Products of advanced glycation in patients with type 2 diabetes and vascular disease

Clinical validation of electrochemical biosensor for the detection of methylglyoxal in subjects with type-2 diabetes mellitus

Methylglyoxal (MG), a highly reactive by-product of glycolysis, is involved in the formation of advanced glycation end-products (AGEs). Elevated levels of MG have been correlated with micro-and macro-angiopathic complications in diabetes, including neuropathy, kidney disease, retinopathy, and cardiovascular disease. Therefore, point-of-care devices for detecting MG may be of great use in the screening of diabetes complications. This study was designed to determine the utility of the developed electrochemical biosensor to measure the level of MG in human plasma from type-2 diabetes mellitus patients. Electrochemical studies were carried out with optimized experimental parameters using the modified Platinum-electrode. Subsequently, clinical studies using 350 blood plasma samples were conducted and the results were validated against the ELISA kit, Normal Glucose Tolerance (NGT), and glycosylated haemoglobin (HbA1c). The MG sensor exhibited a linear range of 1.0-7.5 μM concentration with a sensitivity of 1.02 mA µM-1, a limit of detection of 0.21 µM, a limit of quantification of 0.70 µM and a response time less than 10 s. The sensor showed 90% correlation with ELISA data. The developed biosensor showed a significant correlation with HbA1c and fasting plasma glucose suggesting that it can be used as a point-of-care device to screen for diabetes.

Low Level of Advanced Glycation End Products in Serum of Patients with Allergic Rhinitis and Chronic Epstein-Barr Virus Infection at Different Stages of Virus Persistence

Advanced glycation end products (AGEs) are formed in a nonenzymatic reaction of the reducing sugars with amino groups of proteins, lipids, and nucleic acids of different tissues and body fluids. A relatively small number of studies have been conducted on the role of AGEs in allergic inflammation. In this study, patients with allergic rhinitis (AR) were examined for the presence of Epstein-Barr virus and the content of fluorescent and nonfluorescent AGEs. We have also determined the level of a unique epitope (AGE10) which was recently identified in human serum using monoclonal antibodies against synthetic melibiose-derived AGE (MAGE). The levels of AGE10 determined with an immunoenzymatic method revealed no significant difference in the patients' blood with intermittent AR and chronic EBV persistence in the active and latent phases. It has been shown that there is a statistically significantly smaller amount of AGEs and pentosidine in groups of patients, both with and without viremia, than in healthy subjects. In turn, higher levels of immune complexes than of AGE10 were detected in the groups of patients, in contrast to the control group, which had lower levels of complexes than AGE10 concentration. In patients with active infection, there is even more complexes than of noncomplexed AGE10 antigen. The lower level of AGE in allergic rhinitis patient sera may also be due, besides complexes, to allergic inflammation continuously activating the cells, which effectively remove glycation products from the body.

Bilirubin and atherosclerotic diseases

Bilirubin is the final product of heme catabolism in the systemic circulation. For decades, increased serum/plasma bilirubin levels were considered an ominous sign of an underlying liver disease. However, data from recent years convincingly suggest that mildly elevated bilirubin concentrations are associated with protection against various oxidative stress-mediated diseases, atherosclerotic conditions being the most clinically relevant. Although scarce data on beneficial effects of bilirubin had been published also in the past, it took until 1994 when the first clinical study demonstrated an increased risk of coronary heart disease in subjects with low serum bilirubin levels, and bilirubin was found to be a risk factor for atherosclerotic diseases independent of standard risk factors. Consistent with these results, we proved in our own studies, that subjects with mild elevation of serum levels of unconjugated bilirubin (benign hyperbilirubinemia, Gilbert syndrome) have much lower prevalence/incidence of coronary heart as well as peripheral vascular disease. We have also demonstrated that this association is even more general, with serum bilirubin being a biomarker of numerous other diseases, often associated with increased risk of atherosclerosis. In addition, very recent data have demonstrated biological pathways modulated by bilirubin, which are responsible for observed strong clinical associations.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

