C.-M. Lehr

The potential of mucoadhesive polymers in enhancing intestinal peptide drug absorption. III: Effects of chitosan-glutamate and carbomer on epithelial tight junctions in vitro

Two mucoadhesive polymers, chitosan-glutamate and carbomer, were studied in an in vitro model (Caco-2 cell monolayers) with respect to their ability to enhance intestinal peptide drug delivery. Preparations of the polymers at concentrations of 0.5, 1.0, and 1.5% w/v (chitosan), and of 0.5 and 1.0% w/v (carbomer) were applied to the apical side of Caco-2 cell monolayers. The effects on transepithelial electrical resistance (TEER), paracellular transport of a FITC-dextran of a molecular weight of 4400 (FD-4) and [14C]mannitol were measured. Paracellular transport of FD-4 was visualized by means of confocal laser scanning microscopy (CLSM). Furthermore, the impact of lowering the pH of the polymer solutions to pH 4 on the integrity of the cell layer was determined. The results show that both polymers were able to decrease TEER of Caco-2 cell layers significantly. In the case of carbomer, CLSM revealed a partial opening of epithelial tight junctions. Lowering of the pH in the control and polymer solutions to pH 4 resulted in every case in the irreversible damage of a large percentage of the cells, as shown by CLSM. Transport studies with [14C]mannitol and FD-4 showed only during co-application of carbomer significantly increased fluxes, whereas no difference from the control solution could be detected for chitosan-glutamate. A threshold value of about 50% of TEER reduction has been identified, which allows for transport of hydrophilic compounds across the cell monolayers of the Caco-2 cell model.

Mucoadhesive Polymers in Peroral Peptide Drug Delivery. II. Carbomer and Polycarbophil Are Potent Inhibitors of the Intestinal Proteolytic Enzyme Trypsin

AbstractPurpose. The evaluation of the inhibitory action of two mucoadhesive poly(acrylates), polycarbophil and carbomer, registered by the Food and Drug Administration (FDA), on the intestinal proteolytic enzyme trypsin. Methods. The effect of the polymers on trypsin activity by measuring the degradation of a trypsin specific substrate. Binding of Ca2+ ions and proteins (125I-BSA) to the poly(acrylates). The influence of the polymers on the secondary trypsin structure by circular dichroism. Results. Trypsin inhibition was found to be time-dependent upon addition of Ca2+ in the degradation experiment. Only when Ca2+ was added within 10 min after trypsin incubation, recovery of the enzyme could be observed. Both polymers showed a strong Ca2+ binding ability. Carbomer, which had a higher inhibitory effect on trypsin activity, also revealed a higher Ca2+ binding affinity than polycarbophil. The amount of Ca2+ depleted out of the trypsin structure and the reduction of enzyme activity were comparable. Immobilization of trypsin by binding to the polymers could not be observed at pH 6.7. Circular dichroism studies suggested that, under depletion of Ca2+ from trypsin, the secondary structure changed its conformation, followed by an increased autodegradation of the enzyme. Conclusions. The poly(acrylates) investigated may have potential to protect peptides from tryptic degradation and may be used to master the peroral delivery of peptide drugs.

Nanocarriers for optimizing the balance between interfollicular permeation and follicular uptake of topically applied clobetasol to minimize adverse effects.

The treatment of various hair disorders has become a central focus of good dermatologic patient care as it affects men and women all over the world. For many inflammatory-based scalp diseases, glucocorticoids are an essential part of treatment, even though they are known to cause systemic as well as local adverse effects when applied topically. Therefore, efficient targeting and avoidance of these side effects are of utmost importance. Optimizing the balance between drug release, interfollicular permeation, and follicular uptake may allow minimizing these adverse events and simultaneously improve drug delivery, given that one succeeds in targeting a sustained release formulation to the hair follicle. To test this hypothesis, three types of polymeric nanocarriers (nanospheres, nanocapsules, lipid-core nanocapsules) for the potent glucocorticoid clobetasol propionate (CP) were prepared. They all exhibited a sustained release of drug, as was desired. The particles were formulated as a dispersion and hydrogel and (partially) labeled with Rhodamin B for quantification purposes. Follicular uptake was investigated using the Differential Stripping method and was found highest for nanocapsules in dispersion after application of massage. Moreover, the active ingredient (CP) as well as the nanocarrier (Rhodamin B labeled polymer) recovered in the hair follicle were measured simultaneously, revealing an equivalent uptake of both. In contrast, only negligible amounts of CP could be detected in the hair follicle when applied as free drug in solution or hydrogel, regardless of any massage. Skin permeation experiments using heat-separated human epidermis mounted in Franz Diffusion cells revealed equivalent reduced transdermal permeability for all nanocarriers in comparison to application of the free drug. Combining these results, nanocapsules formulated as an aqueous dispersion and applied by massage appeare to be a good candidate to maximize follicular targeting and minimize drug penetration into the interfollicular epidermis. We conclude that such nanotechnology-based formulations provide a viable strategy for more efficient drug delivery to the hair follicle. Moreover, they present a way to minimize adverse effects of potent glucocorticoids by releasing the drug in a controlled manner and simultaneously decreasing interfollicular permeation, offering an advantage over conventional formulations for inflammatory-based skin/scalp diseases.

