Haptoglobin influences both cholesterol efflux from macrophages and Lecithin-Cholesterol Acyl-Transferase activity.

Aim: Haptoglobin (Hpt) was previously found to inhibit reverse cholesterol transport (RCT), as binding ApoA-I and preventing its stimulation of both cholesterol (C) efflux and Lecithin-Cholesterol Acyl-Transferase (LCAT). This study aimed to find out whether Hpt influences RCT from macrophages differentiated from primary culture of human monocytes. Methods: Monocytes were isolated from human buffy coats, and kept for 6 days in culture for differentiation into macrophages. After treatment with ³H-C for 24 h, the cells were incubated with ApoA-I (0.04 mg/mL), or ApoA-I plus increasing Hpt amounts (0.1-0.75 mg/mL). After 16 h of incubation, homologous plasma was added as LCAT source. After further incubation for 16 h, supernatants were aliquoted from culture medium to measure their radioactivity content, representing the released C. Supernatant lipids were extracted and separated by TLC to measure the LCAT activity as conversion of unesterified ³H-C into C esters. Results: Addition of Hpt increasing amounts to macrophages significantly inhibited both ApoA-I dependent stimulation of C efflux (down to 27% of the control value) and LCAT activity (down to 50% of the control value). The changes were significant (P