Effects Of Advanced Glycation End Products Research Articles

Increased AGE Cross-Linking Reduces the Mechanical Properties of Osteons

AbstractThe osteon is the primary structural component of bone, contributing significantly to its unique toughness and strength. Despite extensive research on osteonal structure, the properties of osteons have not been fully investigated, particularly within the context of bone fragility diseases like type 2 diabetes mellitus (T2DM). This study aims to isolate osteons from bovine bone, simulate the effects of increased advanced glycation end-products (AGEs) in T2DM through ribosylation, and evaluate the mechanical properties of isolated osteons. Osteons extracted from the posterior section of bovine femur mid-diaphysis were processed to achieve a sub-millimeter scale for microscale imaging. Subsequently, synchrotron radiation micro-computed tomography was employed to precisely localize and isolate the osteon internally. While comparable elastic properties were observed between control and ribosylated osteons, the presence of AGEs led to decreased strain to failure. Young’s modulus was quantified (9.9 ± 4.9 GPa and 8.7 ± 3 GPa, respectively), aligning closely with existing literature. This study presents a novel method for the extraction and isolation of osteons from bone and shows the detrimental effect of AGEs at the osteonal level.

Synaptic mitochondria glycation contributes to mitochondrial stress and cognitive dysfunction.

Mitochondrial and synaptic dysfunction are pathological features of brain aging and cognitive decline. Synaptic mitochondria are vital for meeting the high energy demands of synaptic transmission. However, little is known about the link between age-related metabolic changes and the integrity of synaptic mitochondria. To this end, we investigate the mechanisms of advanced glycation endproducts (AGEs)-mediated mitochondrial and synaptic stress and evaluate the strategies to eliminate these toxic metabolites. Using aged brain and novel transgenic mice overexpressing neuronal glyoxalase 1 (GLO1), we comprehensively analyzed alterations in accumulation/buildup of AGEs and related metabolites in synaptic mitochondria and the association of AGE levels with mitochondrial function. We demonstrate for the first time that synaptic mitochondria are an early and major target of AGEs and the related toxic metabolite methylglyoxal (MG), a precursor of AGEs. MG/AGEs-insulted synaptic mitochondria exhibit deterioration of mitochondrial and synaptic function. Such accumulation of MG/AGEs positively correlated with mitochondrial perturbation and oxidative stress in aging brain. Importantly, clearance of AGEs-related metabolites by enhancing neuronal GLO1, a key enzyme for detoxification/of AGEs, reduces synaptic mitochondrial AGEs accumulation and improves mitochondrial and cognitive function in aging and AGE-challenged mice. Furthermore, we evaluated the direct effect of AGEs on synaptic function in hippocampal neurons in live brain slices as an ex-vivo model and in vitro cultured hippocampal neurons by recording long-term potentiation (LTP) and measuring spontaneously occurring miniature excitatory postsynaptic currents (mEPSCs). Neuronal GLO1 rescues deficits in AGEs-induced synaptic plasticity and transmission by fully recovery of decline in LTP or frequency of mEPSC. These studies explore crosstalk between synaptic mitochondrial dysfunction and age-related metabolic changes relevant to brain aging and cognitive decline. Synaptic mitochondria are particularly susceptible to AGEs-induced damage, highlighting the central importance of synaptic mitochondrial dysfunction in synaptic degeneration in age-related cognitive decline. Thus, augmenting GLO1 function to scavenge toxic metabolites represents a therapeutic approach to reduce age-related AGEs accumulation and to improve mitochondrial function and learning and memory.

The effects of advanced glycation end-products on skin and potential anti-glycation strategies.

The advanced glycation end-products (AGEs) are produced through non-enzymatic glycation between reducing sugars and free amino groups, such as proteins, lipids or nucleic acids. AGEs can enter the body through daily dietary intake and can also be generated internally via normal metabolism and external stimuli. AGEs bind to cell surface receptors for AGEs, triggering oxidative stress and inflammation responses that lead to skin ageing and various diseases. Evidence shows that AGEs contribute to skin dysfunction and ageing. This review introduces the basic information, the sources, the metabolism and absorption of AGEs. We also summarise the detrimental mechanisms of AGEs to skin ageing and other chronic diseases. For the potential strategies for counteracting AGEs to skin and other organs, we summarised the pathways that could be utilised to resist glycation. Chemical and natural-derived anti-glycation approaches are overviewed. This work offers an understanding of AGEs to skin ageing and other chronic diseases and may provide perspectives for the development of anti-glycation strategies.

