Analysis and Quantitation of Glycated Hemoglobin by Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry

Structural changes in hemoglobin and glycation

Hemoglobin (Hb) is a hemeprotein found inside erythrocytes and is crucial in transporting oxygen and carbon dioxide in our bodies. In erythrocytes (Ery), the main energy source is glucose metabolized through glycolysis. However, a fraction of Hb can undergo glycation, in which a free amine group from the protein spontaneously binds to the carbonyl of glucose in the bloodstream, resulting in the formation of glycated hemoglobin (HbA1c), widely used as a marker for diabetes. Glycation leads to structural and conformational changes, compromising the function of proteins, and is intensified in the event of hyperglycemia. The main changes in Hb include structural alterations to the heme group, compromising its main function (oxygen transport). In addition, amyloid aggregates can form, which are strongly related to diabetic complications and neurodegenerative diseases. Therefore, this chapter discusses in vitro protocols for producing glycated Hb, as well as the main techniques and biophysical assays used to assess changes in the protein's structure before and after the glycation process. This more complete understanding of the effects of glycation on Hb is fundamental for understanding the complications associated with hyperglycemia and for developing more effective prevention and treatment strategies.

Evaluation of effects from hemoglobin variants on HbA1c measurements by different methods

OBJECTIVES

The impact of seven hemoglobin variants (Hb Q-Thailand, Hb G-Honolulu, Hb Ube-2, Hb New York, Hb J-Bangkok, Hb G-Coushatta, and Hb E) on the outcome of HbA1c was investigated for six methods by comparing with liquid chromatography-tandem mass spectrometry (LC/MS/MS) reference method.

METHODS

Twenty-nine normal and 112 variant samples were measured by LC/MS/MS, Sebia Capillarys 3 TERA, Intelligene Biosystems QuanTOF, Premier Hb9210, Arkray HA-8190V, Bio-Rad D-100, and Tosoh G11, then evaluated for correlation, consistency, and mean relative bias among six methods. The lowest biological variation bias of ±2.8 % was an acceptable standard.

RESULTS

All methods showed poor correlation and consistency with LC/MS/MS for Hb E. The unacceptable biases were observed for Capillarys 3 TERA (-14.4 to -3.7 % for Hb Q-Thailand, Hb Ube-2, Hb New York, Hb J-Bangkok and Hb E), QuanTOF (-8.3 to -2.9 % for Hb Ube-2, Hb New York and Hb G-Coushatta), Premier Hb9210 (-18.3 to -3.6 % for Hb Q-Thailand, Hb Ube-2, Hb New York, Hb J-Bangkok and Hb E), HA-8190V variant mode (-17.3 to 6.6 % for Hb G-Honolulu, Hb Ube-2, Hb New York, Hb G-Coushatta and Hb E). All variant samples showed larger biases than ±2.8 % comparing HA-8190V fast mode, D-100, and G11 with LC/MS/MS.

CONCLUSIONS

The accuracy of different HbA1c methods was influenced by some Hb variants, especially Hb Ube-2 and Hb New York. Thus, laboratories need to choose appropriate methods to measure HbA1c with different Hb variants.

Glycation and drug binding by serum albumin

Accumulation of glycation products in patients with hyperglycaemic conditions can lead to their reaction with the proteins in the human system such as serum albumin, haemoglobin, insulin, plasma lipoproteins, lens proteins and collagen among others which have important biological functions. Therefore, it is important to understand if glycation of these proteins affects their normal action not only qualitatively, but also importantly quantitatively. Glycation of human serum albumin can easily be carried out over period of weeks and its drug transportability may be examined, in addition to characterisation of the amadori products. A combination of ultrasensitive isothermal titration calorimetry, differential scanning calorimetry, spectroscopy and chromatography provides structure-property-energetics correlations which are important to obtain mechanistic aspects of drug recognition, conformation of the protein, and role of amadori products under conditions of glycation. The role of advance glycation end products is important in recognition of antidiabetic drugs. Further, the extent of glycation of the protein and its implication on drug transportability investigated by direct calorimetric methods enables unravelling mechanistic insights into role of functionality on drug molecules in the binding process, and hinderance in the recognition process, if any, as a result of glycation. It is possible that the drug binding ability of the protein under glycation conditions may not be adversely affected, or may even lead to strengthened ability. Rigorous studies on such systems with diverse functionality on the drug molecules is required which is essential in deriving guidelines for improvements in the existing drugs or in the synthesis of new molecular entities directed towards addressing diabetic conditions.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives: An update

