Sei-Young Lim

Introduction Polyphenols, the most diverse group of phytochemicals, have attracted a great deal of attention as potential chemopreventive agents for chronic diseases, such as heart disease, cancer, diabetes, stroke, and arteriosclerosis. Polyphenols are generally considered antioxidants. However, because they are susceptible to oxidation, they are easily converted into their oxidized form. Interestingly, some polyphenols, when oxidized, acquire a new function of reactivity with proteins ( Fig. 1 ).

Lysine N-pyrrolation, a posttranslational modification, which converts lysine residues to Nε-pyrrole-L-lysine, imparts electronegative properties to proteins, causing them to mimic DNA. Apolipoprotein E (apoE) has been identified as a soluble receptor for pyrrolated proteins (pyrP), and accelerated lysine N-pyrrolation has been observed in apoE-deficient (apoE−/−) hyperlipidemic mice.

Abstract Polyphenols, especially catechol-type polyphenols, exhibit lysyl oxidase-like activity and mediate oxidative deamination of lysine residues in proteins. Previous studies have shown that polyphenol-mediated oxidative deamination of lysine residues can be associated with altered electrical properties of proteins and increased cross-reactivity with natural IgM antibodies. This interaction suggested that oxidized proteins could act as innate antigens and elicit an innate immune response.