3-Deoxyglucosone: a potential glycating agent accountable for structural alteration in H3 histone protein through generation of different AGEs

Endogenous advanced glycation end products in the pathogenesis of chronic diabetic complications

Diabetes is a common metabolic illness characterized by hyperglycemia and is linked to long-term vascular problems that can impair the kidney, eyes, nerves, and blood vessels. By increasing protein glycation and gradually accumulating advanced glycation end products in the tissues, hyperglycemia plays a significant role in the pathogenesis of diabetic complications. Advanced glycation end products are heterogeneous molecules generated from non-enzymatic interactions of sugars with proteins, lipids, or nucleic acids via the glycation process. Protein glycation and the buildup of advanced glycation end products are important in the etiology of diabetes sequelae such as retinopathy, nephropathy, neuropathy, and atherosclerosis. Their contribution to diabetes complications occurs via a receptor-mediated signaling cascade or direct extracellular matrix destruction. According to recent research, the interaction of advanced glycation end products with their transmembrane receptor results in intracellular signaling, gene expression, the release of pro-inflammatory molecules, and the production of free radicals, all of which contribute to the pathology of diabetes complications. The primary aim of this paper was to discuss the chemical reactions and formation of advanced glycation end products, the interaction of advanced glycation end products with their receptor and downstream signaling cascade, and molecular mechanisms triggered by advanced glycation end products in the pathogenesis of both micro and macrovascular complications of diabetes mellitus.

Plasma Levels of Advanced Glycation Endproducts and Risk of Cardiovascular Events: Findings From 2 Prospective Cohorts

Background Advanced glycation endproducts (AGEs) have been linked to cardiovascular disease (CVD) in cohorts with and without diabetes. Data are lacking on prospective associations of various α-dicarbonyl-derived AGEs and incident CVD in the general population. We tested the hypothesis that major plasma AGEs are associated with new-onset CVD in 2 population-based cohorts of differing age and comorbidities. Methods and Results Analyses involved a random subcohort (n=466) from the Cardiovascular Health Study and a case-cohort sample (n=1631) from the Multi-Ethnic Study of Atherosclerosis. Five AGEs and 2 oxidative products were measured by liquid chromatography tandem mass spectrometry. Associations with CVD (myocardial infarction and stroke) were evaluated with Cox regression. Participants in the Cardiovascular Health Study were older than the Multi-Ethnic Study of Atherosclerosis, and had more comorbidities, along with higher levels of all AGEs. During median follow-up of 11 years, 439 participants in the Multi-Ethnic Study of Atherosclerosis and 200 in the Cardiovascular Health Study developed CVD. After multivariable adjustment, carboxymethyl-lysine, 3-deoxyglucosone hydroimidazolones and a summary variable of all measured AGEs (principal component 1) were significantly associated with incident CVD in the Cardiovascular Health Study (HRs [95% CI]: 1.20 [1.01, 1.42], 1.45 [1.23, 1.72], and 1.29 [1.06, 1.56], respectively), but not the Multi-Ethnic Study of Atherosclerosis. Oxidative products were not associated with CVD in either cohort. Conclusions We found α-dicarbonyl-derived AGEs to be associated with CVD in an older cohort, but not in a healthier middle-aged/older cohort. Our results suggest that AGEs may exert detrimental cardiovascular effects only under conditions of marked dicarbonyl and oxidative stress. Further investigation of α-dicarbonyl derivatives could lead to potential new strategies for CVD prevention in high-risk older populations.

Integrated Multi-Omics Data Analysis Reveals Associations Between Glycosylation and Stemness in Hepatocellular Carcinoma

Background

Glycosylation plays an essential role in driving the progression and treatment resistance of hepatocellular carcinoma (HCC). However, its function in regulating the acquisition and maintenance of the cancer stemness-like phenotype in HCC remains largely unknown. There is also very little known about how CAD and other potential glycosylation regulators may influence stemness. This study explores the relationship between glycosylation and stemness in HCC.

Methods

Gene set variance analysis (GSVA) was used to assess the TCGA pan-cancer enrichment in glycosylation-related pathways. Univariate, LASSO, and multivariate COX regression were then used to identify prognostic genes in the TCGA-LIHC and construct a prognostic signature. HCC patients were classified into high- and low-risk subgroups based on the signature. The relationship between gene expression profiles and stemness was confirmed using bulk and single-cell RNA-sequencing data. The role of CAD and other genes in regulating the stemness of HCC was also validated by RT-qPCR, CCK-8, and colony formation assay. Copy number variation (CNV), immune infiltration, and clinical features were further analyzed in different subgroups and subsequent gene expression profiles. Sensitive drugs were also screened.

Results

In the pan-cancer analysis, HCC was shown to have specific glycosylation alterations. Five genes, CAD, SLC51B, LGALS3, B3GAT3, and MT3, identified from 572 glycosylation-related genes, were used to construct a gene signature and predict HCC patient survival in the TCGA cohort. The results demonstrated a significant positive correlation between patients in the high-risk group and both elevated gene expression and HCC dedifferentiation status. A significant reduction in the stemness-related markers, CD24, CD44, CD20, FOXM1, and EpCAM, was found after the knockdown of CAD and other genes in HepG2 and Huh7 cells. Frequent mutations increased CNVs, immune-suppressive responses, and poor prognosis were also associated with the high-risk profile. The ICGC-LIRI-JP cohort confirmed a similar relationship between glycosylation-related subtypes and stemness. Finally, 84 sensitive drugs were screened for abnormal glycosylation of HCC, and carfilzomib was most highly correlated with CAD.

