BLOOD-BRAIN-BARRIER TRANSPORT OF LIPID MICROSPHERES CONTAINING CLINPROST, A PROSTAGLANDIN I-2 ANALOG

Because the permeability of the blood-brain barrier to lipid microsphe res (LMs) has not hitherto been demonstrated, blood-brain-barrier perm eability to LM containing the prostaglandin I-2 analogue clinprost has been evaluated for an in-vitro system of primary cultured monolayers of bovine brain capillary endothelial cells (BCECs), by a capillary de pletion study in rats and by an in-situ brain perfusion study in norma l and 4-vessel-occluded fore brain ischaemic rats. Although energy-dep endency was not observed in [H-3]clinprost uptake by BCECs, in accorda nce with results for simple diffusional transport, uptake of [H-3]clin prost contained in lipid microspheres (denoted [H-3]clinprost(LM)) was significantly inhibited by the endocytosis inhibitor, dansylcadaverin e. The transport of LM into BCECs by endocytosis was also confirmed by fluorescence microscopy and flow-cytometric analysis using LM labelle d with a fluorescent probe, -dioctadecyl-3,3,3',3'-tetramethylindocarb ocyanine perchlorate (DiI) The absolute uptake of DiI(LM) by BCECs, me asured by HPLC, was, however, almost 1/10 that of [H-3]clinprost(LM), results which suggest the superiority of simple diffusion of clinprost over endocytosis of its LM form in the uptake of clinprost(LM) by BCE Cs. In the capillary-depletion study with rat-brain-perfused [H-3]clin prost(LM) from the internal carotid artery, the parenchyma apparent di stribution volume was about 45 times larger than that of the capillary , showing that [H-3]clinprost(LM) was transported through the blood-br ain barrier into the brain. The permeability coefficients of [H-3]clin prost and [H-3]clinprost(LM) determined by insitu brain perfusion in n ormal rats were considerably higher than those of the active metabolit e [H-3]isocarbacyclin and its LM form. In addition, the Blood-brain-ba rrier permeabilities to [H-3]clinprost, [H-3]isocarbacyclin and their LM forms in ischaemic rats were almost identical to those in normal ra ts. It was concluded that clinprost(LM) was transported through the bl ood-brain barrier by endocytosis of LM, simple diffusion of clinprost released from LM, and transport of isocarbacyclin generated by hydroly sis of clinprost. The blood-brain-barrier permeability of clinprost(LM ) is not reduced in ischaemic conditions, because the simple diffusion of clinprost released from LM contributed mainly to clinprost(LM) tra nsport.