Monocyte Inhibition by Liposomal Delivery System of BPs

MACROPHAGE/MONOCYTE INHIBITION BY LIPOSOMAL DELIVERY SYSTEM OF BPs 

G-50 column and eluted in 2-(N-Morpholino) ethansulfonic acid hydrate (MES)/N-(2-Hydroxyethyl)piperazine-N-(2-ethane-sulfonic acid) (HEPES) buffer pH 7.2 (50 mM MES, 50 mM HEPES, 75mM NaCl) to remove unencapsulated BPs. Several formulations with different sizes were obtained (0.6, 0.4, 0.2, and 0.1 pm). Liposome size and morphology was determined by dynamic light scattering and cryo-TEM microscopy (Fig. 1). 

The mean sizes obtained were 500 150, 350 77, 192 25, and 100 16, for 0.6, 0.4, 0.2, and 0.1pm liposomes, respectively. Drug concentration was determined by spectrophotometric assay of chromophoric complex between the BP and copper (II) ions (63) or by high performance liquid chromatography (HPLC) (64). Lipid concentration was determined by Bartlett method (65). Stability of the liposomes was determined by examining drug leakage. Then 400 pL of liposomal formulations were centrifuged 

Liposomal size has a pivotal role in macrophage uptake as the size of the liposome increases, there is enhancement of liposome uptake by macrophages, as also reported by others previously (66,67). However, although the trend remains the same, the clearance of liposomes is affected to differing extents depending on the composition (75). 

Further support to the notion that liposomal BPs exert their effects systemically was achieved through the use of liposomes loaded with the fluorescent marker, Rhodamine, with or without a BP (52,69). Marked reduction of the fluorescent signal was observed in blood monocytes (as well as reduced number) and in the liver and spleen of LBP-treated animals. Fluorescent liposomes (FL) were detected in injured but not in intact arteries. FL coadministered with LBPs significantly reduced the fluorescent signal in the injured arterial wall. The inactivation of monocytes after systemic administration of LBPs results in reduction of tissue macrophages in the injured artery. Thus, the outcome of systemic administration was manifested as local treatment for the injured artery. 

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