Structural studies of NMR detected lipids in myocardial ischemia

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Abstract
Lipid-induced abnormalities in myocardial function have been implicated in a number of ischemic events including the accumulation of lipids in human myocardium following myocardial infarction. Although animal models have shown the source of these lipids to be triglycerides, the specific species involved has not been identified. In order to better understand the mechanism(s) defining this lipid accumulation, it follows that the identification of the lipids involved may be important in achieving this aim. Therefore, this study examined the use of NMR probes for delineating the biochemical makeup of the increased 1H NMR observed lipid signal following myocardial infarction. Specifically, the present study demonstrated the utility of the spin-echo pulse sequence for the study of alterations in myocardial lipids following ischemic injury. Spin-echo spectra allowed the analysis of subsets of lipids within the large lipid pool inherent in most myocardium. The analyses of the chemical shifts of the lipid resonances provided a simple yet powerful means for deducing lipid class associated with the ischemic injury and suggested the species arises predominantly from saturated lipids. The examination of the CH2/CH3 NMR ratio provided additional information regarding the species involved, however, because the spin-echo technique was utilized, which may distort certain signal intensities, caution must be exercised in interpreting the specific species involved. With this in mind, a tentative assignment has been given to octanoic acid. Finally, a temperature dependence of the lipid signals was noted and determined to be unique for spin-echo lipid. Although this dependence did not provide the necessary information regarding the gel-to-liquid crystal phase transition temperature which might aid in understanding the origin of the lipid species, it did determine that the species involved was only the spin-echo observed lipid and that the dependence was reversible. Finally, the increase in signal intensity associated with the spin-echo lipid signal at physiologic temperature may provide the necessary means to observe such species utilizing chemical shift imaging methods.