Comprehensive Quantification of Carboxymethyllysine-Modified Peptides in Human Plasma

A prolonged hyperglycemic
condition in diabetes mellitus results
in glycation of plasma proteins. N(ε)-Carboxymethyllysine
(CML) is a well-known protein advanced glycation end product, and
one of its mechanisms of formation is through further oxidation of
Amadori compound modified lysine (AML). Unlike enrichment of AML peptides
using boronate affinity, biochemical enrichment methods are scarce
for comprehensive profiling of CML-modified peptides. To address this
problem, we used AML peptide sequence and site of modification as
template library to identify and quantify CML peptides. In this study,
a parallel reaction monitoring workflow was developed to comprehensively
quantify CML modified peptides in Type 1 diabetic subjects’
plasma with good and poor glycemic control (n = 20
each). A total of 58 CML modified peptides were quantified, which
represented 57 CML modification sites in 19 different proteins. Out
of the 58 peptides, five were significantly higher in poor glycemic
control samples with the area under the receiver operating characteristic
curve ≥0.83. These peptides could serve as promising indicators
of glycemic control in Type 1 diabetes management.