Glyceraldehyde metabolism in mouse brain and the entry of blood-borne glyceraldehyde into the brain

D-Glyceraldehyde, a reactive aldehyde metabolite of fructose and glucose, is neurotoxic in vitro by forming advanced glycation end products (AGEs) with neuronal proteins. In Alzheimer's disease brains, glyceraldehyde-containing AGEs have been detected intracellularly and in extracellular plaques. However, little information exists on how the brain handles D-glyceraldehyde metabolically or if glyceraldehyde crosses the blood-brain barrier from the circulation into the brain. We injected [U-13C]-D-glyceraldehyde intravenously into awake mice and analyzed extracts of serum and brain by 13C nuclear magnetic resonance spectroscopy. 13C-Labeling of brain lactate and glutamate indicated passage of D-glyceraldehyde from blood to brain and glycolytic and oxidative D-glyceraldehyde metabolism in brain cells. 13C-Labeling of serum glucose and lactate through hepatic metabolism of [U-13C]-D-glyceraldehyde could not explain the formation of 13C-labeled lactate and glutamate in the brain. Cerebral glyceraldehyde dehydrogenase and reductase activities, leading to the formation of D-glycerate and glycerol, respectively, were 0.27-0.28 nmol/mg/min; triokinase, which phosphorylates D-glyceraldehyde to D-glyceraldehyde-3-phosphate, has been demonstrated previously at low levels. Thus, D-glyceraldehyde metabolism toward glycolysis could proceed both through D-glycerate, glycerol, and D-glyceraldehyde-3-phosphate. The aldehyde group of D-glyceraldehyde was overwhelmingly hydrated into a diol in aqueous solution, but the diol dehydration rate greatly exceeded glyceraldehyde metabolism and did not restrict it. We conclude that (1) D-glyceraldehyde crosses the blood-brain barrier, and so blood-borne glyceraldehyde could contribute to AGE formation in the brain, (2) glyceraldehyde is taken up and metabolized by brain cells. Metabolism thus constitutes a detoxification mechanism for this reactive aldehyde, a mechanism that may be compromised in disease states.

Deletion of Glyoxalase 1 Exacerbates Acetaminophen-Induced Hepatotoxicity in Mice

Acetaminophen (APAP) overdose triggers a cascade of intracellular oxidative stress events, culminating in acute liver injury. The clinically used antidote, N-acetylcysteine (NAC), has a narrow therapeutic window, and early treatment is essential for a satisfactory therapeutic outcome. For more versatile therapies that can be effective even at late presentation, the intricacies of APAP-induced hepatotoxicity must be better understood. Accumulation of advanced glycation end products (AGEs) and the consequent activation of the receptor for AGEs (RAGE) are considered one of the key mechanistic features of APAP toxicity. Glyoxalase 1 (Glo-1) regulates AGE formation by limiting the levels of methylglyoxal (MEG). In this study, we studied the relevance of Glo-1 in the APAP-mediated activation of RAGE and downstream cell death cascades. Constitutive Glo-1-knockout mice (GKO) and a cofactor of Glo-1, ψ-GSH, were used as tools. Our findings showed elevated oxidative stress resulting from the activation of RAGE and hepatocyte necrosis through steatosis in GKO mice treated with high-dose APAP compared to wild-type controls. A unique feature of the hepatic necrosis in GKO mice was the appearance of microvesicular steatosis as a result of centrilobular necrosis, rather than the inflammation seen in the wild type. The GSH surrogate and general antioxidant ψ-GSH alleviated APAP toxicity irrespective of the Glo-1 status, suggesting that oxidative stress is the primary driver of APAP toxicity. Overall, the exacerbation of APAP hepatotoxicity in GKO mice suggests the importance of this enzyme system in antioxidant defense against the initial stages of APAP overdose.

Interactions between Age-Related Type 2 Diabetes and the Small Intestine

The number of patients with type 2 diabetes is increasing worldwide. The mechanisms leading to type 2 diabetes and its complications is being researched; however, the pathological mechanisms of diabetes in the small intestine remain unclear. Therefore, we examined these pathological mechanisms in the small intestine using a mouse model of type 2 diabetes (KK-Ay/TaJcl) aged 10 and 50 weeks. The results showed that diabetes worsened with age in the mice with type 2 diabetes. In these mice, advanced glycation end products (AGEs) in the small intestine and mast cell expression increased, whereas diamine oxidase (DAO) decreased; increased tumor necrosis factor (TNF)-α and histamine levels in the plasma and small intestine were also detected. Additionally, the expression of zonula occludens (ZO)-1 and Claudin1 and cell adhesion molecules in the small intestine reduced. These results exacerbated with age. These findings indicate that type 2 diabetes causes AGE/mast cell/histamine and TNF-α signal transmission in the small intestine and decreases small intestinal wall cell adhesion molecules cause TNF-α and histamine to flow into the body, worsening the diabetic condition. In addition, this sequence of events is suggested to be strengthened in aged mice with type 2 diabetes, thus exacerbating the disease. These findings of this study may facilitate the elucidation of the pathological mechanisms of type 2 diabetes and its associated complications.

