Advanced Glycation End Accumulation Research Articles

Diabetic Neuropathy: A Repercussion of Vitamin D Deficiency.

Diabetes mellitus is a crucial health issue worldwide. The worldwide ubiquity is 8.8% among adults, which is predicted to rise to 10.4% by 2040. Diabetic neuropathy is a long-term complication associated with the diabetes mellitus condition, which primarily targets Schwann cells, peripheral axons and cell bodies (perikarya) in DRG (dorsal root ganglia). It can be accompanied by different factors such as metabolic factors such as insulin resistance, hypertension, obesity, low HDL level, and hypertriglyceridemia. The etiology of DPN is multifactorial. It is caused by hyperglycemia, micro-angiopathy, HbA1c, duration of diabetes, smoking status, high-density lipoprotein cholesterol and hypertension. Also, increased glucose conditions decrease vitamin D levels. Vitamin D, which is involved in neurotrophins such as NGF (nerve growth factor) and NCH (neuronal calcium homeostasis), plays a neuroprotective role in peripheral nerves. Depletionleads to vitamin D deficiency which further develops peripheral neuropathy in diabetic patients. Accumulation of AGEs (advanced glycation end product) plays a significant role in the pathogenesis of sensory neuronal damage. It contributes to microangiopathy and endoneurial vascular dysfunction in peripheral nerves. With vitamin D supplementation, the neuropathy pain scores were improved.

Treatment With Small Molecule Inhibitors of Advanced Glycation End-Products Formation and Advanced Glycation End-Products-Mediated Collagen Cross-Linking Promotes Experimental Aortic Aneurysm Progression in Diabetic Mice.

Background Although diabetes attenuates abdominal aortic aneurysms (AAAs), the mechanisms by which diabetes suppresses AAAs remain incompletely understood. Accumulation of advanced glycation end- (AGEs) reduces extracellular matrix (ECM) degradation in diabetes. Because ECM degradation is critical for AAA pathogenesis, we investigated whether AGEs mediate experimental AAA suppression in diabetes by blocking AGE formation or disrupting AGE-ECM cross-linking using small molecule inhibitors. Methods and Results Male C57BL/6J mice were treated with streptozotocin and intra-aortic elastase infusion to induce diabetes and experimental AAAs, respectively. Aminoguanidine (AGE formation inhibitor, 200 mg/kg), alagebrium (AGE-ECM cross-linking disrupter, 20 mg/kg), or vehicle was administered daily to mice from the last day following streptozotocin injection. AAAs were assessed via serial aortic diameter measurements, histopathology, and in vitro medial elastolysis assays. Treatment with aminoguanidine, not alagebrium, diminished AGEs in diabetic AAAs. Treatment with both inhibitors enhanced aortic enlargement in diabetic mice as compared with vehicle treatment. Neither enhanced AAA enlargement in nondiabetic mice. AAA enhancement in diabetic mice by aminoguanidine or alagebrium treatment promoted elastin degradation, smooth muscle cell depletion, mural macrophage accumulation, and neoangiogenesis without affecting matrix metalloproteinases, C-C motif chemokine ligand 2, or serum glucose concentration. Additionally, treatment with both inhibitors reversed suppression of diabetic aortic medial elastolysis by porcine pancreatic elastase in vitro. Conclusions Inhibiting AGE formation or AGE-ECM cross-linking enhances experimental AAAs in diabetes. These findings support the hypothesis that AGEs attenuate experimental AAAs in diabetes. These findings underscore the potential translational value of enhanced ECM cross-linking as an inhibitory strategy for early AAA disease.

