Displacement of tight junction proteins from detergent-resistant membrane domains by treatment with sodium caprate

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.

Oral insulin delivery: Barriers, strategies, and formulation approaches: A comprehensive review

Diabetes Mellitus is characterized by a hyperglycemic condition which can either be caused by the destruction of the beta cells or by the resistance developed against insulin in the cells. Insulin is a peptide hormone that regulates the metabolism of carbohydrates, proteins, and fats. Type 1 Diabetes Mellitus needs the use of Insulin for efficient management. However invasive methods of administration may lead to reduced adherence by the patients. Hence there is a need for a non-invasive method of administration. Oral Insulin has several merits over the conventional method including patient compliance, and reduced cost, and it also mimics endogenous insulin and hence reaches the liver by the portal vein at a higher concentration and thereby showing improved efficiency. However oral Insulin must pass through several barriers in the gastrointestinal tract. Some strategies that could be utilized to bypass these barriers include the use of permeation enhancers, absorption enhancers, use of suitable polymers, use of suitable carriers, and other agents. Several formulation types have been explored for the oral delivery of Insulin like hydrogels, capsules, tablets, and patches which have been described briefly by the article. A lot of attempts have been made for developing oral insulin delivery however none of them have been commercialized due to numerous shortcomings. Currently, there are several formulations from the companies that are still in the clinical phase, the success or failure of some is yet to be seen in the future.

Gastrointestinal Permeation Enhancers for the Development of Oral Peptide Pharmaceuticals

Recently, two oral-administered peptide pharmaceuticals, semaglutide and octreotide, have been developed and are considered as a breakthrough in peptide and protein drug delivery system development. In 2019, the Food and Drug Administration (FDA) approved an oral dosage form of semaglutide developed by Novo Nordisk (Rybelsus^®) for the treatment of type 2 diabetes. Subsequently, the octreotide capsule (Mycapssa^®), developed through Chiasma's Transient Permeation Enhancer (TPE) technology, also received FDA approval in 2020 for the treatment of acromegaly. These two oral peptide products have been a significant success; however, a major obstacle to their oral delivery remains the poor permeability of peptides through the intestinal epithelium. Therefore, gastrointestinal permeation enhancers are of great relevance for the development of subsequent oral peptide products. Sodium salcaprozate (SNAC) and sodium caprylate (C8) have been used as gastrointestinal permeation enhancers for semaglutide and octreotide, respectively. Herein, we briefly review two approved products, Rybelsus^® and Mycapssa^®, and discuss the permeation properties of SNAC and medium chain fatty acids, sodium caprate (C10) and C8, focusing on Eligen technology using SNAC, TPE technology using C8, and gastrointestinal permeation enhancement technology (GIPET) using C10.

Influene of Pharmaceutical Excipients on the Membrane Transport of a P-glycoprotein Substrate in the Rat Small Intestine

BACKGROUND AND OBJECTIVES

Generic drugs are generally used worldwide because of affordability compared to brand-name drugs. One of the main differences between brand-name and generic drugs is pharmaceutical excipients. We previously reported the effects of pharmaceutical excipients on the membrane permeation of drugs via the paracellular and transcellular routes, which are passive transport routes. P-glycoprotein (P-gp) is a typical ATP-binding cassette transporter and is mostly responsible for drug-drug interactions involving transporters. In the present study, rhodamine 123 (Rho123) was selected as the P-gp substrate, and the effects of pharmaceutical excipients on its membrane transport in the rat jejunum and ileum were examined.

METHODS

Twenty major pharmaceutical excipients widely used in the pharmaceutical industry were selected. The in vitro diffusion chamber method using the rat jejunum and ileum was employed to investigate the effects of pharmaceutical excipients on the membrane permeation of Rho123.

RESULTS

The results obtained showed that the membrane permeability of Rho123 significantly (P < 0.05) changed under certain dosage conditions of pharmaceutical excipients such as sodium carboxymethyl starch, pullulan, glyceryl monostearate and so on. Furthermore, the effects of pharmaceutical excipients were site specific in the small intestine.

CONCLUSION

The present results demonstrated that some pharmaceutical excipients altered the membrane permeability of Rho123 in the rat small intestine.

