Advanced Glycation Products Research Articles

Relationships among serum C-reactive protein, receptor for advanced glycation products, metabolic dysfunction, and cognitive impairments.

BackgroundWe examined the clinical value of two serum markers of low-grade inflammation, C-reactive protein (CRP) and receptor of advanced glycation products (RAGE), as prognostic indices for cognitive decline.MethodsPatients with cognitive impairment (n = 377) and controls (n = 66) were examined by blood biochemistry tests, including ELISAs of serum CRP and RAGE, the Mini-mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA), and STEAM 1H-MRS of the left hippocampus and thalamus.ResultsCompared to the control group, the cognitive impairment group was older (63.10 ± 9.70 years vs. 55.09 ± 10.77 years, P = 0.000) and had fewer years of formal education (9.01 ± 4.01 vs. 12.94 ± 3.0, P = 0.000). There were no significant differences in the frequencies of type 2 diabetes, hypertension, or hyperlipidemia between groups. Serum CRP and RAGE were higher in the cognitive impairment group (CRP: 2.08 mg/L, range 1.07 − 3.36 mg/L vs. 0.21 mg/L, range 0.18 − 0.42 mg/L; RAGE: 4.01, range 2.49 − 5.71, vs. 2.28, range 1.84 − 3.03; P < 0.05 for both). In patients with cognitive impairment, there were negative correlations between cognitive function (as measured by MMSE and MoCA) and both CRP and RAGE levels (P < 0.05). Patients over 55 years exhibited a positive correlation between CRP and myo-inositol peak area in the left hippocampus (P < 0.05), while there was no relationship between RAGE and any metabolite (P > 0.05). Multiple linear regression revealed that CRP was influenced by hypertension (P = 0.026) and cognitive impairment (P = 0.042).ConclusionsChronic low-grade inflammation is present in patients with cognitive impairment. Serum CRP, RAGE, and left hippocampal myo-inositol may provide prognostic information on cognitive decline.

Study of Fragmentation Behavior of Amadori Rearrangement Products in Lysine-Containing Peptide Model by Tandem Mass Spectrometry

Protein and peptide glycation with reducing sugars through Maillard reaction is recognized as one of the most critical and fundamental reactions in food and in the human body. Amadori rearrangement products (ARPs) are formed at the initial stage of Maillard reaction and then may be converted into intermediate and advanced glycation products. We report here that using electrospray ionization-mass spectrometry (ESI-MS) to directly and rapidly characterize fragmentation behavior of ARPs in a Lysine-containing peptide-reducing sugars unambiguously model and identify the modification sites in glycated tri- and tetrapeptides. Tandem mass spectrometry (MS2) results showthat the sugar moiety was preferentially fragmented, whereby the neutral loss of small molecules, such as 18 Da (-H2O), 36 Da (-2 x H2O), 54 Da (-3 x H2O), 84 Da (-H2O-HCOH) and 162 Da from monosaccharide (glucose) moieties and 18 Da, 36 Da, 216 Da, 246 Da and 324 Da from disaccharide moieties. Among the fragmented ions, (M-84+H)+ of monosaccharides and (M-246+H)+ of disaccharides are relatively stable. Further multi-stage mass spectrometry (MS3) of (M-84+H)+ for tri- and longer peptides displays peptide sequence and glycation sites by providing modified y ions (y*), and/or modified b ions (b*) and even a modified a ion (a*). The study is useful to monitor and characterize PMTs of glycation in complex protein systems based on ESI-MS related techniques.

Structures Required of Polyphenols for Inhibiting Advanced Glycation end Products Formation

