Insulin microcrystal suspension as a long-acting formulation for pulmonary delivery

Biopharmaceutical drug delivery and phototherapy using protein crystals

Biopharmaceutical drugs, including proteins, peptides, and antibodies, are renowned for their high specificity and efficacy, fundamentally transforming disease treatment paradigms. However, their structural complexity presents challenges for their formulation and delivery. Protein crystals, characterized by high purity, high stability and a porous structure for biopharmaceutical drug encapsulation, providing a potential avenue for formulating and delivering biopharmaceutical drugs. There is increasing interest in engineering protein crystals to delivery biopharmaceutical drugs for biomedical applications. This review summarizes the recent advances in biopharmaceutical drug delivery and phototherapy using protein crystals. First, we evaluate the advantages of using protein crystals for biopharmaceutical drugs delivery. Next, we outline the strategies for in vitro and in vivo crystallization to prepare protein crystals. Importantly, the review highlights the advanced applications of protein crystals in biopharmaceutical drug delivery, tumor phototherapy, and other optical fields. Finally, it provides insights into future perspectives of biopharmaceutical drug delivery using protein crystals. This comprehensive review aims to provide effective insights into design of protein crystals to simplify biopharmaceutical drug delivery and improve disease treatment.

Polymorphic nanobody crystals as long-acting intravitreal therapy for wet age-related macular degeneration

Wet age-related macular degeneration (wet AMD) is the most common cause of blindness, and chronic intravitreal injection of anti-vascular endothelial growth factor (VEGF) proteins has been the dominant therapeutic approach. Less intravitreal injection and a prolonged inter-injection interval are the main drivers behind new wet AMD drug innovations. By rationally engineering the surface residues of a model anti-VEGF nanobody, we obtained a series of anti-VEGF nanobodies with identical protein structures and VEGF binding affinities, while drastically different crystallization propensities and crystal lattice structures. Among these nanobody crystals, the P212121 lattice appeared to be denser and released protein slower than the P1 lattice, while nanobody crystals embedding zinc coordination further slowed the protein release rate. The polymorphic protein crystals could be a potentially breakthrough strategy for chronic intravitreal administration of anti-VEGF proteins.

Reversible Morphological Control of Cholecystokinin Tetrapeptide Amyloid Assemblies as a Function of pH

Most amyloid assemblies are seen as irreversible and exhibit polymorphism because their assembly is kinetically controlled and different structures are trapped during the aggregation process. However, in the specific case of peptide hormones, formation of amyloid assemblies for storage purposes has been reported. This suggests a strict control of assembly and the ability to disassemble upon hormone secretion. In the present work, we have sought to test these assertions with a short peptide, the cholecystokinin (or gastrin) tetrapeptide (CCK-4), that has been found in both gastrointestinal tract and central nervous system, and whose sequence is shared by a large number of hormones. We have thus studied in vitro this peptide's self-assembling properties in dense phases at different pH levels, thus mimicking in vivo storage conditions. The solubility and morphology of the supramolecular assemblies have been shown to vary with the pH. At low pH, the tetrapeptide exhibits a low solubility and forms microcrystals. At higher pH levels, peptide solubility increases and above a high enough concentration, peptide monomers self-assemble into typical amyloid fibrils of 10-20 nm diameter. The physical network formed by these fibrils results in a birefringent hydrogel phase. Despite the different morphological features exhibited at different pH, structural analysis shows strong similarities. Both supramolecular assemblies-microcrystals and fibrils-are structured by β-sheets. We also show that all these morphologies are reversible and can be either dissolved or changed into one another by switching the pH. In addition, we demonstrate that a modification in the charge sequence of the peptide by amino acid mutation modifies its self-assembly properties. In conclusion, just as the CCK-4 sequence is the minimal sequence required for a complete biological activity at CCK_B receptors in the brain, it is also sufficient to form amyloid fibers whose properties can be related to hormone storage and release purposes in vivo.

