Glycation and Antioxidants: Hand in the Glove of Antiglycation and Natural Antioxidants.

The non-enzymatic interaction of sugar and protein resulting in the formation of advanced glycation end products responsible for cell signaling alterations ultimately leads to the human chronic disorders such as diabetes mellitus, cardiovascular diseases, cancer, etc. Studies suggest that AGEs upon interaction with receptors for advanced glycation end products (RAGE) result in the production of pro-inflammatory molecules and free radicals that exert altered gene expression effect. To date, many studies unveiled the potent role of synthetic and natural agents in inhibiting the glycation reaction at a lesser or greater extent. This review focuses on the hazards of glycation reaction and its inhibition by natural antioxidants, including polyphenols.

Evaluation of an olive leaf extract as a natural source of antiglycative compounds.

Advanced Glycation End-products (AGEs) have been associated to diabetes, neurodegenerative and cardiovascular diseases. Mitigating the formation of AGEs is a strategy to avoid detrimental physiopathological effects of age-related chronic diseases. An olive leaf extract (OLE), obtained under acidic conditions, and two fractions, obtained by solid-phase extraction, were characterized by LC-MS/MS. Antiglycative capacity of OLE and fractions were investigated in different in vitro models. The OLE significantly inhibited the formation of Amadori products at the early stage as well as the formation of fluorescent AGEs at the advanced stage of the glycation. Carboxymethyllysine was significantly inhibited by the OLE but it showed weaker activity against argpyrimidine and carboxyethyllysine. The antiglycative activity of each OLE fraction independently did not explain the activity reached in the whole extract, being necessary the compounds present in both fractions. OLE and its fractions were highly effective for trapping reactive dicarbonyl compounds (glyoxal, methylglyoxal, 3-deoxyglucosone and 3-deoxygalactosone). Different adducts resulting from the conjugation of methylglyoxal and hydroxytyrosol in OLE were identified. Results pointed out that OLE exert a broad-spectrum in vitro antiglycative activity.

Free α-dicarbonyl compounds in coffee, barley coffee and soy sauce and effects of in vitro digestion.

α-Dicarbonyl (α-DC) compounds were characterised in roasted (coffee, barley coffee) and in fermented (soy sauce) food matrices. Glyoxal (GO), methylglyoxal (MGO), diacetyl (DA) and 3-deoxyglucosone (3-DG) were found in all samples, and hydroxypyruvaldehyde and 5-hydroxypentane-2,3-dione in barley and soy. Cis and trans 3,4-dideoxyglucosone-3-ene (3,4-DGE) isomers and 4-glucosyl-5,6-dihydroxy-2-oxohexanal (4-G,3-DG) were found only in barley, and 3,4-DGE only in soy sauce with molasses. GO, MGO, and DA were quantified. Findings indicate that i) α-DC profiles depend on the food matrix and any technological treatments applied; ii) α-DC quantitation by HPLC requires matrix-specific, validated methods; iii) GO and MGO were the most abundant α-DCs; and iv) barley coffee was the matrix richest in α-DCs both qualitatively and quantitatively. In vitro simulated digestion reduced (coffee) or strongly increased (barley, soy sauce) free α-DC content. These findings suggest that α-DC bioavailability could actually depend not on food content but rather on reactions occurring during digestion.

Effects of methylglyoxal and pyridoxamine in rat brain mitochondria bioenergetics and oxidative status.

