Starch microspheres induce pulsatile delivery of drugs and peptides across the epithelial barrier by reversible separation of the tight junctions

Contemporary Aspects of Designing Marine Polysaccharide Microparticles as Drug Carriers for Biomedical Application

The main goal of modern pharmaceutical technology is to create new drug formulations that are safer and more effective. These formulations should allow targeted drug delivery, improved drug stability and bioavailability, fewer side effects, and reduced drug toxicity. One successful approach for achieving these objectives is using polymer microcarriers for drug delivery. They are effective for treating various diseases through different administration routes. When creating pharmaceutical systems, choosing the right drug carrier is crucial. Biomaterials have become increasingly popular over the past few decades due to their lack of toxicity, renewable sources, and affordability. Marine polysaccharides, in particular, have been widely used as substitutes for synthetic polymers in drug carrier applications. Their inherent properties, such as biodegradability and biocompatibility, make marine polysaccharide-based microcarriers a prospective platform for developing drug delivery systems. This review paper explores the principles of microparticle design using marine polysaccharides as drug carriers. By reviewing the current literature, the paper highlights the challenges of formulating polymer microparticles, and proposes various technological solutions. It also outlines future perspectives for developing marine polysaccharides as drug microcarriers.

The Caco-2 Model: Modifications and enhancements to improve efficiency and predictive performance

The Caco-2 cell model has been widely used to assess the permeability of drug candidates. It has provided a high throughput in vitro platform, functionally resembling the enterocytes. Since the oral route is the most preferred for drug administration, the Caco-2 cell model acts as a very important tool to elucidate the oral "druggability" of a molecule by providing a fairly reliable estimate of its permeability through the intestinal membrane. Despite its shortcomings (the lack of a mucus layer, long cultivation period, inter-lab variability, and differences in expression of enzymes, transporters, and tight junction complexes) it remains heavily used due to its reliability, predictive performance, and wide acceptance. Various modifications have been made: co-culturing with other intestinal cells, applying biosimilar mucus, reducing culturing time, combining Caco-2 monolayer with the dissolution apparatus, enhancing protein expression, and redesigning the sampling apparatus. These modifications are intended to overcome some of the shortcomings of the Caco-2 model in order to make its use easier, quicker, economical, and more representative of the intestine. The aim of this review is to discuss such modifications to enhance this model's utility, predictive performance, and reproducibility.

Biomaterial-tight junction interaction and potential impacts

The active pharmaceutical ingredients (APIs) have to cross the natural barriers and get into the blood to impart the pharmacological effects. The tight junctions (TJs) between the epithelial cells serve as the major selectively permeable barriers and control the paracellular transport of the majority of hydrophilic drugs, in particular, peptides and proteins. TJs perfectly balance the targeted transport and the exclusion of other unexpected pathogens under the normal conditions. Many biomaterials have shown the capability to open the TJs and improve the oral bioavailability and targeting efficacy of the APIs. Nevertheless, there is limited understanding of the biomaterial-TJ interactions. The opening of the TJs further poses the risk of autoimmune diseases and infections. This review article summarizes the most updated literature and presents insights into the TJ structure, the biomaterial-TJ interaction mechanism, the benefits and drawbacks of TJ disruption, and methods for evaluating such interactions.

Innovative pharmaceutical development based on unique properties of nanoscale delivery formulation

The advent of nanotechnology has reignited interest in the field of pharmaceutical science for the development of nanomedicine. Nanomedicinal formulations are nanometer-sized carrier materials designed for increasing the drug tissue bioavailability, thereby improving the treatment of systemically applied chemotherapeutic drugs. Nanomedicine is a new approach to deliver the pharmaceuticals through different routes of administration with safer and more effective therapies compared to conventional methods. To date, various kinds of nanomaterials have been developed over the years to make delivery systems more effective for the treatment of various diseases. Even though nanomaterials have significant advantages due to their unique nanoscale properties, there are still significant challenges in the improvement and development of nanoformulations with composites and other materials. Here in this review, we highlight the nanomedicinal formulations aiming to improve the balance between the efficacy and the toxicity of therapeutic interventions through different routes of administration and how to design nanomedicine for safer and more effective ways to improve the treatment quality. We also emphasize the environmental and health prospects of nanomaterials for human health care.

Clinical study shows improved absorption of desmopressin with novel formulation

PURPOSE

To create improved pharmaceutical formulations for nasal and sublingual administration of desmopressin and investigate their pharmacokinetic profiles in comparison with a commercial nasal liquid spray and finally to evaluate the volunteers' opinions on the different dosage forms.

METHODS

Both formulations were based on the characteristics of interactive mixtures. The nasal powder spray was produced by a rotary evaporator technique with sodium starch glycolate as carrier material and the sublingual tablet by direct compression after dry mixing with mannitol as carrier. The clinical study was an open-label, randomised cross-over pharmacokinetic study in healthy volunteers.

