PEGylated insulin in PLGA microparticles. In vivo and in vitro analysis

A review of recent research and development on GLP-1 receptor agonists-sustained-release microspheres

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly used in treating type 2 diabetes (T2D). However, owing to their limited oral bioavailability, most commercially available GLP-1 RAs are administered through frequent subcutaneous injections, which may result in poor patient compliance during clinical treatment. To improve patients' compliance, sustained-release GLP-1 RA-loaded microspheres have been explored. This review is an overview of recent progress and research in GLP-1 RA-loaded microspheres. First, the fabrication methods of GLP-1 RA-loaded microspheres including the coacervation method, emulsion-solvent evaporation method based on agitation, premix membrane emulsification technology, spray drying, microfluidic droplet technology, and supercritical fluid technology are summarized. Next, the strategies for maintaining GLP-1 RAs' stability and activity in microspheres by adding additives and PEGylation are reviewed. Finally, the effect of particle size, drug distribution, the internal structure of microspheres, and the hydrogel/microsphere composite strategy on improved release behavior is summarized.

Development of an Insulin Nano-Delivery System through Buccal Administration

AIM

To develop a new nano-delivery system for insulin buccal administration.

BACKGROUND

Biodegradable polymeric nanoparticles (PNPs) had viewed countless breakthroughs in drug delivery systems. The main objective of PNPs application in delivering and carrying different promising drugs is to make sure that the drugs being delivered to their action sites. As a result maximizing the desired effect and overcoming their limitations and drawbacks.

OBJECTIVES

The main goals of this study were to produce an insulin consumable nano-delivery system for buccal administration and enhance the mucoadhesive effect in sustaining insulin release.

METHODS

Water in oil in water (W-O-W) microemulsion solvent evaporation technique was used for the preparation of nanoparticles consisting from positively charged poly (D, L-lactide-co-glycolide) coated with chitosan and loaded with insulin. Later, a consumable buccal film was prepared by the spin coating method and loaded with the previously prepared nanoparticles.

RESULTS

The newly prepared nanoparticle was assessed in terms of size, charge and surface morphology using a Scanning Electron Microscope (SEM), zeta potential, Atomic Force Microscope (AFM), and Fourier Transform Infra-red (FTIR) spectroscopy. An in-vitro investigation of the insulin release, from nanoparticles and buccal film, demonstrated controlled as well as sustained delivery over 6 hrs. The cumulative insulin release decreased to about (28.9%) with buccal film in comparing with the nanoparticle (50 %).

CONCLUSION

The buccal film added another barrier for insulin release. Therefore, the release was sustained.

Insulin Granule-Loaded MicroPlates for Modulating Blood Glucose Levels in Type-1 Diabetes

Type-1 diabetes (T1DM) is a chronic metabolic disorder resulting from the autoimmune destruction of β cells. The current standard of care requires multiple, daily injections of insulin and accurate monitoring of blood glucose levels (BGLs); in some cases, this results in diminished patient compliance and increased risk of hypoglycemia. Herein, we engineered hierarchically structured particles comprising a poly(lactic-co-glycolic) acid (PLGA) prismatic matrix, with a 20 × 20 μm base, encapsulating 200 nm insulin granules. Five configurations of these insulin-microPlates (INS-μPLs) were realized with different heights (5, 10, and 20 μm) and PLGA contents (10, 40, and, 60 mg). After detailed physicochemical and biopharmacological characterizations, the tissue-compliant 10H INS-μPL, realized with 10 mg of PLGA, presented the most effective release profile with ∼50% of the loaded insulin delivered at 4 weeks. In diabetic mice, a single 10H INS-μPL intraperitoneal deposition reduced BGLs to that of healthy mice within 1 h post-implantation (167.4 ± 49.0 vs 140.0 ± 9.2 mg/dL, respectively) and supported normoglycemic conditions for about 2 weeks. Furthermore, following the glucose challenge, diabetic mice implanted with 10H INS-μPL successfully regained glycemic control with a significant reduction in AUC_0-120min (799.9 ± 134.83 vs 2234.60 ± 82.72 mg/dL) and increased insulin levels at 7 days post-implantation (1.14 ± 0.11 vs 0.38 ± 0.02 ng/mL), as compared to untreated diabetic mice. Collectively, these results demonstrate that INS-μPLs are a promising platform for the treatment of T1DM to be further optimized with the integration of smart glucose sensors.

