Oral insulin--a perspective

Adsorptive exclusion of crystal violet dye using barium encapsulated alginate/carbon composites: characterization and adsorption modeling studies

The present study is devoted to the removal of crystal violet dye using the synthesized barium alginate/carbon composites abbreviated as BA (barium alginate), BAAC (barium alginate/activated carbon), BASC (barium alginate/starch carbon), and BASSC (barium alginate/starch carbon modified with CTAB). The adsorptive removal of crystal violet as a function of contact time, pH of solution, composite dose, initial dye concentration, and temperature was studied. The uptake of crystal violet (CV) dye for the composites was recorded in the range of 36 mg g-1 to 50 mg g-1 at pH 8.03 ± 0.03 for an equilibrium time of 120 min. The adsorption kinetics and isotherms in compliance with the CV sorption onto BA/carbon composites corroborated the utmost fit of pseudo-second-order and Freundlich isotherm models, respectively. The recycling process was achieved using the barium alginate-treated bead carbons for different initial CV dye concentrations of 10-30 mg L-1 with a scope of zero disposal. The practicability of BA/carbon composites in a groundwater sample spiked with 30 mg L-1 of CV was successfully achieved with a removal efficiency of about 65-74%. Characterization studies for the composites using FTIR, SEM (with EDS), XRD, TGA, and BET were carried out and discussed in the paper.

Development and cytotoxicity evaluation of multiple nanoemulsions for oral co-delivery of 5-fluorouracil and short chain triglycerides for colorectal cancer

Colorectal cancer (CRC) is the third most common cancer in the world, but current chemotherapy options are limited due to adverse effects and low oral bioavailability of drugs. In this study, we investigated the obtainment parameters and composition of new multiple nanoemulsions (MN) based on microemulsions for oral co-delivery of 5-fluorouracil (5FU) and short-chain triglycerides (SCT, either tributyrin or tripropionin). The area of microemulsion formation was increased from 14% to 38% when monocaprylin was mixed with tricaprylin as oil phase. Addition of SCT reduced this value to 24-26%. Using sodium alginate aqueous dispersion as internal aqueous phase (to avoid phase inversion) did not further affected the area but increased microemulsion viscosity by 1.5-fold. To obtain the MN, selected microemulsions were diluted in an external aqueous phase; droplet size was 500 nm and stability improved using polyoxyethylene (den Besten et al., 2013) oleyl ether at 1-2.5% as surfactant in the external phase and a dilution ratio of 1:1 (v/v). 5FU in vitro release could be better described by the Korsmeyer-Peppas model. No pronounced changes in droplet size were observed when selected MNs were incubated in buffers mimicking gastrointestinal fluids. The 5FU cytotoxicity in monolayer cell lines presenting various mutations was influenced by its incorporation in the nanocarrier, presence of SCT and cell mutation status. The MNs selected reduced the viability of tumor spheroids (employed as 3D tumor models) by 2.2-fold compared to 5FU solution and did not affect the survival of the G. mellonella, suggesting effectiveness and safety.

Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications

Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications.

Insulin Inclusion into a Tragacanth Hydrogel: An Oral Delivery System for Insulin

Nanoparticles or microparticles created by physical complexation between two polyelectrolytes may have a prospective use as an excipient for oral insulin administration. Natural polymers such as tragacanth, alginate, dextran, pullulan, hyaluronic acid, gelatin and chitosan can be potential candidates for this purpose. In this research, insulin particles were prepared by the inclusion of insulin into a tragacanth hydrogel. The effect of the pH and concentration relationship involving polyelectrolytes offering individual particle size and zeta potential was assessed by zetasizer and scanning electron microscopy (SEM). Insulin-tragacanth interactions at varying pH (3.7, 4.3, 4.6, or 6), and concentration (0.1%, 0.5%, or 1% w/w) were evaluated by differential scanning calorimetry (DSC) and ATR Fourier transform infrared (ATR-FTIR) analysis. Individual and smaller particles, approximately 800 nm, were acquired at pH 4.6 with 0.5% of tragacanth. The acid gelation test indicated that insulin could be entrapped in the physical hydrogel of tragacanth. DSC thermograms of insulin-tragacanth showed shifts on the same unloaded tragacanth peaks and suggested polyelectrolyte-protein interactions at a pH close to 4.3-4.6. FTIR spectra of tragacanth-insulin complexes exhibited amide absorption bands featuring in the protein spectra and revealed the creation of a new chemical substance.

