Thermosensitive Drug Delivery System of Salmon Calcitonin: In Vitro Release, In Vivo Absorption, Bioactivity and Therapeutic Efficacies

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

Efficient aqueous remote loading of peptides in poly(lactic-co-glycolic acid)

Poly(lactic-co-glycolic acid) (PLGA) long-acting release depots are effective for extending the duration of action of peptide drugs. We describe efficient organic-solvent-free remote encapsulation based on the capacity of common uncapped PLGA to bind and absorb into the polymer phase net positively charged peptides from aqueous solution after short exposure at modest temperature. Leuprolide encapsulated by this approach in low-molecular-weight PLGA 75/25 microspheres slowly and continuously released peptide for over 56 days in vitro and suppressed testosterone production in rats in an equivalent manner as the 1-month Lupron Depot®. The technique is generalizable to encapsulate a number of net cationic peptides of various size, including octreotide, with competitive loading and encapsulation efficiencies to traditional methods. In certain cases, in vitro and in vivo performance of remote-loaded PLGA microspheres exceeded that relative to marketed products. Remote absorption encapsulation further removes the need for a critical organic solvent removal step after encapsulation, allowing for simple and cost-effective sterilization of the drug-free microspheres before encapsulation of the peptide.

Encapsulation of bioactive peptides in slow-release particles is complex and relies on organic solvents. Here, the authors absorb peptides in a polymer phase from water, creating a simple low-cost encapsulation process in a class of polymer depot.

Sulfated alginate based complex for sustained calcitonin delivery and enhanced osteogenesis

Direct medications of salmon calcitonin (sCT) through subcutaneous or intramuscular injection are limited for its low effeciency. Drug delivery systems with sustained delivery property and high bioactivity are imminently needed. In consideration of the clinic application, a cost-effective and effective carrier is demanded, which is still a challenge until now. In this study, a simple alginate/ alginate sulfate-sCT (Alg/AlgS-sCT) complex was succesfully constructed for sustained release of sCT. The negtively charged sulphate groups facilitate the bonding with sCT, which avoids the burst release of sCT and extends the release time up to 15 days (only 2 days for pure sCT). More importantly, the bioactivity of the released sCT is not affected during such long release time, suggesting a conformation similar to native sCT. In vitro analysis implies the biocompatibility of the complex. Moreover, the combination of AlgS and sCT synergistically impoved the osteogenic ability of MC3T3 cells, showing higher ALP level, intracellular and extracellular calcium ions concentrations. Note that the concentration of intracellular calcium ions displays 5.26 fold increments of control group after 10 days of incubation. We envision this simple yet effective system has potential applications in clinical trails and give inspiration for the design of other protein delivery system.

Mass spectrometry in bioresorbable polymer development, degradation and drug-release tracking

A detailed characterization of polymeric matrices and appropriate degradation monitoring techniques are required to sustain the development of new materials as well as to enlarge the applications of the old ones. In fact, polymer analysis is essential for the clarification of the intrinsic relationship between structure and properties that ascertains the industrial applications in diverse fields. In bioresorbable and biodegradable polymers, the role of analytical methods is dual since it is pointed both at the polymeric matrices and at degradation tracking. The structural architectures, the mechanical and morphological properties, and the degradation rate, are of outstanding importance for a specific application. In some cases, the complexity of the polymer structure, the processes of decomposition or the low concentration of the degradation products need the concurrent use of different complementary analytical techniques to give detailed information of the reactions taking place. Several analytical methods are used in bioresorbable polymer development and degradation tracking. Among them, mass spectrometry (MS) plays an essential role and it is used to refine polymer syntheses, for its high sensitivity, to highlight degradation mechanism by detecting compounds present in trace amounts, or to track the degradation product profile and to study drug release. In fact, elucidation of reaction mechanisms and polymer structure, attesting to the purity and detecting defects as well as residual catalysts, in biodegradable and bioresorbable polymers, requires sensitive analytical characterization methods that are essential in providing an assurance of safety, efficacy and quality. This review aims to provide an overview of the MS strategies used to support research and development of resorbable polymers as well as to investigate their degradation mechanisms. It is focused on the most significant studies concerning synthetic bioresorbable matrices (polylactide, polyglycolide and their copolymers, polyhydroxybutyrate, etc.), published in the last ten years.