TRAIL therapy and prospective developments for cancer treatment

Tumor Necrosis Factor (TNF) Related Apoptosis-Inducing Ligand (TRAIL), an immune cytokine of TNF-family, has received much attention in late 1990s as a potential cancer therapeutics due to its selective ability to induce apoptosis in cancer cells. TRAIL binds to cell surface death receptors, TRAIL-R1 (DR4) and TRAIL-R2 (DR5) and facilitates formation of death-inducing signaling complex (DISC), eventually activating the p53-independent apoptotic cascade. This unique mechanism makes the TRAIL a potential anticancer therapeutic especially for p53-mutated tumors. However, recombinant human TRAIL protein (rhTRAIL) and TRAIL-R agonist monoclonal antibodies (mAb) failed to exert robust anticancer activities due to inherent and/or acquired resistance, poor pharmacokinetics and weak potencies for apoptosis induction. To get TRAIL back on track as a cancer therapeutic, multiple strategies including protein modification, combinatorial approach and TRAIL gene therapy are being extensively explored. These strategies aim to enhance the half-life and bioavailability of TRAIL and synergize with TRAIL action ultimately sensitizing the resistant and non-responsive cells. We summarize emerging strategies for enhanced TRAIL therapy in this review and cover a wide range of recent technologies that will provide impetus to rejuvenate the TRAIL therapeutics in the clinical realm.

Emerging Nano- and Micro-Technologies Used in the Treatment of Type-1 Diabetes

Type-1 diabetes is characterized by high blood glucose levels due to a failure of insulin secretion from beta cells within pancreatic islets. Current treatment strategies consist of multiple, daily injections of insulin or transplantation of either the whole pancreas or isolated pancreatic islets. While there are different forms of insulin with tunable pharmacokinetics (fast, intermediate, and long-acting), improper dosing continues to be a major limitation often leading to complications resulting from hyper- or hypo-glycemia. Glucose-responsive insulin delivery systems, consisting of a glucose sensor connected to an insulin infusion pump, have improved dosing but they still suffer from inaccurate feedback, biofouling and poor patient compliance. Islet transplantation is a promising strategy but requires multiple donors per patient and post-transplantation islet survival is impaired by inflammation and suboptimal revascularization. This review discusses how nano- and micro-technologies, as well as tissue engineering approaches, can overcome many of these challenges and help contribute to an artificial pancreas-like system.

The Stability Maintenance of Protein Drugs in Organic Coatings Based on Nanogels

Protein drugs are often loaded on scaffolds with organic coatings to realize a spatiotemporal controlled release. The stability or activity of protein drugs, however, is largely affected by the organic coating, particularly with organic solvents, which can dramatically reduce their delivery efficiency and limit their application scope. In spite of this, little attention has been paid to maintaining the stability of protein drugs in organic coatings, to date. Here, we used catalase as a model protein drug to exploit a kind of chemically cross-linked nanogel that can efficiently encapsulate protein drugs. The polymeric shells of nanogels can maintain the surface hydration shell to endow them with a protein protection ability against organic solvents. Furthermore, the protection efficiency of nanogels is higher when the polymeric shell is more hydrophilic. In addition, nanogels can be dispersed in polylactic acid (PLA) solution and subsequently coated on scaffolds to load catalase with high activity. To the best of our knowledge, this is the first use of hydrophilic nanogels as a protection niche to load protein drugs on scaffolds through an organic coating, potentially inspiring researchers to exploit new methods for protein drug loading.