RESULTS

The nasal powder formulation gave a threefold increase in the absorption, unaltered time to maximum plasma concentration and a tendency to lower variability in the amount absorbed compared with the liquid spray. The powder was reported to be more irritating than the liquid but was still well accepted by the volunteers. The tablet did not improve the uptake of desmopressin, likely because of a poor disintegration sublingually.

CONCLUSIONS

The nasal powder formulation is a promising new dosage form for the delivery of desmopressin and other compounds. The sublingual tablet has a beneficial means of production and may be further developed by decreasing its disintegration time.

Probing Au nanoparticle uptake by enzyme following the digestion of a starch-Au-nanoparticle composite

In this letter, we report on the digestion of starch, when present as a composite with Au nanoparticles (NPs), by alpha-amylase. It has been observed that the rate of digestion of free starch and that in the composite were identical. Also, the well-established iodine test could be carried out to investigate the kinetics in the presence of Au NPs. The investigations revealed that following the digestion of starch in the composite the NPs were released and subsequently attached to the enzyme only and not to the degraded products of starch. Also, the enzyme attached to NPs, following digestion, retained its catalytic activity. The particle sizes of the NPs were not affected in the process because no agglomeration was observed. Experimental observations indicated the possibility of oriented attachment of alpha-amylase to the NPs in comparison to amyloglucosidase, another digestive enzyme. Finally, we observed a change in the surface plasmon resonance (SPR) of the NPs following the digestion of starch in the composite, and thus we could demonstrate that the SPR of the NPs could be used as a direct probe for monitoring the digestion of the composite by the enzyme.

Changes produced by external radiation in parameters influencing intestinal permeability and microparticle uptake in vitro

PURPOSE

To determine the interaction between X-irradiation and in vitro intestinal microparticle uptake through Caco-2 epithelial cells.

METHODS

Caco-2 cells were cultured on 3 microm porous membranes for 21 days, X-irradiated with 2 Gy or sham-irradiated, then incubated for 5 or 30 min and exposed apically for 30 min to 2 microm latex microparticles. Measurements included cell dimensions, from confocal microscope 'optical slices'; transepithelial resistance (TER) for tight junction (TJ) permeability; particle aggregation; and particle numbers on (adsorbed), in (intraepithelial) and through (submembranous) the epithelium.

RESULTS

Irradiation alone reduced TJ permeability more than sham-treatment, more so 5 min than 30 min after treatment. Irradiated epithelia were more permeable to particles than the equivalent sham-irradiated or previously untreated (particle only) groups: the latter two were similar. Irradiation altered adsorbed particle numbers and increased submembranous counts: particle uptake correlated best with cell height.

CONCLUSIONS

2 Gy X-irradiation increased particle uptake and translocation through the epithelium. This correlated well with the TJ opening seen after particle exposure in irradiated samples and changes in cell morphology. New data on cell dimensions underlined the similarity in particle uptake between this in vitro epithelium and that in an in vivo model, highlighting the translational significance of the work.

Past, present, and future technologies for oral delivery of therapeutic proteins

Biological drugs are usually complex proteins and cannot be orally delivered due to problems related to degradation in the acidic and protease-rich environment of the gastrointestinal (GI) tract. The high molecular weight of these drugs often results in poor absorption into the periphery when administered orally. The most common route of administration for these therapeutic proteins is injection. Most of these proteins have short serum half-lives and need to be administered frequently or in high doses to be effective. So, difficulties in the administration of protein-based drugs provides the motivation for developing drug delivery systems (DDSs) capable of maintaining therapeutic drug levels without side effects as well as traversing the deleterious mucosal environment. Employing a polymer as an entrapment matrix is a common feature among the different types of systems currently being pursued for protein delivery. Protein release from these matrices can occur through various mechanisms, such as diffusion through or erosion of the polymer matrix, and sometimes a combination of both. Encapsulation of proteins in liposomes has also been a widely investigated technology for protein delivery. All of these systems have merit and our worthy of pursuit.

Parameters influencing intestinal epithelial permeability and microparticle uptake in vitro

The hypothesis that, in vivo in situ, villous uptake of 2 microm latex microparticles involves changes at enterocyte tight junctions (TJs) was tested using Caco-2 cells on porous membranes. Epithelial permeability was measured by transepithelial resistance (TER) and particle numbers in surface, intraepithelial and sub-epithelial compartments by microscopy. Apical particle or medium addition initially closed TJs, but this was subsequently reversed in particle-treated groups. Peristaltic onward movement of a bolus was simulated by removing apical particles after an exposure period and leaving the remaining particles to interact with the epithelium: this produced marked TJ loosening during the interaction period. For particle exposure groups, the early similarity with particle numbers in vivo taken up in young adult rats became less marked with time, although bolus removal counteracted this tendency. The TJ response to vasoactive intestinal polypeptide (VIP) was time-dependent. Adsorbed and intraepithelial particle numbers increased with particle exposure time; epithelial-associated microparticle aggregation varied with treatment and submembranous particles were seen in all groups. Correlation between TER changes and particle numbers suggests TJ loosening may be important in microparticle uptake. This Caco-2 model gives epithelial particle numbers that approximate well to published figures for microparticle uptake in vivo and allows effective microenvironmental manipulation.

