Trypsin inhibition, calcium and zinc ion binding of starch-g-poly(acrylic acid) copolymers and starch/poly(acrylic acid) mixtures for peroral peptide drug delivery

Mechanical properties of starch esters at particle and compact level - Comparisons and exploration of the applicability of Hiestand's equation to predict tablet strength

Hydrophobic starch esters have potential as tablet matrix formers in controlled drug delivery. The mechanical properties of native starch (SN), starch acetate (SA) and starch propionate (SP) were studied at particle and compact level. Particle microhardness and modulus of elasticity were evaluated by nanoindentation. Force-displacement data of compressed powder were analyzed using Heckel in conjunction with piecewise regression, Kuentz-Leuenberger, Kawakita and Adams models, and yield pressure parameters were derived. Starches were characterized for chemical structure by Raman spectroscopy, crystallinity from powder x-ray diffraction (PXRD) patterns and surface energy from apparent contact angle measurements. A-type starch reflections were absent in the PXRDs of esters indicating greater amorphicity. Consequently, the particle microhardness of starch esters decreased leading to greater deformation during compaction and lower values of yield pressure parameters. These parameters increased with microhardness and ranked the starches in the order: SP < SA < SN. Fitting the experimental data into Hiestand's bonding index equation, a linear correlation (R² = 0.902) was established between experimental and calculated tablet strength describing results of all starches, when Adams (τ_ο') yield pressure was used as the 'effective compression pressure' in the above equation.

Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature

Thiolated polymers designated "thiomers" are obtained by covalent attachment of thiol functionalities on the polymeric backbone of polymers. In 1998 these polymers were first described as mucoadhesive and in situ gelling compounds forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins and crosslinking through inter- and intrachain disulfide bond formation. In the following, it was shown that thiomers are able to form disulfides with keratins and membrane-associated proteins exhibiting also cysteine-rich substructures. Furthermore, permeation enhancing, enzyme inhibiting and efflux pump inhibiting properties were demonstrated. Because of these capabilities thiomers are promising tools for drug delivery guaranteeing a strongly prolonged residence time as well as sustained release on mucosal membranes. Apart from that, thiomers are used as drugs per se. In particular, for treatment of dry eye syndrome various thiolated polymers are in development and a first product has already reached the market. Within this review an overview about the thiomer-technology and its potential for different applications is provided discussing especially the outcome of studies in non-rodent animal models and that of numerous clinical trials. Moreover, an overview on product developments is given.

Self-assembled insulin and nanogels polyelectrolyte complex (Ins/NGs-PEC) for oral insulin delivery: characterization, lyophilization and in-vivo evaluation

Introduction: Insulin is given by injection, because when administered orally, it would be destroyed by enzymes in the digestive system, hence only about 0.1% reaches blood circulation. The purpose of the present study was to use pH sensitive polyelectrolyte methyl methacrylate (MMA)/itaconic acid (IA) nanogels as carriers in an attempt to improve absorption of insulin administered orally.

Methods: Insulin (Ins) was incorporated into the MMA/IA nanogels (NGs) using the polyelectrolyte complexation (PEC) method to form Ins/NGs-PEC. Several parameters, including Ins:NGs ratio, pH, incubation time and stirring rate were optimized during preparation of InsNGs-PEC. The prepared formulations were characterized in terms of particle size (PS), polydispersity index (PdI), zeta potential (ZP) and percent entrapment efficiency (% EE).

Results: The optimized InF12 nanogels had a PS, PdI, ZP and %EE of 190.43 nm, 0.186, −16.70 mV and 85.20%, respectively. The InF12 nanogels were lyophilized in the presence of different concentrations of trehalose as cryoprotectant. The lyophilized InF12 containing 2%w/v trahalose (InF12-Tre2 nanogels) was chosen as final formulation which had a PS, PdI, ZP and %EE of 430.50 nm, 0.588, −16.50 mv and 82.10, respectively. The in vitro release of insulin from InF12-Tre2 nanogels in the SGF and SIF were 28.71% and 96.53%, respectively. The stability study conducted at 5±3°C for 3 months showed that lnF12-Tre2 nanogels were stable. The SDS-PAGE assay indicated that the primary structure of insulin in the lnF12-Tre2 nanogels was intact. The in-vivo study in the diabetic rats following oral administration of InF12-Tre2 nanogels at a dose of 100 IU/kg body weight reduced blood glucose level significantly to 51.10% after 6 hours compared to the control groups.

Conclusions: The pH sensitive MMA/IA nanogels are potential carriers for oral delivery of insulin as they enhanced the absorption of the drug.