Enhanced Hypoglycemic Activity Following Intratracheal Administration of Insulin Microcrystal Suspension with Injection Adjuvant

The pulmonary route appears to be the most attractive alternative for non-invasive systemic delivery of insulin. We have shown the feasibility of insulin microcrystals as a long-acting formulation for pulmonary delivery. In this study, we examined the effects of adjuvant for pulmonary formulations of insulin, such as protamine, zinc, and glycerol. In an in vivo experiment with rats, only zinc enhanced the hypoglycemic effect of insulin microcrystals, with 17% of minimum reductions in blood glucose (%MRBG) and a 44% decrement in the blood glucose level (D%9h).

Photolysis of recombinant human insulin in the solid state: formation of a dithiohemiacetal product at the C-terminal disulfide bond

PURPOSE

Exposure of protein pharmaceuticals to light can result in chemical and physical modifications, potentially leading to loss of potency, aggregation, and/or immunogenicity. To correlate these potential consequences with molecular changes, the nature of photoproducts and their mechanisms of formation must be characterized. The present study focuses on the photochemical degradation of insulin in the solid state.

METHODS

Solid insulin was characterized by solid-state NMR, polarized optical microscopy and scanning electron microscopy; various insulin preparations were exposed to UV light prior to product analysis by mass spectrometry.

RESULTS

UV-exposure of solid human insulin results in photodissociation of the C-terminal intrachain disulfide bond, leading to formation of a CysS(•) thiyl radical pair which ultimately disproportionates into thiol and thioaldehyde species. The high reactivity of the thioaldehyde and proximity to the thiol allow the formation of a dithiohemiacetal structure. Dithiohemiacetal is formed during the UV-exposure of both crystalline and amorphous insulin.

CONCLUSIONS

Dithiohemiacetals represent novel structures generated through the photochemical modification of disulfide bonds. This is the first time that such structure is identified during the photolysis of a protein in the solid state.

An in vivo experiment to improve pulmonary absorption of insulin using microbubbles

BACKGROUND

Gas-filled phospholipid-based ultrasonic microbubbles (PUMs) are widely used in diagnostic imaging. The micro- or nanoparticle size and the physiochemical nature of shell provide the potential for a new way to improve pulmonary absorption for peptides and proteins.

METHODS

Male Sprague-Dawley rats were fasted for 12 h. Then insulin solution and insulin-PUM mixture solution were administered by intratracheal instillation. The hypoglycemic effect was observed to evaluate insulin absorption after lung administration. Fluorescein isothiocyanate-dextran (molecular mass, 4 kDa) was used as the index of evaluating drug alveolar deposition and absorption by visualization techniques.

RESULTS

Administration of insulin solution containing PUMs significantly reduced the blood glucose levels of Sprague-Dawley rats, compared with administration of insulin-only solution. The minimum reductions of the blood glucose concentration produced by insulin solution containing PUMs and by an insulin-only solution reached 60.81% and 34.60% of the initial glucose levels, respectively, and their bioavailabilities relative to subcutaneous injection were 48.58% and 29.09%, respectively. Histopathological study of the lung showed no changes in the morphology of the pulmonary alveoli after administration to these drugs. Only a slight inflammatory cell infiltration in the alveoli could be found in some rats.

CONCLUSION

These results suggested that PUMs might be used as an effective way to improve pulmonary absorption for peptides and proteins.

Pharmacokinetics and pharmacodynamics of controlled release insulin loaded PLGA microcapsules using dry powder inhaler in diabetic rats