Deletion of Glyoxalase 1 exacerbates acetaminophen-induced hepatotoxicity in mice

Acetaminophen (APAP) overdose triggers a cascade of intracellular oxidative stress events culminating in acute liver injury. The clinically used antidote, N-acetylcysteine (NAC) has a narrow therapeutic window and early treatment is essential for satisfactory therapeutic outcome. For more versatile therapies that can be effective even at late-presentation, the intricacies of APAP-induced hepatotoxicity must be better understood. Accumulation of advanced glycation end-products (AGEs) and consequent activation of the receptor for AGEs (RAGE) are considered one of the key mechanistic features of APAP toxicity. Glyoxalase-1 (Glo-1) regulates AGE formation by limiting the levels of methylglyoxal (MEG). In this study, we studied the relevance of Glo-1 in APAP mediated activation of RAGE and downstream cell-death cascades. Constitutive Glo-1 knockout mice (GKO) and a cofactor of Glo-1, ψ-GSH, were employed as tools. Our findings show elevated oxidative stress, activation of RAGE and hepatocyte necrosis through steatosis in GKO mice treated with high-dose APAP compared to wild type controls. A unique feature of the hepatic necrosis in GKO mice is the appearance of microvesicular steatosis as a result of centrilobular necrosis, rather than inflammation seen in wild type. The GSH surrogate and general antioxidant, ψ-GSH alleviated APAP toxicity irrespective of Glo-1 status, suggesting that oxidative stress being the primary driver of APAP toxicity. Overall, exacerbation of APAP hepatotoxicity in GKO mice suggests the importance of this enzyme system in antioxidant defense against initial stages of APAP overdose.

Age-related changes in scalp biophysical parameters: A comparative analysis of the 20s and 50s age groups

BACKGROUND

Age-related changes in scalp parameters affect hair quality and scalp condition. However, detailed data on biophysical parameters of the scalp across age groups remain scarce. We aimed to investigate the differences in scalp parameters between individuals in their 20s and 50s and analyze their sex-specific variations.

MATERIALS AND METHODS

Two hundred participants (160 women and 40 men) were equally divided into 20s and 50s age groups. Biophysical parameters of the scalp, including elasticity, pH, trans-epidermal water loss (TEWL), sebum production, desquamation, firmness, redness, and yellowness, were measured in the vertex, occipital, and temporal regions. Hair density and thickness were measured in the temporal region. The accumulation of advanced glycation end products (AGEs) in the skin was noninvasively measured in a subset of 60 women.

RESULTS

Skin firmness and redness increased with age in women, whereas yellowness increased with age in both sexes. Sebum production and pH levels were significantly lower in the 50s age group than in the 20s age group, particularly in women. TEWL was lower in men in their 50s than in those in their 20s, particularly in the occipital region. A significant reduction in hair density was observed in the 50s age group in both sexes. AGE accumulation in the skin increased with age and was correlated with scalp skin yellowness.

CONCLUSION

Age-related changes in scalp parameters have important implications for hair health and scalp condition. These findings emphasize the importance of considering age and sex when developing hair care strategies.

Inter- and Intraindividual Differences in the Capacity of the Human Intestinal Microbiome in Fecal Slurries to Metabolize Fructoselysine and Carboxymethyllysine

The advanced glycation endproduct carboxymethyllysine and its precursor fructoselysine are present in heated, processed food products and are considered potentially hazardous for human health. Upon dietary exposure, they can be degraded by human colonic gut microbiota, reducing internal exposure. Pronounced interindividual and intraindividual differences in these metabolic degradations were found in anaerobic incubations with human fecal slurries in vitro. The average capacity to degrade fructoselysine was 27.7-fold higher than that for carboxymethyllysine, and degradation capacities for these two compounds were not correlated (R² = 0.08). Analysis of the bacterial composition revealed that interindividual differences outweighed intraindividual differences, and multiple genera were correlated with the individuals' carboxymethyllysine and fructoselysine degradation capacities (e.g., Akkermansia, Alistipes).