The properties of polyphenols as AGEs formation inhibitors have attracted great interest among researchers. This review discusses the antiglycation activities of polyphenols and focuses on the relationship between the AGEs formation inhibitory activities and their chemical structures. The molecular structures influence the inhibition in the following ways: (1) The hydroxylation on both A ring and B ring improved the inhibitory activity on AGEs formation, while hydroxylation on C ring decreased the activity. (2) The methylation generally reduced the anti-AGEs activity of flavonoids, except for the 3-O-methylation of flavonols. (3) The glycosylation of hydroxyls of flavonoids tended to decrease the inhibitory activities on inhibiting AGEs formation, although contradictionary results were existed. (4) Hydrogenation of the C2=C3 double bond of flavones slightly weakened their activities. (5) A 5,7-dihydroxy structure was favorable to the activity of isoflavones. (6) Proanthocyanidins dimer or trimers showed a stronger inhibitory activity than catechins, and the glucosides of anthocyanidin had higher activities than their rutinosides. (7) The hydroxylation on B ring and the methylation of stilbenes decreased the inhibitory activity. (8) Presence of galloyl groups was important for the activity of catechins, and α-hydroxyl group at C-3 was much more effective than β-hydroxyl group at C-3. (9) The phenolic acids with multiple hydroxyls showed strong inhibition against AGEs formation, and an ortho or meta dihydroxyl structure on the benzene ring was vital to the anti-AGEs activity of anthraquinone. (10) Both ellagic acids and ellagitannins showed potent inhibitory activities on AGEs formation, and hydroxylation increased the activities but methylation decreased them.

Abstract TP167: Suppression of High-mobility Group Protein Box-1 Signaling by Eicosapentaenoic Acid Ameliorates Brain Ischemic Damage in Oophorectomized Rats

Background and Purpose— Cerebral ischemia triggers the acute inflammation that has been associated with an increase in brain damage. In male rats exposed to ischemic insult, high-mobility group protein box-1 (HMGB1) activates inflammatory pathways via its receptor for advanced glycation products (RAGE) and its toll-like receptors (TLRs). We examined the role of these molecules in female rats with experimental ischemic brain damage. We further investigated the efficacy of eicosapentaenoic acid (EPA) against cerebral ischemia and its effect on HMGB1 signaling. Methods— Before 90-min middle cerebral artery occlusion-reperfusion, 5-week-old female Sprague-Dawley rats were subjected to bilateral oophorectomy (OVX + ) and pretreated with 500mg/kg/day EPA for 4 weeks. The relationship between the efficacy of EPA and the regulation of HMGB1 signaling were investigated using peroxisome proliferator-activated receptor gamma (PPARγ) agonist pioglitazone, PPARγ inhibitor GW9662, and vehicle-control. Results— In parallel with the expansion of the cortical infarct size, HMGB1 signaling after cerebral ischemia was increased in OVX + rats. The mRNA level of TLR9 and RAGE but not TLR2 and TLR4 was moderately increased by cerebral ischemia and significantly higher in OVX + - than OVX - rats. The HMGB1 signal in the OVX + rats pretreated with EPA was inhibited in a PPARγ-dependent and independent manner. These effects were associated with a reduction in the infarct size. Conclusions— We first demonstrate that cortical infarct facilitated by OVX is associated with augmented HMGB1 signaling and that the augmented HMGB1 signaling was suppressed by EPA. To assess whether EPA treatment is a promising strategy further clinical studies are required in postmenopausal women.

New insights into deleterious impacts of in vivo glycation on albumin antioxidant activities

BackgroundAlbumin constitutes the most abundant circulating antioxidant and prevents oxidative damages. However, in diabetes, this plasmatic protein is exposed to several oxidative modifications, which impact on albumin antioxidant properties. MethodsMost studies dealing on albumin antioxidant activities were conducted on in vitro modified protein. Here we tried to decipher whether reduced antioxidant properties of albumin could be evidenced in vivo. For this, we compared the antioxidant properties of albumin purified from diabetic patients to in vitro models of glycated albumin. ResultsBoth in vivo and in vitro glycated albumins displayed impaired antioxidant activities in the free radical-induced hemolysis test. Surprisingly, the ORAC method (Oxygen Radical Antioxidant Capacity) showed an enhanced antioxidant activity for glycated albumin. Faced with this paradox, we investigated antioxidant and anti-inflammatory activities of our albumin preparations on cultured cells (macrophages and adipocytes). Reduced cellular metabolism and enhanced intracellular oxidative stress were measured in cells treated with albumin from diabetics. NF-kB –mediated gene induction was higher in macrophages treated with both type of glycated albumin compared with cells treated with native albumin. Anti inflammatory activity of native albumin is significantly impaired after in vitro glycation and albumin purified from diabetics significantly enhanced IL6 secretion by adipocytes. Expression of receptor for advanced glycation products is significantly enhanced in glycated albumin-treated cells. Conclusions and general significanceOur results bring new evidences on the deleterious impairments of albumin important functions after glycation and emphasize the importance of in vivo model of glycation in studies relied to diabetes pathology.

