title: Targeted quantification of N-1-(carboxymethyl) valine and N-1-(carboxyethyl) valine peptides of β-hemoglobin for better diagnostics in diabetes.
abstract: BACKGROUND
  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.
  
  
  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-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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Proteomics Facility, Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, 411008 India ; Academy of Scientific and Innovative Research (AcSIR), New Delhi, India.
authors.forename: Mashanipalya G
authors.initials: MG
authors.lastname: Jagadeeshaprasad
authors.affiliation: Proteomics Facility, Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, 411008 India ; Academy of Scientific and Innovative Research (AcSIR), New Delhi, India.
authors.forename: Kedar B
authors.initials: KB
authors.lastname: Batkulwar
authors.affiliation: Department of Diabetes and Endocrine Research, Chellaram Diabetes Institute, Pune, Maharashtra India.
authors.forename: Nishita N
authors.initials: NN
authors.lastname: Meshram
authors.affiliation: Department of Diabetes and Endocrine Research, Chellaram Diabetes Institute, Pune, Maharashtra India.
authors.forename: Shalbha
authors.initials: S
authors.lastname: Tiwari
authors.affiliation: Proteomics Facility, Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, 411008 India.
authors.forename: Arvind M
authors.initials: AM
authors.lastname: Korwar
authors.affiliation: Department of Diabetes and Endocrine Research, Chellaram Diabetes Institute, Pune, Maharashtra India.
authors.forename: Ambika G
authors.initials: AG
authors.lastname: Unnikrishnan
authors.affiliation: Proteomics Facility, Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, 411008 India ; Academy of Scientific and Innovative Research (AcSIR), New Delhi, India.
authors.forename: Mahesh J
authors.identifier: 0000-0003-3932-9092
authors.initials: MJ
authors.lastname: Kulkarni
keywords: Diabetes; Diagnosis; Glycation; Glycemic control; HbA1c; Mass spectrometry