Search

Pyrroloquinoline quinone (PQQ), a redox-active o-quinone found in various foods and mammalian tissues, has received an increasing amount of attention because of a number of health benefits that can be attributed to its ability to enhance mitochondrial biogenesis. However, its underlying molecular mechanism remains incompletely understood. We have now established that the exposure of mouse NIH/3T3 fibroblasts to a physiologically relevant concentration of PQQ significantly stimulates mitochondrial biogenesis. The exposure of NIH/3T3 cells to 10-100 nM PQQ for 48 h resulted in increased levels of Mitotracker staining, mitochondrial DNA content, and mitochondrially encoded cytochrome c oxidase subunit 1 (MTCO1) protein. Moreover, we observed that PQQ treatment induces deacetylation of the peroxisome proliferator-activated receptor-γ-coactivator 1α (PGC-1α) and facilitates its nuclear translocation and target gene expression but does not affect its protein levels, implying increased activity of the NAD + -dependent protein deacetylase sirtuin 1 (SIRT1). Indeed, treatment with a SIRT1 selective inhibitor, EX-527, hampered the ability of PQQ to stimulate PGC-1α-mediated mitochondrial biogenesis. We also found that the PQQ treatment caused a concentration-dependent increase in the cellular NAD + levels, but not the total NAD + and NADH levels. Our results suggest that PQQ-inducible mitochondrial biogenesis can be attributed to activation of the SIRT1/PGC-1α signaling pathway by enhancing cellular NAD + formation.

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.

A simple, practical, and rapid access to quinoxalin-2-ones 1 , 1,2,3,4-tetrahydroquinoxalines 2 , quinoxalines 3 , and quinoxalin-2(1 H )-ones 4 has been achieved, based on the copper-catalyzed quinoxalinone formation of 2-haloanilines and amino acids followed by their reduction and oxidation. The olfactory properties and lipid accumulation inhibitory activity in cultured hepatocytes of the quinoxaline derivatives were also evaluated., Competing Interests: The authors declare no competing financial interest.

Acrolein, a ubiquitous pollutant in the environment, is endogenously formed through oxidation reactions and is believed to be involved in cytopathological effects observed during oxidative stress. Acrolein exerts these effects because of its facile reactivity with biological materials, particularly proteins. In the present study, we quantitatively analyzed the acrolein-specific adducts generated during lipid peroxidation-modification of proteins and identified the acrolein adduct most abundantly generated in the in vitro oxidized low-density lipoproteins (LDL). Taking advantage of the fact that the acrolein-lysine adducts, N(ε)-(3-formyl-3,4-dehydropiperidino)lysine (FDP-lysine) and N(ε)-(3-methylpyridinium)lysine (MP-lysine), have stable core structures resistant to the acid hydrolysis condition of proteins, we examined the formation of these adducts in proteins using high performance liquid chromatography with online electrospray ionization tandem mass spectrometry. However, only MP-lysine was detected as a minor product in the iron/ascorbate-mediated oxidation of polyunsaturated fatty acids in the presence of proteins and in the oxidized low-density lipoproteins (LDL). However, using a reductive amination-based pyridylamination method, we analyzed the acrolein-specific adducts with a carbonyl functionality and found that acrolein modification of the protein produced a number of carbonylated amino acids, including an acrolein-histidine adduct. On the basis of the chemical and spectroscopic evidence, this adduct was identified as N(τ)-(3-propanal)histidine. More notably, N(τ)-(3-propanal)histidine appeared to be one of the major adducts generated in the oxidized LDL. These data suggest that acrolein generated during lipid peroxidation may primarily react with histidine residues of proteins to form N(τ)-(3-propanal)histidine.

The breakdown of collagenous networks with aging results in hypoactive changes in the skin. Accordingly, reviving stagnant collagen synthesis can help protect dermal homeostasis against aging. We searched for type I collagen biosynthesis-inducing substances in various foods using human dermal fibroblasts and found that cinnamon extract facilitates collagen biosynthesis. Cinnamon extract potently up-regulated both mRNA and protein expression levels of type I collagen without cytotoxicity. We identified cinnamaldehyde as a major active component promoting the expression of collagen by HPLC and NMR analysis. Since insulin-like growth factor-I (IGF-I) is the most potent stimulator of collagen biosynthesis in fibroblasts, we examined the effect of cinnamaldehyde on IGF-I signaling. Treatment with cinnamaldehyde significantly increased the phosphorylation levels of the IGF-I receptor and its downstream signaling molecules such as insulin receptor substrate-1 and Erk1/2 in an IGF-I-independent manner. These results suggested that cinnamon extract is useful in antiaging treatment of skin.

The oxidation of dietary polyphenols with a catechol structure leads to the formation of an o-quinone structure, which rapidly reacts with sulfhydryls such as glutathione and protein cysteine residues. This modification may be important for understanding the redox regulation of cell functions by polyphenols. In this study, to investigate the catechol modification of protein sulfhydryls, we used 3,4-dihydroxyphenyl acetic acid (DPA) as a model catechol compound and developed a new probe to directly detect protein modification by catechol type polyphenols using a biotinylated DPA (Bio-DPA). The oxidation-dependent electrophilic reactivity of DPA with peptide sulfhydryls was confirmed by both mass spectrometry and nuclear magnetic resonance spectroscopy. When RL34 cells were treated with Bio-DPA, the significant incorporation of Bio-DPA into a 40 kDa protein was observed by Western blot analysis. The band was identified by mass spectrometry as the cytoskeletal protein, beta-actin. This identification was confirmed by the pull-down assay with anti-beta-actin antibody. To examine the reactivity of the catechol type polyphenols, such as flavonoids, to endogenous beta-actin, RL34 cells were coexposed to Bio-DPA and the flavonoids quercetin, (-)-epicatechin, and (-)-epicatechin gallate. Upon exposure of the cells to Bio-DPA in the presence of the flavonoids, we observed a significant decrease in the DPA-modified beta-actin. These results indicate that beta-actin is one of the major targets of protein modification by catechol type polyphenols and that Bio-DPA is an useful probe for understanding the redox regulation by dietary polyphenols. Furthermore, Keap1, a scaffold protein to the actin cytoskeleton controlling cytoprotective enzyme genes, was also identified as another plausible target of the catechol type polyphenols by oxidative modification of the intracellular sulfhydryls. These results provide an alternative approach to understand that catechol type polyphenol is a potential modifier of redox-dependent cellular events through sulfhydryl modification.