Claudin 19 Is Regulated by Extracellular Osmolality in Rat Kidney Inner Medullary Collecting Duct Cells

The inner medullary collecting duct (IMCD) is subject to severe changes in ambient osmolality and must either allow water transport or be able to seal the lumen against a very high osmotic pressure. We postulate that the tight junction protein claudin-19 is expressed in IMCD and that it takes part in epithelial adaptation to changing osmolality at different functional states. Presence of claudin-19 in rat IMCD was investigated by Western blotting and immunofluorescence. Primary cell culture of rat IMCD cells on permeable filter supports was performed under different osmotic culture conditions and after stimulation by antidiuretic hormone (AVP). Electrogenic transepithelial transport properties were measured in Ussing chambers. IMCD cells cultivated at 300 mosm/kg showed high transepithelial resistance, a cation selective paracellular pathway and claudin-19 was mainly located in the tight junction. Treatment by AVP increased cation selectivity but did not alter transepithelial resistance or claudin-19 subcellular localization. In contrast, IMCD cells cultivated at 900 mosm/kg had low transepithelial resistance, anion selectivity, and claudin-19 was relocated from the tight junctions to intracellular vesicles. The data shows osmolality-dependent transformation of IMCD epithelium from tight and sodium-transporting to leaky, with claudin-19 expression in the tight junction associated to tightness and cation selectivity under low osmolality.

Mechanistic Studies on the Absorption-Enhancing Effects of Gemini Surfactant on the Intestinal Absorption of Poorly Absorbed Hydrophilic Drugs in Rats

Generally, the use of absorption enhancers might be the most effective approaches to ameliorate the enteric absorption of poorly absorbed substances. Among numerous absorption enhancers, we already reported that a gemini surfactant, sodium dilauramidoglutamide lysine (SLG-30) with two hydrophobic and two hydrophilic moieties, is a novel and promising adjuvant with a high potency in improving the absorption safely. Here, we examined and elucidated the absorption-improving mechanisms of SLG-30 in the enteric absorption of substances. SLG-30 increased the intestinal absorption of 5(6)-carboxyfluorescein (CF) to a greater level than the typical absorption enhancers, including sodium glycocholate and sodium laurate, as evaluated by an in situ closed-loop method. Furthermore, SLG-30 significantly lowered the fluorescence anisotropy of dansyl chloride (DNS-Cl), suggesting that it might increase the fluidity of protein sections in the intestinal cell membranes. Moreover, SLG-30 significantly lowered the transepithelial-electrical resistance (TEER) values of Caco-2 cells, suggesting that it might open the tight junctions (TJs) between the enteric epithelial cells. Additionally, the levels of claudin-1 and claudin-4 expression decreased in the presence of SLG-30. These outcomes propose that SLG-30 might improve the enteric transport of poorly absorbed substances through both transcellular and paracellular routes.

Intestinal Permeation Enhancers for Oral Delivery of Macromolecules: A Comparison between Salcaprozate Sodium (SNAC) and Sodium Caprate (C10)

Salcaprozate sodium (SNAC) and sodium caprate (C10) are two of the most advanced intestinal permeation enhancers (PEs) that have been tested in clinical trials for oral delivery of macromolecules. Their effects on intestinal epithelia were studied for over 30 years, yet there is still debate over their mechanisms of action. C10 acts via openings of epithelial tight junctions and/or membrane perturbation, while for decades SNAC was thought to increase passive transcellular permeation across small intestinal epithelia based on increased lipophilicity arising from non-covalent macromolecule complexation. More recently, an additional mechanism for SNAC associated with a pH-elevating, monomer-inducing, and pepsin-inhibiting effect in the stomach for oral delivery of semaglutide was advocated. Comparing the two surfactants, we found equivocal evidence for discrete mechanisms at the level of epithelial interactions in the small intestine, especially at the high doses used in vivo. Evidence that one agent is more efficacious compared to the other is not convincing, with tablets containing these PEs inducing single-digit highly variable increases in oral bioavailability of payloads in human trials, although this may be adequate for potent macromolecules. Regarding safety, SNAC has generally regarded as safe (GRAS) status and is Food and Drug Administration (FDA)-approved as a medical food (Eligen®-Vitamin B12, Emisphere, Roseland, NJ, USA), whereas C10 has a long history of use in man, and has food additive status. Evidence for co-absorption of microorganisms in the presence of either SNAC or C10 has not emerged from clinical trials to date, and long-term effects from repeat dosing beyond six months have yet to be assessed. Since there are no obvious scientific reasons to prefer SNAC over C10 in orally delivering a poorly permeable macromolecule, then formulation, manufacturing, and commercial considerations are the key drivers in decision-making.

Ceramide synthase 2 deficiency aggravates AOM-DSS-induced colitis in mice: role of colon barrier integrity

