Cholesterol and lecithin implants for sustained release of antigen: release and erosion in vitro, and antibody response in mice

Solid implantable devices for sustained drug delivery

Implantable drug delivery systems (IDDS) are an attractive alternative to conventional drug administration routes. Oral and injectable drug administration are the most common routes for drug delivery providing peaks of drug concentrations in blood after administration followed by concentration decay after a few hours. Therefore, constant drug administration is required to keep drug levels within the therapeutic window of the drug. Moreover, oral drug delivery presents alternative challenges due to drug degradation within the gastrointestinal tract or first pass metabolism. IDDS can be used to provide sustained drug delivery for prolonged periods of time. The use of this type of systems is especially interesting for the treatment of chronic conditions where patient adherence to conventional treatments can be challenging. These systems are normally used for systemic drug delivery. However, IDDS can be used for localised administration to maximise the amount of drug delivered within the active site while reducing systemic exposure. This review will cover current applications of IDDS focusing on the materials used to prepare this type of systems and the main therapeutic areas of application.

Co-Spray Dried Nafamostat Mesylate with Lecithin and Mannitol as Respirable Microparticles for Targeted Pulmonary Delivery: Pharmacokinetics and Lung Distribution in Rats

Coronavirus disease 2019 (COVID-19), caused by a new strain of coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is spreading rapidly worldwide. Nafamostat mesylate (NFM) suppresses transmembrane serine protease 2 and SARS-CoV-2 S protein-mediated fusion. In this study, pharmacokinetics and lung distribution of NFM, administered via intravenous and intratracheal routes, were determined using high performance liquid chromatography analysis of blood plasma, lung lumen using bronchoalveolar lavage fluid, and lung tissue. Intratracheal administration had higher drug delivery and longer residual time in the lung lumen and tissue, which are the main sites of action, than intravenous administration. We confirmed the effect of lecithin as a stabilizer through an ex vivo stability test. Lecithin acts as an inhibitor of carboxylesterase and delays NFM decomposition. We prepared inhalable microparticles with NFM, lecithin, and mannitol via the co-spray method. The formulation prepared using an NFM:lecithin:mannitol ratio of 1:1:100 had a small particle size and excellent aerodynamic performance. Spray dried microparticles containing NFM, lecithin, and mannitol (1:1:100) had the longest residual time in the lung tissue. In conclusion, NFM-inhalable microparticles were prepared and confirmed to be delivered into the respiratory tract, such as lung lumen and lung tissue, through in vitro and in vivo evaluations.

Vaccine implants: current status and recent advancements

Implants have long been used in the field of drug delivery as controlled release vehicles and are now being investigated as single-shot vaccine technologies. Implants have shown great promise, minimizing the need for multiple immunizations while stimulating potent immune responses with reduced doses of vaccine. Synchronous release of vaccine components from implants over an appropriate period of time is important in order to avoid issues including immune tolerance, sequestration or deletion. Traditionally, implants require surgical implantation and removal, which can be a barrier to their widespread use. Degradable and in situ implants are now being developed that can be administered using minimally invasive subcutaneous or intramuscular injection techniques. Injectable hydrogels remain the most commonly studied approach for sustained vaccine delivery due to their ease of administration and tunable degradation properties. Despite exciting advancements in the field of vaccine implants, few technologies have progressed to clinical trials. To increase the likelihood of clinical translation of vaccine implants, strategic testing of disease-relevant antigens in appropriate species is essential. In this review, the significance of vaccine implants and the different types of implants being developed to deliver vaccines are discussed.

Towards controlled release of BDNF — Manufacturing strategies for protein-loaded lipid implants and biocompatibility evaluation in the brain

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.

NIR spectroscopy—a non-destructive analytical tool for protein quantification within lipid implants

Lipid implants have been proposed as promising sustained release devices for the parenteral application of pharmaceutical proteins. Near infrared spectroscopy (NIRS) has been reported in the literature to be a non-destructive tool for drug quantification within controlled release matrix systems based on poly-(lactic-co-glycolic) acid (PLGA). The objective of this study was to evaluate the potential application of NIRS for protein content determination within lipid matrices containing stabilizing and release modifying additives. Bovine serum albumin (BSA) and rh-interferon alpha-2a (IFN alpha-2a) were initially lyophilized with trehalose and then blended with tristearin (matrix material) and optionally with polyethylene glygol 6000 (PEG, release modifier). Implants were prepared by compression. NIR transmittance spectra were measured on a NIRTab spectrometer. Partial least squares regression (PLSR) calibration models were developed to predict protein content in implants from the NIRS results. Additional samples were measured after performing release studies. It could be shown that NIRS allowed protein quantification in complex matrix systems with good accuracy after implant manufacture and during release studies [e.g., standard error of prediction (SEP) between 57 microg-176 microg]. In addition, small protein amounts down to 70 microg of incorporated protein per implant could be determined, thus demonstrating the low detection limit of NIRS.

