Identification of molecular species of phosphatidylcholine hydroperoxides in native and copper-oxidized triglyceride-rich lipoproteins in humans

Abstract

Background Triglyceride-rich lipoproteins are considered to be independent predictors of atherosclerotic cardiovascular disease. The molecular basis of its atherogenicity is uncertain. Here, we aim to identify molecular species of phosphatidylcholine hydroperoxides (PCOOH) in triglyceride-rich lipoproteins. For comparison, copper-oxidized triglyceride-rich lipoproteins were investigated as well. Methods A fasting EDTA blood sample was collected from six healthy human volunteers to isolate two major triglyceride-rich lipoproteins fractions – very low-density lipoproteins (VLDL) and intermediate-density lipoproteins (IDL) using sequential ultracentrifugation. Triglyceride-rich lipoproteins and plasma samples were studied for PCOOH by liquid chromatography (LC) coupled with Orbitrap mass spectrometry. Results Twelve molecular species of PCOOH in triglyceride-rich lipoproteins and/or plasma were identified using the following criteria: (1) high-resolution mass spectrometry (MS) with mass accuracy within 5\u2009ppm, (2) retention time in LC and (3) fragmentation pattern in MS2 and MS3. PC36:4-OOH was most often detected in VLDL, IDL and plasma. The ratio of total PCOOH to phosphatidylcholine progressively increased with the duration of oxidation in both VLDL and IDL. Conclusion This study demonstrated the presence of 12 molecular species of PCOOH in native triglyceride-rich lipoproteins. The frequent detection of PCOOH in triglyceride-rich lipoproteins provides a molecular basis of the atherogenicity of triglyceride-rich lipoproteins. PCOOH in triglyceride-rich lipoproteins might serve as a molecular basis of the atherogenicity of triglyceride-rich lipoproteins.