High Molecular Weight Fucoidan Restores Intestinal Integrity by Regulating Inflammation and Tight Junction Loss Induced by Methylglyoxal-Derived Hydroimidazolone-1

Fucoidan from brown seaweeds has several biological effects, including preserving intestinal integrity. To investigate the intestinal protective properties of high molecular weight fucoidan (HMWF) from Undaria pinnatifida on intestinal integrity dysfunction caused by methylglyoxal-derived hydroimidazolone-1 (MG-H1), one of the dietary advanced-glycation end products (dAGEs) in the human-colon carcinoma-cell line (Caco-2) cells and ICR mice. According to research, dAGEs may damage the intestinal barrier by increasing gut permeability. The findings of the study showed that HMWF + MG-H1 treatment reduced by 16.8% the amount of reactive oxygen species generated by MG-H1 treatment alone. Furthermore, HMWF + MGH-1 treatment reduced MG-H1-induced monolayer integrity disruption, as measured by alterations in transepithelial electrical resistance (135% vs. 75.5%) and fluorescein isothiocyanate incorporation (1.40 × 10^-6 cm/s vs. 3.80 cm/s). HMWF treatment prevented the MG-H1-induced expression of tight junction markers, including zonula occludens-1, occludin, and claudin-1 in Caco-2 cells and mouse colon tissues at the mRNA and protein level. Also, in Caco-2 and MG-H1-treated mice, HMWF plays an important role in preventing receptor for AGEs (RAGE)-mediated intestinal damage. In addition, HMWF inhibited the nuclear factor kappa B activation and its target genes leading to intestinal inflammation. These findings suggest that HMWF with price competitiveness could play an important role in preventing AGEs-induced intestinal barrier dysfunction.

Impact of Dietary Advanced Glycation End Products on Female Reproduction: Review of Potential Mechanistic Pathways

Advanced glycation end products (AGEs), a heterogenous group of products formed by the reaction between protein and reducing sugars, can form endogenously due to non-enzymatic reactions or by exogenous sources such as diet where considerable increase in AGEs is observed due to the modification of food mainly by thermal processing. Recent studies have suggested that AGEs could impact, via inducing inflammation and oxidative stress, the reproductive health and fertility in both males and females. This review presents a summary of recently published data pertaining to the pathogenesis of dietary AGEs and their receptors as well as their potential impact on female reproductive health. More specifically, it will present data pertaining to dietary AGEs’ involvement in the mechanistic pathogenesis of polycystic ovary syndrome, ovarian dysfunction, as well as the AGEs’ effect perinatally on the female offspring reproduction. Understanding the mechanistic impact of dietary AGEs on female reproduction can help contribute to the development of targeted pharmacological therapies that will help curb rising female infertility.

Erectile Dysfunction in Individuals with Type 1 Diabetes is Associated with Long-term Metabolic Control and Diabetic Complications: A Cross-Sectional Study

Background  Erectile dysfunction (ED) affects approximately 38% of individuals with type 1 diabetes (T1DM). Skin autofluorescence (AF) reflects skin advanced glycation end product (AGE) deposits and is a marker of long-term glycemia control. Objective  The study investigates the relationship between ED and diabetes control in patients with T1DM. Methods  Adult patients with T1DM visiting the Diabetology Department were cross-sectionally investigated. Medical history, anthropometric features, and laboratory findings were collected. All individuals filled the International Index of Erectile Function (IIEF-5). IIEF-5 total score < 22 represented the presence of ED. AF was measured on the volar aspect of the forearm using AGE Reader. Insulin resistance (IR) was assessed by the estimated glucose disposal rate. Descriptive statistics and multivariate logistic regression analyses were performed. The adjusted covariates were general risk factors of ED. Results  Of a total of n  = 70 patients, n  = 30 (42.9%) suffered from ED. The presence of ED was associated with higher glycated hemoglobin level (OR, 95% CI; 1.62, 1.02-2.60; p  = 0.043), presence of at least one diabetic complication (3.49, 1.10-11.03; p  = 0.03), and skin AF (9.20, 1.60-52.94; p  = 0.01), but not with IR (0.78, 0.57-2.60; p  = 0.12). Skin AF values ≥ 2.2 indicates presence of ED with a sensitivity of 70.0% and a specificity of 77.5%. Area under the curve was equal to 0.72 (95% CI: 0.60-0.85). Conclusions  The presence of ED in individuals with T1DM is associated with HbA1c, the presence of at least one diabetic complication, and skin AF.

