Advanced glycation end-product peptides are associated with impaired renal function, but not with biochemical markers of endothelial dysfunction and inflammation, in non-diabetic individuals

Skin Autofluorescence Mirrors Surrogate Parameters of Vascular Aging: An Enable Study

Advanced glycation end-products (AGEs) are implicated in vascular aging due to their pro-inflammatory properties. Skin autofluorescence (SAF) is a measure to estimate their deposition. It is an easily quantifiable marker that has been shown to correlate with cardiovascular risk and parameters of metabolic diseases. Herein, we compared skin autofluorescence with other techniques indicating increased cardiovascular diseases, namely, pulse wave velocity (PWVao) and intima–media thickness (IMT). We also studied the impacts of other parameters in deeply phenotyped cohorts of young, middle-aged, and older individuals. SAF, aortic PWVao, and IMT proved to be significantly correlated with each other and with age. However, based on a moderator analysis, we could not show that these associations were affected by age. Some specific parameters such as creatinine and CRP were found to be significantly associated with skin AGE values after adjusting for confounding variables. In conclusion, SAF is a simple screening tool for vascular health with comparable power to more elaborated technical tests.

Accumulation rate of advanced glycation end products in recent onset psychosis: A longitudinal study

Schizophrenia is associated with excessive oxidative stress. Production of advanced glycation end products (AGEs) in the skin is strongly associated with oxidative stress. Increased skin AGE-levels have been demonstrated at cross-sectional level in recent onset psychosis and chronic schizophrenia, indicating increased cardiovascular risk. We aimed to investigate factors underlying AGE-accumulation and accumulation rate of AGEs in recent onset psychosis. From December 2016 through May 2017, 66 patients and 160 (highly educated) healthy controls from a previous case-control study of AGE-levels were assessed for a follow-up measurement 12-24 months after baseline. Possible determinants of AGE-accumulation were analyzed. AGE-accumulation rates in patients and controls were compared adjusted for relevant confounders. In healthy controls, a significant association of AGE-accumulation with ethnicity and tobacco exposure was found. An indication of a markedly higher AGE-accumulation rate was found in patients suffering from recent onset psychosis compared to healthy controls, independent of ethnicity and tobacco smoking, but not independent of cannabis use (more prevalent in patients than controls), although results were not significant.

The Course of Skin and Serum Biomarkers of Advanced Glycation Endproducts and Its Association with Oxidative Stress, Inflammation, Disease Severity, and Mortality during ICU Admission in Critically Ill Patients: Results from a Prospective Pilot Study

Background

Advanced glycation end products (AGEs) have been implicated in multiple organ failure, predominantly via their cellular receptor (RAGE) in preclinical studies. Little is known about the time course and prognostic relevance of AGEs in critically ill human patients, including those with severe sepsis.

Objective

1) To explore the reliability of Skin Autofluorescence (AF) as an index of tissue AGEs in ICU patients, 2) to compare its levels to healthy controls, 3) to describe the time course of AGEs and influencing factors during ICU admission, and 4) to explore their association with disease severity, outcome, and markers of oxidative stress and inflammation.

Methods

Skin AF, serum N"-(carboxyethyl)lysine (CEL), N"-(carboxymethyl)lysine (CML), and soluble RAGE (sRAGE) were serially measured for a maximum of 7 days in critically ill ICU patients with multiple organ failure and compared to age-matched healthy controls. Correlations with (changes in) clinical parameters of disease severity, LDL dienes, and CRP were studied and survival analysis for in-hospital mortality was performed.

Results

Forty-five ICU patients (age: 59±15 years; 60% male), and 37 healthy controls (59±14; 68%) were included. Skin AF measurements in ICU patients were reproducible (CV right-left arm: 13%, day-to-day: 10%), with confounding effects of skin reflectance and plasma bilirubin levels. Skin AF was higher in ICU patients vs healthy controls (2.7±0.7 vs 1.8±0.3 au; p<0.001). Serum CEL (23±10 vs, 16±3 nmol/gr protein; p<0.001), LDL dienes (19 (15–23) vs. 9 (8–11) μmol/mmol cholesterol; <0.001), and sRAGE (1547 (998–2496) vs. 1042 (824–1388) pg/ml; p = 0.003) were significantly higher in ICU patients compared to healthy controls, while CML was not different (27 (20–39) vs 29 (25–33) nmol/gr protein). While CRP and LDL dienes decreased significantly, Skin AF and serum AGEs and sRAGE did not change significantly during the first 7 days of ICU admission. CML and CEL were strongly correlated with SOFA scores and CML above the median at baseline was associated with increased risk for mortality (Hazard ratio 3.3 (1.3–8.3); p = 0.01). All other markers did not correlate with disease severity and did not predict mortality.

