Measurement of Human Plasma Phospholipid Transfer Protein by Sandwich ELISA

Background: Plasma phospholipid transfer protein (PLTP) plays a central role in the remodeling of HDLs. Reliable and accurate methods for assaying PLTP concentration are required. Methods: A sandwich ELISA for PLTP has been developed, using two monoclonal antibodies against recombinant human PLTP (rhPLTP) expressed in Chinese hamster ovary cells. The ELISA allows for the quantification of PLTP in the range 0.625–15.0 ng/assay (1.2–30.0 mg/L). Intra- and interassay CVs were <3.0% and <4.2% respectively. The assay was used to quantify plasma PLTP concentrations in 132 Japanese subjects (75 males and 57 females). Results: PLTP concentrations were 12.0 ± 3.0 mg/L (mean ± SD; range, 4.9–20.5 mg/L). No sex difference was observed. Plasma PLTP concentration was positively correlated with HDL-cholesterol (r = 0.72; P <0.001), apolipoprotein (apo) A-I (r = 0.62; P <0.001) and HDL2-cholesterol (r = 0.72; P <0.001), and was negatively correlated with triacylglycerol (r = −0.45; P <0.001). There was no correlation with plasma apo A-II. These results agree with other evidence that plasma PLTP is associated with large apo A-I-containing lipoproteins. There was no correlation (r = −0.01) between plasma PLTP and plasma phosphatidylcholine transfer activity (range, 3.5–10.5 μmol · mL−1 · h−1), suggesting that PLTP may exist in active and inactive forms. Conclusion: This new ELISA will be of value for further studies of PLTP in health and disease.

Biological Variation Data Applied to the Selection of Serum Lipid Ratios Used as Risk Markers of Coronary Heart Disease

The biological variation of several relative lipid quantities, calculated as the ratios between the concentrations of various serum lipids and apolipoproteins, has been estimated over a one-year period. The medians of the within-subject biological coefficient of variation, separated by sex when significant differences exist, were 15.4% for [apolipoprotein A-I]/[apolipoprotein B], 6.8% for [high-density lipoprotein (HDL)-cholesterol]/[cholesterol], 10.5% and 17.6% (women and men, respectively) for [HDL2-cholesterol]/[HDL-cholesterol], 13.6% for [HDL2-cholesterol]/[HDL3-cholesterol], 10.6% for [low-density lipoprotein (LDL)-cholesterol]/[apolipoprotein B], 10.6% and 8.7% (women and men, respectively) for [LDL-cholesterol]/[cholesterol], and 6.3% for [LDL-cholesterol]/[HDL-cholesterol]. From these data, we have calculated the critical difference for significant change detection, the index of individuality, and the goal for the between-day imprecision. Concerning within-subject biological variation, the best ratios for the detection of risk of coronary heart disease and the monitoring of intervention are [LDL-cholesterol]/[HDL-cholesterol] and [HDL-cholesterol]/[cholesterol]. The index of individuality obtained in this study indicates that the use of population-based reference values is inadequate for interpreting the ratios studied.