Transcriptome analysis provides insights into the molecular mechanism of liver inflammation and apoptosis in juvenile largemouth bass Micropterus salmoides fed low protein high starch diets

The present study was conducted to investigate the regulatory mechanism of liver injury in largemouth bass Micropterus salmoides (LMB) fed low protein high starch diets. Two isolipidic and isoenergetic diets were formulated with different protein and starch ratios, being named as diets P49S9 (48.8 % protein and 9.06 % starch) and P42S18 (42.4 % protein and 18.2 % starch). Each diet was fed to triplicate replicates of LMB (initial body weight, 4.65 ± 0.01 g) juveniles. Fish were fed to visual satiation for 8 weeks. The results indicated that though the P42S18 fish up-regulated the feeding ratio to meet their protein requirements, feeding efficiency ratio and growth performance were impaired in treatment P42S18 as compared to treatment P49S9. Periodic acid-Schiff (PAS) staining showed glycogen accumulated in the liver of LMB fed low protein high starch diets, and the reason should be attributed to down-regulated expression of the glycogenolytic glycogen debranching enzyme. Lower liver lipid level was associated with feeding low protein high starch diets in LMB, which should be resulted from the changes in hepatic glycerolipid metabolism regulated by lipoprotein lipase (representative of triglyceride synthesis, up-regulated) and diacylglycerol acyltransferase (representative of triglyceride breakdown, down-regulated). Though fasting plasma glucose level was comparable, treatment P42S18 performed inferior glucose tolerance to treatment P49S9. Hematoxylin-eosin (HE) and TdT-mediated dUTP Nick-End Labeling (TUNEL) staining suggested that feeding low protein high starch diets induced disruption of structural integrity, inflammation and apoptosis in the hepatocytes of LMB. As expected, KEGG pathways analysis indicated that many of the up-regulated differentially expressed genes were enriched in AGE (advanced glycation end product)/RAGE (receptor for AGE), Toll-like receptor and apoptosis signaling pathways. Our transcriptome data revealed that feeding low protein high starch diets might promote the accumulation of AGEs in LMB, which bound to RAGE and subsequently induced PI3K/Akt signal pathway. The activation of Akt induced NF-κB translocation into the nucleus thus releasing proinflammatory factors including tumor necrosis factor-α (TNF-α) and interleukin-8. The release of these inflammatory factors concomitantly induced T cell stimulation and natural killer cells chemotactic effects through Toll-like receptor signaling pathway. Besides mediating inflammation and immune response, TNF-α signal transduction participated in mediating apoptosis through the receptor of TNF (TNF-R1) pathway by up-regulating the expression of caspase 8 and cytochrome c. In conclusion, our results demonstrated that feeding low protein and high starch diets induced hepatocytes inflammation and apoptosis in LMB through the PI3K/Akt/NF-κB signaling pathway.

Research advances on the mechanism of refractory healing of diabetic foot ulcer

The number of patients with diabetic foot ulcer (DFU) has increased progressively year by year. Refractory DFU has brought great burden to the country and individuals. How to accelerate the healing of DFU has become the main emphasis of research. However currently, the mechanism of its refractory healing is not fully elucidated, and the correlation between the various mechanisms are not high. Therefore, its clinical standardization, and precise clinical diagnosis and treatment still face several challenges. Based on the progress of clinical research and basic research at home and abroad, this paper reviewed the specific mechanisms that lead to refractory DFU, with the focus on chronic inflammation, bacteria biofilm formation, high oxidative stress, growth factor inhibition, impaired microcirculation, and accumulation of advanced glycation end products.

Altered glucose metabolism in Alzheimer's disease: Role of mitochondrial dysfunction and oxidative stress.

