Cytotoxicity of absorption enhancers in Caco-2 cell monolayers

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Nanoarchitectonics of Layer-by-Layer (LbL) coated nanostructured lipid carriers (NLCs) for Enzyme-Triggered charge reversal

HYPOTHESIS

Combined usage of Layer-by-Layer (LbL) coating and alkaline phosphatase (ALP) - responsive charge reversal strategies can improve the cellular internalisation of the colloidal drug delivery systems by also decreasing their cytotoxic effects.

EXPERIMENTS

Anionic core NLCs were formed by combining the melt emulsification method and ultrasonication. The resulting core NLCs were coated sequentially first with protamine (Prot NLCs) and then with sodium tripolyphosphate (TPP) or sodium polyphosphate (Graham's salt, PP) generating TPP or PP NLCs, respectively. The developed NLCs were characterised regarding their size and zeta potential. Enzyme-induced charge reversal of the TPP and PP NLCs was evaluated by zeta potential measurements upon their incubation with alkaline phosphatase (ALP). In parallel, time-dependent phosphate release was monitored in the presence of isolated as well as cell-associated ALP. Morphological evaluations were performed by scanning electron microscopy (SEM) studies. Moreover, cell viability and cellular uptake studies were carried out in vitro on Caco-2 cells.

FINDINGS

The core NLCs were obtained with a mean size of 272.27 ± 5.23 nm and a zeta potential of -25.70 ± 0.26 mV. Upon coating with protamine, the zeta potential raised to positive values with a total change up to Δ29.3 mV also displaying an increase in particle size. The second layer coating with TPP and PP provided a negative surface charge. Subsequent to ALP treatment, the zeta potential of the TPP and PP NLCs reversed from negative to positive values with total changes of Δ8.56 and Δ7.47 mV, respectively. Conformably, significant amounts of phosphate were released from both formulations. Compared with core NLCs, improved cellular viability as well as increased cellular uptake were observed in case of Prot, TPP and PP NLCs.

Optimization of phytic acid-crosslinked chitosan microspheres for oral insulin delivery using response surface methodology

Although oral administration is favorable mode of insulin delivery, it is the most challenging route, owing to poor oral bioavailability. In this study, a chitosan (CS)-based insulin delivery system was developed by ionic crosslinking with phytic acid (PA). CS-PA microspheres were optimized with different crosslinking conditions of CS and PA using response surface methodology to retain insulin during preparation and gastric digestion. Furthermore, the in vitro release profile, morphological structure, cytotoxicity, and intestinal permeability of the optimized microspheres, and its hypoglycemic effect in diabetic rats were evaluated. Under optimal conditions, the entrapment efficiency was 97.1%, and 67.0% of insulin was retained in the microspheres after 2 h of gastric digestion followed by a sustained-release in intestinal fluid. Insulin was primarily distributed in the microsphere core with a monodisperse diameter of 663.3 μm. The microspheres increased the permeability of insulin across Caco-2/HT-29 monolayers by 1.6 times with negligible cytotoxicity. The microspheres had a relative pharmacological bioavailability of 10.6% and significantly reduced blood glucose levels with a long-lasting hypoglycemic effect after oral administration in diabetic rats. This study demonstrated that an optimized formulation of a simple ionic crosslinking system using CS and PA could facilitate efficient oral delivery of insulin.

Proteomic characterization of HaCaT keratinocytes provides new insights into changes associated with SDS exposure

Background

Using human keratinocyte HaCaT cell line model, we screened for proteins that changed their content due to SDS exposure in non-toxic dose (25 μg/ml, as determined by the MTT assay and microscopic examination) during 48 h.

Methods

The altered level of proteins from HaCaT keratinocytes exposed to SDS was analyzed by LC-MS/MS approach and quantified using Progenesis LC software.

Results

The Pathview map of 131 upregulated proteins was built, and enhancement of glycolysis/gluconeogenesis was found.

Conclusions

The results of our study admit the possibility of promotion of the cutaneous neoplasia and/or the peculiarity of the response of immortalized keratinocytes to the SDS treatment and provide new insights into possible role of SDS as integrator of diverse signaling that influence cell fate decisions.

A Self-Nanoemulsifying Drug Delivery System for Enhancing the Oral Bioavailability of Candesartan Cilexetil: Ex Vivo and In Vivo Evaluation

The drug delivery of candesartan cilexetil encounters an obstacle of low absolute oral bioavailability which is attributed mainly to its low aqueous solubility and efflux by intestinal P-glycoprotein (P-gp) transporters. However, the extent of P-gp contribution in the reduced oral bioavailability of candesartan cilexetil is not clear. In this study, a previously developed candesartan cilexetil-loaded self-nanoemulsifying drug delivery system (SNEDDS) was evaluated for its ability to increase the drug oral bioavailability via the inhibition of intestinal P-gp transporters. Despite the developed SNEDDS showing P-gp inhibition activity, P-gp-mediated efflux was found to have a minor role in the reduced oral bioavailability of candesartan cilexetil. On the other hand, the high surfactant concentration used in SNEDDS formulation represents a major challenge toward their widespread application especially for chronically administered drugs. The designed acute and subacute toxicity studies revealed that the degree of intestinal mucosal damage decreases as the treatment period increases. The latter observation was attributed to the reversibility of surfactant-induced mucosal damage. Thus, the developed SNEDDS could be considered as a promising delivery system for enhancing the oral bioavailability of chronically administered drugs.

