Properties of normal and glycated human hemoglobin in presence and absence of antioxidant

Protective Effects of Kaempferol on D-Ribose-Induced Mesangial Cell Injury

Recently, it has been found that the level of urinary D-ribose in type 2 diabetes is notably higher than that in age-matched normal control, and D-ribose is more reactive in the glycation than D-glucose and induces oxidative stress. Kaempferol is one of the main bioactive components in Astragalus membranaceus, with numerous physiological actives, such as antioxidant. The present study investigated the protective effects of kaempferol on D-ribose-treated mesangial cells. CCK-8 and LDH assay were used to test cell viability and cell toxicity. Immunofluorescence and flow cytometry were used to detect the AGE formation and ROS accumulation. GSH level was measured to reflect oxidation resistance. Cell apoptosis was evaluated by Hoechst 33258 staining, AO/EB staining, and western blot. Mitochondrial membrane integrity was detected by JC-1 staining, western blot, and RT-PCR. The change of autophagy level was tested by western blot. The results indicated that D-ribose induced not only cell damage and increased AGE formation and ROS accumulation but also GSH depletion. Further studies demonstrated that D-ribose induced mitochondrial depolarization and the activation of caspase-9/3. But kaempferol could partly block these damages. Subsequently, it was confirmed that kaempferol repaired the autophagy disturbance induced by D-ribose, and 3-MA could reverse the protective effect of kaempferol under D-ribose condition. Our study demonstrated that D-ribose induced AGE accumulation and ROS production in mesangial cell and caused mitochondrial apoptosis, but kaempferol could attenuate these changes and its protective effect might be related to the repair of autophagy.

The inhibitory influence of 3-β-hydroxybutyrate on calf thymus DNA glycation by glucose

Glycation can change DNA structure and cause strand breaks, mutations, and changes in gene expression.

Excited state proton transfer of natural flavonoids and their chromophores in duplex and tetraplex DNAs

Fisetin (3,7,3',4'-tetrahydroxyflavone) and quercetin (3,5,7,3',4'-pentahydroxyflavone) are the bioactive plant flavonoids that are potentially useful therapeutic drugs for the treatment of a broad spectrum of diseases, including atherosclerosis, cardiovascular disease, obesity, hypertension, and cancer. 3-Hydroxyflavone (3HF) and 7-hydroxyflavone (7HF) are the synthetic chromophores of fisetin and quercetin. We have exploited dual luminescence properties of fisetin and quercetin along with 3-HF and 7HF to examine their efficacy of binding and compare their interactions with DNA, which is one of the macromolecular targets of flavonoids in physiological systems. Following the sequence of the human telomeric DNA 5'-d (CCCTAA-)n/(-TTAGGG)n-5', two single-stranded DNA oligonucleotides, 5'-d(C3TA2)3C3-3' and 5'-d(T2AG3)4-3', and their duplex were used as receptors to study binding by the ligands quercetin, fisetin, and their chromophores. Circular dichroism, differential absorption, UV thermal melting, and size exclusion chromatographic studies indicated the formation of unusual DNA structures (such as C4 and G4 tetraplexes) for both the C- and G-rich single-stranded DNAs. Upon binding to DNA, dramatic changes were observed in the intrinsic fluorescence behavior of the flavonoids. Molecular docking studies were performed to describe the likely binding sites for the ligands. The spectroscopic studies on flavonoid-DNA interactions described herein demonstrate a powerful approach for examining their DNA binding through exploiting the highly sensitive intrinsic fluorescence properties of the flavonoids as their own "reporter" for their interactions with macromolecular targets.

Autoimmune response to AGE modified human DNA: Implications in type 1 diabetes mellitus

Aims

Non-enzymatic glycation of DNA both in vivo and in vitro results in generation of free radicals, known as glycoxidation. Glycoxidation leads to structural perturbation of DNA resulting in generation of neo-antigenic epitopes having implication in autoimmune disorders like diabetes mellitus. In this study human placental DNA was glycated with methylglyoxal (MG) and lysine (Lys) in the presence of Cu²⁺ and its auto-antibody binding was probed in Type 1 diabetes patients.

Methods

Glycation was carried out by incubating DNA with MG, Lys and Cu²⁺ for 24 h at 37 °C. Carboxyethyl deoxyguanosine (CEdG) formed in glycation reaction was studied by LC-MS and the pathway for Amadori formation was studied by ESI-MS techniques. Furthermore, binding characteristics of auto-antibodies in diabetes patients were assessed by direct binding, competitive ELISA and band shift assay.