Structural characterization of S100A15 reveals a novel zinc coordination site among S100 proteins and altered surface chemistry with functional implications for receptor binding

BackgroundS100 proteins are a family of small, EF-hand containing calcium-binding signaling proteins that are implicated in many cancers. While the majority of human S100 proteins share 25-65% sequence similarity, S100A7 and its recently identified paralog, S100A15, display 93% sequence identity. Intriguingly, however, S100A7 and S100A15 serve distinct roles in inflammatory skin disease; S100A7 signals through the receptor for advanced glycation products (RAGE) in a zinc-dependent manner, while S100A15 signals through a yet unidentified G-protein coupled receptor in a zinc-independent manner. Of the seven divergent residues that differentiate S100A7 and S100A15, four cluster in a zinc-binding region and the remaining three localize to a predicted receptor-binding surface.ResultsTo investigate the structural and functional consequences of these divergent clusters, we report the X-ray crystal structures of S100A15 and S100A7D24G, a hybrid variant where the zinc ligand Asp24 of S100A7 has been substituted with the glycine of S100A15, to 1.7 Å and 1.6 Å resolution, respectively. Remarkably, despite replacement of the Asp ligand, zinc binding is retained at the S100A15 dimer interface with distorted tetrahedral geometry and a chloride ion serving as an exogenous fourth ligand. Zinc binding was confirmed using anomalous difference maps and solution binding studies that revealed similar affinities of zinc for S100A15 and S100A7. Additionally, the predicted receptor-binding surface on S100A7 is substantially more basic in S100A15 without incurring structural rearrangement.ConclusionsHere we demonstrate that S100A15 retains the ability to coordinate zinc through incorporation of an exogenous ligand resulting in a unique zinc-binding site among S100 proteins. The altered surface chemistry between S100A7 and S100A15 that localizes to the predicted receptor binding site is likely responsible for the differential recognition of distinct protein targets. Collectively, these data provide novel insight into the structural and functional consequences of the divergent surfaces between S100A7 and S100A15 that may be exploited for targeted therapies.

PP125. High mobility group box 1 protein (HMGB1): A pathogenic role in preeclampsia?

A central pathogenic mechanism of preeclampsia is believed to be the production by the hypoxic placenta of various mediators which promote inflammation and oxidative stress when released into the maternal circulation. The high mobility group box 1 protein (HMGB1) is a ubiquitous nuclear protein. In conditions of hypoxic cellular stress or necrosis, HMGB1 is released into the extracellular milieu. Extracellular HMGB1 has proinflammatory effects, due to the engagement of various cell membrane receptors, notably the receptor for advanced glycation products (RAGE). In preeclampsia, there is evidence for activation of RAGE, and enhanced amounts of HMGB1 have also been demonstrated in the placenta and amniotic fluid, but not, so far, in maternal blood. We hypothesize therefore that, in preeclampsia, the concentration of HMGB1 is abnormally high in maternal blood. We enrolled 16 women in third trimester pregnancy and suffering from preeclampsia (blood pressure > 140/90mmHg with significant proteinuria), 16 women with normal pregnancies who were matched pairwise with the former for BMI and gestation week, and 16 non pregnant healthy women, matched for age with the other two groups. HMGB1 was assessed in peripheral blood with a commercial ELISA kit. The variance between the three groups was appreciated using an ANOVA analysis. Significance was considered for a probability value of < 0.5. The median [interquartile range] HMGB1 concentrations (in ng/mL) were 2.1 [1.1-3.2] in preeclamptic pregnancies, 1.1 [1.0-1.2] in normal pregnancies (p<0.05 vs preeclamptic group), and 0.6 [0.5-0.8] in non pregnant women (p<0.01 vs both other groups). In third trimester pregnancy, the presence of preeclampsia is associated with an approximately two-fold increase of HMGB1 concentration in maternal peripheral blood. Considering its known proinflammatory effects, HMGB1 could be one mediator responsible for the maternal manifestations of preeclampsia.