Long-term glycemic control and prevention of diabetes complications in vivo using oleic acid-grafted-chitosan‑zinc-insulin complexes incorporated in thermosensitive copolymer

Daily injections for basal insulin therapy are far from ideal resulting in hypo/hyperglycemic episodes associated with fatal complications in type-1 diabetes patients. Here we report a delivery system that provides controlled release of insulin closely mimicking physiological basal insulin requirement for an extended period following a single subcutaneous injection. Stability of insulin was significantly improved by formation of zinc-insulin hexamers, further stabilized by electrostatic complex formation with chitosan polymer. Insulin complexes were homogenously incorporated into PLA-PEG-PLA, a biodegradable thermogel copolymer, that instantaneously forms a subcutaneous gel-depot following injection. Chitosan polymer was hydrophobically modified using oleic acid prior to complex formation with insulin to enable distribution of oleic acid-grafted-chitosan‑zinc-insulin complexes into the hydrophobic core of PLA-PEG-PLA thermogel-copolymer micelles. In vivo, daily administration of marketed long-acting insulin, glargine, resulted in fluctuating blood glucose levels between 91 and 443 mg/dL in type 1 diabetic rats. However, single administration of thermogel copolymeric formulation successfully demonstrated slow diffusion of insulin complexes maintaining peak-free basal insulin level of 21 mU/L for 91 days. Sustained release of basal insulin also correlated with efficient glycemic control (blood glucose <120 mg/dL), prevention of diabetic ketoacidosis and absence of cataract development, unlike other treatment groups. Moreover, there was no sign of inflammation, tissue damage, or collagen deposition around depot site, suggesting exceptional biocompatibility of the formulation for long-term use.

In Vitro and in Vivo Optimization of Phase Sensitive Smart Polymer for Controlled Delivery of Rivastigmine for Treatment of Alzheimer's Disease

PURPOSE

Alzheimer's disease is a neurodegenerative disorder, and most common form of dementia afflicting over 35 million people worldwide. Rivastigmine is a widely used therapeutic for ameliorating clinical manifestations of Alzheimer's disease. However, current treatments require frequent dosing either orally or via transdermal patch that lead to compliance issues and administration errors risking serious adverse effects. Our objective was to develop a smart polymer based delivery system for controlled release of rivastigmine over an extended period following a single subcutaneous injection.

METHODS

Rivastigmine release was optimized by tailoring critical factors including polymer concentration, polymer composition, drug concentration, solvent composition, and drug hydrophobicity (rivastigmine tartrate vs base). Optimized in vitro formulation was evaluated in vivo for safety and efficacy.

RESULTS

Formulation prepared using PLGA (50:50) at 5% w/v in 95:5 benzyl benzoate: benzoic acid demonstrated desirable controlled drug release characteristics in vitro. The formulation demonstrated sustained release of rivastigmine tartrate for 7 days in vivo with promising biocompatibility and acetylcholinesterase inhibition efficacy for 14 days.

CONCLUSION

The results exemplify an easily injectable controlled release formulation of rivastigmine prepared using phase-sensitive smart polymer. The optimized formulation significantly increases the dosing interval, and can potentially improve patient compliance as well as quality of life of patients living with Alzheimer's disease.

Smart Thermosensitive Copolymer Incorporating Chitosan-Zinc-Insulin Electrostatic Complexes for Controlled Delivery of Insulin: Effect of Chitosan Chain Length

This work was designed to optimize thermosensitive copolymeric depot-based system for delivering insulin at a controlled rate for a prolonged period following a single subcutaneous injection. Intrinsic ability of insulin to form hexamers in the presence of zinc and electrostatic complexes with chitosan (CS) were explored for improving stability and release characteristics of insulin through the copolymeric depot. CS-zinc-insulin complexes were prepared using CS of different chain lengths (5, 30, 50, 200 kDa). Effect of different chain lengths of CS on the thermal stability, binding constant, and release profile of insulin was determined. Increasing chain length of CS demonstrated increasing thermal stability of insulin. However, higher chain length of CS adversely affected the release profile of insulin. Hydrolytic degradation analysis showed rapid degradation of copolymer in formulation containing higher chain length of CS (200 kDa)-zinc-insulin complexes, implying formation of bigger pores and channels in copolymeric matrix during initial release in this system. However, formulation containing smaller chain length of CS (5 kDa)-zinc-insulin complexes demonstrated slow copolymer degradation and sustained insulin release profile. Additionally, CS-zinc-insulin complexes were effective in preserving stability of insulin during the entire duration of release and storage.