Release of tissue inhibitor of metalloproteinase-2 from alginate microcapsule encapsulating genetically engineered cells

Background

In this study, 293T cells were genetically engineered to secrete tissue inhibitor of metalloproteinase-2 (TIMP2) and encapsulated into alginate microcapsules to continuously release TIMP2 protein.

Methods

The anti-invasive potential of the microcapsules was studied in vitro using brain tumor cells. The TIMP2 gene was transfected to 293T cells, and genetically engineered 293TIMP2 cells were encapsulated into alginate microcapsules. Release of TIMP2 protein was detected with Western blot analysis and the anti-invasive potential against U87MG cells was tested using gelatin zymography and a Matrigel assay.

Results

Cell viability within the alginate microcapsules was maintained at a cell density of 5 × 10⁶. Because polycationic polymers are helpful for maintaining the mechanical strength of microcapsules with good cell viability, the alginate microcapsules were reinforced with chitosan (0.1% w/v). Expression of TIMP2 protein in cell lysates and secretion of TIMP2 into the conditioned medium was confirmed by Western blot analysis. Alginate microcapsules encapsulating 293TIMP2 cells released TIMP2 protein into the medium efficiently, where the TIMP2 protein participated in degradation of the matrix metalloproteinase-2 enzyme and inhibited invasion of U87MG cells.

Conclusion

Alginate microcapsules encapsulating 293TIMP2 cells are promising candidates for anti-invasive treatment of glioma.

Facilitated nanoscale delivery of insulin across intestinal membrane models

The effect of nanoparticulate delivery system on enhancing insulin permeation through intestinal membrane was evaluated in different intestinal epithelial models using cell cultures and excised intestinal tissues. Multilayered nanoparticles were formulated by encapsulating insulin within a core consisting of alginate and dextran sulfate nucleating around calcium and binding to poloxamer, stabilized by chitosan, and subsequently coated with albumin. Insulin permeation through Caco-2 cell monolayer was enhanced 2.1-fold, facilitated by the nanoparticles compared with insulin alone, 3.7-fold through a mucus-secreting Caco-2/HT29 co-culture, and 3.9-fold through excised intestinal mucosa of Wistar rats. Correlation of Caco-2/HT29 co-culture cells with the animal-model intestinal membrane demonstrates that the mucus layer plays a significant role in determining the effectiveness of oral nanoformulations in delivering poorly absorbed drugs. Albumin was applied to the nanoparticles as outermost coat to protect insulin through shielding from proteolytic degradation. The effect of the albumin layering on insulin permeation was compared with albumin-free nanoparticles that mimic the result of albumin being enzymatically removed during gastric and intestinal transport. Results showed that albumin layering is important toward improving insulin transport across the intestinal membrane, possibly by stabilizing insulin in the intestinal conditions. Transcellular permeation was evidenced by internalization of independently labeled insulin and nanoparticles into enterocytes, in which insulin appeared to remain associated with the nanoparticles. Transcellular transport of insulin through rat intestinal mucosa may represent the predominant mechanism by which nanoparticles facilitate insulin permeation. Nanoformulations demonstrated biocompatibility with rat intestinal mucosa through determination of cell viability via monitoring of mitochondrial dehydrogenases. Insulin permeation facilitated by the biocompatible nanoparticles suggests a potential carrier system in delivering protein-based drugs by the oral route.