Microparticles, microcapsules and microspheres: A review of recent developments and prospects for oral delivery of insulin

Diabetes mellitus is a chronic metabolic health disease affecting the homeostasis of blood sugar levels. However, subcutaneous injection of insulin can lead to patient non-compliance, discomfort, pain and local infection. Sub-micron sized drug delivery systems have gained attention in oral delivery of insulin for diabetes treatment. In most of the recent literature, the terms "microparticles" and "nanoparticle" refer to particles where the dimensions of the particle are measured in micrometers and nanometers respectively. For instance, insulin-loaded particles are defined as microparticles with size larger than 1 μm by most of the research groups. The size difference between nanoparticles and microparticles proffers numerous effects on the drug loading efficiency, aggregation, permeability across the biological membranes, cell entry and tissue retention. For instance, microparticulate drug delivery systems have demonstrated a number of advantages including protective effect against enzymatic degradation, enhancement of peptide stability, site-specific and controlled drug release. Compared to nanoparticulate drug delivery systems, microparticulate formulations can facilitate oral absorption of insulin by paracellular, transcellular and lymphatic routes. In this article, we review the current status of microparticles, microcapsules and microspheres for oral administration of insulin. A number of novel techniques including layer-by-layer coating, self-polymerisation of shell, nanocomposite microparticulate drug delivery system seem to be promising for enhancing the oral bioavailability of insulin. This review draws several conclusions for future directions and challenges to be addressed for optimising the properties of microparticulate drug formulations and enhancing their hypoglycaemic effects.

Ascorbate as a pro-oxidant: mild N-terminal modification with vinylboronic acids

We describe divergent reactivity of vinylboronic acids for protein modification. In addition to previously reported copper-catalyzed backbone N-H modification, ascorbate in air mediates N-terminal functionalization with the same vinylboronate reagents. This mild and selective aqueous reactivity enables selective single-modification of the B chain of human insulin.

Recent advances in testing of microsphere drug delivery systems

INTRODUCTION

This review discusses advances in the field of microsphere testing.

AREAS COVERED

In vitro release-testing methods such as sample and separate, dialysis membrane sacs and USP apparatus IV have been used for microspheres. Based on comparisons of these methods, USP apparatus IV is currently the method of choice. Accelerated in vitro release tests have been developed to shorten the testing time for quality control purposes. In vitro-in vivo correlations using real-time and accelerated release data have been developed, to minimize the need to conduct in vivo performance evaluation. Storage stability studies have been conducted to investigate the influence of various environmental factors on microsphere quality throughout the product shelf life. New tests such as the floating test and the in vitro wash-off test have been developed along with advancement in characterization techniques for other physico-chemical parameters such as particle size, drug content, and thermal properties.

EXPERT OPINION

Although significant developments have been made in microsphere release testing, there is still a lack of guidance in this area. Microsphere storage stability studies should be extended to include microspheres containing large molecules. An agreement needs to be reached on the use of particle sizing techniques to avoid inconsistent data. An approach needs to be developed to determine total moisture content of microspheres.

Polymeric nanoparticles and microparticles for the delivery of peptides, biologics, and soluble therapeutics

Biologically derived therapeutics, or biologics, are the most rapidly growing segment of the pharmaceutical marketplace. However, there are still unmet needs in improving the delivery of biologics. Injectable polymeric nanoparticles and microparticles capable of releasing proteins and peptides over time periods as long as weeks or months have been a major focus in the effort to decrease the frequency of administration. These particle systems fit broadly into two categories: those composed of hydrophilic and those composed of hydrophobic polymeric scaffolds. Here we review the factors that contribute to the slow and controlled release from each class of particle, as well as the effects of synthesis parameters and product design on the loading, encapsulation efficiency, biologic integrity, and release profile. Generally, hydrophilic scaffolds are ideal for large proteins while hydrophobic scaffolds are more appropriate for smaller biologics without secondary structure. Here we also introduce a Flash NanoPrecipitation method that has been adopted for encapsulating biologics in nanoparticles (40-200nm) at high loadings (50-75wt.%) and high encapsulation efficiencies. The hydrophilic gel interior and hydrophobic shell provide an opportunity to combine the best of both classes of injectable polymeric depots.

