Effect of the biologically active fragment of zonula occludens toxin, delta G, on the intestinal paracellular transport and oral absorption of mannitol

Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.

Target specific tight junction modulators

Intercellular tight junctions represent a formidable barrier against paracellular drug absorption at epithelia (e.g., nasal, intestinal) and the endothelium (e.g., blood-brain barrier). In order to enhance paracellular transport of drugs and increase their bioavailability and organ deposition, active excipients modulating tight junctions have been applied. First-generation of permeation enhancers (PEs) acted by unspecific interactions, while recently developed PEs address specific physiological mechanisms. Such target specific tight junction modulators (TJMs) have the advantage of a defined specific mechanism of action. To date, merely a few of these novel active excipients has entered into clinical trials, as their lack in safety and efficiency in vivo often impedes their commercialisation. A stronger focus on the development of such active excipients would result in an economic and therapeutic improvement of current and future drugs.

Using peptides to increase transport across the intestinal barrier

The oral route is the preferred for the administration of drugs; however, it has some serious limitations. One of the main disadvantages is poor permeability across the intestinal barrier. Various approaches are currently being adopted to overcome this issue. In this review, we describe the alternatives that use peptides to enhance intestinal absorption. First, we define the various sources of peptide enhancers followed by the analysis of the absorption mechanism used. We then comment on the possible toxic effects derived from their use as permeation enhancers, as well as potential formulation strategies. Finally, the advantages and drawbacks of peptides as intestinal enhancers are examined.

A novel method for imaging sites of paracellular passage of macromolecules in epithelial sheets

Understanding the dynamics of intestinal barrier function is key to elucidating oral delivery routes of therapeutics as well as to understanding various diseases that involve the mucosal immune system. Passage of macromolecules across barrier-forming epithelia is classically analyzed by means of various tracer flux measurements. This approach averages over contributions from many cells and lacks labeling of passage-sites. Thus, abundance and nature of involved cells have remained unidentified. We present a novel method that allowed for optical analysis of passage of various macromolecules on large-scale and single-cell level. To achieve tracking of passage loci in epithelia at submicrometer resolution we used biotinylated and fluorescent macromolecules that bind to basolateral membranes pre-labeled with cell-adherent avidin. We applied this method to epithelial cell lines and isolated mucosae in order to 3-dimensionally determine barrier leak properties over time. Tracer passage was found in all epithelia examined. However, it was infrequent, strikingly inhomogeneous, depended on culture duration and tightness of the monolayer. Stimulating passage with barrier-perturbing agents increased the number of leaks exposition time-dependently in cell lines and explanted mucosae. After stepwise opening of the paracellular passage pathway, integrated tracer-signal measured by our assay strictly correlated to simultaneously performed standard fluxes. Thus, our assay allows for the study of transepithelial macromolecule passage in various physiological and pathological conditions.

Pathways and progress in improving drug delivery through the intestinal mucosa and blood-brain barriers

One of the major hurdles in developing therapeutic agents is the difficulty in delivering drugs through the intestinal mucosa and blood-brain barriers (BBB). The goal here is to describe the general structures of the biological barriers and the strategies to enhance drug delivery across these barriers. Prodrug methods used to improve drug penetration via the transcellular pathway have been successfully developed, and some prodrugs have been used to treat patients. The use of transporters to improve absorption of some drugs (e.g., antiviral agents) has also been successful in treating patients. Other methods, including blocking the efflux pumps to improve transcellular delivery, and modulation of cell-cell adhesion in the intercellular junctions to improve paracellular delivery across biological barriers, are still in the investigational stage.

Paracellular permeation-enhancing effect of AT1002 C-terminal amidation in nasal delivery

BACKGROUND

The identification of permeation enhancers has gained interest in the development of drug delivery systems. A six-mer peptide, H-FCIGRL-OH (AT1002), is a tight junction modulator with promising permeation-enhancing activity. AT1002 enhances the transport of molecular weight markers or agents with low bioavailability with no cytotoxicity. However, AT1002 is not stable in neutral pH or after incubation under physiological conditions, which is necessary to fully uncover its permeation-enhancing effect. Thus, we increased the stability or mitigated the instability of AT1002 by modifying its terminal amino acids and evaluated its subsequent biological activity.