Loss of intestinal barrier functions is a hallmark of inflammatory bowel disease like ulcerative colitis. The molecular mechanisms are not well understood, but likely involve dysregulation of membrane composition, fluidity, and permeability, which are all essentially regulated by sphingolipids, including ceramides of different chain length and saturation. Here, we used a loss-of-function model (CerS2+/+ and CerS2-/- mice) to investigate the impact of ceramide synthase 2, a key enzyme in the generation of very long-chain ceramides, in the dextran sodium salt (DSS) evoked model of UC. CerS2-/- mice developed more severe disease than CerS2+/+ mice in acute DSS and chronic AOM/DSS colitis. Deletion of CerS2 strongly reduced very long-chain ceramides (Cer24:0, 24:1) but concomitantly increased long-chain ceramides and sphinganine in plasma and colon tissue. In naive CerS2-/- mice, the expression of tight junction proteins including ZO-1 was almost completely lost in the colon epithelium, leading to increased membrane permeability. This could also be observed in vitro in CerS2 depleted Caco-2 cells. The increase in membrane permeability in CerS2-/- mice did not manifest with apparent clinical symptoms in naive mice, but with slight inflammatory signs such as an increase in monocytes and IL-10. AOM/DSS and DSS treatment alone led to a further deterioration of membrane integrity and to severe clinical symptoms of the disease. This was associated with stronger upregulation of cytokines in CerS2-/- mice and increased infiltration of the colon wall by immune cells, particularly monocytes, CD4+ and Th17+ T-cells, and an increase in tumor burden. In conclusion, CerS2 is crucial for the maintenance of colon barrier function and epithelial integrity. CerS2 knockdown, and associated changes in several sphingolipids such as a drop in very long-chain ceramides/(dh)-ceramides, an increase in long-chain ceramides/(dh)-ceramides, and sphinganine in the colon, may weaken endogenous defense against the endogenous microbiome.

Angubindin-1, a novel paracellular absorption enhancer acting at the tricellular tight junction

A limiting barrier for mucosal absorption of drugs is the tight junction (TJ). TJs exist between two adjacent cells (bicellular TJ, bTJ) and at the sites where three cells meet (tricellular TJ, tTJ). We present a novel approach which employs a physiologically regulated pathway for the passage of large molecules through the tTJ. Main barrier-relevant tTJ proteins are tricellulin and angulin-1 to -3. We developed an angulin binder from Clostridium perfringens iota-toxin (Ib) whose receptor is angulin-1. An Ib fragment corresponding to amino acids 421-664 (Ib421-664) of iota-toxin proved to bind in cells expressing angulin-1 and -3, but not angulin-2. This binding led to removal of angulin-1 and tricellulin from the tTJ which enhanced the permeation of macromolecular solutes. Ib421-664 enhanced intestinal absorption in rats and mice. Our findings indicate that Ib421-664, which we designate angubindin-1, is a modulator of the tTJ barrier and that modulation of that barrier qualifies for a new strategy of developing a mucosal absorption enhancer.

Porcine milk induces a strengthening of barrier function in porcine jejunal epithelium in vitro

Milk contains a variety of components that have been shown to affect the expression and localization of epithelial tight junction proteins and therefore the intestinal barrier. Thus, we hypothesized that milk would have an effect on intestinal barrier properties, owing to effects on the tight junction in an intraspecies porcine intestinal in vitro model. Jejunal samples of piglets derived from different age groups were analyzed. Transepithelial electrical resistance was recorded employing the Ussing chamber technique. Porcine milk or predigested milk in buffer solution was added to the apical side, and effects were compared to untreated controls. Unidirectional paracellular flux measurements were performed using sodium fluorescein. Tight junction protein expression and localization were analyzed by immunoblotting and immunofluorescence microscopy. Incubation with milk or predigested milk led to an increase in transepithelial electrical resistance, while paracellular permeability for sodium fluorescein did not result in significant changes. Densitometric analysis of immunoblot signals did not show significant alterations in claudin expression, but a reduction of claudin signals in apicolateral membrane compartments in both approaches became apparent via immunohistology. The functional effect might reflect a physiological protective mechanism, when offspring exclusively rely on their mother's milk and are exposed to a plethora of potentially barrier-perturbing factors.

Parathyroid hormone controls paracellular Ca2+ transport in the thick ascending limb by regulating the tight-junction protein Claudin14

Renal Ca²⁺ reabsorption is essential for maintaining systemic Ca²⁺ homeostasis and is tightly regulated through the parathyroid hormone (PTH)/PTHrP receptor (PTH1R) signaling pathway. We investigated the role of PTH1R in the kidney by generating a mouse model with targeted deletion of PTH1R in the thick ascending limb of Henle (TAL) and in distal convoluted tubules (DCTs): Ksp-cre;Pth1r^fl/fl Mutant mice exhibited hypercalciuria and had lower serum calcium and markedly increased serum PTH levels. Unexpectedly, proteins involved in transcellular Ca²⁺ reabsorption in DCTs were not decreased. However, claudin14 (Cldn14), an inhibitory factor of the paracellular Ca²⁺ transport in the TAL, was significantly increased. Analyses by flow cytometry as well as the use of Cldn14-lacZ knock-in reporter mice confirmed increased Cldn14 expression and promoter activity in the TAL of Ksp-cre;Pth1r^fl/fl mice. Moreover, PTH treatment of HEK293 cells stably transfected with CLDN14-GFP, together with PTH1R, induced cytosolic translocation of CLDN14 from the tight junction. Furthermore, mice with high serum PTH levels, regardless of high or low serum calcium, demonstrated that PTH/PTH1R signaling exerts a suppressive effect on Cldn14. We therefore conclude that PTH1R signaling directly and indirectly regulates the paracellular Ca²⁺ transport pathway by modulating Cldn14 expression in the TAL. Finally, systemic deletion of Cldn14 completely rescued the hypercalciuric and lower serum calcium phenotype in Ksp-cre;Pth1r^fl/fl mice, emphasizing the importance of PTH in inhibiting Cldn14. Consequently, suppressing CLDN14 could provide a potential treatment to correct urinary Ca²⁺ loss, particularly in patients with hypoparathyroidism.