The pulmonary route is an alternative route of administration for the systemic delivery of peptide and proteins with short-half lives. A long-acting formulation of insulin was prepared by encapsulation of protein into respirable, biodegradable microcapsules prepared by an oil in oil emulsification/solvent evaporation method. Insulin-loaded PLGA microcapsules prepared as a dry powder inhaler formulation were administered via the pulmonary route to diabetic rats and serum insulin and glucose concentrations were monitored. Control treatments consisted of respirable spray-dried insulin (RSDI) powder administered by intratracheal insufflation, insulin-loaded PLGA microcapsules and NPH (long-acting) insulin administered by subcutaneous (SC) administration. Pharmacokinetic analysis demonstrated that insulin administered in PLGA microcapsules illustrated a sustained release profile which resulted in a longer mean residence time, 4 and 5 fold longer than those after pulmonary administration of RSDI and SC injection of NPH insulin, respectively. Accordingly, the hypoglycemic profile followed a stable and sustained pattern which remained constant between 10 and 48 h. Results of the in vitro experiments were in good agreement with those of in vivo studies. Bronchoalveolar lavage fluid analysis indicated that microcapsules administration did not increase the activities of lactate dehydrogenase and total protein. However, histological examination of the lung tissue indicated a minor but detectable effect on the normal physiology of the rat lung. These findings suggest that the encapsulation of peptides and proteins into PLGA microcapsules technique could be a promising controlled delivery system for pulmonary administration.

Pure insulin nanoparticle agglomerates for pulmonary delivery

Diabetes is a set of diseases characterized by defects in insulin utilization, either through autoimmune destruction of insulin-producing cells (Type I) or insulin resistance (Type II). Treatment options can include regular injections of insulin, which can be painful and inconvenient, often leading to low patient compliance. To overcome this problem, novel formulations of insulin are being investigated, such as inhaled aerosols. Sufficient deposition of powder in the peripheral lung to maximize systemic absorption requires precise control over particle size and density, with particles between 1 and 5 microm in aerodynamic diameter being within the respirable range. Insulin nanoparticles were produced by titrating insulin dissolved at low pH up to the pI of the native protein, and were then further processed into microparticles using solvent displacement. Particle size, crystallinity, dissolution properties, structural stability, and bulk powder density were characterized. We have demonstrated that pure drug insulin microparticles can be produced from nanosuspensions with minimal processing steps without excipients, and with suitable properties for deposition in the peripheral lung.

Recent challenges in insulin delivery systems: a review

Relatively, a large percentage of world population is affected by diabetes mellitus, out of which approximately 5-10% with type 1 diabetes while the remaining 90% with type 2. Insulin administration is essential for type 1 patients while it is required at later stage by the patients of type 2. Current insulin delivery systems are available as transdermal injections which may be considered as invasive. Several non-invasive approaches for insulin delivery are being pursued by pharmaceutical companies to reduce the pain, and hypoglycemic incidences associated with injections in order to improve patient compliance. While any new insulin delivery system requires health authorities' approval, to provide long term safety profile and insuring patients' acceptance. The inhalation delivery system Exubera((R)) has already become clinically available in the United States and Europe for patients with diabetes as non-invasive delivery system.

Controlling the release of proteins/peptides via the pulmonary route

The inhalation route is seen as the most promising non-invasive alternative for the delivery of proteins; however, the short duration of activity of drugs delivered via this route brought about by the activities of alveolar macrophages and mucociliary clearance means there is a need to develop controlled release system to prolong the activities of proteins delivered to the lung. Polymeric materials such as (D,L)-poly(lactic glycolic acid) (PLGA), chitosan and poly(ethylene glycol) (PEGs) have been used for controlled release of proteins. Other systems such as liposomes and microcrystallization have also proved effective. This chapter gives a more detailed understanding of these techniques and the manufacture of the delivery systems.

Engineering protein particles for pulmonary drug delivery

Pulmonary delivery of proteins requires particles for delivery to be in the aerodynamic size range 1-5 microm for deep lung deposition. However, the traditional particle size reduction technique of jet-milling normally used for inhalation is not suitable for processing these protein particles because of their lability brought about by the weak physical interactions making up their higher order structures. Advanced techniques such as spray drying, spray freeze drying and the use of supercritical fluid technology have been developed to produce particles in the suitable size range and morphology for deep long deposition without altering the native conformation of these biomolecules. Judicious use of excipients and operating conditions are some of the factors needed for a successful particle design.