Results

DNA glycation with MG, Lys and Cu²⁺ results in the formation of CEdG (marker of DNA glycation) which was confirmed by LC-MS. The intermediate stages of glycation were confirmed by ESI-MS technique. Serum from diabetes patients exhibited enhanced binding and specificity for glycated DNA as compared to native form.

Conclusions

Glycation of DNA has resulted in structural perturbation causing generation of neo-antigenic epitopes thus recognizing auto-antibodies in diabetes.

Localization and interaction of hydroxyflavones with lipid bilayer model membranes: a study using DSC and multinuclear NMR

The localization and interaction of six naturally occurring flavones (FLV, 5HF, 6HF, 7HF, CHY and BLN) in DPPC bilayers were studied using DSC and multi-nuclear NMR. DSC results indicate that FLV and 6HF interact with alkyl chains. The (1)H NMR shows interaction of flavones with the sn-glycero region. Ring current induced chemical shifts indicate that 6HF and BLN acquire parallel orientation in bilayers. 2D NOESY spectra indicate partitioning of the B-ring into the alkyl chain region. The DSC, NMR and binding studies indicate that 5HF and 7HF are located near head group region, while 6HF, CHY and BLN are located in the vicinity of sn-glycero region, and FLV is inserted deepest in the membrane.

Fisetin inhibits hyperglycemia-induced proinflammatory cytokine production by epigenetic mechanisms

Diabetes is characterized by a proinflammatory state, and several inflammatory processes have been associated with both type 1 and type 2 diabetes and the resulting complications. High glucose levels induce the release of proinflammatory cytokines. Fisetin, a flavonoid dietary ingredient found in the smoke tree (Cotinus coggygria), and is also widely distributed in fruits and vegetables. Fisetin is known to exert anti-inflammatory effects via inhibition of the NF-κB signaling pathway. In this study, we analyzed the effects of fisetin on proinflammatory cytokine secretion and epigenetic regulation, in human monocytes cultured under hyperglycemic conditions. Human monocytic (THP-1) cells were cultured under control (14.5 mmol/L mannitol), normoglycemic (NG, 5.5 mmol/L glucose), or hyperglycemic (HG, 20 mmol/L glucose) conditions, in the absence or presence of fisetin. Fisetin was added (3–10 μM) for 48 h. While the HG condition significantly induced histone acetylation, NF-κB activation, and proinflammatory cytokine (IL-6 and TNF-α) release from THP-1 cells, fisetin suppressed NF-κB activity and cytokine release. Fisetin treatment also significantly reduced CBP/p300 gene expression, as well as the levels of acetylation and HAT activity of the CBP/p300 protein, which is a known NF-κB coactivator. These results suggest that fisetin inhibits HG-induced cytokine production in monocytes, through epigenetic changes involving NF-κB. We therefore propose that fisetin supplementation be considered for diabetes prevention.

A CRITICAL STUDY ON THE INTERACTIONS OF HESPERITIN WITH HUMAN HEMOGLOBIN: FLUORESCENCE SPECTROSCOPIC AND MOLECULAR MODELING APPROACH

Hesperitin, a ubiquitous bioactive flavonoid abundant in citrus fruits is known to possess antioxidant, anti-carcinogenic, hypolipidemic, vasoprotective and other important therapeutic properties. Here we have explored the interactions of hesperitin with normal human hemoglobin (HbA), using steady state and time resolved fluorescence spectroscopy, far UV circular dicroism (CD) spectroscopy, combined with molecular modeling computations. Specific interaction of the flavonoid with HbA is confirmed from flavonoid-induced static quenching which is evident from steady state fluorescence as well as lifetime data. Both temperature dependent fluorescence measurements and molecular docking studies reveal that apart from hydrogen bonding and van der Waals interactions, electrostatic interactions also play crucial role in hesperitin-HbA interactions. Furthermore, electrostatic surface potential calculations indicate that the hesperitin binding site in HbA is intensely positive due to the presence of several lysine and histidine residues.

Glycated human DNA is a preferred antigen for anti-DNA antibodies in diabetic patients

AIMS

Glycation of proteins and DNA, results in the generation of free radicals causing structural modification of biomacromolecule. This leads to the generation of neo-antigenic epitopes having implication in diabetes mellitus. In this study, human placental DNA was glycated with fructose and its binding was probed with the serum antibodies from type 1 and 2 diabetes patients.

METHODS

Glycation was carried out by incubating DNA (10 μg/ml) with fructose (25 mM) for 5 days at 37°C. The induced structural changes in DNA were studied by spectroscopic techniques, thermal denaturation studies and agarose gel electrophoresis. Furthermore, binding characteristics of autoantibodies in diabetes (type 1 and 2) patients were assessed by direct binding and competitive ELISA.