AGEs-Induced and Endoplasmic Reticulum Stress/Inflammation-Mediated Regulation of GLUT4 Expression and Atherogenesis in Diabetes Mellitus

In recent decades, complex and exquisite pathways involved in the endoplasmic reticulum (ER) and inflammatory stress responses have been demonstrated to participate in the development and progression of numerous diseases, among them diabetes mellitus (DM). In those pathways, several players participate in both, reflecting a complicated interplay between ER and inflammatory stress. In DM, ER and inflammatory stress are involved in both the pathogenesis of the loss of glycemic control and the development of degenerative complications. Furthermore, hyperglycemia increases the generation of advanced glycation end products (AGEs), which in turn refeed ER and inflammatory stress, contributing to worsening glycemic homeostasis and to accelerating the development of DM complications. In this review, we present the current knowledge regarding AGEs-induced and ER/inflammation-mediated regulation of the expression of GLUT4 (solute carrier family 2, facilitated glucose transporter member 4), as a marker of glycemic homeostasis and of cardiovascular disease (CVD) development/progression, as a leading cause of morbidity and mortality in DM.

Glyoxal-Lysine Dimer, an Advanced Glycation End Product, Induces Oxidative Damage and Inflammatory Response by Interacting with RAGE

The glyoxal-lysine dimer (GOLD), which is a glyoxal (GO)-derived advanced glycation end product (AGE), is produced by the glycation reaction. In this study, we evaluated the effect of GOLD on the oxidative damage and inflammatory response in SV40 MES 13 mesangial cells. GOLD significantly increased the linkage with the V-type immunoglobulin domain of RAGE, a specific receptor of AGE. We found that GOLD treatment increased RAGE expression and reactive oxygen species (ROS) production in mesangial cells. GOLD remarkably regulated the protein and mRNA expression of nuclear factor erythroid 2-related factor 2 (NRF2) and glyoxalase 1 (GLO1). In addition, mitochondrial deterioration and inflammation occurred via GOLD-induced oxidative stress in mesangial cells. GOLD regulated the mitogen-activated protein kinase (MAPK) and the release of proinflammatory cytokines associated with the inflammatory mechanism of mesangial cells. Furthermore, oxidative stress and inflammatory responses triggered by GOLD were suppressed through RAGE inhibition using RAGE siRNA. These results demonstrate that the interaction of GOLD and RAGE plays an important role in the function of mesangial cells.

Revealing Advanced Glycation End Products Associated Structural Changes in Serum Albumin

Structural alterations in proteins have a significant impact on their function and body physiology. Glycation via nonenzymatic forms of cross-linking leads to proteins' conformational changes, the macromolecule being recognized as a stable fibrillary structure, oligomerization, and becoming advanced glycation end products (AGEs). Protein that undergoes glycation-related modifications, namely, β-sheet enriched structural changes, are recognized as amyloid. In the current study, we characterized a single protein modified in vitro under physiological conditions to represent a protein glycation model. The glycation altered the helical conformation of serum albumin (SA) and promoted the formation of a β-sheet enriched with amyloid fibrils detected at multidimensional levels. The nanoscale resolution by spectroscopy in the presence of thioflavin-T (ThT) and 8-anilinonaphthalene-1-sulfonic acid (8-ANS) showed binding of the fibrils formed in the presence of glucose (GLU) and the carbonyl metabolites methylglyoxal (MGO) and glycolaldehyde (GAD). In the presence of MGO and GAD, the SA becomes insoluble aggregates, demonstrated by TEM microscopy and dynamic light scattering (DLS). The protein oligomerization was visualized when separated via SDS gel electrophoresis and mass photometry (MP) assays. Following the glycation, eventually, the material polymerized and became stiffer. The level of stiffness was analyzed by a rheometer that revealed a quick alteration under MGO and GAD. This is the first study to combine multiple spectroscopy assays, imaging, and rheology measurements of SA and to demonstrate a resolution on a nanoscale structural toward better resolution of the conformational changes of glycated SA, oligomerization, and protein aggregations under physiological conditions.

