Key structural and functional differences between early and advanced glycation products

Inhibition of toxic metal-alpha synuclein interactions by human serum albumin

Human serum albumin (HSA), the most abundant protein in plasma and cerebrospinal fluid, not only serves as a crucial carrier of various exogenous and endogenous ligands but also modulates the aggregation of amyloidogenic proteins, including alpha synuclein (αSyn), which is associated with Parkinson's disease and other α-synucleinopathies. HSA decreases αSyn toxicity through the direct binding to monomeric and oligomeric αSyn species. However, it is possible that HSA also sequesters metal ions that otherwise promote aggregation. Cu(ii) ions, for example, enhance αSyn fibrillization in vitro, while also leading to neurotoxicity by generating reactive oxygen species (ROS). However, it is currently unclear if and how HSA affects Cu(ii)-binding to αSyn. Using an integrated set of NMR experiments, we show that HSA is able to chelate Cu(ii) ions from αSyn more efficiently than standard chelators such as EDTA, revealing an unexpected cooperativity between the HSA metal-binding sites. Notably, fatty acid binding to HSA perturbs this cooperativity, thus interfering with the sequestration of Cu(ii) ions from αSyn. We also observed that glycation of HSA diminished Cu(ii)-binding affinity, while largely preserving the degree of cooperativity between the HSA metal-binding sites. Additionally, our results show that Cu(ii)-binding to HSA stabilizes the interactions of HSA with αSyn primarily at two different regions, i.e. the N-terminus, Tyr 39 and the majority of the C-terminus. Our study not only unveils the effect of fatty acid binding and age-related posttranslational modifications, such as glycation, on the neuroprotective mechanisms of HSA, but also highlights the potential of αSyn as a viable NMR-based sensor to investigate HSA-metal interactions.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives: An update

1-Amino-1-deoxy-d-fructose (fructosamine, FN) derivatives are omnipresent in all living organisms, as a result of non-enzymatic condensation and Amadori rearrangement reactions between free glucose and biogenic amines such as amino acids, polypeptides, or aminophospholipids. Over decades, steady interest in fructosamine was largely sustained by its role as a key intermediate structure in the Maillard reaction that is responsible for the organoleptic and nutritional value of thermally processed foods, and for pathophysiological effects of hyperglycemia in diabetes. New trends in fructosamine research include the discovery and engineering of FN-processing enzymes, development of advanced tools for hyperglycemia monitoring, and evaluation of the therapeutic potential of both fructosamines and FN-recognizing proteins. This article covers developments in the field of fructosamine and its derivatives since 2010 and attempts to ascertain challenges in future research.

The association between orthostatic blood pressure changes and arterial stiffness

OBJECTIVE

Although orthostatic hypotension (OH) and orthostatic hypertension (OHT) can independently predict cardiovascular events, the underlying mechanisms remain controversial. Our study aimed to examine the relationships between orthostatic blood pressure (BP) changes and arterial stiffness.

METHODS

In this cross-sectional analysis, 1820 participants were divided into three groups according to BP changes within 3 min of orthostatism: the OH group had a decrease of >20 mmHg in SBP or >10 mmHg in DBP, the OHT group had an increase of ≥20 mmHg in SBP, and the orthostatic normotensive (ONT) group had normal changes. Arterial stiffness was assessed by measuring the carotid-femoral pulse wave velocity (cfPWV).

RESULTS

OH and OHT were observed in 257 (14.1%) and 62 (3.4%) participants, respectively. Subjects in the OH group were significantly older, were more likely to have hypertension and diabetes, and had higher cfPWV than those in the ONT group ( P  < 0.05); however, no differences were found between the ONT and OHT groups. Stepwise multiple regression analysis of the subgroups stratified by hypertension and diabetes revealed that age was related to increased cfPWV in all stratifications, and the change in SBP was significantly positively correlated with cfPWV in hypertensive subjects; however, this association was not observed in nonhypertensive subjects.

CONCLUSION

We found that arterial stiffness was closely related to OH but not to OHT. In addition to expanding current knowledge of the relationship between orthostatic BP changes and arterial stiffness, our study underlines the importance of age, SBP changes, and hypertension in evaluating arterial stiffness.