Conclusions

Glycosylation-related molecular subtypes are associated with HCC stemness and disease prognosis. These results provide new directions for further research on the relationship between glycosylation and stemness phenotypes.

Nonenzymatic glycosylation of isolated human immunoglobulin-G by D-ribose

Glycation is vital in terms of its damaging effect on macromolecules resulting in the formation of end products, which are highly reactive and cross-linked irreversible structures, known as advanced glycation end products (AGEs). The continuous accumulation of AGEs is associated with severe diabetes and its associated ailments. Saccharides with their reducing ends can glycate amino acid side chains of proteins, among them glucose is well-known for its potent glycating capability. However, other reducing sugars can be more reactive glycating agents than glucose. The D-ribose is a pentose sugar-containing an active aldehyde group in its open form and is responsible for affecting the biological processes of the cellular system. D-ribose, a key component of many biological molecules, is more reactive than most reducing sugars. Protein glycation by reducing monosaccharides such as D-ribose promotes the accelerated formation of AGEs that could lead to cellular impairments and dysfunctions. Also, under a physiological cellular state, the bioavailability rate of D-ribose is much higher than that of glucose in diabetes, which makes this species much more active in protein glycation as compared with D-glucose. Due to the abnormal level of D-ribose in the biological system, the glycation of proteins with D-ribose needs to be analyzed and addressed carefully. In the present study, human immunoglobulin G (IgG) was isolated and purified via affinity column chromatography. D-ribose at 10 and 100 mM concentrations was used as glycating agent, for 1-12 days of incubation at 37°C. The postglycation changes in IgG molecule were characterized by UV-visible and fluorescence spectroscopy, nitroblue tetrazolium assay, and various other physicochemical analyses for the confirmation of D-ribose mediated IgG glycation.

Glyoxal induced glycative insult suffered by immunoglobulin G and fibrinogen proteins: A comparative physicochemical characterization to reveal structural perturbations

Glycation of proteins results in structural alteration, functional deprivation, and generation of advanced glycation end products (AGEs). Reactive oxygen species (ROS) that are generated during in vivo autoxidation of glucose induces glycoxidation of intermediate glycation-adducts, which in turn give rise to aldehyde and/or ketone groups containing dicarbonyls or reactive carbonyl species (RCS). RCS further reacts non-enzymatically and starts the glycation-oxidation vicious cycle, thus exacerbating oxidative, carbonyl, and glycative stress in the physiological system. Glyoxal (GO), a reactive dicarbonyl that generates during glycoxidation and lipid peroxidation, contributes to glycation. This in vitro physicochemical characterization study focuses on GO-induced glycoxidative damage suffered by immunoglobulin G (IgG) and fibrinogen proteins. The structural alterations were analyzed by UV-vis, fluorescence, circular dichroism, and Fourier transform infrared (FT-IR) spectroscopy. Ketoamines, protein carbonyls, hydroxymethylfurfural (HMF), free lysine, free arginine, carboxymethyllysine (CML), and protein aggregation were also quantified. Structural perturbations, increased concentration of ketoamines, protein carbonyls, HMF, and malondialdehyde (MDA) were reported in glycated proteins. The experiment results also validate increased oxidative stress and AGEs formation i.e. IgG-AGEs and Fib-AGEs. Thus, we can conclude that AGEs formation during GO-mediated glycation of IgG and fibrinogen could hamper normal physiology and might play a significant role in the pathogenesis of diabetes-associated secondary complications.

Unconventional metabolites in chromatin regulation

Chromatin, the complex of DNA and histone proteins, serves as a main integrator of cellular signals. Increasing evidence links cellular functional to chromatin state. Indeed, different metabolites are emerging as modulators of chromatin function and structure. Alterations in chromatin state are decisive for regulating all aspects of genome function and ultimately have the potential to produce phenotypic changes. Several metabolites such as acetyl-CoA, S-adenosylmethionine (SAM) or adenosine triphosphate (ATP) have now been well characterized as main substrates or cofactors of chromatin-modifying enzymes. However, there are other metabolites that can directly interact with chromatin influencing its state or that modulate the properties of chromatin regulatory factors. Also, there is a growing list of atypical enzymatic and nonenzymatic chromatin modifications that originate from different cellular pathways that have not been in the limelight of chromatin research. Here, we summarize different properties and functions of uncommon regulatory molecules originating from intermediate metabolism of lipids, carbohydrates and amino acids. Based on the various modes of action on chromatin and the plethora of putative, so far not described chromatin-regulating metabolites, we propose that there are more links between cellular functional state and chromatin regulation to be discovered. We hypothesize that these connections could provide interesting starting points for interfering with cellular epigenetic states at a molecular level.

Dietary Advanced Glycation End Products Shift the Gut Microbiota Composition and Induce Insulin Resistance in Mice

OBJECTIVE

This study aimed to explore the associations between gut microbiota characteristics and glycometabolic profiles in mice fed diets high in advanced glycation end products (AGEs).

METHODS

C57BL/6 mice were exposed to a heat-treated diet or exogenous AGEs for 24 weeks, and glucose metabolism was assessed via the intraperitoneal glucose-tolerance test (IPGTT). Serum AGE and lipopolysaccharide-binding protein (LBP) levels were quantified using ELISA kits. 16S rDNA sequencing was performed to analyze the changes in gut microbiota according to α- and β-diversity. Key operational taxonomic units (OTUs) were evaluated, and co-abundance groups (CAGs) were delineated using weighted correlation network analysis. Associations between CAGs and clinical parameters were analyzed using Spearman correlation; predictive functional analysis of gut microbiota was performed using Kyoto Encyclopedia of Genes and Genomes data.