PEGylated apoptotic protein-loaded PLGA microspheres for cancer therapy

The aim of the current study was to investigate the antitumor potential of poly (D,L-lactic-co-glycolic acid) microspheres (PLGA MSs) containing polyethylene glycol (PEG)-conjugated (PEGylated) tumor necrosis factor–related apoptosis-inducing ligand (PEG-TRAIL). PEG-TRAIL PLGA MSs were prepared by using a water-in-oil-in-water double-emulsion method, and the apoptotic activities of supernatants released from the PLGA MSs at days 1, 3, and 7 were examined. The antitumor effect caused by PEG-TRAIL PLGA MSs was evaluated in pancreatic Mia Paca-2 cell-xenografted mice. PEG-TRAIL PLGA MS was found to be spherical and 14.4±1.06 μm in size, and its encapsulation efficiency was significantly greater than that of TRAIL MS (85.7%±4.1% vs 43.3%±10.9%, respectively). The PLGA MS gradually released PEG-TRAIL for 14 days, and the released PEG-TRAIL was shown to have clear apoptotic activity in Mia Paca-2 cells, whereas TRAIL released after 1 day had a negligible activity. Finally, PEG-TRAIL PLGA MS displayed remarkably greater antitumor efficacy than blank or TRAIL PLGA MS in Mia Paca-2 cell-xenografted mice in terms of tumor volume and weight, apparently due to increased stability and well-retained apoptotic activity of PEG-TRAIL in PLGA MS. We believe that this PLGA MS system, combined with PEG-TRAIL, should be considered a promising candidate for treating pancreatic cancer.

Novel drug delivery system: an immense hope for diabetics

CONTEXT

Existing medication systems for the treatment of diabetes mellitus (DM) are inconvenient and troublesome for effective and safe delivery of drugs to the specific site. Therefore, investigations are desired to deliver antidiabetics using novel delivery approaches followed by their commercialization.

OBJECTIVE

The present review aims to provide a compilation on the latest development in the field of novel drug delivery systems (NDDSs) for antidiabetics with special emphasis on particulate, vesicular and miscellaneous systems.

METHODS

Review of literature (restricted to English language only) was done using electronic databases like Pubmed® and Scirus, i.e. published during 2005-2013. The CIMS/MIMS India Medical Drug Information eBook was used regarding available marketed formulation of antidiabetic drugs. Keywords used were "nanoparticle", "microparticle", "liposomes", "niosomes", "transdermal systems", "insulin", "antidiabetic drugs" and "novel drug delivery systems". Single inclusion was made for one article. If in vivo study was not done then article was seldom included in the manuscript.

RESULTS

The curiosity to develop NDDSs of antidiabetic drugs with special attention to the nanoparticulate system followed by microparticulate and lipid-based system is found to emerge gradually to overcome the problems associated with the conventional dosage forms and to win the confidence of end users towards the higher acceptability.

CONCLUSION

In the current scientific panorama when the area of novel drug delivery system has been recognized for its palpable benefits, unique potential of providing physical stability, sustained and site-specific drug delivery for a scheduled period of time can open new vistas for precise, safe and quality treatment of DM.

Injectable controlled release depots for large molecules

Biodegradable, injectable depot formulations for long-term controlled drug release have improved therapy for a number of drug molecules and led to over a dozen highly successful pharmaceutical products. Until now, success has been limited to several small molecules and peptides, although remarkable improvements have been accomplished in some of these cases. For example, twice-a-year depot injections with leuprolide are available compared to the once-a-day injection of the solution dosage form. Injectable depots are typically prepared by encapsulation of the drug in poly(lactic-co-glycolic acid) (PLGA), a polymer that is used in children every day as a resorbable suture material, and therefore, highly biocompatible. PLGAs remain today as one of the few "real world" biodegradable synthetic biomaterials used in US FDA-approved parenteral long-acting-release (LAR) products. Despite their success, there remain critical barriers to the more widespread use of PLGA LARproducts, particularly for delivery of more peptides and other large molecular drugs, namely proteins. In this review, we describe key concepts in the development of injectable PLGA controlled-release depots for peptides and proteins, and then use this information to identify key issues impeding greater widespread use of PLGA depots for this class of drugs. Finally, we examine important approaches, particularly those developed in our research laboratory, toward overcoming these barriers to advance commercial LAR development.