Abnormal levels of age-elastin derived peptides in sera of diabetic patients with arterial hypertension

Introduction

An important factor in vascular wall alterations is degradation of elastic fiber major protein – elastin. As a result, elastin derived peptides (EDP) are found in circulation. Advanced glycation might also involve elastin, because it is a protein with slow metabolism. The aim of our study was to measure serum levels of glycated elastin derived peptides (AGE-EDP) of elastin in patients with type 2 diabetes mellitus (T2DM) and arterial hypertension (AH).

Material and methods

We adapted an ELISA technique for the determination of AGE-EDP. Sera of 93 patients with T2DM and AH (mean age 61.4 ±11.3 years, diabetes duration 9.88 ±3.12 years; hypertension duration 9.28 ±4.98) were tested. These values were compared to 42 age- and sex-matched controls. Diabetics were divided in two groups according to presence – Group 1 (n = 67) or absence – Group 2 (n = 26) of microangiopathy.

Results

Patients with T2DM and AH showed statistically significantly higher levels of AGEEDP in comparison with healthy controls 0.060 (0.053÷0.065) vs. 0.039 (0.031÷0.044) (KW = 35.2; p < 0.0001). Group 1 showed significantly higher levels of AGE-EDP than the control group 0.069 (0.051÷0.070) vs. 0.039 (0.031÷0.044) (KW = 33.0; p < 0.0001). Group 2 also showed significantly higher levels of AGE-EDP than controls 0.058 (0.049÷0.064) vs. 0.039 (0.031÷0.044) (KW = 22.1; p < 0.0001). AGE-EDP showed a correlation with an insulin dose (r = –0.28; p = 0.05), systolic blood pressure (r = 0.25; p = 0.01), BMI (r = 0.39; p = 0.01) and retinopathy (r = 0.18; p = 0.05).

Conclusions

The measurement of non-invasive markers of elastin glycation may be useful in monitoring development of vascular wall alterations and therapeutic interventions.

Glycation Products as Markers and Predictors of the Progression of Diabetic Complications

The structure of a growing number of glycation and advanced glycation end products has been elucidated. Measuring these products can be used to assess cumulative glycemic and glycoxidative damage in diabetes and other chronic conditions. The predictive power of a given glycation product can be tested in large prospective studies that evaluate the risk of developing diabetic micro- and macrovascular disease over years following the quantitative determination of that marker. This article provides a comprehensive review of the field, comparing the merits of each marker, whether in skin, serum, or other tissue. Several conclusions are drawn, one of which identifies skin glycation products as powerful predictors of the risk of developing diabetic complications.

Serum AGE-elastin derived peptides among diabetic children

The purpose of the study was to measure advanced glycated end products (AGE) of elastin in human serum. In the present study, we adapted an ELISA technique for the determination of AGE-elastin-derived peptides (AGE-EDP) in human sera of healthy and diabetic subjects. This test makes use of human aortic elastin hydrolyzed by a chemical procedure (alpha-elastin) and AGE-Hemocyanin. Polyclonal sera from rabbit against AGE-Hemocyanin and from sheep against alpha-elastin were obtained and their specificity was tested via direct and competitive ELISA. Sera of 60 Type 1 (insulin-dependent) diabetic children and 28 healthy subjects were tested. The patients with vascular complications showed significant higher levels of age, diabetes duration, systolic blood pressure (SBP), diastolic blood pressure (DBP), dose, EDP and AGE-EDP than those without vascular complications. AGE-EDP concentrations of all diabetics correlated with triglycerides (r=0.19; p=0.04). The correlation was found between AGE-EDP and DBP in the subgroup of patients with microalbuminuria+retinopathy (r=0.94; p=0.0006). The subgroup of patients with microalbuminuria (n=19) showed correlation with age (r=0.24; p=0.008), AGE-EDP (r=0.65; p=0.0001), EDP (r=0.51; p=0.0001) and SBP (r=0.33; p=0.0003). Further studies are necessary to elucidate the relationship between the serum level of AGE-elastin degradation products and diabetic vascular complications. The measurement of non-invasive markers of elastin synthesis and degradation may be useful in monitoring development and therapeutic intervention in diabetic vascular complications.

