Structure characterization of polysaccharide isolated from Ribes nigrum L. and it's bioactivity against gout

Gout mainly caused by the increase of uric acid level in serum poses a threat to human health. Inhibition on the activity of xanthine oxidase (XOD) usually an effective method for treating gout, so finding XOD inhibitors without side effects is crucial. In this study, two heteropolysaccharides were extracted from blackcurrant by microwave-assisted aqueous two-phase technology, and the top phase (PRNP-1) and bottom phase (PRNP-2) polysaccharides at high purity (>86%) were obtained after column chromatography separation. Methylation and NMR analyses confirmed the potential structural backbone of PRNP-1 may be composed of →3)-α-L-Araf-(1 → 3)-β-D-Galp-(1 → 4)-β-D-Manp-(1 → 5)-α-Araf-(1 → 4)-α-D-GalpA-(1 → 3,6)-β-D-Glup-(1→, while PRNP-2 exhibited a differing repeating unit of →4)-β-D-Manp-(1 → 3)-α-D-Araf-(1 → 3)-β-D-Galp-(1 → 5)-α-Araf-(1 → 4)-α-D-GalpA-(1 → 3,6)-β-D-Glup-(1→. Compared to PRNP-1 (4.87 × 10⁴ kDa), PRNP-2 with low molecular weight (2.30 × 10⁴ kDa) exhibited better dispersivity, homogeneity, water solubility and thermal stability, as well as XOD inhibitory activity. Both PRNP-1 and PRNP-2 demonstrated a competitive, reversible inhibition towards XOD and quenched its fluorescence through forming polysaccharide-XOD complexes. Molecular docking and molecular dynamics simulation assays revealed that PRNP-2 exhibited a better binding capacity with XOD than PRNP-1. PRNPs markedly decreased the serum concentration of uric acid and creatinine, and XOD activity in hyperuricemia mice model. Therefore, PRNPs may be the potential natural therapeutic agents for the treatment of gout.