Diabetic Retinopathy: Understanding Pathologic Angiogenesis and Exploring its Treatment Options

Diabetic retinopathy is the major cause of blindness at working age. The pathogenesis behind visual loss is re- lated with retinal angiogenesis and increased retinal vascular permeability. These changes seem to be the result of chronic hyperglycemia and hypoxia. Several mechanisms have been proposed to cause the retinal and vasculature cellular dam- age. They include the formation of advanced end glycation products, aldose reductase activity and reactive oxygen spe- cies. Ultimately, they lead to the expression of VEGF-A. This growth factor seems to play the pivotal role in the devel- opment of the complications associated with the disease including break down of the inner blood retinal barrier, macular edema and vasoproliferation. Other mechanisms like inflammation, protein kinase C activity and erythropoietin have been strongly associated with the pathogenesis. Laser therapy is still the standard of care for diabetic retinopathy and prevents severe vision loss in 95% of patients if timely treatment is performed. The better understanding of the disease has led to the production of new management op- tions that may become important adjuvants for the disease. They include intravitreal anti-VEGF therapy, intravitreal ster- oid therapy and systemic protein kinase C inhibitors. Vitrectomy is an important option for advanced cases of the disease such as tractional retinal detachment or non-absorbing vitreous hemorrhages.

Abstract 2244: Synergistic Benefit Of Combined Amlodipine Plus Atorvastatin On Neuronal Damage After Stroke In Zucker Metabolic Rat

Stroke is a major neurologic disorder and a leading cause of death in the world. We compared neuroprotective effects of single or combination therapy of amlodipine (AM) and atorvastatin (AT) in such a metabolic syndrome model Zucker rat after 90min of transient middle cerebral artery occlusion (tMCAO). The animals were pretreated with vehicle, AM, AT, or the combination of AM plus AT for 28 days, and at 24 h of tMCAO, infarct volume and immunohistochemical analyses were performed. The combination of AM plus AT treatment decreased the infarct volume stronger than each single treatment withAMor AT. The numbers of positive cells of oxidative stress markers such as 8-hydroxy-2′-deoxyguanosin (8-OHdG), 4-hydroxy-2-nonenal (4-HNE), and advanced end glycation products (AGE) and inflammation markers such as tumor necrosis factor alpha (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) decreased dramatically in the combination-treated group compared with single AM or AT-treated group. The present study showed that single AM or AT treatment showed neuroprotective effects both with antioxidative and anti-inflammatory mechanisms, but combination therapy of AM plus AT presented a further synergistic benefit in acute ischemic neural damages. Moreover, the single treatment with AM or AT itself exerted neuroprotective effects with reducing inductions of MMP-9 and AT2R, as well as with preserving collagen IV, and the combination therapy of AM plus AT showed a further synergistic benefit against acute ischemic neural damages. Single AT was more protective on these 3 molecules than single AM at this time point of 24 h after tMCAO. Thus, the combination therapy with AM plus AT extended the neuroprotectives effect of single treatment with AM or AT on a part of neurovascular unit and a hypertension related receptor.

Characterization of the glycated human cerebrospinal fluid proteome

Protein glycation is a nonenzymatic modification that involves pathological functions in neurological diseases. Despite the high number of studies showing accumulation of advanced end glycation products (AGEs) at clinical stage, there is a lack of knowledge about which proteins are modified, where those modifications occur, and to what extent. The goal of this study was to achieve a comprehensive characterization of proteins modified by early glycation in human cerebrospinal fluid (CSF). Approaches based on glucose diferential labeling and mass spectrometry have been applied to evaluate the glycated CSF proteome at two physiological conditions: native glucose level and in vitro high glucose content. For both purposes, detection of glycated proteins was carried out by HCD-MS2 and CID-MS3 modes after endoproteinase Glu-C digestion and boronate affinity chromatography. The abundance of glycation was assessed by protein labeling with (13)C(6)-glucose incubation. The analysis of native glycated CSF identified 111 glycation sites corresponding to 48 glycated proteins. Additionally, the in vitro high glucose level approach detected 265 glycation sites and 101 glycated proteins. The comparison of glycation levels under native and 15 mM glucose conditions showed relative concentration increases up to ten folds for some glycated proteins. This report revealed for the first time a number of key glycated CSF proteins known to be involved in neuroinflammation and neurodegenerative disorders. Altogether, the present study contains valuable and unique information, which should further help to clarify the pathological role of glycation in central nervous system pathologies. This article is part of a Special Issue entitled: Translational Proteomics.