Antifungal and Mucoadhesive Properties of an Orally Administered Chitosan-Coated Amphotericin B Nanostructured Lipid Carrier (NLC)

Surface-modified nanostructured lipid carriers (NLC) represent a promising mode of drug delivery used to enhance retention of drugs at absorption site. Formulated chitosan-coated amphotericin-B-loaded NLC (ChiAmp NLC) had a size of 394.4 ± 6.4 nm, encapsulation and loading efficiencies of 86.0 ± 3% and 11.0 ± 0.1% respectively. Amphotericin-B release from NLCs was biphasic with no changes in physical properties upon exposure to simulated gastrointestinal conditions. Antifungal properties of Amphotericin-B and ChiAmpB NLC were comparable but ChiAmpB NLC was twice less toxic to red blood cells and ten times safer on HT-29 cell lines. In vitro mucoadhesion data were observed ex vivo, where ChiAmpB NLC resulted in higher retention within the small intestine compared to the uncoated formulation. The data strongly offers the possibility of orally administering a non-toxic, yet effective Amphotericin-B nanoformulation for the treatment of systemic fungal infections.

The absorption enhancer sodium deoxycholate promotes high gene transfer in skeletal muscles

Gene delivery to skeletal muscle is a promising strategy for the treatment of muscle disorders and for the systemic secretion of therapeutic proteins. In addition, muscle is an attractive target tissue because it is easily accessible. However, very few synthetic vectors proved capable of surpassing naked DNA mediated muscle gene transfer. In fact, only neutral copolymers, in particular poloxamers, demonstrated capacities to increase transgene expression in skeletal muscles. Here, we studied in vitro and in vivo behaviour of different bile salts. We report that sodium deoxycholate (DOC) and derivatives thereof increase after intramuscular injection by more than 100-fold the levels of the reporter gene luciferase compared to naked DNA. Using a LacZ expression cassette, we found that more than 20% of the muscle fibers expressed the reporter gene. Prolonged expression of a secreted reporter gene derived from a natural murine alkaline phosphatase enzyme could be documented. Altogether, our results demonstrate that bile salts belong to the most efficient chemicals identified so far for skeletal muscle gene transfer. Importantly, since these compounds are naturally found in the body, there is no risk of immune response against them and in addition several bile salts are already used in human medicine. Bile salt mediated muscle gene transfer may thus have broad applications in gene therapy.

Physicochemical, morphological and cellular uptake properties of lutein nanodispersions prepared by using surfactants with different stabilizing mechanisms

In this study, we prepared a series of lutein nanodispersions via the solvent displacement method, by using surfactants with different stabilizing mechanisms. The surfactants used include Tween 80 (steric stabilization), sodium dodecyl sulfate (SDS; electrostatic stabilization), sodium caseinate (electrosteric stabilization) and SDS-Tween 80 (electrostatic-steric stabilization). We then characterized the resulting lutein nanodispersions in terms of their particle size, particle size distribution, zeta potential, lutein content, flow behavior, apparent viscosity, transmittance, color, morphological properties and their effects on cell viability and cellular uptake. The type of surfactant used significantly (p < 0.05) affected the physical properties of the nanodispersions, but the chemical properties (lutein content) remained unaffected. Transmission electron microscopy (TEM) images obtained from this study demonstrated that the solvent displacement method was capable of producing lutein nanodispersions containing spherical particles with sizes ranging from 66.20-125.25 nm, depending on the type of surfactant used. SDS and SDS-Tween 80 surfactants negatively affected the viability of the HT-29 cells used in this study. Thus, for the cellular uptake determination, only Tween 80 and sodium caseinate surfactants were used. The cellular uptake of the lutein nanodispersion stabilized by sodium caseinate was higher than that which was stabilized by Tween 80. All things considered, the type of surfactant with different stabilizing mechanisms did produce lutein nanodispersions with different characteristics. These findings would aid in future selection of surfactants in order to produce nanodispersions with desirable properties.

Effect of permeability enhancers on paracellular permeability of acyclovir

Objectives

According to Biopharmaceutics Classification System (BCS), acyclovir is a class III (high solubility, low permeability) compound, and it is transported through paracellular route by passive diffusion. The aim of this study was to investigate the effect of various pharmaceutical excipients on the intestinal permeability of acyclovir.

Methods

The single-pass in-situ intestinal perfusion (SPIP) method was used to estimate the permeability values of acyclovir and metoprolol across different intestinal segments (jejunum, ileum and colon). Permeability coefficient (Peff) of acyclovir was determined in the absence and presence of a permeation enhancer such as dimethyl β-cyclodextrin (DM-β-CD), sodium lauryl sulfate (SLS), sodium caprate (Cap-Na) and chitosan chloride.

Key findings

All enhancers increased the permeability of paracellularly transported acyclovir. Although Cap-Na has the highest permeability-enhancing effect in all segments, permeation-enhancing effect of chitosan and SLS was only significant in ileum. On the other hand, DM-β-CD slightly decreased the permeability in all intestinal segments.

Conclusions

These findings have potential implication concerning the enhancement of absorption of paracellularly transported compounds with limited oral bioavailability. In the case of acyclovir, Cap-Na either alone or in combination with SLS or chitosan has the potential to improve its absorption and bioavailability and has yet to be explored.

A preliminary technical study on sodium dodecyl sulfate-induced changes of the nano-structural and macro-mechanical properties in human iliotibial tract specimens

INTRODUCTION

Acellular scaffolds are frequently used for the surgical repair of ligaments and tendons. Even though data on the macro-mechanical properties related to the acellularization process exist, corresponding data on the nano-structural properties are still lacking. Such data would help identify target proteins of the formed extracellular matrix that are chemically altered by the acellularization. In this study we examined the altered structure by comparing molecular properties of collagens from native and acellular iliotibial tract samples to the macroscopic stress-strain behavior of tract samples.