Impact of Enhanced Phagocytosis of Glycated Erythrocytes on Human Endothelial Cell Functions

Diabetes is associated with a high mortality rate due to vascular complications. Chronic hyperglycemia in diabetes leads to enhanced oxidative stress and glycation. Here, we explored the impact of glycation on human erythrocyte characteristics and capacity to affect endothelial cell function following erythrophagocytosis. Native and glucose-mediated glycated erythrocytes were prepared and characterized in terms of structural and deformability modifications. Erythrocyte preparations were tested for their binding and phagocytosis capacity as well as the potential functional consequences on human endothelial cell lines and primary cultures. Oxidative modifications were found to be enhanced in glycated erythrocytes after determination of their deformability, advanced glycation end-product content and eryptosis. Erythrophagocytosis by endothelial cells was significantly increased when incubated in the presence of glycated erythrocytes. In addition, higher iron accumulation, oxidative stress and impaired endothelial cell permeability were evidenced in cells previously incubated with glycated erythrocytes. When cultured under flow conditions, cellular integrity was disrupted by glycated erythrocytes at microvessel bifurcations, areas particularly prone to vascular complications. This study provides important new data on the impact of glycation on the structure of erythrocytes and their ability to alter endothelial cell function. Increased erythrophagocytosis may have a deleterious impact on endothelial cell function with adverse consequences on diabetic vascular complications.

Synergism between obesity and HFpEF on neutrophils phenotype and its regulation by adipose tissue-molecules and SGLT2i dapagliflozin

The adiposity invokes innate immune activity, coronary microvascular dysfunction and consequently heart failure preserved ejection fraction (HFpEF). Our aim was to study the neutrophils profile on obesity and cardiovascular disease and its regulation by adipose tissue-secretome and dapagliflozin. We have isolated neutrophils from patients undergoing open heart surgery (19 women and 51 men). Its migration activity was performed with culture-transwell, transcriptional studies of proteolytic enzymes, adhesion molecules or receptors were analysed by real-time PCR and proteomics (from 20 patients) analysis by TripleTOF mass spectrometer. Differentiated HL-60 (dHL-60) was used as a preclinical model on microfluidic for endothelial cells attaching assays and genes regulation with epicardial and subcutaneous fat secretomes from patients (3 women and 9 men) or dapagliflozin 1-10 μM treatments. The transcriptional and proteomics studies have determined higher levels of adhesion molecules in neutrophils from patients with obesity. The adhesion molecule CD11b levels were higher in those patients with the combined obesity and HFpEF factors (1.70 ± 0.06 a.u. without obesity, 1.72 ± 0.04 a.u. obesity or HFpEF without obesity and 1.79 ± 0.08 a.u. obesity and HFpEF; p < .01). While fat-secretome induces its upregulation, dapagliflozin can modulated it. Because CD11b upregulation is associated with higher neutrophils migration and adhesion into endothelial cells, dapagliflozin might modulate this mechanism on patients with obesity and HFpEF.

Haemodynamic-dependent arrest of circulating tumour cells at large blood vessel bifurcations as new model for metastasis

Homing of circulating tumour cells (CTC) at distant sites represents a critical event in metastasis dissemination. In addition to physical entrapment, probably responsible of the majority of the homing events, the vascular system provides with geometrical factors that govern the flow biomechanics and impact on the fate of the CTC. Here we mathematically explored the distribution of velocities and the corresponding streamlines at the bifurcations of large blood vessel and characterized an area of low-velocity at the carina of bifurcation that favours the residence of CTC. In addition to this fluid physics effect, the adhesive capabilities of the CTC provide with a biological competitive advantage resulting in a marginal but systematic arrest as evidenced by dynamic in vitro recirculation in Y-microchannels and by perfusion in in vivo mice models. Our results also demonstrate that viscosity, as a main determinant of the Reynolds number that define flow biomechanics, may be modulated to limit or impair CTC accumulation at the bifurcation of blood vessels, in agreement with the apparent positive effect observed in the clinical setting by anticoagulants in advanced oncology disease.

Controlled Formation of Carboxymethyllysine in Bone Matrix through Designed Glycation Reaction

