High-throughput quantification of carboxymethyl lysine in serum and plasma using high-resolution accurate mass Orbitrap mass spectrometry

An immunosensor for the detection of N-(carboxymethyl)lysine - a diabetic biomarker

Carboxymethyl-lysine (CML) is a well-known lysine product that strongly correlates with type 2 diabetes mellitus (T2DM), and its elevated levels are significantly associated with renal impairment and T2DM-related complications. Thus, it is imperative to quantify CML levels and recognize the onset of hyperglycemia and its consequences. In this context, the development of an electrochemical immunosensor for the rapid and ultralow-level detection of CML was attempted. The fabrication of the working electrode involves the covalent immobilization of anti-CML/EDC-NHS on the surface of a carbon quantum dot (CQD)-modified glassy carbon electrode (GCE). The immunosensor exhibited two discrete linear concentration ranges of 0.5-5.0 ng mL-1 and 5.5-10.0 ng mL-1, with limits of detection and quantification of 0.027 and 0.087 ng mL-1 and 0.16 and 0.51 ng mL-1, respectively. The observed specificity and other merits of the sensor make it suitable for testing human plasma samples.

Assessing metal-induced glycation in French fries

Non-enzymatic glycation is the chemical reaction between the amine group of an amino acid and the carbonyl group of a reducing sugar. The final products of this reaction, advanced glycation end-products (AGEs), are known to play a key role in aging and many chronic diseases. The kinetics of the AGE formation reaction depends on several factors, including pH, temperature, and the presence of prooxidant metals, such as iron and copper. In this study, the effect of iron and copper on the rate and outcome of non-enzymatic glycation was examined in the test tube and a food model, using chromatography and spectrometry methods. Binding efficiencies of several chelating agents to selected metals were also assessed. Phytic acid was the most efficient of the tested chelating agents. The effect of phytic acid on AGE formation in French fries was evaluated. While phytic acid treatment increased the amounts of UV-absorbing compounds in fries, a food ingredient rich in phytic acid showed the opposite effect. This study suggests that prooxidant metals can affect the rate, outcome, and yield of the non-enzymatic glycation reaction and that they do so differently when free or chelated. Moreover, despite being an excellent iron chelator, phytic acid can promote AGE formation in fried food potentially via mechanisms other than metal-induced glycation.

UPLC-MS/MS method for quantitative determination of the advanced glycation endproducts Nε-(carboxymethyl)lysine and Nε-(carboxyethyl)lysine

During blood storage, red blood cells (RBCs) undergo physical, chemical, and metabolic changes that may contribute to post-transfusion complications. Due to the hyperglycemic environment of typical solutions used for RBC storage, the formation of advanced glycation endproducts (AGEs) on the stored RBCs has been implicated as a detrimental chemical change during storage. Unfortunately, there are limited studies involving quantitative determination and differentiation of carboxymethyl-lysine (CML) and carboxyethyl-lysine (CEL), two commonly formed AGEs, and no reported studies comparing these AGEs in experimental storage solutions. In this study, CML and CEL were identified and quantified on freshly drawn blood samples in two types of storage solutions, standard additive solution 1 (AS-1) and a normoglycemic version of AS-1 (AS-1N). To facilitate detection of the AGEs, a novel method was developed to reliably extract AGEs from RBCs, provide Food and Drug Administration (FDA) bioanalytical guidance criteria, and enable acceptable selectivity for these analytes. Ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) was utilized to identify and quantify the AGEs. Results show this method is accurate, precise, has minimal interferences or matrix effects, and overcomes the issue of detecting AGE byproducts. Importantly, AGEs can be detected and quantified in both types of blood storage solutions (AS-1 and AS-1N), thereby enabling long-term (6 weeks) blood storage related studies.

Molecular Damage in Aging

Cellular metabolism generates molecular damage affecting all levels of biological organization. Accumulation of this damage over time is thought to play a central role in the aging process, but damage manifests in diverse molecular forms complicating its assessment. Insufficient attention has been paid to date to the role of molecular damage in aging-related phenotypes, particularly in humans, in part because of the difficulty in measuring its various forms. Recently, omics approaches have been developed that begin to address this challenge, because they are able to assess a sizeable proportion of age-related damage at the level of small molecules, proteins, RNA, DNA, organelles and cells. This review describes the concept of molecular damage in aging and discusses its diverse aspects from theoretical models to experimental approaches. Measurement of multiple types of damage enables studies of the role of damage in human aging outcomes and lays a foundation for testing interventions to reduce the burden of molecular damage, opening new approaches to slowing aging and reducing its consequences.

Comprehensive Quantification of Carboxymethyllysine-Modified Peptides in Human Plasma

A prolonged hyperglycemic condition in diabetes mellitus results in glycation of plasma proteins. N(ε)-Carboxymethyllysine (CML) is a well-known protein advanced glycation end product, and one of its mechanisms of formation is through further oxidation of Amadori compound modified lysine (AML). Unlike enrichment of AML peptides using boronate affinity, biochemical enrichment methods are scarce for comprehensive profiling of CML-modified peptides. To address this problem, we used AML peptide sequence and site of modification as template library to identify and quantify CML peptides. In this study, a parallel reaction monitoring workflow was developed to comprehensively quantify CML modified peptides in Type 1 diabetic subjects' plasma with good and poor glycemic control (n = 20 each). A total of 58 CML modified peptides were quantified, which represented 57 CML modification sites in 19 different proteins. Out of the 58 peptides, five were significantly higher in poor glycemic control samples with the area under the receiver operating characteristic curve ≥0.83. These peptides could serve as promising indicators of glycemic control in Type 1 diabetes management.

Development and Application of Mass Spectroscopy Assays for Nε-(1-Carboxymethyl)-L-Lysine and Pentosidine in Renal Failure and Diabetes

BACKGROUND

Advanced glycation end products (AGEs) are formed via the nonenzymatic glycation of sugars with amino acids. Two AGEs, Nε-(1-carboxymethyl)-L-Lysine (CML) and pentosidine, have been observed to be elevated in subjects suffering from a multitude of chronic disease states, and accumulation of these compounds may be related to the pathophysiology of disease progression and aging.

METHODS

We describe here the development and validation of a specific and reproducible LC-MS/MS method to quantify CML and pentosidine in human serum with lower limits of quantitation of 75 ng/mL and 5 ng/mL, respectively. The analyte calibration curve exhibited excellent linearity at a range of 0-10 900 ng/mL for CML and 0-800 ng/mL for pentosidine. High-low linearity of 5 serum pairs was assessed, with a mean recovery of 103% (range 94-116%) for CML, and 104% (range 97-116%) for pentosidine.

RESULTS

Serum concentrations of CML and pentosidine were quantified in 30 control and 30 subjects with chronic renal insufficiency. A significant increase in both analytes was observed in renal failure compared to control subjects (2.1-fold and 8.4-fold, respectively; P < 0.001 for both). In a separate cohort of 49 control versus 95 subjects with type 2 diabetes mellitus (T2DM), serum CML but not serum pentosidine, was significantly elevated in the T2DM patients, and CML was also correlated with glycemic control, as assessed by hemoglobin A1c (r = 0.34, P < 0.001).

CONCLUSIONS

These mass spectroscopy-based assays for serum CML and pentosidine should be useful in accurately evaluating circulating levels of these key AGEs in various disease states.