MATERIAL AND METHODS

Matched pairs of five human iliotibial tract samples were obtained from five donors (mean age 28.2±4.7 years). One of each pair was acellularized using 1vol% sodium dodecyl sulfate (SDS) for 7 days. (13)C magic angle spinning nuclear magnetic resonance spectroscopy ((13)C CP MAS NMR) was utilized to compare the collagen overall secondary structure and internal dynamics of collagen-typical amino acid proteins. The resulting data was compared to age-matched stress-strain data of tract samples obtained in an uniaxial tensile setup and histologically.

RESULTS

Typical and nearly identical collagen (13)C CP MAS NMR spectra were found in the tract samples before and after acellularization with SDS. The characteristic collagen backbone remained intact in the native and acellular samples. Collagen molecular composition was largely unaltered in both conditions. Furthermore, a similar dynamic behavior was found for the amino acids Hyp γ, Pro α/Hyp α, Ala α, Gly α and Ala β. These minute alterations in the collagens' molecular properties related to acellularization with SDS were in line with the similarly minute changes in the macro-mechanical tensile behavior, such as the elastic modulus and ultimate stress. Histology showed intact type I collagens, minute amounts of elastins before and after acellularization and evidence for acellularization-induced reductions of proteoglycans.

DISCUSSION

Nano-structural properties of collagens are minutely affected by SDS treatment for acellularization, indicated by the molecular composition and dynamics. The lacking acellularization-related changes in the molecular structure properties of collagens in iliotibial tract samples are in line with the small alterations in their macro-mechanical tensile behavior. Though the given setup approaches soft tissue mechanics from both scaling extremes of mechanical testing, further structural analyzes are needed in a larger sample size to substantiate these findings.

Drug Permeation Characterization of Inhaled Dry Powder Formulations in Air-Liquid Interfaced Cell Layer Using an Improved, Simple Apparatus for Dispersion

PURPOSE

An improved, simple apparatus was developed to easily and uniformly disperse dry powders onto an air-liquid interfaced cultured cell layer. We investigated drug permeation in cell cultures with access to the air-liquid interface (ALI) following deposition of a dry powder using the apparatus.

METHOD

The improved apparatus for dispersing the powders was assembled. Dry powders containing model drugs were prepared and dispersed onto the cell layer with ALI. After the dispersion, the permeation of each model drug was measured and compared with other samples (solutions with the same compositions).

RESULTS

The improved apparatus could with ease uniformly disperse 40% of the loading dose onto the cell layer with ALI. Dry powders showed higher drug permeability compared to the samples. without cytotoxicity or an effect on tight junctions. The high drug permeability of dry powders was independent of the molecular weight of model drugs. The contribution of active transport was small, while an increase in passive drug transport via trans- and paracellular routes was observed.

CONCLUSIONS

Inhaled dry powder formulations achieved higher drug permeability than their solution formulations in ALI. A high local concentration of drugs on the cell layer, caused by direct attachment of the inhaled dry powder, contributed to increased drug permeability via both trans- and paracellular routes.

Release of angiotensin converting enzyme-inhibitor peptides during in vitro gastrointestinal digestion of Parmigiano Reggiano PDO cheese and their absorption through an in vitro model of intestinal epithelium

The occurrence of 8 bovine casein-derived peptides (VPP, IPP, RYLGY, RYLG, AYFYPEL, AYFYPE, LHLPLP, and HLPLP) reported as angiotensin converting enzyme-inhibitors (ACE-I) was investigated in the 3-kDa ultrafiltered water-soluble extract (WSE) of Parmigiano Reggiano (PR) cheese samples by ultra-performance liquid chromatography coupled to high-resolution mass spectrometry via an electrospray ionization source. Only VPP, IPP, LHLPLP, and HLPLP were revealed in the WSE, and their total amount was in the range of 8.46 to 21.55 mg/kg of cheese. Following in vitro static gastrointestinal digestion, the same ACE-I peptides along with the newly formed AYFYPEL and AYFYPE were found in the 3 kDa WSE of PR digestates. Digestates presented high amounts (1,880-3,053 mg/kg) of LHLPLP, whereas the remaining peptides accounted for 69.24 to 82.82 mg/kg. The half-maximal inhibitory concentration (IC50) values decreased from 7.92 ± 2.08 in undigested cheese to 3.20 ± 1.69 after in vitro gastrointestinal digestion. The 3-kDa WSE of digested cheeses were used to study the transport of the 8 ACE-I peptides across the monolayers of the Caco-2 cell culture grown on a semipermeable membrane of the transwells. After 1h of incubation, 649.20 ± 148.85 mg/kg of LHLPLP remained in the apical compartment, whereas VPP, IPP, AYFYPEL, AYFYPE, and HLPLP accounted in total for less than 36.78 mg/kg. On average, 0.6% of LHLPLP initially present in the digestates added to the apical compartment were transported intact to the basolateral chamber after the same incubation time. Higher transport rate (2.9%) was ascertained for the peptide HLPLP. No other intact ACE-I peptides were revealed in the basolateral compartment. For the first time, these results demonstrated that the ACE-I peptides HLPLP and LHLPLP present in the in vitro digestates of PR cheese are partially absorbed through an in vitro model of human intestinal epithelium.