Conclusions

This study demonstrates that markers for the AGE-RAGE axis are elevated in critically ill patients compared to healthy controls but remain stable for at least 7 days despite clearly fading inflammation and oxidative stress. Circulating AGEs may be associated with disease severity and outcome. Further research should be conducted to elucidate the role of the AGE-RAGE axis in the exaggerated inflammatory response leading to multiple organ failure and death, and whether or not this may be a target for treatment.

Molecular effects of advanced glycation end products on cell signalling pathways, ageing and pathophysiology

Advanced glycation end-products (AGEs) are a heterogeneous group of compounds formed by the Maillard chemical process of non- enzymatic glycation of free amino groups of proteins, lipids and nucleic acids. This chemical modification of biomolecules is triggered by endogeneous hyperglycaemic or oxidative stress-related processes. Additionally, AGEs can derive from exogenous, mostly diet-related, sources. Considering that AGE accumulation in tissues correlates with ageing and is a hallmark in several age-related diseases it is not surprising that the role of AGEs in ageing and pathology has become increasingly evident. The receptor for AGEs (RAGE) is a single transmembrane protein being expressed in a wide variety of human cells. RAGE binds a broad repertoire of extracellular ligands and mediates responses to stress conditions by activating multiple signal transduction pathways being mostly responsible for acute and/or chronic inflammation. RAGE activation has been implicated in ageing as well as in a number of age-related diseases, including atherosclerosis, neurodegeneration, arthritis, stoke, diabetes and cancer. Here we present a synopsis of findings that relate to AGEs-reported implication in cell signalling pathways and ageing, as well as in pathology. Potential implications and opportunities for translational research and the development of new therapies are also discussed.

Advanced glycation end products (AGEs) are cross-sectionally associated with insulin secretion in healthy subjects

It has been postulated that chronic exposure to high levels of advanced glycation end products (AGEs), in particular from dietary sources, can impair insulin secretion. In the present study, we investigated the cross-sectional relationship between AGEs and acute insulin secretion during an intravenous glucose tolerance test (IVGTT) and following a 75 g oral glucose tolerance test (OGTT) in healthy humans. We report the cross-sectional association between circulating AGE concentrations and insulin secretory function in healthy humans (17 F: 27 M, aged 30 ± 10 years) with a wide range of BMI (24.6-31.0 kg/m(2)). Higher circulating concentrations of AGEs were related to increased first phase insulin secretion during IVGTT (r = 0.43; p < 0.05) and lower 2-h glucose concentrations during OGTT (r = -0.31; p < 0.05). In addition, fasting (r = -0.36; p < 0.05) and 2-h glucose concentrations were negatively related to circulating levels of soluble receptor for AGE (RAGE) isoforms (r = -0.39; p < 0.01). In conclusion, in healthy humans, we show a cross-sectional association between advanced glycation end products and acute insulin secretion during glucose tolerance testing.

Role of Dietary Advanced Glycation End Products in Diabetes Mellitus

Dietary advanced glycation end products (AGEs) can be formed via the Maillard reaction and several alternative pathways. AGEs exert their deleterious effects by damaging protein structure and function, as well as through activation of cellular mechanisms. At the cellular level, the damaging effects of AGEs have been attributed to several AGE-binding proteins. Increased levels of AGEs have been implicated in several chronic diseases, including diabetes-related complications such as renal diseases, retinopathy, neuropathy, and cardiovascular diseases, as well as delayed wound healing. To investigate the role of AGEs thoroughly, a reliable assessment of dietary AGEs is needed. Varying methodology, diverse food preparation, and quantification of a variety of dietary AGEs makes this a complex goal. In addition, some antiglycation food products may balance or offset the negative impact of dietary AGEs.

Glycated albumin is independently associated with estimated glomerular filtration rate in nondiabetic patients with chronic kidney disease

BACKGROUND

Glycated albumin (GA) may contribute to diabetic nephropathy, but the clinical significance of GA in patients with chronic kidney disease (CKD) is unknown.