RESULTS

We identified significant increases in fasting blood glucose (FBG) and fasting insulin levels, as well as homeostatic model assessment insulin resistance (HOMA-IR) and glucose area under the receiver operating characteristic curve from IPGTT, in the high-AGE diet groups relative to controls at week 24. Serum AGE and LBP levels were elevated, and the α- and β-diversity of gut microbiota reduced in high-AGE diet groups. We identified 92 key OTUs that clustered into six CAGs, revealing positive correlations between CAG2/3/5 and insulin levels and mice weight and negative correlations between CAG1/3/4/5 and AGE, FBG, and LBP levels and HOMA-IR in mice fed high-AGE diets. We observed a reduced abundance of butyrate-producing bacteria, including Bacteroidales_S24-7, Ruminococcaceae, and Lachnospiraceae, in mice fed high-AGE diets, with pathway analysis of gut microbiota revealing significantly enriched fructose and mannose metabolism.

CONCLUSION

High-AGE diets altered the gut microbiota composition and structure, and induced insulin resistance in mice. In the pathogenesis of insulin resistance, the loss of butyrate-producing bacteria might impair the colonic epithelial barrier, thereby triggering chronic low-grade inflammation.

The roles of inducible chromatin and transcriptional memory in cellular defense system responses to redox-active pollutants

People are exposed to wide range of redox-active environmental pollutants. Air pollution, heavy metals, pesticides, and endocrine disrupting chemicals can disrupt cellular redox status. Redox-active pollutants in our environment all trigger their own sets of specific cellular responses, but they also activate a common set of general stress responses that buffer the cell against homeostatic insults. These cellular defense system (CDS) pathways include the heat shock response, the oxidative stress response, the hypoxia response, the unfolded protein response, the DNA damage response, and the general stress response mediated by the stress-activated p38 mitogen-activated protein kinase. Over the past two decades, the field of environmental epigenetics has investigated epigenetic responses to environmental pollutants, including redox-active pollutants. Studies of these responses highlight the role of chromatin modifications in controlling the transcriptional response to pollutants and the role of transcriptional memory, often referred to as "epigenetic reprogramming", in predisposing previously exposed individuals to more potent transcriptional responses on secondary challenge. My central thesis in this review is that high dose or chronic exposure to redox-active pollutants leads to transcriptional memories at CDS target genes that influence the cell's ability to mount protective responses. To support this thesis, I will: (1) summarize the known chromatin features required for inducible gene activation; (2) review the known forms of transcriptional memory; (3) discuss the roles of inducible chromatin and transcriptional memory in CDS responses that are activated by redox-active environmental pollutants; and (4) propose a conceptual framework for CDS pathway responsiveness as a readout of total cellular exposure to redox-active pollutants.

Physico-chemical Changes Induced in the Serum Proteins Immunoglobulin G and Fibrinogen Mediated by Methylglyoxal

BACKGROUND

Non-enzymatic glycation of proteins plays a significant role in the pathogenesis of secondary diabetic complications via the formation of advanced glycation end products (AGEs) and increased oxidative stress. Methylglyoxal (MG), a highly reactive dicarbonyl of class α-oxoaldehyde that generates during glucose oxidation and lipid peroxidation, contributes to glycation.

OBJECTIVE

This comparative study focuses on methylglyoxal induced glycoxidative damage suffered by immunoglobulin G (IgG) and fibrinogen, and to unveil implication of structural modification of serum proteins in diabetes-associated secondary complications.

METHODS

The methylglyoxal induced structural alterations in IgG and fibrinogen were analyzed by UVvis, fluorescence, circular dichroism and Fourier transform infrared (FT-IR) spectroscopy. Ketoamine moieties, carbonyl contents, 5-Hydroxymethylfurfural (HMF) and malondyaldehyde were also quantified. Free lysine and arginine estimation, detection of non-fluorogenic carboxymethyllysine (CML) and fibril formation were confirmed by thioflavin T (ThT) assay.

RESULTS

Structural alterations, increased carbonyl contents and ketoamines were reported in MG glycated IgG and fibrinogen against their native analogues.

CONCLUSION

The experiment results validate structural modifications, increased oxidative stress and AGEs formation. Thus, we can conclude that IgG-AGEs and Fib-AGEs formed during MG induced glycation of IgG and fibrinogen could impede normal physiology and might initiates secondary complications in diabetic patients.

Recent Advances in Histone Glycation: Emerging role in Diabetes and Cancer

Ever increasing information on genome and proteome has offered fascinating details and new opportunities to understand the molecular biology. It is now known that histone proteins surrounding the DNA play a crucial role in the chromatin structure and function. Histones undergo a plethora of post-translational enzymatic modifications that influence nucleosome dynamics and affect DNA activity. Earlier research offered insights into the enzymatic modifications of histones; however attention has been diverted to histone modifications induced by by-products of metabolism without enzymatic engagement in the last decade. Non enzymatic modifications of histones are believed to be crucial for epigenetic landscape, cellular fate and for role in human diseases. Glycation of histone proteins constitutes the major non enzymatic modifications of nuclear proteins that have implications in diabetes and cancer. It has emerged that glycation damages nuclear proteins, modifies amino acids of histones at crucial locations, generates adducts affecting histone chromatin interaction, develops neo-epitopes inducing specific immune response and impacts cell function. Presence of circulating antibodies against glycated histone proteins in diabetes and cancer has shown immunological implications with diagnostic relevance. These crucial details make histone glycation an attractive focus for investigators. This review article, therefore, makes an attempt to exclusively summarize the recent researches in histone glycation, its impact on structural integrity of chromatin and elaborates on their role in diabetes and cancer. The work offers insights for future scientists who investigate the link between metabolism, bio-molecular structures, glycobiology, histone-DNA interactions in relation to diseases in humans.