Factors influencing intestinal microparticle uptake in vivo

The aim of this study is to compare microparticle uptake in animals of different ages, gender and species and at different time points. The 2mum latex/in vivo in situ model uses the observation of animal responses or post-mortem changes and also particle identification by fluorescence microscopy in nine sequential intestinal segments and secondary sites. The wide size range of animals studied requires particle numbers in tissue compartments to be related to intestinal tissue section area through a circumference measurement. Area under the curve (AUC) data for particles in intestinal tissue are plotted against measurements of intestinal length, allowing comparisons to be made across different ages and species and between males and females. The percentage uptake of administered dose and particle numbers in macerated tissue are also reported. Some parameters, in particular species, do not appear to affect the extent of microparticle uptake, which ranges from 0.12 to 0.32% of the administered dose. Particle uptake does, however, vary with age, being significantly greater in young adult males (7 weeks) than in younger (3 weeks) and older (17 and 52 weeks) age groups. It is concluded that age is more important in determining the extent of uptake than gender or species.

Development and characterisation of interactive mixtures with a fine-particulate mucoadhesive carrier for nasal drug delivery

The aim of this study was to investigate whether mucoadhesive interactive mixtures can be created using carrier particles in a size range appropriate for nasal administration, i.e. 10-50 microm. We also used theoretical models to investigate if homogeneity measurements can be used to evaluate the formation of interactive mixtures containing carrier particles in this size range. Sodium starch glycolate (SSG) was used as carrier material and sodium salicylate (SS) as the model fine-particulate drug. The size ranges of SSG particles and amounts of SS were varied to find the smallest carrier particle size and highest amount of drug that still resulted in an interactive mixture. Visual inspection of the mixtures by scanning electron microscopy showed that interactive mixtures could be formed with carrier particles as small as 30 microm and containing up to 4% (w/w) of SS. Comparisons with theoretical models highlighted the difficulties of using homogeneity measurements to determine if interactive mixtures were formed. The measured coefficients of variation (CV) for the amount of drug in the samples were low and inferior mixtures were associated with only a slight increase. It was thus concluded that mucoadhesive interactive mixtures can be created in an appropriate size range for nasal administration, but that visual inspection of these mixtures is initially necessary to confirm the formation of an interactive mixture.

Nasal clearance in health and disease

This paper reviews the anatomical and physiological factors of importance for nasal drug delivery and discusses in particular the influence of the nasal mucociliary clearance mechanism on the nasal absorption of drugs. The effect of nasal pathological conditions on the mucociliary clearance mechanism and the possible effect of such disease states on nasal drug transport are also discussed. Strategies for the exploitation of bioadhesive drug delivery systems and especially nasal absorption enhancers for the improvement of nasal drug delivery are evaluated to include considerations of the mechanism of action and correlation between the degree of bioadhesion and absorption enhancement and transport of drugs across the nasal membrane. A range of studies involving bioadhesive/absorption enhancer systems are detailed. A selected bioadhesive material, chitosan, which has been shown to have excellent absorption enhancer properties for a variety of drugs is discussed in some detail.

Particle uptake by Peyer's patches: a pathway for drug and vaccine delivery

Particle uptake by Peyer's patches offers the possibility of tailoring vaccines that can be delivered orally. However, particle uptake by the follicle-associated epithelium in the gastrointestinal tract depends on several different factors that are the physicochemical properties of the particles, the physiopathological state of the animal, the analytical method used to evaluate the uptake and finally the experimental model. These parameters do not allow a clear idea about the optimal conditions to target the Peyer's patches. The goal of this review is to clarify the role of each factor in this uptake.

In situ gelling, bioadhesive nasal inserts for extended drug delivery: in vitro characterization of a new nasal dosage form

The purpose of this study was the preparation and characterization of sponge-like, in situ gelling inserts based on bioadhesive polymers. Hydrophilic polymers (carrageenan, Carbopol, chitosan, hydroxypropyl methylcellulose (HPMC) K15M and E5, sodium alginate, sodium carboxy methylcellulose (NaCMC), polyvinyl pyrrolidone (PVP) 90, xanthan gum) were dissolved with/without the model drug oxymetazoline HCl in demineralized water and lyophilized into small inserts. The drug release, water uptake, mechanical properties, X-ray diffraction and bioadhesion potential of the nasal inserts were investigated. A sponge-like structure of nasal inserts was formed with amorphous, but not with crystalline polymers during the freeze-drying process. The insert hardness increased with the glass transition temperature of the polymer (PVP25<PVP30<PVP90). The bioadhesion potential was governed by the polymer ability to interact with mucin/agar (highest for carrageenan, Carbopol, xanthan gum and NaCMC). Inserts prepared from low molecular weight polymers resulted in polymer dissolution and fast drug release (HPMC E5, Na-alginate, PVP90). The drug release from inserts prepared from high molecular weight polymers (carrageenan, Carbopol, chitosan, HPMC K15M, NaCMC, xanthan gum) was a complex interplay of osmotic forces, water uptake and electrostatic interactions between drug and polymer. The drug release decreased with higher polymer content and increased drug loading of the insert. Bioadhesive nasal inserts have a high potential as new nasal dosage form for extended drug delivery.

