Lipid dynamics in human low density lipoproteins and human aortic tissue with fibrous plaques. A study by high field 13C NMR spectroscopy.

Natural abundance 13C NMR spectroscopy at 63.4 kG was used to probe the temperature dependence of lipid dynamics in low density lipoproteins (LDL) and in aortic fibrous plaques (i&ma-media sections). Spectra of LDL from normals and a familial type II were essentially indistinguishable. At 37”C, tissue spectra exhibit numerous narrow fatty acid and cholesteryl ester ring resonances, no peaks attributable to unesterified cholesterol, and a broad choline methyl peak as the only detectable phospholipid resonance; these spectra are similar to spectra of thermally disrupted LDL samples which showed, in comparison with native LDL spectra, marked broadening of resonances attributable to polar lipids. At 36”-37”C, linewidths of cholesterol ring resonances in LDL and tissue spectra were quantitatively similar, and temperature-dependent spectra showed a liquid -+ ordered change for cholesterol rings of cholesteryl esters in native LDL and in plaque-containing tissue occurring several degrees below physiological temperature. Low temperature (lo”-17°C) spectra of LDL and tissue had distinguishing differences from spectra of isolated cholesteryl esters in a smectic mesophase. The molecular dynamics of cholesteryl esters, the principal lipid component of fibrous plaques, appear to be similar in LDL and in atherosclerotic tissue and show significant differences from the dynamics of neat cholesteryl esters and cholesteryl esters in intact high density and very low density lipoproteins of human plasma.