Strategies for improving diabetic therapy via alternative administration routes that involve stimuli-responsive insulin-delivering systems

The encapsulation of insulin in micro- or nanodelivery systems may eliminate the need for frequent subcutaneous injections, improving the quality of life of diabetic patients. Formulations for oral, intranasal, pulmonary, subcutaneous, and transdermal administration have been developed. The use of stimuli-responsive polymeric carriers that can release the encapsulated drug in response to changes of the environmental stimuli or external activation enables the design of less invasive or non-invasive systems for smart insulin delivery from depots in the body. This article will look at strategies for the development of responsive delivery systems and the future meeting of the demands of new modes of insulin delivery.

Poly Methacrylic Acid-Alginate Semi-IPN Microparticles for Oral Delivery of Insulin: A Preliminary Investigation

Microparticles of Poly methacrylic acid (P1) and novel semi-interpenetrating network composed of Poly methacrylic acid-alginate (P2) were prepared and their application in oral insulin delivery was evaluated. The microparticles were characterized by scanning electron microscopy (SEM) for morphological studies. Insulin loading onto the microparticles was performed by the diffusion filling method and insulin encapsulated microparticles were subjected to in vitro release study in buffer solution of pH 1.2 and 7.4. The release kinetics at pH 7.4 exhibited sustained release of insulin for more than 5 h in case of PMAA microparticles whereas burst release of insulin (90% of total insulin loaded) within 1 h of study was observed in the case of PMAA-alginate microparticles. At pH 1.2, around 30% of insulin loaded was released from both microparticles within 2 h of study.

Adsorption of lead (II) ions onto novel cassava starch 5-choloromethyl-8-hydroxyquinoline polymer from an aqueous medium

Adsorption of lead (II) ions onto cassava starch 5-choloromethyl-8-hydroxyquinoline polymer (CSCMQ) was investigated with the variation in the parameters of pH, contact time, lead (II) ions concentration, temperature and the adsorbent dose. The Langmuir and Freundlich models have been applied. CSCMQ was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Results showed that the adsorption process was better described by the Langmuir model. Adsorption kinetics data obtained for the metal ions sorption were investigated using pseudo-first-order, pseudo-second-order and intraparticle diffusion model. The maximum adsorption capacities (qm) were 46.512, 43.859 and 42.735 mg/g at 25, 35 and 45 °C, respectively. The dynamical data fit well with the second-order kinetics model. The results indicate that CSCMQ could be employed as low-cost material for the adsorption of Pb(II) ions from aqueous medium.

Scale inhibitors with a hyper-branched structure: preparation, characterization and scale inhibition mechanism

In order to improve the scale inhibition efficiency of existing scale inhibitors for industrial water and to reduce the phosphorus pollution of water bodies, a new type of scale inhibitor with a hyper-branched structure has been developed.

Resistant starch as a carrier for oral colon-targeting drug matrix system

In this study, a novel tablet of protein drug matrix for colon targeting was developed using resistant starch as a carrier prepared by pre-gelatinization and cross-linking of starch. The effects of pre-gelatinization and cross-linking on the swelling and enzymatic degradation of maize starch as well as the release rate of drug from the matrix tablets were examined. Cross-linked pre-gelatinized maize starches were prepared by double modification of pre-gelatinization and cross-linked with POCl(3), and bovine serum albumin was used as a model drug. For in vitro drug release assays, the resistant starch matrix tablets were incubated in simulated gastric fluid, simulated intestinal fluid and simulated colonic fluid, respectively. The content of resistant starch and swelling property of maize starch were increased by pre-gelatinization and cross-linking, which retarded its enzymatic degradation. Drug release studies have shown that the matrix tablets of cross-linked pre-gelatinized maize starch could delivery the drug to the colon. These results indicate that the resistant starch carrier prepared by pre-gelatinization and cross-linking can be used for a potential drug delivery carrier for colon-targeting drug matrix delivery system.

The addition of calcium ions to starch/Carbopol mixtures enhances the nasal bioavailability of insulin

To evaluate the influence of calcium poly(acrylates) on the nasal absorption of insulin in rabbits, starch/poly(acrylic acid) (ratio 25/75) (SD 25/75) was neutralised with NaOH and/or Ca(OH)(2). After neutralisation, a mixture of sodium and/or calcium carboxylate was formed depending on the Ca(OH)(2) concentration in the formulation. IR spectroscopy confirmed that most of the calcium molecules in the formulation interacted with acid groups of the acrylic acid polymer. Addition of Ca(OH)(2) to aqueous dispersions containing starch/poly(acrylic acid) yielded powders with an enhanced absorption of insulin after nasal delivery to rabbits in comparison with the equivalent powder without Ca(OH)(2). A mixture of SD 25/75 and Ca(OH)(2) at a ratio of 90/10 neutralised to pH 7.4 with NaOH induced the highest absorption of insulin, obtaining a bioavailability of +/-29% (vs. 19% for an equivalent formulation without Ca(OH)(2)). This increase in nasal delivery was possibly due to a higher elasticity after dispersing this formulation in nasal fluid and to a higher water absorbing capacity. Furthermore, after nasal delivery of (SD 25/75)/Ca(OH)(2) 90/10, a decrease in t(max) was observed, possibly due to a progressive dissociation of Ca(2+)-ions after hydration of the powder resulting in the closing of the tight junctions.