Quil A–lipid powder formulations releasing ISCOMs and related colloidal stuctures upon hydration

The aim of the present study was to prepare solid Quil A-cholesterol-phospholipid formulations (as powder mixtures or compressed to pellets) by physical mixing or by freeze-drying of aqueous dispersions of these components in ratios that allow spontaneous formation of ISCOMs and other colloidal structures upon hydration. The effect of addition of excess cholesterol to the lipid mixtures on the release of a model antigen (PE-FITC-OVA) from the pellets was also investigated. Physical properties were evaluated by X-ray powder diffractometry (XPRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and polarized light microscopy (PLM). Characterization of aqueous colloidal dispersions was performed by negative staining transmission electron microscopy (TEM). Physically mixed powders (with or without PE-FITC-OVA) and pellets prepared from the same powders did not spontaneously form ISCOM matrices and related colloidal structures such as worm-like micelles, ring-like micelles, lipidic/layered structures and lamellae (hexagonal array of ring-like micelles) upon hydration as expected from the pseudo-ternary diagram for aqueous mixtures of Quil A, cholesterol and phospholipid. In contrast, spontaneous formation of the expected colloids was demonstrated for the freeze-dried lipid mixtures. Pellets prepared by compression of freeze-dried powders released PE-FITC-OVA slower than those prepared from physically mixed powders. TEM investigations revealed that the antigen was released in the form of colloidal particles (ISCOMs) from pellets prepared by compression of freeze-dried powders. The addition of excess cholesterol slowed down the release of antigen. The findings obtained in this study are important for the formulation of solid Quil A-containing lipid articles as controlled particulate adjuvant containing antigen delivery systems.

Melted glyceryl palmitostearate (GPS) pellets for protein delivery

Lysozyme was incorporated into glyceryl palmitostearate (GPS) pellets by compression and melting at loadings of 2, 5 and 10% (w/w). Released lysozyme from both compressed and melted pellets showed good retention of enzymatic activity (>80% active). The percentage lysozyme recovered during in vitro release experiments, over 120 h, was significantly lower from the melted pellets (<15%) compared with compressed pellets (71-85%). Scanning electron microscopy suggested this difference in release was due to differences in porosity of the compressed and melted pellets. Inclusion of hydrophilic components, PEG 4000 and Gelucire 50/13, in the melted matrices increased the percentage of lysozyme released in vitro. Lysozyme released from GPS/PEG 4000 matrices showed good retention of enzymatic activity (>88% active) while that from GPS/Gelucire 50/13 showed reduced activity (68 and 51% active). PEG 4000 was not completely miscible with GPS at the concentrations studied and heterogenous systems resulted. At a loading of 20-35% (w/w) PEG 4000 in GPS greater than 80% of the incorporated lysozyme was released, indicating the likely achievement of interconnecting hydrophilic channels throughout the GPS matrix. In conclusion, melted GPS demonstrated potential as a matrix for the controlled release of proteins and release rates could be modified by inclusion of hydrophilic components.

Biodegradable implants for the delivery of veterinary vaccines: design, manufacture and antibody responses in sheep

Biodegradable implants made from cholesterol and lecithin (C:L) were used to deliver a recombinant antigen (recombinant Dichelobacter nodosus pili) and adjuvant (Quil A) to sheep. Implants (5.5- x 1.8-mm) were placed subcutaneously and compared to a conventional vaccination regime (2 injections, 4 weeks apart) for antibody responses and tissue compatibility. Release profiles of antigen and adjuvant were also studied in vitro and in vivo. The presence of Quil A in vaccine implants had a marked effect on the rate at which antigen was released with 29 and 44% being released in the first 24 h from implants containing pili alone and pili with Quil A, respectively. Sheep produced significant levels of antibody when immunized with implants, however the response was short-lived and of significantly lower intensity than the response stimulated by two injections of antigen with Quil A (P < 0.01). A second implant system was developed where implants coated with C:L to delay antigen release, were used in combination with uncoated implants to deliver a priming dose and boosting dose of antigen. Antibody titres stimulated by the 4 double implant system were equivalent to those stimulated by a conventional regime of two injections (four weeks apart) for the first six weeks of the experiment. After this time, antibody levels in the groups which received implants dropped significantly. In vitro studies revealed that some of the implant coatings had caused a delay in the release of antigen (the rate of release peaked at 72 h), however this was not long enough to provide a significant boosting effect. In all cases, implants were well tolerated by sheep and caused less local reaction than injected vaccines.

The release of macromolecules from fatty acid matrices: complete factorial study of factors affecting release

A replicated complete factorial design to study the main effects and interactions of four factors: bovine serum albumin (BSA) particle size (Factor A); stearic acid particle size (Factor B); BSA loading (Factor C); and compression force (Factor D), on the release of BSA from compressed stearic acid pellets was performed in isotonic phosphate buffer pH 7.4 at 37 degrees C. Samples were withdrawn over 64 h. Analysis of variance of the percentage released at 64 h showed that A, B, and C, but not D, affected the release and the interactions AB, BC, ABC were highly significant. At low loading (5%), the surface release depended on BSA particle size. The release increased when BSA particle size was large. At high loading (20%), more release was shown when stearic acid particle size was large. More release with increasing BSA particle size occurred only when stearic acid particle size was small. It is proposed that release is due to the interconnected pore networks created, not only by BSA particles, but also by the void space between stearic acid particles. These void spaces vary according to particle size-dependent arrangements of stearic acid and BSA particles. An increase in the pellet thickness was observed probably due to the relaxation of compacted stearic acid particles.

Vaccines against blood-sucking arthropods

This paper provides selected personal insights on the development of vaccines against blood-sucking arthropods, with particular emphasis on vaccines against ticks. The emergence of novel or concealed antigens of haematophagous ectoparasites as candidate vaccine antigens is reviewed and the effect of feeding by the parasite on the expression of protective antigens is considered. The distribution of protective antigens through life cycle stages, the stage of the life cycle targeted by protective responses, and the nature of these responses, are commented on briefly. Concealed antigens of the gut, including the peritrophic membrane, and other internal organs, are evaluated for the role they play in induction of immunity artificially. Some of the work carried out to purify and characterise protective antigens of tick guts is described. A commentary is developed on vaccines that combine both "concealed" and "exposed" antigens. Some of the problems associated with the infestation and challenge of vaccinated hosts in the field are identified and the delivery of parasite antigens as vaccines that are both protective and "user-friendly" is emphasised as a major problem to be solved.