Mactosylceramide prevents glial cell overgrowth by inhibiting insulin and fibroblast growth factor receptor signaling

Receptor tyrosine kinase (RTK) signaling controls key aspects of cellular differentiation, proliferation, survival, metabolism, and migration. Deregulated RTK signaling also underlies many cancers. Glycosphingolipids (GSL) are essential elements of the plasma membrane. By affecting clustering and activity of membrane receptors, GSL modulate signal transduction, including that mediated by the RTK. GSL are abundant in the nervous system, and glial development in Drosophila is emerging as a useful model for studying how GSL modulate RTK signaling. Drosophila has a simple GSL biosynthetic pathway, in which the mannosyltransferase Egghead controls conversion of glucosylceramide (GlcCer) to mactosylceramide (MacCer). Lack of elongated GSL in egghead (egh) mutants causes overgrowth of subperineurial glia (SPG), largely due to aberrant activation of phosphatidylinositol 3-kinase (PI3K). However, to what extent this effect involves changes in upstream signaling events is unresolved. We show here that glial overgrowth in egh is strongly linked to increased activation of Insulin and fibroblast growth factor receptors (FGFR). Glial hypertrophy is phenocopied when overexpressing gain-of-function mutants of the Drosophila insulin receptor (InR) and the FGFR homolog Heartless (Htl) in wild type SPG, and is suppressed by inhibiting Htl and InR activity in egh. Knockdown of GlcCer synthase in the SPG fails to suppress glial overgrowth in egh nerves, and slightly promotes overgrowth in wild type, suggesting that RTK hyperactivation is caused by absence of MacCer and not by GlcCer accumulation. We conclude that an early product in GSL biosynthesis, MacCer, prevents inappropriate activation of insulin and fibroblast growth factor receptors in Drosophila glia.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Enhanced oral delivery of alendronate by sucrose fatty acids esters in rats and their absorption-enhancing mechanisms

Oral delivery is the most fascinating route for interminable drug remedy. However, the intestinal absorption of alendronate (ALN), a bisphosphonate drug after oral administration is very poor. Absorption enhancers, which help to achieve the efficiency-safety balance, are considered one of the most promising agents for the improvement the intestinal absorption of drugs. In the current study, we focused on using sucrose fatty acid esters (SEs) as promising absorption enhancers to enhance the intestinal absorption of alendronate using an in situ closed-loop method in rats. The intestinal absorption of alendronate was significantly enhanced in the presence of SEs, especially L-1695. In addition, no considerable increase was observed in the activity of lactate dehydrogenase (LDH) or in protein release from the intestinal epithelium in the presence of sugar esters at concentrations equivalent to or lower than 1.0% (w/v), suggesting that these compounds are safe. Furthermore, mechanistic studies revealed increased membrane fluidity and loosening of the tight junctions (TJs) might be the underlying mechanism by which SEs improve the intestinal intake of alendronate, via transcellular and paracellular routes, respectively. These findings suggest that SEs are effective absorption enhancers for improving the intestinal absorption of alendronate, without causing serious damage to the enteric epithelium.

Systems Proteomics View of the Endogenous Human Claudin Protein Family

Claudins are the major transmembrane protein components of tight junctions in human endothelia and epithelia. Tissue-specific expression of claudin members suggests that this protein family is not only essential for sustaining the role of tight junctions in cell permeability control but also vital in organizing cell contact signaling by protein-protein interactions. How this protein family is collectively processed and regulated is key to understanding the role of junctional proteins in preserving cell identity and tissue integrity. The focus of this review is to first provide a brief overview of the functional context, on the basis of the extensive body of claudin biology research that has been thoroughly reviewed, for endogenous human claudin members and then ascertain existing and future proteomics techniques that may be applicable to systematically characterizing the chemical forms and interacting protein partners of this protein family in human. The ability to elucidate claudin-based signaling networks may provide new insight into cell development and differentiation programs that are crucial to tissue stability and manipulation.