Increasing evidence suggests that abnormal cerebral glucose metabolism is largely present in Alzheimer's disease (AD). The brain utilizes glucose as its main energy source and a decline in its metabolism directly reflects on brain function. Weighing on recent evidence, here we systematically assessed the aberrant glucose metabolism associated with amyloid beta and phosphorylated tau accumulation in AD brain. Interlink between insulin signaling and AD highlighted the involvement of the IRS/PI3K/Akt/AMPK signaling, and GLUTs in the disease progression. While shedding light on the mitochondrial dysfunction in the defective glucose metabolism, we further assessed functional consequences of AGEs (advanced glycation end products) accumulation, polyol activation, and other contributing factors including terminal respiration, ROS (reactive oxygen species), mitochondrial permeability, PINK1/parkin defects, lysosome-mitochondrial crosstalk, and autophagy/mitophagy. Combined with the classic plaque and tangle pathologies, glucose hypometabolism with acquired insulin resistance and mitochondrial dysfunction potentiate these factors to exacerbate AD pathology. To this end, we further reviewed AD and DM (diabetes mellitus) crosstalk in disease progression. Taken together, the present work discusses the emerging role of altered glucose metabolism, contributing impact of insulin signaling, and mitochondrial dysfunction in the defective cerebral glucose utilization in AD.

Porphyromonas gingivalis lipopolysaccharide and glycated serum albumin increase the production of several pro-inflammatory molecules in human gingival fibroblasts via NFκB

ObjectiveDiabetes increases the incidence/severity of periodontal diseases by inducing a chronic inflammation, driven by accumulation of AGEs (advanced glycation end products). We tested whether glycated human serum albumin (G-HSA, a form of AGE), representing a diabetic state, augments the pro-inflammatory response of human gingival fibroblasts (hGFs) to a bacterial challenge (Porphyromonas gingivalis Lipopolysaccharide (LPS)). MethodsPrimary hGFs were incubated with LPS (0.5–5 μg/mL) and G-HSA (50–200 μg/mL) and the production and gene expression of IL-1β, IL-6, IL-8, MMP-1, MCP-1, and TNFα were analyzed by Magnetic Luminex Assay and real-time PCR, respectively. Non-glycated serum albumin (HSA) served as negative control. Cytotoxicity of the 2 agents was tested with an XTT assay. NFκB activation (p65 phosphorylation) was measured with an ELISA. ResultsP. gingivalis LPS and G-HSA were not toxic to hGFs and increased the amount of MMP-1, MCP-1, IL-6, and IL-8, (but not TNFα and IL-1β) secreted into the medium at 24 h. Control HSA had no effect. Many LPS/G-HSA combinations displayed a synergistic stimulation of these molecules. Both agents increased mRNA levels of these 4 molecules at 6 h, 12 h or both (IL-6). NFκB activation at 6 h was caused by both agents with a possible synergism at the higher concentrations. Conclusionsglycated albumin augments the pro-inflammatory response of human gingival fibroblasts to P. gingivalis LPS. Thus, AGE accumulation in diabetes could aggravate periodontal inflammation by augmenting the pro-inflammatory response of host GFs to P. gingivalis, a well-recognized periopathogenic bacteria.

NONINVASIVE DETECTION OF AGES ACCUMULATION IN THE EYES’ LENS MAY BE A POWERFUL TECHNIQUE FOR MONITORING ALZHEIMER'S DISEASE

We successfully demonstrated a noninvasive method to measure fluorescence emitted from the eyes lens, showing the fluorescence intensity from diabetic patients was significantly higher than that from normal subjects in chronological age manner1. With advance in electronic technology, we theorize to develop a miniaturized new device for monitoring AGE (advanced glycation end product)-dependent fluorescence for the development of Alzheimer's Disease (AD). Evidences demonstrate AGEs enhance accumulation of amyloid plaques and tau protein in AD. Hyperglycemia-enhanced AGEs result in AD development, via activation of insulin signaling, cerebral glucose dysfunction, oxidative stress, resulting in neuroinflammation and degeneration2-7. Overlapping biological relevance for pathogenesis between AD and diabetes support our hypothesis that detection of AGE-dependent fluorescence in the eyes lens may serve as a biomarker for monitoring AD development. Blue LED source at about 434 nm in the visible region was used to excite specific fluorophors in lens proteins of the human eyes. The light pinpoints exact depths of the lens. Emission of fluorescence at about 490 nm was collected with correction of Rayleigh scattering. With modern information/electronic technology, the normalized fluorescence intensity was processed and digitized, creating a miniaturized device that will have the virtues of noninvasive detection of AGEs in the eyes lens, hand-held, self-scanned, not requiring pupil dilation, and less than 5 second measurement time. We successfully miniaturize a new device for detecting AGE-dependent fluorescence in human eyes lens, which are capable of monitoring AGEs accumulation that reflects the development of AD. The hand-held device is noninvasive, fast, and low cost. The new miniaturized device may be a powerful tool for monitoring the progression of AD in a noninvasive, fast, and inexpensive manner. This unique technology can be of great use in self-referenced detection at different stages of AD and possible early detection of AD so that the disease can be reversed or prevented.

