Modulation of Glucose Metabolism Along the Intestine–Pancreas–Liver In Vitro Axis by Mulberry, Bilberry, and Black Currant Extracts: A Mechanistic Approach

Background: The regulation of glucose metabolism is contingent on a multifaceted interaction between intestinal absorption, pancreatic endocrine function, and the hepatic response to insulin. Axis disruption contributes to insulin resistance and type 2 diabetes. Methods: This study tested mulberry, bilberry, and black currant extracts individually and in combination in an integrated in vitro gut, pancreas, and liver model. The extracts were phytochemically characterised and tested at optimal concentrations selected through dose–response studies. Results: The combined treatment preserved and enhanced the intestinal barrier, as evidenced by increased tight-junction levels and reduced oxidative stress. In the pancreas, the combination significantly improved cell viability, enhanced insulin and C-peptide secretion, and increased glucokinase expression, indicating improved glucose-sensing function. In the liver, the combined treatment synergistically activated insulin signalling, increasing the expression of IRS1, GLUT2, AMPK, AKT, and PGC-1α. This resulted in increased glucose absorption, glycogen synthesis, and a marked reduction in extracellular glucose levels under hyperglycaemic conditions. The results show that combining mulberry, bilberry, and blackcurrant produces additive benefits for intestinal barrier integrity and synergistically modulates key elements of hepatic insulin signalling. Conclusions: These findings support a mechanistic rationale for exploring multi-targeted nutraceutical formulations as complementary approaches to modulating processes involved in glycaemic regulation.