The Taming of Nuclear Factor Erythroid-2-Related Factor-2 (Nrf2) Deglycation by Fructosamine-3-Kinase (FN3K)-Inhibitors-A Novel Strategy to Combat Cancers

Simple Summary

Aim of this review is to provide an overview on (a) Fructosamine-3-Kinase (FN3K) and its role in regulating Nuclear Factor Erythorid-2-Related Factor-2 (Nrf2); (b) the role of glycation and deglycation mechanisms in modulating the functional properties of proteins, in particular, the Nrf2; (c) the dual role of Nrf2 in the prevention and treatment of cancers. Since controlling the glycation of Nrf2 is one of the key mechanisms determining the fate of a cell; whether to get transformed into a cancerous one or to stay as a normal one, it is important to regulate Nrf2 and deglycating FN3K using pharmacological agents. Inhibitors of FN3K are being explored currently to modulate Nrf2 activity thereby control the cancers.

Abstract

Glycated stress is mediated by the advanced glycation end products (AGE) and the binding of AGEs to the receptors for advanced glycation end products (RAGEs) in cancer cells. RAGEs are involved in mediating tumorigenesis of multiple cancers through the modulation of several downstream signaling cascades. Glycated stress modulates various signaling pathways that include p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor kappa–B (NF-κB), tumor necrosis factor (TNF)-α, etc., which further foster the uncontrolled proliferation, growth, metastasis, angiogenesis, drug resistance, and evasion of apoptosis in several cancers. In this review, a balanced overview on the role of glycation and deglycation in modulating several signaling cascades that are involved in the progression of cancers was discussed. Further, we have highlighted the functional role of deglycating enzyme fructosamine-3-kinase (FN3K) on Nrf2-driven cancers. The activity of FN3K is attributed to its ability to deglycate Nrf2, a master regulator of oxidative stress in cells. FN3K is a unique protein that mediates deglycation by phosphorylating basic amino acids lysine and arginine in various proteins such as Nrf2. Deglycated Nrf2 is stable and binds to small musculoaponeurotic fibrosarcoma (sMAF) proteins, thereby activating cellular antioxidant mechanisms to protect cells from oxidative stress. This cellular protection offered by Nrf2 activation, in one way, prevents the transformation of a normal cell into a cancer cell; however, in the other way, it helps a cancer cell not only to survive under hypoxic conditions but also, to stay protected from various chemo- and radio-therapeutic treatments. Therefore, the activation of Nrf2 is similar to a double-edged sword and, if not controlled properly, can lead to the development of many solid tumors. Hence, there is a need to develop novel small molecule modulators/phytochemicals that can regulate FN3K activity, thereby maintaining Nrf2 in a controlled activation state.

Effects of the age/rage axis in the platelet activation

Platelet activity is essential in cardiovascular diseases. Therefore our objective was to evaluate the main effects of activating RAGE in platelets which are still unknown. A search for RAGE expression in different databases showed poor or a nonexistent presence in platelets. We confirmed the expression in platelets and secreted variable of RAGE (sRAGE). Platelets from elderly adults expressed in resting showed 3.2 fold more RAGE from young individuals (p < 0.01) and 3.3 fold with TRAP-6 (p < 0.001). These results could indicate that the expression of RAGE is more inducible in older adults. Then we found that activating RAGE with AGE-BSA-derived from methylglyoxal and subthreshold TRAP-6, showed a considerable increase with respect to the control in platelet aggregation and expression of P-selectin (respectively, p < 0.01). This effect was almost completely blocked by using a specific RAGE inhibitor (FSP-ZM1), confirming that RAGE is important for the function and activation platelet. Finally, we predict the region stimulated by AGE-BSA is located in region V of RAGE and 13 amino acids are critical for its binding. In conclusion, the activation of RAGE affects platelet activation and 13 amino acids are critical for its stimulation, this information is crucial for future possible treatments for CVD.

Oxidative, Reductive, and Nitrosative Stress Effects on Epigenetics and on Posttranslational Modification of Enzymes in Cardiometabolic Diseases

Oxidative (OS), reductive (RS), and nitrosative (NSS) stresses produce carbonylation, glycation, glutathionylation, sulfhydration, nitration, and nitrosylation reactions. OS, RS, and NSS are interrelated since RS results from an overactivation of antioxidant systems and NSS is the result of the overactivation of the oxidation of nitric oxide (NO). Here, we discuss the general characteristics of the three types of stress and the way by which the reactions they induce (a) damage the DNA structure causing strand breaks or inducing the formation of 8-oxo-d guanosine; (b) modify histones; (c) modify the activities of the enzymes that determine the establishment of epigenetic cues such as DNA methyl transferases, histone methyl transferases, acetyltransferases, and deacetylases; (d) alter DNA reparation enzymes by posttranslational mechanisms; and (e) regulate the activities of intracellular enzymes participating in metabolic reactions and in signaling pathways through posttranslational modifications. Furthermore, the three types of stress may establish new epigenetic marks through these reactions. The development of cardiometabolic disorders in adult life may be programed since early stages of development by epigenetic cues which may be established or modified by OS, RS, and NSS. Therefore, the three types of stress participate importantly in mediating the impact of the early life environment on later health and heritability. Here, we discuss their impact on cardiometabolic diseases. The epigenetic modifications induced by these stresses depend on union and release of chemical residues on a DNA sequence and/or on amino acid residues in proteins, and therefore, they are reversible and potentially treatable.

