Quantification of C=C isomers Using Aziridine-Based Isobaric Mass Tagging

In response to environmental stress, living organisms are known to actively alter their membrane lipid compositions in their cell membranes to maintain cellular function and integrity. Glycerophospholipids, a main component of bacterial and human cell membranes, consist of a phosphate headgroup, glycerol backbone, and two fatty acids chains attached at either the sn-1 or sn-2 positions. Recent studies revealed the shift in the relative abundance of sn-positional and C=C isomers in disease(1-3). Therefore, understanding the lipid concentration at the isomer level is significant not only in deep profiling of lipids in various biological samples, but also holding promise as biomarker for abnormal lipid metabolism in disease progression. Labeling using isobaric tag for relative and absolute quantitation (iTRAQ) was developed to achieve enhanced lipid isomer quantification by an aziridine-based isobaric tag labeling strategy using hydroxylamine-O-sulfonic acid (HOSA) and a Rh2esp2 catalyst to activate C=C bonds. Following isobaric tag labeling and the addition of lithium ions to the tagged lipid, a lithiated tagged lipid forms. The sn-positional diagnostic ions which carry isobaric tags are identified and quantified by CID and HCD tandem MS(4). This strategy was applied to human colon cancer plasma and showed significant concentration change in 7 PCs.

Reference:

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3. Yang, T.; Tang, S.; Kuo, S. T.; Freitas, D.; Edwards, M.; Wang, H.; Sun, Y.; Yan, X. Lipid mass tags via aziridination for probing unsaturated lipid isomers and accurate relative quantification. Angew. Chem., Int. Ed. 2022, 61, e202207098
4. Yang, T.; Tang, S.; Feng, J.; Yan, X. Lipid Isobaric Mass Tagging for Enhanced Relative Quantification of Unsaturated sn-Positional Isomers. ACS Meas. Sci. Au 2024, 4 (2), 213– 222