Analysis of Hemoglobin Glycation Using Microfluidic CE-MS: A Rapid, Mass Spectrometry Compatible Method for Assessing Diabetes Management.

Diabetes has become a significant health problem worldwide with the rate of diagnosis increasing rapidly in recent years. Measurement of glycated blood proteins, particularly glycated hemoglobin (HbA1c), is an important diagnostic tool used to detect and manage the condition in patients. Described here is a method using microfluidic capillary electrophoresis with mass spectrometry detection (CE-MS) to assess hemoglobin glycation in whole blood lysate. Using denaturing conditions, the hemoglobin (Hb) tetramer dissociates into the alpha and beta subunits (α- and ß-Hb), which are then separated via CE directly coupled to MS detection. Nearly baseline resolution is achieved between α-Hb, ß-Hb, and glycated ß-Hb. A second glycated ß-Hb isomer that is partially resolved from ß-Hb is detected in extracted ion electropherograms for glycated ß-Hb. Glycation on α-Hb is also detected in the α-Hb mass spectrum. Additional modifications to the ß-Hb are detected, including acetylation and a +57 Da species that could be the addition of a glyoxal moiety. Patient blood samples were analyzed using the microfluidic CE-MS method and a clinically used immunoassay to measure HbA1c. The percentage of glycated α-Hb and ß-Hb was calculated from the microfluidic CE-MS data using peak areas generated from extracted ion electropherograms. The values for glycated ß-Hb were found to correlate well with the HbA1c levels derived in the clinic, giving a slope of 1.20 and an R(2) value of 0.99 on a correlation plot. Glycation of human serum albumin (HSA) can also be measured using this technique. It was observed that patients with elevated glycated Hb levels also had higher levels of HSA glycation. Interestingly, the sample with the highest HbA1c levels did not have the highest levels of glycated HSA. Because the lifetime of HSA is shorter than Hb, this could indicate a recent lapse in glycemic control for that patient. The ability to assess both Hb and HSA glycation has the potential to provide a more complete picture of a patient's glycemic control in the months leading up to blood collection. The results presented here demonstrate that the microfluidic CE-MS method is capable of rapidly assessing Hb and HSA glycation from low volumes of whole blood with minimal sample preparation and has the potential to provide more information in a single analysis step than current technologies.

Characterization of Intact Antibody Drug Conjugate Variants Using Microfluidic Capillary Electrophoresis-Mass Spectrometry.

In this work, we utilize capillary electrophoresis-mass spectrometry (CE-MS) in an integrated microfluidic platform to analyze an intact, lysine-linked antibody drug conjugate (ADC) in order to assess post translational modifications and drug load variants. The initial charge heterogeneity of the unconjugated IgG-2 monoclonal antibody (mAb) was assessed by separating intact charge variants. Three main charge variants were resolved in the CE dimension. These variants were attributed to pyroglutamic acid formation and decarboxylation on the primary structure of the mAb through characteristic mass shifts and changes in electrophoretic mobility. Additionally, glycoforms of the antibody charge variants were identified in the deconvoluted mass spectra. The observed glycoforms and their distribution compared favorably to a released N-glycan analysis performed on the mAb. After conjugation, the ADC was analyzed using the same microchip CE-MS method. The addition of a drug load resulted in a decrease in mobility and an increase in mass of 3145 Da. Five main species that differed in their respective drug-to-antibody ratios (DAR) were fully resolved in the CE separation, with each DAR displaying the same variant population observed on the unconjugated mAb. A DAR range of 0-4 was observed with an average of 1.7 drug loads. The DAR distribution generated from the microfluidic CE-MS data compared favorably to results from infusion-ESI-MS and imaging CE (iCE) analysis of the ADC, techniques commonly used for intact mAb and ADC characterization.

Integrated microfluidic capillary electrophoresis-electrospray ionization devices with online MS detection for the separation and characterization of intact monoclonal antibody variants.

Here, we demonstrate an integrated microfluidic capillary electrophoresis-electrospray ionization (CE-ESI) device for the separation of intact monoclonal antibody charge variants with online mass spectrometric (MS) identification. The need for dynamic coating and zwitterionic background electrolyte (BGE) additives has been eliminated by utilizing surface chemistry within the device channels to control analyte adsorption and electroosmotic flow (EOF) while maintaining separation efficiency. The effectiveness of this strategy was illustrated with the separation of charge variants of Infliximab. Three major species corresponding to C-terminal lysine variants were separated with an average resolution of 0.80 and identified by mass difference. In addition to the lysine variants, masses were determined for minor acidic and basic species. The separation of these variants prior to MS analysis facilitated the identification of glycosylation patterns for each of the variants. The general applicability of this method was demonstrated by analyzing two additional monoclonal antibody species: an IgG2 antibody and an IgG1 antibody conjugate. The IgG2 proved to have similar modifications to Infliximab with lower relative abundances of the lysine variants. Analysis of the IgG1 drug conjugate further exemplified the advantages of MS detection; differences in the extent of antibody conjugation were detectable despite limited CE resolution. The CE-ESI-MS methodology described here is a rapid and generic strategy for the separation of intact mAb charge variants and facilitates the identification of variants through MS detection.