1-Amino-1-deoxy-d-fructose (fructosamine, FN) derivatives are omnipresent in all living organisms, as a result of non-enzymatic condensation and Amadori rearrangement reactions between free glucose and biogenic amines such as amino acids, polypeptides, or aminophospholipids. Over decades, steady interest in fructosamine was largely sustained by its role as a key intermediate structure in the Maillard reaction that is responsible for the organoleptic and nutritional value of thermally processed foods, and for pathophysiological effects of hyperglycemia in diabetes. New trends in fructosamine research include the discovery and engineering of FN-processing enzymes, development of advanced tools for hyperglycemia monitoring, and evaluation of the therapeutic potential of both fructosamines and FN-recognizing proteins. This article covers developments in the field of fructosamine and its derivatives since 2010 and attempts to ascertain challenges in future research.

Comparability of different methods of glycated hemoglobin measurement for samples of patients with variant and non-variant hemoglobin

BACKGROUND

Glycated hemoglobin (e.g., HbA_1c) is measured to monitor patients with diabetes. However, the measurement results can vary according to the analysis method and presence of variant hemoglobin. Thus, we compared HbA_1c results between liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the reference method and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS).

METHODS

%HbA_1c were measured using the 2 methods in 45 non-variant and 73 heterozygous variant samples. Precision was calculated; the results were compared using Passing-Bablok regression and the concordance correlation coefficient (CCC). The average bias between methods was compared with the lowest bias of 2.3% for biological variation.

RESULTS

The precision of the 2methods was <2%. The R² for the non-variant samples were 0.986 and the CCC was 0.99. Based on α- and β-chain, the variant samples were divided into 4 groups: α-chain, α-chain negligible, β-chain, and β-chain negligible variants. The R² between the 2 methods of the 4 groups were ＞0.95; However, the average biases of α-chain and β-chain variants were above the minimum bias.

CONCLUSION

LC-MS/MS and MALDI-TOF MS had good comparability in the measurement of HbA_1c in non-variant samples, but the existence of variant hemoglobin caused discrepancies.

A Novel Hemoglobin Variant Hb Liaobu [α107(G14)Val→Leu, HBA2: c.322G>C] Detected by Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry

We here describe a novel hemoglobin (Hb) variant, Hb Liaobu [α107(G14)Val→Leu, HBA2: c.322G>C], in a Chinese family. The structurally abnormal α chain variant could not be detected using capillary electrophoresis (CE) and was subsequently characterized by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS), and further confirmed by reversed phase high performance liquid chromatography (HPLC). Sanger sequencing revealed a novel base mutation on the α2-globin gene and RNA analysis by reverse transcription polymerase chain reaction (RT-PCR) showed the presence of an abnormal HBA transcript. The isopropanol stability test indicated the stable state of this structural Hb variant. In conclusion, a new Hb variant, Hb Liaobu, was discovered and characterized. It was proven to be a nonpathogenic variant. Our study resolved the confusion in the clinical diagnosis of individuals with this novel Hb variant in this family.

A Novel α-Globin Chain Variant, Hb Nanchang [HBA2: c.46G>A, Codon 15 (GGT>AGT) (Gly→Ser)], Detected by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

Here we report a new α chain variant accidentally discovered during Hb A_1c measurement by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) that revealed the presence of a variant α chain with a mass of 15155 Da. However, this hemoglobin (Hb) variant cannot be detected by the first-line methods such as cation exchange high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Sanger sequencing confirmed the presence of a heterozygous missense mutation [HBA2: c.46G>A, codon 15 (GGT>AGT), (Gly→Ser)]. The theoretical mass difference (30 Da) due to the substitution of amino acid glycine to serine matched the actual measured mass difference (29 Da). As this is the first report of the mutation, we named it Hb Nanchang after the place of residence of the proband.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Potential of MALDI-TOF mass spectrometry to overcome the interference of hemoglobin variants on HbA1c measurement

Objectives

Hemoglobin (Hb) variants remain an important cause of erroneous HbA1c results. We present an approach to overcome the interference of Hb variants on HbA1c measurements using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Methods

Samples containing or not containing Hb variants were analyzed for HbA1c using an MALDI-TOF MS system (QuanTOF) and a boronate affinity comparative method (Ultra2). For QuanTOF, two sets of HbA1c values were obtained through α- and β-chain glycation.