Advanced glycation end products (AGEs) and methylglyoxal (MG), an important intermediate in AGEs synthesis, are thought to contribute to protein aging and to the pathogenesis of age-and diabetes-associated complications. This study was intended to investigate brain mitochondria bioenergetics and oxidative status of rats previously exposed to chronic treatment with MG and/or with pyridoxamine (PM), a glycation inhibitor. Brain mitochondrial fractions were obtained and several parameters were analyzed: respiratory chain [states 3 and 4 of respiration, respiratory control ratio (RCR), and ADP/O index] and phosphorylation system [transmembrane potential (ΔΨm), ADP-induced depolarization, repolarization lag phase, and ATP levels]; hydrogen peroxide (H2O2) production levels, mitochondrial aconitase activity, and malondialdehyde levels as well as non-enzymatic antioxidant defenses (vitamin E and glutathione levels) and enzymatic antioxidant defenses (glutathione disulfide reductase (GR), glutathione peroxidase (GPx), and manganese superoxide dismutase (MnSOD) activities). MG treatment induced a statistical significant decrease in RCR, aconitase and GR activities, and an increase in H2O2 production levels. The administration of PM did not counteract MG-induced effects and caused a significant decrease in ΔΨm. In mitochondria from control animals, PM caused an adaptive mechanism characterized by a decrease in aconitase and GR activities as well as an increase in both α-tocopherol levels and GPx and MnSOD activities. Altogether our results show that high levels of MG promote brain mitochondrial impairment and PM is not able to reverse MG-induced effects.

Effect of Cd(II) and Se(IV) exposure on cellular distribution of both elements and concentration levels of glyoxal and methylglyoxal in Lepidium sativum.

In this work, the effect of cadmium (0-5.0 mg L(-1) as cadmium chloride, Cd(II)) and selenium (0-2.0 mg L(-1) as sodium selenite, Se(IV)) was studied in Lepidium sativum with specific focus on glyoxal (GO) and methylglyoxal (MGO) and on the cellular distribution of both elements under different exposure conditions. The concentrations of two reactive α-ketoaldehydes present as natural metabolites and as by-products of lipid peroxidation, were increased in plants treated with Cd(II), providng complementary experimental evidence on element phytotoxicity in garden cress, in terms of oxidative damage. Even though for higher than 1.0 mg L(-1) Se in medium similar adverse effect was found, under simultaneous exposure to both elements the changes in GO and MGO concentrations were clearly attenuated as compared to a single stressor treatment. This effect was accompanied by lower uptake of the two elements, significant decrease of their relative distribution in the fraction containing polar compounds and their increase in fraction corresponding to insoluble cell fragments/components, suggesting that the direct in vivo interaction between two element forms might be involved in the favorable effects of simultaneous treatment with Cd(II) + Se(IV). The fluorescence spectra obtained for biomass extracts corresponding to different exposure conditions suggested possible in vivo formation of CdSe quantum dots; however further studies are needed for ultimate identification and characterization of such nanoparticulate species.

Methylglyoxal: its presence and potential scavengers.

Hyperglycemia is the most important factor for the onset and progress of diabetic complications. A growing body of evidence indicates that the increase in reactive carbonyl intermediates such as methylglyoxal (MG) is a consequence of hyperglycemia in diabetes. Several studies have shown that higher levels of MG are present in diabetic patients' plasma compared to non-diabetics. Glyoxal (GO) and MG, the two major alpha-dicarbonyl compounds found in humans, are very reactive and lead to nonenzymatic glycation in vivo. Glycation is a complex series of reactions between reducing sugars and amino compounds, and it will lead to the formation of advanced glycation end products (AGEs). AGEs and dicarbonyl species are both linked to possible clinical significance in chronic and age-related diseases. It is well-known that tea is rich in polyphenolic compounds and that it has potential health benefits, including the prevention of diabetes. We have shown in a previous study that all tea polyphenols have very good MG trapping abilities. In this study, using time course, we have further indicated that one molecule form black tea, theaflavins-3,3'-digallate, can trap two molecules of MG under simulated physiological conditions. In addition, we have discovered that commercial carbonated beverages contain extremely high levels of MG. The potential hazardous effects of dietary MG on humans remain to be explored.

Cytocompatible gel formation of chitosan-glycerol phosphate solutions supplemented with hydroxyl ethyl cellulose is due to the presence of glyoxal.