Wheat can cause severe IgE-mediated systematic reactions, but knowledge on relevant wheat allergens at the molecular level is scanty. The aim of the present study was to achieve a more detailed and comprehensive characterization of the wheat allergens involved in food allergy to wheat using proteomic strategies, referred to as "allergenomics". Whole flour proteins were separated by two-dimensional gel electrophoresis with isoelectric focusing and lithium dodecyl sulfate-polyacrylamide gel electrophoresis. Then, IgE-binding proteins were detected by immunoblotting with sera of patients with a food allergy to wheat. After tryptic digestion, the peptides of IgE-binding proteins were analyzed by matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry. In this study, we identified four previously reported wheat allergens or their sequentially homologous proteins [serpin, alpha-amylase inhibitor, gamma-gliadin, and low molecular weight (LMW) glutenin] by a database search. As a result of the high resolution of two-dimensional gel electrophoresis, nine subunits of LMW glutenins were identified as the most predominant IgE-binding antigens. The two-dimensional allergen map can be beneficial in many ways. It could be used, for example, for precise diagnosis of wheat-allergic patients and assessment of wheat allergens in food. Additionally, we compared allergenomics to conventional biochemical methods and evaluated the usefulness of a proteomic strategy for identifying putative allergens to wheat allergy.

Dopamine (DA) is an unstable neurotransmitter that readily oxidizes to the DA quinone and forms reactive oxygen species, such as superoxide and hydrogen peroxide. The oxidized dopamine also forms thiol conjugates with sulfhydryl groups on cysteine, glutathione, and proteins. In the present study, we determined the redox potential of the protein-bound DA and established a novel mechanism for the oxidative modification of the protein, in which the DA-cysteine adduct generated in the DA-modified protein causes oxidative modification of the DA-bound protein in the presence of Cu2+. Exposure of a sulfhydryl enzyme, glyceraldehyde-3-phosphate dehydrogenase, to DA resulted in a significant loss of sulfhydryl groups and the formation of the DA-cysteine adduct. When the DA-modified protein was incubated with Cu2+, we observed aggregation and degradation of the DA-bound protein and concomitant formation of a protein carbonyl, a marker of an oxidatively modified protein. Furthermore, we analyzed the carbonyl products generated during the Cu2+-catalyzed oxidation of the DA-modified protein and revealed the production of glutamic and aminoadipic semialdehydes, consisting of the protein carbonyls generated. The cysteinyl-DA residue generated in the DA-modified protein was suggested to represent a redox-active adduct, based on the observations that the cysteinyl-DA adduct, 5-S-cysteinyldopamine, produced by the reaction of cysteine with DA, gave rise to the oxidative modification of bovine serum albumin in the presence of Cu2+. These data suggest that the DA-modified protein may be involved in redox alteration under oxidative stress, whereby DA covalently binds to cysteine residues, generating the redox-active cysteinyl-DA adduct that causes the metal-catalyzed oxidation of protein.

Alpha-aminoadipic semialdehyde (AAS) and gamma-glutamic semialdehyde (GGS) are identified as the major carbonyl products in oxidized proteins. To elucidate the formation pathway of AAS and GGS in vivo, we developed and validated a new quantification method. AAS and GGS in proteins were derivatized by reductive amination with NaCNBH(3) and p-aminobenzoic acid, a fluorescent reagent, followed by acid hydrolysis. It is noteworthy that the fluorescent derivatives were completely stable during acid hydrolysis. The present method permitted the specific, accurate, and sensitive quantification of both semialdehydes by fluorometric high-performance liquid chromatography. Analysis of proteins oxidized by various oxidation systems revealed that AAS and GGS are notably generated by the reaction of proteins with (*)OH, which is produced by metal-catalyzed oxidation (MCO). Furthermore, exposure of transferrin and human plasma to ascorbic acid and H(2)O(2) significantly promoted the formation of AAS and GGS in vitro, suggesting that both semialdehydes can be generated by MCO in vivo. We also demonstrated their generation through oxidative stress induced by acute iron overload in vivo. In this paper, we describe this analytical technique for simple and precise measurement of AAS and GGS and discuss their formation mechanism in vivo.

Oxidative deamination by various polyphenolic compounds is presumed to be due to the oxidative conversion of polyphenols to the corresponding quinones through autoxidation. Here we examined the oxidative deamination by the polyphenol-rich beverages green tea, black tea, and coffee at a physiological pH and temperature. Green tea, black tea, and coffee extracts oxidatively deaminated benzylamine and the lysine residues of bovine serum albumin to benzaldehyde and alpha-aminoadipic delta-semialdehyde residues, respectively, in sodium phosphate buffer (pH 7.4) at 37 degrees C in both the presence and absence of Cu2+, indicating the occurrence of an amine (lysyl) oxidase-like reaction. We also examined the effects of pH and metal ions on the reaction. The possible biological effects of drinking polyphenol-rich beverages on human are also discussed.