Abstract 447: Acrolein-Modified HDL Impairs Cholesterol Transport and HDL Function

Abstract

The interaction between scavenger receptor BI (SR-BI) and HDL reduces the risk for cardiovascular disease (CVD) by playing key roles in the reverse cholesterol transport pathway (RCT). In the beginning of RCT, SR-BI stimulates release of free cholesterol (FC) from peripheral macrophages to HDL, whereas in the final step of RCT, HDL binds to hepatic SR-BI for delivery of excess cholesteryl esters (CE) into the liver for excretion via bile. While “functioning” HDL is crucial in protection against CVD, environmental factors such as acrolein, a highly reactive aldehyde found in tobacco smoke, can induce oxidative stress that promotes HDL modifications and renders the particle “dysfunctional”. Although there is a strong correlation between cigarette smoking and CVD risk, much less is known about the effects of smoking on RCT. We hypothesized that acrolein modifications to HDL (acro-HDL) generate a dysfunctional particle by: (i) impairing SR-BI-mediated selective uptake of HDL-CE and efflux of FC and (ii) upregulating inflammatory pathways in macrophages that promote atherogenesis. To test this hypothesis, human HDL was modified with 250μM acrolein and acrolein adducts on HDL were confirmed by immunoblot analysis and mass spectrometry. To evaluate acro-HDL’s functionality at the beginning of RCT, SR-BI-mediated FC release to native- or acro-HDL was measured in SR-BI-transfected COS-7 cells. Our data revealed that there was 30% less efflux of FC in the presence of acro-HDL as compared to native HDL. To assess acro-HDL functionality at the end of RCT, HDL binding and HDL-CE uptake assays were performed and acro-HDL (0-50μg/mL) was 10-25% less efficient at delivering CE to cells via SR-BI. Finally, to determine whether acro-HDL was rendered atherogenic, we used qRT-PCR to demonstrate that acro-HDL, but not native HDL, paralleled the effects of oxidized LDL by upregulating mRNA scavenger receptor expression (CD36 and LOX-1) and inflammatory marker expression (MCP-1, IL-6, ICAM-1) in THP-1 macrophages. Altogether, our data reveal that acrolein modification produces a dysfunctional HDL particle that upregulates inflammatory pathways. More detailed investigations into the impact of acrolein adducts on HDL function may help prevent smoking-related CVD deaths.