METHODS

C-terminal-amidated (FCIGRL-NH2, Pep1) and N-terminal-acetylated (Ac-FCIGRL, Pep2) peptides were analyzed by liquid chromatography-mass spectrometry. We further assessed cytotoxicity on cell monolayers, as well as the permeation-enhancing activity following nasal administration of the paracellular marker mannitol.

RESULTS

Pep1 was nontoxic to cell monolayers and showed a relatively low decrease in peak area compared to AT1002. In addition, administration of mannitol with Pep1 resulted in significant increases in the area under the plasma concentration-time curve and peak plasma concentration at 3.63-fold and 2.68-fold, respectively, compared to mannitol alone. In contrast, no increase in mannitol concentration was shown with mannitol/AT1002 or mannitol/Pep2 compared to the control. Thus, Pep1 increased the stability or possibly reduced the instability of AT1002, which resulted in an increased permeation-enhancing effect of AT1002.

CONCLUSION

These results suggest the potential usefulness of C-terminal-amidated AT1002 in enhancing nasal drug delivery, which may lead to the development of a practical drug delivery technology for drugs with low bioavailability.

Investigation of effects ofGiardia duodenalison transcellular and paracellular transport in enterocytes usingin vitroUssing chamber experiments

The mechanisms by which different genotypes ofGiardia duodenalisresult in different symptoms remain unresolved. In particular, we lack detailed knowledge on which transport mechanisms (transcellular or paracellular) are affected by differentGiardiaisolates. Using horse radish peroxidase (HRP) and creatinine as transcellular and paracellular probes, respectively, we developed a robust assay that can be used with an Ussing chamber to investigate epithelial transport, as well as short-circuit current as an indicator of net ion transport. We investigated 2Giardiaisolates, both Assemblage A, one a lab-adapted strain and the other a field isolate. Results indicate that products from sonicatedGiardiatrophozoites increase both transcellular and paracellular transport. A non-significant increase in transepithelial electrical resistance (TEER) and short-circuit current were also noted. The paracellular transport was increased significantly more in the field isolate than in the lab-adapted strain. Our results indicate that while both transcellular and paracellular transport mechanisms may be increased following exposure of cells toGiardiatrophozoite sonicate, perhaps by inducing non-specific increases in cellular traffic, it is important thatin vitrostudies ofGiardiapathophysiology are conducted with differentGiardiaisolates, not just lab-attenuated strains.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Recent progress in tight junction modulation for improving bioavailability

INTRODUCTION

Currently, there are many novel drugs that belong to class III or IV of the Biopharmaceutics Classification System, showing low bioavailability. Tight junction (TJ) modulation offers an approach to increase bioavailability of pharmaceutical compounds. Furthermore, some diseases are accompanied by disturbed barrier function or TJ dysregulation and thus represent a second application for TJ modulators.

AREAS COVERED

This review contains a summary of three different TJ modulators: AT1002, PN159 and labradimil. Within this summary, the authors provide a description of their effects on TJs, their adverse effects and their success in clinical trials. Furthermore, the authors present the current understanding of TJ regulation and highlight opportunities to develop new TJ modulators; they also review the problems that might occur.

EXPERT OPINION

The development of new mechanism-based (MB) TJ modulators is a very promising field of research. MB approaches are expected to have the best future prospects. Further elucidation of signaling pathways and TJ regulation will be necessary for advancing MB TJ modulator research.