Methylglyoxal-Lysine Dimer, an Advanced Glycation End Product, Induces Inflammation via Interaction with RAGE in Mesangial Cells

INTRODUCTION

Advanced glycation end products (AGEs) and receptor of advanced glycation end products (RAGE) mediate renal function during diabetic and non-diabetic nephropathy development. Methylglyoxal-lysine dimer (MOLD), a typical toxic advanced glycation end product (TAGE), contributes to inflammatory responses during renal diseases. This study determines the effect of MOLD on inflammatory responses in mouse mesangial cells.

METHODS AND RESULTS

The murine mesangial cell line SV40 MES 13 is used to assess nuclear factor-kappa B (NF-κB) expression, reactive oxygen species (ROS) production, and mitochondria labeling. The interaction model between RAGE and MOLD is also determined. MOLD treatment of mesangial cells markedly increases RAGE expression and the linkage with V-type Ig domain of RAGE. MOLD induces ROS production and mitochondrial dysfunction. MOLD activates phosphatidylinositol 3-kinase-protein kinase B (PI3KB) and NF-κB signaling pathways. It is confirmed that these changes are reversed when ROS is suppressed. These effects may be regulated through mitogen-activated protein kinases and pro-inflammatory cytokines in circulatory inflammation responses.

CONCLUSION

MOLD plays a major role in nephropathy via ROS production and mitochondrial dysfunction through direct association with RAGE. Further, the NF-kB and PI3K/AKT signaling pathways triggered by ROS mediate the inflammatory response to exacerbate MOLD-induced damages in inflammation-related diabetic and non-diabetic renal diseases.

The Role of Protein Adduction in Toxic Neuropathies of Exogenous and Endogenous Origin

The peripheral (axonal) neuropathy associated with repeated exposure to aliphatic and aromatic solvents that form protein-reactive γ-diketones shares some clinical and neuropathological features with certain metabolic neuropathies, including type-II diabetic neuropathy and uremic neuropathy, and with the largely sub-clinical nerve damage associated with old age. These conditions may be linked by metabolites that adduct and cross-link neuroproteins required for the maintenance of axonal transport and nerve fiber integrity in the peripheral and central nervous system.

Skin autofluorescence predicts cancer in subjects with type 2 diabetes

INTRODUCTION

Subjects with type 2 diabetes have an excess risk of cancer. The potential role of advanced glycation end products (AGEs) accumulated during long-term hyperglycemia in cancer development has been suggested by biological studies but clinical data are missing. AGEs can be estimated by measuring the skin autofluorescence. We searched whether the skin autofluorescence could predict new cancers in persons with type 2 diabetes.

RESEARCH DESIGN AND METHODS

From 2009 to 2015, we measured the skin autofluorescence of 413 subjects hospitalized for uncontrolled or complicated type 2 diabetes, without any history of cancer. The participants were followed for at least 1 year and the occurrences of new cancers were compared according to their initial skin autofluorescences.

RESULTS

The participants were mainly men (57.9%), with poorly controlled (HbA1c 72±14 mmol/mol or 8.7%±1.8%) and/or complicated type 2 diabetes. Their median skin autofluorescence was 2.6 (2.2-3.0) arbitrary units. Forty-five new cancer cases (10.9%) were registered during 4.8±2.3 years of follow-up: 75.6% of these subjects had skin autofluorescence higher than the median (χ²: p=0.001). By Cox regression analysis adjusted for age, gender, body mass index, history of smoking and renal parameters, skin autofluorescence >2.6 predicted a 2.57-fold higher risk of cancer (95% CI 1.28 to 5.19, p=0.008). This association remained significant after excluding the eight cancers that occurred in the 4 years after inclusion (OR 2.95, 95% CI 1.36 to 6.38, p=0.006). As a continuous variable, skin autofluorescence was also related to new cancers (OR 1.05, 95% CI 1.01 to 1.10, p=0.045).

CONCLUSIONS

Skin autofluorescence, a potential marker of glycemic memory, predicts the occurrence of cancer in subjects with type 2 diabetes. This relation provides a new clinical argument for the role of AGEs in cancer. Their estimation by measuring the skin autofluorescence may help select subjects with diabetes in cancer screening programs.

Low Soluble Receptor for Advanced Glycation End Products Precedes and Predicts Cardiometabolic Events in Women With Rheumatoid Arthritis

Background: Cardiovascular disease (CVD) causes premature mortality in rheumatoid arthritis (RA). Levels of soluble (s)RAGE change with aging, hypertension and hypercholesterolemia. We assessed whether sRAGE was associated with increased risk of CVD in RA patients.

