Advanced glycation end products (AGE) and diabetes: cause, effect, or both?

Abdominal aortic aneurysms and diabetes mellitus

There is accumulating evidence that risk profiles differ between coronary artery disease and abdominal aortic aneurysms (AAAs). However, diabetes mellitus (DM) appears to be negatively associated with AAA formation. The underlying mechanisms for this negative relationship are far from defined, but may include: increased arterial wall matrix formation via advanced glycation end products; suppression of plasmin and reduction of levels and activity of matrix metalloproteinases (MMP)-2 and 9; diminished aortic wall macrophage infiltration, elastolysis and neovascularization. In addition, the effect of pharmacological agents used for the treatment of patients with DM on AAA formation has been studied with rather controversial results. Statins, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, fenofibrate, antibiotics and some hypoglycemic agents are beginning to be appreciated for a potential modest protection from AAAs, but further studies are needed.

Effect of diet-derived advanced glycation end products on inflammation

Advanced glycation end products (AGEs) formed via the Maillard reaction during the thermal processing of food contributes to the flavor, color, and aroma of food. A proportion of food-derived AGEs and their precursors is intestinally absorbed and accumulates within cells and tissues. AGEs have been implicated in the pathogenesis of diabetes-related complications and several chronic diseases via interaction with the receptor for AGEs, which promotes the transcription of genes that control inflammation. The dicarbonyls, highly reactive intermediates of AGE formation, are also generated during food processing and may incite inflammatory responses through 1) the suppression of protective pathways, 2) the incretin axis, 3) the modulation of immune-mediated signaling, and 4) changes in gut microbiota profile and metabolite sensors. In animal models, restriction of dietary AGEs attenuates chronic low-grade inflammation, but current evidence from human studies is less clear. Here, the emerging relationship between excess dietary AGE consumption and inflammation is explored, the utility of dietary AGE restriction as a therapeutic strategy for the attenuation of chronic diseases is discussed, and possible avenues for future investigation are suggested.

Advanced Glycation-Modified Human Serum Albumin Evokes Alterations in Membrane and Eryptosis in Erythrocytes

Increased burden of advanced glycation end-products (AGEs) in case of hyperglycemic conditions leads to the development of retinopathy, nephropathy, and cardiovascular and neurological disorders such as Alzheimer's disease. AGEs are considered as pro-oxidants, and their accumulation increases the oxidative stress. The prolonged exposure to these AGEs is the fundamental cause of chronic oxidative stress. Abnormal morphology of red blood cells (RBCs) and excessive eryptosis has been observed in diabetes, glomerulonephritis, dyslipidemia, and obesity, but yet the contribution of extracellular AGEs remains undefined. In this study, we investigated the effect of AGEs on erythrocytes to determine their impact on the occurrence of different pathological forms of these blood cells. Specifically, carboxymethyllysine (CML), carboxyethyllysine (CEL), and Arg-pyrimidine (Arg-P) which have been reported to be the most pre-dominant AGEs formed under in vivo conditions were used in this study. Results suggested the eryptotic properties of CML, CEL, and Arg-P for RBCs, which were evident from the highly damaged cell membrane and occurrence of abnormal morphologies. Methylglyoxal-modified albumin showed more severe effects, which can be attributed to the high reactivity and pro-oxidant nature of glycation end products. These findings suggest the possible role of AGE-modified albumin towards the morphological changes in erythrocyte's membrane associated with diabetic conditions.

Inhibitory effect of zinc on the advanced glycation end product-induced apoptosis of mouse osteoblastic cells

Osteoporosis and diabetes have become serious health problems worldwide. Previous studies have suggested that diabetes is associated with osteoporosis and increased fracture risk. However, the mechanism underlying diabetes‑induced osteoporosis remains to be elucidated. Therefore, the present study aimed to examine the mechanism underlying diabetes‑induced osteoporosis, and determine the protective effects of zinc, which is known to be closely associated with osteoporosis and diabetes. The results of the present study demonstrated that zinc inhibited advanced glycation end product (AGE)‑induced MC3T3‑E1 cell apoptosis by attenuating the production of reactive oxygen species, inhibiting caspase‑3 and caspase‑9 activation, and inhibiting the release of cytochrome c from between the mitochondria and the cytosol. Furthermore, zinc was found to protect cells against AGE‑induced apoptosis via the mitogen‑activated protein kinase/extracellular signal‑regulated kinase and phosphoinositide 3‑kinase/AKT signaling pathways. In conclusion, these findings enable a better understanding of the mechanism underlying diabetes‑induced osteoporosis, and may indicate a novel target for its prevention and treatment.