Cyclodextrin-based star polymers as a versatile platform for nanochemotherapeutics: Enhanced entrapment and uptake of idarubicin.

A series of cyclodextrin-based star polymers were synthesized using β-cyclodextrin (CD) as hydrophilic core, methyl methacrylate (MMA) and tert-butyl acrylate (tBA) as hydrophobic arms. Star polymers, either homopolymers or random/block copolymers, showed narrow molecular weight distributions. Grafting hydrophobic arms created CD-based nanoparticles (CD-NPs) in the size range (130-200nm) with narrow PdI <0.15 and slightly negative ζ-potential. Particle surface could be modified with chitosan to impart a positive surface charge. Colloidal stability of CD-NPs was a function of pH as revealed by the pH-titration curves. CD-NPs were used as carrier for the chemotherapeutic drug idarubicin (encapsulation efficiency, EE ∼40%) ensuring prolonged release profile (∼80% after 48h). For cell-based studies, coumarin-6 was encapsulated as a fluorescent marker (EE ∼75%). Uptake studies carried out on A549 and Caco-2 cell lines proved the uptake of coumarin-loaded NPs as a function of time and preferential localization in the cytoplasm. Uptake kinetics revealed no saturation or plateau over 6h. Chitosan-modified NPs showed significantly improved, concentration-dependent cellular uptake. Meanwhile, CD-NPs were non-cytotoxic on both cell lines over the concentration range (0.25-3mg/ml) as studied by MTT and LDH assays. In conclusion, CD star polymers can be considered a versatile platform for a new class of biocompatible nanochemotherapy.

Enhanced uptake and siRNA-mediated knockdown of a biologically relevant gene using cyclodextrin polyrotaxane

Ideal cationic polymers for siRNA delivery could result in its enhanced cellular internalization, escape from endosomal degradation, and rapid release in cell cytoplasm, to facilitate knockdown of the target gene. In this study, we have investigated the ability of an in-house synthesized cationic polyrotaxane to bind siRNA into nanometric complexes. This polymer, which had earlier shown improved transfection of model siRNA (luciferase), was used to improve the cellular internalization of the siRNA molecule with therapeutic implications. In cellular assays, the polymer enhanced the knockdown of a gene involved in the pathogenesis of tuberculosis, when the nanocomplexes were compared with free siRNA. The efficacy and cellular non-toxicity of this polymer encourage its further exploitation in animal models of tuberculosis and other intracellular bacterial infections.

Preparation of nanosized coacervates of positive and negative starch derivatives intended for pulmonary delivery of proteins

Proteins and peptides represent a large fraction of the compounds currently in drug development pipelines. Their application however often depends on the use of carrier systems. Nanoparticles (NPs) are widely used such carrier systems for protein delivery. The aim of this study was to design a new drug delivery system (DDS), prepared under mild conditions in aqueous solution without the requirement of a stabilizer. The biodegradability and biocompatibility of the designed system was explored with a view to specifically determine its potential to facilitate the pulmonary delivery of proteins. As a first step, anionic and cationic water soluble starch-derivatives were synthesized. These starch polymers allowed for NP formation via coacervation, as well as protein loading. Physicochemical characterization of the prepared NPs was then carried out: NPs were found to have a narrow size distribution with an average size ranging from 140 to 350 nm, and a ζ-potential ranging from -10 to -35 mV, depending on the formulation conditions. In a proof of concept study, starch NPs were found to be readily degraded by the human enzyme α-amylase, and showed good biocompatibility with A549 cells after 4 h. Upon nebulization, NPs were seen to be internalized by air-liquid interface cultivated A549 cells as well as 16HBE14o- cells. To evaluate the ability of starch NPs to load proteins of various characteristics, NPs were loaded with four model proteins/peptides possessing different molecular weights and isoelectric points - IgG1, RNAse A, insulin, and vancomycin. The greatest loading was achieved in the case of vancomycin with up to 23% drug loading and 43% encapsulation efficiency, indicating an optimal loading of proteins with an isoelectric point close to the pH of the NP suspension. In conclusion, starch NPs prepared by the developed mild and straightforward technique show potential as a safe platform for pulmonary delivery of proteins and peptides.

