The correlation between the peak area of ATEHLSTLSEK to unmodified M148 peptides was weak (r = 0.42, p < 0.001), possibly due to the susceptibility of methionine residues to oxidation. To validate the selleck inhibitor measurement of protein concentrations using MRM, four HDL samples were sent to Myriad RBM that has a CLIA certified laboratory with the ability of running multiplexed immunoassays. Concentrations of albumin, Apo B100, and ApoA-I (ATEHLSTLSEK) measured using the multiplexed immunoassays at Myriad were strongly correlated to measurements

by MRM (r > 0.95, p < 0.001 for all three proteins). The ratio of ATEHLSTLSEK peptide to the corresponding SIS peptide was used to calculate the concentrations of ApoA-I on HDL ( Table 2) in the clinical samples. SIS peptides for the unmodified M148 was not synthesized, and thus we were unable to determine ApoA-I concentrations based on the M148 peptide. Thirty-four participants were recruited to examine the impact of disease on ApoA-I methionine oxidations. As shown in Table 2, controls were leaner, and had a lower systolic blood pressure (p < 0.005). Participants with diabetes and heart disease were taking more statins, aspirin, and blood pressure medication compared to controls or diabetics without a prior history GKT137831 clinical trial of a cardiac event. Participants with diabetes and CVD had significantly decreased HDL ApoA-I concentrations compared to participants with diabetes

but without CVD (p = 0.029 for the group comparison by ANOVA, and p = 0.027 for the group with CVD vs. diabetes without CVD). The relative ratio of oxidized to native M148 peptide in HDL was three times as high in the diabetes and CVD group, and 1.5 times as high in the diabetic group without prior CVD, compared to the control group (p < 0.001 for the group comparison by ANOVA, with p < 0.001 for both diabetes and CVD vs. control, and for diabetes without CVD vs. control, Fig. 2). In this study, we defined MRM transitions to monitor the relative ratio of M148 oxidations compared to M148 peptide on ApoA-I. Our results demonstrated that monitoring the relative ratio

of the M148(O)- to the M148-containing peptide was highly reproducible with a CV <5% Racecadotril using MRM. We did not measured the molar % oxidized M148 in this proof-of-concept study, because this would have required absolute quantitation of both forms of this peptide. Clinically, HDL isolated from participants with diabetes and CVD had a significantly increased ratio of oxidized M148 to unoxidized M148. These proof-of-concept findings suggest a role for M148(O) as a biomarker for CVD; however, larger clinical studies are needed to validate this role. M148 lies at the center of LCAT activation domain. Shao et el. demonstrated that oxidation of M148(O) was associated with decreased capacity to activate LCAT [6]. In addition, reversing M148 oxidation using methionine sulfoxide reductase restored the ability of ApoA-I to activate LCAT.