It has been a challenge to establish a link between specific advanced glycation end products (AGEs) as causal agents of different pathologies and age‐related diseases, primarily because of the lack of suitable in vitro experimental strategies facilitating increased formation of a specific AGE, here carboxymethyllysine (CML), over other AGEs under controlled conditions. CML is of considerable importance to various oxidative stress–related diseases, because in vivo formation of this AGE is connected with cellular oxidative/carbonyl metabolism. The mechanistic implications of CML accumulation in bone remain to be elucidated. To facilitate such studies, we developed a new in vitro strategy that allows preferential generation of CML in bone matrix over other AGEs. Using bone samples from human donors of different age (young, middle‐age, and elderly), we show successful in vitro generation of the desired levels of CML and show that they mimic those observed in vivo in several bone disorders. Formation of such physiologically relevant CML levels was achieved by selecting two oxidative/carbonyl stress compounds naturally produced in the human body, glyoxal and glyoxylic acid. Kinetic studies using the two compounds revealed differences not only between their reaction rates but also in the progression and enhanced formation of CML over other AGEs (measured by their collective fluorescence as fluorescent AGEs [fAGEs]) Consequently, through the regulation of reaction time, the levels of CML and fAGEs could be controlled and separated. Given that the developed approach does not fully eliminate the formation of other uncharacterized glycation products, this could be considered as the study limitation. We expect that the concepts of our experimental approach can be used to develop diverse strategies facilitating production of the desired levels of selected AGEs in bone and other tissues, and thus, opens new avenues for investigating the role and mechanistic aspects of specific AGEs, here CML, in bone. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Microfluidic devices manufacturing with a stereolithographic printer for biological applications

Stereolithographic printers have revolutionized many manufacturing processes with their capacity to easily produce highly detailed structures. In the field of microfluidics, this technique avoids the use of complex steps and equipment of the conventional technologies. The potential of low force stereolithography technology is analysed for the first time using a Form 3B printer and seven printing resins through the fabrication of microchannels and pillars. Manufacturing performance of internal and superficial channels and pillars is studied for the seven printing resins in different configurations. A complete characterization of printed structures is carried out by optical, confocal and SEM microscopy, and EDX analysis. Internal channels with unobstructed lumen are obtained for diameters and angles greater than 500 μm and 60°, respectively. Outward and inward superficial channels in the range of hundreds of microns can be fabricated with an accurate profile, printing them with a perpendicular orientation respect to the base, allowing a proper uncured resin evacuation. Outward channels are replicated by soft lithography using polydimethylsiloxane. Clear, Model and Tough resins show a good behaviour to be used as master, but Amber and Dental resins present a poor topology transference from the master to the replica. According to the needs of devices used for biological and biomedical research, transparency as well as superficial biocompatibility of some resins is evaluated. Human umbilical vein endothelial cells (HUVEC) adhesion is confirmed on Amber, Dental and Clear resins, but these cells were only able to grow and progress as a cell culture over the Amber resin. Therefore, Amber showed an adequate biocompatibility, in terms of cell adhesion and growth for HUVEC.

Soluble angiotensin-converting enzyme levels in heart failure or acute coronary syndrome: revisiting its modulation and prognosis value

The main objective was to compare the meaning of soluble angiotensin-converting enzyme-2 (sACE2) plasma levels modulation on the prognosis of two cohorts of heart failure (HF) and acute coronary syndrome (ACS). We conducted an observational clinical study where sACE2 was measured in two cohorts of HF or ACS (102 patients each), matched by age and gender. The primary endpoint (cardiac death) and the secondary endpoints (non-fatal myocardial infarction or HF readmission) were registered during a 5-year follow-up period. Association with pharmacotherapy was studied, and the effects of cardiovascular drugs on ACE isoforms expression were analysed in human umbilical vein endothelial cells (HUVEC) in vitro. The levels of sACE2 were significantly higher in the HF than ACS cohort. sACE2 was inversely related with the leukocytes number and directly with urea levels. In the ACS cohort, sACE2 was associated with age and glycaemic parameters, but in the HF cohort, the association was with N-terminal pro-B-type natriuretic peptide. The levels of sACE2 were related to long-term prognosis and confirmed as a non-independent predictor in the HF cohort. Soluble ACE2 was higher in patients treated with angiotensin receptors blockers and β-blockers, accordingly with losartan and metoprolol upregulation of ACE1 and ACE2 in HUVECs. Plasma levels of sACE2 were higher in HF than in ACS, independently of age and gender, and were related to long-term cardiac death in the HF cohort. Losartan and metoprolol, but not enalapril, upregulated ACE expression in endothelial cells, accordingly with higher levels of sACE2 in patients using these drugs.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Minimal invasive fluorescence methods to quantify advanced glycation end products (AGEs) in skin and plasma of humans