Pathological Mechanisms Linking Diabetes Mellitus and Alzheimer's Disease: the Receptor for Advanced Glycation End Products (RAGE)

Diabetes and Alzheimer’s disease (AD) place a significant burden on health care systems in the world and its aging populations. These diseases have long been regarded as separate entities; however, advanced glycation end products (AGEs) and the receptors for AGEs (RAGE) may be a link between diabetes and AD. In our study, mice injected with AGEs through stereotaxic surgery showed significant AD-like features: behavior showed decreased memory; immunofluorescence showed increased phosphorylated tau and APP. These results suggest links between diabetes and AD. Patients with diabetes are at a higher risk of developing AD, and the possible underlying molecular components of this association are now beginning to emerge.

Mechanistic insights into the urea-induced denaturation of a non-seleno thiol specific antioxidant human peroxiredoxin 6

Peroxiredoxin 6 (Prdx6) is a unique enzyme among mammalian peroxiredoxins as it lacks resolving cysteine. It is found to be involved in number of different diseases including tumours and its expression level is highest in lungs as compared to other organs. It has been found that Prdx6 plays a significant role different metabolic diseases, ocular damage, neurodegeneration and male infertility. It is a bifunctional protein having phospholipase A₂ and peroxidase (also has the ability to reduce phospholipid hydroperoxides) activities. In order to complete the peroxidise reaction cycle it requires glutathione catalyzed by glutathione S-transferase. Equilibrium unfolding and conformational stability of Prdx6 was studied by using urea as a chemical denaturant to understand the changes it goes under cellular stress conditions. Three different spectroscopic methods were employed to monitor urea-induced denaturation. From the results obtained, it was found that the urea denaturation of Prdx6 follows a variable two state process due to non-coincidence of the normalized transition curves obtained from different optical probes. The different denaturation curves were normalized and thermodynamic parameters, ΔG_D^o, Gibbs free energy change related to the urea-induced denaturation, midpoint of denaturation (C_m), and m = (δΔG_D / [urea]) were obtained. The structural information of Prdx6 were further analysed by several parameters obtained by 100 ns MD simulation. The results of MD simulation clearly favour the outcome of spectroscopic studies.

Chromatin as a key consumer in the metabolite economy

In eukaryotes, chromatin remodeling and post-translational modifications (PTMs) shape the local chromatin landscape to establish permissive and repressive regions within the genome, orchestrating transcription, replication, and DNA repair in concert with other epigenetic mechanisms. Though cellular nutrient signaling encompasses a huge number of pathways, recent attention has turned to the hypothesis that the metabolic state of the cell is communicated to the genome through the type and concentration of metabolites in the nucleus that are cofactors for chromatin-modifying enzymes. Importantly, both epigenetic and metabolic dysregulation are hallmarks of a range of diseases, and this metabolism-chromatin axis may yield a well of new therapeutic targets. In this Perspective, we highlight emerging themes in the inter-regulation of the genome and metabolism via chromatin, including nonenzymatic histone modifications arising from chemically reactive metabolites, the expansion of PTM diversity from cofactor-promiscuous chromatin-modifying enzymes, and evidence for the existence and importance of subnucleocytoplasmic metabolite pools.

Changes in the Density of Corneal Endothelial Cells in Elderly Diabetic Patients After Combined Phacovitrectomy and Ex-PRESS Glaucoma Implants

BACKGROUND & OBJECTIVE

Corneal endothelial cells (ECD) are characterized by limited regenerative potential, which is additionally impaired in patients with diabetes. This retrospective study included 27 patients aged 58.1±13.6, 16 female and 11 males, who underwent 23-gauge vitrectomy in combination with cataract surgery (phacovitrectomy) and further Ex-PRESS shunt implantation throughout 2013-2017 at St. Barbara Hospital in Sosnowiec, Poland.

METHODS

In our study, we distinguished 4 periods: initial period; post phacovitrectomy and removal of oil tamponade; and 3 and 12 months post implantation of the Ex-PRESS shunt. Statistical analysis was performed at the level of statistical significance of p<0.05. It included an analysis of variance (ANOVA) and Tukey's post-hoc test in order to determine the differences in the density of ECD cells/mm2 between the periods of observation. The paired-samples t-Student test was also performed to determine whether the differences in visual acuity values before and after PPV and before and after Ex-PRESS shunt were statistically significant.

RESULTS

The initial count of ECD cells was 2381.1±249, which decreased to 1872.8±350.7 cell/mm2 and finally to 1677.9±327 at the endpoint. Differences in the density of ECD cells/mm2 were observed to be statistically significant between the periods: after PPV vs. initial number of ECD (p = 0.000138); before 3 months after Ex-PRESS shunt vs. initial number of ECD (p = 0.000138); 12 months after Ex- PRESS shunt vs. initial number of ECD (p = 0000138). Analyzing the changes in visual acuity, we observed a deterioration both before and 3 months after Ex-PRESS shunt (p = 0.007944) and before and after PPV (p = 0.060334). In turn, correlation analysis indicated that there is a statistically significant, moderate, positive relationship. The relationship between visual acuity after Ex-PRESS shunt and ECD cells/mm2 density turned out to be statistically significant (r = +0.521381; p < 0.05).