Amadori‐Glycated Phosphatidylethanolamine, a Potential Marker for Hyperglycemia, in Streptozotocin‐Induced Diabetic Rats

It has been demonstrated in vivo that lipid glycation products such as Amadori-glycated phosphatidylethanolamine (Amadori-PE) accumulate in the plasma of diabetic humans and animals, but how lipid glycation products are formed under hyperglycemic conditions are not clear. We sought to clarify the occurrence of lipid glycation and its relationships with lipid peroxidation and protein glycation during the development of hyperglycemia using the streptozotocin (STZ)-induced diabetic rat model. A significant increase in Amadori-PE was observed in STZ rats 7days after STZ treatment, and Amadori-PE (especially 18:0-20:4 Amadori-PE) was found at high levels in the blood and in organs that are strongly affected by diabetes, such as the kidney. Significant changes in Amadori-PE appeared to occur prior to changes in levels of oxidized lipids, which increased after 21-28days. In addition, accumulation of Nε-(carboxymethyl)lysine (CML), a protein glycation product, proceeded somewhat more slowly and moderately than that of Amadori-PE, suggesting that Amadori-PE and CML are early and advanced glycation products, respectively. Our results suggest that Amadori-PE may be a useful predictive marker for hyperglycemia, particularly in the early stages of diabetes. Similar speculations have been made from previous human studies, but this study provides a direct evidence to support the speculations in rat study.

Quantitative analysis of glycation patterns in human serum albumin using 16O/18O-labeling and MALDI–TOF MS

BackgroundThe glycation of human serum albumin (HSA) during diabetes can affect the ability of this protein to bind drugs and small solutes in blood. This study describes the use of 16O/18O-labeling and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to compare the levels of modification that occur throughout HSA under various glycation conditions in vitro. These quantitative studies build on a recent report that has identified the early and advanced glycation products that are formed on such samples of HSA. MethodsGlycated HSA samples were prepared by incubating 42g/l HSA with 0 to 15mmol/l glucose at pH 7.4 and 37°C for up to 5weeks. A control HSA sample was digested in 16O-enriched water and glycated HSA samples were digested in the presence of 18O-enriched water. These 2 types of samples were then mixed and the amounts of 16O- vs. 18O-labeled peptides were measured to determine the levels of modification that were occurring throughout HSA. ResultsThe largest levels of modification occurred in residues 101–119, 1–10 or 42–51, 87–100, 360–372, 521–531, and 275–286 of HSA after 2weeks of glycation, and in residues 21–41, 1–10 or 42–51, 521–531, 82–93, and 146–160 after 5weeks of glycation. Some of these regions contained the N-terminus, K199, K439, and K525, which have been previously identified as major glycation sites on HSA. The glycation pattern of HSA was dominated by early glycation products (e.g., fructosyl-lysine) after a reaction period of 2weeks for mildly glycated HSA, while advanced glycation end products became more prominent at longer reaction times. ConclusionsThe time course of the observed modifications indicated that the pattern of glycation products changed as HSA was incubated over longer periods of time with glucose. Several regions found to have significant levels of modification were at or near the major drug binding regions on HSA. These results explain why the interaction of some drugs with HSA has been observed to vary with the level of glycation for this protein.

A Glimpse of Various Pathogenetic Mechanisms of Diabetic Nephropathy

Diabetic nephropathy is a well-known complication of diabetes and is a leading cause of chronic renal failure in the Western world. It is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments and by the thickening and hyalinization of intrarenal vasculature. The various cellular events and signaling pathways activated during diabetic nephropathy may be similar in different cell types. Such cellular events include excessive channeling of glucose intermediaries into various metabolic pathways with generation of advanced glycation products, activation of protein kinase C, increased expression of transforming growth factor β and GTP-binding proteins, and generation of reactive oxygen species. In addition to these metabolic and biochemical derangements, changes in the intraglomerular hemodynamics, modulated in part by local activation of the renin-angiotensin system, compound the hyperglycemia-induced injury. Events involving various intersecting pathways occur in most cell types of the kidney.