How dietary advanced glycation end products could facilitate the occurrence of food allergy

BackgroundFood allergy (FA) is one of the most common chronic conditions in the pediatric age with an increasing prevalence under the pressure of environmental factors in predisposed individuals. It has been hypothesized that the increased consumption of ultra-processed foods, containing high levels of dietary advanced glycation end-products (AGEs), could facilitate the occurrence of food allergy. ObjectiveHere we provide preclinical and clinical evidence on the potential role of AGEs in facilitating the occurrence of FA. MethodsHuman enterocytes, human small intestine organ culture, and peripheral mononuclear blood cells (PBMCs) from children at risk for allergy were used to investigate the direct effect of AGEs on gut barrier, inflammation, Th2 cytokines response and mitochondrial function.The intake of the three most commonly glycation products in Western diet-foods Nε -(carboxymethyl) lysine (CML), Nε -(1-carboxyethyl) lysine (CEL), and Nδ -(5-hydro-5- methyl-4-imidazolon-2-yl)-ornithine (MG-H1), and the skin AGEs accumulation were comparatively investigated in children with FA and in age-matched healthy controls. ResultsHuman enterocytes exposed to AGEs showed alteration in gut barrier, AGEs receptor expression, reactive oxygen species production and autophagy, with increased transepithelial passage of food antigens. Small intestine organ culture exposed to AGEs showed an increase of CD25+ cells and proliferating crypt enterocytes. PBMCs exposed to AGEs showed alteration in proliferation rate, AGEs receptor activation, release of inflammatory and Th2 cytokines, and mitochondrial metabolism.Significant higher dietary AGEs intake and skin accumulation were observed in FA children (n=42) compared with age-matched healthy controls (n=66). ConclusionsThese data, supporting a potential role for dietary AGEs in facilitating the occurrence of FA, suggest the importance of limiting the AGEs exposure in the pediatric age as potential preventive strategy against this common condition.

Effects of advanced glycation end-products, diabetes and metformin on the osteoblastic transdifferentiation capacity of vascular smooth muscle cells: In vivo and in vitro studies

AimsOur objective was to study the vascular smooth muscle cells (VSMC) osteoblastic transdifferentiation in AGE exposed cells or those from diabetic animals, and its response to metformin treatment. MethodsVSMC were obtained from non-diabetic rats, grown with or without AGE; while VSMC of in vivo-ex vivo studies were obtained from non-diabetic control animals (C), diabetic (D), C treated with metformin (M) and D treated with metformin (D-M). We studied the osteoblastic differentiation by evaluating alkaline phosphatase (ALP), type I collagen (Col) and mineral deposit. ResultsIn vitro, AGE increased proliferation, migration, and osteoblastic differentiation of VSMC. Metformin cotreatment prevented the AGE induced proliferation and migration. Both AGE and metformin stimulated the expression of ALP and Col. AGE induced mineralization was prevented by metformin. VSMC from D expressed a higher production of Col and ALP. Those from D-M showed an ALP increase vs C and M, and a partial decrease vs D. Cultured in osteogenic medium, ALP, Col and mineralization increased in D vs C, remained unchanged in M, and were prevented in D-M animals. ConclusionBoth AGE and DM favor VSMC differentiation towards the osteogenic phenotype and this effect can be prevented by metformin.

Methylglyoxal-derived hydroimidazolone, MG-H1, increases food intake by altering tyramine signaling via the GATA transcription factor ELT-3 in Caenorhabditis elegans.