Results

A robust correlation between the glycation degrees of the α- and β-chains was found, and HbA1c values derived from α- and β-chain glycation correlated well with the Ultra2 results. Statistically significant differences (p<0.01) were found for all the Hb variants tested. When using the conventional β-chain glycation to determine HbA1c, clinically significant differences were only found among samples containing β-chain variants detected by QuanTOF (i.e., Hb J-Bangkok, Hb G-Coushatta, and Hb G-Taipei). In contrast, based on α-chain glycation, no clinically significant differences were found for these three variants.

Conclusions

In addition to conventional β-chain glycation, α-chain glycation can be used to calculate HbA1c values. The interference of Hb variants on HbA1c quantification can be overcome by employing the glycation of the globin chain without a genetic variant to estimate HbA1c values.

Proteomic applications in pathology and laboratory medicine: Present state and future prospects

Clinical mass spectrometry applications have traditionally focused on small molecules, particularly in the areas of therapeutic drug monitoring, toxicology, and measurement of endogenous and exogenous steroids. More recently, the use of matrix assisted laser desorption/ionization time of flight mass spectrometry for the identification of microbial pathogens has been widely implemented. Following this evolution, there has been an expanding role for the measurement of peptides and proteins in pathology and laboratory medicine. This review explores the current state of protein measurement by clinical mass spectrometry and the analytical strategies employed, as well as emerging applications in clinical chemistry, clinical microbiology and anatomical pathology.

Complexity, cost, and content – three important factors for translation of clinical protein mass spectrometry tests, and the case for apolipoprotein C-III proteoform testing

Complexity, cost, and content are three important factors that can impede translation of clinical protein mass spectrometry (MS) tests at a larger scale. Complexity stems from the many components/steps involved in bottom-up protein MS workflows, making them significantly more complicated than enzymatic immunoassays (EIA) that currently dominate clinical testing. This complexity inevitably leads to increased costs, which is detrimental in the price-competitive clinical marketplace. To successfully compete, new clinical protein MS tests need to offer something new and unique that EIAs cannot – a new content of proteoform detection. The preferred method for proteoform profiling is intact protein MS analysis, in which all proteins are measured as intact species thus allowing discovery of new proteoforms. To illustrate the importance of intact proteoform testing with MS and its potential clinical implications, we discuss here recent findings from multiple studies on the distribution of apolipoprotein C-III proteoforms and their correlations with key clinical measures of dyslipidemia. Such studies are only made possible with assays that are low in cost, avoid unnecessary complexity, and are unique in providing the content of proteoforms.

Emerging role of clinical mass spectrometry in pathology

Mass spectrometry-based assays have been increasingly implemented in various disciplines in clinical diagnostic laboratories for their combined advantages in multiplexing capacity and high analytical specificity and sensitivity. It is now routinely used in areas including reference methods development, therapeutic drug monitoring, toxicology, endocrinology, paediatrics, immunology and microbiology to identify and quantify biomolecules in a variety of biological specimens. As new ionisation methods, instrumentation and techniques are continuously being improved and developed, novel mass spectrometry-based clinical applications will emerge for areas such as proteomics, metabolomics, haematology and anatomical pathology. This review will summarise the general principles of mass spectrometry and specifically highlight current and future clinical applications in anatomical pathology.

Maillard Proteomics: Opening New Pages

Protein glycation is a ubiquitous non-enzymatic post-translational modification, formed by reaction of protein amino and guanidino groups with carbonyl compounds, presumably reducing sugars and α-dicarbonyls. Resulting advanced glycation end products (AGEs) represent a highly heterogeneous group of compounds, deleterious in mammals due to their pro-inflammatory effect, and impact in pathogenesis of diabetes mellitus, Alzheimer's disease and ageing. The body of information on the mechanisms and pathways of AGE formation, acquired during the last decades, clearly indicates a certain site-specificity of glycation. It makes characterization of individual glycation sites a critical pre-requisite for understanding in vivo mechanisms of AGE formation and developing adequate nutritional and therapeutic approaches to reduce it in humans. In this context, proteomics is the methodology of choice to address site-specific molecular changes related to protein glycation. Therefore, here we summarize the methods of Maillard proteomics, specifically focusing on the techniques providing comprehensive structural and quantitative characterization of glycated proteome. Further, we address the novel break-through areas, recently established in the field of Maillard research, i.e., in vitro models based on synthetic peptides, site-based diagnostics of metabolism-related diseases (e.g., diabetes mellitus), proteomics of anti-glycative defense, and dynamics of plant glycated proteome during ageing and response to environmental stress.