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

• Published in: Clinical proteomics Vol. 13; no. 1; p. 7
• Main Authors: Jagadeeshaprasad, Mashanipalya G, Batkulwar, Kedar B, Meshram, Nishita N, Tiwari, Shalbha, Korwar, Arvind M, Unnikrishnan, Ambika G, Kulkarni, Mahesh J
• Format: Journal Article
• Language: English
• Published: England BioMed Central 2016
• Subjects: Glycemic control; Diabetes; Diagnosis; HbA1c; Mass spectrometry; Glycation
• ISSN: 1542-6416; 1559-0275
• DOI: 10.1186/s12014-016-9108-y

N-1-(Deoxyfructosyl) valine (DFV) β-hemoglobin (β-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-β-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 β-Hb would be useful in assessing actual glycemic status.
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-β-valine undergoes carboxyethylation and mass spectrometric quantification of CMV and CEV peptides of β-hemoglobin. Carboxymethylation was found to be the most abundant modification of N-1-β-valine. Both CMV-β-Hb and CEV-β-Hb peptides showed better correlation with severity of diabetes in terms of fasting glucose, postprandial glucose and microalbuminuria.
This study reports carboxymethylation as a predominant modification of N-1-β-valine of Hb, and quantification of CMV-β-Hb and CEV-β-Hb could be useful parameter for assessing the severity of diabetes.