Advanced glycation end products (AGEs) are non-enzymatic modifications of proteins and lipids, which are spontaneously produced in the body in relation with several human diseases. Their relevance on protein functions alteration, either structural or enzymatic is under study, but their value as biomarkers or predictors of disease progression and clinical outcomes is unquestionable. The heterogeneity and amplitude of these modifications make their analysis difficult, although, different methods have been developed for specific AGEs based on colorimetric reactions, immunoassays or chromatography. However, for a massive application on human population, methods based on the autofluorescence of some AGEs stand out. Several qualities of these methods such as label-free measurement, rapidity, cost-effectiveness, and minimal invasiveness make them very useful for periodic measurements in critically ill patients and for the analysis of large populations. Here we explain the rationale of these methods, and we present a step-by-step protocol and the equipment requirements to carry out the estimation of AGE content in skin and plasma. AGE plasma content and skin accumulation are temporally related, so AGE plasmatic levels are a possible predictor of skin AGE content. On the other hand, AGE skin accumulation is a surrogate or an indicator of past AGE levels in plasma and in the rest of the body. AGE levels or their variations have shown to be related with prognosis of several diseases, so they can be used as predictor biomarkers for clinicians.

Advanced glycation end-products disrupt brain microvascular endothelial cell barrier: The role of mitochondria and oxidative stress

During diabetes mellitus, advanced glycation end-products (AGEs) are major contributors to the development of alterations in cerebral capillaries, leading to the disruption of the blood-brain barrier (BBB). Consequently, this is often associated with an amplified oxidative stress response in microvascular endothelial cells. As a model to mimic brain microvasculature, the bEnd.3 endothelial cell line was used to investigate cell barrier function. Cells were exposed to native bovine serum albumin (BSA) or modified BSA (BSA-AGEs). In the presence or absence of the antioxidant compound, N-acetyl-cysteine, cell permeability was assessed by FITC-dextran exclusion, intracellular free radical formation was monitored with H₂DCF-DA probe, and mitochondrial respiratory and redox parameters were analyzed. We report that, in the absence of alterations in cell viability, BSA-AGEs contribute to an increase in endothelial cell barrier permeability and a marked and prolonged oxidative stress response. Decreased mitochondrial oxygen consumption was associated with these alterations and may contribute to reactive oxygen species production. These results suggest the need for further research to explore therapeutic interventions to restore mitochondrial functionality in microvascular endothelial cells to improve brain homeostasis in pathological complications associated with glycation.

Carrageenan-based physically crosslinked injectable hydrogel for wound healing and tissue repairing applications

In this study, a novel injectable hydrogel based on iota and kappa carrageenan, locust bean gum and gelatin was prepared for wound healing and tissue repairing applications. This injectable hydrogel was obtained via physical crosslinking. FTIR analysis confirmed the physical interaction between the biopolymeric components of the hydrogel. The prepared injectable hydrogel exhibited shear-thinning characteristics and could be injected for minimally invasive applications. Also, the hydrogel showed a porous structure, physiological and mechanical stability and biocompatibility. The in vitro cell culture studies showed that fibroblasts were able to grow, adhere and spread inside the hydrogel, indicating that hydrogel could support tissue repair. Moreover, hydrogel could be useful for the delivery of biomolecules. Vascular endothelial growth factor was encapsulated within the hydrogel and subsequently released, which accelerated the migration of human umbilical vein endothelial cells and facilitated in vitro wound healing. Overall, the results indicate that hydrogel can be a potential injectable delivery vehicle for wound healing and tissue repair.

Enhanced oxidative stress and damage in glycated erythrocytes

Diabetes is associated with a dramatic mortality rate due to its vascular complications. Chronic hyperglycemia in diabetes leads to enhanced glycation of erythrocytes and oxidative stress. Even though erythrocytes play a determining role in vascular complications, very little is known about how erythrocyte structure and functionality can be affected by glycation. Our objective was to decipher the impact of glycation on erythrocyte structure, oxidative stress parameters and capacity to interact with cultured human endothelial cells. In vitro glycated erythrocytes were prepared following incubation in the presence of different concentrations of glucose. To get insight into the in vivo relevance of our results, we compared these data to those obtained using red blood cells purified from diabetics or non-diabetics. We measured erythrocyte deformability, susceptibility to hemolysis, reactive oxygen species production and oxidative damage accumulation. Altered structures, redox status and oxidative modifications were increased in glycated erythrocytes. These modifications were associated with reduced antioxidant defence mediated by enzymatic activity. Enhanced erythrocyte phagocytosis by endothelial cells was observed when cultured with glycated erythrocytes, which was associated with increased levels of phosphatidylserine-likely as a result of an eryptosis phenomenon triggered by the hyperglycemic treatment. Most types of oxidative damage identified in in vitro glycated erythrocytes were also observed in red blood cells isolated from diabetics. These results bring new insights into the impact of glycation on erythrocyte structure, oxidative damage and their capacity to interact with endothelial cells, with a possible relevance to diabetes.