The Maillard reaction, a chemical reaction between amino acids and sugars, is exploited to produce flavorful food ubiquitously, from the baking industry to our everyday lives. However, the Maillard reaction also occurs in all cells, from prokaryotes to eukaryotes, forming advanced glycation end-products (AGEs). AGEs are a heterogeneous group of compounds resulting from the irreversible reaction between biomolecules and α-dicarbonyls (α-DCs), including methylglyoxal (MGO), an unavoidable byproduct of anaerobic glycolysis and lipid peroxidation. We previously demonstrated that Caenorhabditis elegans mutants lacking the glod-4 glyoxalase enzyme displayed enhanced accumulation of α-DCs, reduced lifespan, increased neuronal damage, and touch hypersensitivity. Here, we demonstrate that glod-4 mutation increased food intake and identify that MGO-derived hydroimidazolone, MG-H1, is a mediator of the observed increase in food intake. RNAseq analysis in glod-4 knockdown worms identified upregulation of several neurotransmitters and feeding genes. Suppressor screening of the overfeeding phenotype identified the tdc-1-tyramine-tyra-2/ser-2 signaling as an essential pathway mediating AGE (MG-H1)-induced feeding in glod-4 mutants. We also identified the elt-3 GATA transcription factor as an essential upstream regulator for increased feeding upon accumulation of AGEs by partially controlling the expression of tdc-1 gene. Furthermore, the lack of either tdc-1 or tyra-2/ser-2 receptors suppresses the reduced lifespan and rescues neuronal damage observed in glod-4 mutants. Thus, in C. elegans, we identified an elt-3 regulated tyramine-dependent pathway mediating the toxic effects of MG-H1 AGE. Understanding this signaling pathway may help understand hedonistic overfeeding behavior observed due to modern AGE-rich diets.

Pyridoxamine protects human granulosa cells against advanced glycation end-products-induced steroidogenesis disturbances.

Ovarian advanced glycation end-products (AGEs) accumulation is associated with ovarian granulosa cells (GCs) dysfunction. Vitamin B6 derivatives positively affected reproduction. The current study was conducted to elucidate the AGEs effects on human luteinized mural GCs steroidogenesis in the presence or absence of pyridoxamine (PM). Isolated GCs of 50 healthy women were divided into four parts and treated with media alone (Control), PM alone, or human glycated albumin (HGA) with/without PM. Main steroidogenic enzymes and hormones were assessed by qRT-PCR and ELISA. The AGE receptor (RAGE) protein was also determined using Western blotting. The non-toxic concentration of HGA increased the expression of RAGE, StAR, 3β-HSD, and 17β-HSD (P < 0.0001 for all) but decreased the expression of CYP19A1 at mRNA levels. The increased RAGE protein expression was also confirmed by western blot analysis. These effects resulted in declined estradiol (E2), slightly, and a sharp rise in progesterone (P4) and testosterone (T) levels, respectively. PM, on its own, ameliorated the HGA-altered enzyme expression and, thereby, corrected the aberrant levels of E2, P4, and T. These effects are likely mediated by regulating the RAGE gene and protein expression. This study indicates that hormonal dysfunctions induced by the AGEs-RAGE axis in luteinized GCs are likely rectified by PM treatment. This effect is likely acquired by reduced expression of RAGE. A better understanding of how AGEs and PM interact in ovarian physiology and pathology may lead to more targeted therapy for treating ovarian dysfunction.

Oxidative Stress and Its Regulation in Diabetic Retinopathy.

Diabetic retinopathy is the retinal disease associated with hyperglycemia in patients who suffer from type 1 or type 2 diabetes. It includes maculopathy, involving the central retina and characterized by ischemia and/or edema, and peripheral retinopathy that progresses to a proliferative stage with neovascularization. Approximately 10% of the global population is estimated to suffer from diabetes, and around one in 5 of these individuals have diabetic retinopathy. One of the major effects of hyperglycemia is oxidative stress, the pathological state in which elevated production of reactive oxygen species damages tissues, cells, and macromolecules. The retina is relatively prone to oxidative stress due to its high metabolic activity. This review provides a summary of the role of oxidative stress in diabetic retinopathy, including a description of the retinal cell players and the molecular mechanisms. It discusses pathological processes, including the formation and effects of advanced glycation end-products, the impact of metabolic memory, and involvements of non-coding RNA. The opportunities for the therapeutic blockade of oxidative stress in diabetic retinopathy are also considered.

