Methylglyoxal functions as Hill oxidant and stimulates the photoreduction of O(2) at photosystem I: a symptom of plant diabetes

We elucidated the metabolism of methylglyoxal (MG) in chloroplasts of higher plants. Spinach chloroplasts showed MG-dependent NADPH oxidation because of aldo-keto reductase (AKR) activity. K(m) for MG and V(max) of AKR activity were 6.5 mm and 3.3 μmol NADPH (mg Chl)(-1) h(-1) , respectively. Addition of MG to illuminated chloroplasts induced photochemical quenching (Qp) of Chl fluorescence, indicating that MG stimulated photosynthetic electron transport (PET). Furthermore, MG enhanced the light-dependent uptake of O(2) into chloroplasts. After illumination of chloroplasts, accumulation of H(2) O(2) was observed. K(m) for MG and V(max) of O(2) uptake were about 100 μm and 200 μmol O(2) (mg Chl)(-1) h(-1) , respectively. MG-dependent O(2) uptake was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). Under anaerobic conditions, the Qp of Chl fluorescence was suppressed. These results indicate that MG was reduced as a Hill oxidant by the photosystem I (PSI), and that O(2) was reduced to O(2) (-) by the reduced MG. In other words, MG produced in chloroplasts is preferentially reduced by PSI rather than through AKR. This triggers a type of oxidative stress that may be referred to as 'plant diabetes', because it ultimately originates from a common metabolite of the primary pathways of sugar anabolism and catabolism.     

Evaluation of urinary biomarkers of oxidative/nitrosative stress in adolescents and adults with Down syndrome

Urinary biomarkers of oxidative stress have been little studied in adults with Down syndrome (DS), usually no more than two biomarkers have been measured in the population studied and controversial results are reported in literature. Thus, we aimed to assess a set of oxidative and nitrosative stress biomarkers in urine samples of adolescents and adults with DS, with and without hypothyroidism, which comprise: 8-hydroxy-2′-deoxyguanosine (8-OHdG), isoprostane 15-F_2t-IsoP, thiobarbituric acid-reacting substances (TBARS), advanced glycation end products (AGEs), dityrosine (diTyr), hydrogen peroxide (H₂O₂) and nitrite/nitrate (NOx). Fluorimetric and spectrophotometric assays were performed in DS (n = 78), some of them taking levothyroxine for hypothyroidism (n = 24), and in their healthy age-matched controls (n = 65). We found that levels of AGEs, diTyr, H₂O₂ and NOx are increased in DS patients in any or in all age groups, whereas Cr levels were lower in DS than in controls in all age groups. Besides, correlations with age in DS were positive for diTyr and negative for Cr, TBARS, 15-F_2t-IsoP and NOx. We also found lower levels of Cr from 15 to 19 years, higher levels of TBARS and AGEs from 20 to 40 years and higher levels of diTyr from 15 to 40 years in DS patients receiving levothyroxine than in DS without hypothyroidism diagnosed. We conclude that AGEs, diTyr, H₂O₂ and NOx could be used as oxidative stress biomarkers in DS in contrast to 8-OHdG, 15-F_2t-IsoP and TBARS, at least with the methods used. However, renal impairment could occur in DS and Cr adjustment may bias the results, particularly in hypothyroid patients.     

Solution structure of the soluble receptor for advanced glycation end products (sRAGE)

The receptor for advanced glycation end products (RAGE) is a multiligand cell surface receptor involved in various human diseases, as it binds to numerous molecules and proteins that modulate the activity of other proteins. Elucidating the three-dimensional structure of this receptor is therefore most important for understanding its function during activation and cellular signaling. The major alternative splice product of RAGE comprises its extracellular region that occurs as a soluble protein (sRAGE). Although the structures of sRAGE domains were available, their assembly into the functional full-length protein remained unknown. We observed that the protein has concentration-dependent oligomerization behavior, and this is also mediated by the presence of Ca(2+) ions. Moreover, using synchrotron small angle x-ray scattering, the solution structure of human sRAGE was determined in the monomeric and dimeric forms. The model for the monomer displays a J-like shape, whereas the dimer is formed through the association of the two N-terminal domains and has an elongated structure. These results provide insights into the assembly of the RAGE homodimer, which is essential for signal transduction, and the sRAGE:RAGE heterodimer that leads to blockage of the receptor signaling, paving the way for the design of therapeutic strategies for a large number of different pathologies.     