Recent developments in protein and peptide parenteral delivery approaches

Discovery of insulin in the early 1900s initiated the research and development to improve the means of therapeutic protein delivery in patients. In the past decade, great emphasis has been placed on bringing protein and peptide therapeutics to market. Despite tremendous efforts, parenteral delivery still remains the major mode of administration for protein and peptide therapeutics. Other routes such as oral, nasal, pulmonary and buccal are considered more opportunistic rather than routine application. Improving biological half-life, stability and therapeutic efficacy is central to protein and peptide delivery. Several approaches have been tried in the past to improve protein and peptide in vitro/in vivo stability and performance. Approaches may be broadly categorized as chemical modification and colloidal delivery systems. In this review we have discussed various chemical approaches such as PEGylation, hyperglycosylation, mannosylation, and colloidal carriers including microparticles, nanoparticles, liposomes, carbon nanotubes and micelles for improving protein and peptide delivery. Recent developments on in situ thermosensitive gel-based protein and peptide delivery have also been described. This review summarizes recent developments on some currently existing approaches to improve stability, bioavailability and bioactivity of peptide and protein therapeutics following parenteral administration.

Supercritical fluid technology based large porous celecoxib-PLGA microparticles do not induce pulmonary fibrosis and sustain drug delivery and efficacy for several weeks following a single dose

Although pulmonary dosing of large porous particles has been shown to sustain drug delivery for a few days, there are no reports on safety or long term delivery. In this study we prepared large porous poly(lactide-co-glycolide) (PLGA) microparticles of celecoxib using supercritical fluid pressure-quench technology and demonstrated 4.8-, 15.7-, and 2.1-fold greater drug levels in lung, bronchoalveolar lavage fluid (BAL), and plasma compared to conventional microparticles on day 21 after a single intratracheal dosing of dry powders in A/J mice. Porous particle based delivery was 50.2-, 95.5-, and 7.7-fold higher compared to plain drug in the lung, BAL, and plasma, respectively. Toxicity of the formulations was assessed on day 21 following a fibrosis assessment protocol in A/J mice. There was no significant change in lactate dehydrogenase (LDH), total protein, and total cell counts in the BAL, and soluble collagen levels in the lung tissue following particle or drug treatments. Lung histology indicated no significant hyperplasia, granuloma, or collagen deposition in the treated groups. Chemopreventive potential of celecoxib porous particles was assessed in a benzo[a]pyrene (B[a]P) induced lung cancer model in A/J mice, on day 60 following a single intratracheal dose with or without single intravenous paclitaxel/carboplatin treatment. The combination group was more effective than individual groups, with the inhibition of tumor multiplicity and reduction of vascular endothelial growth factor in the BAL being 70 and 58%, respectively. Thus, large porous celecoxib-PLGA microparticles prepared using supercritical fluid technology exhibited sustained drug delivery and anti-tumor efficacy, without causing any significant toxicity.

Intestinal patches with an immobilized solid-in-oil formulation for oral protein delivery

Oral administration of biomolecular drugs such as peptides, proteins, and DNA is an attractive delivery method because of the safety and convenience of delivery in contrast to injection administration. However, oral delivery of biomolecules has several potential barriers such as enzymatic degradation in the gastrointestinal tract and low permeability across an intestinal membrane. In this study, we proposed an intestinal patch system that included surfactant-coated insulin for oral delivery. The intestinal patches, which have mucoadhesive and drug-impermeable layers, induced sustained unidirectional insulin release toward intestinal mucosa and inhibition of insulin leakage from the patches. Moreover, the surfactant-coated insulin, which has high compatibility with cell membranes, enhanced insulin transport across the intestinal membrane. This study demonstrates that the intestinal patches might improve protein permeability in the intestinal mucosa, thereby offering an innovative therapeutic strategy.

Effect of PLGA hydrophilia on the drug release and the hypoglucemic activity of different insulin-loaded PLGA microspheres

The effects of viscosity and hydrophilic characteristics of different PLGA polymers on the microencapsulation of insulin have been studied in vitro and in vivo after subcutaneous administration to hyperglycemic rats. Hydrophilic PLGA polymers produced a higher burst effect than the hydrophobic ones. Moreover, an incomplete insulin release was observed with the hydrophilic PLGA polymers in comparison with the hydrophobic ones. An explanation for that incomplete release can be the development of polymer-insulin interactions associated to the polymer hydrophilic/hydrophobic character, as detected by DSC analysis. Differences in the release rate of microsphere formulations lead to differences in the hypoglycemic action and the weight of animals. Hydrophobic PLGA was able to prolong the hypoglycemic action up to 4 weeks which is at least double than that obtained with hydrophilic PLGA of a similar viscosity. Comparing insulin microspheres with an immediate release formulation, microspheres can increase insulin relative bioavailability up to four times.