Resveratrol Alleviates Advanced Glycation End-Products-Related Renal Dysfunction in D-Galactose-Induced Aging Mice.

The elderly have higher concentrations of advanced glycation end-products (AGEs). AGEs are considered risk factors that accelerate aging and cause diabetic nephropathy. The effects of AGEs on renal function in the elderly remain to be clarified. This study aimed to explore the role of AGEs in renal function decline in the elderly and the protective effect of resveratrol, a stilbenoid polyphenol, comparing it with aminoguanidine (an AGEs inhibitor). A D-galactose-induced aging mouse model was used to explore the role of AGEs in the process of renal aging. The mice were administered D-galactose subcutaneously for eight weeks in the presence or absence of orally administered aminoguanidine or resveratrol. The results showed that the serum levels of AGEs and renal function markers BUN, creatinine, and cystatin C in the mice significantly increased after the administration of D-galactose, and this outcome could be significantly reversed by treatment with aminoguanidine or resveratrol. The protein expression levels for apoptosis, fibrosis, and aging-related indicators in the kidneys were significantly increased, which could also be reversed by treatment with aminoguanidine or resveratrol. These findings suggest that resveratrol could alleviate AGEs-related renal dysfunction through the improvement of renal cellular senescence, apoptosis, and fibrosis in D-galactose-induced aging in mice.

Co-Stimulation of AGEs and LPS Induces Inflammatory Mediators through PLCγ1/JNK/NF-κB Pathway in MC3T3-E1 Cells.

Advanced glycation end-products (AGEs) are increased under hyperglycemia in vivo and are associated with the onset of diabetes. According to previous studies, AGEs exacerbate inflammatory diseases. However, the mechanism by which AGEs aggravate osteoblast inflammation remains unknown. Therefore, the aim of this study was to determine the effects of AGEs on the production of inflammatory mediators in MC3T3-E1 cells and the underlying molecular mechanisms. Co-stimulation with AGEs and lipopolysaccharide (LPS) was found to increase the mRNA and protein levels of cyclooxygenase 2 (COX2), interleukin-1α (IL-1α), S100 calcium-binding protein A9 (S100A9), and the production of prostaglandin E2 (PGE2) compared to no stimulation (untreated control) or individual stimulation with LPS or AGEs. In contrast, the phospholipase C (PLC) inhibitor, U73122, inhibited these stimulatory effects. Co-stimulation with AGEs and LPS also increased the nuclear translocation of nuclear factor-kappa B (NF-κB) compared to no stimulation (untreated control) or individual stimulation with LPS or AGE. However, this increase was inhibited by U73122. Co-stimulation with AGEs and LPS-induced phosphorylated phospholipase Cγ1 (p-PLCγ1) and phosphorylated c-Jun N-terminal kinase (p-JNK) expression compared to no stimulation or individual stimulation with LPS or AGEs. U73122 inhibited the effects induced by co-stimulation. siPLCγ1 did not increase the expression of p-JNK and the translocation of NF-κB. Overall, co-stimulation with AGEs and LPS may promote inflammation mediators in MC3T3-E1 cells by activating the nuclear translocation of NF-κB via PLCγ1-JNK activation.

The influence of AGEs and enzymatic cross-links on the mechanical properties of collagen fibrils