Nifedipine prevents sodium caprate-induced barrier dysfunction in human epidermal keratinocyte cultures

Tight junctions (TJs) of the epidermis play an important role in maintaining the epidermal barrier. TJ breakdown is associated with skin problems, such as wrinkles and transepidermal water loss (TEWL). Clinical studies have reported that topical nifedipine is effective in reducing the depth of wrinkles and improving TEWL. However, it remains unknown whether nifedipine influences the TJ function in the epidermis. In the present study, we investigated the effect of nifedipine on epidermal barrier dysfunction in normal human epidermal keratinocytes (NHEKs) treated with sodium caprate (C10), a TJ inhibitor. Nifedipine reversed the C10-decreased transepithelial electrical resistance values as a measure of disruption of the epidermal barrier. Immunocytochemical observations revealed that nifedipine improved the C10-induced irregular arrangement of claudin-1, a key protein in TJs. Taken together, these findings suggest that nifedipine prevents epidermal barrier dysfunction, at least in part, by reconstituting the irregular claudin-1 localization at TJs in C10-treated NHEKs.

Nonvascular drug-eluting stent coated with sodium caprate-incorporated polyurethane for the efficient penetration of paclitaxel into tumor tissue

To increase the therapeutic potency of nonvascular drug-eluting stents, sodium caprate was employed as a drug-penetration enhancer. A polytetrafluoroethylene-covered drug-eluting stent was coated with a mixture containing sodium caprate, paclitaxel, and polyurethane via the rolling coating technique. The coated stent has a smooth membrane surface with a 40-µm membrane thickness. Paclitaxel was released from the coated stent for two months. In the multilayered cell sheet model, sodium caprate in the polyurethane membrane (PUSC10) showed the possibility of enhancing the paclitaxel tissue penetration. The amount of penetrated paclitaxel for the sodium caprate-containing polyurethane membrane (PUSC10) was two times higher than that of sodium caprate-free polyurethane membrane. Additionally, the potential of sodium caprate was confirmed by a tumor-bearing small animal model. PUSC10 incorporated with Nile red (as a model fluorescence dye for visualization of drug penetration; PUSC10–Nile red) or PUSC10 incorporated with paclitaxel (PUSC10–paclitaxel) membrane was implanted at tumor sites in Balb/c mice. In the case of PUSC10–Nile red, the tissue penetration depth of Nile red was significantly increased from 30 µm (without sodium caprate) to 1060 µm (with sodium caprate). After seven days, an almost four times higher therapeutic area of PUSC10–paclitaxel was observed compared to that of polyurethane–paclitaxel (without sodium caprate) by a terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The results indicate that sodium caprate improves the penetration and therapeutic efficiencies of drugs in drug-eluting stents, and thus, it has potential for local stent therapy.

Trends in drug delivery through tissue barriers containing tight junctions

A limitation in the uptake of many drugs is the restricted permeation through tissue barriers. There are two general ways to cross barriers formed by cell layers: by transcytosis or by diffusion through the intercellular space. In the latter, tight junctions (TJs) play the decisive role in the regulation of the barrier permeability. Thus, transient modulation of TJs is a potent strategy to improve drug delivery. There have been extensive studies on surfactant-like absorption enhancers. One of the most effective enhancers found is sodium caprate. However, this modulates TJs in an unspecific fashion. A novel approach would be the specific modulation of TJ-associated marvel proteins and claudins, which are the main structural components of the TJs. Recent studies have identified synthetic peptidomimetics and RNA interference techniques to downregulate the expression of targeted TJ proteins. This review summarizes current progress and discusses the impact on TJs' barrier function.

Lipid rafts and detergent-resistant membranes in epithelial keratinocytes

Our understanding of the plasma membrane has markedly increased since Singer and Nicolson proposed the fluid mosaic model in 1972. While their revolutionary theory of the lipid bilayer remains largely valid, it is now known that lipids and proteins are not randomly dispersed throughout the plasma membrane but instead may be organized within membrane microdomains, commonly referred to as lipid rafts. Lipid rafts are highly dynamic, detergent resistant, and enriched with both cholesterol and glycosphingolipids. The two main types are flotillin-rich planar lipid rafts and caveolin-rich caveolae. It is proposed that flotillin and caveolin proteins regulate cell communication by compartmentalizing and interacting with signal transduction proteins within their respective lipid microdomains. Consequently, membrane rafts play an important role in vital cellular functions including migration, invasion, and signaling; thus, alterations in their microenvironment can initiate signaling pathways that affect cellular function and behavior. Therefore, the identification of lipid rafts and their associated proteins is integral to the study of transmembrane signaling. Here, we review the current standard protocols and biochemical approaches used to isolate and define raft proteins from epithelial cells and tissues. Furthermore, in Section 3 of this chapter, detailed protocols are offered for isolating lipid rafts by subjection to detergent and sucrose density centrifugation, as well as an approach for selectively isolating caveolae. Methods to manipulate rafts with treatments such as methyl-β-cyclodextrin and flotillin III are also described.