Optimizing the replacement of basal insulin in type 1 diabetes mellitus: no longer an elusive goal in the post-NPH era

In physiology, insulin is released continuously by the pancreas at a nearly constant rate between meals and in the fasting state (basal insulin secretion). The pivotal role of basal insulin is to restrain release of glucose from the liver and free fatty acids from adipose tissue, thus preventing hyperglycemia and ketosis. In type 1 diabetes mellitus (T1DM) (absolute insulin deficiency), the replacement of basal insulin is challenging because the currently available pharmacological preparations of long-acting insulin do not exactly reproduce the fine physiology of flat action profile of basal insulin of subjects without diabetes. NPH and NPH-based insulin mixtures no longer have a place in the treatment of T1DM because of their early peak effects and relatively short duration of action, which result into risk of nocturnal hypoglycemia and fasting hyperglycemia, respectively, after the evening injection. Only continuous subcutaneous (s.c.) insulin infusion (CSII) or long-acting analogs such as glargine (>24 h in duration, once a day) and detemir (<24 h in duration, once or more often twice a day) should be used as basal insulin in T1DM in combination with mealtime rapid-acting analogs. CSII and the long-acting analogs are nearly peakless and therefore reduce the risk for hypoglycemia (especially at night), blood glucose (BG) variability, and lower A1C with similar or less hypoglycemia. CSII is the "gold standard" of replacement of basal insulin because of better reproducibility of subcutaneous absorption of soluble insulin. Although CSII is not superior to multiple daily insulin injections in the general T1DM population, CSII might be indicated in subsets of T1DM (long-term T1DM with insulin "supersensitivity" and needs for low-dose insulin, some individuals with variable subcutaneous absorption of long-acting analogs) to minimize BG variability, reduce hypoglycemia, and benefit A1C.

PEGylation of interleukin-10 for the mitigation of enhanced pain states

The anti-inflammatory cytokine interleukin-10 (IL-10) shows promise for the treatment of neuropathic pain, but for IL-10 to be clinically useful as a short-term therapeutic its duration needs to be improved. In this study, IL-10 was covalently modified with polyethylene glycol (PEG) with the goal of stabilizing and increasing protein levels in the CSF to improve the efficacy of IL-10 for treating neuropathic pain. Two different PEGylation methods were explored in vitro to identify suitable PEGylated IL-10 products for subsequent in vivo testing. PEGylation of IL-10 by acylation yielded a highly PEGylated product with a 35-fold in vitro biological activity reduction. PEGylation of IL-10 by reductive amination yielded products with a minimal number of PEG molecules attached and in vitro biological activity reductions of approximately 3-fold. In vivo collections of cerebrospinal fluid after intrathecal administration demonstrated that 20 kDa PEG attachment to IL-10 increased the concentration of IL-10 in the cerebrospinal fluid over time. Relative to unmodified IL-10, the 20 kDa PEG-IL-10 product exhibited an increased therapeutic duration and magnitude in an animal model of neuropathic pain. This suggests that PEGylation is a viable strategy for the short-term treatment or, in conjunction with other approaches, the long-term treatment of enhanced pain states.

Central nervous system delivery of large molecules: challenges and new frontiers for intrathecally administered therapeutics

IMPORTANCE OF THE FIELD

Therapeutic proteins and DNA constructs offer promise for the treatment of central nervous system disorders, yet significant biological barriers limit the ability of these molecules to reach the central nervous system from the bloodstream. Direct administrations to the cerebrospinal fluid (intrathecal administration) comprise an emerging field to facilitate the efficient delivery of these biological macromolecules to central nervous system tissues.

AREAS COVERED IN THIS REVIEW

Previous reports from 1990 to the present time describing the interactions and turnover of the cerebrospinal fluid within the intrathecal space, characterizations of the effects that therapeutic proteins and DNA have shown after intrathecal delivery through a lumbar route, and reports of emerging technologies to address the limitations of intrathecally administered macromolecules are reviewed.

WHAT THE READER WILL GAIN

This review provides an overview of the limitations that must be overcome for intrathecally administered biological macromolecules and the recent advances and promising approaches for surmounting these limitations.