Systemic and mucosal delivery of drugs within polymeric microparticles produced by spray drying

Encapsulation of therapeutic and diagnostic materials into polymeric particles is a means to protect and control or target the release of active substances such as drugs, vaccines, and genetic material. In terms of mucosal delivery, polymeric encapsulation can be used to promote absorption of the active substance, while particles can improve the half-life of drugs administered systemically. Spray drying is an attractive technology used to produce such microparticles, because it combines both the encapsulation and drying steps in a rapid, single-step operation. Even so, spray drying is not classically associated with processes used for drug and therapeutic material encapsulation, since elevated temperatures could potentially denature the active substance. However, a comprehensive review of the literature revealed a number of studies demonstrating that spray drying can be used to produce microparticulate formulations with labile therapeutics. Polymers commonly employed include synthetics such as methacrylic copolymers and polyesters, and natural materials including chitosan and alginate. Drugs and active substances are diverse and included antibiotics, anti-inflammatory agents, and chemotherapeutics. Regarding the delivery of spray-dried particles, the pulmonary, oral, colonic, and nasal mucosal routes are often investigated because they offer a convenient means of administration, which promotes physician and patient compliance. In addition, spray drying has been widely used to produce polymeric microparticles for systemic delivery in order to control the delivery of drugs, vaccines, or genetic material that may exhibit poor pharmacokinetic profiles or pose toxicity concerns. This review presents a brief introduction to the technology of spray drying and outlines the delivery routes and the applications of spray-dried polymeric microparticles.

Nanoparticulate biopolymers deliver insulin orally eliciting pharmacological response

The aim of this study was to characterize and evaluate a novel oral insulin nanoparticulate system based on alginate-dextran sulfate core, complexed with a chitosan-polyethylene glycol-albumin shell. Insulin-loaded nanospheres (25, 50, 100 IU/kg) administered orally to diabetic rats reduced glycemia in a dose dependent manner. This effect lasted over 24 h with a maximal effect after 14 h. Nanospheres increased insulin plasma level and improved glycemic response to an oral glucose overload. After 4 days oral administration (50 IU/kg/day), the metabolic status of diabetic rats improved with a reduction in water intake, urine excretion and proteinuria. FITC-insulin-loaded nanospheres administered to an isolated intestinal loop were taken up by the intestinal mucosa. They strongly adhered to villus apical enterocytes and markedly labeled Peyer's patches. It is concluded that nanospheres preserve insulin and exert an antidiabetic effect after oral administration. This is explained by a protective effect against proteolytic enzymes by the albumin coating, by the mucoadhesive properties of chitosan-polyethylene glycol, and by the possibility of chitosan reversibly altering tight junctions leading to an improved absorption of insulin. This formulation demonstrates beneficial effects on diabetic symptoms and will be of interest in the treatment of diabetes with oral insulin.

Tricalcium Phosphate Delayed Release Formulation for Oral Delivery of Insulin: A Proof-of-Concept Study

Several attempts have been made for delivering insulin orally utilizing several polymers with varying degrees of effectiveness. A major obstacle associated with polymeric delivery system for protein or polypeptide drugs is the poor retention of the structure and its biological activity of encapsulated proteins particularly for the unstable insulin. Calcium phosphate ceramic is considered highly compatible to protein or peptide drugs, particularly insulin. Therefore, an attempt has been made to load insulin in tricalcium phosphate (TCP) microspheres and coat with pH sensitive polymer of methacrylate derivative, and to study the stability and conformational variations of loaded insulin, and finally the biological activity of the formulation in diabetic rats. TCP microspheres were prepared by a standard procedure. Human insulin was loaded in to these porous microspheres by diffusion filling and coated with Eudragit S100. This was subjected to in vitro release studies in simulated fluids and the stability and conformational variations of the released insulin were studied using photon correlation spectroscopy and circular dichroism (CD). Biological activity of the formulation was studied on induced diabetic rats. Insulin released in the intestinal fluid (SIF) maintained the native conformation without showing any aggregation. A dose dependent reduction of blood glucose level (BGL) was achieved in streptozotocin induced diabetic Wistar rats, demonstrating its biological activity. It has been established from this preliminary study that insulin loaded in to TCP microspheres is highly compatible with no degradation or loss of biological activity of loaded insulin. The TCP microsphere based delayed release formulation of insulin has effected a decrease in elevated glucose level in induced diabetic rats, establishing its feasibility towards the development of a noninvasive delivery device.

