Abstract Th0015: Unesterified cholesterol is abundant in <i>Scarb1</i> null mouse plasma even without <i>Abcg1</i> .

Aim: High plasma unesterified cholesterol is one of the causes of atherosclerosis and infertility. The classical lipid-lowering drug probucol reduces plasma unesterified cholesterol levels in mice by an unknown mechanism. Our previous results suggest that the accumulated high levels of unesterified cholesterol are mainly on the HDL particle. Here, we generated Scarb1 / Abcg1 double null mice to investigate the involvement of ABCG1 on the source of plasma HDL free cholesterol levels in Scarb1 null mice. Method: Abcg 1 null mice were crossed bread with Scarb1 +/- mice by feeding probucol- and tocopherol-containing chow. Mouse genotype was determined by tail DNA. After 4 weeks of normal chow feeding, mouse plasma was collected, and determined their plasma lipids. Mouse plasma unesterified cholesterol level was determined by a SF-CHO-N reagent (SEKISUI MEDICAL Co. Ltd., Japan), and the total cholesterol was detected by LabAssay® Cholesterol kit (Fujifilm Wako pure chemical, JAPAN). Results: This project was the first to generate Scarb1 null mice on an Abcg1 null mouse background. Plasma FC of WT, Abcg1 null, Scarb1 null, Scarb1 / Abcg1 double null, and Scarb1 / Apoa1 double null were 0.2, 0.3, 0.8, 1.0, and 0.7 µg/µL. The FC/TC ratios were 21, 25, 58, 52, and 60%, respectively. Conclusions: The high level of unesterified cholesterol in the plasma of Scarb1 / Abcg1 double-null mice suggests that the cause of the accumulation of unesterified cholesterol on lipoproteins is not the ABCG1 transporter. ABCG1 in the liver and other tissues is unlikely to pump cellular unesterified cholesterol to the large HDL that we detected in Scarb1 null mice. The gel permeability HPLC-based plasma lipoprotein profile of these mice will be analyzed by LipoSEARCH® (Immuno-Biological Laboratories, Co. Ltd., Japan) for further information.