The Effect of Free and Protein‐Bound Maillard Reaction Products N‐ε‐Carboxymethyllysine, N‐ε‐Fructosyllysine, and Pyrraline on Nrf2 and NFκB in HCT 116 Cells

Abstract

ScopeMaillard reaction products (MRPs) are believed to interact with the receptor for advanced glycation endproducts (RAGE) and lead to a pro‐inflammatory cellular response. The structural basis for this interaction is scarcely understood. This study investigates the effect of individual lysine modifications in free form or bound to casein on human colon cancer cells.Methods and resultsSelectively glycated casein containing either protein‐bound N‐ε‐carboxymethyllysine (CML), N‐ε‐fructosyllysine (FL), or pyrraline is prepared and up to 94%, 97%, and 61% of lysine modification could be attributed to CML, FL, or pyrraline, respectively. HCT 116 cells are treated with free CML, pyrraline, FL, or modified casein for 24 h. Native casein is used as control. Intracellular MRP content is analyzed by UPLC‐MS/MS. Microscopic analysis of the transcription factors shows no activation of NFκB by free or protein‐bound FL or CML, whereas casein containing protein‐bound pyrraline activates Nrf2. RAGE expression is not influenced by free or casein‐bound MRPs. Activation of Nrf2 by pyrraline‐modified casein is confirmed by analyzing Nrf2 target proteins NAD(P)H dehydrogenase (quinone 1) (NQO1) and heme oxygenase‐1 (HO‐1).ConclusionStudies on the biological effects of glycated proteins require an individual consideration of defined structures. General statements on the effect of “AGEs” in biological systems are scientifically unsound.

Comparative Study of the Effects of Dietary-Free and -Bound Nε-Carboxymethyllysine on Gut Microbiota and Intestinal Barrier

“…Additionally, although we chose the bioactive marker of AGEs, CML, to study its effects on gut microbiota and intestinal barrier, due to the complex variety and origin of AGEs, the specific active ingredients of AGEs might cause different biological effects. For example, Raupbach et al 65 found that free or protein-bound CML did not activate NFκB and Nrf2 in human colon cancer cells (HCT 116 cells), whereas casein-bound pyrraline activated Nrf2, and RAGE expression was not affected by free or casein-bound CML or pyrraline. However, Mastrocola et al 45 demonstrated that a diet enriched with MG-H1-modified casein (formed by mixing 10% solution of sodium caseinate with MGO and heating for 4 h) decreased SCFA-producing bacteria, increased RAGE expression in the ileum, and induced metabolic derangements.…”