Edoxaban's contribution to key endothelial cell functions

BACKGROUND

We aimed to study the effects of the new oral anticoagulant edoxaban, a factor X activated (FXa) inhibitor, on key endothelial functions that could contribute to cardiovascular benefit.

METHODS

Human umbilical endothelial cells (HUVEC) were obtained from donated umbilical cords and used to analyse 1) structural functions like cell proliferation, migration, and angiogenesis in appropriate assays; 2) anti-inflammatory reactions as mononuclear cell (PBMC) or platelet adhesion to HUVEC monolayers; and 3) haemostasis control by fibrin formation or plasminogen activator modulation. Key molecular effectors and signalling pathways on each function were explored by profiled protein arrays, mRNA, or protein expression analyses.

RESULTS

Edoxaban promoted viability and growth in HUVEC cultures, as well as counteracted the promigratory and antiangiogenic effects of FXa, through action on the PI3K/AKT pathway. Edoxaban inhibited the adhesion to endothelial cells and the transmigration through endothelial monolayers of PBMC, and even counteracted the action of pro-inflammatory stimuli such as FXa by blocking the FXa-induced expression of cell adhesion molecules via the PAR 1-2/PI3K/NF-kB pathway. Haemostatic control of edoxaban could be exerted from the endothelium by the reduction of platelets' adhesion to endothelial cells and the possible acute activation of urokinase plasminogen activator.

CONCLUSIONS

Edoxaban is a safe and structural stabilizing factor for endothelial cells and also has remarkable anti-inflammatory action, preventing PBMC adhesion and transmigration through the endothelium. It may also contribute to haemostasis control by reducing platelet adhesion. Its main molecular mechanism seems to be the control of the PI3K/NF-κB pathways.

Antirhea borbonica Aqueous Extract Protects Albumin and Erythrocytes from Glycoxidative Damages

Diabetes constitutes a major health problem associated with severe complications. In hyperglycemic conditions, chronically increased oxidation and glycation of circulating components lead to advanced glycation end-products (AGEs) formation, a key contributor in diabetes complication progression. In line with literature documenting the beneficial properties of herbal teas, this study evaluates the antioxidant/glycant properties of Antirhea borbonica (Ab). Ab aqueous extract effects were tested on human albumin or erythrocytes submitted to methyl glyoxal-mediated glycoxidative damages. By using mass spectrometry, Ab aqueous extracts revealed to be rich in polyphenols. All tested biomarkers of oxidation and glycation, such as AGE, ketoamine, oxidized thiol groups, were decreased in albumin when glycated in the presence of Ab aqueous extract. Ab extract preserve erythrocyte from methylglyoxal (MGO)-induced damages in terms of restored membrane deformability, reduced oxidative stress and eryptosis phenomenon. Antioxidant capacities of Ab extract on erythrocytes were retrieved in vivo in zebrafish previously infused with MGO. These results bring new evidences on the deleterious impacts of glycation on albumin and erythrocyte in diabetes. Furthermore, it reveals antioxidant and antiglycant properties of Ab that could be used for the dietary modulation of oxidative stress and glycation in hyperglycemic situations.

Comparison of Hemoglobin Alc, Glycated Albumin and Fasting Plasma Glucose for Prediction of Arterial Stiffness in Chinese Adults

OBJECTIVE

Although diabetes is closely related to cardiovascular disease, there are some disputes whether diabetes can promote arterial stiffness. Therefore, the objective of this study is to compare the predictive abilities of related-glycemic markers including fast plasma glucose (FPG), glycated hemoglobin (HbAlc) and glycated albumin (GA) for the arterial stiffness.

METHODS

In the present study, 3640 subjects (2171 men, 1469 women) were enrolled, and anthropometrics, brachial ankle pulse wave velocity (baPWV) and other laboratory data were obtained. Spearman correlation and multivariate logistic regression analyses were used to evaluate the relationships between FPG, HbAlc, GA and baPWV.

RESULTS

Age, BMI, blood pressure, blood lipids, γ-Glutamyl transpeptidase, uric acid, hypersensitive C-reactive protein, baPWV, FPG, HbAlc, GA, estimated glomerular filtration rate and the incidences of diabetes and hypertension in high baPWV group were much greater than those in control group. Moreover, these above three glycemic markers were positively related to baPWV, and the correlation coefficient of HbAlc was the highest. After adjusting the above factors, HbAlc and FPG, but not GA, were still positively associated with baPWV regardless of diabetes status.