Acylation of salmon calcitonin modulates in vitro intestinal peptide flux through membrane permeability enhancement

Acylation of peptide drugs with fatty acid chains has proven beneficial for prolonging systemic circulation, as well as increasing enzymatic stability and interactions with lipid cell membranes. Thus, acylation offers several potential benefits for oral delivery of therapeutic peptides, and we hypothesize that tailoring the acylation may be used to optimize intestinal translocation. This work aims to characterize acylated analogues of the therapeutic peptide salmon calcitonin (sCT), which lowers blood calcium, by systematically increasing acyl chain length at two positions, in order to elucidate its influence on intestinal cell translocation and membrane interaction. We find that acylation drastically increases in vitro intestinal peptide flux and confers a transient permeability enhancing effect on the cell layer. The analogues permeabilize model lipid membranes, indicating that the effect is due to a solubilization of the cell membrane, similar to transcellular oral permeation enhancers. The effect is dependent on pH, with larger effect at lower pH, and is impacted by acylation chain length and position. Compared to the unacylated peptide backbone, N-terminal acylation with a short chain provides 6- or 9-fold increase in peptide translocation at pH 7.4 and 5.5, respectively. Prolonging the chain length appears to hamper translocation, possibly due to self-association or aggregation, although the long chain acylated analogues remain superior to the unacylated peptide. For K(18)-acylation a short chain provides a moderate improvement, whereas medium and long chain analogues are highly efficient, with a 12-fold increase in permeability compared to the unacylated peptide backbone, on par with currently employed oral permeation enhancers. For K(18)-acylation the medium chain acylation appears to be optimal, as elongating the chain causes greater binding to the cell membrane but similar permeability, and we speculate that increasing the chain length further may decrease the permeability. In conclusion, acylated sCT acts as its own in vitro intestinal permeation enhancer, with reversible effects on Caco-2 cells, indicating that acylation of sCT may represent a promising tool to increase intestinal permeability without adding oral permeation enhancers.

Permeapad™ for investigation of passive drug permeability: The effect of surfactants, co-solvents and simulated intestinal fluids (FaSSIF and FeSSIF)

The aim of the present work was to investigate the potential of the new and innovative artificial barrier, Permeapad™, when exposed to surfactants and co-solvents, often employed for poorly water soluble compounds. The barrier was in addition also exposed to fasted and fed state simulated intestinal fluids versions 1 and 2 (FaSSIF and FeSSIF), all of which the Permeapad™ barrier was compatible with based upon relative comparison of the permeability of the hydrophilic marker calcein in phosphate buffer. The new barrier therefore holds a huge potential due to its functional stability and robustness. It can be used as a standard tool to investigate permeability of drugs in the presence of different surfactants and co-solvents, from DMSO stock solutions at even high concentrations and for the evaluation of permeability in the presence of biomimetic media (BMM).

Sodium caprate-induced increases in intestinal permeability and epithelial damage are prevented by misoprostol

Epithelial damage caused by intestinal permeation enhancers is a source of debate concerning safety. The medium chain fatty acid, sodium caprate (C10), causes reversible membrane perturbation at high dose levels required for efficacy in vivo, so the aim was to model it in vitro. Exposure of Caco-2 monolayers to 8.5mM C10 for 60min followed by incubation in fresh buffer led to (i) recovery in epithelial permeability (i.e. transepithelial electrical resistance (TEER) and apparent permeability coefficient (Papp) of [(14)C]-mannitol), (ii) recovery of cell viability parameters (monolayer morphology, plasma membrane potential, mitochondrial membrane potential, and intracellular calcium) and (iii) reduction in mRNA expression associated with inflammation (IL-8). Pre-incubation of monolayers with a mucosal prostaglandin cytoprotectant was attempted in order to further decipher the mechanism of C10. Misoprostol (100nM), inhibited C10-induced changes in monolayer parameters, an effect that was partially attenuated by the EP1 receptor antagonist, SC51322. In rat isolated intestinal tissue mucosae and in situ loop instillations, C10-induced respective increases in the [(14)C]-mannitol Papp and the AUC of FITC-dextran 4000 (FD-4) were similarly inhibited by misoprostol, with accompanying morphological damage spared. These data support a temporary membrane perturbation effect of C10, which is linked to its capacity to mainly increase paracellular flux, but which can be prevented by pre-exposure to misoprostol.

High-content analysis for drug delivery and nanoparticle applications

High-content analysis (HCA) provides quantitative multiparametric cellular fluorescence data. From its origins in discovery toxicology, it is now addressing fundamental questions in drug delivery. Nanoparticles (NPs), polymers, and intestinal permeation enhancers are being harnessed in drug delivery systems to modulate plasma membrane properties and the intracellular environment. Identifying comparative mechanistic cytotoxicity on sublethal events is crucial to expedite the development of such systems. NP uptake and intracellular routing pathways are also being dissected using chemical and genetic perturbations, with the potential to assess the intracellular fate of targeted and untargeted particles in vitro. As we discuss here, HCA is set to make a major impact in preclinical delivery research by elucidating the intracellular pathways of NPs and the in vitro mechanistic-based toxicology of formulation constituents.

Acylation of Glucagon-like peptide-2: interaction with lipid membranes and in vitro intestinal permeability

Background

Acylation of peptide drugs with fatty acid chains has proven beneficial for prolonging systemic circulation as well as increasing enzymatic stability without disrupting biological potency. Acylation has furthermore been shown to increase interactions with the lipid membranes of mammalian cells. The extent to which such interactions hinder or benefit delivery of acylated peptide drugs across cellular barriers such as the intestinal epithelia is currently unknown. The present study investigates the effect of acylating peptide drugs from a drug delivery perspective.

Purpose

We hypothesize that the membrane interaction is an important parameter for intestinal translocation, which may be used to optimize the acylation chain length for intestinal permeation. This work aims to characterize acylated analogues of the intestinotrophic Glucagon-like peptide-2 by systematically increasing acyl chain length, in order to elucidate its influence on membrane interaction and intestinal cell translocation in vitro.

Results

Peptide self-association and binding to both model lipid and cell membranes was found to increase gradually with acyl chain length, whereas translocation across Caco-2 cells depended non-linearly on chain length. Short and medium acyl chains increased translocation compared to the native peptide, but long chain acylation displayed no improvement in translocation. Co-administration of a paracellular absorption enhancer was found to increase translocation irrespective of acyl chain length, whereas a transcellular enhancer displayed increased synergy with the long chain acylation.

