Efficient drug delivery to atherosclerotic lesions and the antiatherosclerotic effect by dexamethasone incorporated into liposomes in atherogenic mice

In order to confirm the efficacy of dexamethasone (DXM) incorporated into liposomes (DXM-liposomes) on atherosclerosis, drug delivery to atherosclerotic lesions and the antiatherosclerotic effect by DXM-liposomes were investigated in atherogenic mice. DXM-liposomes were prepared with egg yolk phosphatidylcholine, cholesterol and dicetylphosphate in a lipid molar ratio of 7/2/1 by the hydration method and then adjusted to three different particle sizes to clarify the influence of particle size on the drug delivery to atherosclerotic lesions and the effect on atherosclerosis. The particle sizes of DXM-liposomes were 519 nm (L500), 202 nm (L200) and 68.6 nm (L70), respectively. In both size, DXM concentration and DXM/lipid molar ratio in DXM-liposomes suspension were 1 mg DXM/ml and 0.134 mol DXM/mol total lipids, respectively. Atherogenic mice used as an experimental model develop an atherosclerotic lesion in the aorta and they were prepared by feeding an atherogenic diet for 14 weeks. The aortic pharmacokinetics of DXM-liposomes was examined by intravenous administration to atherogenic mice. The aortic uptake clearance of DXM in atherogenic mice treated with L200 was 2.6 - 3.2 fold greater than that in animals treated with L500, L70 or free DXM ( f-DXM). Furthermore, the effects of DXM-liposomes on atherosclerosis were examined by intravenous administration to atherogenic mice once a week from 8 to 14 weeks. The antiatherosclerotic effects of DXM-liposomes were evaluated by determination of the aortic cholesterol ester (CE) level. The aortic CE level in atherogenic mice treated with L200 (55 mu g DXM/kg) was significantly lower than that in animals treated with PBS. The antiatherosclerotic effect of L200 ( 55 mg DXM/kg) was significantly more potent than that of f-DXM ( 550 mu g DXM/kg). These findings suggest that efficient delivery of DXM to the atherosclerotic lesions by L200 induces an excellent antiatherosclerotic effect at a lower dose. Therefore, L200 may be useful in the development of drug delivery systems for atherosclerotic therapy.