CONCLUSION

Regardless of the period of observation and the choice of ophthalmic treatment of diabetic complications, we observed a decrease in the number of ECD cells and a deterioration in visual acuity. It is, therefore, reasonable to provide the patient with complete information about the proposed procedures and to consider the risk-benefit balance.

Glyoxal Induced Transition of Transferrin to Aggregates: Spectroscopic, Microscopic and Molecular Docking Insight

BACKGROUND & OBJECTIVE

The present study was aimed at characterizing the conformational alterations induced in human transferrin, the iron regulatory protein by glyoxal. Since protein aggregation is at the core of many disorders, thus interest in this domain has increased significantly during the past years.

METHODS

In our present study, the effect of glyoxal was monitored on human transferrin using multispectroscopic and multi-microscopic studies.

RESULTS

Intrinsic fluorescence spectroscopy suggested changes in native conformation of human transferrin evident by decreased fluorescence and blue shift in the presence of glyoxal. Further, extrinsic fluorescence was retorted and the results showed the formation of aggregates; apparent by increased Congo red (CR) absorbance, Thioflavin T (ThT) and ANS fluorescence and TEM of human transferrin in the presence of glyoxal. Molecular docking was also employed to see which residues are at core of human transferrin and glyoxal interaction. Reactive oxygen species (ROS) generation assays revealed enhanced ROS levels by human transferrin after treatment with glyoxal.

CONCLUSION

Thus, our study proposes that glyoxal induces the formation of aggregates in human transferrin. These aggregates further generate ROS which are key players in the complications associated with diabetes mellitus, giving our study clinical perspective.

Modification of Glutenin and Associated Changes in Digestibility Due to Methylglyoxal during Heat Processing

Glutenin is the main protein of flour and is a very important source of protein nutrition for humans. Methylglyoxal (MGO) is an important product of the Maillard reaction that occurs during the hot-processing of flour products, and it reacts with glutenin to facilitate changes in glutenin properties. Here, the effects of MGO on glutenin digestion during the heating process were investigated using a simulated MGO-glutenin system. MGO significantly reduced the digestibility of glutenin. The structure of MGO-glutenin and physicochemical properties were studied to understand the mechanism of the decrease of digestibility. These data suggest that changes in digestibility were caused by decreases in surface hydrophobicity and increases in disulfide bonds. MGO induces strong aggregation of glutenin after heating that led to the masking of cleavage sites for proteases. Moreover, carbonyl oxidation induced by MGO leads to intermolecular cross-linking of glutenin that increasingly masks or even destroys cleavage sites, further decreasing digestibility.

Oxidative post-translational modifications in histones

Epigenetic regulation is attracting much attention because it explains many of the effects that the external environment induces in organisms. Changes in the cellular redox status and even more specifically in its nuclear redox compartment is one of these examples. Redox changes can induce modulation of the epigenetic regulation in cells. Here we present a few cases where reactive oxygen or nitrogen species induces epigenetic marks in histones. Posttranslational modification of these proteins like histone nitrosylation, carbonylation, or glutathionylation together with other mechanisms not reviewed here are the cornerstones of redox-related epigenetic regulation. We currently face a new field of research with potential important consequences for the treatment of many pathologies.

Characterization of methylglyoxal induced advanced glycation end products and aggregates of human transferrin: Biophysical and microscopic insight

Protein aggregation and glycation is gaining increased attention in recent times as protein aggregates and advanced glycation end products (AGEs) play a pivotal role in many disorders. The purpose of our study was to have an insight into AGEs and aggregates formation of human transferrin (hTF) in the presence of methylglyoxal (MG) employing intrinsic, ANS, Thioflavin T fluorescence, circular dichroism (CD) spectroscopy, docking studies and microscopy. In our study, effect of varying concentration of MG was observed on hTF retorting multispectroscopic, in silico and microscopic approach. Intrinsic fluorescence showed an increase in fluorescence of hTF in presence of MG. The obtained AGEs of hTF in the presence of MG were characterized with respect to fluorescence of AGEs specific adducts. Further, aggregates of hTF were characterized employing ThT fluorescence, transmission electron microscopy (TEM) and fluorescence microscopy. Fluorescence microscopy and TEM confirmed the presence of hTF aggregates in the presence of 50 mM MG; aggregates to be globular in nature. Molecular docking was also employed highlighting the important residues playing a pivotal role in this interaction. Thus, our study characterized the AGEs and aggregates of clinically important protein, hTF; level of MG increases in various pathological conditions giving our study clinical perspective.

A study on hepatopathic, dyslipidemic and immunogenic properties of fructosylated-HSA-AGE and binding of autoantibodies in sera of obese and overweight patients with fructosylated-HSA-AGE

Over consumption of fructose may lead to obesity and dyslipidemia and cause fructosylation-induced alterations in the structure and function of proteins. The aim of this study was to investigate the role of fructosylated-HSA-AGE in the pathogenesis of fatty liver (NAFLD and NASH) by biochemical, immunological and histological studies. Immunogenicity of fructosylated-HSA-AGE was probed by inducing antibodies in rabbits. Fructosylated-HSA-AGE was found to be highly immunogenic. Furthermore, fructosylated-HSA-AGE caused mild fibrosis with steatosis and portal inflammation of hepatocytes in experimental animals. Liver function test and dyslipidemic parameters in immunized animals were also found to be raised. Ultrasonography, which should form part of the assessment of chronically raised transaminases, shows fatty infiltration. Interestingly, alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin, total cholesterol (TC) and triglyceride (TG) profiles confirms USG images of overweight, obese patients. Thus, present study demonstrates that fructosylated-HSA-AGE is hepatotoxic, immunologically active and may cause dyslipidemia.

