Polysaccharide from Ribes nigrum L. Ameliorates Diabetic Kidney Injury in Mice by Modulating the GUDCA/GPBAR1 Axis through the Remodeling of the Gut Microbiota

Diabetic nephropathy (DN) is a major microvascular complication of diabetes, requiring effective therapies. This study showed polysaccharide from Ribes nigrum L. (blackcurrant polysaccharides (BCP)) exerted therapeutic effects in high-fat diet/streptozotocin-induced diabetic mice, improving glucose homeostasis and alleviating renal inflammation and fibrosis. 16S rRNA sequencing revealed BCP altered gut microbiota and notably enriched Akkermansia muciniphila, which was validated via fecal microbiota transplantation and exogenous A. muciniphila administration. Combined 16S rRNA sequencing and metabolomic analysis identified a positive correlation between A. muciniphila and glycoursodeoxycholic acid (GUDCA). Exogenous A. muciniphila supplementation significantly increased the level of serum GUDCA in DN mice. Elevated GUDCA activated the bile acid receptor GPBAR1 in the kidney, suppressing NF-κB/NLRP3 inflammasome and TGF-β-mediated fibrosis. BCP improves renal outcomes by regulating bile acid metabolism through gut microbiota modulation, supporting its potential as a novel dietary strategy for DN.