Conclusions

These results show that membrane interactions play a prominent role during intestinal translocation of an acylated peptide. Acylation benefits permeation for shorter and medium chains due to increased membrane interactions, however, for longer chains insertion in the membrane becomes dominant and hinders translocation, i.e. the peptides get ‘stuck’ in the cell membrane. Applying a transcellular absorption enhancer increases the dynamics of membrane insertion and detachment by fluidizing the membrane, thus facilitating its effects primarily on membrane associated peptides.

A permeation enhancer for increasing transport of therapeutic macromolecules across the intestine

Delivery of therapeutic macromolecules is limited by the physiological limitations of the gastrointestinal tract including poor intestinal permeability, low pH and enzymatic activity. Several permeation enhancers have been proposed to enhance intestinal permeability of macromolecules; however their utility is often hindered by toxicity and limited potency. Here, we report on a novel permeation enhancer, Dimethyl palmitoyl ammonio propanesulfonate (PPS), with excellent enhancement potential and minimal toxicity. PPS was tested for dose- and time-dependent cytotoxicity, delivery of two model fluorescent molecules, sulforhodamine-B and FITC-insulin in vitro, and absorption enhancement of salmon calcitonin (sCT) in vivo. Caco-2 studies revealed that PPS is an effective enhancer of macromolecular transport while being minimally toxic. TEER measurements in Caco-2 monolayers confirmed the reversibility of the effect of PPS. Confocal microscopy studies revealed that molecules permeate via both paracellular and transcellular pathways in the presence of PPS. In vivo studies in rats showed that PPS enhanced relative bioavailability of sCT by 45-fold after intestinal administration. Histological studies showed that PPS does not induce damage to the intestine. PPS is an excellent permeation enhancer which provides new opportunities for developing efficacious oral/intestinal delivery systems for therapeutic macromolecules.

Oral delivery of macromolecules: rationale underpinning Gastrointestinal Permeation Enhancement Technology (GIPET)

Oral delivery of macromolecular drugs, particularly peptides and proteins, is the focus of many academic and industrial laboratories. Armed with an increased understanding of the structure and regulation of intestinal epithelial junctional complexes of the paracellular barrier, the development of permeation enhancement technology initially focused on the specific and reversible opening of tight junctions in order to enable oral delivery. Despite intense research, none of these specific tight junction-opening technologies has yet been approved in an oral drug product, likely because of poor efficacy. Less specific enhancer technologies with a long history of safe use in man have additional surfactant-like effects on the transcellular pathway that lead to improved efficacy. These are likely to be the first to market for selected poorly permeable peptides. This review presents a summary of some approaches taken to intestinal permeation enhancement and explores in detail the oral delivery system developed by Merrion Pharmaceuticals, Gastrointestinal Permeation Enhancement Technology (GIPET).

Protein and Peptide drug delivery: oral approaches

Till recent, injections remained the most common means for administering therapeutic proteins and peptides because of their poor oral bioavailability. However, oral route would be preferred to any other route because of its high levels of patient acceptance and long term compliance, which increases the therapeutic value of the drug. Designing and formulating a polypeptide drug delivery through the gastro intestinal tract has been a persistent challenge because of their unfavorable physicochemical properties, which includes enzymatic degradation, poor membrane permeability and large molecular size. The main challenge is to improve the oral bioavailability from less than 1% to at least 30-50%. Consequently, efforts have intensified over the past few decades, where every oral dosage form used for the conventional small molecule drugs has been used to explore oral protein and peptide delivery. Various strategies currently under investigation include chemical modification, formulation vehicles and use of enzyme inhibitors, absorption enhancers and mucoadhesive polymers. This review summarizes different pharmaceutical approaches which overcome various physiological barriers that help to improve oral bioavailability that ultimately achieve formulation goals for oral delivery.

Thiolated polycarbophil/glutathione: defining its potential as a permeation enhancer for oral drug administration in comparison to sodium caprate

Thiolated polyacrylates were shown to be permeation enhancers with notable potential. The aim of this study was to evaluate the permeation enhancing properties of a thiolated polycarbophil/glutathione (PCP-Cys/GSH) system for oral drug application in comparison to a well-established permeation enhancer, namely sodium caprate. In vitro permeation studies were conducted in Ussing-type chambers with sodium fluoresceine (NaFlu) and fluoresceine isothiocyanate labeled dextran (molecular mass 4 kDa; FD4) as model compounds. Bioavailability studies were carried out in Sprague Dawley rats with various formulations. Moreover, cytotoxic effects of both permeation enhancers were compared. Permeation enhancement ratios of 1% sodium caprate were found to be 3.0 (FD4) and 2.3 (NaFlu), whereas 1% PCP-Cys/0.5% GSH displayed enhancement ratios of 2.4 and 2.2. Both excipients performed at a similar level in vivo. Sodium caprate solutions increased oral bioavailability 2.2-fold (FD4) and 2.3-fold (NaFlu), while PCP-Cys hydrogels led to a 3.2-fold and 2.2-fold enhancement. Cell viability experiments revealed a significantly higher tolerance of Caco-2 cells towards 0.5% PCP-Cys (81% survival) compared to 0.5% sodium caprate (5%). As PCP-Cys is not absorbed from mucosal membranes due to its comparatively high molecular mass, systemic side-effects can be excluded. In conclusion, both systems displayed a similar potency for permeation enhancement of hydrophilic compounds. However, PCP-Cys seems to be less harmful to cultured cells.