Dietary advanced glycation end products and their role in health and disease

Over the past 2 decades there has been increasing evidence supporting an important contribution from food-derived advanced glycation end products (AGEs) to the body pool of AGEs and therefore increased oxidative stress and inflammation, processes that play a major role in the causation of chronic diseases. A 3-d symposium (1st Latin American Symposium of AGEs) to discuss this subject took place in Guanajuato, Mexico, on 1-3 October 2014 with the participation of researchers from several countries. This review is a summary of the different presentations and subjects discussed, and it is divided into 4 sections. The first section deals with current general knowledge about AGEs. The second section dwells on mechanisms of action of AGEs, with special emphasis on the receptor for advanced glycation end products and the potential role of AGEs in neurodegenerative diseases. The third section discusses different approaches to decrease the AGE burden. The last section discusses current methodologic problems with measurement of AGEs in different samples. The subject under discussion is complex and extensive and cannot be completely covered in a short review. Therefore, some areas of interest have been left out because of space. However, we hope this review illustrates currently known facts about dietary AGEs as well as pointing out areas that require further research.

Distribution of advanced glycation end products and their receptor in the stomach of diabetic rats

AIM: To observe the distribution of advanced glycation end products (AGEs) and their receptor (RAGE) in the stomach of diabetic rats.

METHODS: Diabetes mellitus (DM) and control (CON) rats were reared for eight weeks. Fasting plasma glucose (FPG), glycated serum protein (GSP) and gastric layer thickness were measured. The expression of AGEs and RAGE was detected by immunohistochemical staining.

RESULTS: The thickness of the mucosa (781.47 μm ± 137.82 μm vs 709.85 μm ± 169.41 μm) and submucosa (233.39 μm ± 134.05 μm vs 109.32 μm ± 44.43 μm) increased significantly in the DM group compared with the CON group (P < 0.05). The expression of AGEs and RAGE in the mucosa (5.66 ± 1.90 vs 2.25 ± 0.52, 2.79 ± 0.54 vs 1.70 ± 0.30) and muscle (37.37 ± 7.38 vs 24.32 ± 4.02, 4.26 ± 0.80 vs 3.59 ± 0.37) layers of the stomach was significantly higher in the DM group than in the CON group (P < 0.05).

CONCLUSION: The expression of AGEs and RAGE is up-regulated in the stomach of diabetic rats. The increased levels of AGE and RAGE in gastric tissue may contribute to diabetic gastrointestinal dysfunction.

Rosmarinic acid modulates the antioxidant status and protects pancreatic tissues from glucolipotoxicity mediated oxidative stress in high-fat diet: streptozotocin-induced diabetic rats

Persistent hyperglycemia and elevated levels of free fatty acids (FFA) contribute to oxidative stress, a proximate cause for the onset and progression of diabetes and its complications. The present study was hypothesized to evaluate the anti-diabetic potential of Rosmarinic acid (RA) during high-fat diet (HFD)-streptozotocin (STZ)-induced type 2 Diabetes (T2D) in wistar albino rats. Oral administration of RA (100 mg/kg b.w) significantly (p < 0.05) increased the insulin sensitivity index (ISI0,120), while the levels of blood glucose, HbA1c, advanced glycation end products (AGE), TNF-α, IL-1β, IL 6, NO, p-JNK, P38 MAPK and NF-κB were significantly reduced, with a concomitant elevation in the plasma insulin levels in diabetic rats. Furthermore, RA treatment significantly (p < 0.05) reduced the levels of triglycerides, FFA and cholesterol in serum, and reduced the levels of lipid peroxides, AOPP's and protein carbonyls in the plasma and pancreas of diabetic rats. The diminished activities of pancreatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) and the decreased levels of plasma ceruloplasmin, vitamin C, vitamin E and reduced glutathione (GSH) in diabetic rats were also significantly (p < 0.05) recovered upon RA treatment denoting its antioxidant potential which was confirmed by Nrf-2, hemeoxyenase (HO-1) levels. Histological, ultrastructural and immunohistochemical data demonstrate that oral administration of RA protects pancreatic β-cells from oxidative niche in HFD-STZ-induced experimental diabetes. Our findings suggest that the oral treatment with RA alleviates pancreatic β-cell dysfunction and glucolipotoxicity-mediated oxidative stress during HFD-STZ-induced T2DM, perhaps through its antioxidant potential.

The low AGE diet: a neglected aspect of clinical nephrology practice?

Increasing evidence in the literature suggests an important role for advanced glycation end products (AGEs) in the generation of a state of increased oxidative stress and chronic subclinical inflammation, which underlies most modern chronic diseases, including diabetes, cardiovascular disease and chronic kidney disease (CKD). Although AGEs were originally thought to form only endogenously, primarily as the result of the hyperglycemia of diabetes, it is now clear that exogenous AGEs, specially incorporated in foods, are an important contributor to the body pool of AGEs. Over the past decade, several clinical trials have been performed in a variety of conditions demonstrating that the application of an AGE-restricted diet reduces not only the systemic levels of AGEs but also the levels of markers of oxidative stress and inflammation. This has been shown in CKD patients before and after the initiation of dialysis and either in the presence or absence of coexistent diabetes. Reduction of the AGE content in food is obtained by simple changes in culinary techniques and appears to be a feasible, easily applicable and safe intervention, even in advanced CKD patients.