METHODS

Patients were classified with the NKF/DOQI classification system as mild (stage I, II), moderate (stage III), or advanced CKD (stage IV). Those undergoing dialysis or with CKD stage V were excluded. GA was measured using the Lucica TM GA-L assay kit. The relationship between GA and renal dysfunction was analyzed in patients with or without diabetes.

RESULTS

A total of 187 subjects were enrolled. GA values in those with normal, mild, moderate and advanced CKD were 18.4 ± 1.4%, 18.4 ± 3.1%, 19.0 ± 3.8%, 20.4 ± 6.4%, respectively, in diabetic patients (N=67, p=0.5), and were 14.1 ± 1.9%, 14.2 ± 2.2%, 15.9 ± 1.9%, 15.0 ± 1.7%, respectively, in nondiabetic patients (N=120, p=0.004). GA value was negatively correlated to eGFR in nondiabetic patients (r=-0.35, p<0.001) but not in diabetic patients (r=-0.11, p=0.39). In the adjusted model, GA is independently correlated to eGFR only in nondiabetic subjects.

CONCLUSIONS

Increased GA concentrations are independently associated with renal dysfunction in nondiabetic patients with CKD.

Does accumulation of advanced glycation end products contribute to the aging phenotype?

BACKGROUND

Aging is a complex multifactorial process characterized by accumulation of deleterious changes in cells and tissues, progressive deterioration of structural integrity and physiological function across multiple organ systems, and increased risk of death.

METHODS

We conducted a review of the scientific literature on the relationship of advanced glycation end products (AGEs) with aging. AGEs are a heterogeneous group of bioactive molecules that are formed by the nonenzymatic glycation of proteins, lipids, and nucleic acids.

RESULTS

Humans are exposed to AGEs produced in the body, especially in individuals with abnormal glucose metabolism, and AGEs ingested in foods. AGEs cause widespread damage to tissues through upregulation of inflammation and cross-linking of collagen and other proteins. AGEs have been shown to adversely affect virtually all cells, tissues, and organ systems. Recent epidemiological studies demonstrate that elevated circulating AGEs are associated with increased risk of developing many chronic diseases that disproportionally affect older individuals.

CONCLUSIONS

Based on these data, we propose that accumulation of AGEs accelerate the multisystem functional decline that occurs with aging, and therefore contribute to the aging phenotype. Exposure to AGEs can be reduced by restriction of dietary intake of AGEs and drug treatment with AGE inhibitors and AGE breakers. Modification of intake and circulating levels of AGEs may be a possible strategy to promote health in old age, especially because most Western foods are processed at high temperature and are rich in AGEs.

Circulating soluble receptor of advanced glycation end product inversely correlates with atherosclerosis in patients with chronic kidney disease

The soluble receptor of advanced glycation end product (sRAGE) prevents vascular damage in experimental animal models, and observational studies in the general population support the hypothesis that sRAGE may exert a protective role on the vasculature. To test this in patients with chronic kidney disease, we determined the relationship between plasma sRAGE and carotid atherosclerosis in 142 patients with an average estimated glomerular filtration rate (eGFR) of 32 ml/min per 1.73 m(2) and 49 healthy control individuals matched for age and gender. Plasma sRAGE was significantly higher in patients with chronic kidney disease than in the control cohort. In an aggregate analysis of the patients and controls, there was a significant inverse relationship between eGFR and sRAGE, with a breakpoint in the regression line at 64 ml/min per 1.73 m(2). Significant inverse relationships were found for sRAGE to intima-media thickness and plaque number in the patients with chronic kidney disease, but no such associations were found in the controls. On covariance analysis, the slopes of intima-media thickness and plaque number to sRAGE were significantly steeper in patients with chronic kidney disease than in the controls. Furthermore, a significant interaction was found between sRAGE and smoking for predicting atherosclerotic plaques in patients with chronic kidney disease. The pathophysiological significance of this correlation will have to await more mechanistic studies.

Diabetic threesome (hyperglycaemia, renal function and nutrition) and advanced glycation end products: evidence for the multiple-hit agent?