Use of Raman spectroscopy to screen diabetes mellitus with machine learning tools

Type 2 diabetes mellitus (DM2) is one of the most widely prevalent diseases worldwide and is currently screened by invasive techniques based on enzymatic assays that measure plasma glucose concentration in a laboratory setting. A promising plan of action for screening DM2 is to identify molecular signatures in a non-invasive fashion. This work describes the application of portable Raman spectroscopy coupled with several supervised machine-learning techniques, to discern between diabetic patients and healthy controls (Ctrl), with a high degree of accuracy. Using artificial neural networks (ANN), we accurately discriminated between DM2 and Ctrl groups with 88.9-90.9% accuracy, depending on the sampling site. In order to compare the ANN performance to more traditional methods used in spectroscopy, principal component analysis (PCA) was carried out. A subset of features from PCA was used to generate a support vector machine (SVM) model, albeit with decreased accuracy (76.0-82.5%). The 10-fold cross-validation model was performed to validate both classifiers. This technique is relatively low-cost, harmless, simple and comfortable for the patient, yielding rapid diagnosis. Furthermore, the performance of the ANN-based method was better than the typical performance of the invasive measurement of capillary blood glucose. These characteristics make our method a promising screening tool for identifying DM2 in a non-invasive and automated fashion.

Metabolic Effects of Metformin in the Failing Heart

Accumulating evidence shows that metformin is an insulin-sensitizing antidiabetic drug widely used in the treatment of type 2 diabetes mellitus (T2DM), which can exert favorable effects on cardiovascular risk and may be safely used in patients with heart failure (HF), and even able to reduce the incidence of HF and to reduce HF mortality. In failing hearts, metformin improves myocardial energy metabolic status through the activation of AMP (adenosine monophosphate)-activated protein kinase (AMPK) and the regulation of lipid and glucose metabolism. By increasing nitric oxide (NO) bioavailability, limiting interstitial fibrosis, reducing the deposition of advanced glycation end-products (AGEs), and inhibiting myocardial cell apoptosis metformin reduces cardiac remodeling and hypertrophy, and thereby preserves left ventricular systolic and diastolic functions. While a lot of preclinical and clinical studies showed the cardiovascular safety of metformin therapy in diabetic patients and HF, to confirm observed benefits, the specific large-scale trials configured for HF development in diabetic patients as a primary endpoints are necessary.

Methylglyoxal and Advanced Glycation End products: Insight of the regulatory machinery affecting the myogenic program and of its modulation by natural compounds

Methylglyoxal (MG) is a reactive dicarbonyl intermediate and a precursor of advanced glycation end products (AGEs). The authors investigated the role played by AGEs in muscle myopathy and the amelioration of its effects by curcumin and gingerol. In addition to producing phenotypical changes, MG increased oxidative stress and reduced myotube formation in C2C12 cells. RAGE (receptor for AGEs) expression was up-regulated and MYOD and myogenin (MYOG) expressions were concomitantly down-regulated in MG-treated cells. Interestingly, AGE levels were higher in plasma (~32 fold) and muscle (~26 fold) of diabetic mice than in control mice. RAGE knock-down (RAGE_kd) reduced the expressions of MYOD and MYOG and myotube formation in C2C12 cells. In silico studies of interactions between curcumin or gingerol and myostatin (MSTN; an inhibitor of myogenesis) and their observed affinities for activin receptor type IIB (ACVRIIB) suggested curcumin and gingerol reduce the interaction between MSTN and ACVRIIB. The findings of this study suggest enhanced AGE production and subsequent RAGE-AGE interaction obstruct the muscle development program, and that curcumin and gingerol attenuate the effect of AGEs on myoblasts.

An insight on the association of glycation with hepatocellular carcinoma

Hepato-cellular carcinoma (HCC) is one of the frequent cause of cancer-related death worldwide and dominant form of primary liver cancer. However, the reason behind a steady increase in the incidence of this form of cancer remains elusive. Glycation has been reported to play a significant role in the induction of several chronic diseases including cancer. Several risk factors that could induce HCC have been reported in the literature. Deciphering the complex patho-physiology associated with HCC is expected to provide new targets for the early detection, prevention, progression and recurrence. Even-though, some of the causative aspects of HCC is known, the advanced glycation end products (AGEs) related mechanism still needs further research. In the current manuscript, we have tried to uncover the possible role of glycation in the induction of HCC. In the light of the available scientific literature, we advocate in-depth comprehensive studies which will shed light towards mechanistic association of glycation with HCC.