Elucidating the signal responses of multi-parametric surface plasmon resonance living cell sensing: a comparison between optical modeling and drug-MDCKII cell interaction measurements

In vitro cell-based assays are widely used during the drug discovery and development process to test the biological activity of new drugs. Most of the commonly used cell-based assays, however, lack the ability to measure in real-time or under dynamic conditions (e.g. constant flow). In this study a multi-parameter surface plasmon resonance approach in combination with living cell sensing has been utilized for monitoring drug-cell interactions in real-time, under constant flow and without labels. The multi-parameter surface plasmon resonance approach, i.e. surface plasmon resonance angle versus intensity plots, provided fully specific signal patterns for various cell behaviors when stimulating cells with drugs that use para- and transcellular absorption routes. Simulated full surface plasmon resonance angular spectra of cell monolayers were compared with actual surface plasmon resonance measurements performed with MDCKII cell monolayers in order to better understand the origin of the surface plasmon resonance signal responses during drug stimulation of cells. The comparison of the simulated and measured surface plasmon resonance responses allowed to better understand and provide plausible explanations for the type of cellular changes, e.g. morphological or mass redistribution in cells, that were induced in the MDCKII cell monolayers during drug stimulation, and consequently to differentiate between the type and modes of drug actions. The multi-parameter surface plasmon resonance approach presented in this study lays the foundation for developing new types of cell-based tools for life science research, which should contribute to an improved mechanistic understanding of the type and contribution of different drug transport routes on drug absorption.

The impact of AT1002 on the delivery of ritonavir in the presence of bioadhesive polymer, carrageenan

New insights into the modification of the tight junctions theoretically offer the opportunity to regulate the diffusion barrier and then make it possible to investigate a permeation enhancer of low-bioavailability therapeutic agents. AT1002, a minimum biologically active fragment of zonula occludens toxin which reversibly opens intercellular tight junctions after binding to the Zonulin receptor, increased the transport of various molecular weight markers or low-bioavailability agents. The objective of this study was continuously to evaluate the permeation-enhancing ability of AT1002 in the presence of the bioadhesive agent, carrageenan after intranasal administration of the antiretroviral drug, ritonavir, and the permeation enhancement ratio compared with the previous results. The permeation-enhancing effect of AT1002 was significantly promoted by the bioadhesive agent, carrageenan. The administration of ritonavir with AT1002 and carrageenan resulted in a 2.55-fold increase in AUC(0-240min) and a 2.48-fold increase in C(max) compared with the control group. However, AT1002 in the absence of carrageenan did not produce a statistic enhancement in the absorption of ritonavir. Hence, AT1002 together with the addition of carrageenan may open a new approach of research in the tight junction modulated permeation enhancer, and allow the development of the mucosal drug delivery of therapeutic agents.

The influence of AT1002 on the nasal absorption of molecular weight markers and therapeutic agents when co-administered with bioadhesive polymers and an AT1002 antagonist, AT1001

OBJECTIVES

The purpose of this study was to demonstrate the effects of the tight junction permeation enhancer, AT1002, on the nasal absorption of molecular weight markers and low bioavailable therapeutic agents co-administered with bioadhesive polymers or zonulin antagonist.

METHODS

The bioadhesive polymers, carrageenan and Na-CMC, were prepared with AT1002 to examine the permeation-enhancing effect of AT1002 on the nasal absorption of inulin, calcitonin and saquinavir after nasal administration to Sprague-Dawley rats. Blood samples were collected over a 6-hour period from a jugular cannula. In addition, we determined whether AT1002 exerts a permeation-enhancing effect via activation of PAR-2 specific binding to a putative receptor of zonulin. To examine this zonulin antagonist, AT1001, was administered 30 min prior to dosing with an AT1002/inulin solution and blood samples were collected over a 6-hour period.

KEY FINDINGS

The bioadhesive polymers did not directly increase the absorption of inulin, calcitonin and saquinavir, but promoted the permeation-enhancing effect of AT1002 when delivered nasally, thereby significantly increasing the absorption of each drug. Pre-treatment with AT1001 antagonized the zonulin receptor and significantly minimized the permeation-enhancing effect of AT1002.

