Advanced Glycation Endproducts (AGEs) are a heterogeneous group of molecules produced from non-enzymatic glycation. Accumulation of AGEs in vivo plays an important role in the pathology of chronic human diseases including type-2 diabetes and Alzheimer's disease. Natural AGEs inhibitors such as the pomegranate (Punica granatum) fruit show great potential for the management of these diseases. Herein, we investigated the in vitro anti-glycation effects of a pomegranate fruit extract (PE), its phenolic constituents [punicalagin (PA), ellagic acid (EA) and gallic acid (GA)], and their in vivo derived colonic metabolites [urolithin A (UA) and urolithin B (UB)]. All of the samples showed anti-glycation activities and PE, PA, and EA were more potent inhibitors than the positive control, aminoguanidine. PE and the purified phenolics also exhibited carbonyl scavenger reactivity. Our study suggests that pomegranate may offer an attractive dietary strategy for the prevention and treatment of AGE-related diseases such as type-2 diabetes and Alzheimer's disease.

No abstract

Glucitol-core containing gallotannins (GCGs) are polyphenols containing galloyl groups attached to a 1,5-anhydro-D-glucitol core, which is uncommon among naturally occurring plant gallotannins. GCGs have only been isolated from maple (Acer) species, including the red maple (Acer rubrum), a medicinal plant which along with the sugar maple (Acer saccharum), are the major sources of the natural sweetener, maple syrup. GCGs are reported to show antioxidant, α-glucosidase inhibitory, and antidiabetic effects, but their antiglycating potential is unknown. Herein, the inhibitory effects of five GCGs (containing 1–4 galloyls) on the formation of advanced glycation end-products (AGEs) were evaluated by MALD-TOF mass spectroscopy, and the BSA-fructose, and G.K. peptide-ribose assays. The GCGs showed superior activities compared to the synthetic antiglycating agent, aminoguanidine (IC50 15.8–151.3 vs. > 300 μM) at the early, middle, and late stages of glycation. Circular dichroism data revealed that the GCGs were able to protect the secondary structure of BSA protein from glycation. The GCGs did not inhibit AGEs formation by the trapping of reactive carbonyl species, namely, methylglyoxal, but showed free radical scavenging activities in the DPPH assay. The free radical quenching properties of the GCGs was further confirmed by electron paramagnetic resonance spectroscopy using ginnalin A (contains 2 galloyls) as a representative GCG. In addition, this GCG chelated ferrous iron, an oxidative catalyst of AGEs formation, supporting a potential antioxidant mechanism of antiglycating activity for these polyphenols. Therefore, GCGs should be further investigated for their antidiabetic potential given their antioxidant, α-glucosidase inhibitory, and antiglycating properties.