Elevated cardiac 3-deoxyglucosone, a highly reactive intermediate in glycation reaction, in doxorubicin-induced cardiotoxicity in rats

3-Deoxyglucosone (3-DG) is a highly reactive carbonyl intermediate in glycation reaction (also known as Maillard reaction) and plays an important role in diabetic complications. We investigated the potential involvement of 3-DG in doxorubicin (DXR)-induced cardiotoxicity. Male Crl:CD(SD) rats received intravenous injections of DXR at 2mg/kg, once weekly, for 6 weeks, with/without daily intraperitoneal treatment with 3-DG scavenging agents, i.e., aminoguanidine (AG, 25mg/kg/day) and pyridoxamine (PM, 60mg/kg/day). Cardiac levels of 3-DG, thiobarbituric acid reactive substances (TBARS), fructosamine, and pentosidine, plasma glucose levels and cardiac troponin I (cTnI), echocardiography, and histopathology were assessed at 4 and 6 weeks after treatment. Cardiac 3-DG levels were significantly increased by DXR treatment at 4 and 6 weeks. Cardiac fructosamine levels and plasma glucose were not altered by DXR; however, TBARS levels in the heart were significantly increased at 4 and 6 weeks, suggesting that the enhanced generation of 3-DG is not attributed to any abnormal glycemic status, but may be related to oxidative stress by DXR. An advanced glycation end-product, pentosidine, was significantly increased by DXR treatment at 6 weeks. Intervention by AG and PM ameliorated the DXR-induced echocardiographic abnormalities, increased cTnI in plasma, and histopathological lesion as well as normalizing the elevation of 3-DG and pentosidine levels. These results suggest that 3-DG is generated by DXR and involved, at least in part, in the pathogenesis of DXR-cardiotoxicity through glycation reaction.

Oxidative stress signaling to chromatin in health and disease

Oxidative stress has a significant impact on the development and progression of common human pathologies, including cancer, diabetes, hypertension and neurodegenerative diseases. Increasing evidence suggests that oxidative stress globally influences chromatin structure, DNA methylation, enzymatic and non-enzymatic post-translational modifications of histones and DNA-binding proteins. The effects of oxidative stress on these chromatin alterations mediate a number of cellular changes, including modulation of gene expression, cell death, cell survival and mutagenesis, which are disease-driving mechanisms in human pathologies. Targeting oxidative stress-dependent pathways is thus a promising strategy for the prevention and treatment of these diseases. We summarize recent research developments connecting oxidative stress and chromatin regulation.

Green synthesis of silver nanoparticles and characterization of their inhibitory effects on AGEs formation using biophysical techniques

Advanced glycation end-products (AGEs) resulting from non-enzymatic glycation are one of the major factors implicated in secondary complications of diabetes. Scientists are focusing on discovering new compounds that may be used as potential AGEs inhibitors without affecting the normal structure and function of biomolecules. A number of natural and synthetic compounds have been proposed as AGE inhibitors. In this study, we investigated the inhibitory effects of AgNPs (silver nanoparticles) in AGEs formation. AgNPs (~30.5 nm) synthesized from Aloe Vera leaf extract were characterized using UV-Vis spectroscopy, energy-dispersive X-ray spectroscopy (EDX), high resolution-transmission electron microscopy, X-ray diffraction and dynamic light scattering (DLS) techniques. The inhibitory effects of AgNPs on AGEs formation were evaluated by investigating the degree of reactivity of free amino groups (lysine and arginine residues), protein-bound carbonyl and carboxymethyl lysine (CML) content, and the effects on protein structure using various physicochemical techniques. The results showed that AgNPs significantly inhibit AGEs formation in a concentration dependent manner and that AgNPs have a positive effect on protein structure. These findings strongly suggest that AgNPs may play a therapeutic role in diabetes-related complications.

Glycation of H1 Histone by 3-Deoxyglucosone: Effects on Protein Structure and Generation of Different Advanced Glycation End Products

Advanced glycation end products (AGEs) culminate from the non-enzymatic reaction between a free carbonyl group of a reducing sugar and free amino group of proteins. 3-deoxyglucosone (3-DG) is one of the dicarbonyl species that rapidly forms several protein-AGE complexes that are believed to be involved in the pathogenesis of several diseases, particularly diabetic complications. In this study, the generation of AGEs (N^ε-carboxymethyl lysine and pentosidine) by 3-DG in H1 histone protein was characterized by evaluating extent of side chain modification (lysine and arginine) and formation of Amadori products as well as carbonyl contents using several physicochemical techniques. Results strongly suggested that 3-DG is a potent glycating agent that forms various intermediates and AGEs during glycation reactions and affects the secondary structure of the H1 protein. Structural changes and AGE formation may influence the function of H1 histone and compromise chromatin structures in cases of secondary diabetic complications.

Biochemical and immunological parameters as indicators of osteoarthritis subjects: role of OH-collagen in auto-antibodies generation

Osteoarthritis (OA) is characterized by inflammation of the knee joint, which is caused by accumulation of cytokines and C-reactive protein (CRP) in the extracellular matrix as an early immune response to infection. The articular cartilage destruction is discernible by elevated tumour necrosis factor-α (TNF-α). In this study, blood samples of knee osteoarthritis patients were analyzed for biochemical and physiological parameters based on the lipid profile, uric acid, total leukocyte count (TLC), hemoglobin percentage (Hb%) and absolute lymphocyte count (ALC). Furthermore, immunological parameters including TNF-α , interleukin-6 (IL-6) and CRP were analyzed. The presence of antibodies against hydroxyl radical modified collagen-II (^•OH-collagen-II) was also investigated in arthritis patients using direct binding ELISA. The uric acid and lipid profiles changed extensively. Specifically, increased uric acid levels were associated with OA in both genders, as were enhanced immunological parameters. The TNF-α level also increased in both genders suffering from OA. Finally, auto-antibodies against OH-collagen II antigen were found in the sera of arthritis patients. These results indicated that immunological parameters are better predictors or indexes for diagnosis of OA than biochemical parameters.