Pitfalls of Direct HDL-Cholesterol Measurements in Mouse Models of Hyperlipidemia and Atherosclerosis

Mice have become important models in lipoprotein and atherosclerosis research (1)(2). Certain strains of mice, such as C57BL/6, develop hyperlipidemia—as a result of the accumulation in plasma of cholesterol-rich remnant particles—and aortic atherosclerosis when fed a high fat, high cholesterol diet (atherogenic diet) (1)(2). Apolipoprotein E-deficient [apoE(−)] mice also develop hyperlipidemia—as a result of the accumulation of remnant lipoproteins that float mainly as VLDL and intermediate-density lipoprotein—and massive atherosclerosis even when they are fed a diet of regular chow, which is only 4% fat (1). These two mouse models currently are being used to study the effect of gene expression in atherosclerosis with at least two main goals: to understand the mechanisms underlying the genesis and progression of atherosclerosis, and to investigate the feasibility of different genetic and pharmacological interventions to stop or regress atherosclerosis and prevent its complications. Previous studies have already been instrumental in defining the role of the different HDL particles with respect to atherosclerosis (3)(4). Indeed, any study of this kind requires accurate and reproducible measurement of the cholesterol concentrations associated with the different lipoprotein fractions. For these purposes, fast protein liquid chromatography (FPLC) has been used to isolate HDL and to measure its cholesterol content (HDL-C) (5). This procedure can be performed using smaller volumes of plasma than with ultracentrifugation, which usually requires the use of plasma pooled from different mice. However, both preparative methods are labor-intensive. Because current experiments in mice require an increasingly larger number of animals, HDL has been also isolated by precipitation of apolipoprotein B (apoB)-containing lipoproteins using a variety of reagents (3). Recently, several new direct methods for testing HDL-C have been developed and adapted to many clinical chemistry laboratories (6). These methods eliminate the need for precipitation and separation steps and use smaller …