CONCLUSION

These findings will assist in understanding the permeation-enhancing capability of and the receptor binding of AT1002. Further, combining AT1002 with carrageenan supports the development of the mucosal delivery of therapeutic agents that have low bioavailability even with bioadhesive agents.

Multifaceted interactions of bacterial toxins with the gastrointestinal mucosa

The digestive tract is one of the ecosystems that harbors the largest number and greatest variety of bacteria. Among them, certain bacteria have developed various strategies, including the synthesis of virulence factors such as toxins, to interact with the intestinal mucosa, and are responsible for various pathologies. A large variety of bacterial toxins of different sizes, structures and modes of action are able to interact with the gastrointestinal mucosa. Some toxins, termed enterotoxins, directly stimulate fluid secretion in enterocytes or cause their death, whereas other toxins pass through the intestinal barrier and disseminate by the general circulation to remote organs or tissues, where they are active. After recognition of a membrane receptor on target cells, toxins can act at the cell membrane by transducing a signal across the membrane in a hormone-like manner, by pore formation or by damaging membrane compounds. Other toxins can enter the cells and modify an intracellular target leading to a disregulation of certain physiological processes or disorganization of some structural architectures and cell death. Toxins are fascinating molecules, which mimic or interfere with eukaryotic physiological processes. Thereby, they have permitted the identification and characterization of new natural hormones or regulatory pathways. Besides use as protective antigens in vaccines, toxins offer multiple possibilities in pharmacology, such as immune modulation or specific delivery of a protein of interest into target cells.

Multiple facets of intestinal permeability and epithelial handling of dietary antigens

The intestinal epithelium, the largest interface between the host and environment, regulates fluxes of ions and nutrients and limits host contact with the massive load of luminal antigens. Local protective and tolerogenic immune responses toward luminal content depend on antigen sampling by the gut epithelial layer. Whether, and how exaggerated, the entrance of antigenic macromolecules across the gut epithelium might initiate and/or perpetuate chronic inflammation as well as the respective contribution of paracellular and transcellular permeability remains a matter of debate. To this extent, experimental studies involving the in vivo assessment of intestinal permeability using small inert molecules do not necessarily correlate with the uptake of larger dietary antigens. This review analyzes both the structural and functional aspects of intestinal permeability with special emphasis on antigen handling in healthy and diseased states and consequences on local immune responses to food antigens.

The ethanol metabolite acetaldehyde increases paracellular drug permeability in vitro and oral bioavailability in vivo

Alcohol consumption leads to the production of the highly reactive ethanol metabolite, acetaldehyde, which may affect intestinal tight junctions and increase paracellular permeability. We examined the effects of elevated acetaldehyde within the gastrointestinal tract on the permeability and bioavailability of hydrophilic markers and drug molecules of variable molecular weight and geometry. In vitro permeability was measured unidirectionally in Caco-2 and MDCKII cell models in the presence of acetaldehyde, ethanol, or disulfiram, an aldehyde dehydrogenase inhibitor, which causes acetaldehyde formation when coadministered with ethanol in vivo. Acetaldehyde significantly lowered transepithelial resistance in cell monolayers and increased permeability of the low-molecular-weight markers, mannitol and sucrose; however, permeability of high-molecular-weight markers, polyethylene glycol and inulin, was not affected. In vivo permeability was assessed in male Sprague-Dawley rats treated for 6 days with ethanol, disulfiram, or saline alone or in combination. Bioavailability of naproxen was not affected by any treatment, whereas that of paclitaxel was increased upon acetaldehyde exposure. Although disulfiram has been shown to inhibit multidrug resistance-1 P-glycoprotein (P-gp) in vitro, our data demonstrate that the known P-gp substrate paclitaxel is not affected by coadministration of disulfiram. In conclusion, we demonstrate that acetaldehyde significantly modulates tight junctions and paracellular permeability in vitro as well as the oral bioavailability of low-molecular-weight hydrophilic probes and therapeutic molecules in vivo even when these molecules are substrates for efflux transporters. These studies emphasize the significance of ethanol metabolism and drug interactions outside of the liver.

