Fructose Promotes Oxidative Stress, Sphingolipid Remodelling and Transient Intestinal Barrier Dysfunction in Differentiated Caco-2 Cells

Abstract

Background/Objectives: High dietary fructose consumption has been linked to impaired intestinal barrier function and several metabolic disorders. Although oxidative stress has been proposed as a mediator of fructose-related epithelial injury, the involvement of tight-junction (TJ) proteins and sphingolipid metabolism is still not fully defined. Here, differentiated Caco-2 monolayers were exposed to fructose (1–50 mM) to examine changes in epithelial barrier integrity and associated molecular responses. Methods: Cell viability, transepithelial electrical resistance (TEER), reactive oxygen species (ROS), intracellular reduced and oxidized glutathione (GSH/GSSG) ratio, nitrites as an indirect assessment of nitric oxide (NO) production, TJ protein level (ZO-1, JAM-A and occludin), sphingolipid profile by UHPLC-QTOF-MS, and expression of the ceramide synthases CERS2 and CERS6 were evaluated. Results: Fructose did not affect cell viability but induced a rapid, concentration-dependent increase in ROS generation, an early reduction in the GSH/GSSG ratio, and increased nitrites production. The observed alterations were concurrent with a temporary reduction in TEER, which returned to control levels at subsequent time points. Fructose selectively reduced JAM-A and ZO-1 protein expression, whereas occludin remained unaffected. Lipidomic analysis revealed sphingolipid remodelling, characterised by increased ceramide species and reduced sphingomyelins, while gene expression analysis showed downregulation of CERS2, with CERS6 remaining unchanged. The altered sphingolipid profile mainly involved long- and very-long-chain ceramides, suggesting a possible link between altered membrane lipid homeostasis and barrier dysfunction. Conclusions: Fructose exposure transiently compromises intestinal epithelial barrier function and is associated with oxidative stress, changes in TJ proteins, and sphingolipid remodelling. These preliminary findings identify sphingolipid remodelling as a candidate contributor to fructose-induced intestinal barrier dysfunction, warranting confirmation through dedicated mechanistic follow-up studies.