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

摘要

Background: N-1-(Deoxyfructosyl) valine (DFV) beta-hemoglobin (beta-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-beta-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 beta-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, carboxymethyl-ated and carboxyethylated peptides of hemoglobin were quantified in clinical samples from healthy control, pre-dia-betes, diabetes and poorly controlled diabetes. For the first time, we report N-1-beta-valine undergoes carboxyethylation and massspectrometric quantification of CMV and CEV peptides of beta-hemoglobin. Carboxymethylation was found to be the most abundant modification of N-1-beta-valine. Both CMV-beta-Hb and CEV-beta-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 -beta-valine of Hb, and quantification of CMV-P-Hb and CEV-|3-Hb could be useful parameter for assessing the severity of diabetes. Poorly controlled diabetes leads to variety of complications including blindness, amputations and, kidney failure [1]. Thus, glycemic control is crucial in management of diabetes [2]. Diagnosis and management of diabetes heavily relies on detection of levels of HbAlc [AT-l-(deoxyfructosyi) valine (DFV) P-hemoglobin], which is considered as a gold standard for assessing the glycemic status over preceding 90-120 days [3, 4]. In normal individuals, HbAlc ranges from 3 to 6.5 % and up to 15 % in poorly controlled diabetes [5]. However, previous studies have suggested that the HbAlc is slowly reversible, and for a given glucose concentration it eventually reaches equilibrium.