Abstract
It was the aim of this study to establish triglyceride matrices as potential carriers for long-term release of brain-derived neurotrophic factor (BDNF), a potential therapeutic for Huntington's disease. First, four different manufacturing strategies were investigated with lysozyme as a model substance: either lyophilized protein was mixed with lipid powder, or suspended in organic solution ...
Abstract
It was the aim of this study to establish triglyceride matrices as potential carriers for long-term release of brain-derived neurotrophic factor (BDNF), a potential therapeutic for Huntington's disease. First, four different manufacturing strategies were investigated with lysozyme as a model substance: either lyophilized protein was mixed with lipid powder, or suspended in organic solution thereof (s/o). Or else, an aqueous protein solution was dispersed by w/o emulsion in organic lipid solution. Alternatively, a PEG co-lyophilization was performed prior to dispersing solid protein microparticles in organic lipid solution. After removal of the solvent(s), the resulting powder formulations were compressed at 250 N to form mini-cylinders of 2 mm diameter, 2.2 mm height and 7 mg weight. Protein integrity after formulation and release was evaluated from an enzyme activity assay and SDS-PAGE. Confocal microscopy revealed that the resulting distribution of FITC-lysozyme within the matrices depended strongly on the manufacturing method, which had an important impact on matrix performance: matrices with a very fine and homogeneous protein distribution (PEG co-lyophilization) continually released protein for 2 months. The other methods did not guarantee a homogeneous distribution and either failed in sustaining release for more than I week (powder mixture), completely liberating the loading (s/o dispersion) or preserving protein activity during manufacturing (w/o emulsion, formation of aggregates and 25% activity loss). Based on these results, miniature-sized implants of I mm diameter, 0.8 mm height and I mg weight were successfully loaded by the PEG co-lyophilization method with 2% BDNF and 2% PEG. Release studies in phosphate buffer PH 7.4 at 4 and 37 degrees C revealed a controlled release of either 20 or 60% intact protein over one month as determined by ELISA. SDS-PAGE detected only minor aggregates in the matrix during release at higher temperature. In vivo evaluation of lipid cylinders in the striatum of rat brains revealed a biocompatibility comparable to silicone reference cylinders. (C) 2007 Elsevier B.V. All rights reserved.
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