Methods: Serum sRAGE was measured in 184 female RA patients and analyzed with respect to CVD risk estimated by the Framingham algorithm (eCVR), metabolic profile and inflammation. Levels of sRAGE in 13 patients with known cardio-metabolic morbidity defined the cut-off for low sRAGE. Prospective 5-year follow-up of new CV and metabolic events was completed.

Results: Low sRAGE was significantly associated with previous history and with new imminent cardiometabolic events in the prospective follow-up of RA patients. In both cases, low sRAGE reflected higher estimation of CVR in those patients. Low sRAGE was attributed to adverse metabolic parameters including high fasting plasma glucose and body fat content rather than inflammation. The association of sRAGE and poor metabolic profile was prominent in patients younger than 50 years.

Conclusions: This study points at low sRAGE as a marker of metabolic failure developed during chronic inflammation. It highlights the importance for monitoring metabolic health in female RA patients for timely prevention of CVD.

Trial registration:ClinicalTrials.gov with ID NCT03449589. Registered 28, February 2018.

Plasma Concentration of Advanced Glycation End-Products From Wild Canids and Domestic Dogs Does Not Change With Age or Across Body Masses

Dogs provide a physiological paradox: In domestic dogs, small breeds live longer lives than large breed dogs. Comparatively, a wild canid can be a similar size than many large breed dogs and outlive their domestic cousin. We have previously shown that oxidative stress patterns between domestic and wild canids differ, so that wild canids invest in a robust antioxidant system across their lives; whereas domestic dogs tend to accumulate lipid damage with age. There is a close association between oxidative stress and the production of a carbohydrate based-damage, Advanced Glycation End-products (AGEs). AGEs can bind to their receptor (RAGE), which can lead to increases in reactive oxygen species (ROS) production, and decreases in antioxidant capacity. Here, I used plasma from wild and domestic canids to address whether blood plasma AGE-BSA concentration associated with body mass and age in domestic dogs; And whether AGE-BSA concentration patterns in blood plasma from wild canids are similar to those found in domestic dogs. I found no correlation between circulating AGE-BSA concentration and body size or age in either domestic dogs and wild canids. These data suggest that AGEs formation may be a conserved trait across the evolution of domesticated dogs from wild ancestors, in opposition to oxidative stress patterns between these two groups. And, that, in domestic dogs, lipid metabolism, rather than carbohydrate metabolism, may be upregulated to yield the previously found differences in circulating lipid damage across lifespan and body sizes.

Activation of Notch1 signaling in podocytes by glucose-derived AGEs contributes to proteinuria

INTRODUCTION

Advanced glycation end-products (AGEs) are implicated in the pathogenesis of diabetic nephropathy (DN). Previous studies have shown that AGEs contribute to glomerulosclerosis and proteinuria. Podocytes, terminally differentiated epithelial cells of the glomerulus and the critical component of the glomerular filtration barrier, express the receptor for AGEs (RAGE). Podocytes are susceptible to severe injury during DN. In this study, we investigated the mechanism by which AGEs contribute to podocyte injury.

RESEARCH DESIGN AND METHODS

Glucose-derived AGEs were prepared in vitro. Reactivation of Notch signaling was examined in AGE-treated human podocytes (in vitro) and glomeruli from AGE-injected mice (in vivo) by quantitative reverse transcription-PCR, western blot analysis, ELISA and immunohistochemical staining. Further, the effects of AGEs on epithelial to mesenchymal transition (EMT) of podocytes and expression of fibrotic markers were evaluated.

RESULTS

Using human podocytes and a mouse model, we demonstrated that AGEs activate Notch1 signaling in podocytes and provoke EMT. Inhibition of RAGE and Notch1 by FPS-ZM1 (N-Benzyl-4-chloro-N-cyclohexylbenzamide) and DAPT (N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenyl glycine t-butylester), respectively, abrogates AGE-induced Notch activation and EMT. Inhibition of RAGE and Notch1 prevents AGE-induced glomerular fibrosis, thickening of the glomerular basement membrane, foot process effacement, and proteinuria. Furthermore, kidney biopsy sections from people with DN revealed the accumulation of AGEs in the glomerulus with elevated RAGE expression and activated Notch signaling.

CONCLUSION

The data suggest that AGEs activate Notch signaling in the glomerular podocytes. Pharmacological inhibition of Notch signaling by DAPT ameliorates AGE-induced podocytopathy and fibrosis. Our observations suggest that AGE-induced Notch reactivation in mature podocytes could be a novel mechanism in glomerular disease and thus could represent a novel therapeutic target.