Fatty acids as therapeutic auxiliaries for oral and parenteral formulations

Many drugs have decreased therapeutic activity due to issues with absorption, distribution, metabolism and excretion. The co-formulation or covalent attachment of drugs with fatty acids has demonstrated some capacity to overcome these issues by improving intestinal permeability, slowing clearance and binding serum proteins for selective tissue uptake and metabolism. For orally administered drugs, albeit at low level of availability, the presence of fatty acids and triglycerides in the intestinal lumen may promote intestinal uptake of small hydrophilic molecules. Small lipophilic drugs or acylated hydrophilic drugs also show increased lymphatic uptake and enhanced passive diffusional uptake. Fatty acid conjugation of small and large proteins or peptides has exhibited protracted plasma half-lives, site-specific delivery and sustained release upon parenteral administration. These improvements are most likely due to associations with lipid-binding serum proteins, namely albumin, LDL and HDL. These molecular interactions, although not fully characterized, could provide the ability of using the endogenous carrier systems for improving therapeutic outcomes.

Changes in the expression levels of tight junction components during reconstruction of tight junction from mucosal lesion by intestinal ischemia/reperfusion

Tight junction (TJ) is composed of the most apical components of the intercellular junctional complex in epithelial cells; TJ has cell polarity and functions as a major determinant of epithelial barrier function. In this study, to clarify the components of TJ required for its reconstruction and functional acquisition, we examined the changes in intestinal mucosal structure that depended on mucosal lesion by intestinal I/R, that is, the changes in mRNA and protein expression of the claudin family and scaffold proteins. We used an in vivo intestinal I/R model made using the spring scale and surgical sutures, and examined the mRNA and protein expression levels of TJ components by real-time RT-PCR and Western blotting, respectively. Changes in mRNA and protein expression levels of TJ components by intestinal I/R were observed. Among them, characteristic changes were observed in claudin-2 and claudin-4. In addition, the expression behavior of multi-PDZ domain protein (MPDP) mRNA was similar to that of claudin-4. In conclusion, in the recovery process of TJ from mucosal lesion by intestinal I/R, it was suggested that claudin-2 and claudin-4 strongly participate in the reconstruction and functional acquisition of TJ, respectively. Furthermore, it was suggested that MPDZ, which is scaffold protein, also has an important role in these processes.

Percolation analysis in electrical conductivity of Madin-Darby canine kidney and Caco-2 cells by permeation-enhancing agents

The control of permeability through the paracellular route has been paid great attention to for enhanced bioavailability of macromolecular and hydrophilic drugs. The paracellular permeability is controlled by tight junctions (TJ), and claudins are the major constituents of TJ. Despite numerous studies on TJ modulation, the dynamics is not well understood, although it could be crucial for clinical applications. Here, we studied the time (t) course of electrical conductivity (Σ) in a monolayer of Madin-Darby canine kidney (MDCK) and Caco-2 cells upon treatment with modulators, the C-terminus fragments of Clostridium perfringens enterotoxin (C-CPE) and sodium caprate (C10). For C-CPE treatment, Σ remains approximately constant, then starts increasing at t=tc (percolation threshold). For C10, on the other hand, Σ increases to 1.6-2.0 fold of the initial value, stays constant, and then starts increasing again for both MDCK and Caco-2 cells at t=tc. We find that this behavior can be explained within a framework of percolation, where Σ shows a logarithmic dependence on t-tc with the power of μ; μ denotes the critical exponent. We obtain μ=1.1-1.2 regardless of cell type or modulator. Notably, μ depends only on the dimensionality (d) of the system, and these values correspond to those for d=2. Percolation is thus the operative mechanism for the increase in Σ through TJ modulation. The findings provide fundamental knowledge, not only on controlled drug delivery, but also on bio-nanotechnologies including the fabrication of biological devices.

Ductal barriers in mammary epithelium

Tissue barriers play an integral role in the biology and pathobiology of mammary ductal epithelium. In normal breast physiology, tight and adherens junctions undergo dynamic changes in permeability in response to hormonal and other stimuli, while several of their proteins are directly involved in mammary tumorigenesis. This review describes first the structure of mammary ductal epithelial barriers and their role in normal mammary development, examining the cyclical changes in response to puberty, pregnancy, lactation and involution. It then examines the role of adherens and tight junctions and the participation of their constituent proteins in mammary tumorigenic functions such as migration, invasion and metastasis. Finally, it discusses the potential of these adhesion proteins as both prognostic biomarkers and potential therapeutic targets in breast cancer.