Starch microparticles as vaccine adjuvant

The demand for new vaccine adjuvants is well documented. New purified antigens from parasites, bacterial or viral pathogens, as well as recombinant subunit antigens and synthetic peptides, are often inherently weak immunogens; therefore, they need some kind of adjuvant to help initiate an immune response. In addition, there are very few adjuvants using the potential of the mucosal immune system, which may play an important role in the defence against air- and food-borne infections. Starch is a natural biocompatible and biodegradable polymer that is suitable for the production of various particulate adjuvant formulations, which can induce mucosal as well as systemic immune responses. This review gives an account of the different starch adjuvants used in immunisation studies. In particular, the properties of polyacryl starch microparticles as an oral vaccine adjuvant that induce protective immune responses in mice challenge experiments are summarised. In addition, a diphtheria booster vaccine has been proposed to be used to proving the concept in man and the possibilities to design an efficient vaccine formulation for human use are discussed.

Microparticles for oral delivery of vaccines

Nonreplicating antigens are poorly immunogenic when given orally, either due to their degradation in the gastrointestinal tract or because they are not efficiently taken up in the gut. Studies in laboratory animals have clearly demonstrated that microparticles can significantly improve the immunogenicity of orally administered antigens. However, the oral delivery of vaccines using microparticles has not been explored extensively in humans and large animals. In this article the progress in oral microparticle antigen delivery will be reviewed and, where possible, studies in humans and large animals will be highlighted. In addition, possible approaches that have the potential to significantly improve microparticle delivery of oral vaccines will be suggested.

Preparation and characterization of starch/cyclodextrin bioadhesive microspheres as platform for nasal administration of Gabexate Mesylate (Foy®) in allergic rhinitis treatment

Bioadhesive and biodegradable microspheres were obtained by chemical cross-linking with epichlorohydrin of an alkaline solution of a mixture of starch and alpha-, beta-, or gamma-cyclodextrin (CyD). Microspheres were characterized by scanning electron microscopy, swelling degree, and water retention. The percentage of the effective CyD in microspheres was estimated by measuring the amount of iodine and typical organic compounds (TOCs) retained in the hydrophobic cavity of CyD. Gabexate Mesylate (trade name Foy); GM), an antiallergic drug, was included in microspheres by soaking in an aqueous solution containing the drug, followed by solvent evaporation or lyophilization. UV, IR, and DSC data indicated that despite the fact that GM is a hydrophilic drug, its hydrophobic moiety close to the benzene ring is able to penetrate the CyD cavity and to form stable inclusion complexes. Values of the association equilibrium constant for GM binding to CyD, obtained by UV differential spectroscopy, indicated that the affinity of the drug for alpha- and gamma-CyD is higher than that for beta-CyD. In vitro, GM was gradually released during 1h. Even if the release rate of the drug is relatively fast, the microspheres might actually provide the best platform since the material adheres to the nasal mucosa which was proved by adhesion tests. The GM integrity was checked by comparing its anti-trypsin activity before and after release.

Novel complexation hydrogels for oral peptide delivery: in vitro evaluation of their cytocompatibility and insulin-transport enhancing effects using Caco-2 cell monolayers

Poly[methacrylic acid-grafted-poly(ethylene glycol)] [P(MAA-g-EG)] is a complexation hydrogel molecularly designed for oral peptide delivery. In this work, the cytotoxicity and insulin-transport enhancing effect of P(MAA-g-EG) microparticles on intestinal epithelial cells were evaluated using Caco-2 cell monolayers. A series of P(MAA-g-EG) microparticles with different polymer compositions were prepared by a photo-initiated free radical solution polymerization and subsequent pulverization. The hydrogel microparticles were preswollen in either Ca2+-containing (CM+) or Ca2+-free medium (CM-; pH 7.4) and applied to the apical side of the Caco-2 monolayers. No significant cytotoxic effects, as determined by a calorimetric assay with P(MAA-g-EG) microparticles preswollen in the CM+, were observed at doses ranging from 3 to 31 mg/cm2 of cell monolayer. Transepithelial electrical resistance (TEER) measurements showed that the P(MAA-g-EG) microparticles induced a Ca2+ concentration-dependent lowering in TEER values. The reduction effect in CM- media was greater than that in CM+ media (17 +/- 2% reduction in CM+ and 45 +/- 3% reduction in CM-, respectively). Insulin transport in the presence of the preswollen P(MAA-g-EG) microparticles was also strongly depended on the Ca2+ concentration in the medium. The respective estimated permeability for insulin alone and the insulin with hydrogels in CM+ were 0.77 and 1.16 x 10(-8) cm/s, whereas those in CM- were 1.18 and 24.78 x 10(-8) cm/s. The results demonstrate that the P(MAA-g-EG) hydrogel microparticles could be used as a cytocompatible carrier possessing the transport-enhancing effect of insulin on the intestinal epithelial cells.