S100B alters neuronal survival and dendrite extension via RAGE‐mediated NF‐κB signaling

S100B is a soluble protein secreted by astrocytes that exerts pro-survival or pro-apoptotic effects depending on the concentration reached in the extracellular millieu. The S100B receptor termed RAGE (for receptor for advanced end glycation products) is highly expressed in the developing brain but is undetectable in normal adult brain. In this study, we show that RAGE expression is induced in cortical neurons of the ischemic penumbra. Increased RAGE expression was also observed in primary cortical neurons exposed to excitotoxic glutamate (EG). S100B exerts effects on survival pathways and neurite extension when the cortical neurons have been previously exposed to EG and these S100B effects were prevented by anti-RAGE blocking antibodies. Furthermore, nuclear factor kappa B (NF-κB) is activated by S100B in a dose- and RAGE-dependent manner and neuronal death induced by NF-κB inhibition was prevented by S100B that restored NF-κB activation levels. Together, these findings suggest that excitotoxic damage can induce RAGE expression in neurons from ischemic penumbra and demonstrate that cortical neurons respond to S100B through engagement of RAGE followed by activation of NF-κB signaling. In addition, basal NF-κB activity in neurons is crucial to modulate the extent of pro-survival or pro-death S100B effects.

Synergistic benefit of combined amlodipine plus atorvastatin on neuronal damage after stroke in Zucker metabolic rat

Stroke is a major neurologic disorder and a leading cause of death in the world. We compared neuroprotective effects of single or combination therapy of amlodipine (AM) and atorvastatin (AT) in such a metabolic syndrome model Zucker rat after 90 min of transient middle cerebral artery occlusion (tMCAO). The animals were pretreated with vehicle, AM, AT, or the combination of AM plus AT for 28 days, and at 24 h of tMCAO, infarct volume and immunohistochemical analyses were performed. The combination of AM plus AT treatment decreased the infarct volume stronger than each single treatment with AM or AT. The numbers of positive cells of oxidative stress markers such as 8-hydroxy-2′-deoxyguanosin (8-OHdG), 4-hydroxy-2-nonenal (4-HNE), and advanced end glycation products (AGE) and inflammation markers such as tumor necrosis factor alpha (TNF-α) and monocyte chemoattractant protein-1(MCP-1) decreased dramatically in the combination-treated group compared with single AM- or AT-treated group. The present study showed that single AM or AT treatment showed neuroprotective effects both with antioxidative and anti-inflammatory mechanisms, but combination therapy of AM plus AT presented a further synergistic benefit in acute ischemic neural damages.

Anaerobic vs aerobic pathways of carbonyl and oxidant stress in human lens and skin during aging and in diabetes: A comparative analysis

The effects of anaerobic (lens) vs aerobic (skin) environment on carbonyl and oxidant stress are compared using de novo and existing data on advanced glycation and oxidation products in human crystallins and collagen. Almost all modifications increase with age. Methylglyoxal hydroimidazolones, carboxymethyllysine, and carboxyethyllysine are severalfold higher in lens than in skin and markedly increase upon incubation of lens crystallins with 5 mM ascorbic acid. In contrast, fructose-lysine, glucosepane crosslinks, glyoxal hydroimidazolones, metal-catalyzed oxidation (allysine), and H 2O 2-dependent modifications (2-aminoapidic acid and methionine sulfoxide) are markedly elevated in skin, but relatively suppressed in the aging lens. In both tissues ornithine is the dominant modification, implicating arginine residues as the principal target of the Maillard reaction in vivo. Diabetes (here mostly type 2 studied) increases significantly fructose-lysine and glucosepane in both tissues ( P < 0.001) but has surprisingly little effect on the absolute level of most other advanced glycation end products. However, diabetes strengthens the Spearman correlation coefficients for age-related accumulation of hydrogen peroxide-mediated modifications in the lens. Overall, the data suggest that oxoaldehyde stress involving methylglyoxal from either glucose or ascorbate is predominant in the aging noncataractous lens, whereas aging skin collagen undergoes combined attack by nonoxidative glucose-mediated modifications, as well as those from metal-catalyzed oxidation and H 2O 2.