Tight junctions in skin: new perspectives

Tight junctions (TJs) are intercellular contacts that seal the space between the individual cells of an epithelial sheet or stratifying epithelia, such as the epidermis, so that they can collectively separate tissue compartments. Intercellular junctions, such as adherens and TJs, play a crucial role in the formation and maintenance of epithelial and endothelial barriers. A variety of components including claudins, occludin, tricellulin, zonula occluden proteins and junctional adhesion molecules have been identified in complex localization patterns in mammalian epidermis. In several skin diseases that are characterized by impaired skin barrier function, altered proliferation/differentiation of the epidermis and/or infiltration of inflammatory cells, altered expression patterns of TJ proteins have been observed. This review is aimed at providing an insight into the molecular composition, tools for identification and understanding the role of TJs in skin diseases and barrier function regulation.

Sodium caprate as an enhancer of macromolecule permeation across tricellular tight junctions of intestinal cells

Sodium caprate is a promising candidate for inducing drug absorption enhancement. The mechanism of that uptake-enhancing effect is not fully understood so far. We investigated how caprate acts in an established human intestinal cell line, HT-29/B6, on the transient opening of transcellular (across the cell membranes) and paracellular (across the tight junction) pathways. Sodium caprate (10 mm) caused a rapid and reversible decrease of transepithelial resistance which is based, as measured by two-path impedance spectroscopy, exclusively on resistance changes of the paracellular pathway. Measurements of paracellular marker fluxes revealed an increased permeability for fluorescein (330 Da) and FITC-dextran (4 and 10 kDa), indicating an opening of the paracellular barrier. Confocal microscopy revealed a marked reduction of tricellulin in tricellular tight junctions and of claudin-5 in bicellular tight junctions. This was not due to altered protein expression, as occludin, claudins or tricellulin were not significantly changed in Western blots. Visualization of the translocation site of the cell membrane-impermeable marker molecule sulpho-NHS-SS-biotin (607 Da) indicated the tricellular tight junction to be the predominant pathway. We suggest that caprate's known enhancing effect on intestinal drug uptake is based on increased permeability in tricellular cell contacts, mediated by reversible removal of tricellulin from the tricellular tight junction.

Changes in protein and mRNA expression levels of claudin family after mucosal lesion by intestinal ischemia/reperfusion

Ischemia/reperfusion (I/R) injury of the intestine is the leading cause of organ dysfunction after restoration of blood flow after diverse events, including shock and intestinal transplantation. I/R injury must be overcome for successful small intestinal transplantation. Tight junctions (TJ) are the most apical component of the intercellular junctional complex in epithelial cells; they establish cell polarity and functioning as major determinants of epithelial barrier function. Among the proteins that comprise TJ, the claudin family is thought to play a crucial role in homeostasis in multicellular organisms. Therefore, the aim of this study was to examine the changes in function of TJ and behavior of the claudin family during intestinal I/R. Wistar/ST rats underwent intestinal ischemia by using the spring scale and surgical suture for 1h, followed by 24h of reperfusion. We examined the changes in area under the blood concentration curve (AUC) after oral administration of FD-4, which is a paracellular marker, and claudin-1, -2, -4, and -7 mRNA and protein expression levels in ileum. The structure of ileal mucosa was partly damaged and its function was diminished by intestinal I/R until 3h after reperfusion, but were almost recovered 24h after reperfusion. However, a time difference was shown between the recoveries of mucosal structure and function. Furthermore, a difference in the expression among various kinds of claudin was found. It was suggested that claudin-4 and multi-PDZ domain protein, which is a scaffolding protein, regulate intestinal paracellular permeability during intestinal I/R. Moreover, the changes in the expression level of claudin-2 were unique.

Acidic bile salts modulate the squamous epithelial barrier function by modulating tight junction proteins

Experimental models for esophageal epithelium in vitro either suffer from poor differentiation or complicated culture systems. An air-liquid interface system with normal human bronchial epithelial cells can serve as a model of esophageal-like squamous epithelial cell layers. Here, we explore the influence of bile acids on barrier function and tight junction (TJ) proteins. The cells were treated with taurocholic acid (TCA), glycocholic acid (GCA), or deoxycholic acid (DCA) at different pH values, or with pepsin. Barrier function was measured by transepithelial electrical resistance (TEER) and the diffusion of paracellular tracers (permeability). The expression of TJ proteins, including claudin-1 and claudin-4, was examined by Western blotting of 1% Nonidet P-40-soluble and -insoluble fractions. TCA and GCA dose-dependently decreased TEER and increased paracellular permeability at pH 3 after 1 h. TCA (4 mM) or GCA (4 mM) did not change TEER and permeability at pH 7.4 or pH 4. The combination of TCA and GCA at pH 3 significantly decreased TEER and increased permeability at lower concentrations (2 mM). Pepsin (4 mg/ml, pH 3) did not have any effect on barrier function. DCA significantly decreased the TEER and increased permeability at pH 6, a weakly acidic condition. TCA (4 mM) and GCA (4 mM) significantly decreased the insoluble fractions of claudin-1 and claudin-4 at pH 3. In conclusion, acidic bile salts disrupted the squamous epithelial barrier function partly by modulating the amounts of claudin-1 and claudin-4. These results provide new insights for understanding the role of TJ proteins in esophagitis.