Molecular variants and derivatives of insulin for improved glycemic control in diabetes

Insulin is a historic molecule. It presents many first instances, such as the first protein to be fully sequenced, one of the first proteins to be crystallized in pure form, one among the early proteins whose structure was investigated using X-ray crystallography, the first protein to be chemically synthesized and the first Biotech drug. Therefore, the development of insulin in the early years is intricately intertwined with the progress in molecular and structural biology. In recent years, development of a range of insulin analogs has led to better control of glucose levels, thus preventing secondary complications and improving the quality of life in diabetic patients. Such analogs were obtained by modification of the native insulin sequence. They vary with regard to their pharmacokinetic profile, stability, tissue specificity and mode of administration. In addition, alterations involving incorporation of various chemical moieties in insulin and its co-crystallization with insoluble derivatives are used to modulate the time-action profile of the drug. This article traces the development of molecular variants and derivatives of insulin. It discusses future directions for further improvement in their properties to produce still better insulin therapeutics for tight glycemic control.

Release property of temperature-sensitive alginate beads containing poly(N-isopropylacrylamide)

The graft copolymer (APN) of alginate and poly(N-isopropylacrylamide) (PNIPAM) were synthesized and APN beads were prepared by dropping the aqueous solution of the copolymer into an aqueous solution of Ca(2+) solution. Alginate chains were employed to play a role in forming beads by electrostatic interactions with a multivalent ion, Ca(2+). Grafted PNIPAM segments were adopted to act as a valve for the pores of the beads, since they exhibit the properties of thermal contraction and expansion. The percent of release of blue dextran from APN beads was higher at 40 degrees C than at 25 degrees C. The difference in the release between two temperatures became more distinguishable when the content of PNIPAM in APN beads is higher. Below lower critical solution temperature (LCST), the expanded PNIPAM would close the pores of the beads, resulting in a lower release rate. Above LCST, the thermally contracted polymer would open the pores, resulting in a higher release rate. The percent of release from APN beads were investigated when the temperature of the release medium is altered. The release rate was relatively low at 25 degrees C. The temperature, however, changed up to 40 degrees C, a marked increase in the release rate was observed. These trends were found to be reproducible when the temperature was repeatedly altered between 25 and 40 degrees C. As a result, a stepwise response to the temperature alteration was obtained.

Development and in vivo evaluation of an oral insulin–PEG delivery system

Insulin-monomethoxypoly(ethylene glycol) derivatives were obtained by preparation of mono- and di-terbutyl carbonate insulin derivatives, reaction of available protein amino groups with activated 750 Da PEG and, finally, amino group de-protection. This procedure allowed for obtaining high yield of insulin-1PEG and insulin-2PEG. In vivo studies carried out by subcutaneous injection into diabetic mice demonstrated that the two bioconjugates maintained the native biological activity. In vitro, PEGylation was found to enhance the hormone stability towards proteases. After 1 h incubation with elastase, native insulin, insulin-1PEG and insulin-2PEG undergo about 70, 30 and 10% degradation, respectively, while in the presence of pepsin protein degradation was 100, 70 and 50%, respectively. The attachment of low molecular weight PEG did not significantly (P >0.05) alter insulin permeation behavior across the intestinal mucosa. Insulin-1PEG was formulated into mucoadhesive tablets constituted by the thiolated polymer poly(acrylic acid)-cysteine. The therapeutic agent was sustained released from these tablets within 5 h. In vivo, by oral administration to diabetic mice, the glucose levels were found to decrease of about 40% since the third hour from administration and the biological activity was maintained up to 30 h. According to these results, the combination of PEGylated insulin with a thiolated polymer used as drug carrier matrix might be a promising strategy for oral insulin administration.