Enhancement of intestinal absorption of 2-methyl cytidine prodrugs

The purpose of this study was to investigate the in vivo absorption enhancement of a nucleoside (phosphoramidate prodrug of 2'-methyl-cytidine) anti-viral agent of proven efficacy by means of intestinal permeation enhancers. Natural nucleosides are hydrophilic molecules that do not rapidly penetrate cell membranes by diffusion and their absorption relies on specialized transporters. Therefore, the oral absorption of nucleoside prodrugs and the target organ concentration of the biologically active nucleotide can be limited due to poor permeation across the intestinal epithelium. In the present study, the specificity, concentration dependence, and effect of four classes of absorption promoters, i.e. fatty acids, steroidal detergents, mucoadhesive polymers, and secretory transport inhibitors, were evaluated in a rat in vivo model. Sodium caprate and alpha-tocopheryl-polyethyleneglycol-1000-succinate (TPGS) showed a significant effect in increasing liver concentration of nucleotide (5-fold). These results suggested that both excipients might be suited in a controlled release matrix for the synchronous release of the drug and absorption promoter directly to the site of absorption and highlights that the effect is strictly dependent on the absorption promoter dose. The feasibility of such a formulation approach in humans was evaluated with the aim of developing a solid dosage form for the peroral delivery of nucleosides and showed that these excipients do provide a potential valuable tool in pre-clinical efficacy studies to drive discovery programs forward.

In-vitro permeability screening of melt extrudate formulations containing poorly water-soluble drug compounds using the phospholipid vesicle-based barrier

Objectives

The phospholipid vesicle-based barrier has recently been introduced as an in-vitro permeation model mimicking gastro-epithelial barriers in terms of passive diffusion of drugs. The aim of this study was to investigate whether the phospholipid vesicle-based barrier was suitable for permeability screening of complex formulations such as solid dispersions.

Methods

Solid dispersions containing the poorly water-soluble drugs HIV-PI 1 (log P = 6.2, molar mass = 628.80 g/mol) and HIV-PI 2 (log P = 5.3, molar mass = 720.95 g/mol), a hydrophilic polymer and different surfactants were tested with respect to their influence on integrity of the barrier in terms of electrical resistance and permeability for calcein. Furthermore, utilisation of a more biologically relevant medium, Hank's balanced salt solution supplemented with Mg2+- and Ca2+-ions (HBSS (Mg2+, Ca2+)), has been tested.

Key findings

Except for the polyoxyl 40 hydrogenated castor oil-containing solid dispersion, no influence on the phospholipid vesicle-based barrier could be observed from the tested samples. Presence of active pharmaceutical ingredients (APIs) in the solid dispersions led to the same results as the corresponding placebo results. First experiments analysing the passive diffusion of both APIs in HBSS (Mg2+, Ca2+), evaluated as suitable transport medium, have shown promising results regarding the suitability of the phospholipid vesicle-based barrier for investigation of solid dispersions.

Conclusions

The study indicated that the phospholipid vesicle-based barrier was compatible with selected melt extrudate formulations. The model seemed capable to reveal different transport routes in comparison with Caco-2 cell permeability tests.

Safety and efficacy of sodium caprate in promoting oral drug absorption: from in vitro to the clinic

A major challenge in oral drug delivery is the development of novel dosage forms to promote absorption of poorly permeable drugs across the intestinal epithelium. To date, no absorption promoter has been approved in a formulation specifically designed for oral delivery of Class III molecules. Promoters that are designated safe for human consumption have been licensed for use in a recently approved buccal insulin spray delivery system and also for many years as part of an ampicillin rectal suppository. Unlike buccal and rectal delivery, oral formulations containing absorption promoters have the additional technical hurdle whereby the promoter and payload must be co-released in high concentrations at the small intestinal epithelium in order to generate significant but rapidly reversible increases in permeability. An advanced promoter in the clinic is the medium chain fatty acid (MCFA), sodium caprate (C(10)), a compound already approved as a food additive. We discuss how it has evolved to a matrix tablet format suitable for administration to humans under the headings of mechanism of action at the cellular and tissue level as well as in vitro and in vivo efficacy and safety studies. In specific clinical examples, we review how C(10)-based formulations are being tested for oral delivery of bisphosphonates using Gastro Intestinal Permeation Enhancement Technology, GIPET (Merrion Pharmaceuticals, Ireland) and in a related solid dose format for antisense oligonucleotides (ISIS Pharmaceuticals, USA).

Assessment of methylsulfonylmethane as a permeability enhancer for regional EDTA chelation therapy

Pharmacologic chelators do not effectively penetrate cell membranes and blood-brain barrier. This study assesses methylsulfonylmethane (MSM) as a permeability enhancer and an excipient to facilitate EDTA transport across biologic membranes, and to make possible localized, regional chelation. Topical application of MSM with C(14)EDTA onto the rat cornea led to uptake of the C(14)EDTA in all tested ocular tissues. Without MSM, EDTA did not penetrate the eye. The ability of MSM to deliver EDTA into an eye provides an opportunity for regional chelation therapy. Additionally, these studies suggest that MSM could also be an adjuvant for delivering ciprofloxacin and other chemical compounds to specific, local tissue sites.

Transepithelial Electrical Resistance is Not a Reliable Measurement of the Caco-2 Monolayer Integrity in Transwell

The significance of monitoring transepithelial electrical resistance (TEER) value during the study on drug absorption through Caco-2 monolayers in Transwells was re-evaluated. TEER value was monitored before, during, and after the absorption of Streptokinase (45 KD). Four enhancers--disodium ethylenediaminetetracetate (disodium EDTA), sodium cholate (NaC), sodium taurocholate (NaTC), and sodium caprate along with alpha-hemolysin (a cell membrane pore-forming toxin)--were used to signify the outcome of this study. Modified trypan blue exclusion technique was used to examine the Caco-2 cell viability throughout the absorption studies. The enhancers at the used concentration exhibited toxic effect on the Caco-2 cells as evident from the trypan blue exclusion studies. This toxic effect was not reflected by the TEER profile because TEER value dropped after the addition of the absorption enhancers. But it came back to its initial value after the cell culture media was replaced by enhancer-free media. This toxic effect was confirmed by the antiproliferation studies on the four enhancers and alpha-hemolysin against Caco-2 cells. Therefore, we concluded that the measurement of TEER is not a reliable method to determine the absorption enhancers toxicity or integrity of the Caco-2 monolayers in the Transwells.