Current challenges in non-invasive insulin delivery systems: a comparative review

The quest to eliminate the needle from insulin delivery and to replace it with non- or less-invasive alternative routes has driven rigorous pharmaceutical research to replace the injectable forms of insulin. Recently, various approaches have been studied involving many strategies using various technologies that have shown success in delivering insulin, which are designed to overcome the inherent barriers for insulin uptake across the gastrointestinal tract, mucosal membranes and skin. This review examines some of the many attempts made to develop alternative, more convenient routes for insulin delivery to avoid existing long-term dependence on multiple subcutaneous injections and to improve the pharmacodynamic properties of insulin. In addition, this article concentrates on the successes in this new millennium in developing potential non-invasive technologies and devices, and on major new milestones in modern insulin delivery for the effective treatment of diabetes.

Sustained-release self-dissolving micropiles for percutaneous absorption of insulin in mice

Microparticles-adsorbed insulin and zinc insulin (PenfilN) were molded to self-dissolving micropiles (SDMPs) with chondroitin sulfate as the base for the percutaneous administration of insulin. Porous silicon dioxide (Sylysia 320, 440 and 730) and porous calcium silicate (FloriteRE) were used as microparticles. As a reference, insulin loaded SDMPs were prepared. SDMPs were percutaneously administered to mice at the insulin dose level of 2.5 IU/kg. After the insertion of SDMPs to mouse skin, blood samples were collected for 8 h and plasma glucose levels were measured. There were not significant differences on minimum plasma glucose levels between the test preparations. However, T(mins), the time when the minimum glucose level appeared were 1.5 +/- 0.2 h (Sylysia 320), 1.3 +/- 0.2 h (Sylysia 440), 1.6 +/- 0.4 h (Sylysia 730), 2.1 +/- 0.3 h (Florite) and 1.7 +/- 0.3 h (zinc insulin) which were greater than insulin SDMP, 0.8 +/- 0.1 h. In addition, greater hypoglycemic effects were observed with SDMPs containing adsorbent-insulin and/or zinc insulin than insulin SDMP. The mean AACs (area above the plasma glucose level vs. time curve) of SDMPs containing adsorbent-insulin and zinc insulin were 357.8% h for FloriteRE, 333.1% h for Sylysia 320, 308.1% h for Sylysia 440, 328.1% h for Sylysia 730, and 374.7% h for zinc insulin, respectively, which were about two folds higher than that of insulin SDMN, 161.2% h. Those results suggest the usefulness of SDMPs composed of adsorbent-insulin as a long-acting percutaneous insulin preparation.

Characterization of human insulin microcrystals and their absorption enhancement by protease inhibitors in rat lungs

Pulmonary route appears to be an attractive alternative as a non-invasive systemic delivery for peptide and protein drugs. An appropriate formulation, however, is important for increasing their bioavailability in lung. In this study, the human insulin microcrystals were produced. The particle size analysis and scanning electron microscopy (SEM) showed that the microcrystals were uniform and had a monodispersed size distribution (mean diameter = 0.95 microm) for pulmonary delivery. The physicochemical properties of the microcrystals developed were similar to those of the commercial crystalline powder in powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. The percentage of high molecular weight proteins (%HMWP), the percentage of other insulin related compounds (%OIRC) and the percentage of A-21 desamido insulin (%D) of the microcrystals were very low. In addition, the cytotoxicity of microcrystals developed and protease inhibitors (aprotinin, bacitracin and soybean-trypsin inhibitor) was investigated, and the enhancement of insulin absorption in the presence of these protease inhibitors at various concentrations was studied. The cell viability of A549 was over 80% at various concentrations of aprotinin and soybean-trypsin inhibitor, except for bacitracin (below 60%). The percent of decrease in blood glucose (D%) was 42.68+/-1.62% after intratracheal instillation of insulin microcrystals (5 U/kg). An enhancement of hypoglycemic effect with protease inhibitors was also found. Soybean-trypsin inhibitor (48.86+/-3.24% at 10 mg/ml; 55.78+/-0.71% at 5 mg/ml; 51.49+/-5.27% at 1 mg/ml) and aprotinin (52.57+/-8.78% at 10 mg/ml; 51.97+/-1.98% at 5 mg/ml; 56.90+/-3.42% at 1 mg/ml) were effective for absorption enhancement. These findings suggest that the use of insulin microcrystals and protease inhibitors would be useful to improve the hypoglycemic effect in pulmonary route.