RESULTS

DNA glycation with fructose resulted in single strand breaks, hyperchromicity in UV spectrum and increased fluorescence intensity. Thermal denaturation studies demonstrated the unstacking of bases and early onset of duplex unwinding. Type 1 diabetes patients exhibited enhanced binding with glycated DNA as compared to native form, while for type 2 diabetes only those with secondary complications (Nephropathy) showed higher binding.

CONCLUSIONS

Glycation of DNA has resulted in structural perturbation causing generation of neo-antigenic epitopes that are better antigens for antibodies in diabetes patients.

Efeito do extrato aquoso de alecrim (Rosmarinus officinalis L.) sobre o estresse oxidativo em ratos diabéticos

OBJETIVO: Avaliar o efeito do extrato aquoso de alecrim sobre o estresse oxidativo em ratos diabéticos. MÉTODOS: O extrato aquoso de alecrim foi obtido por método sequencial. Os fenólicos totais foram determinados pelo método de Folin Ciocateau e a atividade antioxidante in vitro foi determinada através de três métodos: β-caroteno/ácido linoleico, varredura do radical 2,2 Difenil-1-Picril-hidrazil e oxigen radical absorbance capacity. Ratos Wistar machos foram distribuídos em 5 grupos: controle, diabético, e três grupos de animais diabéticos tratados com extrato aquoso de alecrim em concentrações diferentes: 25, 50 ou 100mg/kg por via oral durante 30 dias. O diabetes foi induzido por estreptozotocina e, no final do experimento, foi coletado sangue para avaliar o percentual de hemoglobina glicada e os tecidos hepático e cerebral para determinação das enzimas antioxidantes: superóxido dismutase, catalase, glutationa peroxidase e glutationa redutase. RESULTADOS: Constatou-se que o extrato aquoso de alecrim apresentou altos teores de compostos fenólicos totais e expressiva atividade antioxidante in vitro nos três métodos de avaliação. O extrato aquoso de alecrim na concentração de 50mg/kg diminuiu o percentual de hemoglobina glicada e aumentou a atividade das enzimas catalase e glutationa peroxidase no fígado, e da superóxido dismutase no cérebro de ratos diabéticos. No entanto, não foi observado efeito dose-resposta nas demais concentrações analisadas. CONCLUSÃO: O extrato aquoso de alecrim apresenta significativa capacidade antioxidante in vitro, atribuída à presença de compostos fenólicos em sua composição. E, quando administrado em ratos na concentração de 50mg/kg, demonstrou-se eficiente na atenuação do estresse oxidativo presente no diabetes experimental.

Probing the interactions of hemoglobin with antioxidant flavonoids via fluorescence spectroscopy and molecular modeling studies

Steady state and time resolved fluorescence spectroscopy, combined with molecular modeling computations, have been used to explore the interactions of two therapeutically important flavonoids, fisetin (3,7,3',4'-OH-flavone) and 3-hydroxyflavone (3-HF), with normal human hemoglobin (HbA). Distinctive 'two color' fluorescence signatures and fairly high fluorescence anisotropy (r=0.12-0.28) of fisetin and 3-HF reveal their specific interactions with HbA. Binding constants estimated from the fluorescence studies were ≈4.00 × 10(4)M(-1) and 9.83 × 10(3)M(-1) for fisetin and 3-HF respectively. Specific interactions with HbA were further confirmed from flavonoid-induced static quenching of the protein tryptophan fluorescence as indicated by: (a) bimolecular quenching constant K(q)≫diffusion controlled limit (b) closely matched values of Stern-Volmer quenching constant and binding constant (c) τ(o)/τ≈1 (where τ(o) and τ are the unquenched and quenched tryptophan fluorescence lifetimes respectively). Molecular docking and electrostatic surface potential calculations reveal contrasting binding modes of fisetin and 3-HF with HbA.

Binding of the bioflavonoid robinetin with model membranes and hemoglobin: Inhibition of lipid peroxidation and protein glycosylation

Recent years have witnessed burgeoning interest in plant flavonoids as novel therapeutic drugs targeting cellular membranes and proteins. Motivated by this scenario, we explored the binding of robinetin (3,7,3',4',5'-pentahydroxyflavone, a bioflavonoid with remarkable 'two color' intrinsic fluorescence properties), with egg yolk phosphatidylcholine (EYPC) liposomes and normal human hemoglobin (HbA), using steady state and time resolved fluorescence spectroscopy. Distinctive fluorescence signatures obtained for robinetin indicate its partitioning (K(p)=8.65x10(4)) into the hydrophobic core of the membrane lipid bilayer. HbA-robinetin interaction was examined using both robinetin fluorescence and flavonoid-induced quenching of the protein tryptophan fluorescence. Specific interaction with HbA was confirmed from three lines of evidence: (a) bimolecular quenching constant K(q)>>diffusion controlled limit; (b) closely matched values of Stern-Volmer quenching constant and binding constant; (c) tau(0)/tau=1 (where tau(0) and tau are the unquenched and quenched tryptophan fluorescence lifetimes, respectively). Absorption spectrophotometric assays reveal that robinetin inhibits EYPC membrane lipid peroxidation and HbA glycosylation with high efficiency.