Collagen, one of the main building blocks for various tissues, derives its mechanical properties directly from its structure of cross-linked tropocollagen molecules. The cross-links are considered to be a key component of collagen fibrils as they can change the fibrillar behavior in various ways. For instance, enzymatic cross-links (ECLs), one particular type of cross-links, are known for stabilizing the structure of the fibril and improving material properties, while cross-linking AGEs (Advanced-Glycation Endproducts) have been shown to accumulate and impair the mechanical properties of collageneous tissues. However, the reasons for whether and how a given type of cross-link improves or impairs the material properties remain unknown, and the exact relationship between the cross-link properties and density, and the fibrillar behavior is still not well understood. Here, we use coarse-grained steered molecular models to evaluate the effect of AGEs and ECLs cross-links content on the deformation and failure properties of collagen fibrils. Our simulations show that the collagen fibrils stiffen at high strain levels when the AGEs content exceeds a critical value. In addition, the strength of the fibril increases with AGEs accumulation. By analyzing the forces within the different types of cross-links (AGEs and ECLs) as well as their failure, we demonstrate that a change of deformation mechanism is at the origin of these observations. A high AGEs content reinforces force transfer through AGEs cross-links rather than through friction between sliding tropocollagen molecules, which leads to failure by breaking of bonds within the tropocollagen molecules. We show that this failure mechanism, which is associated with lower energy dissipation, results in more abrupt failure of the collagen fibril. Our results provide a direct and causal link between increased AGEs content, inhibited intra-fibrillar sliding, increased stiffness, and abrupt fibril fracture. Therefore, they explain the mechanical origin of bone brittleness as commonly observed in elderly and diabetic populations. Our findings contribute to a better understanding of the mechanisms underlying impaired tissue behavior due to elevated AGEs content and could enable targeted measures regarding the reduction of specific collagen cross-linking levels.

Detrimental actions of obesity-associated advanced glycation end-products on endometrial epithelial cell proliferation are alleviated by antioxidants

Advanced glycation end-products (AGE) are elevated in the uterine environment of obese infertile women. Can the detrimental effects of AGE on endometrial epithelial cells be mitigated with therapeutics, and recapitulated in a more physiologically relevant primary model (organoids)? Human endometrial epithelial cells (ECC-1) were exposed to AGE at concentrations physiologically representative of uterine fluid in lean or obese individuals, and three potential therapeutics: 25nmol/l receptor for AGE (RAGE) antagonist FPS-ZM1, 100μmol/l metformin, or a combination of antioxidants (10μmol/l N-acetyl-l-cysteine, 10μmol/l N-acetyl-l-carnitine and 5μmol/l α-lipoic acid). Real-time cell analysis (xCELLigence, ACEA Biosciences) determined the rate of adhesion and proliferation. The proliferation of organoid-derived cells and secretion of cytokines from organoids was characterized in the presence of AGE (n = 5). The uterine fluid of women undergoing assisted reproduction was profiled for AGE-associated inflammatory markers (n = 77). ECC-1 proliferation was reduced by AGE from obese versus lean conditions and vehicle control (P = 0.04 and P<0.001, respectively), and restored to a proliferation corresponding to lean conditions by antioxidants. AGE influenced organoid derived primary endometrial epithelial cell proliferation in a donor-dependent manner. AGE increased the organoid secretion of the proinflammatory cytokine CXCL16 (P = 0.006). Clinically, CXCL16 correlated positively to maternal body mass index (R = 0.264, P = 0.021) and intrauterine glucose concentration (R = 0.736, P<0.0001). Physiologically relevant concentrations of AGE alter endometrial epithelial cell function. Antioxidants restore the rate of proliferation of AGE-treated endometrial epithelial (ECC-1) cells. Primary endometrial epithelial cells, cultured as organoids, demonstrate altered proliferation and CXCL16 secretion in the presence of AGE equimolar with the uterine fluid from obese individuals.

Effects of Allergen-Specific and Non-Specific AGEs on the Allergenicity of Ovalbumin in a Mouse Model of Food Allergy.

Epidemiologic studies suggest a link between the incidence of food allergy and the consumption of dietary advanced glycation end-products (AGEs). However, the pathogenic role of dietary AGEs in food allergy is largely unknown. This study aims to investigate the effect of allergen-specific and non-specific AGEs on the allergenic manifestation of ovalbumin (OVA), a typical food allergen in vivo. OVA is glycated by methylglyoxal to prepare allergen-specific AGEs (i.e., OVA-AGE), and a standard AIN-93G diet is heated to obtain allergen-non-specific AGEs. A BALB/c mouse model orally sensitizes to OVA with different forms of AGEs is established and the outcomes are measured as clinical signs, specific antibodies, type-2/type-2 cytokines, immune cell subpopulations, intestinal barrier function, and gut microbiota (GM) composition. The OVA-AGE which has a lower immunoglobulin E (IgE)-binding level in vitro does not reduce the allergenicity of OVA but promotes a stronger T helper 2 cells (Th2)-response than native OVA in vivo. Both forms of AGEs up-regulate the expression of splenic RAGE and aggravate the destruction of gut barrier and GM dysbiosis, especially when exposes to non-relevant AGEs. This study highlights the role of dietary AGEs in food allergy and helps to understand the biological consequences of immune-toxic compounds in modern diet.