Importance of Advanced Glycation End Products (AGE) in Human Disease and Diagnosis

Advanced Glycation End (AGE) is a product of non-enzymatic reaction between reducing sugars of carbonyls and proteins. AGE accumulates with age. It may be derived from methylglyoxal (MG), glyoxal, and 3-deoxyglucosone (3DG) groups. AGEs are chemically heterogeneous group of compounds with only 25 AGE structures fully characterized. Among these Nε-carboxymethyl-lysine (CML) is the simplest and best characterized AGE. It is involved in the pathophysiological conditions like diabetes, cardiovascular diseases, atherosclerosis and aging disease like Alzheimer disease. So, it is important to measure the AGE level in human diseases. Skin autofluorescence (AF) is a noninvasive measurement of AGE accumulation. In this review, different methods of determination of AGE level in human will be discussed because of standard method of measurement of AGE have not been established yet. It is suggested that AGE may play an important in assessing diagnosis, prognosis and prevention of some high risk disease in near future.

Urea-induced ROS cause endothelial dysfunction in chronic renal failure

ObjectiveThe pathogenic events responsible for accelerated atherosclerosis in patients with chronic renal failure (CRF) are poorly understood. Here we investigate the hypothesis that concentrations of urea associated with CRF and increased ROS production in adipocytes might also increase ROS production directly in arterial endothelial cells, causing the same pathophysiologic changes seen with hyperglycemia. MethodsPrimary cultures of human aortic endothelial cells (HAEC) were exposed to 20mM urea for 48 h. C57BL/6J wild-type mice underwent 5/6 nephrectomy or a sham operation. Randomized groups of 5/6 nephrectomized mice and their controls were also injected i.p. with a SOD/catalase mimetic (MnTBAP) for 15 days starting immediately after the final surgical procedure. ResultsUrea at concentrations seen in CRF induced mitochondrial ROS production in cultured HAEC. Urea-induced ROS caused the activation of endothelial pro-inflammatory pathways through the inhibition of GAPDH, including increased protein kinase C isoforms activity, increased hexosamine pathway activity, and accumulation of intracellular AGEs (advanced glycation end products). Urea-induced ROS directly inactivated the anti-atherosclerosis enzyme PGI2 synthase and also caused ER stress. Normalization of mitochondrial ROS production prevented each of these effects of urea. In uremic mice, treatment with MnTBAP prevented aortic oxidative stress, PGI2 synthase activity reduction and increased expression of the pro-inflammatory proteins TNFα, IL-6, VCAM1, Endoglin, and MCP-1. ConclusionsTaken together, these data show that urea itself, at levels common in patients with CRF, causes endothelial dysfunction and activation of proatherogenic pathways.

The Effect of Systemic Delivery of Aminoguanidine versus Doxycycline on the Resorptive Phase of Alveolar Bone Following modified Widman Flap in Diabetic Rats: A Histopathological and Scanning Electron Microscope (SEM) study.