Hypochlorous acid generates N epsilon-(carboxymethyl)lysine from Amadori products

Since the accumulation of N^ε-(carboxymethyl)lysine (CML), a major antigenic advanced glycation end product, is implicated in tissue disorders in hyperglycemia and inflammation, the identification of the pathway of CML formation will provide important information regarding the development of potential therapeutic strategies for these complications. The present study was designed to measure the effect of hypochlorous acid (HOCl) on CML formation from Amadori products. The incubation of glycated human serum albumin (glycated-HSA), a model of Amadori products, with HOCl led to CML formation, and an increasing HOCl concentration and decreasing pH, which mimics the formation of these products in inflammatory lesions. CML formation was also observed when glycated-HSA was incubated with activated neutrophils, and was completely inhibited in the presence of an HOCl scavenger. These data demonstrated that HOCl-mediated CML formation from Amadori products plays a role in CML formation and tissue damage at sites of inflammation.     

Association study of AGER gene polymorphism and hypertension in Han Chinese population

Background

Advanced glycation end products (AGEs) are produced by non-enzymatic glycation or glycoxidation of proteins, lipids and nucleic acids. The bond of AGEs and the receptor of AGE (AGER) in a pro-oxidant environment could induce immune and inflammation reaction involved in progress of microvascular disease. Accumulated evidence warrant further study on AGE–AGER pathway and genetic susceptibility to hypertension (HT).

Methods

We designed a two-stage association study to evaluate the association of AGER polymorphism and HT. In stage 1, seven tagSNPs were tested in 524 cases and 531 controls and the significant SNPs (P < 0.05) would enter into stage 2 including 807 cases and 869 controls. Furthermore, joint analysis was performed for all 2731 subjects including 1331 cases and 1400 controls, and meta-analysis was applied to evaluate combined estimations from the subgroups of stage 1 and stage 2.

Results

In stage 1, rs204994 had significant association with HT (P < 0.05) and enter stage 2. Neither joint analysis nor meta-analysis found statistical association of rs204994 with HT after adjusted for the covariates in the whole population. However, further stratification analysis found that rs204994 was significantly associated with HT in < 50 years and ≥ 50 years groups, ORs (95%CI) of dominant model were 1.623 (1.054–2.500) and 0.721 (0.546–0.952) respectively. No significant correlation was found between blood pressure and the polymorphisms of rs204994.

Conclusions

Our data suggests that age might modulate the genetic effects of variation of rs204994 in AGER on HT and further replications in other populations and functional studies should be warranted.     

Aldose-reductase- and protein-glycation-inhibitory principles from the whole plant of Duchesnea chrysantha

Ellagic acid (1), 3,3'-di-O-methylellagic acid (2), 3,3',4-tri-O-methylellagic acid (3), isovitexin (4), kaempferol 3-O-beta-D-glucuronide methyl ester (5), quercetin 3-O-alpha-L-arabinopyranosyl-(1-->6)-beta-D-galactopyranoside (6), ursolic acid, pomolic acid, tormentic acid, euscaphic acid, euscaphic acid 28-O-beta-D-glucopyranoside, and maslinic acid were isolated from the AcOEt- and BuOH-soluble MeOH extract of Duchesnea chrysantha (whole plant). The isolates were subjected to in vitro bioassays to evaluate their inhibitory activity on rat-lens aldose reductase (RLAR) and formation of advanced glycation end products (AGEs). The ellagic acids and flavonoids, compounds 1-6, exhibited moderate inhibitory effects on RLAR. However, compounds 1 and 4-6 showed excellent inhibitory activities towards the formation of AGEs. This is the first report that 4 and 6 exhibit inhibitory activity towards AR and AGEs formation.     