To deliver and retain viable repair cells in a surgically prepared cartilage lesion, we previously developed an adhesive in situ-gelling cell carrier by suspending cells in a solution of hydroxyethyl cellulose (HEC), which was then mixed with chitosan-glycerol phosphate to form a chitosan-GP/HEC gel. The purpose of this study was to elucidate the mechanism of gelation to maximally control gel time and viability of encapsulated cells. We analyzed the role of osmolality, pH, gelation temperature, gel shrinkage, and HEC. A chitosan-GP solution at pH 6.8 with cytocompatible osmotic pressure (419 mOsm/kg) was achieved by lowering disodium GP concentration from 370 to 135 mM. This solution was still thermogelling but only at 73 degrees C. We next discovered that glyoxal, a common additive in ether cellulose manufacturing, was responsible for chitosan gelation. Monolayer cells survived and proliferated in up to 1 mM of glyoxal, however only a very narrow range of glyoxal concentration in chitosan-GP/HEC, 0.1-0.15 mM, permitted gel formation, cell survival, and cell proliferation. Chitosan gels containing HEC required slightly less glyoxal to solidify. Chitosan-GP/HEC loaded with viable chondrocytes formed an adhesive seal with ex vivo mosaic arthroplasty defects from sheep knee joints. In mosaic arthroplasty defects of live sheep, bleeding occurred beneath part of the hydrogel carrier, and the gel was cleared after 1 month in vivo. These data indicate that chitosan-GP/HEC is suitable as an adhesive and injectable delivery vehicle for clinical orthopedic applications involving single use treatments that guide acute cartilage repair processes.

Liver carcinogenesis and formation of 8-hydroxy-deoxyguanosine in C3H/HeN mice by oxidized dietary oils containing carcinogenic dicarbonyl compounds.

Oxidized dietary oils (lard, soybean oil, and sardine oil) were orally administered to C3H/HeN male mice. After 6 months, benign hepatocellular adenoma was observed in the mice treated with all three oxidized dietary oils. After 12 months, malignant hepatocellular carcinoma and hepatoblastoma were observed in addition to the benign tumor. Oxidized sardine oil caused the highest tumor incidence (35%) and malignant tumors (27.5%) among the oxidized dietary oils tested. Mice treated with oxidized lard and sardine oil exhibited a significant increase of 8-OH-dG in the livers. The amounts of 8-OH-dG found in the mice treated with oxidized sardine oil correlated with the rates of tumor incidence. After 6 months, mRNA decreased in the case of oxidized lard and sardine oil, whereas it increased in the case of oxidized soybean oil, either in 8-oxoguanine-DNA glycosylase (OGG1) or in 8-oxo-dGTPase. On the other hand, there was no appreciable change in mRNA, in either OGG1 or 8-oxo-dGTPase, after 12 months. Oxidized sardine oil contained the highest level of malonaldehyde (MA) (713+/-91.1 nmol/g) and glyoxal (33.3+/-5.2 nmol/g) among three oxidized oils. The malignant tumor incidence correlated with the high level of MA and glyoxal found in the dietary oils tested.

Deoxycytidine glyoxal: lesion induction and evidence of repair following vitamin C supplementation in vivo.

Oxidative DNA damage is postulated to be involved in carcinogenesis, and as a consequence, dietary antioxidants have received much interest. A recent report indicates that vitamin C facilitates the decomposition of hydroperoxides in vitro, generating reactive aldehydes. We present evidence for the in vivo generation of glyoxal, an established product of lipid peroxidation, glucose/ascorbate autoxidation, or free radical attack of deoxyribose, following supplementation of volunteers with 400 mg/d vitamin C. Utilizing a monoclonal antibody to a deoxycytidine-glyoxal adduct (gdC), we measured DNA lesion levels in peripheral blood mononuclear cells. Supplementation resulted in significant (p =.001) increases in gdC levels at weeks 11, 16, and 21, with corresponding increases in plasma malondialdehyde levels and, coupled with previous findings, is strongly suggestive of a pro-oxidative effect. However, continued supplementation revealed a highly significant (p =.0001) reduction in gdC levels. Simultaneous analysis of cyclobutane thymine dimers revealed no increase upon supplementation but, as with gdC, levels decreased. Although no single mechanism is identified, our data demonstrate a pro-oxidant event in the generation of reactive aldehydes following vitamin C supplementation in vivo. These results are also consistent with our hypothesis for a role of vitamin C in an adaptive/repair response and indicate that nucleotide excision repair specifically may be affected.