Physiological, pathological, and therapeutic implications of zonulin-mediated intestinal barrier modulation: living life on the edge of the wall

The anatomical and functional arrangement of the gastrointestinal tract suggests that this organ, beside its digestive and absorptive functions, regulates the trafficking of macromolecules between the environment and the host through a barrier mechanism. Under physiological circumstances, this trafficking is safeguarded by the competency of intercellular tight junctions, structures whose physiological modulation is mediated by, among others, the recently described protein zonulin. To prevent harm and minimize inflammation, the same paracellular pathway, in concert with the gut-associated lymphoid tissue and the neuroendocrine network, controls the equilibrium between tolerance and immunity to nonself antigens. The zonulin pathway has been exploited to deliver drugs, macromolecules, or vaccines that normally would not be absorbed through the gastrointestinal mucosal barrier. However, if the tightly regulated trafficking of macromolecules is jeopardized secondary to prolonged zonulin up-regulation, the excessive flow of nonself antigens in the intestinal submucosa can cause both intestinal and extraintestinal autoimmune disorders in genetically susceptible individuals. This new paradigm subverts traditional theories underlying the development of autoimmunity, which are based on molecular mimicry and/or the bystander effect, and suggests that the autoimmune process can be arrested if the interplay between genes and environmental triggers is prevented by re-establishing intestinal barrier competency. Understanding the role of zonulin-dependent intestinal barrier dysfunction in the pathogenesis of autoimmune diseases is an area of translational research that encompasses many fields.

Structure-activity relationship studies of permeability modulating peptide AT-1002

AT-1002 a 6-mer synthetic peptide belongs to an emerging novel class of compounds that reversibly increase paracellular transport of molecules across the epithelial barrier. The aim of this project was to elaborate on the structure-activity relationship of this peptide with the specific goal to replace the P2 cysteine amino acid. Herein, we report the discovery of peptides that exhibit reversible permeability enhancement properties with an increased stability profile.

Enhanced nasal absorption of hydrophilic markers after dosing with AT1002, a tight junction modulator

AT1002 is a six-mer synthetic peptide, H-FCIGRL-OH, that retains the delta G and Zot biological activity of reversibly opening tight junctions and increases the paracellular transport of drugs. The objective of this study was to evaluate the possible use of AT1002 in enhancing the nasal availability of macromolecules using large paracellular markers as model agents. Male Sprague-Dawley rats cannulated in the jugular vein were randomly assigned to receive radiolabelled paracellular markers, [14C]PEG4000 or [14C]inulin, with/without AT1002, for each intranasal study. The plasma concentration of PEG4000 with AT1002 (10mg/kg) was significantly higher than that from PEG4000 control over 360 min following intranasal administration. The AUC0-360 min and Cmax from the PEG4000/AT1002 (10mg/kg) treatment were statistically (p<0.05) increased to 235% and 357%, of control, respectively. When inulin was administered with AT1002 (10 mg/kg), the plasma concentration was significantly higher (p<0.05) than control over 360 min, and increases (p<0.05) of 292% and 315% for AUC0-360 min and Cmax over control were observed, respectively. AT1002 significantly increased the nasal absorption of molecular weight markers, PEG4000 and inulin. This study suggests that AT1002 may be used to enhance the systemic availability of macromolecules when administered concurrently.

Zonula occludens toxin synthetic peptide derivative AT1002 enhances in vitro and in vivo intestinal absorption of low molecular weight heparin