Protective effect of Carbopol on enzymatic degradation of a peptide-like substrate. I: Effect of various concentrations and grades of Carbopol and other reaction variables on trypsin activity

The purpose of this study was to determine and compare the effect of various concentrations and grades of Carbopol on trypsin-induced degradation of a prototype substrate, N(alpha)-benzoyl-L-arginine ethyl ester hydrochloride (BAEE). Effect of other reaction variables, such as viscosity and ionic strength of the medium on the trypsin activity, was also analyzed simultaneously. Four concentrations and three commercially available grades of Carbopol were used. The effect of Carbopol was expressed in terms of change in the velocity of degradation reaction. A modified trypsin assay was developed and used for analysis. Up to a concentration of 0.35% w/v, Carbopol 934P showed a concentration-dependent increase in its ability to reduce the rate of enzymatic hydrolysis of BAEE. Similar inhibitory effect was observed with all three grades of Carbopol. The activity of trypsin was unaffected by other reaction variables, suggesting that interaction between the protein and the polymer could be the mechanism responsible for reduced trypsin activity. This study suggests that Carbopol can be a useful excipient for oral delivery of bioactive proteins and peptides, due to its ability to reduce the enzyme-induced degradation of these agents.

Preparation and characterization of pH sensitive comb-shaped chitosan material for the controlled release of coenzyme A

A novel kind of pH sensitive comb-shaped copolymer P(CS-Ma-PEGMA) was synthesized with chitosan (CS), maleic anhydride (Ma) and Poly (ethylene glycol) methacrylate (PEGMA) by grafting and co-polymerization. The structure of P(CS-Ma-PEGMA) was characterized by FT-IR and (1)H-NMR, and it was found that PEGMA was grafted onto CS and PEGMAylated chitosan was soluble. The copolymer was subjected to coenzyme A adsorption study in order to assess its application in biomedical area. The factors affecting release behavior, such as concentration and pH were discussed in this paper. The higher concentration of the copolymer showed higher absorbance peak than the lower one. The pH of the solution also had significant impact on the release of coenzyme A, and the mechanism of adsorption was suggested. The results suggested that the novel copolymer could be used as drug delivery carrier.

Preparation and characterization of temperature and pH-sensitive chitosan material and its controlled release on coenzyme A

A novel copolymer P(CS-Ma-DMAEMA) was synthesized with chitosan (CS), maleic anhydride (Ma) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) by grafting and copolymerization. The copolymer obtained was analyzed by FT-IR, (1)H NMR and UV, and the molecular weight and polydispersity were determined by gel permeation chromatography (GPC). The average size and distribution of copolymer micelles were determined by dynamic light scattering (DLS). Their aqueous solution properties and controlled coenzyme A delivery were also studied. It was found that the copolymer had temperature sensitivity and pH sensitivity. The factors affecting release behavior, such as concentration, pH and temperature were discussed in this paper. The higher concentration of the copolymer aqueous solution absorbed more coenzyme A than the lower one. The increasing temperature accelerated the drug release from the copolymer. The pH of the copolymer solution had significant impact on the release of coenzyme A. The results suggested that the novel copolymer could be used as drug delivery carrier.

In vitro evaluation of calcium binding capacity of chitosan and thiolated chitosan poly(isobutyl cyanoacrylate) core-shell nanoparticles

The ability of chitosan and its derivatives to bind cations is well known. Chitosan and thiolated chitosan were recently associated with poly(isobutyl cyanoacrylate) (PIBCA) nanoparticles leading to very promising results in terms of bioadhesion and permeation enhancement properties. Taking into account the influence that cations concentration have in the maintenance of both the permeation and the enzymatic barrier of the oral route, the possible cation binding capacity of these colloidal systems might be interesting in the use of these nanocarriers for the oral administration of pharmacologically active peptides. The aim of the present work was to in vitro evaluate the capacity of these colloidal systems to bind calcium, a model cation of physiological interest in the intestinal tract. The presence of chitosan on the nanoparticle surface importantly increased the calcium binding ability, in comparison to non-coated PIBCA nanoparticles. In addition, its presentation in the gel layer surrounding the nanoparticles, also beneficiated its binding capacity, obtaining 2-3 folds higher values when the polymer coated the nanoparticles than when it was in solution. The cross-linked structure observed for thiolated chitosan, due to the formation of inter- and intra-chain disulphide bonds, diminished the accessibility of cation to active sites of the polymer, decreasing the binding capacity of the calcium ion. However, when the amount of free thiol groups on the nanoparticle surface was high enough, the binding behaviour observed was higher than for nanoparticles elaborated with non-modified polymer.

