Plasma phosphatidylcholine/free cholesterol ratio as an indicator for atherosclerosis.

Plasma lipid profiles were determined in two inbred strains of mice, C57BR/cdJ and CBA/J, fed either a normal chow or an atherogenic diet for a 15-week period, starting at 10 weeks of age. On the chow diet, the C57BR/cdJ had significantly higher mean free cholesterol, esterified cholesterol, and total lipid values, and a significantly lower mean phosphatidylcholine/free cholesterol ratio than the CBA/J mice. On the atherogenic diet, the C57BR/cdJ had significantly higher mean levels for all lipids classes, except triacylglycerols, than the CBA/J mice. The mean plasma free cholesterol and esterified cholesterol levels of the C57BR/cdJ were four times greater than those of the CBA/J strain on the atherogenic diet. The mean plasma phosphatidylcholine/free cholesterol ratio of the C57BR/cdJ mice on the high cholesterol diet was 0.87 compared to 1.91 for CBA/J mice. These plasma lipid changes were associated with a marked development of atheromatous deposits in the wall of the aortic sinus of the C57BR/cdJ compared to the CBA/J animals. The phosphatidylcholine/free cholesterol ratios of the liver lipids of both strains decreased from 2.5-2.7 on the chow diet to 1.0-1.1 on the high cholesterol diet. It is suggested that a plasma phosphatidylcholine/free cholesterol ratio less than 1 represents a supersaturation of the vascular system and the vessel wall with cholesterol, which leads to a destabilization of the plasma membranes of the endothelial and smooth muscle cells, and an infiltration of the vessel wall by the plasma lipids.