Identification of Polyphenol-Specific Innate Epitopes That Originated from a Resveratrol Analogue

Abstract

Polyphenols have received a significant amount of attention in disease prevention because of their unique chemical and biological properties. However, the underlying molecular mechanism for their beneficial effects remains unclear. We have now identified a polyphenol as a source of innate epitopes detected in natural IgM and established a unique gain-of-function mechanism in the formation of innate epitopes by polyphenol via the polymerization of proteins. Upon incubation with bovine serum albumin (BSA) under physiological conditions, several polyphenols converted the protein into the innate epitopes recognized by the IgM Abs. Interestingly, piceatannol, a naturally occurring hydroxylated analogue of a red wine polyphenol, resveratrol, mediated the modification of BSA, whose polymerized form was specifically recognized by the IgMs. The piceatannol-mediated polymerization of the protein was associated with the formation of a lysine-derived cross-link, dehydrolysinonorleucine. In addition, an oxidatively deaminated product, α-aminoadipic semialdehyde, was detected as a potential precursor for the cross-link in the piceatannol-treated BSA, suggesting that the polymerization of the protein might be mediated by the oxidation of a lysine residue by piceatannol followed by a Schiff base reaction with the ε-amino group of an unoxidized lysine residue. The results of this study established a novel mechanism for the formation of innate epitopes by small dietary molecules and support the notion that many of the beneficial effects of polyphenols could be attributed, at least in part, to their lysyl oxidase-like activity. They also suggest that resveratrol may have beneficial effects on human health because of its conversion to piceatannol.

Oxidative deamination of lysine residues by polyphenols generates an equilibrium of aldehyde and 2-piperidinol products

“…Hence, to determine if oxidation products of Bt-APA function as an innate epitope, we fractionated the products obtained by incubating the lysine analog with ESM by HPLC, and the immunoreactivity of each fraction with natural IgM antibodies was evaluated. For this purpose, IgM mAb SBM3, showing specificity to the EGCG-modified proteins ( 17 ), established from specific pathogen-free–maintained BALB/c mice was used. The ELISA analysis of the HPLC fractions indicated that the antibody has an immunoreactivity with multiple fractions containing products I to III ( Fig.…”

“…Our previous study ( 16 ) showed that innate IgM antibodies recognized EGCG-treated proteins and speculated on the involvement of polyphenol-mediated electrical conversion of proteins in antibody recognition. Then, based on the discovery that protein polymerization is involved in the crossreactivity of polyphenol-derived epitopes with IgM, we provided the basis for the hypothesis that they may be due, at least in part, to polymerized proteins ( 17 ). However, despite these extensive research efforts on the identification of structural elements of modified proteins involved in recognition by natural antibodies, few studies have clearly shown the structure of the epitope.…”

“…In addition, we studied the polymerization of proteins mediated by piceatannol, a naturally occurring hydroxylated analog of a red wine polyphenol resveratrol, and found that the polymerization was associated with the formation of a lysine-derived crosslink, dehydrolysinonorleucine ( Fig. 1 C ) ( 17 ). More interestingly, we have shown that polyphenols, including EGCG, can be a source of innate epitopes recognized by natural immunoglobulin M (IgM) antibodies and suggested a possible mechanism by which the electronegativity of polyphenol-treated proteins might be involved in antibody recognition ( 16 , 17 ).…”

“…1 C ) ( 17 ). More interestingly, we have shown that polyphenols, including EGCG, can be a source of innate epitopes recognized by natural immunoglobulin M (IgM) antibodies and suggested a possible mechanism by which the electronegativity of polyphenol-treated proteins might be involved in antibody recognition ( 16 , 17 ). Despite these unique properties of polyphenol-treated proteins, the details of the underlying molecular mechanism for oxidative deamination by polyphenols remain unclear.…”

Hemp (Cannabis sativa L.) Seed Protein–EGCG Conjugates: Covalent Bonding and Functional Research

“…Free amino content groups in HPI were expected to decrease after covalent bonding with EGCG, because the amino acid residues bind to quinone after EGCG oxidation. The ε-amino group contained in lysine was oxidized to form a carbonyl group, and a condensation reaction occurred with the free amino groups, thus reducing the number of amino groups [ 29 ].…”