Air-liquid interface (ALI) culture of human bronchial epithelial cell monolayers as an in vitro model for airway drug transport studies

Serially passaged normal human bronchial epithelial (NHBE) cell monolayers were established on Transwell inserts via an air-liquid interface (ALI) culture method. NHBE cells were seeded on polyester Transwell inserts, followed by an ALI culture from day 3, which resulted in peak TEER value of 766+/-154 Omegaxcm2 on the 8th day. Morphological characteristics were observed by light microscopy and SEM, while the formation of tight junctions was visualized by actin staining, and confirmed successful formation of a tight monolayer. The transepithelial permeability (Papp) of model drugs significantly increased with the increase of lipophilicity and showed a good linear relationship, which indicated that lipophilicity is an important factor in determining the Papp value. The expression of P-gp transporter in NHBE cell monolayers was confirmed by the significantly higher basolateral to apical permeability of rhodamine123 than that of reverse direction and RT-PCR of MDR1 mRNA. However, the symmetric transport of fexofenadine.HCl in this NHBE cell monolayers study seems to be due to the low expression of P-gp transporter and/or to its saturation with high concentration of fexofenadine.HCl. Thus, the development of tight junction and the expression of P-gp in the NHBE cell monolayers in this study imply that they could be a suitable in vitro model for evaluation of systemic drug absorption via airway delivery, and that they reflect in vivo condition better than P-gp over-expressed cell line models.

Particle Engineering for Pulmonary Drug Delivery

With the rapidly growing popularity and sophistication of inhalation therapy, there is an increasing demand for tailor-made inhalable drug particles capable of affording the most efficient delivery to the lungs and the most optimal therapeutic outcomes. To cope with this formulation demand, a wide variety of novel particle technologies have emerged over the past decade. The present review is intended to provide a critical account of the current goals and technologies of particle engineering for the development of pulmonary drug delivery systems. These technologies cover traditional micronization and powder blending, controlled solvent crystallization, spray drying, spray freeze drying, particle formation from liquid dispersion systems, supercritical fluid processing and particle coating. The merits and limitations of these technologies are discussed with reference to their applications to specific drug and/or excipient materials. The regulatory requirements applicable to particulate inhalation products are also reviewed briefly.

Particle engineering techniques for inhaled biopharmaceuticals

Formulation of biopharmaceuticals for pulmonary delivery is faced with the challenge of producing particles with the optimal properties for deep lung deposition without altering the native conformation of these molecules. Traditional techniques such as milling are continuously being improved while newer and more advanced techniques such as spray drying, spray freeze drying and supercritical fluid technology are being developed so as to optimize pulmonary delivery of biopharmaceuticals. While some of these techniques are quite promising, some are harsh and impracticable. Method scale up, cost-effectiveness and safety issues are important factors to be considered in the choice of a technique. This paper reviews the presently developed techniques for particle engineering biopharmaceuticals.

Prospects of formulating proteins/peptides as aerosols for pulmonary drug delivery

Formulation of proteins/peptides for therapeutic uses has often posed some challenges to drug formulators. The main problem is the relatively weak forces involved in the native conformation of these proteins and so making them quite labile. Furthermore, their susceptibility to proteolytic enzymes in the gut makes oral administration quite challenging. While various routes like, ocular, transdermal, nasal and buccal have been tried, none of these routes has proved to be a potential alternative to the invasive injection. However, various studies have been performed on the formulation of these proteins as aerosols for pulmonary delivery and promising results have been obtained. This article looks at the prospects of inhaled proteins as a delivery route for systemic activity.