Complex chemical processes termed non-enzymic glycation that operate in vivo and similar chemical interactions between sugars and proteins that occur during thermal processing of food (known as the Maillard reaction) are one of the interesting examples of a potentially-harmful interaction between nutrition and disease. Non-enzymic glycation comprises a series of reactions between sugars, alpha-oxoaldehydes and other sugar derivatives and amino groups of amino acids, peptides and proteins leading to the formation of heterogeneous moieties collectively termed advanced glycation end products (AGE). AGE possess a wide range of chemical and biological properties and play a role in diabetes-related pathology as well as in several other diseases. Diabetes is, nevertheless, of particular interest for several reasons: (1) chronic hyperglycaemia provides the substrates for extracellular glycation as well as intracellular glycation; (2) hyperglycaemia-induced oxidative stress accelerates AGE formation in the process of glycoxidation; (3) AGE-modified proteins are subject to rapid intracellular proteolytic degradation releasing free AGE adducts into the circulation where they can bind to several pro-inflammatory receptors, especially receptor of AGE; (4) kidneys, which are principally involved in the excretion of free AGE adducts, might be damaged by diabetic nephropathy, which further enhances AGE toxicity because of diminished AGE clearance. Increased dietary intake of AGE in highly-processed foods may represent an additional exogenous metabolic burden in addition to AGE already present endogenously in subjects with diabetes. Finally, inter-individual genetic and functional variability in genes encoding enzymes and receptors involved in either the formation or the degradation of AGE could have important pathogenic, nutrigenomic and nutrigenetic consequences.

Soluble RAGE, diabetic nephropathy and genetic variability in the AGER gene

Diabetes mellitus, especially when complicated with decline of renal function due to diabetic nephropathy (DN), is associated with accumulation of advanced glycation end products (AGEs) exerting their adverse effects via receptor of AGE (RAGE). Soluble RAGE (sRAGE) is a truncated form of RAGE functioning as an inhibitor of AGE-mediated signalling. We studied relationships between sRAGE, renal function and genetic variability in the AGER gene in diabetic subjects. Study comprised a total of 265 diabetics (type 1 or 2 or LADA) with normoalbuminuria (n = 94) or DN (n = 171). sRAGE (assessed by ELISA) was significantly higher in DN than normoalbuminuria subjects (P = 0.007) and positively correlated with age, S-urea, S-creatinine and albuminuria and AGEs (determined spectrofluorimetrically), negatively with GFR (all P < 0.05); however, multivariate regression revealed that GFR was the only independent variable associated with sRAGE (P = 0.047). sRAGE did not correspond with carrier state of risk-haplotype copies (RAGE2) (P > 0.05). In conclusion, GFR is a principal determinant of sRAGE concentration and gradual sRAGE increase in subjects with advancing impairment of renal function is paralleled by AGEs.

Markers of endothelial activity are related to components of the metabolic syndrome, but not to circulating concentrations of the advanced glycation end-product Nɛ-carboxymethyl-lysine in healthy Swedish men

Endothelial function is considered important in the development of cardiovascular diseases and type 2 diabetes. Circulating advanced glycation end-products (AGEs) and dietary components have been shown to affect endothelial function in type 2 diabetics, but determinants of endothelial function in a non-diabetic population are more poorly investigated. Therefore, we investigated relationships between dietary habits, AGEs and endothelial activation in men with isolated metabolic disturbances. Circulating markers of endothelial activation (soluble forms of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, E-selectin and von Willebrand factor) and plasma N epsilon-carboxymethyl-lysine (CML, the predominant AGE in human plasma) were analyzed in a cross-sectional study of 294 healthy men. Individuals completed a 7-day dietary record, and metabolic and inflammatory parameters were determined. NCEP/ATPIII-criteria were used to define the metabolic syndrome. Endothelial activation was higher in individuals with the metabolic syndrome, and was positively related to certain features of the syndrome (insulin, glucose, inflammation and obesity), but not to others (triacylglycerol and blood pressure). Dietary factors were related to endothelial activation, but CML was not. Multivariate analysis revealed energy and alcohol intake, along with insulin and markers of oxidative stress and inflammation, to be positive predictors of endothelial activation. In this cohort of otherwise healthy men, endothelial activation was increased in individuals with the full metabolic syndrome, but not in those with only some of the components of the metabolic syndrome. Insulin resistance, inflammation, oxidative stress, the dietary intake of energy and alcohol, but not plasma CML, predicted endothelial activation in these men.