CONCLUSION

Our data demonstrated that, regardless of diabetes status, HbAlc and FPG were superior to GA for predicting arterial stiffness and HbAlc had the highest correlation with arterial stiffness, revealing that HbAlc may be regarded as an early diagnosis marker for atherosclerosis.

Influence of Human Serum Albumin Glycation on the Binding Affinities for Natural Flavonoids

Increasing the degree of glycation in diabetes could affect the ability of plasma proteins in binding to small molecules and active compounds. In this study, the influence of glycation of Human serum albumin (HSA) on the binding affinities for six dietary flavonoids was investigated by fluorescence spectra. Glycated HSA was prepared through incubation with glucose and characterized by several methods to confirm the glycation. It was found that the level of glycation increased with the increasing incubation time. The glycation of HSA increased the binding affinities for flavonoids by 1.40 to 48.42 times, which indicates that modifications caused by the glycation may have different influences on the interactions of flavonoids with HSA at separate binding sites on this protein. These results are valuable for understanding the influence of diabetes on the metabolism of flavonoids and other bioactive small molecules in human body.

Advanced glycation end-products disrupt human endothelial cells redox homeostasis: new insights into reactive oxygen species production

Advanced glycation end-products (AGEs) trigger multiple metabolic disorders in the vessel wall that may in turn lead to endothelial dysfunction. The molecular mechanisms by which AGEs generate these effects are not completely understood. Oxidative stress plays a key role in the development of deleterious effects that occur in endothelium during diabetes. Our main objectives were to further understand how AGEs contribute to reactive oxygen species (ROS) overproduction in endothelial cells and to evaluate the protective effect of an antioxidant plant extract. The human endothelial cell line EA.hy926 was treated with native or modified bovine serum albumin (respectively BSA and BSA-AGEs). To monitor free radicals formation, we used H₂DCF-DA, dihydroethidium (DHE), DAF-FM-DA and MitoSOX Red dyes. To investigate potential sources of ROS, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial inhibitors were used. The regulation of different types of ROS by the polyphenol-rich extract from the medicinal plant Doratoxylon apetalum was also studied for a therapeutic perspective. BSA-AGEs exhibited not only less antioxidant properties than BSA, but also pro-oxidant effects. The degree of albumin glycoxidation directly influenced oxidative stress through a possible communication between NADPH oxidase and mitochondria. D. apetalum significantly decreased intracellular hydrogen peroxide and superoxide anions mainly detected by H₂DCF-DA and DHE respectively. Our results suggest that BSA-AGEs promote a marked oxidative stress mediated at least by NADPH oxidase and mitochondria. D. apetalum plant extract appeared to be an effective antioxidant compound to protect endothelial cells.

A novel monoclonal antibody targeting carboxymethyllysine, an advanced glycation end product in atherosclerosis and pancreatic cancer

Advanced glycation end products are formed by non-enzymatic reactions between proteins and carbohydrates, causing irreversible lysine and arginine alterations that severely affect protein structure and function. The resulting modifications induce inflammation by binding to scavenger receptors. An increase in advanced glycation end products is observed in a number of diseases e.g. atherosclerosis and cancer. Since advanced glycation end products also are present in healthy individuals, their detection and quantification are of great importance for usage as potential biomarkers. Current methods for advanced glycation end product detection are though limited and solely measure total glycation. This study describes a new epitope-mapped single chain variable fragment, D1-B2, against carboxymethyllysine, produced from a phage library that was constructed from mouse immunizations. The phage library was selected against advanced glycation end product targets using a phage display platform. Characterization of its binding pattern was performed using large synthetic glycated peptide and protein libraries displayed on microarray slides. D1-B2 showed a preference for an aspartic acid, three positions N-terminally from a carboxymethyllysine residue and also bound to a broad collection of glycated proteins. Positive immunohistochemical staining of mouse atherosclerotic plaques and of a tissue microarray of human pancreatic tumors confirmed the usability of the new scFv for advanced glycation end product detection in tissues. This study demonstrates a promising methodology for high-throughput generation of epitope-mapped monoclonal antibodies against AGE.

