Characterization of squash polysaccharide and the anti-diabetic effect on type 2 diabetic rat revealed by urine metabolomics analysis

The present study reports the structural characteristics of three polysaccharide fractions (SPS-F1, SPS-F2 and SPS-F3) isolated and purified from squash. SPS-F1(Mw=12.30 kDa) and SPS-F2 (Mw=19.40 kDa) were likely to contain HG and RG-I domain of pectic polysaccharide, respectively. SPS-F2 (Mw=270.4 kDa) was mainly composed of rhamnose, galactose and arabinose. The treatment with SPS decreased body weight gain, glucose and TG levels in T2DM rats. Twenty-five differential metabolites were identified based on urinary metabolomics analysis, which are crucial to the anti-diabetic effect of SPS. The regulation of Nicotinamide N-oxide, Histamine, cis-Aconitate, Citrate, L-Malic acid, 3-(3-Hydroxyphenyl) propanoic acid and N-Acetyl-L-aspartic acid was mainly associated with energy metabolism, gut microbiota and inflammation. Study of surface plasmon resonance revealed the binding kinetics with galectin-3 (Gal-3) and fibroblast growth factor 2 (FGF2). The K_D value of SPS-F2 and SPS-F3 to Gal-3 are 4.97 × 10^-3 M and 1.48 × 10^-3 M, indicating a weak binding affinity. All three fractions showed moderate binding to FGF2 and the affinity was SPS-F3 > SPS-F2 > SPS-F1. Thus, the metabolomics and SPR approach were proved to be a promising tool in exploring the anti-diabetes effects of SPS and provided a deep understanding of the mechanisms.