Tight junctional changes upon microwave and x-ray irradiation

Tight junctions (zonulae occludentes, ZO) are cellularly regulated dynamic structures sensitive to environmental stress agents including ionizing radiation. Radiation induced pathological alterations of the small intestine (gastrointestinal radiation syndrome) are related to altered ZO-mediated paracellular transport. We carried out a quantitative morphological evaluation of the murine jejunal epithelial tight junctional structure in freeze fracture replicas as changed upon whole body X-ray irradiation and low energy microwave exposition. X-ray treatment (4 Gy, 1, 24 h) brought about a partial dearrangement of the ZO strand network which regenerated only partially by 24 h. This observation is in line with data on paracellular permeability increases and ZO-bound calcium drop caused by X-ray irradiation. On the other hand, microwave treatment (16 Hz-modulated 2.45 GHz wave, 1 mW/cm2 power density, I h exposition, samples at I and 3 h after exposition) did not cause dearrangement but, rather an increase in the integration of thight junctional structure, which is in agreement with an increase in cytochemically detectable ZO-bound calcium.

Developments in the area of bioadhesive drug delivery systems

This paper aims to review the current progress in bioadhesion for drug delivery applications as well as new techniques related to this field. Research started with mucoadhesive polymers that had already been in use as excipients and were rapidly used in new formulations. Their major drawback was found in their unspecific binding, as they adhere to almost any mucosal surface. As some of the polymers showed additional properties such as enzyme inhibition and permeation enhancement, however, they remain interesting as multifunctional excipients. In contrast to mucoadhesion, the concept of specific bioadhesion by use of lectins and other adhesion molecules is now gaining increasing attention as these substances bind directly to receptors on the cell surface rather than to the mucus gel layer. Since specific binding to the cell surface is often followed by uptake and intracellular transport, new chances for drug delivery evolved. Bioadhesion may, thus, enable researchers to deliver macromolecular drugs directly to specific target cells and has implications also relevant to other fields of science, such as tissue engineering, gene delivery and nanotechnology.

Bioadhesive starch microspheres and absorption enhancing agents act synergistically to enhance the nasal absorption of polypeptides

This paper investigates the effect of starch microspheres on the absorption enhancing efficiency of various enhancer systems in formulations with insulin after application in the nasal cavity of sheep. The enhancers studied were lysophosphatidylcholine, glycodeoxycholate and sodium taurodihydroxyfusidate, a bile salt derivative. The enhancers were selected on the basis of their perceived or proven mechanism of action and worked predominantly by interacting with the lipid membrane. The bioadhesive starch microspheres were shown to increase synergistically the effect of the absorption enhancers on the transport of the insulin across the nasal membrane. Dependent on the potency of the enhancer system the increment in absorption enhancement was shown to be from 1.4 times to 5 times that obtained for the absorption enhancer in solution.

Scintigraphic evaluation in rabbits of nasal drug delivery systems based on carbopol 971p((R)) and carboxymethylcellulose

The residence time of apomorphine mucoadhesive preparations incorporating 99mTc labeled colloidal albumin in rabbit nasal cavity was evaluated by gamma scintigraphy. This technique was used to compare the nasal clearance of preparations based either on Carbopol 971P((R)) or lactose (control), each with and without apomorphine, or carboxymethylcellulose with apomorphine. The planar 1-min images showed an excipient-dependent progressive migration of radioactivity with time from the nasal cavity to the stomach and intestine. Thirty minutes post insufflation, the percentages of the formulations cleared from the nasal cavity were 47% for lactose, 26% for lactose/apomorphine, 10% for Carbopol 971P((R)), and 3% for both Carbopol 971P((R))/apomorphine and carboxymethylcellulose/apomorphine. Three hours post insufflation, the percentages of the formulations cleared from the nasal cavity were 70% for lactose, 58% for lactose/apomorphine, 24% for Carbopol 971P((R)), 12% for Carbopol 971P((R))/apomorphine, and 27% for carboxymethylcellulose/apomorphine. Apomorphine inhibited nasal mucociliary clearance since migration of the radioactivity administered with apomorphine containing preparations was in all cases slower than that of the corresponding powder without apomorphine. The peak plasma concentration of apomorphine was attained while all the formulations were still within the nasal cavity. The use of mucoadhesive polymers such as Carbopol 971P((R)) or carboxymethylcellulose in nasal dosage forms increases their residence time within the nasal cavity and provides the opportunity for sustained nasal drug delivery.

