Decreased plasma phosphatidylcholine/free cholesterol ratio as an indicator of risk for ischemic vascular disease

As part of a population survey and a follow-up study of plasma lipid profiles by high temperature gas-liquid chromatography, we have determined the quantities and relative proportions of all major chemical classes and molecular species of lipids of plasma from 1200 subjects at Visit 2 of the Toronto-McMaster Lipid Research Clinic Prevalence Study. We have compared these values between our 24 subjects with ischemic vascular disease and 73 control subjects matched for age, sex, and plasma total cholesterol and triacylglycerols. The phosphatidylcholine/free cholesterol ratio showed the highest association with ischemic vascular disease of any of over 10 other lipid parameters and all the common risk indicators except high density lipoprotein cholesterol. The phosphatidylcholine/free cholesterol ratio had a relative risk ratio of 20/4 (95% confidence limits, 15/9, 23/1) and high density lipoprotein cholesterol, a risk ratio of 23/1 (95% confidence limits, 24/0, 19/5) for ischemic vascular disease. The average ratio of phosphatidylcholine/free cholesterol for the ischemic vascular disease group was 1.36 and for the controls 1.51, the population average being 1.50. Plasma high density lipoprotein cholesterol had a significant correlation (R = 0.15) with the phosphatidylcholine/free cholesterol ratio in the total population sample. The increased risk for ischemic vascular disease from a lower phosphatidylcholine/free cholesterol ratio may possibly be explained on the basis of decreased fluidity and stability of the lipoproteins due to a relative oversaturation with free cholesterol.