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The incidence of diseases associated with a high sugar diet has increased in the past years, and numerous studies have focused on the effect of high sugar intake on obesity and metabolic syndrome. However, how a high sugar diet influences gut homeostasis is still poorly understood. In this study, we used Drosophila melanogaster as a model organism and supplemented a culture medium with 1 M sucrose to create a high sugar condition. Our results indicate that a high sugar diet promoted differentiation of intestinal stem cells through upregulation of the JNK pathway and downregulation of the JAK/STAT pathway. Moreover, the number of commensal bacteria decreased in the high sugar group. Our data suggests that the high caloric diet disrupts gut homeostasis and highlights Drosophila as an ideal model system to explore gastrointestinal disease.

Purpose Retinal-derived fluorophores that accumulate as RPE lipofuscin are implicated in pathological mechanisms of AMD. One component of RPE lipofuscin has been characterized as pdA2E, a pyridinium adduct derived from all-trans-retinal and excess ethanolamine. One-step preparation and biosynthetic studies of pdA2E and its novel isomer called isopdA2E are reported. Methods Biosynthetic reaction mixtures, RPE/choroids and neural retinas dissected from bovines, eyes harvested from Abca4(-/-)Rdh8(-/-) mice, irradiated samples, and enzyme-treated solutions were analyzed by HPLC, mass spectrometry, nuclear magnetic resonance spectroscopy, fluorescence spectrophotometry, and density functional theory (DFT). Results Optimization of the in vitro synthesis of pdA2E resulted in a biomimetic preparation of this pigment in a yield of 15%; this protocol also allowed the identification of isopdA2E, a double-bond isomer of pdA2E at the C13C14 position in bovine RPE lipofuscin. Interconversion between these two molecules occurs when either pdA2E or isopdA2E is exposed to light. A phospholipase D-based assay demonstrated the possibility of pdA2-PE being formed in neural retina and served as a precursor of pdA2E in the biosynthetic pathway. DFT calculations revealed that the 492-nm absorbance was assigned to the long arm of pdA2E/isopdA2E and the 340/342-nm absorbance to the short arm. Fluorescence efficiency of pdA2E and isopdA2E is very similar, but is much weaker in comparison with A2E, isoA2E, and iisoA2E. Conclusions Our results facilitate the understanding of compositions and biosynthetic pathways of adverse RPE lipofuscin.

Toxic lipofuscin in the RPE (retinal pigment epithelium) is implicated in blindness in AMD (age-related macular degeneration) or recessive Stargardt's disease patients. In the present study, we identified a novel fluorescent lipofuscin component in human and bovine RPEs. Using 1D and 2D NMR and MS, we confirmed the structure of this pigment and called it pdA2E. It exhibits absorbance maxima at 492 and 342 nm, and is susceptible to photocatalytic isomerization and oxidation. This fluorophore was also detected in the eyecup extracts of Abca4−/−Rdh8−/− (Abca4 encodes ATP-binding cassette transporter 4 and Rdh8 encodes retinol dehydrogenase 8) mice, an AMD/recessive Stargardt's disease model. Excess amassing of pdA2E within RPE cells caused significant cell viability loss and membrane damage. The formation of pdA2E occurred when atRAL (all-trans-retinal) reacted with excess ethanolamine in the absence of acetic acid, and the process is likely to involve the participation of three atRAL molecules. Our findings suggest that endogenous pdA2E may serve as a sensitizer for yielding singlet oxygen and a singlet oxygen quencher, as well as a by-product of retinal metabolism, and its complete characterization facilitates the understanding of biosynthetic pathways by which adverse RPE lipofuscin constituents form.