Glycation of human serum albumin impairs binding to the glucagon-like peptide-1 analogue liraglutide

The long-acting glucagon-like peptide-1 analogue liraglutide has proven efficiency in the management of type 2 diabetes and also has beneficial effects on cardiovascular diseases. Liraglutide's protracted action highly depends on its capacity to bind to albumin via its palmitic acid part. However, in diabetes, albumin can undergo glycation, resulting in impaired drug binding. Our objective in this study was to assess the impact of human serum albumin (HSA) glycation on liraglutide affinity. Using fluorine labeling of the drug and ¹⁹F NMR, we determined HSA affinity for liraglutide in two glycated albumin models. We either glycated HSA in vitro by incubation with glucose (G25- or G100-HSA) or methylglyoxal (MGO-HSA) or purified in vivo glycated HSA from the plasma of diabetic patients with poor glycemic control. Nonglycated commercial HSA (G0-HSA) and HSA purified from plasma of healthy individuals served as controls. We found that glycation decreases affinity for liraglutide by 7-fold for G100-HSA and by 5-fold for MGO-HSA compared with G0-HSA. A similarly reduced affinity was observed for HSA purified from diabetic individuals compared with HSA from healthy individuals. Our results reveal that glycation significantly impairs HSA affinity to liraglutide and confirm that glycation contributes to liraglutide's variable therapeutic efficiency, depending on diabetes stage. Because diabetes is a progressive disease, the effect of glycated albumin on liraglutide affinity found here is important to consider when diabetes is managed with this drug.

Maillard Proteomics: Opening New Pages

Protein glycation is a ubiquitous non-enzymatic post-translational modification, formed by reaction of protein amino and guanidino groups with carbonyl compounds, presumably reducing sugars and α-dicarbonyls. Resulting advanced glycation end products (AGEs) represent a highly heterogeneous group of compounds, deleterious in mammals due to their pro-inflammatory effect, and impact in pathogenesis of diabetes mellitus, Alzheimer's disease and ageing. The body of information on the mechanisms and pathways of AGE formation, acquired during the last decades, clearly indicates a certain site-specificity of glycation. It makes characterization of individual glycation sites a critical pre-requisite for understanding in vivo mechanisms of AGE formation and developing adequate nutritional and therapeutic approaches to reduce it in humans. In this context, proteomics is the methodology of choice to address site-specific molecular changes related to protein glycation. Therefore, here we summarize the methods of Maillard proteomics, specifically focusing on the techniques providing comprehensive structural and quantitative characterization of glycated proteome. Further, we address the novel break-through areas, recently established in the field of Maillard research, i.e., in vitro models based on synthetic peptides, site-based diagnostics of metabolism-related diseases (e.g., diabetes mellitus), proteomics of anti-glycative defense, and dynamics of plant glycated proteome during ageing and response to environmental stress.

Protective, repairing and fibrinolytic effects of rivaroxaban on vascular endothelium

AIMS

Rivaroxaban, a direct inhibitor of activated factor X (FXa), is the only new oral anticoagulant approved for secondary prevention after acute coronary syndrome. Our objective was to identify the possible molecular mechanisms of rivaroxaban that contribute to endothelial function.

METHODS

Cell viability and growth of human umbilical vein endothelial cells (HUVEC) were registered. Gene expression studies comparing the effects of rivaroxaban and FXa were conducted by a selective RNA array and confirmed by protein quantification. Wound-healing experiments on HUVEC, platelet adhesion, enzymatic activity, and cell-based assays for fibrin formation were performed with rivaroxaban.

RESULTS

Rivaroxaban (50 nM) only altered (>2 fold change) the expression of matrix metallopeptidase 2 and urokinase plasminogen activator (u-PA), but counteracted the FXa (9 nM)-induced upregulation of several pro-inflammatory genes (P < 0.05) and FXa-enhanced platelet adhesion over HUVEC. Rivaroxaban increased u-PA protein expression in HUVEC supernatants and enhanced u-PA activity (up to 4 IU ng^-1 of u-PA). Rivaroxaban (1 nM-1 μM) showed a significant and dose-dependent positive effect on HUVEC growth that was inhibited by BC-11-hydroxibromide, an inhibitor of u-PA. Healing properties after a wound on HUVEC cultures, and fibrinolytic properties were also shown by rivaroxaban. Both effects were reversed by BC-11-hydroxibromide.

CONCLUSIONS

Rivaroxaban enhanced viability, growth and migration of HUVEC, mainly by u-PA activation and upregulation, which also participate in the rivaroxaban-induced fibrinolytic activity at endothelial level. Rivaroxaban also protected from the pro-inflammatory effects of FXa on HUVEC. Altogether may improve endothelial functionality and could contribute to the cardiovascular benefits of rivaroxaban.