Zonula occludens toxin (Zot) is an enterotoxin obtained from the bacterium vibrio cholerae that has been shown to reversibly and safely open the tight junctions and enhance paracellular transport. AT1002 is a novel synthetic hexapeptide derived from Zot. The hypothesis to be tested in this study is that AT1002 enhances the oral absorption of ardeparin, a low molecular weight heparin (LMWH). To test this hypothesis, drug transport through Caco-2 cell monolayers was monitored in the presence and absence of AT1002. Regional permeability studies using rat intestine were performed. Cell viability in the presence of various concentrations of enhancer was determined. The absorption of ardeparin after oral administration in rats was measured by anti-factor Xa assay. Furthermore, the eventual mucosal and epithelial damage was histologically evaluated. Higher ardeparin permeability (approximately 2-fold) compared to control was observed in the presence of 0.025% of AT1002. Regional permeability studies revealed that the permeability of ardeparin across the duodenal membrane was improved by the AT1002. Cell viability studies showed no significant cytotoxicity below 0.0028% of AT1002. In the presence of 100 microg/kg of AT1002, ardeparin oral bioavailability was significantly increased (F(relative/s.c) approximately 20.5%). Furthermore, AT1002 at a dose of 100 microg/kg did not induce any observable morphological damage on gastrointestinal (GI) tissues in vivo. These in vivo and in vitro results suggest that the co-administration of LMWH with AT1002 may be a useful delivery strategy to increase its permeability and hence oral absorption.

Enhancement of brain distribution of anticancer agents using ΔG, the 12kDa active fragment of ZOT

OBJECTIVE

The objective of this study was to evaluate the ability of DeltaG, the 12 kDa active fragment of ZOT, to increase the brain distribution of MTX and paclitaxel, two commonly used anticancer agents with poor distribution into the brain.

METHODS

As part of dose estimation of DeltaG, [14C]-sucrose (40 microCi/kg), a hydrophilic paracellular marker, was co-administered with DeltaG (0, 400 and 800 microg/kg) with and without protease inhibitors to male Sprague-Dawley rats (n=3 per group) via an intracarotid cannula. MTX (50 mg/kg) and [3H]-paclitaxel (120 microCi/kg) were co-administered with the effective doses of DeltaG determined from the above study via the intracarotid cannula. Animals were euthanized by carbon dioxide asphyxiation at the specified time periods and brain and plasma samples were analyzed for the respective drug.

RESULTS

The brain distribution of [14C]-sucrose was significantly enhanced at both doses of DeltaG. A fold enhancement in the B/P ratios of 1.88 and 2.68 was observed at the 400 and 800 microg/kg doses respectively, when the protein was protected from metabolic degradation with PIs. DeltaG significantly increased the brain distribution of MTX at each of the doses administered, with over a seven-fold increase at the 600 microg/kg dose. [3H]-paclitaxel brain AUC(0-60 min) was significantly higher in the presence of DeltaG (800 microg/kg with PIs) with a 2.5-fold enhancement in brain exposure.

CONCLUSIONS

DeltaG significantly enhances the brain distribution of MTX (hydrophilic) and paclitaxel (lipophilic) and has the potential to be further developed as adjunct therapy to increase delivery of poorly permeable chemotherapeutic and other CNS targeted compounds.

Current strategies used to enhance the paracellular transport of therapeutic polypeptides across the intestinal epithelium

The intent of this paper is to update the reader on various strategies which have been utilized to increase the paracellular permeability of protein and polypeptide drugs across the intestinal epithelium. Structural features of protein and polypeptide drugs, together with the natural anatomical and physiological features of the gastrointestinal (GI) tract, have made oral delivery of this class of compounds extremely challenging. Interest in the paracellular route for the transport of therapeutic proteins and polypeptides following oral administration has recently intensified and continues to be explored. The assumption that molecules with a large molecular weight are not able to diffuse through the tight junctions of the intestinal membrane has been challenged by current research, along with an increased understanding of tight junction physiology.

