Insights into the Progression of Labile Hb A_1cto Stable Hb A_1cviaa Mechanistic Assessment of 2,3-Bisphosphoglycerate Facilitation of the Slow Nonenzymatic Glycation Process

Abstract

Nonenzymatic glycation (NEG) of human hemoglobin (Hb A) consists of initial non covalent, reversible steps involving glucose and amino acid residues, which may also involve effector reagent(s) in the formation of labile Hb A 1c (the conjugate acid of the Schiff base). Labile Hb A 1c can then undergo slow, largely irreversible, formation of stable Hb A 1c (the Amadori product). Stable Hb A 1c is measured to assess diabetic progression after labile Hb A 1c removal. This study aimed to increase the understanding of the distinctions between labile and stable Hb A 1c from a mechanistic perspective in the presence of 2,3-bisphosphoglycerate (2,3-BPG). 2,3-Bisphosphoglycerate is an effector reagent that reversibly binds in the Hb A 1c pocket and modestly enhances overall NEG rate. The deprotonation of C2 on labile Hb A 1c in the formation of the Amadori product was previously proposed to be rate-limiting. Computational chemistry was used here to identify the mechanism(s) by which 2,3-BPG facilitates the deprotonation of C2 on labile Hb A 1c. 2,3-Bisphosphoglycerate is capable of abstracting protons on C2 and the α-nitrogen of labile Hb A 1c and can also deprotonate water and/or amino acid residues, therefore preparing these secondary reagents to deprotonate labile Hb A 1c. Parallel reactions not leading to an Amadori product were found that include formation of the neutral Schiff base, dissociation of glucose from the protein, and cyclic glycosylamine formation. These heretofore under appreciated parallel reactions may help explain both the selective removal of labile from stable Hb A 1c and the slow rate of NEG.

Unmeasurable Hemoglobin A1c due to Extreme Hyperglycemia in High-performance Liquid Chromatography Method: A Case Report

“…However, glycation occurs by the attachment of glucose to the N-terminal valine of the hemoglobin β-chain without enzymatic attachment in the case of hemoglobin. Labile HbA1c (Schiff base) formed by such non-enzymatic attachment undergoes slow and almost irreversible glycation by Amadori rearrangement, and the final product is the best-known HbA1c (stable ketoamine) (Figure 3) [11], [12], [13]. While HbA1c is a major biomarker used as a gold standard for assessing longterm glycemic control, it is imperative to acknowledge certain aspect concerning the interconnection between the lifespan of erythrocytes and HbA1c.…”

Discordance Between Self-Reported and Lab-Measured A1C Among U.S. Adults with Diabetes: Findings from the National Health and Nutrition Examination Survey (2013-2020)

“…Measures were obtained with appropriate protocols for quality and consistency, using an assay which could differentiate between glycated and non-glycated forms of A1C [23]. The percent of glycated hemoglobin was measured [24][25][26].…”

Estimation of Glycated Hemoglobin A (HbA1c) at time of Pregnancy Diagnosis as a discriminative Early test for Women vulnerable to develop Gestational Diabetes Mellitus at the 24th Gestational Week

“…The reaction consists of initial non-covalent, reversible steps involving glucose and amino acid residues for the formation of labile Hb A1c [3] . Then, labile Hb A1c undergo slow irreversible formation of stable Hb A1c (the Amadori product), which is measured to assess diabetic progression [4] .…”