Serum glycated albumin, glycated hemoglobin, and arterial stiffness in a general Chinese population

BACKGROUND

Both glycated albumin (GA) and glycated hemoglobin (HbA1c) reflect the mean glucose levels. This study was conducted to investigate the relationships among GA, HbA1c, and arterial stiffness in the general population.

METHODS

A total of 11,014 participants were included. Serum GA; HbA1c; and arterial stiffness indices, including brachial-ankle pulse wave velocity (baPWV) and central systolic blood pressure (cSBP), were measured. Single-factor and multivariate regression analyses were performed. Receiver operating characteristic (ROC) analysis was performed to compare the predictive value of GA, HbA1c, and their combination for arterial stiffness. All analyses were stratified by sex.

RESULTS

Men had a lower GA level than women. GA, HbA1c, and plasma glucose levels were correlated. The levels of baPWV and cSBP increased across sex-specific quartiles of GA and HbA1c (P for trend<0.001 for all). Both GA and HbA1c were positively related to elevated baPWV and cSBP after adjusting for conventional factors (P<0.05 for all). These relationships remained significant when participants were divided into groups with normal glucose tolerance, prediabetes, or diabetes. Regarding screening for elevated baPWV and cSBP, the values of the area under the ROC curve (AUC) for GA were similar to those for HbA1c in men but were lower than those for HbA1c in women. The combination of GA and HbA1c did not improve the AUC compared with HbA1c alone.

CONCLUSIONS

Both GA and HbA1c were associated with arterial stiffness. The predictive value of GA for arterial stiffness was similar in men but lower in women compared with that of HbA1c.

Diabetes-induced hepatic oxidative stress: a new pathogenic role for glycated albumin

Increased oxidative stress and advanced glycation end-product (AGE) formation are major contributors to the development of type 2 diabetes. Here plasma proteins e.g. albumin can undergo glycoxidation and play a key role in diabetes onset and related pathologies. However, despite recent progress linking albumin-AGE to increased oxidative stress and downstream effects, its action in metabolic organs such as the liver remains to be elucidated. The current study therefore investigated links between oxidative perturbations and biochemical/structural modifications of plasma albumin, and subsequent downstream effects in transgenic db/db mouse livers and HepG2 cells, respectively. Our data reveal increased oxidative stress biomarkers and lipid accumulation in plasma and livers of diabetic mice, together with albumin glycoxidation. Purified mouse albumin modifications resembled those typically found in diabetic patients, i.e. degree of glycation, carbonylation, AGE levels and in terms of chemical composition. Receptor for AGE expression and reactive oxygen species production were upregulated in db/db mouse livers, together with impaired proteolytic, antioxidant and mitochondrial respiratory activities. In parallel, acute exposure of HepG2 cells to glycated albumin also elicited intracellular free radical formation. Together this study demonstrates that AGE-modified albumin can trigger damaging effects on the liver, i.e. by increasing oxidative stress, attenuating antioxidant capacity, and by impairment of hepatic proteolytic and respiratory chain enzyme activities.

Local application of low-dose insulin in improving wound healing after deep burn surgery

The clinical effects of local application of low-dose insulin in improving wound healing after deep burn self-skin transplantation surgery were examined. Fifty-eight patients with deep burns were selected and randomly divided into 3 groups. In the blank control group, normal saline was injected to the subcutaneous tissue of wounds; in large dose insulin group, 1.0 µ long-term suspended zinc insulin was locally injected; and in the low-dose insulin group, 0.1 µ long-term suspended zinc insulin was locally injected. The healing effects were compared. After 7 and 14 days of treatments, wound surface area in the low-dose group was significantly smaller than in the other groups, and differences were statistically significant (P<0.05); wound healing duration and infection rate for patients in the low-dose group were significantly lower, class A healing rate was significantly improved, and the differences were statistically significant (P<0.05). Insulin resistance index (HOMA-IR) in the low-dose group was significantly lower, insulin secretion index (HOMA-β) and the insulin sensitivity index (HOMA-ISI) significantly increased. The expression levels of vascular endothelial growth factor and tumor necrosis factor-α in local tissue for the low-dose group were significantly higher than those in the other two groups. Differences were statistically significant (P<0.05). In conclusion, local application of low-dose insulin can effectively improve wound healing after deep burn surgeries.