Glycation induces conformational changes in the amyloid-ß peptide and enhances its aggregation propensity: molecular insights.

The cytotoxicity of the amyloid beta (Aß) peptide, implicated in the pathogenesis of Alzheimer's disease (AD), can be enhanced by its post-translational glycation, a series of non-enzymatic reactions with reducing sugars and reactive dicarbonyls. However, little is known about the underlying mechanisms that potentially enhance the cytotoxicity of the advanced glycation modified Aß. In this work, fully atomistic molecular dynamics (MD) simulations are exploited to obtain direct molecular insights into the process of early Aß self-assembly in the presence and absence of glycated lysine residues. Analyses of data exceeding cumulative timescales of 1 microsecond for each system reveal that glycation results in a stronger enthalpy of association between Aß monomers and lower conformational entropy, in addition to a sharp overall increase in the beta-sheet content. Further analyses reveal that the enhanced interactions originate, in large part, due to markedly stronger, as well as new, inter-monomer salt bridging propensities in the glycated variety. Interestingly, these conformational and energetic effects are broadly reflected in preformed protofibrillar forms of Aß small oligomers modified with glycation. Our combined results imply that glycation consolidates Aß self-assembly regardless of its point of occurrence in the pathway. They provide a basis for further mechanistic studies and therapeutic endeavors that could potentially result in novel ways of combating AGE related AD progression.

Targeted quantification of N-1-(carboxymethyl) valine and N-1-(carboxyethyl) valine peptides of ß-hemoglobin for better diagnostics in diabetes.

BACKGROUND: N-1-(Deoxyfructosyl) valine (DFV) ß-hemoglobin (ß-Hb), commonly referred as HbA1c, is widely used diagnostic marker in diabetes, believed to provide glycemic status of preceding 90-120 days. However, the turnover of hemoglobin is about 120 days, the DFV-ß-Hb, an early and reversible glycation product eventually may undergo irreversible advanced glycation modifications such as carboxymethylation or carboxyethylation. Hence quantification of N-1-(carboxymethyl) valine (CMV) and N-1-(carboxyethyl) valine (CEV) peptides of ß-Hb would be useful in assessing actual glycemic status. RESULTS: Fragment ion library for synthetically glycated peptides of hemoglobin was generated by using high resolution-accurate mass spectrometry (HR/AM). Using parallel reaction monitoring, deoxyfructosylated, carboxymethylated and carboxyethylated peptides of hemoglobin were quantified in clinical samples from healthy control, pre-diabetes, diabetes and poorly controlled diabetes. For the first time, we report N-1-ß-valine undergoes carboxyethylation and mass spectrometric quantification of CMV and CEV peptides of ß-hemoglobin. Carboxymethylation was found to be the most abundant modification of N-1-ß-valine. Both CMV-ß-Hb and CEV-ß-Hb peptides showed better correlation with severity of diabetes in terms of fasting glucose, postprandial glucose and microalbuminuria. CONCLUSIONS: This study reports carboxymethylation as a predominant modification of N-1-ß-valine of Hb, and quantification of CMV-ß-Hb and CEV-ß-Hb could be useful parameter for assessing the severity of diabetes.

Investigation of phosphoproteome in RAGE signaling.

The receptor for advanced glycation end products (RAGE) is one of the most important proteins implicated in diabetes, cardiovascular diseases, neurodegenerative diseases, and cancer. It is a pattern recognition receptor by virtue of its ability to interact with multiple ligands, RAGE activates several signal transduction pathways through involvement of various kinases that phosphorylate their respective substrates. Only few substrates have been known to be phosphorylated in response to activation by RAGE (e.g., nuclear factor kappa B); however, it is possible that these kinases can phosphorylate multiple substrates depending upon their expression and localization, leading to altered cellular responses in different cell types and conditions. One such example is, glycogen synthase kinase 3 beta which is known to phosphorylate glycogen synthase, acts downstream to RAGE, and hyperphosphorylates microtubule-associated protein tau causing neuronal damage. Thus, it is important to understand the role of various RAGE-activated kinases and their substrates. Therefore, we have reviewed here the details of RAGE-activated kinases in response to different ligands and their respective phosphoproteome. Furthermore, we discuss the analysis of the data mined for known substrates of these kinases from the PhosphoSitePlus (http://www.phosphosite.org) database, and the role of some of the important substrates involved in cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In summary, this review provides information on RAGE-activated kinases and their phosphoproteome, which will be helpful in understanding the possible role of RAGE and its ligands in progression of diseases.

Molecular investigations of protriptyline as a multi-target directed ligand in Alzheimer's disease.

Alzheimer's disease (AD) is a complex neurodegenerative disorder involving multiple cellular and molecular processes. The discovery of drug molecules capable of targeting multiple factors involved in AD pathogenesis would greatly facilitate in improving therapeutic strategies. The repositioning of existing non-toxic drugs could dramatically reduce the time and costs involved in developmental and clinical trial stages. In this study, preliminary screening of 140 FDA approved nervous system drugs by docking suggested the viability of the tricyclic group of antidepressants against three major AD targets, viz. Acetylcholinesterase (AChE), ß-secretase (BACE-1), and amyloid ß (Aß) aggregation, with one member, protriptyline, showing highest inhibitory activity. Detailed biophysical assays, together with isothermal calorimetry, fluorescence quenching experiments, kinetic studies and atomic force microscopy established the strong inhibitory activity of protriptyline against all three major targets. The molecular basis of inhibition was supported with comprehensive molecular dynamics simulations. Further, the drug inhibited glycation induced amyloid aggregation, another important causal factor in AD progression. This study has led to the discovery of protriptyline as a potent multi target directed ligand and established its viability as a promising candidate for AD treatment.