Advanced glycation end products and oxidative stress in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a very complex and multifactorial metabolic disease characterized by insulin resistance and β cell failure leading to elevated blood glucose levels. Hyperglycemia is suggested to be the main cause of diabetic complications, which not only decrease life quality and expectancy, but are also becoming a problem regarding the financial burden for health care systems. Therefore, and to counteract the continually increasing prevalence of diabetes, understanding the pathogenesis, the main risk factors, and the underlying molecular mechanisms may establish a basis for prevention and therapy. In this regard, research was performed revealing further evidence that oxidative stress has an important role in hyperglycemia-induced tissue injury as well as in early events relevant for the development of T2DM. The formation of advanced glycation end products (AGEs), a group of modified proteins and/or lipids with damaging potential, is one contributing factor. On the one hand it has been reported that AGEs increase reactive oxygen species formation and impair antioxidant systems, on the other hand the formation of some AGEs is induced per se under oxidative conditions. Thus, AGEs contribute at least partly to chronic stress conditions in diabetes. As AGEs are not only formed endogenously, but also derive from exogenous sources, i.e., food, they have been assumed as risk factors for T2DM. However, the role of AGEs in the pathogenesis of T2DM and diabetic complications—if they are causal or simply an effect—is only partly understood. This review will highlight the involvement of AGEs in the development and progression of T2DM and their role in diabetic complications.

Effect of advanced glycosylation end products on apoptosis in human adipose tissue-derived stem cells in vitro

Background

Both apoptosis and caspase-3 activity in adipose tissue-derived stem cells play an important role in the therapeutic process of diabetes patients. The purpose of this study was to investigate the effect of advanced glycation end products-human serum albumin (AGE-HSA) on apoptosis in human adipose tissue-derived stem cells (ADSCs) and to characterize the signal transduction pathways activated by AGEs that are involved in apoptosis regulation.

Results

AGE-HSA promoted apoptosis and caspase-3 activity in ADSCs. However, the effects of AGE-HSA were significantly attenuated by an inhibitor of p38 MAPK, but not by inhibitors of JNK MAPK or ERK MAPK. AGE-HSA also upregulated the expression of RAGE. Silencing of the RAGE gene inhibited AGE-HSA-induced apoptosis, and activation and expression of phosphorylated p38 MAPK.

Conclusions

These results suggest that AGE-HSA promote the apoptosis of ADSCs in vitro via a RAGE-dependent p38 MAPK pathway.

Crosstalk between advanced glycation end products (AGEs)-receptor RAGE axis and dipeptidyl peptidase-4-incretin system in diabetic vascular complications

Advanced glycation end products (AGEs) consist of heterogenous group of macroprotein derivatives, which are formed by non-enzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids, and whose process has progressed at an accelerated rate under diabetes. Non-enzymatic glycation and cross-linking of protein alter its structural integrity and function, contributing to the aging of macromolecules. Furthermore, engagement of receptor for AGEs (RAGE) with AGEs elicits oxidative stress generation and subsequently evokes proliferative, inflammatory, and fibrotic reactions in a variety of cells. Indeed, accumulating evidence has suggested the active involvement of accumulation of AGEs in diabetes-associated disorders such as diabetic microangiopathy, atherosclerotic cardiovascular diseases, Alzheimer's disease and osteoporosis. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins, gut hormones secreted from the intestine in response to food intake, both of which augment glucose-induced insulin release, suppress glucagon secretion, and slow gastric emptying. Since GLP-1 and GIP are rapidly degraded and inactivated by dipeptidyl peptidase-4 (DPP-4), inhibition of DPP-4 and/or DPP-4-resistant GLP-1 analogues have been proposed as a potential target for the treatment of diabetes. Recently, DPP-4 has been shown to cleave multiple peptides, and blockade of DPP-4 could exert diverse biological actions in GLP-1- or GIP-independent manner. This article summarizes the crosstalk between AGEs-RAGE axis and DPP-4-incretin system in the development and progression of diabetes-associated disorders and its therapeutic intervention, especially focusing on diabetic vascular complications.

Silybin, a flavonolignan from milk thistle seeds, restrains the early and advanced glycation end product modification of albumin

Silybin exhibited a protective effect towards the non-enzymatic glycation mediated structure functional changes in albumin.