Characterisation of instantaneous water absorption properties of pharmaceutical excipients

Powders absorb water by both capillary imbibition and swelling. The capillary process is almost instantaneous but swelling occurs over a period of time. An isothermal transient ionic current technique was used in this study to characterise the instantaneous absorption properties (rate and capacity) of a few selected pharmaceutical excipients. The results indicate that the instantaneous and long term water absorption properties of pharmaceutical powders can differ considerably. The rate of instantaneous water absorption appears to correlate with the total surface area while the absorption capacity correlates more with the porosity of the powder.

Intestinal absorption of peptides through the enterocytes

Transport of intact peptides and proteins from the intestinal lumen into the blood is a unique phenomenon, which differs from the regular process of food digestion and absorption. Intestinal absorption of minute amounts of proteins is, however, being considered as a normal physiological process. It is thus important to define and understand the routes for protein transfer from the intestinal lumen to the blood and the mechanisms by which the macromolecules overcome the sieving barrier of the intestinal wall. The study on insulin has demonstrated that, upon proper introduction into the intestinal lumen, insulin is absorbed by the epithelial cells and transferred to the circulation. The peptides absorbed and transferred to the blood retained their biological activity and induced significant lowering of blood glucose levels. The efficiency of the absorption does not differ among the ileum, duodenum, and colon. Morphological examination demonstrated no alteration of the structural integrity of the epithelia, the enterocytes stay intact with well-developed microvilli, and the cells remain joined by tightly closed junctions. Application of immunocytochemistry on thin tissue sections revealed insulin antigenic sites at different locations depending on the time point. Insulin detected in the lumen of the intestinal tract is absorbed through the endosomal compartment of the epithelial cells rather than passing between cells. Internalization occurs through invaginations of the luminal plasma membrane and vesicular structures of the endosomal compartment. In 5-10 minutes, insulin is transferred to the basolateral membrane and released into the interstitial space to reach the circulation. Definition of the transcytotic pathway will contribute to a better understanding of drug delivery for potential therapeutic applications.

Anionic mucoadhesive polymers as auxiliary agents for the peroral administration of (poly)peptide drugs: influence of the gastric juice

The incorporation of (poly)peptide drugs in mucoadhesive polymers is a promising strategy for their peroral administration. In this study, the protective effect of various polymers toward an artificial gastric fluid and the influence of an enteric coating on the adhesive properties have been investigated. Tablets containing 30 mg of carbomer (C934P), neutralized carbomer (NaC934P), or sodium carboxymethylcellulose (NaCMC), 0.1 mg of the model protein peroxidase, and 19.9 mg of mannitol were incubated at 37 degrees C for 2.5 hr with a simulated gastric fluid with and without pepsin. All polymers--although anionogenic--displayed quick swelling behavior in the acid milieu, leading to an unintended protein release. Moreover, pepsin is capable of penetrating into the polymeric carrier systems, thereby rapidly degrading the embedded protein. Enteric coating, on the other hand, leads to strongly reduced adhesive properties. Only NaC934P tablets coated with polymethacrylate containing 9% triethylcitrate displayed no significant (p < .05) reduction in adhesive strength. Results give essential basic information for the development of peroral (poly)peptide dosage forms based on mucoadhesive polymers.

Bioavailability of apomorphine following intranasal administration of mucoadhesive drug delivery systems in rabbits

PURPOSE

The purpose of this study was to investigate both the in vitro and in vivo release of apomorphine from mucoadhesive powder formulations of Carbopol 971P and polycarbophil.

METHODS

The in vitro drug release from the mucoadhesive formulations was studied using a modified USP XXII rotating basket. The pharmacokinetics of apomorphine given as a solution was determined after subcutaneous and intranasal administrations to rabbits. The animals also received intranasally the mucoadhesive dosage forms and immediate release lactose powder mixture. Comparisons were made between the salient pharmacokinetic parameters of the different dosage forms.

RESULTS

Sustained in vitro drug release was obtained from the mucoadhesive formulations. Apomorphine was absorbed more rapidly in rabbits when administered intranasally than as a subcutaneous injection. The mucoadhesive formulations both gave sustained plasma drug concentrations and bioavailabilities comparable to subcutaneous injections. The times taken to achieve peak plasma drug concentrations from these mucoadhesive formulations were more than three-fold that of lactose. With these mucoadhesive formulations apomorphine lasted longer in the blood. It could be detected for up to 6-8 h compared to approximately 3 h for the other forms of administration.

CONCLUSIONS

The nasal bioavailability of powders is higher than that of solutions. Drug release from the mucoadhesive powders was sustained and there was no significant difference between Carbopol 971P and polycarbophil.