Can advanced glycation end-products and their receptors be affected by weight loss? A systematic review

Advanced glycation end products (AGEs) have been implicated in the pathogenesis of most chronic diseases. Therefore, identification of treatments that can attenuate the effects of these compounds and prevent cardiometabolic complications is of extreme public health interest. Recently, body weight management interventions showed positive results on reducing serum AGE concentrations. Moreover, the soluble receptor for advanced glycation end products (sRAGE) is considered to be a novel biomarker to identify patients with obesity most likely to benefit from weight management interventions. This systematic review aimed to critically analyze papers evaluating the effects of weight loss on serum AGEs and its receptors in adults with excess body weight. MEDLINE, Cochrane, Scopus, and Lilacs databases were searched. Three studies evaluating the response of AGEs to energy-restricted diets and six assessing sRAGE as the primary outcome were included. Energy-restricted diets and bariatric surgery reduced serum AGE concentrations, but effects on endogenous secretory RAGE (esRAGE) and sRAGE concentrations are conflicting. These results may be associated with mechanisms related to changes in dietary intake and limiting endogenous AGE formation. Therefore, the role of energy-restricted diets and bariatric surgery on lowering serum AGE concentrations, as well as its effects on AGEs receptors, deserves further investigation.

Effect of reducing dietary advanced glycation end products on obesity-associated complications: a systematic review

CONTEXT

Consumption of dietary advanced glycation end products (AGEs) is associated with oxidative stress, inflammation, and other chronic conditions commonly associated with obesity.

OBJECTIVE

To analyze the effects of dietary AGEs on complications associated with obesity.

DATA SOURCES

This systematic review was conducted and reported according to PRISMA guidelines. The PubMed, Cochrane, and Scopus databases were searched, using the terms "advanced glycation end products," "overweight," and "obesity." The last search was performed in October 2018.

DATA EXTRACTION

Six studies that evaluated the effects of low-AGE and high-AGE diets were included in the review. The duration of the studies ranged from 1 day to 12 weeks. A comparison of all the compiled data was conducted by the authors.

DATA ANALYSIS

Circulating and urinary AGE markers, besides soluble receptor for AGEs, were considered as the primary outcomes. The secondary outcomes were cardiometabolic, inflammatory, glycemic, anthropometric, and renal markers.

CONCLUSIONS

AGE-RAGE interactions can activate the NF-κB (nuclear factor kappa B) signaling pathway and inhibit the PI3K-AKT pathway in adipocytes, which may explain their association with chronic diseases. This interaction can be considered as a novel explanation for the pathogenesis of obesity. AGEs can also be used as a biomarker for monitoring responses to dietary interventions in overweight and obese people.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42018082745.

Androgens Increase Accumulation of Advanced Glycation End Products in Granulosa Cells by Activating ER Stress in PCOS

Polycystic ovary syndrome (PCOS) is associated with hyperandrogenism, and we previously found that androgens activate endoplasmic reticulum (ER) stress in granulosa cells from patients with PCOS. In addition, recent studies demonstrated the accumulation of advanced glycation end products (AGEs) in granulosa cells from PCOS patients, which contribute to the pathology. Therefore, we hypothesized that androgens upregulate the receptor for AGEs (RAGE) expression in granulosa cells by activating ER stress, thereby increasing the accumulation of AGEs in these cells and contributing to the pathology. In the present study, we show that testosterone increases RAGE expression and AGE accumulation in cultured human granulosa-lutein cells (GLCs), and this is reduced by pretreatment with tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor in clinical use. Knockdown of the transcription factor C/EBP homologous protein (CHOP), an unfolded protein response factor activated by ER stress, inhibits testosterone-induced RAGE expression and AGE accumulation. The expression of RAGE and the accumulation of AGEs are upregulated in granulosa cells from PCOS patients and dehydroepiandrosterone-induced PCOS mice. Administration of the RAGE inhibitor FPS-ZM1 or TUDCA to PCOS mice reduces RAGE expression and AGE accumulation in granulosa cells, improves their estrous cycle, and reduces the number of atretic antral follicles. In summary, our findings indicate that hyperandrogenism in PCOS increases the expression of RAGE and accumulation of AGEs in the ovary by activating ER stress, and that targeting the AGE-RAGE system, either by using a RAGE inhibitor or a clinically available ER stress inhibitor, may represent a novel approach to PCOS therapy.

