Structural characterization of Euglena gracilis polysaccharide and its in vitro hypoglycemic effects by alleviating insulin resistance

Guava polysaccharides attenuate high fat and STZ-induced hyperglycemia by regulating gut microbiota and arachidonic acid metabolism

This study investigated the hypoglycemic mechanism of guava polysaccharides (GP) through the gut microbiota (GM) and related metabolites. Our findings demonstrated that GP significantly mitigated high-fat diet- and streptozotocin-induced hyperglycemia, insulin resistance, hyperlipidemia, elevated alanine aminotransferase, high hepatic inflammation levels, and prevented pancreatic atrophy and hepatomegaly. Interestingly, the benefits of GP were attributed to alterations in the GM. GP decreased the ratio of Firmicutes to Bacteroidetes, significantly inhibiting deleterious bacteria, including Uncultured_f_Desulfovibrionaceae, Bilophila, and Desulfovibrio, while promoting the proliferation of probiotic Bifidobacterium and Bacteroides. In addition, GP promoted the generation of short-chain fatty acids. Notably, the arachidonic acid (AA) metabolism pathway was enriched in liver metabolites. GP significantly elevated hepatic AA and 15-hydroxyeicosatetraenoic acid, while reducing prostaglandin E2 and 5- and 12-hydroxyeicosatetraenoic acid. This modulation is accompanied by the downregulation of hepatic cyclooxygenase-1, 12-lipoxygenase, P38, and c-Jun N-terminal kinase mRNA expression, and the upregulation of cytochrome P4502J5 and insulin receptor substrate 1/2 mRNA expression. However, GP antibiotic treatment did not induce significant alterations in FBG and AA levels or gene expression. Overall, our findings suggest that the hypoglycemic effect of GP may be intricately linked to alterations in AA metabolism, which depends on the GM.

Identification and structural characterization of key prebiotic fraction of soluble dietary fiber from grapefruit peel sponge layer and its regulation effect on gut microbiota

In this study, the key prebiotic fraction of grapefruit peel sponge layer soluble dietary fiber (GSLSDF) was identified, and its structure characteristics and modulatory effect on intestinal microorganisms were investigated. Firstly, two fractions (GSLSDF-1 and GSLSDF-2) were isolated from GSLSDF, and the GSLSDF-1 showed a better prebiotic activity. Subsequently, GSLSDF-1 was found to have a low molecular weight and crystallinity, a loose and porous microstructure, and a high glucose content. Meanwhile, GSLSDF-1 was a dextran with a main chain linked by β-1, 4 glycosidic bonds and branched by a β-1, 6 glycosidic bonds. These structural characteristics were responsible for the favorable prebiotic activity of GSLSDF-1. Finally, the regulation effect of GSLSDF-1 on gut microbiota was analyzed in vitro fecal fermentation. Compared with the blank and GSLSDF groups, GSLSDF-1 could increase the relative abundances of Lactobacillus, Bacteroides, Bifidobacterium and Faecalibacterium coupled with decrease the relative abundances of Clostridium and Clostridioides. Furthermore, GSLSDF-1 promoted the production of short-chain fatty acids (SCFAs) by modulating the SCFAs synthesis pathway of intestinal microorganisms, while the NH3-N synthesis of intestinal microorganisms was inhibited by GSLSDF-1. Above results indicated that GSLSDF-1 was the key prebiotic fraction of GSLSDF, which could effectively optimize the intestinal microorganism composition.