Aminoguanidine (guanylhydrazinehydrochloride) is a drug that prevents many of the classical systemic complications of diabetes including diabetic osteopenia through its inhibitory activity on the accumulation of advanced glycation end -products (AGEs). The aim of the present study was to evaluate the effectiveness of aminoguanidine versus doxycycline in reducing alveolar bone resorption following mucoperiosteal flap in diabetic rats, using the conventional histopathology and scanning electron microscope (SEM). Twenty-seven male albino rats were used in this study. Periodontal defects were induced experimentally on lower anterior teeth. All rats were subjected to induction of diabetes, by IV injection of the pancreatic B-cells toxin alloxan monohydrate. After eight weeks following the establishment of periodontal defects in all rats, the ligation was removed and 3 rats were scarified as negative control (group 1). The remaining animals were divided into three group based on treatment applied following mucoperiosteal flap surgery. Group 2 received saline treatment only, group 3 received doxycycline periostat (1.5 mg/kg/day) for 3 weeks, and group 4 received aminoguanidine (7.3 mmol/kg) for 3 weeks. The fasting glucose level was measured weekly post operatively. After 21 days all rats were sacrificed. Three anterior parts of the mandible of each group was prepared for histopathological examination and two parts were prepared for SEM. Aminoguanidine treated group (group 4) showed statistically significant increased new bone formation, higher number of osteoblasts and decrease osteoclasts number, resorptive lacunae and existing inflammatory cell infiltration as compared to positive control group (group 2) (P<0.05). Doxycycline was also effective in reducing bone loss as documental by histopathological study. The present study showed that aminoguanidine was significantly effective in reducing alveolar bone loss and can modify the detrimental effects of diabetes in alveolar bone resorption.

Curcumin Alleviates Diabetic Cardiomyopathy in Experimental Diabetic Rats

ObjectivesDiabetic cardiomyopathy (DCM), characterized by myocardial structural and functional changes, is an independent cardiomyopathy that develops in diabetic individuals. The present study was sought to investigate the effect of curcumin on modulating DCM and the mechanisms involved.MethodsAn experimental diabetic rat model was induced by low dose of streptozoticin(STZ) combined with high energy intake on rats. Curcumin was orally administrated at a dose of 100 or 200 mg·kg−1·d−1, respectively. Cardiac function was evaluated by serial echocardiography. Myocardial ultrastructure, fibrosis area and apoptosis were assessed by histopathologic analyses. Metabolic profiles, myocardial enzymes and oxidative stress were examined by biochemical tests. Inflammatory factors were detected by ELISA, and interrelated proteins were measured by western blot.ResultsRats with DCM showed declined systolic myocardial performance associated with myocardial hypertrophy and fibrosis, which were accompanied with metabolism abnormalities, aberrant myocardial enzymes, increased AGEs (advanced glycation end products) accumulation and RAGE (receptor for AGEs) expression, elevated markers of oxidative stress (MDA, SOD, the ratio of NADP+/NADPH, Rac1 activity, NADPH oxidase subunits expression of gp91phox and p47phox ), raised inflammatory factor (TNF-α and IL-1β), enhanced apoptotic cell death (ratio of bax/bcl-2, caspase-3 activity and TUNEL), diminished Akt and GSK-3β phosphorylation. Remarkably, curcumin attenuated myocardial dysfunction, cardiac fibrosis, AGEs accumulation, oxidative stress, inflammation and apoptosis in the heart of diabetic rats. The inhibited phosphorylation of Akt and GSK-3β was also restored by curcumin treatment.ConclusionsTaken together, these results suggest that curcumin may have great therapeutic potential in the treatment of DCM, and perhaps other cardiovascular disorders, by attenuating fibrosis, oxidative stress, inflammation and cell death. Furthermore, Akt/GSK-3β signaling pathway may be involved in mediating these effects.