Intranasal insulin delivery and therapy

Intranasal insulin delivery has been widely investigated as an alternative to subcutaneous injection for the treatment of diabetes. The pharmacokinetic profile of intranasal insulin is similar to that obtained by intravenous injection and, in contrast to subcutaneous insulin delivery, bears close resemblance to the 'pulsatile' pattern of endogenous insulin secretion during meal-times. The literature suggests that intranasal insulin therapy has considerable potential for controlling post-prandial hyperglycaemia in the treatment of both IDDM and NIDDM. However, effective insulin absorption via the nasal route is unlikely without employing the help of absorption enhancers or promoters which are able to modulate nasal epithelial permeability to insulin and/or prolong the residence time of the drug formulation in the nasal cavity. This article discusses the structure and function of the nasal cavity, the barriers which prevent nasal insulin absorption and through the use of absorption enhancers or promoters methods by which these barriers may be overcome.

Absorption enhancement in intestinal epithelial Caco-2 monolayers by sodium caprate: assessment of molecular weight dependence and demonstration of transport routes

Sodium caprate (C10), a medium chain fatty acid, is used clinically to enhance rectal absorption of the low molecular weight (MW) drug ampicillin. The main aim of this study was to investigate whether C10 also enhances the permeability of high MW model drugs in a model of the intestinal epithelium. The second aim was to present visual evidence of the route of enhanced transport across the epithelial cell layer. The studies were performed in Caco-2 monolayers cultured on permeable supports. The effects of non-toxic concentrations (< or = 13 mM) of C10 on drug transport across the monolayers was studied using monodisperse 14C-polyethylene glycols (MW 238-502; 14C-PEGs), 125I-Arg5-vasopressin (MW 1,208), 125I-insulin (MW 6,000) and FITC-labelled dextrans (MW 4,400 and 19,600; FD4 and FD20 respectively) as model drugs. Electron and confocal laser scanning microscopy were used to demonstrate transport routes across the epithelium. 10 mM C10 increased the permeability of all 14C-PEGs to approximately the same extent. 13 mM C10 increased the permeability of 125I-Arg8-vasopressin 10-fold. Only small increases in FD4 and FD20 permeabilities were observed. After C10 exposure, both tight junctions with normal morphology and those with dilatations showed an increased permeability to ruthenium red, indicating that C10 enhanced the paracellular transport of molecules with a MW < 1,000. Confocal microscopy showed that C10 increased the transport of FD4 and FD20 by the paracellular route. In conclusion, non-toxic concentrations of C10 can be used to enhance the permeability of drugs of MW up to approximately 1,200. Enhancement of the absorption of molecules larger than 4,000 is quantitatively insignificant. The enhanced permeability occurred via the paracellular pathway.

Enhancement of immune response to intranasal influenza HA vaccine by microparticle resin

We evaluated the potential application of ion-exchange resins for the enhancement of intranasal immune response to influenza HA vaccine in mice. Female Balb/c mice were intranasally immunized with inactivated influenza HA vaccine with one of four kinds of resin microparticles: sodium polystyrene sulfonate, calcium polystyrene sulfonate, polystyrene benzyltrimetylammonium chloride, or polystyrene divinylbenzene. Haemagglutinin-inhibiting antibodies were measured in the serum and IgA antibodies in the nasal wash after 4 weeks. The results demonstrated that intranasal administration of influenza HA vaccine in combination with the 20-45 microns sized particles of sodium polystyrene sulfonate resin induced the highest levels of mucosal IgA, and enhanced systemic haemagglutinin-inhibiting antibodies. While the Th2-type cytokine IL-4 was detected in the sera after intranasal immunization with HA vaccine and sodium polystyrene sulfonate, neither IFN-gamma nor IL-2 could be detected. Furthermore, mice intranasally immunized with HA vaccine together with sodium polystyrene sulfonate resin showed higher protection against viral challenge than those that received HA vaccine alone. Intranasal administration of influenza HA vaccine with sodium polystyrene sulfonate resin might be both a safe and an effective means of immunization.

Microparticle resins as a potential nasal drug delivery system for insulin

The application of various resins for the nasal delivery of insulin was examined in rabbits. Intranasal administration of human insulin (28 U, 1 mg) mixed with fractionated sodium polystyrene sulfonate powder (an anionic resin with a particle size of 20-45 microns) caused a rapid increase of the plasma insulin level 413.0 +/- 71.7 microU/ml (mean +/- S.D.) after 15 min, while intranasal administration of insulin alone caused little increase. The blood glucose level decreased from 118.8 +/- 18.5 mg/dl to 65.8 +/- 13.8 mg/dl at 45 min after administration. These results were superior to those obtained with the unfractionated resin. Styrene-divinylbenzene copolymer (a nonionic resin; 20-45 microns fraction) showed similar enhancement of nasal insulin absorption. In contrast, polyacrylester (a nonionic resin; 20-45 microns fraction) and cholestyramine (a cationic resin) did not promote insulin absorption. These results suggest that some resins may be useful for nasal delivery of insulin.