Improvements in chemical carriers of proteins and peptides

The successful intracellular delivery of biologically active proteins and peptides plays an important role for therapeutic applications. Indeed, protein/peptide delivery could overcome some problems of gene therapy, for example, controlling the expression levels and the integration of transgene into the host cell genome. Thus, protein/peptide drug delivery showed a promising and safe approach for treatment of cancer and infectious diseases. Due to the unique physical and chemical properties of proteins, their production (e.g., isolation, purification & formulation) and delivery represented significant challenges in pharmaceutical studies. Modification in the structural moieties of these protein/peptide drugs could improve their solubility, stability, crystallinity, lipophilicity, enzymatic susceptibility and targetability, and subsequently, therapies and cures against various diseases. Using the structural modification of protein/peptide, their delivery provided overall higher success rates including high specificity, high activity, bioreactivity and safety. Recently, biotechnological and pharmaceutical companies have tried to find novel techniques for the modifications and improve delivery systems/carriers. However, each carrier has its own benefits and drawbacks, and an appropriate carrier is often established by the physicochemical properties of protein or peptide, the ideal route of injection, and clinical characteristics of therapy. In this review, an attempt was made to give an overview on the chemical carriers for proteins and peptides as well as the recent advances in this field.

Controlled Delivery of Salmon Calcitonin Using Thermosensitive Triblock Copolymer Depot for Treatment of Osteoporosis

Osteoporosis is a common metabolic bone disorder associated with fragility and bone fracture. Worldwide, osteoporosis results in more than 8.9 million fractures annually. Additionally, steroid treatments can cause osteoporosis as a side effect. Salmon calcitonin (sCT) is injected daily for those on steroid treatments as a means to prevent and treat osteoporosis side effects. Frequent dosing is inconvenient, uncomfortable, and often leads to compliance issues. Our objective was to develop a monomethoxy poly(ethylene glycol) (mPEG) and poly-lactic-co-glycolic acid (PLGA) thermosensitive triblock copolymer (mPEG-PLGA-mPEG)-based controlled release delivery system at an increased lactide to glycolide ratio (3.5:1, 4.5:1, and 5:1) to deliver sCT in its active conformation in a controlled fashion for a prolonged period following a single subcutaneous injection. Increasing lactide to glycolide ratio increases hydrophobicity of the PLGA block, which slows degradation of copolymer, thereby prolonging release and reducing burst release. Proton nuclear magnetic resonance spectroscopy and gel permeation chromatography confirmed structural composition and polydispersity index, respectively. Critical micelle concentration of the copolymer was 25 μg/mL. The delivery system was biocompatible as determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability assay. Moreover, the copolymeric system maintained sCT in a conformationally stable form for the entire duration of storage and release.

Inhibition of the fibrillation of highly amyloidogenic human calcitonin by cucurbit[7]uril with improved bioactivity

Protein/peptide fibrillation is an important challenge for biotechnological drug development. Salmon calcitonin (sCT) is currently used in the clinical treatment of bone-related diseases such as osteoporosis and hypercalcemia, but it still has the risk of immune responses. Although human calcitonin (hCT) would be a better choice in terms of immunogenicity, it has a strong tendency to irreversibly aggregate in aqueous solutions and form long amyloid fibrils, which significantly reduces its bioavailability and therapeutic potency. Here, we demonstrate that cucurbit[7]uril (CB[7]) can inhibit hCT fibrillation by supramolecular interaction with its aromatic groups (affinity: Phe16 > Tyr12 > Phe19 > Phe22). The hCT-CB[7] complex exhibits low cytotoxicity, even promotes osteoblast proliferation and osteogenic capacity of MC3T3 cells. Meanwhile the hCT-CB[7] complexes shows higher bioactivity compared to hCT in reducing blood calcium levels in rats, and also decreases the immunogenicity of hCT. These results suggest that CB[7] has the potential to improve the therapeutic potency of amyloidogenic protein/peptide drugs such as hCT.

