Abstract 3624: Inflammation Impairs Reverse Cholesterol Transport In Vivo
HDL’s antiatherogenic activity is in part mediated by its role in reverse cholesterol transport (RCT). However, there is growing evidence that modified HDL may become dysfunctional. We have adapted and modified the method of Rader to measure reverse RCT from cholesterol loaded and labeled bone-marrow derived macrophages injected s.c. into the back flank of recipient mice. The appearance of [3H]cholesterol derived radioactivity in the plasma and feces was monitored daily for 3– 4 days. Assay validation was performed by comparing RCT in apoAI-deficient (A0), wild type (WT), and apoAI over expressing transgenic (AI Tg) mice. After 3 days 0.38 ± 0.09%, 2.1 ± 0.3%, and 4.0 ± 0.7% (mean ± S.D.) of the injected radioactivity was found in the plasma of the A0, WT, and AI Tg mice respectively (p<0.001 for all pairwise comparisons by ANOVA). Cumulative RCT to the feces after 3 days was also dependent upon apoAI status with 3.1 ± 0.7%, 4.8 ± 1.2%, and 5.6 ± 1.9% RCT in the A0, WT, and AI Tg mice respectively (p<0.05 for AI0 vs. AI Tg by ANOVA). Sterile inflammation was induced by i.p. injection of zymosan, a yeast cell wall extract capable of both recruiting and activating neutrophils and monocytes. A dose of 70 mg/kg was found to lead to efficient leukocyte recruitment. Zymosan induced inflammation led to 13 to 21% decreases in RCT to the plasma compartment over 4 days, and a cumulative 23% decrease in RCT to the feces (p<0.01). Feces weight was reduced by zymosan only during the first day, and cumulative RCT to the feces was not correlated with feces weight. In order to determine whether myeloperoxidase (MPO) modification of apoAI or HDL played a role in the inflammation mediated inhibition of RCT, we compared the effects of zymosan in WT and MPO-deficient mice. Over 3 days zymosan inhibited RCT to the feces by 23% in the WT mice (p<0.01), but there was only a 9% inhibition in the MPO-deficient mice (not significant). Inflammation impairs RCT at least in part through the action of MPO, an enzyme that is capable of modifying apoAI and inhibiting its ability to act as an acceptor of cellular cholesterol.