Novel pH responsive polymethacrylic acid-chitosan-polyethylene glycol nanoparticles for oral peptide delivery

In present study, novel pH sensitive polymethacrylic acid-chitosan-polyethylene glycol (PCP) nanoparticles were prepared under mild aqueous conditions via polyelectrolyte complexation. Free radical polymerization of methacrylic acid (MAA) was carried out in presence of chitosan (CS) and polyethylene glycol (PEG) using a water-soluble initiator and particles were obtained spontaneously during polymerization without using organic solvents or surfactants/steric stabilizers. Dried particles were analyzed by scanning electron microscopy (SEM) and particles dispersed in phosphate buffer (pH 7.0) were visualized under transmission electron microscope (TEM). SEM studies indicated that PCP particles have an aggregated and irregular morphology, however, TEM revealed that these aggregated particles were composed of smaller fragments with size less than 1 micron. Insulin and bovine serum albumin (BSA) as model proteins were incorporated into the nanoparticles by diffusion filling method and their in vitro release characteristics were evaluated at pH 1.2 and 7.4. PCP nanoparticles exhibited good protein encapsulation efficiency and pH responsive release profile was observed under in vitro conditions. Trypsin inhibitory effect of these PCP nanoparticles was studied using casein substrate and these particles displayed lesser inhibitory effect than reference polymer carbopol. Preliminary investigation suggests that these particles can serve as good candidate for oral peptide delivery.

Controlling the mechanism of trypsin inhibition by the numbers of α-cyclodextrins and carboxyl groups in carboxyethylester-polyrotaxanes

Carboxyethylester-polyrotaxanes (CEE-polyrotaxanes) with the various number of CEE-modified alpha-cyclodextrins (CEE-alpha-CDs) were synthesized, and the effects of the number of CEE-alpha-CDs on calcium binding and trypsin inhibition were investigated. Calcium binding affinity was dependent on the density of the CEE groups accompanied with the number of alpha-CD threading in the CEE-polyrotaxanes. The high number of CEE-alpha-CDs leads to greater inhibition of trypsin activity than poly(acrylic acid), which is mainly due to the good calcium binding affinity. The CEE-polyrotaxane with the smallest number of CEE-alpha-CDs temporally interacted with trypsin, which was well correlated with the inhibition and recovery of trypsin activity. Therefore, the number of CEE-alpha-CDs in the CEE-polyrotaxanes can control the inhibition mechanism of trypsin activity.

Peroral absorption of octreotide in pigs formulated in delivery systems on the basis of superporous hydrogel polymers

PURPOSE

The aim of this study was to investigate the enhancement of peroral octreotide absorption using delivery systems based on superporous hydrogel (SPH) and SPH composite (SPHC) polymers.

METHODS

Six female pigs (BW of 23.5 kg) were used in this study. SPH-based delivery systems were made of two components: 1) a conveyor system made of SPH and SPHC; 2) a core that contained octreotide. The core was inserted into the conveyor system (core inside, c.i.) or attached to the surface of the conveyor system (core outside, c.o.). Four different peroral formulations were investigated: c.i., c.o., core outside including trimethyl chitosan chloride (c.o.t.), and octreotide only in the absence of any polymer (o.o.). All formulations were placed in enteric-coated gelatin capsules (size 000) and administered perorally. Intravenous administration was used to determine bioavailability (F) values. Blood samples taken from the cannulated jugular vein were analyzed by radioimmunoassay.

RESULTS

Peroral administration of 15 mg o.o. resulted in low F values of 1.0 +/- 0.6% (mean +/- SEM) whereas c.i. and c.o. administrations resulted in remarkably higher F values of 12.7 +/- 3.6% and 8.7 +/- 2.4%, respectively. By the addition of trimethyl chitosan chloride as an extra absorption enhancer to c.o.t., the highest bioavailability (16.1 +/- 3.3%) was achieved.

CONCLUSIONS

These novel delivery systems based on SPH and SPHC polymers are able to increase the peroral bioavailability of octreotide by mechanical fixation and increasing the retention of the dosage form at the absorption site.