Advanced Glycation End Products Effects on Adipocyte Niche Stiffness and Cell Signaling.

Adipose tissue metabolism under hyperglycemia results in Type II diabetes (T2D). To better understand how the adipocytes function, we used a cell culture that was exposed to glycation by adding intermediate carbonyl products, which caused chemical cross-linking and led to the formation of advanced glycation end products (AGEs). The AGEs increased the cells and their niche stiffness and altered the rheological viscoelastic properties of the cultured cells leading to altered cell signaling. The AGEs formed concomitant with changes in protein structure, quantified by spectroscopy using the 8-ANS and Nile red probes. The AGE effects on adipocyte differentiation were viewed by imaging and evidenced in a reduction in cellular motility and membrane dynamics. Importantly, the alteration led to reduced adipogenesis, that is also measured by qPCR for expression of adipogenic genes and cell signaling. The evidence of alteration in the plasma membrane (PM) dynamics (measured by CTxB binding and NP endocytosis), also led to the impairment of signal transduction and a decrease in AKT phosphorylation, which hindered downstream insulin signaling. The study, therefore, presents a new interpretation of how AGEs affect the cell niche, PM stiffness, and cell signaling leading to an impairment of insulin signaling.

Advanced Glycation End-Products (AGEs) Promote Endothelial Cell Pyroptosis Under Cerebral Ischemia and Hypoxia via HIF-1α-RAGE-NLRP3.

This work mainly aimed to explore the role and mechanism of advanced glycation end-products (AGEs) in inducing cerebrovascular endothelial cell pyroptosis under oxygen glucose deprivation (OGD) condition. The mouse cerebral microvascular endothelial cells (BMECs and bEnd.3) were used as the objects to construct the OGD model in vitro. Then, cells were pretreated with AGE-modified human serum albumin (AGE-HSA). Thereafter, CCK-8 assay was conducted to detect cell viability, and flow cytometry (FCM) was performed to measure cell pyroptosis level. Meanwhile, the expression of inflammatory factors was detected by enzyme-linked immunosorbent assay (ELISA). The expression of HIF-α, NLRP3, and RAGE was detected by fluorescence staining. The opening status of cell membrane pore was observed under the electron microscope, and the expression levels of FL-GSDMD, NT-GSDMD, and caspase-1 were measured through Western Blot (WB) assay. Moreover, bEnd.3 cells were treated with siRAN-silenced NLRP3 and HIF-α inhibitor, so as to observe the effect of AGEs on cell pyroptosis level. In the mouse model, the middle cerebral artery occlusion (MCAO) model was constructed by the suture-occluded method. After intraperitoneal injection of AGEs, the pathological changes in mouse brain tissues were detected; the expression levels of NLRP3, ZO-1, and CD31 were determined by histochemical staining, and the levels of inflammatory factors and pyroptosis-related proteins were also detected. Under OGD condition, AGEs induced the pyroptosis of bEnd.3 cells, and the cell pyroptosis rate increased, higher than that of the OGD group. Meanwhile, the levels of inflammatory factors were up-regulated; the expression of HIF-α, NLRP3, and RAGE in cells increased; and the levels of NT-GSDMD and caspase-1 were markedly higher than those of the control and OGD groups. siRNA-NLRP3 or HIF-α inhibitor treatment suppressed pyroptosis and reduced the inflammatory factor levels. In mouse experiments, AGE injection aggravated brain injury in the MCAO mouse model, decreased the expression of ZO-1 and CD31, and elevated the levels of NLRP3 and inflammatory factors. Under cerebral ischemia condition, AGEs can induce endothelial cell pyroptosis via HIF-α-RAGE-NLRP3, thereby further aggravating brain injury.

