Abstract 11835: An Alternative Method to Measure in vivo Reverse Cholesterol Transport in Hyperlipidemic Hamsters
Objectives- Intraperitoneal injection of 3H-cholesterol labeled macrophages is a relevant method to measure reverse cholesterol transport (RCT). However, the contribution of intraperitoneal macrophages in cholesterol uptake and egress is questionable. Indeed, cholesterol from atherogenic particles, such as oxidized LDL (oxLDL), is efficiently cleared from plasma by liver resident macrophages (Kupffer cells) for further cholesterol egress in plasma, HDL, bile and feces. We therefore injected 3H-cholesteryl oleate labeled/oxidized LDL intravenously (oxLDL-RCT) and compared this alternative method with the 3H-cholesterol labeled macrophages (macrophage-RCT) experiment in hamsters.
Methods and results- Hamsters were fed a chow or hyperlipidemic diet over 25 days (n=16/group). Each group was then separated into 2 sets to simultaneously measure in vivo RCT using the oxLDL- or macrophage-RCT methods over 72 hours. When RCT was measured using the oxLDL-RCT method, 99% of the injected radioactivity disappeared from plasma within 5 minutes after 3H-oxLDL injection. One hour after injection, 3H-tracer continuously reappeared in plasma and HDL over 72 hours. Compared to chow diet, hyperlipidemic hamsters showed a significant ∼36% decrease in 3H-tracer appearance in HDL. After 72 hours, 3H-tracer was increased by 266% in liver and decreased by 80% in bile (both p<0.001 vs. chow). 3H-tracer appearance increased by 37% in fecal cholesterol, while fecal 3H-bile acids was decreased by 38% (both p<0.05). Although similar results were noticed using the macrophage-RCT method, the lower 3H-tracer appearance in both HDL and fecal bile acids in hyperlipidemic hamsters was not observed, indicating a different metabolism for 3H-cholesterol deriving from intraperitoneal macrophages. To further validate the oxLDL-RCT method, the effects of LXR agonist GW3965 (30mg/kg twice daily for 10 days) were measured in hyperlipidemic hamsters. As expected, GW3965 increased 3H-tracer appearance in plasma, liver, bile and fecal cholesterol after 3H-oxLDL injection.
Conclusion- Our data suggest that the oxLDL-RCT method may better trace cholesterol metabolism in vivo and may be useful to evaluate drugs affecting RCT.
- © 2011 by American Heart Association, Inc.