Effects of MPO treatment on HDL cholesterol efflux capacity. apoA-I/apoA-II heterodimer formation is induced by MPO oxidation. HDL treated with MPO (0, 1, or 5 nM) for 1 hr was subjected to SDS-PAGE followed by immunoblotting for apoA-I (a) and apoA-II (b). Arrows indicate the apoA-I/apoA-II heterodimer. Molecular masses of the standards are listed on the left. The amount of protein was 3 μg/lane. [3H]-labeled cholesterol-loaded THP-1 macrophages were cultured in medium containing 50 μg/mL HDL treated with 0, 1, or 5 nM MPO for 1 hr. Cholesterol efflux was determined after 4 hrs of incubation. Efflux media without HDL and with apoA-I (10 μg/mL) were used as a negative control and for comparison, respectively. Results are means ± SD of three independent experiments. ns: nonsignificant.