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 1 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 1 mm diameter, 0.8 mm height and 1 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.