A Drug Carrier for Sustained Zero-Order Release of Peptide Therapeutics

Peptides have great potential as therapeutic agents, however, their clinic applications are severely hampered by their instability and short circulation half-life. Zero-order release carriers could not only extend the circulation lifetime of peptides, but also maintain the plasma drug level constant, and thus maximize their therapeutic efficacy and minimize their toxic effect. Here using PEGylated salmon calcitonin (PEG-sCT)/tannic acid (TA) film as an example, we demonstrated that hydrogen-bonded layer-by-layer films of a PEGylated peptide and a polyphenol could be a platform for zero-order peptide release. The films were fabricated under mild conditions. The second component, TA, is a natural product and presents potential therapeutic activities itself. Unlike common carriers, the new carrier releases the peptide via gradual disintegration of the film because of its dynamic nature. The release of PEG-sCT follows a perfect zero-order kinetics without initial burst release. In addition the release rate could be tuned via external stimuli, such as pH and temperature. When implanted in rats, the films could remain the plasma level of PEG-sCT constant over an extended period. Accordingly, the serum calcium level was reduced and maintained constant over the same period, suggesting an improved therapeutic efficacy of the released drug.

Supramolecular nanoparticles of calcitonin and dipeptide for long-term controlled release

Salmon calcitonin (sCT) is a therapeutic polypeptide drug widely used to treat bone diseases such as osteoporosis (more than 200 million patients all over the world). The half-life of sCT is very short (~1h), thus various delivery systems have been developed for sCT in order to avoid frequent injections. However, most delivery systems use polymeric materials, which may limit their applications in clinic formulations due to the biocompatibility issue. We observed that a very simple dipeptide (Asp-Phe, DF) was co-assembled with sCT into supramolecular nanoparticles. These nanoparticles can significantly prolong the acting time of sCT to beyond one month after just a single subcutaneous injection. The assembling and releasing mechanisms were thoroughly investigated by both in vitro and in vivo methods, as well as by molecular dynamics simulations. This work provides an alternative strategy of designing protein/peptide drug delivery systems with long-lasting therapeutic effects.

Novel delivery systems for improving the clinical use of peptides

Peptides have long been recognized as a promising group of therapeutic substances to treat various diseases. Delivery systems for peptides have been under development since the discovery of insulin for the treatment of diabetes. The challenge of using peptides as drugs arises from their poor bioavailability resulting from the low permeability of biological membranes and their instability. Currently, subcutaneous injection is clinically the most common administration route for peptides. This route is cost-effective and suitable for self-administration, and the development of appropriate dosing equipment has made performing the repeated injections relatively easy; however, only few clinical subcutaneous peptide delivery systems provide sustained peptide release. As a result, frequent injections are needed, which may cause discomfort and additional risks resulting from a poor administration technique. Controlled peptide delivery systems, able to provide required therapeutic plasma concentrations over an extended period, are needed to increase peptide safety and patient compliancy. In this review, we summarize the current peptidergic drugs, future developments, and parenteral peptide delivery systems. Special emphasis is given to porous silicon, a novel material in peptide delivery. Biodegradable and biocompatible porous silicon possesses some unique properties, such as the ability to carry exceptional high peptide payloads and to modify peptide release extensively. We have successfully developed porous silicon as a carrier material for improved parenteral peptide delivery. Nanotechnology, with its different delivery systems, will enable better use of peptides in several therapeutic applications in the near future.

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.

In vitro and in vivo characterisation of a novel peptide delivery system: amphiphilic polyelectrolyte-salmon calcitonin nanocomplexes

The cationic peptide, salmon calcitonin (sCT) was complexed with the cationic amphiphilic polyelectrolyte, poly(allyl)amine, grafted with palmitoyl and quaternary ammonium moieties at pH 5.0 and 7.4 to yield particulates (sCT-QPa). The complexes were approximately 200 nm in diameter, had zeta potentials ranging from +20 to +50 mV, and had narrow polydispersity indices (PDIs). Differential scanning calorimetry revealed the presence of an interaction between sCT and QPa in the complexes. Electron microscopy confirmed the zeta-size data and revealed a vesicular bilayer structure with an aqueous core. Tyrosine- and Nile red fluorescence indicated that the complexes retained gross physical stability for up to 7 days, but that the pH 5.0 complexes were more stable. The complexes were more resistant to peptidases, serum and liver homogenates compared to free sCT. In vitro bioactivity was measured by cAMP production in T47D cells and the complexes had EC50 values in the nM range. While free sCT was unable to generate cAMP following storage for 7 days, the complexes retained approximately 33% activity. When the complexes were injected intravenously to rats, free and complexed sCT (pH 5.0 and 7.4) but not QPa reduced serum calcium over 120 min. Free and complexed sCT but not QPa also reduced serum calcium over 240 min following intra-jejunal administration. In conclusion, sCT-QPa nanocomplexes that have been synthesised are stable, bioactive and resistant to a range of peptidases. These enhanced features suggest that they may have the potential for improved efficacy when formulated for injected and oral delivery.