Studies of novel glycine-containing lipids that differ greatly in type 2 diabetes
White, Autumn Brooke.
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Type 2 Diabetes (T2D) is a growing problem that affects hundreds of millions of people. This work focused on understanding the pathogenesis of T2D by studying novel glycine-containing lipids found greatly changed in T2D with glycine linked via the carboxyl end to a hydrophobic moiety (Bowden, 2011). Different forms of these novel lipids were found in fasting Type 2 Diabetes (F-T2D), fasting healthy control (F-HC), and non-fasting healthy control (NF-HC) plasma by separation on Reverse Phase-High Performance Liquid Chromatography (RP-HPLC). The ratio in F-T2D/F-HC differed by approximately fifty-fold, but both were present in NF-HC plasma, along with several additional forms with different RP retention. We isolated compounds of interest from the plasma from NF-HC volunteers and pooled enough plasma in hopes for structural elucidation using Nuclear Magnetic Resonance (NMR). Since these compounds were found to be carried by Human Serum Albumin (HSA), HSA was purified from human plasma. A 2:1 Dichloromethane (DCM):Methanol (MeOH) modified Folch-extraction (Folch, 1957) was used to extract the hydrophobic metabolites from HSA. The lipid mixture was separated by RP-HPLC and a small portion of each fraction was derivatized by pentafluorobenzyl-bromide (PFB-Br) and analyzed by LC-MS. A portion of each underivatized fraction, based on the results of the PFB-Br reaction, was analyzed by LCMS. Each prominent peak was fragmented using collision-induced dissociation tandem mass spectrometry (CID-MS/MS). Peaks of the most interest showed neutral loss masses corresponding to glycine and phosphate. This evidence led to the hypothesis that the glycine moiety is attached to a phosphate via a mixed acyl-phospho anhydride linkage. This linkage is thought to be consistent with the rapid hydrolysis of the compounds of interest under mild conditions during sample preparation. Compounds were synthesized that could be followed in the HSA work-up procedure to determine the stability of the anhydride linkages at different steps of the work-up. It is also possible that the linkage could be a mixed-acyl anhydride and this linkage was also synthesized and studied by mass spectrometry (MS) and CID-MS/MS. Understanding these structures could provide new insights into the mechanisms of T2D and perhaps lead to enhanced prevention and treatment.