Abstract 406: In Vivo Measurement of Cholesterol Deposition in Peripheral Macrophages

Cholesterol accumulation in macrophages contained in peripheral tissue is an initial step in the initiation and progression of atherosclerosis. Due to the difficulty in harvesting atherosclerotic macrophages and the complexity of atherosclerotic plaques, it is difficult to obtain reliable measurements of cholesterol mass contained in these cells in vivo. We describe a method for measuring cholesterol accumulation in vivo in peripheral macrophages and demonstrate rapid cholesterol deposition in macrophages when transplanted in a mouse with an atherosclerotic genetic background. Previously, we described a novel method for measuring in vivo cholesterol mass changes in macrophages by entrapping macrophages from donor mice into porous hollow fibers and then implanting the fibers into the peritoneal cavity of a recipient mouse. This procedure allows for the recovery of the cells after recovery of the fibers. We now show that subcutaneous implantation of macrophage-containing fibers results in cholesterol mass changes when the fibers are implanted for 24h. Using this system, we implanted fibers containing wild type peritoneal macrophages subcutaneously into mice with three different genetic backgrounds: 1) wild type, 2) LDLr apoBec dKO and 3) LDLr apoBec dKO/human apoB background. Serum cholesterol levels for the LDLr apoBec dKO and LDLr apoBec dKO/human apoB was 484±101 and 917±12mg/dl respectively, whereas serum cholesterol content of in wild-type controls was 108±6mg/dl. Significant cholesterol deposition in the macrophages was detected as early as 4h after implantation. Following 24h of implantation there was a 3-fold increase in cholesterol mass in the macrophages implanted in the LDLr apoBec dKO, and a five-fold increase in cholesterol content in the macrophages implanted in the LDLr apoBec dKO/human apoB mice. This increase in cell cholesterol mass was a result of expansion of both the unesterified and esterified cholesterol pools, resulting in a 50% / 50% distribution after 24h.