The Function of PPARγ/AMPK/SIRT-1 Pathway in Inflammatory Response of Human Articular Chondrocytes Stimulated by Advanced Glycation End Products

Accumulation of advanced glycation end products (AGEs) in the articular cartilage is a major risk factor for osteoarthritis (OA). To determine the mechanistic basis of AGE action in OA, we treated human articular chondrocytes with AGEs, and found that they not only up-regulated the pro-inflammatory cytokines interleukin (IL)-1β and tumor necrosis factor (TNF)-α, but also inhibited AMP-activated protein kinase (AMPK) phosphorylation and decreased sirtuin 1 (SIRT-1) levels in a concentration- and time-dependent manner. Pioglitazone, a peroxisome proliferator-activated receptor-γ (PPARγ) agonist restored the inhibited AMPK and SIRT-1 by AGEs. Pre-treatment of the cells with the agonists or antagonists of AMPK and SIRT-1 respectively abolished and augmented the inflammatory state induced by AGEs. Furthermore, AMPK agonist also restored the levels of SIRT-1 in the AGE-stimulated chondrocytes. Our findings indicate AGEs induce an inflammatory response in human articular chondrocytes via the PPARγ/AMPK/SIRT-1 pathway, which is therefore a potential target in OA therapy.

Effect of Glyoxal Modification on a Critical Arginine Residue (Arg-31α) of Hemoglobin: Physiological Implications of Advanced Glycated end Product an in vitro Study

BACKGROUND

Non-enzymatic protein glycation is involved in structure and stability changes that impair protein functionality, resulting in several human diseases, such as diabetes and amyloidotic neuropathies (Alzheimer's disease, Parkinson's disease and Andrade's syndrome). Glyoxal, an endogenous reactive oxoaldehyde, increases in diabetes and reacts with several proteins to form advanced glycation end products through Maillard-like reaction.

OBJECTIVE

Human hemoglobin, the most abundant protein in blood cells is subjected to nonenzymatic modification by reactive oxoaldehydes in diabetic condition. In the present study, the effect of a low concentration of glyoxal (5 μM) on hemoglobin (10 μM) has been investigated following a period of 30 days incubation in vitro.

METHODS

Different techniques, mostly biophysical and spectroscopic (e.g. circular dichroism, differential scanning calorimetric study, dynamic light scattering, mass spectrometry, etc.) were used to study glyoxal-induced changes of hemoglobin.

RESULTS

Glyoxal-treated hemoglobin exhibits decreased absorbance around 280 nm, decreased fluorescence and reduced surface hydrophobicity compared to normal hemoglobin. Glyoxal treatment enhances the stability of hemoglobin and lowers its susceptibility to thermal aggregation compared to control hemoglobin as seen by different studies. Finally, peptide mass fingerprinting study showed glyoxal to modify an arginine residue of α-chain of hemoglobin (Arg-31α) to hydroimidazolone.

CONCLUSION

Increased level of glyoxal in diabetes mellitus as well as its high reactivity may cause modifications of the heme protein. Thus, considering the significance of glyoxal-induced protein modification under physiological conditions, the observation appears clinically relevant in terms of understanding hydroimidazolone-mediated protein modification under in vivo conditions.

Molecular and Cellular Bases of Immunosenescence, Inflammation, and Cardiovascular Complications Mimicking "Inflammaging" in Patients with Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an archetype of systemic autoimmune disease, characterized by the presence of diverse autoantibodies and chronic inflammation. There are multiple factors involved in lupus pathogenesis, including genetic/epigenetic predisposition, sexual hormone imbalance, environmental stimulants, mental/psychological stresses, and undefined events. Recently, many authors noted that "inflammaging", consisting of immunosenescence and inflammation, is a common feature in aging people and patients with SLE. It is conceivable that chronic oxidative stresses originating from mitochondrial dysfunction, defective bioenergetics, abnormal immunometabolism, and premature telomere erosion may accelerate immune cell senescence in patients with SLE. The mitochondrial dysfunctions in SLE have been extensively investigated in recent years. The molecular basis of normoglycemic metabolic syndrome has been found to be relevant to the production of advanced glycosylated and nitrosative end products. Besides, immunosenescence, autoimmunity, endothelial cell damage, and decreased tissue regeneration could be the results of premature telomere erosion in patients with SLE. Herein, the molecular and cellular bases of inflammaging and cardiovascular complications in SLE patients will be extensively reviewed from the aspects of mitochondrial dysfunctions, abnormal bioenergetics/immunometabolism, and telomere/telomerase disequilibrium.