Glyoxal-derived advanced glycation end-products, Nε-carboxymethyl-lysine, and glyoxal-derived lysine dimer induce apoptosis-related gene expression in hepatocytes.

Advanced glycation end-products (AGEs) are proteins or lipids that have been glycated nonenzymatically by reducing sugars and their derivatives such as methylglyoxal. AGEs are known to cause inflammation, oxidative stress, and diseases in the human body. The toxic effects of AGEs and their structures on the origin of the protein being modified have not been well studied. Five different types of AGEs: AGE1 (glucose-derived), AGE2 (glyceraldehyde-derived), AGE3 (glycolaldehyde-derived), AGE4 (methylglyoxal-derived), and AGE5 (glyoxal-derived); were used to examine the effect of AGEs on HepG2 cells. AGE2 through 5 increase the production of reactive oxygen species (ROS) in liver cells, an initiating factor for apoptosis. At the mRNA and protein levels, AGE5 treatment showed the greatest increase in expression of apoptosis-related factors such as Bax, p53, and Caspase 3. Quantitative analysis revealed that Nε-carboxymethyl-lysine (CML) and glyoxal-lysine dimer (GOLD) were the important types of AGE5. The ROS generation and the expression of apoptotic factors both increased when cells were treated with CML and GOLD. These findings suggest that AGE5 treatment activates the apoptosis-related gene expression in hapatocytes, with CML and GOLD as potential major AGE compounds.

Advanced glycation end-products change placental barrier function and tight junction in rats with gestational diabetes mellitus via the receptor for advanced glycation end products/nuclear factor-κB pathway

The placenta plays an important role in nutrient transport to maintain the growth and development of the embryo. Gestational diabetes mellitus (GDM), the most common complication during pregnancy, highly affects placental function in late gestation. Advanced glycation end-products (AGEs), a complex and heterogeneous group of compounds engaged by the receptor for AGEs (RAGE), are closely associated with diabetes-related complications. In this study, AGEs induced a decrease in the expression of tight junction (TJ) proteins in BeWo cells and increased the paracellular permeability of trophoblast cells by regulating RAGE/NF-κB. Sprague-Dawley (SD) rats injected with 100 mg/kg AGEs-rat serum albumin (RSA) via the tail vein from embryo day 2 were set as the placental barrier dysfunction model group (n = 10). The effect of AGEs on placental permeability was determined using the EvansBlue dye extravasation method. The ultrastructure of the placenta samples was observed by transmission electron microscopy. The effects of AGEs on the placenta were confirmed by treating rats with RAGE antagonist FPS-ZM1 and soluble forms of RAGE (sRAGE). AGEs treatment increased placental permeability and disrupted the tight junctions in pregnant rat placenta, but has no effect on blood glucose. The expression of TJ-related proteins, including ZO-1, Occludin, and Claudin 5, were downregulated after AGEs treatment. Further, AGEs treatment increased the expression of RAGE and nuclear factor-κB in the placenta of rats and upregulated the levels of vascular endothelial growth factor. The effects of AGEs on the placenta were blocked by RAGE antagonist FPS-ZM1 and sRAGE. This study demonstrates the mechanism underlying AGEs-induced disturbance in placental function in pregnant rats and highlights the potential of AGEs in the treatment of GDM.

Association between Advanced Glycation End-Products, Carotenoids, and Severe Erectile Dysfunction.