Carbonyl trapping and antiglycative activities of olive oil mill wastewater

The use of natural compounds as antiglycative agents to reduce the load of advanced glycation end products from diet is very promising.

NADPH Oxidases in Chronic Liver Diseases

Oxidative stress is a common feature observed in a wide spectrum of chronic liver diseases including viral hepatitis, alcoholic, and nonalcoholic steatohepatitis. The nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are emerging as major sources of reactive oxygen species (ROS). Several major isoforms are expressed in the liver, including NOX1, NOX2, and NOX4. While the phagocytic NOX2 has been known to play an important role in Kupffer cell and neutrophil phagocytic activity and inflammation, the nonphagocytic NOX homologues are increasingly recognized as key enzymes in oxidative injury and wound healing. In this review, we will summarize the current advances in knowledge on the regulatory pathways of NOX activation, their cellular distribution, and their role in the modulation of redox signaling in liver diseases.

Differential effects of glycation on protein aggregation and amyloid formation

Amyloids are a class of insoluble proteinaceous substances generally composed of linear un-branched fibrils that are formed from misfolded proteins. Conformational diseases such as Alzheimer's disease, transmissible spongiform encephalopathies, and familial amyloidosis are associated with the presence of amyloid aggregates in the affected tissues. The majority of the cases are sporadic, suggesting that several factors must contribute to the onset and progression of these disorders. Among them, in the past 10 years, non-enzymatic glycation of proteins has been reported to stimulate protein aggregation and amyloid deposition. In this review, we analyze the most recent advances in this field suggesting that the effects induced by glycation may not be generalized as strongly depending on the protein structure. Indeed, being a post-translational modification, glycation could differentially affects the aggregation process in promoting, accelerating and/or stabilizing on-pathway and off-pathway species.

Systemic stiffening of mouse tail tendon is related to dietary advanced glycation end products but not high-fat diet or cholesterol

Tendon pathology is related to metabolic disease and mechanical overloading, but the effect of metabolic disease on tendon mechanics is unknown. This study investigated the effect of diet and apolipoprotein E deficiency (ApoE(-/-)) on mechanical properties and advanced glycation end product (AGE) cross-linking of non-weight-bearing mouse tail tendons. Twenty ApoE(-/-) male mice were used as a model for hypercholesterolemia along with 26 wild-type (WT) mice. One-half of the mice from each group was fed a normal diet (ND) and the other half was fed a high-fat diet (HFD) to induce obesity. All were killed at 40 wk, and tail tendon fascicles were mechanically tested to failure and analyzed for AGEs. Diets were also analyzed for AGEs. ApoE(-/-) mice displayed a 14% increase in plateau modulus compared with WT mice (P < 0.05), whereas HFD mice displayed a 13% decrease in plateau modulus (P < 0.05) and a 12% decrease in total modulus (P < 0.05) compared with ND mice. Tail tendons of HFD mice had significantly lower concentrations of AGEs [carboxymethyllysine (CML): 26%, P < 0.0001; methylglyoxal-derived hydroimidazolone 1 (MG-H1): 15%, P < 0.005; pentosidine: 13%, P < 0.0005]. The HFD had ∼44-fold lower content of CML (P < 0.01), ∼29-fold lower content of carboxyethyllysine (P < 0.005), and ∼16-fold lower content of MG-H1 (P < 0.05) compared with ND. ApoE(-/-) increased, whereas HFD decreased mouse tail tendon stiffness. Dietary AGE content may be a crucial determinant for accumulation of AGE cross-links in tendons and for tissue compliance. The results demonstrate how systemic metabolic factors may influence tendon health.

Nutritional psychiatry research: an emerging discipline and its intersection with global urbanization, environmental challenges and the evolutionary mismatch

In 21st-century public health, rapid urbanization and mental health disorders are a growing global concern. The relationship between diet, brain function and the risk of mental disorders has been the subject of intense research in recent years. In this review, we examine some of the potential socioeconomic and environmental challenges detracting from the traditional dietary patterns that might otherwise support positive mental health. In the context of urban expansion, climate change, cultural and technological changes and the global industrialization and ultraprocessing of food, findings related to nutrition and mental health are connected to some of the most pressing issues of our time. The research is also of relevance to matters of biophysiological anthropology. We explore some aspects of a potential evolutionary mismatch between our ancestral past (Paleolithic, Neolithic) and the contemporary nutritional environment. Changes related to dietary acid load, advanced glycation end products and microbiota (via dietary choices and cooking practices) may be of relevance to depression, anxiety and other mental disorders. In particular, the results of emerging studies demonstrate the importance of prenatal and early childhood dietary practices within the developmental origins of health and disease concept. There is still much work to be done before these population studies and their mirrored advances in bench research can provide translation to clinical medicine and public health policy. However, the clear message is that in the midst of a looming global epidemic, we ignore nutrition at our peril.