Influence of the intermediate digestion phases of common formulation lipids on the absorption of a poorly water‐soluble drug

The influence of different model intestinal phases (modelled on those likely to be produced in vivo after the digestion of commonly used formulation lipids) on the absorption profile of cinnarizine has been studied. Combinations of C8, C12, or C18:1 fatty acid and monoglyceride and simulated endogenous intestinal fluid were formulated to provide examples of liquid (L1), lamellar (L(alpha)), and cubic (C) liquid crystalline phases. Phases containing cinnarizine were dosed intraduodenally and absorption was assessed in an anesthetized rat model. Bile duct ligation was performed to inhibit the effects of digestion/dilution on the phase structure. Absorption from the L(alpha) phases (C8 and C12 lipids) was statistically higher (p < 0.05) than a cinnarizine suspension: however, a statistically significant difference was not observed from the L1 and C phases. The rigid C18:1 C phase showed evidence of providing for sustained drug absorption. Experiments in bile intact rats with the C8 L(alpha) and C18:1 C phase highlighted that the absorption-modifying properties of these phases were influenced by dilution in the endogenous bile milieu, with absorption from L(alpha) phase reducing (possibly through precipitation of solubilized drug) and increasing in the case of the C18:1 C phase, possibly through the coexistence of L1 and C upon dilution permitting more efficient transfer of solubilized drug.

The effect of delta G on the transport and oral absorption of macromolecules

Delta G (DeltaG) is the biologically active fragment of Zonula Occludens Toxin (Zot), an absorption enhancer, that reversibly opens the tight junctions of epithelial and endothelial cells in the small intestine and brain. This study evaluates the possible use of DeltaG in enhancing the oral bioavailability of macromolecules using large paracellular markers as model agents. The transport of [(14)C]Inulin and [(14)C]PEG4000 was evaluated across Caco-2 cells with DeltaG (0, 100, 180 microg/ml). The apparent permeability coefficients (P(app)) were calculated. The in vitro toxicity of DeltaG (180 microg/ml) was assessed. Sprague Dawley rats were dosed intraduodenally (ID) with the following treatments: [(14)C]Inulin or [(14)C]PEG4000 (30 microci/kg) w/o DeltaG (720 microg/kg)/protease inhibitors (PI). Blood was collected and plasma was analyzed for radioactivity. DeltaG (180 microg/ml) increased [(14)C]Inulin and [(14)C]PEG4000 P(app) by 82.6 and 24.4%, respectively, without any toxicity. After ID administration with DeltaG/PI, C(max) and AUC were significantly (p < 0.05) increased for both Inulin and PEG4000. However, Inulin displayed greater enhancement ratios in vitro and in vivo. This study suggests that DeltaG may be used to enhance the oral bioavailability of macromolecules (e.g., proteins) after coadministration through modulation of paracellular transport.

The impact of DeltaG on the oral bioavailability of low bioavailable therapeutic agents

Low oral bioavailability continues to drive research toward identifying novel approaches to enhance drug delivery. Over the past few years, emphasis on the use of absorption enhancers has been overwhelming despite their major adverse effects. Zonula occludens toxin (Zot) was recently established as a safe and effective absorption enhancer, reversibly opening the tight junctions for hydrophilic markers and hydrophobic drugs across the small intestine and the blood brain barrier. DeltaG, the biologically active fragment of Zot, was isolated and shown to increase the in vitro transport and in vivo absorption of paracellular markers. The objective of this study was to examine the effect of DeltaG on the oral bioavailability of low bioavailable therapeutic agents. Jugular vein cannulated Sprague-Dawley rats were randomly assigned to receive the following treatments intraduodenally (ID): [(3)H]cyclosporin A, [(3)H]ritonavir, [(3)H]saquinavir, or [(3)H]acyclovir at (120 microCi/kg) alone, with protease inhibitors (PIs), or with DeltaG (720 microg/kg)/PI. Serial blood samples were collected, and plasma was analyzed for radioactivity. After ID administration with DeltaG/PI, C(max) significantly (p < 0.05) increased over a range of 197 to 5700%, whereas area under the plasma concentration time curve displayed significant increases extending over a range of 123.8 to 4990.3% for the investigated drugs. DeltaG significantly increased the in vivo oral absorption of some low bioavailable drugs in the presence of PI. This study suggests that DeltaG-mediated tight junction modulation, combined with metabolic protection, may be used to enhance the low oral bioavailability of certain drugs when administered concurrently.