Selenized polysaccharides from Pteridium aquilinum: Fractionation, characterization, activities in vitro and...

The effects of selenium (Se) modifications on the structural characteristics and biological activities of Pteridium aquilinum polysaccharides (PAPs) were investigated. Two derivatives, SePAP1 and SePAP2 (SePAP1-2), with Se contents of 7035.48 ± 148.497 and 13,505.26 ± 103.138 μg/g, respectively, were prepared. PAP, SePAP1, and SePAP2 were primarily composed of rhamnose (Rha), mannose (Man), glucose (Glu), galactose (Gal), and arabinose (Ara), with mole ratios of 0.281:0.128:1.171:4.966:1.126, 0.499:0.288:4.183:0.771:2.694, and 0.568:0.316:2.701:0.8497:2.862, respectively. The UV-vis, FT-IR, XPS, SEM, and EDS revealed that Se conjugated with PAP successfully. SePAP1-2 demonstrated significantly enhanced antioxidant capacity, immunomodulatory properties, and α-glucosidase inhibitory activity compared to the original PAP. Notably, a positive relationship was observed between Se content and the majority of these bioactivities. To guide accurate application, SePAP1-2 was separated into three fractions with varying molecular weight ranges. The 100-300 kDa or <300 kDa fraction exhibited stronger antioxidant properties, whereas the >300 kDa fraction displayed superior immunomodulatory and α-glucosidase inhibitory activities. For the mechanism study, these polysaccharides suppressed α-glucosidase activity through a mixed inhibition pattern. PAP quenched the fluorescence of α-glucosidase in a dynamic mechanism, whereas SePAP1 and SePAP2 exhibited mixed quenching styles, highlighting that the introduction of Se might alter the action mechanism. The western blot demonstrated that SePAP1-2 displayed a stronger immune activation effect than PAP by upregulating the phosphorylation levels of ERK1/2, JNK, p38, and p65 in the macrophages. These findings suggested the PAP could be developed into a health food supplement by selenylation modification.