Nasal mucociliary clearance as a factor in nasal drug delivery

The nasal mucociliary clearance system transports the mucus layer that covers the nasal epithelium towards the nasopharynx by ciliary beating. Its function is to protect the respiratory system from damage by inhaled substances. Impairment of nasal mucociliary clearance can result in diseases of the upper airways. Therefore, it is important to study the effects of drugs and drug excipients on nasal mucociliary clearance. A large number of methods are used to assess mucociliary clearance. These methods study the effects of drug and excipients on the mucociliary system in vitro or in vivo in animals and humans. In some cases, the results of different in vitro and in vivo measurements do not correlate well. In vitro methods, especially ciliary beat frequency measurements, have been demonstrated to be valuable tools for toxicity screening. However, in vivo studies are essential to confirm the safety of nasal drug formulations. Nasal mucociliary clearance also has implications for nasal drug absorption. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in fast systemic drug absorption. Several approaches are discussed to increase the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. However, more experimental evidence is needed to support the conclusion that this improved absorption is caused by a longer residence time of the nasal drug formulation.

Microspheres as nasal drug delivery systems

All types of microspheres that have been used as nasal drug delivery systems are water-insoluble but absorb water into the sphere's matrix, resulting in swelling of the spheres and the formation of a gel. The building materials in the microspheres have been starch, dextran, albumin and hyaluronic acid, and the bioavailability of several peptides and proteins has been improved in different animal models. Also, some low-molecular weight drugs have been successfully delivered in microsphere preparations. The residence time in the cavity is considerably increased for microspheres compared to solutions. However, this is not the only factor to increase the absorption of large hydrophilic drugs. Microspheres also exert a direct effect on the mucosa, resulting in the opening of tight junctions between the epithelial cells. Starch and dextran microspheres have been administered repeatedly and can be classified as safe dosage forms.

Oral controlled release technology for peptides: status and future prospects

In spite of significant efforts in academic and commercial laboratories, major breakthroughs in oral peptide and protein formulation have not been achieved. The major barriers to developing oral formulations for peptides and proteins include poor intrinsic permeability, lumenal and cellular enzymatic degradation, rapid clearance, and chemical and conformational stability. Pharmaceutical approaches to address these barriers, which have been successful with traditional, small, organic drug molecules, have not readily translated into effective peptide and protein formulations. The success achieved by Sandoz with cyclosporin formulations remains one clear example of what can be achieved, although it is likely that effective oral formulations for peptides and proteins will remain highly compound specific. Although the challenges are significant, the potential therapeutic benefit remains high, particularly with the increasing identification of potential peptide and protein drug candidates emerging from the biotechnology arena. Successful formulations will most likely require a systematic and careful merger of formulation and design delivery systems which maximize the potential for absorption across the epithelial cell layer.

Current concepts in intestinal peptide absorption

Today there is considerable interest in oral peptide delivery. However, oral administration of peptides is limited by a low bioavailability and a high variability in plasma levels. A review is given of the literature describing the major barriers in peptide absorption, the basic mechanisms of intestinal peptide transport, the experimental models and the pharmaceutical approaches currently used in the investigation of peptide and protein absorption processes.

From sticky stuff to sweet receptors--achievements, limits and novel approaches to bioadhesion

About 10 years ago, the concept of bioadhesion was introduced into the pharmaceutical literature and has since stimulated much research and development both in academia and in industry. The first generation of bioadhesive drug delivery systems (BBDS) were based on so-called mucoadhesive polymers, i.e. natural or synthetic macromolecules, often already well accepted and used as pharmaceutical excipients for other purposes, which show the remarkable ability to 'stick' to humid or wet mucosal tissue surfaces. While these novel dosage forms were mainly expected to allow for a possible prolongation, better localization or intensified contact to mucosal tissue surfaces, it had to be realized that these goals were often not so easily accomplished, at least not by means of such relatively straightforward technology. However, although not always convincing as a 'pharmaceutical glue', some of the mucoadhesive polymers were found to display other, possibly even more important biological activities, namely to inhibit proteolytic enzymes and/or to modulate the permeability of usually tight epithelial tissue barriers. Such features were found to be particularly useful in the context of peptide and protein drug delivery. But still, the interest in realizing 'true' bioadhesion continues: instead of mucoadhesive polymers, plant or bacterial lectins, i.e. adhesion molecules which specifically bind to sugar moieties of the epithelial cell membrane, are now widely being investigated as drug delivery adjuvants. These second-generation bioadhesives not only provide for cellular binding, but also for subsequent endo- and transcytosis. This makes the novel, specifically bioadhesive molecules particularly interesting for the controlled delivery of DNA/RNA molecules in the context of antisense or gene therapy.