The effect of polymer size and charge of molecules on permeation through synovial membrane and accumulation in hyaline articular cartilage

The treatment of joint related diseases often involves direct intra-articular injections. For rational development of novel delivery systems with extended residence time in the joint, detailed understanding of transport and retention phenomena within the joint is mandatory. This work presents a systematic study on the in vitro permeation, penetration and accumulation of model polymers with differing charges and molecular weights in bovine joint tissue. Permeation experiments with bovine synovial membrane were performed with PEG polymers (6-200 kDa) and methylene blue in customized diffusion chambers. For polyethylene glycol, 2-fold (PEG 6 kDa), 3-fold (PEG 10 kDa) and 13-fold (PEG 35 kDa) retention by the synovial membrane in reference to the small molecule methylene blue was demonstrated. No PEG 200 kDa was found in the acceptor in detectable amounts after 48 h. This showed the potential for a distinct extension of joint residence times by increasing molecular weights. In addition, experiments with bovine cartilage tissue were conducted. The ability for positively charged, high molecular weight chitosans and HEMA-Co-TMAP (HCT) polymers (up to 233 kDa) to distribute throughout the entire cartilage matrix was demonstrated. In contrast, a distribution into cartilage was not observed for neutral PEG polymers (6-200 kDa). Furthermore, the positive charge density of different compounds (chitosan, HEMA-Co-TMAP, methylene blue, MSC C1 (neutral NCE) and MSC D1 (positively charged NCE) was found to correlate with their accumulation in bovine cartilage tissue. In summary, the results offer pre-clinical in vitro data, indicating that the modification of molecular size and charge of a substance has the potential to decelerate its clearance through the synovial membrane and to promote accumulation inside the cartilage matrix.

Polyester-idarubicin nanoparticles and a polymer-photosensitizer complex as potential drug formulations for cell-mediated drug delivery.

Cell-mediated transport of therapeutics has emerged as promising alternative to classical drug delivery approaches. To preserve viability and functions of carrier cells, encapsulation of active drugs in protective nanoparticles or the use of inducible therapeutics has been proposed. Here, we compared the effects of novel polymeric formulations of an active and a stimulus-sensitive anti-cancer drug on human T lymphocytes to identify suitable drug preparations for cell-mediated drug delivery. For the first approach, the chemotherapeutic agent idarubicin (IDA) was encapsulated in poly(lactic-co-glycolic-acid) (PLGA) and newly developed maleate-polyester (MPE) nanoparticles. PLGA- and MPE-encapsulated IDA was efficiently internalized by ex vivo activated human T lymphocytes; however, both encapsulations could not prevent premature T cell death resulting from IDA-uptake. In contrast, loading with a poly(styrene sulfonate) (PSS)-complex of the light-sensitive pharmaceutical 5,10,15,20-tetrakis(meso-hydroxyphenyl)porphyrin (mTHPP) did not affect T cell viability if upon loading the cells were kept in the dark. The photosensitizer was transferred from loaded T lymphocytes to co-cultivated carcinoma cells, and induced cancer cell death if co-cultures were exposed to light. Inducible drugs, such as photosensitizers, thus, may help to overcome the limitations of encapsulated active drugs and open up new perspectives for the use of cells as drug transporters in cancer therapy.

Improved Oral Peptide Delivery by Means of Mucoadhesion

Mucoadhesion implicates the possibility to achieve a very close contact between drug delivery system and biological membrane. This may increase the concentration gradient and also reduce the enzymatic degradation of peptide drugs during the absorption process.