To investigate the association between skin advanced glycation end-products (AGEs) levels, blood antioxidative vitamin and carotenoid concentrations, and severe erectile dysfunction (ED) in community-dwelling men. This cross-sectional study used the 5-Item International Index of Erectile Function to identify 335 community-dwelling men with ED. The accumulation of skin AGEs was assessed noninvasively by measuring skin autofluorescence. Background-adjusted multivariable logistic regression analyses using the inverse probability of treatment weighting method were performed to evaluate the effects of AGEs, vitamins, and carotenoids on severe ED. Moreover, multiple linear regression analyses were performed to assess the association between skin AGEs levels and serum carotenoid concentrations. The median age of study participants was 57 years. Of the 335 men, 289 (86.3%) and 46 (13.7%) were classified into the mild/moderate and severe ED groups, respectively. Multivariable analyses revealed that skin AGEs levels, blood vitamins C and E, lutein, zeaxanthin, β-cryptoxanthin, α-carotene, β-carotene, total lycopene, and cis-lycopenes concentrations were significantly associated with severe ED, whereas all-trans lycopene concentrations were not. In the multiple linear regression analyses, serum zeaxanthin concentrations were negatively and significantly correlated with skin AGEs levels. Higher skin AGEs levels and lower blood antioxidative vitamin and carotenoid concentrations were significantly associated with severe ED. Serum zeaxanthin levels were negatively and significantly correlated with skin AGEs levels, suggesting the possible effects of zeaxanthin on ED by decreasing tissue AGEs levels.

Effects of Toxic AGEs (TAGE) on Human Health.

The habitual and excessive consumption of sugar (i.e., sucrose and high-fructose corn syrup, HFCS) is associated with the onset and progression of lifestyle-related diseases (LSRD). Advanced glycation end-products (AGEs) have recently been the focus of research on the factors contributing to LSRD. Approaches that inhibit the effects of AGEs may be used to prevent and/or treat LSRD; however, since the structures of AGEs vary depending on the type of reducing sugars or carbonyl compounds to which they respond, difficulties are associated with verifying that AGEs are an etiological factor. Cytotoxic AGEs derived from glyceraldehyde, a triose intermediate in the metabolism of glucose and fructose, have been implicated in LSRD and are called toxic AGEs (TAGE). A dietary imbalance (the habitual and excessive intake of sucrose, HFCS, or dietary AGEs) promotes the generation/accumulation of TAGE in vivo. Elevated circulating levels of TAGE have been detected in non-diabetics and diabetics, indicating a strong relationship between the generation/accumulation of TAGE in vivo and the onset and progression of LSRD. We herein outline current findings on “TAGE as a new target” for human health.

S-allylmercapto-N-acetylcysteine protects bone cells from oxidation and improves femur microarchitecture in healthy and diabetic mice.

Oxidative stress is involved in the deterioration of bone quality and mechanical strength in both diabetic and aging adults. Therefore, we studied the ability of the antioxidant compound, S-allylmercapto-N-acetylcysteine (ASSNAC) to protect bone marrow stromal cells (BMSCs) from advanced glycation end-products (AGEs) cytotoxicity and improve bone microarchitecture of adult healthy and obese/diabetic (db/db) female mice. ASSNAC effect on AGEs-treated cultured rat BMSCs was evaluated by Neutral Red and XTT cell survival and reactive oxygen species (ROS) level assays. Its effect on healthy (C57BL/6) and obese/diabetic (C57BLKS/J Leprdb+/+; db/db) female mice femur parameters, such as (1) number of adherent BMSCs, (2) percentage of CD73+/CD45- cells in bone marrow (BM), (3) glutathione level in BM cells, and (4) femur microarchitecture parameters by microcomputed tomography, was studied. ASSNAC treatment protected BMSCs by significantly decreasing AGEs-induced ROS production and increasing their cellular resistance to the cytotoxic effect of AGEs. ASSNAC treatment of healthy female mice (50 mg/kg/day; i.p.; age 12-20 weeks) significantly increased the number of BMSCs (+60%), CD73+/CD45- cells (+134%), and glutathione level (+110%) in the femur bone marrow. Furthermore, it increased the femur length (+3%), cortical diameter (+3%), and cortical areal moment of inertia (Ct.MOI; +10%) a surrogate for biomechanical strength. In db/db mice that demonstrated a compromised trabecular bone and growth plate microarchitecture, ASSNAC treatment restored the trabecular number (Tb.N, +29%), bone volume fraction (Tb.BV/TV, +130%), and growth plate primary spongiosa volumetric bone mineral density (PS-vBMD, +7%) and thickness (PS-Th, +18%). In conclusion, this study demonstrates that ASSNAC protects bone marrow cells from oxidative stress and may improve bone microarchitecture in adult healthy and diabetic female mice.