Molecular Mechanism of Lotus Seedpod Oligomeric Procyanidins Inhibiting the Absorption of Oligopeptide-Advanced Glycation End Products.

Research on advanced glycation end product (AGEs) inhibition has generally focused on food processing, but many protein-AGEs will still be taken. Oligopeptide (OLP)-AGEs, as the main form after digestion, will damage human health once absorbed. Here, we investigated the ability of lotus seedpod oligomeric procyanidins (LSOPC) to inhibit the absorption of the OLP-AGEs and elucidated the underlying mechanism. Our results showed that the inhibition rate of LSOPC on the absorption of OLP-AGEs was about 50 ± 5.38%. 0.1, 0.2, and 0.3 mg/mL could upregulate the expression of ZO-1 and downregulate the expression of PepT1 and clathrin. Molecular docking showed that LSOPC could compete with the binding of OLP-AGEs to PepT1 and AP-2, thus inhibiting the absorption of OLP-AGEs. Furthermore, the interaction of LSOPC with the OLP-AGEs reduced the surface hydrophobicity of OLP-AGEs. It altered the secondary structure of the OLP-AGEs, thus weakening the affinity of the OLP-AGEs to the transporter protein to inhibit the absorption of OLP-AGEs. Together, our data revealed potential mechanisms by which LSOPC inhibit the absorption of OLP-AGEs and opened up new perspectives on the application of LSOPC in reducing the increasing health risks posed by OLP-AGEs.

Protective mechanism of fruit vinegar polyphenols against AGEs-induced Caco-2 cell damage.

Accumulation of advanced glycation end products (AGEs) is linked with development or aggravation of many degenerative processes or disorders. Fruit vinegars are rich in polyphenols that can be a good dietary source of AGEs inhibitors. In this study, eight kinds of vinegars were prepared. Among them, the highest polyphenol and flavonoid content were orange vinegar and kiwi fruit vinegar, respectively. Ferulic acid, vanillic acid, chlorogenic acid, p-coumaric acid, caffeic acid, catechin, and epicatechin were main polyphenols in eight fruit vinegars. Then, we measured the inhibitory effect of eight fruit vinegars on fluorescent AGEs, and found that orange vinegar had the highest inhibitory rate. Data here suggested that orange vinegar and its main components catechin, epicatechin, and p-coumaric acid could effectively reduce the level of ROS, RAGE, NADPH and inflammatory factors in Caco-2 cells. Our research provided theoretical basis for the application of orange vinegar as AGEs inhibitor.

Role of glycated proteins in vivo: Enzymatic glycated proteins and non-enzymatic glycated proteins.

Glycated protein is a kind of substance that often exists in the human body through the combination of sugar and protein under enzyme or non-enzyme conditions. Enzyme-catalyzed glycated proteins are widely distributed in the human body and participate in life activities such as human growth and immune regulation. Non-enzymatic glycated protein is often related to cancer, aging, diabetes and other diseases, but in vitro non-enzymatic glycated protein has utility value after modification. This review not only discussed the effects of enzymatic glycated protein on human intestinal health, immune regulation and cancer prevention. The inhibition methods of non-enzymatic glycated protein in food processing, digestion, absorption and metabolism were also elucidated.

Comparative study of the inhibitory effects of lotus seedpod oligomeric procyanidins on dietary AGE released from glycated casein during digestion.

Glycation of protein results in the formation of advanced glycation end-products (AGEs), which are further absorbed by the body through digestion in the gastrointestinal tract. The inhibitory properties of procyanidin for the release of AGEs from glycated proteins are of great significance in promoting, accelerating or stabilizing gastrointestinal folding intermediates, although the mechanism of action remains unclear. With the background of dairy processing, the study investigated the inhibitory effect of lotus seedpod oligomeric procyanidins (LSOPC) and its three monomers on AGE release from glycated casein (G-CS) during gastrointestinal digestion. In gastrointestinal microenvironments, multispectral and microscopy analysis were used to investigate interaction mechanisms. Results showed that the binding force of the protein-procyanidin complexes were hydrogen bonding and hydrophobic interaction and LSOPC leaded the G-CS secondary structure transformations furtherly. In the gastric environment, all monomers displayed stronger binding to pepsin but in the intestinal environment, results were opposite. Molecular docking showed that procyanidins were bound in the internal cavity of G-CS, pepsin and pancreatin, thereby forming a relatively stable binding conformation. Moreover, procyanidins enhanced the antioxidant capacity of G-CS, which could attenuate postprandial oxidative stress in the gastrointestinal tract caused by the release of AGEs. Together, this study improves our understanding of dietary AGEs during gastrointestinal digestion.

Catechin Inhibits the Release of Advanced Glycation End Products during Glycated Bovine Serum Albumin Digestion and Corresponding Mechanisms In Vitro.

Glycated proteins are the main source of dietary advanced glycation end products (AGEs). Glycated proteins are enzymatically hydrolyzed in the gastrointestinal tract, which releases more absorbable and smaller potentially harmful AGEs. This study investigated the inhibitory effect of catechin on AGE release from glycated bovine serum albumin (G-BSA) during gastrointestinal digestion. Catechin inhibited AGE release during gastrointestinal digestion, especially in the gastric digestion stage. Additionally, catechin altered these peptides in the small intestine by reducing G-BSA digestibility. The proposed mechanism involves interactions between catechin and G-BSA/digestive enzymes, inhibiting digestive enzyme activity and changing the conformation of G-BSA. Catechin reduced G-BSA ß-sheet content and protected the helical conformation. Moreover, catechin enhanced the antioxidant capacity of G-BSA, which could attenuate postprandial oxidative stress in the gastrointestinal tract caused by the release of AGEs. This study improves our understanding of the nutritional and health effects of catechin on dietary AGEs during gastrointestinal digestion.