Synthesis and RT inhibitory activity evaluation of new pyrimidine-based seco-nucleosides

Eleven new 3',4'-seco acyclic nucleosides (4-14) were prepared by nucleophilic substitution of protected pyrimidine bases on ethyl 3,3-diethoxypropanoate (3). Structures were characterized spectroscopically and a brief analysis of their conformation in solution was performed by the vicinal coupling constants (3)JH2'aH3' and (3)JH2'bH3'. In solid state, compound 6 forms a homodimer linked by hydrogen bonding. In preliminary tests all compounds show low toxicity and gentle activity against HIV-1 RT in vitro.

In vitro Interactions Between the Oral Absorption Promoter, Sodium Caprate (C10) and S. typhimurium in Rat Intestinal Ileal Mucosae

PURPOSE

The medium chain fatty acid, sodium caprate (C(10)), is a promising oral drug delivery agent that may promote permeability of peptides through increasing paracellular permeability of the intestinal epithelium. One safety concern is that it may permit co-absorption of by-stander agents including pathogens. The purpose of this in vitro study was to examine the effects of C(10) on rat intestinal ileal mucosae in the presence of co-administered Salmonella typhimurium in a low volume vertical Ussing chamber.

METHODS

C(10) or S. typhimurium was added to rat ileal mucosae mounted in chambers and the flux of the paracellular flux of [(14)C]-mannitol examined. S. typhimurium adherence and uptake by ileal mucosae was also examined by counting. Bacterial growth curves were assessed in the presence of C(10). Minimum inhibitory- and bacteriocidal concentrations of C(10) were determined against a range of bacteria.

RESULTS

Apical addition of either C(10) or S. typhimurium to rat ileal mucosae mounted in modified diffusion chambers significantly increased the flux of [(14)C]-mannitol in a concentration-dependent fashion. Co-exposure with increasing concentrations of C(10) attenuated the Salmonella-induced increase in mannitol flux. Histological evaluation revealed that C(10) inhibited both adhesion and invasion of S. typhimurium to intestinal mucosae. Short term bacterial growth studies in the presence of C(10) showed evidence of concentration-dependent inhibition. C(10) was bacteriocidal in mM concentrations against S. typhimurium and selected gram positive and negative bacteria.

CONCLUSIONS

C(10) does not promote the permeation of a common bacterium across isolated intestinal tissue upon acute co-exposure. It prevents S. typhimurium attachment to epithelia and impedes growth of a range of different bacterial strains.

Progress in absorption enhancers based on tight junction

Absorption enhancers have been investigated since the 1960s, in order to assist the transfer of drugs across the paracellular space in the intestinal epithelium. However, few absorption enhancers are presently used clinically, due to the difficulty of developing enhancers with high specificity and low toxicity. Using high-throughput genomic techniques, new drug candidates such as, non-Lipinski molecules, peptides, antibodies and nucleic acids, are being discovered, so the need for oral drug delivery strategies using absorption enhancers is gaining importance. The key to addressing this issue is to understand the molecular mechanism of the paracellular route in epithelial cell sheets. Towards this end, basic research in cell biology has revealed the components that regulate the paracellular route, and how the transport of substances is regulated. Based on these findings, novel strategies for enhancing drug absorption have been proposed. In this article, the authors first survey the development of absorption enhancers, then outline recent progress in the cell biology of tight junctions, and finally discuss novel approaches for absorption enhancers based on these advances.

Chemical modification and formulation approaches to elevated drug transport across cell membranes

Drug delivery across cellular barriers, such as intestinal, nasal, buccal, alveolar, vaginal, ocular and blood-brain, is a challenging task. Multiple physiological mechanisms, such as cellular organisation, efflux, and chemical and enzymatic degradation, as well as physicochemical properties of the drug molecule itself, determine the penetration of xenobiotics across epithelial cell layers. Limited intestinal absorption of many novel and highly potent lead compounds has stimulated an intense search for strategies that can effectively enhance permeation across these biological barriers. This review discusses some of the approaches that have been, and are currently being, investigated for transepithelial drug delivery. Transdermal drug delivery requires a separate discussion on its own and is thus outside the scope of this review article.

Synergistic absorption enhancement of salmon calcitonin and reversible mucosal injury by applying a mucolytic agent and a non-ionic surfactant

The present study investigated the intestinal absorption enhancement of salmon calcitonin (SCT) and the intestinal mucosal damage when a mucolytic agent and a non-ionic surfactant were administered simultaneously to rats. N-acetylcysteine (NAC) and p-t-octyl phenol polyoxyethylene-9.5 (Triton X -100, TX-100) were chosen as the model mucolytic agent and the non-ionic surfactant, respectively. Dosing solutions containing these agents were administered directly into the rat jejunum, and the bioavailability of SCT up to 2 h was determined. NAC and TX-100, when they were used alone at a dose of 1 mg/head, did not show the apparent enhancement compared to the control. However, simultaneous use of NAC and TX-100 enhanced the intestinal absorption of SCT in a synergistic manner, and absolute bioavailability increased 12.5-fold compared to the control. The effect of NAC and TX-100 on SCT absorption was not dependent on their doses over the range of 0.2-2 mg/head, and the maximum effect was obtained at a dose of 1mg/head. Absorption enhancement of SCT by a combination of NAC and TX-100 was compared to those from the classical absorption enhancers. Absorption-enhancing ability of the combination of NAC and TX-100 was significantly higher than those of sodium deoxycholate, citrate, and the combination of citrate and taurocholate, and was comparable with that of the combination of citrate and taurodeoxycholate. Finally, the intestinal mucosal damage caused by the combination of NAC and TX-100 was assessed using a capsule device. Acute damage on intestinal mucosa was observed when they were exposed into rat intestine, but this morphological damage was found to be reversible. All these results suggest that simultaneous use of a mucolytic agent and a non-ionic surfactant would offer a potentiality for peroral delivery of peptide drugs like SCT.