Monitoring proteins using in vivo near-infrared time-domain optical imaging after 2-O-hexyldiglycerol-mediated transfer to the brain

Purpose

The aim of the present study was to gain insight into the penetration, biodistribution, and fate of globulins in the brain after 2-O-hexyldiglycerol-induced blood–brain barrier opening.

Procedures

The spatial distribution of fluorescence probes was investigated after blood–brain barrier opening with intracarotid 2-O-hexyldiglycerol injection. Fluorescence intensity was visualized by microscopy (mice and rats) and by in vivo time-domain optical imaging.

Results

There was an increased 2-O-hexyldiglycerol-mediated transfer of fluorescence-labeled globulins into the ipsilateral hemisphere. Sequential in vivo measurements revealed that the increase in protein concentration lasted at least 96 h after administration. Ex vivo detection of tissue fluorescence confirmed the results obtained in vivo.

Conclusion

Globulins enter the healthy brain in conjunction with 2-O-hexyldiglycerol. Sequential in vivo near-infrared fluorescence measurements enable the visualization of the spatial distribution of antibodies in the brain of living small animals.

Absorption enhancement effect of acylcarnitines through changes in tight junction protein in Caco-2 cell monolayers

We investigated the effects of lauroylcarnitine and palmitoylcarnitine on major tight junction proteins such as claudins in Caco-2 cell monolayers and also examined the involvement of cholesterol in the effects induced by both acylcarnitines on these proteins. We investigated the effects of lauroylcarnitine and palmitoylcarnitine on the barrier function of tight junctions by measuring transepithelial electrical resistance (TEER) and fluorescein isothiocyanate dextran 40,000 (FD-40) flux. A decrease in the TEER value and an increase in FD-40 flux were observed after incubating Caco-2 cell monolayers with lauroylcarnitine and palmitoylcarnitine for 1 h, suggesting the loss of the barrier function of tight junctions. In addition, lauroylcarnitine and palmitoylcarnitine decreased the protein levels of claudin 1, 4, and 5 but not those of claudin 2, 3, 6, or 7. In addition, palmitoylcarnitine and methyl-β-cyclodextrin increased cholesterol release from the plasma membrane. It is suggested that the effects of palmitoylcarnitine and methyl-β-cyclodextrin on claudin 4 and 5 may be associated with cholesterol leakage from the plasma membrane into the apical side. These results indicate that the protein levels of claudin 4 and 5 are decreased by treatment with palmitoylcarnitine and lauroylcarnitine, and that this change is involved in the absorption-enhancing mechanism.

Spray freeze drying with polyvinylpyrrolidone and sodium caprate for improved dissolution and oral bioavailability of oleanolic acid, a BCS Class IV compound

Spray-freeze-drying (SFD) of oleanolic acid (OA), a BCS Class IV compound, with polyvinylpyrrolidone-40 (PVP-40) as stabilizer and sodium caprate (SC) as wetting agent and penetration enhancer produced kinetically stable, amorphous solid dispersion systems with superior in vitro dissolution performance, and better and more uniform absorption in comparison with commercial OA tablet. Relative to the SC-free formulation, the presence of SC in the formulation resulted in a significant increase in the in vivo absorption rate of OA while exerting no apparent impact on the extent of OA absorption. The SFD-processed OA formulations and commercial OA tablet generally exhibited large inter-animal variability in oral bioavailability, consistent with the absorption characteristics of BCS Class IV compounds. Inclusion of SC coupled with the replacement of OA with its sodium salt (OA-Na) in the formulation was shown to substantially decrease the observed absorption variability. Above results suggested that increases in both dissolution rate and intestinal permeability of BCS Class IV compounds, as exemplified by the SFD-processed dispersion system containing both OA-Na and SC, are critical to reducing the large inter-individual absorption variability commonly observed with this class of drugs.

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).

Tight junction modulator and drug delivery

Recent progress in pharmaceutical technology based on genomic and proteomic research has provided many drug candidates, including not only chemicals but peptides, antibodies and nucleic acids. These candidates do not show pharmaceutical activity without their absorption into systemic flow and movement from the systemic flow into the target tissue. Epithelial and endothelial cell sheets play a pivotal role in the barrier between internal and external body and tissues. Tight junctions (TJs) between adjacent epithelial cells limit the movement of molecules through the intercellular space in epithelial and endothelial cell sheets. Thus, a promising strategy for drug delivery is the modulation of TJ components to allow molecules to pass through the TJ-based cellular barriers. In this review, we discuss recent progress in the development of TJ modulators and the possibility of absorption enhancers and drug-delivery systems based on TJ components.