Increased serum glycated albumin level is associated with the presence and severity of coronary artery disease in type 2 diabetic patients

BACKGROUND

Glycated albumin is the predominant circulating Amadori-type glycated protein in vivo and plays a major role in the development of diabetic vascular complications. The aim of this study was to assess the relationship between increased serum glycated albumin level and the presence and severity of coronary artery disease (CAD) in patients with type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

In a total of 320 consecutive patients with T2DM, coronary angiography revealed normal coronary arteries in 83 patients (control group) and significant coronary stenosis (> or = 70% luminal diameter narrowing) in 237, of whom 51 patients had 1-vessel disease (Group I), 80 had 2-vessel disease (Group II), and 106 had 3-vessel disease (Group III). Serum glycated albumin, hemoglobin A(1c) (HbA(1c)) and tumor necrosis factor (TNF)-alpha levels, lipid profile, and renal function were measured. Logistic regression analysis was performed to determine the relative risk of serum glycated albumin level for the presence and severity of CAD. Multivariate stepwise linear regression analysis was done to identify independent determinants of the glycated albumin level. Serum glycated albumin (21.2+/-5.3% vs 19.4+/-4.3%, p=0.005) and TNF-alpha levels (123 +/-115 pg/ml vs 65+/-59 pg/ml, p<0.001) were significantly higher in patients with CAD than in controls, but serum HbAlc level did not significantly differ between them (7.6+/-1.3% vs 7.4+/-1.2%, p=0.19). There was a significant difference in serum glycated albumin level between Groups I and III (19.5+/-3.3% vs 21.8+/-5.7%, p<0.001). The serum glycated albumin level correlated with the number of diseased arteries (Spearman r=0.205, p<0.001), and was closely related to serum levels on admission of glucose (r=0.495, p<0.001), TNF-alpha (r=0.123, p=0.028), blood urea nitrogen (r=0.167, p=0.004), triglycerides (r=0.129, p=0.021), and HbA(1c) (r=0.795, p<0.001). Multivariate analysis indicated that serum levels of glucose (p<0.0001), TNF-alpha (p=0.001), blood urea nitrogen (p=0.004) and triglycerides (p=0.035) were independent determinants for glycated albumin. Logistic regression analysis revealed that glycated albumin > or = 19% (odds ratio (OR) 2.9, p<0.001) was an independent predictor for CAD and glycated albumin > or = 21% (OR 2.3, p=0.032) for 3-vessel disease prediction. The area under the receiver-operating characteristic curve for glycated albumin (0.620, 95% confidence interval (CI) 0.548 to 0.691, p=0.001) was superior to that for HbA(1c) (0.543, 95% CI 0.473 to 0.613, p=0.243).

CONCLUSIONS

An increased serum level of glycated albumin is associated with the presence and severity of CAD, and may be useful in screening patients with T2DM.

Skin autofluorescence, a novel marker for glycemic and oxidative stress-derived advanced glycation endproducts: an overview of current clinical studies, evidence, and limitations

BACKGROUND

Advanced glycation endproducts (AGEs) predict long-term complications in agerelated diseases. However, there are no clinically applicable markers for measuring AGEs in vivo.

METHODS

We have recently introduced the AGE-Reader (DiagnOptics B.V., Groningen, The Netherlands) to noninvasively measure AGE accumulation in the human skin of the forearm, making use of the characteristic autofluorescence (AF) pattern that AGEs encompass. Skin AF is calculated as a ratio of mean intensities detected from the skin between 420-600 nm and 300-420 nm. It correlates with collagen-linked fluorescence and specific skin AGE levels from skin biopsies in diabetes, renal failure, and control subjects. Skin AF levels are increased in patients with diabetes and renal failure and are associated with the presence of vascular complications. Additionally, skin AF is strongly related to the progression of coronary heart disease and mortality, independently of traditional risk factors. Since skin pigmentation might influence skin AF, we have investigated the relation of relative skin reflectance (R%) to skin AF in subjects with varying skin phototypes (SPT).

RESULTS

The data presented in this article suggest that only in subjects with an SPT of V and VI or R% <12%, no reliable measurement can be performed. Therefore, the current prototype of the AGE-Reader is suitable for subjects with SPT I-IV or R% >12%, and more research is needed for a broader application.

CONCLUSION

The AGE-Reader is useful as a noninvasive clinical tool for assessment of risk for long-term vascular complications in diabetes and in other conditions associated with AGE accumulation.