Degradation of an Old Human Protein

Long-lived proteins exist in a number of tissues in the human body; however, little is known about the reactions involved in their degradation over time. Lens proteins, which do not turn over, provide a useful system to examine such processes. Using a combination of Western blotting and proteomic methodology, age-related changes to a major protein, γS-crystallin, were studied. By teenage years, insoluble intact γS-crystallin was detected, indicative of protein denaturation. This was not the only change, however, because blots revealed evidence of significant cross-linking as well as cleavage of γS-crystallin in all adult lenses. Cleavage at a serine residue near the C terminus was a major reaction that caused the release of a 12-residue peptide, SPAVQSFRRIVE, which bound tightly to lens cell membranes. Several other crystallin-derived peptides with double basic residues also lodged in the cell membrane fraction. Model studies showed that once cleaved from γS-crystallin, SPAVQSFRRIVE adopts a markedly different shape from that in the intact protein. Further, the acquired helical conformation may explain why the peptide seems to affect water permeability. This observation may help explain the changes to cell membranes known to be associated with aging in human lenses. Age-related cleavage of long-lived proteins may therefore yield peptides with untoward biological activity.

Accumulation of advanced glycation end (AGEs) products in intensive care patients: an observational, prospective study

BackgroundOxidative stress plays an important role in the course and eventual outcome in a majority of patients admitted to the intensive care unit (ICU). Markers to estimate oxidative stress are not readily available in a clinical setting. AGEs accumulation has been merely described in chronic conditions, but can also occur acutely due to oxidative stress. Since AGEs have emerged to be stable end products, these can be a marker of oxidative stress. Skin autofluorescence (AF) is a validated marker of tissue content of AGEs. We hypothesized that AGEs accumulate acutely in ICU patients.MethodsWe performed an observational prospective study in a medical surgical ICU in a university affiliated teaching hospital. All consecutively admitted ICU patients in a 2 month period were included. Skin AF was measured using an AGE reader in 35 consecutive ICU patients > 18 yrs. As a comparison, historical data of a control group (n = 231) were used. These were also used to calculate age-adjusted AF-levels (AFadj). Values are expressed as median and interquartile range [P25-P75]. Differences between groups were tested by non parametric tests. P < 0.05 was considered statistically significant.ResultsAFadj values were higher in ICU patients (0.33 [0.00 - 0.68]) than in controls (-0.07 [-0.29 - 0.24]; P < 0.001). No differences in skin AFadj were observed between acute or planned admissions, or presence of sepsis, nor was skin AFadj related to severity of disease as estimated by APACHE-II score, length of ICU, hospital stay or mortality.ConclusionAcute AGE accumulation in ICU patients was shown in this study, although group size was small. This can possibly reflect oxidative stress in ICU patients. Further studies should reveal whether AGE-accumulation will be a useful parameter in ICU patients and whether skin AF has a predictive value for outcome, which was not shown in this small study.

Accumulation of fructosyl-lysine and advanced glycation end products in the kidney, retina and peripheral nerve of streptozotocin-induced diabetic rats.

The accumulation of AGEs (advanced glycation end products) in diabetes mellitus has been implicated in the biochemical dysfunction associated with the chronic development of microvascular complications of diabetes--nephropathy, retinopathy and peripheral neuropathy. We investigated the concentrations of fructosyl-lysine and AGE residues in protein extracts of renal glomeruli, retina, peripheral nerve and plasma protein of streptozotocin-induced diabetic rats and normal healthy controls. Glycation adducts were determined by LC with tandem MS detection. In diabetic rats, the fructosyl-lysine concentration was increased markedly in glomeruli, retina, sciatic nerve and plasma protein. The concentrations of N (epsilon)-carboxymethyl-lysine and N (epsilon)-carboxyethyl-lysine were increased in glomeruli, sciatic nerve and plasma protein, and N(epsilon)-carboxymethyl-lysine also in the retina. Hydroimidazolone AGEs derived from glyoxal, methylglyoxal and 3-deoxylglucosone were major AGEs quantitatively. They were increased in the retina, nerve, glomeruli and plasma protein. AGE accumulation in renal glomeruli, retina, peripheral nerve and plasma proteins is consistent with a role for AGEs in the development of nephropathy, retinopathy and peripheral neuropathy in diabetes. High-dose therapy with thiamine and Benfotiamine suppressed the accumulation of AGEs, and is a novel approach to preventing the development of diabetic complications.