Effect of lipid-free apoE and apoAI on cholesterol efflux.

<p>(A–B) RAW 264.7 macrophages were incubated at 37°C for 48 h with 1 µCi/ml of ³H-cholesterol and 20 µg/ml apoE-free (E⁻) lipoprotein, followed by incubation with the indicated amount of apoE3 (E3) or apoE4 (E4) for an additional 5 h. Thereafter, cells were incubated with 20 µg/ml of apoAI or base medium alone for 2 h. Cholesterol efflux was determined as described in the Materials and Methods. ApoAI mediated cholesterol efflux was calculated as the total efflux in the presence of apoAI minus the efflux to the base medium without apoAI. (C) The cells were loaded with ³H-cholesterol as abovementioned, and then incubated with 0.44 µM of lipid free apoA1 (12.35 µg/ml), apoE3 or apoE4 (15 µg/ml), or culture medium alone as a control (ctrl) for 6 h. Total cholesterol efflux was determined as described in the Materials and Methods. Data represent the mean ± SEM from 3–4 separate experiments. *<i>P</i><0.05 or **<i>P</i><0.01 relative to controls; <b>^#</b><i>P</i><0.05 relative to apoE4.