Abstract 5468: Fluorescence-Mediated-Tomography For Non-invasive In-vivo Imaging Of Atherosclerotic Lesion-stabilization Mediated By Short Term FTY720 Treatment In ApoE deficient Mice
Background: High density lipoproteins (HDL) reduce monocyte adhesion to endothelial cells (EC) and thereby prevent macrophage (MØ) accumulation in the arterial wall. HDLs anti-adhesive effect has been attributed in part to its sphingosine 1-phosphate (S1P) content. The influence of S1P on MØ accumulation in the arterial wall has been not yet assessed under in vivo conditions. We tested the effect of a two-day treatment with the S1P analogue FTY720 on MØ content using Fluorescence-Mediated-Tomography (FMT) in the ApoE−/− model and examined EC activating properties of lipoproteins after FTY720 treatment in vitro.
Methods: 26 ApoE−/− and wild type (WT) mice were used after 16 weeks on western diet. For FMT studies, 5x106 thioglycolate-elicited peritoneal MØ labeled with near infrared fluorescent dye (DiR) were given IV to a subgroup of mice on day 0. On day 2 and 3 FTY720 (1μg/g b.w.) was administered IP. FMT was used for quantification of MØ infiltration in a region of interest placed to cover aortic valve and arch prior to and 48h after treatment. Endogenous MØ (CD68) were stained on aortic-arch cryosections. Prior to adhesion assays using fluorophor-labeled MØ murine EC (fEnd.5) were incubated (4h) with FPLC-separated LDL from apoE−/− mice treated with FTY720 or vehicle. The effect of FTY720 on anti-adhesive properties of HDL was studied.
Results: Mean fluorescence intensity in FMT decreased in FTY720 treated mice by 35% and increased in controls by 50% (day 3 vs day 1, n=4, p<0.05). FTY720 reduced MØ-positive lesion area by 16% with unchanged plaque size (FTY vs Ctrl, n=9, p<0.05). MØ accumulation at the lesion base was reduced after FTY720 treatment by 25% (Ctrl vs. FTY, n=9, p<0.05). In an ex vivo approach, LDL augmented MØ adhesion to EC (215±30% LDL vs Ctrl, p<0.01, n=6). LDL from FTY-treated mice had an attenuated proinflammatory effect (166±27%, FTY−LDL vs Ctrl, p=n.s., n=6). HDL reduced LDL pro-adhesive effect (215±30 vs 120±8, % of Ctrl, LDL vs LDL+HDL, p<0.05, n=6). FTY−HDL further decreased MØ adhesion (120±8 vs 86±8, % of Ctrl, LDL+HDL vs LDL+FTY−HDL, p<0.05, n=6).
Conclusions: FTY720 improves HDL function by augmenting the anti-inflammatory potential. MØ content of atherosclerotic lesions is reduced after very brief FTY720 treatment of ApoE−/− mice.