Effects of Compounds Isolated from the Fruits of Rumex japonicus on the Protein Glycation

An anthraquinone, emodin ( 1 ), and five flavonoids, kaempferol‐3‐O‐β‐D ‐glucoside ( 2 ), quercetin ( 3 ), quercitrin ( 4 ), isoquercitrin ( 5 ), and (+)‐catechin ( 6 ), were isolated from an AcOEt‐soluble extract of the fruits of Rumex japonicus. Their structures were determined by spectroscopic data interpretation. All the isolates were evaluated for their potential to inhibit AGEs (advanced glycation end products) formation and AGEs cross‐linking, and to break already formed AGEs cross‐links.     

糖化终末产物对大肠杆菌增殖与粘附的影响

糖化终末产物(AGEs)具有广泛的致病作用,但对细菌的生物学特性有何影响尚未见报道.通过倾注培养计数菌落数、E.coli K12β-半乳糖苷酶活性测定和计数E.coli K12粘附尿道上皮细胞的数目等,观察了培养液中加入不同浓度AGEs,对E.coli K12增殖与粘附的影响.与对照组相比,实验组平板中菌落数明显增多,E.coli K12β半乳糖苷酶活性明显升高,尿道上皮细胞粘附的细菌数显著增多,并随AGEs的浓度增高而增加.表明AGEs能够促进E.coli K12增殖,增强E.coli K12对尿道上皮细胞粘附的能力.结果提示AGEs可能对E.coli K12致病过程中有一定的促进作用.     

Hypochlorous acid generates Nε-(carboxymethyl)lysine from Amadori products

Since the accumulation of N^ε-(carboxymethyl)lysine (CML), a major antigenic advanced glycation end product, is implicated in tissue disorders in hyperglycemia and inflammation, the identification of the pathway of CML formation will provide important information regarding the development of potential therapeutic strategies for these complications. The present study was designed to measure the effect of hypochlorous acid (HOCl) on CML formation from Amadori products. The incubation of glycated human serum albumin (glycated-HSA), a model of Amadori products, with HOCl led to CML formation, and an increasing HOCl concentration and decreasing pH, which mimics the formation of these products in inflammatory lesions. CML formation was also observed when glycated-HSA was incubated with activated neutrophils, and was completely inhibited in the presence of an HOCl scavenger. These data demonstrated that HOCl-mediated CML formation from Amadori products plays a role in CML formation and tissue damage at sites of inflammation.     

Pyridinium-carbaldehyde: active Maillard reaction product from the reaction of hexoses with lysine residues

Besides the formation of the aminotriazine N6-[4-(3-amino-1,2,4-triazin-5-yl)-2,3-dihydroxybutyl]-L-lysine, the reaction of [1-13C]D-glucose with lysine and aminoguanidine leads to the generation of 6-[2-([[amino(imino)methyl]hydrazono]methyl)pyridinium-1-yl]-L-norleucine (14-13C1). The dideoxyosone N6-(2,3-dihydroxy-5,6-dioxohexyl)-L-lysine was shown to be a precursor in the formation of 14-13C1, which proceeds via the reactive carbonyl intermediate 6-(2-formylpyridinium-1-yl)-L-norleucine (13-13C1). In order to study the reactivity of 13-13C1, the model compound 1-butyl-2-formylpyridinium (18) was prepared in a two-step procedure starting from 2-pyridinemethanol. The reaction of the pyridinium-carbaldehyde 18 with L-lysine yielded the Strecker analogous degradation product 2-(aminomethyl)-1-butylpyridinium and another compound, which was shown to be as 1-butyl-2-[(2-oxopiperidin-3-ylidene)methyl]pyridinium. Reaction of 18 with the C-H acidic 4-hydroxy-5-methylfuran-3(2H)-one leads to the formation of the condensation product 1-butyl-2-[hydroxy-(4-hydroxy-5-methyl-3-oxofuran-2(3H)-ylidene)methyl]-pyridinium.