TAKE HOME MESSAGE

Emerging approaches that stabilize and sustain the delivery of intrathecally administered biological macromolecules may enhance substantially the clinical relevance of promising therapeutic proteins and DNA constructs for the treatment of various central nervous system disorders.

Preparation, characterization, and in vivo evaluation of insulin-loaded PLA-PEG microspheres for controlled parenteral drug delivery

AIM

The aim of this study was to prepare insulin-loaded poly(lactic acid)-polyethylene glycol microspheres that could control insulin release at least for 1 week and evaluate their in vivo performance in a streptozotocin-induced diabetic rat model.

METHODS

The microspheres were prepared using a water-in-oil-in-water double emulsion solvent evaporation technique. Different formulation variables influencing the yield, particle size, entrapment efficiency, and in vitro release profiles were investigated. The pharmacokinetic study of optimized formulation was performed with single dose in comparison with multiple dose of Humulin 30/70 as a reference product in streptozotocin-induced diabetic rats.

RESULTS

The optimized formulation of insulin microspheres was nonporous, smooth-surfaced, and spherical in structure under scanning electron microscope with a mean particle size of 3.07 microm and entrapment efficiency of 42.74% of the theoretical amount incorporated. The in vitro insulin release profiles was characterized by a bimodal behavior with an initial burst release because of the insulin adsorbed on the microsphere surface, followed by slower and continuous release corresponding to the insulin entrapped in polymer matrix.

CONCLUSIONS

The optimized formulation and reference were comparable in the extent of absorption. Consequently, these microspheres can be proposed as new controlled parenteral delivery system.

Development and in-vivo evaluation of insulin-loaded chitosan phthalate microspheres for oral delivery

Novel chitosan phthalate microspheres containing insulin were prepared by emulsion cross-linking technique. The feasibility of these microspheres as oral insulin delivery carriers was evaluated. The pH-responsive release behaviour of insulin from microspheres was analysed. The ability of chitosan phthalate-insulin microspheres to enhance intestinal absorption and improve the relative pharmacological availability of insulin was investigated by monitoring the plasma glucose and insulin level of streptozotocin-induced diabetic rats after oral administration of microspheres at insulin dose of 20 IU kg−1. In simulated gastric fluid (pH 2.0), insulin release from the microspheres was very slow. However, as the pH of the medium was changed to simulated intestinal fluid (pH 7.4), a rapid release of insulin occurred. The relative pharmacological efficacy for chitosan phthalate microspheres (18.66 ± 3.84%) was almost four-fold higher than the efficacy of the chitosan phthalate-insulin solution administration (4.08 ± 1.52%). Chitosan phthalate microspheres sustained the plasma glucose at pre-diabetic level for at least 16 h. These findings suggest that the microsphere is a promising carrier as oral insulin delivery system.

Poly(ethylene glycol)-modified proteins: implications for poly(lactide-co-glycolide)-based microsphere delivery

The reduced injection frequency and more nearly constant serum concentrations afforded by sustained release devices have been exploited for the chronic delivery of several therapeutic peptides via poly(lactide-co-glycolide) (PLG) microspheres. The clinical success of these formulations has motivated the exploration of similar depot systems for chronic protein delivery; however, this application has not been fully realized in practice. Problems with the delivery of unmodified proteins in PLG depot systems include high initial "burst" release and irreversible adsorption of protein to the biodegradable polymer. Further, protein activity may be lost due to the damaging effects of protein-interface and protein-surface interactions that occur during both microsphere formation and release. Several techniques are discussed in this review that may improve the performance of PLG depot delivery systems for proteins. One promising approach is the covalent attachment of poly(ethylene glycol) (PEG) to the protein prior to encapsulation in the PLG microspheres. The combination of the extended circulation time of PEGylated proteins and the shielding and potential stabilizing effects of the attached PEG may lead to improved release kinetics from PLG microsphere system and more complete release of the active conjugate.

