore, the efficacy of FUP-1 exceeded that of FUP-C suggesting that it is the bioactive component of F. unibracteata. This study provides a molecular explanation for the traditional efficacy of F. unibracteata, thereby laying a chemical foundation for exploring its potential biological activities and medicinal value.