Nonenzymatic Post-Translational Modification Derived Products: New Biomarkers of Protein Aging

N-Glycosylation Pattern of Human Placental Insulin-Like Growth Factor and Insulin Receptors in Well-Controlled Pregestational Diabetes Mellitus

Diabetes mellitus is a complex disease that leads to alterations in the glycosylation of proteins. Insulin-like growth factor and insulin receptors are involved in the regulation of fetal and placental growth and development. In this work the N-glycans of these receptors, originating from placentas obtained from pregnancies complicated by pregestational insulin dependent diabetes mellitus, were studied. Diabetic mothers were under regular insulin therapy. Solubilised membrane samples from healthy and diabetic placentas were analysed using lectin-affinity chromatography. N-glycans bound to insulin-like growth factor and insulin receptors were studied in terms of their interaction with eleven agarose-immobilised lectins: wheat germ agglutinin, succinylated wheat germ agglutinin,Ricinus communisagglutinin I,Sambucus nigraagglutinin,Erythrina cristagallilectin,Ulex europaeusagglutinin,Lens culinarisagglutinin,Canavalia ensiformislectin,Phaseolus vulgariserythro- and leukoagglutinin andMaackia amurensisagglutinin. A very similar type of N-glycans and content of the terminal saccharide residues were found in both groups of placentas. The results of this work suggest that the tight glycemic control may prevent alterations in the glycosylation of insulin-like growth factor and insulin receptors, thus maintaining physiological homeostasis during pregnancy and fetal growth.

Adiponectin, Non-Esterified Fatty Acids and Antiphospholipid Antibodies in Type II Diabetes Mellitus

The importance of the association of antiphospholipid antibodies (aPL Abs) with the features of type II diabetes mellitus has not yet been elucidated. The aim of this work was to investigate the association of aPL Abs with adiponectin and non-esterified fatty acids (NEFA) in type II diabetes mellitus patients without micro and/or macrovascular complications, and to analyze the differences between the male and female patients with regard to the abovementioned parameters. Male patients with type II diabetes mellitus showed a positive correlation between NEFA concentrations and anti-oxLDL antibodies (r=0.334, p=0.019). A weak, but statistically significant correlation between adiponectin concentrations and the IgM isotype of anti-annexin A5 antibodies was found in type II diabetes mellitus patients (r=0.285, p=0.011). The presence of a positive correlation between NEFA and anti-oxLDL antibodies might be useful in the detection of patients with premature atherosclerosis in type II diabetes mellitus patients without any micro and/or macrovascular complications among type II diabetes mellitus patients.

Role of Redox Metals, Oxidative Protein Products and Antioxidant Potentials of Thiols in Diabetic Retinopathy

Oxidative stress has been proved in the pathogenesis of diabetes mellitus (DM) and diabetic retinopathy (DR) not only by the reactive oxygen species (ROS) but also due to non-enzymatic protein glycosylation, auto-oxidation of glucose, impaired glutathione metabolism, alteration in the antioxidants and advanced oxidative protein product formation. The current study was undertaken to establish the relationship between iron, copper and antioxidants like reduced glutathione (GSH), total thiols, and advanced oxidation protein products (AOPP) as well as total protein and albumin. The study group consisted of a total of 90 subjects which included non-diabetic healthy controls (n=30), diabetes mellitus patients (n=30), and diabetic retinopathy patients (n=30). All the parameters were measured using spectrophotometric methods. AOPP levels showed a very highly significant increase in DR patients and in DM patients compared to normal controls, the AOPP levels being higher in the DR compared to the DM patients (p= 0.001). The levels of thiols showed a very highly significant decrease in DR and DM as compared to normal subjects. The total proteins level showed a very highly significant decrease (P = 0.001) in DR and DM compared to normal. There was no change in the level of albumin. A significant increase in the levels of iron was observed in DR when compared to DM and control. The levels of copper in DR showed a very highly significant increase when compared to DM and controls (p = 0.001). Our study indicates a possible increase in the copper and iron-mediated generation of ROS thereby leading to increased consumption of antioxidants in the body.

What is a Biomarker? From its Discovery to Clinical Application

The term biomarker in medicine most often stands for a protein measured in the circulation (blood) whose concentration indicates a normal or a pathological response of the organism, as well as a pharmacological response to the applied therapy. From a wider perspective, a biomarker is any indicator that is used as an index of the intensity of a disease or other physiological state in the organism. This means that biomarkers have a very important role in medical research and practice providing insight into the mechanism and course of a disease. Since a large number of biomarkers exist today that are used for different purposes, they have been classified into: 1) antecedent biomarkers, indicating risk of disease occurrence, 2) screening biomarkers, used to determine a subclinical form of disease, 3) diagnostic biomarkers, revealing an existing disease, 4) staging biomarkers, that define the stage and severity of a disease, and 5) prognostic biomarkers, that confirm the course of disease, including treatment response. Regardless of their role, their clinical significance depends on their sensitivity, specificity, predictive value, and also precision, reliability, reproducibility, and the possibility of easy and wide application. For a biomarker to become successful, it must undergo the process of validation, depending on the level of use. It is very important for every suggested biomarker, according to its purpose or its nature, to possess certain characteristics and to meet the strict requirements related to sensitivity, accuracy and precision, in order for the proper outcome to be produced in the estimation of the state for which it is intended. Finally, the development of guidelines for biomarker application is very important, based on well defined and properly conducted assessments of biomarker determination, providing the means by which research is translated into practice and allowing evidence based on facts to promote the clinical application of new biomarkers.

Glycans as Biomarkers: Status and Perspectives

Protein glycosylation is a ubiquitous and complex co- and post-translational modification leading to glycan formation, i.e. oligosaccharide chains covalently attached to peptide backbones. The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is widely recognized. Thus, glycans are considered as unique structures to diagnose, predict susceptibility to and monitor the progression of disease. In the »omics« era, the glycome, a glycan analogue of the proteome and genome, holds considerable promise as a source of new biomarkers. In the design of a strategy for biomarker discovery, new principles and platforms for the analysis of relatively small amounts of numerous glycoproteins are needed. Emerging glycomics technologies comprising different types of mass spectrometry and affinity-based arrays are next in line to deliver new analytical procedures in the field of biomarkers. Screening different types of glycomolecules, selection of differentially expressed components, their enrichment and purification or identification are the most challenging parts of experimental and clinical glycoproteomics. This requires large-scale technologies enabling high sensitivity, proper standardization and validation of the methods to be used. Further progress in the field of applied glycoscience requires an integrated systematic approach in order to explore properly all opportunities for disease diagnosis.