Evaluation of Parenteral Depot Insulin Formulation using PLGA and PLA Microparticles

PLGA and PLA microparticles entrapping insulin are prepared by solvent evaporation method and are evaluated in diabetes-induced rat for its efficacy in maintaining blood sugar level from a single intramuscular dose. In vitro release of insulin from PLGA and PLA microparticles are 75.35 ± 1.73% and 67.536 ± 2.23%, respectively in 168 h (7 days). Released insulin from polymer particles are mostly in monomeric form without aggregation. Optimal use of stabilizers during particle formulation helps in reducing protein denaturation and thus results in stabilized insulin-loaded polymer particles. Intramuscular administration of insulin-loaded PLGA (50 : 50) and PLA microparticles (equivalent to 25 IU insulin/kg of animal weight) in alloxaninduced diabetic rats result in 53.86 ± 4.2% and 39.52 ± 6.7% reduction in blood glucose level, respectively in 96 h. This effect continued up to 7 days in case of PLGA and PLA microparticles.

Albinterferon alpha-2b: a genetic fusion protein for the treatment of chronic hepatitis C

Treatment regimens based on the use of interferon-alpha (IFN-alpha) remain the cornerstone of therapy for chronic hepatitis C virus infection, which affects nearly 170 million people worldwide. Treatment options include unmodified IFN-alpha given three times weekly or pegylated IFNs given once weekly. The albumin-fusion platform takes advantage of the long half-life of human albumin to provide a new treatment approach that allows the dosing frequency of IFN-alpha to be reduced in individuals with chronic hepatitis C. Albinterferon alpha-2b (alb-IFN), a recombinant polypeptide composed of IFN-alpha2b genetically fused to human albumin, has an extended half-life and early evidence indicates that it is efficacious and well tolerated. Pharmacodynamic modeling supports treatment with alb-IFN at 2- or 4-week intervals. Phase 3 registration trials are in progress. The albumin-fusion platform is currently being applied to other important bioactive peptides with short half-lives. These fusion proteins, which are at present in different phases of clinical development, might lead to improved therapies across a broad range of diseases.

PEGylated bioactive molecules in biodegradable polymer microparticles

Injectable peptide and oligonucleotide biotherapeutics offer great promise for treatment of serious chronic diseases but almost always need further formulation work to increase stability and circulation lifetimes. Covalent attachment of poly(ethylene glycol) (PEG) will increase circulation lifetimes up to a week or so and decrease degradation in favorable cases. Encapsulation in biodegradable polymer microparticles has been highly successful, mostly for peptides to provide sustained release up to several months after injection. Although products are on the market using these technologies, PEGylation and microparticle encapsulation each have drawbacks that prevent more widespread use. When they are combined, the limitations of one technology may be resolved by the other. Work in several laboratories on encapsulation of PEGylated bioactive molecules has revealed a synergy. Activity reduction and restricted circulation lifetimes for PEGylated bioactive agents is addressed by microencapsulation and using a lower PEG molecular weight. Chemical degradation, excessive burst release and limited drug content are typical problems for microparticles that are ameliorated by using PEGylated actives. The case for synergy between PEGylation and microencapsulation is illustrated in this review by work with several proteins and peptides including insulin, and the oligonucleotide therapeutic, pegaptanib.

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.

Peptide Drug Delivery Strategies for the Treatment of Diabetes

Drug delivery strategies for diabetes have included a wide range of scientific and engineering approaches, including molecular design, formulation and device design. Molecular engineering has resulted in modified pharmacokinetics, such as rapid-acting or slow-release analogs of insulin. Long-acting insulin formulations are designed to meet the body's basal needs, whereas rapid-acting insulin formulations are designed to cover mealtime glucose spikes. Furthermore, the discovery of new therapeutic biomolecules, which like insulin need to be injected, will drive the need for more flexible and universally applicable delivery systems. Formulation design, such as particle engineering, can be used to modify pharmacokinetic profiles. In general, suspension formulations of insulin commonly demonstrate reduced solubility and result in sustained release. Similarly, depot injections can result in precipitation of insulin at the site of injection, again resulting in lower solubility and sustained release. Particle engineering also has been applied to pulmonary formulations for delivery to the deep lung. The creation of novel drug delivery methods for the treatment of diabetes should remove barriers to insulin therapy and increase patient acceptance and compliance. Eliminating routine injections with needle-free injectors, insulin pumps, inhalation, buccal sprays, intra-nasal delivery, and transdermal patches may offer increasingly attractive alternatives.