Car@PLGA-NPs target gut microbiota-ER stress axis to combat diabetes

Background Previous studies have demonstrated that carvacrol (Car) ameliorates vascular and hepatic injury in db/db mice, but its low bioavailability limits clinical translation. Methods To address this, this study constructed carvacrol-loaded polymeric nanoparticles (Car@PLGA-NPs) to enhance carvacrol bioavailability and fully explore its novel mechanisms of action on islet function and gut homeostasis in a diabetic model. We used C57BL/6J db/db mice to measure serum fasting blood glucose, oral glucose tolerance (OGTT), insulin tolerance (ITT), and lipid profiles. Fecal samples were collected for 16S rRNA sequencing to analyze gut microbiota composition and its correlation with host indices. Pancreatic and intestinal tissues underwent histopathological staining, immunofluorescence, and Western blotting to detect endoplasmic reticulum (ER) stress-related protein expression levels (p-IRE1α, XBP1S, PERK, p-ElF2α). Results Results demonstrated that Car@PLGA-NPs, compared to free carvacrol, significantly improved insulin sensitivity, reduced fasting blood glucose, ameliorated dyslipidemia, attenuated inflammation, and mitigated oxidative stress in db/db mice. 16S rRNA sequencing revealed that Car@PLGA-NPs remodeled the gut microbiota composition, with Alloprevotella abundance showing a negative correlation with colonic ER stress proteins (p-IRE1α and p-ElF2α). Immunofluorescence and Western blotting further confirmed that Car@PLGA-NPs significantly suppressed the expression of ER stress-related proteins (p-IRE1α, XBP1S, PERK, p-ElF2α) in both islet and colonic tissues, demonstrating superior efficacy to free carvacrol. Conclusions Collectively, this study confirms that the PLGA nanocarrier effectively enhances carvacrol bioavailability. Car@PLGA-NPs improve islet function and intestinal homeostasis in diabetic mice by remodeling the gut microbiota and subsequently inhibiting ER stress in pancreatic and intestinal tissues, providing a novel nano-drug delivery system and a “microbiota-ER stress” regulatory axis for diabetes treatment.