Absorption enhancement, mechanistic and toxicity studies of medium chain fatty acids, cyclodextrins and bile salts as peroral absorption enhancers

The objective of the present investigation was to evaluate an oral 'drug delivery' approach, which involves co-administration of absorption enhancers (AEs). The representative low permeable hydrophilic (biopharmaceutic classification system (BCS) Class III) drugs used in the study comprised of cefotaxime sodium and ceftazidime pentahydrate, whereas low permeable lipophilic (BCS Class IV) drugs include cyclosporin A and lovastatin. AEs from three different chemical classes, namely, medium chain fatty acids (sodium caprylate and caprate), cyclodextrins (beta-cyclodextrin, hydroxypropyl beta-cyclodextrin) and bile salts (sodium cholate and deoxycholate) were evaluated for absorption enhancement efficacy, mechanism of action and toxicity using in vitro everted intestinal sac model. These AEs were found to enhance intestinal permeability of drugs from 2- to 27-fold. Light microscopy studies of intestinal sac incubated with AEs for 120 min revealed morphological changes in absorptive mucosa and rank order of toxicity were cyclodextrins>bile salts congruent with medium chain fatty acids. Fluorescence polarization studies indicated that brush bordered membrane vesicles labeled with lipophilic (DPH, 12AS) and hydrophilic dyes (ANS), when treated with AEs exhibited concentration and time dependent decrease in fluorescence polarization. Total protein released in presence of AEs was more than control but considerably less than EDTA (0.58% w/v), which is known to cause toxic release of proteins from cell. Overall, AEs were found to significantly enhance drug permeability by decreasing lipid membrane fluidity and/or interacting with hydrophilic domains of membrane, and has the potential to improve oral delivery.

Enhanced intestinal absorption of salmon calcitonin (sCT) from proliposomes containing bile salts

PURPOSE

The feasibility of using proliposomes containing salmon calcitonin (sCT) and absorption enhancing agents, as an oral delivery system, to improve the intestinal absorption of sCT was explored using rats and Caco-2 cell systems.

METHODS

Seventeen surfactants were examined for their effects with reference to accelerating the permeability of sCT (300 microg/ml) across Caco-2 cell monolayers, and damage to the intestinal epithelial cells, as measured by the change in transepithelial electrical resistance (TEER) across the cell monolayer. Proliposomes containing sCT (0.75%, w/w) and sodium taurodeoxycholate (NaTDC, 2.5%, w/w) (TDC proliposomes) were prepared according to the standard method using sorbitol and phosphatidylcholine as core and wall-forming materials, respectively, administered intra-duodenally to rats, and plasma concentrations of sCT were subsequently determined by LC-MS.

RESULTS

Among the surfactants examined, some bile salts including NaTDC appeared to be the most advantageous when estimated based on the balance between the permeation enhancement (e.g., a 10.8-fold increase in the permeability of sCT for 0.1% NaTDC) and damage to the cells (e.g., a 3.55-fold decrease in the TEER value for 0.1% NaTDC). The administration of TDC proliposomes resulted in a 7.1-fold increase in the bioavailability (i.e., 0.49%) of sCT, when administered duodenally to rats. The size of the reconstituted liposomes in water was significantly smaller (e.g., 23.2 nm, number weighted diameter), and the entrapment efficiency (EE) of sCT in the reconstituted liposomes was 2.8-fold larger (54.9%), for TDC proliposomes, compared to proliposomes prepared without NaTDC (sCT proliposomes).

CONCLUSION

A 7.1-fold increase in the bioavailability of sCT could be achieved from the TDC proliposomes. In addition to the intrinsic activity of the bile salt to fluidize the membrane, the simultaneous delivery of sCT and NaTDC to the site of absorption in the intestine via proliposomes and the subsequent formation of lipophilic ion-pair complexes between sCT and NaTDC at the site might have been contributing factors in this outstanding absorption enhancement.

Critical Role of Tight Junctions in Drug Delivery across Epithelial and Endothelial Cell Layers

Epithelia in multicellular organisms constitute the frontier that separates the individual from the environment. Epithelia are sites of exchange as well as barriers, for the transit of ions and molecules from and into the organism. Therapeutic agents, in order to reach their target, frequently need to cross epithelial and endothelial sheets. Two routes are available for such purpose: the transcellular and the paracellular pathways. The former is employed by lipophilic drugs and by molecules selectively transported by channels, pumps and carriers present in the plasma membrane. Hydrophilic molecules cannot cross biological membranes, therefore their transepithelial transport could be significantly enhanced if they moved through the paracellular pathway. Transit through this route is regulated by tight junctions (TJs). The discovery in recent years of the molecular mechanisms of the TJ has allowed the design of different procedures to open the paracellular route in a reversible manner. These strategies could be used to enhance drug delivery across epithelial and endothelial barriers. The procedures employed include the use of peptides homologous to external loops of integral TJ proteins, silencing the expression of TJ proteins with antisense oligonucleotides and siRNAs as well as the use of toxins and proteins derived from microorganisms that target TJ proteins.