Ground and excited state proton transfer and antioxidant activity of 7-hydroxyflavone in model membranes: absorption and fluorescence spectroscopic studies

Steady state and time resolved fluorescence spectroscopy have been used to probe microenvironments of the therapeutically active intrinsically fluorescent flavonoid, 7-hydroxyflavone (7-HF), in model membranes consisting of multilamellar phosphatidylcholine liposomes. Additionally, the antioxidant effects of 7-HF against lipid peroxidation have been evaluated using spectrophotometric assay. Large Stokes shifted emissions with distinct spectroscopic signatures, are observed from the excited state proton transfer (ESPT) tautomer (which is generated by a solvent mediated mechanism) and the ground state anion of 7-HF. The neutral (7-HFN) and anionic (7-HFA) species' appear to be located in the non-polar acyl chain and the polar head group regions of the lipid vesicles respectively. The partition coefficients of 7-HFN and 7-HFA in these vesicles have also been estimated using their intrinsic fluorescence. Anisotropy (r) versus temperature (T) measurements reveal the utility of the tautomer fluorescence anisotropy as a sensitive parameter for exploring structural changes in the membranes. Fluorescence decay kinetics studies indicate heterogeneity in the microenvironments of both 7-HFN and 7-HFA. Furthermore, we demonstrate that lipid peroxidation of the model membranes is partially arrested upon 7-HF binding, suggesting its potential usefulness as an inhibitor of peroxidative damage of cell membranes.

Effect of Glycation on the Structure and Dynamics of DNA: A Critical Spectroscopic Approach

Glycated DNA is considered to be a pathogenic factor for diabetes mellitus. Here we present a novel and preliminary study on normal and glycated (with fructose and glucose-6-phosphate as reducing sugars) human placenta DNA using agarose gel electrophoresis and photon correlation spectroscopy. The former is used to find structural alterations, while the latter is exploited to observe differences in the dynamics between normal (i.e., pure) and glycated DNA molecules. For scattering angles up to 90 degrees , we obtained a quasi-single-exponential relaxation process for the pure DNA, whereas at higher scattering angles the relaxation of pure DNA becomes broader with a stretching parameter beta approximately 0.6 at 130 degrees. Interestingly, for both the glycated DNAs stretched relaxation profiles and higher relaxation rates (Omega) are observed for all scattering angles. Moreover, a separate and very fast relaxation (e.g., relaxation time tau approximately 2 micros at 90 degrees ) can be noticed for both the glycated DNAs at all the studied scattering angles. Thus, the dramatic changes in the relaxation parameters (Omega, tau, and beta) of the glycated DNA show at the molecular level, for the first time, that the structure and dynamics of DNA are strongly affected by glycation. Implications of the results are discussed.

Exploring the antioxidant property of bioflavonoid quercetin in preventing DNA glycation: A calorimetric and spectroscopic study

Reducing sugars for example glucose, fructose, etc., and their phosphate derivatives non-enzymatically glycate biological macromolecules (e.g., proteins, DNA and lipids) and is related to the production of free radicals. Here we present a novel study, using differential scanning calorimetry (DSC) along with UV/Vis absorption and photon correlation spectroscopy (PCS), on normal and glycated human placenta DNA and have explored the antioxidant property of the naturally occurring polyhydroxy flavone quercetin (3,3',4',5,7-pentahydroxyflavone) in preventing the glycation. The decrease in the absorption intensity of DNA in presence of sugars clearly indicates the existence of sugar molecules between the two bases of a base pair in the duplex DNA molecule. Variations were perceptible in the PCS relaxation profiles of normal and glycated DNA. The melting temperature of placenta DNA was decreased when glycated suggesting a decrease in the structural stability of the double-stranded glycated DNA. Our DSC and PCS data showed, for the first time, that the dramatic changes in the structural properties of glycated DNA can be prevented to a significant extent by adding quercetin. This study provides valuable insights regarding the structure, function, and dynamics of normal and glycated DNA molecules, underlying the manifestation of free radical mediated diseases, and their prevention using therapeutically active naturally occurring flavonoid quercetin.