Nanoparticles are not the only method to increase drug bioavailability. Another approach to reduce RES uptake and to overcome the BBB is the preparation of magnetic micro-spheres combined with the application of a magnetic field to the brain of rats after intracarotid injection . Two different types of microspheres of 1-2 |m diameter size were prepared: magnetic neutral dextran and cationic aminodex-tran microspheres. Both kinds of microspheres are prepared by an emulsification process using polysorbate 80 as the emulsifier. The magnetic particles were then injected into the carotid arteries of healthy rats and rats with implanted brain tumor (gliom-2/RG-2). A magnetic field was then applied to the brain. The rats were killed after 30 min and 6 h, and the magnetic particle concentration in the tissues was determined by atomic absorption spectroscopy. In healthy rats only low brain concentrations but high lung and spleen concentrations were found for both microspheres. In tumor-bearing rats, the brain concentration of magnetic cationic particles was increased compared with that of neutral particles. In general, these experiments with magnetic microspheres resulted in increased brain concentrations and decreased concentrations in peripheral organs, but did not show any significance because of the high variability among the groups.
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