Quantitative measurement of 4-hydroxyalkenals in oxidized low-density lipoprotein by gas chromatography-mass spectrometry

Previously, we reported on the determination of 4-hydroxyalkenals as pentafluorobenzyl oxime derivatives by gas chromatography-mass spectrometry. In this study, an improved method is presented which allows quantitative detection of 4-hydroxyalkenals in tissues by using two stable isotope-labeled internal standards, 9D₃-4-hydroxynonenal and 9D₃-4-hydroxyhexenal. This assay was used to quantitate 4-hydroxyalkenals in copper-oxidized human low-density lipoprotein, and we found more 4-hydroxynonenal than 4-hydroxyhexenal. This is consistent with the fact that there are more ω-6 than ω-3 fatty acids in human low-density lipoprotein samples, which are the sources of 4-hydroxynonenal and 4-hydroxyhexenal, respectively.