Blockade of late stages of autoimmune diabetes by inhibition of the receptor for advanced glycation end products

Ligation of the receptor for advanced glycation end products (RAGE) occurs during inflammation. Engagement of RAGE results in enhanced expression of addressins and it is therefore, not surprising that previous studies have shown a role of RAGE/ligand interactions in immune responses including cell/cell contact but the role of RAGE in spontaneous autoimmunity has not been clearly defined. To study the role of RAGE/ligand interactions in autoimmune diabetes, we tested the ability of soluble RAGE, a scavenger of RAGE ligands, in late stages of diabetes development in the NOD mouse-disease transferred with diabetogenic T cells and recurrent disease in NOD/scid recipients of syngeneic islet transplants. RAGE expression was detected on CD4(+), CD8(+), and B cells from diabetic mice and transferred to NOD/scid recipients. RAGE and its ligand, S100B, were found in the islets of NOD/scid mice that developed diabetes. Treatment of recipient NOD/scid mice with soluble RAGE prevented transfer of diabetes and delayed recurrent disease in syngeneic islet transplants. RAGE blockade was associated with increased expression of IL-10 and TGF-beta in the islets from protected mice. RAGE blockade reduced the transfer of disease with enriched T cells, but had no effect when diabetes was transferred with the activated CD4(+) T cell clone, BDC2.5. We conclude that RAGE/ligand interactions are involved in the differentiation of T cells to a mature pathogenic phenotype during the late stages of the development of diabetes.

Urinary excretion of advanced glycation endproducts in patients with type 2 diabetes and various stages of proteinuria

OBJECTIVE

The objective of the study was to detect AGE-immunoreactive proteins in urine, and to evaluate AGE excretion at various stages of diabetic nephropathy in type 2 diabetes assessed by the level of proteinuria.

METHODS

AGEs were measured in 24-h urine collection of patients with normoalbuminuria (N) (n=22), microalbuminuria (Mi) (n=31), macroalbuminuria (Ma) (n=28), and overt proteinuria with elevated serum creatinine level (PC) (n=25). A competitive ELISA with polyclonal anti-AGE antibodies was used to monitor AGE excretion.

RESULTS

Multiple comparison of urine AGE content among various stages of proteinuria showed significant differences (summary p<0.000). Fifty percent of samples from the group of normoalbuminuric, and only 15% of samples from the group of microalbuminuria patients were AGE negative. However, there was no significant difference in AGE excretion between the patients with persistent proteinuria and elevated serum creatinine, and those with macroalbuminuria (PC vs Ma, p=0.265). None of the samples from these two groups of patients with highest AGE content in 24-h urine was negative for AGE-immunoreactivity. In addition, the ratio between 24-h urinary AGEs and urinary albumin excretion was calculated to determine whether total 24-h urinary AGE content is an index of the toxic form of albumin released in the course of diabetic nephropathy. The ratio values were log-transformed and bivariate comparison showed significant differences between the N vs Mi (p=0.006) and Mi vs Ma (p=0.000) groups. However, there was no significant difference (p=0.407) between values in the Ma and PC groups of patients. Multiple stepwise regression analysis indicated a relationship of urinary AGE-immunoreactivity with creatinine clearance values (r=0.52, p<0.001).

CONCLUSION

The study demonstrated the presence of AGE-immunoreactivity in the urine of diabetic patients with various stages of proteinuria. Study results pointed to creatinine clearance as the main predictor of AGE excretion. Therefore, the measurement of urinary AGE appears to offer limited extra information in patients with impaired renal function.