4-Oxo-2(E)-nonenal (ONE),

LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1) is an endothelial scavenger receptor that is important for the uptake of OxLDL (oxidized low-density lipoprotein) and contributes to the pathogenesis of atherosclerosis. However, the precise structural motifs of OxLDL that are recognized by LOX-1 are unknown. In the present study, we have identified products of lipid peroxidation of OxLDL that serve as ligands for LOX-1. We used CHO (Chinese-hamster ovary) cells that stably express LOX-1 to evaluate the ability of BSA modified by lipid peroxidation to compete with AcLDL (acetylated low-density lipoprotein). We found that HNE (4-hydroxy-2-nonenal)-modified proteins most potently inhibited the uptake of AcLDL. On the basis of the findings that HNE-modified BSA and oxidation of LDL resulted in the formation of HNE-histidine Michael adducts, we examined whether the HNE-histidine adducts could serve as ligands for LOX-1. The authentic HNE-histidine adduct inhibited the uptake of AcLDL in a dose-dependent manner. Furthermore, we found the interaction of LOX-1 with the HNE-histidine adduct to have a dissociation constant of 1.22×10(-8) M using a surface plasmon resonance assay. Finally, we showed that the HNE-histidine adduct stimulated the formation of reactive oxygen species and activated extracellular-signal-regulated kinase 1/2 and NF-κB (nuclear factor κB) in HAECs (human aortic endothelial cells); these signals initiate endothelial dysfunction and lead to atherosclerosis. The present study provides intriguing insights into the molecular details of LOX-1 recognition of OxLDL.

␣,␤-Unsaturated aldehydes generated during lipid peroxidation, such as 4-oxoalkenals and 4-hydroxyalkenals, can give rise to protein degeneration in a variety of pathological states. Although the covalent modification of proteins by these end products has been well studied, the reactivity of unstable intermediates possessing a hydroperoxy group, such as 4-hydroperoxy-2-nonenal (HPNE), with protein has received little attention. We have now established a unique protein modification in which the 4-hydroperoxy group of HPNE is involved in the formation of structurally unusual lysine adducts. In addition, we showed that one of the HPNE-specific lysine adducts constitutes the epitope of a monoclonal antibody raised against the HPNEmodified protein. Upon incubation with bovine serum albumin, HPNE preferentially reacted with the lysine residues. By employing N ␣ -benzoylglycyl-lysine, we detected two major products containing one HPNE molecule per peptide. Based on the chemical and spectroscopic evidence, the products were identified to be the N ␣ -benzoylglycyl derivatives of N ⑀ -4-hydroxynonanoic acid-lysine and N ⑀ -4-hydroxy-(2Z)-nonenoyllysine, both of which are suggested to be formed through mechanisms in which the initial HPNE-lysine adducts undergo Baeyer-Villiger-like reactions proceeding through an intramolecular oxidation catalyzed by the hydroperoxy group. On the other hand, using an HPNE-modified protein as the immunogen, we raised a monoclonal antibody against the HPNE-modified protein and identified one of the HPNE-specific lysine adducts, N ⑀ -4-hydroxynonanoic acid-lysine, as an intrinsic epitope of the monoclonal antibody. Furthermore, we demonstrated that the HPNE-specific epitopes were produced not only in the oxidized low density lipoprotein in vitro but also in the atherosclerotic lesions. These results indicated that HPNE is not just an intermediate but also a reactive molecule that could covalently modify proteins in biological systems.

4-Oxo-2-nonenal (ONE), an aldehyde originating from the peroxidation of omega6 polyunsaturated fatty acids, preferentially reacts with the cysteine residues of protein. Despite the fact that there has been significant recent interest in the protein reactivity and biological activity of ONE, the structural basis of the ONE-cysteine adducts remain to be established. In the present study, to gain a structural insight into the sulfhydryl modification by ONE, we characterized reaction products that originated from the initial ONE-cysteine Michael adducts. N-Acetyl-L-cysteine (10 mM) was incubated with an equimolar concentration of ONE in 0.1 M phosphate buffer (pH 7.4) at 37 degrees C. Within 1 h of incubation, the reaction of N-acetyl-L-cysteine with ONE resulted in the formation of two (C-2 and C-3) Michael addition products possessing a carbonyl functionality. Subsequent incubation of the reaction mixture resulted in their disappearance and concomitant formation of advanced reaction products, including a minor product III and major products IVa, IVb, and V. Product III was identified to be a thiomorpholine derivative, 4-acetyl-5-hydroxyl-6-(2-oxoheptyl)thiomorpholine-3-carboxylic acid, which might have originated from the C-2 Michael addition product. The major products were identified to be the novel 2-cyclopentenone derivatives, that is, 2-(acetylamino)-3-[(3-butyl-4-oxocyclopent-2-en-1-yl)sulfanyl]propionic acid (IVa and its isomer IVb) and 2-(acetylamino)-3-[(4-butyl-5-oxocyclopent-3-en-1-yl)sulfanyl]propionic acid (V), which might be generated through the base-catalyzed cyclization of the C-2 and C-3 Michael addition products, respectively. The furan derivative, which has been reported as the end product of the Michael adducts, was found to be formed only under acidic conditions. Thus, this study identified the novel ONE-cysteine adducts, including the most prominent 2-cyclopentenone derivatives, that originated from the initial Michael adducts.

We isolated a new ellagitannin, davicratinic acid A (5), together with four known ellagitannins, davidiin (1), granatin A (2), pedunculagin (3), and 3-O-galloylgranatin A (4), from an aqueous acetone extract of dried Davidia involucrata leaves. The known ellagitannins were identified based on spectroscopic data. The structure of davicratinic acid A (5), a monomeric ellagitannin possessing a unique, skew-boat glucopyranose core, was established based on spectroscopic data. Additionally, we examined the effects of several tannins with good yields from this plant on drug-resistant bacteria and human oral squamous cell carcinomas, and found that davidiin (1) exhibited the most potent antibacterial and antitumor properties among the tannins examined.