Effect of elementary and advanced glycation products of nisin on its preservative efficacy and digestibility

Nisin used as a natural preservative in variety of food systems was subjected to glycation at 95 °C in high molar concentration. The elementary glycation end products (EGEs) and the advanced glycated end products (AGEs) formed were tested as compared to non-glycation nisin (NN) for their antibacterial activity against some food spoilage organisms such as Staphylococcus aureus, Bacillus cereus, Micrococcus luteus, Clostridium botulinum and Lactobacillus sake. The extent of hydrolysis of EGEs and AGEs by trypsin was also compared with the (NN) as control. The results have illustrated that antibacterial activity of nisin was substantially affected by the process of glycation in case of all the five organisms selected for the study, suggesting that the glycation of nisin, whether in vivo or in vitro will adversely affect the preservation of foods. Moreover glycation also reduced the tryptic digestibility of EGEs by 5.2% and AGEs by 50.325% as compared to NN. The data indicated that amount of nisin, if added to carbohydrate consisting foods should be increased accordingly to claim the reported shelf life of the products and food labelling in such products needs cardinal modification. Although hydrolysis of glycated nisin by trypsin is slightly decreased, however; it will not produce any adverse effect on human digestion in view of the minute amount of nisin present in the food system.

Non-enzymatic glycation of proteins: from diabetes to cancer

Incubation of proteins with glucose leads to their non-enzymatic glycation and formation of Amadori products known as an early glycation product. Oxidative cleavage of Amadori products is considered as a major route to advanced glycation endproducts (AGEs) formation in vivo. Nonenzymatic glycation of proteins or Maillard reaction is increased in diabetes mellitus due to hyperglycemia and leads to several complications such as blindness, heart disease, nerve damage and kidney failure. Accumulation of the early and advanced glycation products in plasma and tissues of diabetic patients and causes production of autoantibodies against corresponding products. The advanced glycation products are also associated with other diseases like cancer. This review summarizes current knowledge of these stage specific glycated products as common and early diagnostic biomarkers for the associated diseases and the complications with the aim of a novel therapeutic target for the diseases.

Targeting Leukostasis for the Treatment of Early Diabetic Retinopathy

Leukocyte-endothelial interaction plays an important role in the early phase of the development of diabetic retinopathy. It has been studied extensively linking inflammatory processes to its development conducted to date in rats and mice, and have focused on insulin-deficient models. The molecular and functional changes that are characteristics of inflammation have been detected in retinas from diabetic animals and humans with involvement of multiple pathways that results in the final sequelae of increased permeability of the blood retinal barrier and finally ischemia that drives angiogenesis. Increased expression of Intracellular adhesion molecules heralds the onset of changes that results in attraction of leucocytes such as neutrophils. The consequent release of cytokines and growth factors such as vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha, and interleukin 1-Beta results in increased permeability and retinal edema. Other indirect mediators involved include pathways such as the protein kinase C (PKC), renin-angiotensin system, enzymes such as the poly ADP-ribose polymerase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, nitric oxide synthetase and finally advanced glycation products. Therapy for early diabetic retinopathy may inhibit one or more of these pathways using drugs that can be given systemically, with local ocular applications having a more direct effect as in other eye diseases.

Vascular dysfunction in the diabetic placenta: causes and consequences

The development and functioning of the human fetoplacental vascular system are vulnerable to the maternal diabetic milieu. These vessels are in direct continuum with the fetal vascular system and are therefore also vulnerable to fetal endocrine derangements. Increased angiogenesis, altered junctional maturity and molecular occupancy, together with increased leakiness, constitute a well-described phenotype of vessels in the Type 1 diabetic human placenta and can be related to increased levels of placental vascular endothelial growth factor. The causes of these observed changes, whether maternal hyperglycaemia or fetal hyperinsulinaemia, still remain to be shown in the human placenta. Mechanistic studies using different vascular systems have shown high glucose and insulin to have profound vascular effects, with elevations in vascular endothelial growth factor, nitric oxide and protein kinase C being behind alterations in junctional adhesion molecules such as occludin and vascular endothelial-cadherin and vascular leakage of albumin. The role of advanced glycation products and oxidative stress in this vascular pathology is also discussed. The altered molecular mechanisms underlying the vascular changes in the diabetic human placenta may reflect similar consequences of high glucose and hyperinsulinaemia.