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PubMed1994

Effect of bis (tributyl tin) oxide on permeability of the blood-brain barrier: a transient increase.

OBJECTIVES: To study the effect of bis (tributyl tin) oxide (TBTO) on permeability of the blood-brain barrier. METHODS: Electron microscopy and an x ray microanalyser with lanthanum chloride as a tracer were used, and blood tin concentrations were determined with an atomic absorption spectrophotometer. Adult male wistar rats received 0.05 ml/kg body weight of TBTO orally. RESULTS: A transient increase in paracellular permeability at the blood-brain barrier was found 2 h after the dose of TBTO. Electron dense lanthanum deposits penetrated tight junctions of the endothelia and permeated the subendothelial space. The x ray microprobe data showed an accumulation of TBTO at the tight junctions at 2 h. Leakage of tracer did not occur at 4 h, but oedematous changes in the surrounding glial cells were prominent between 4 and 8 h and had almost returned to normal by 24 h. By atomic absorption analysis, it was seen that blood tin concentrations rapidly increased at 1 h and rose to a maximum peak at 8 h, then gradually decreased to reach zero at 24 h. CONCLUSIONS: Accumulated TBTO at tight junctions could have caused the temporary replacement of calcium ion by tin, which induces a transient increase in paracellular permeability throughout the blood-brain barrier.

Animals↗
PubMed2006

Listeria monocytogenes invades the epithelial junctions at sites of cell extrusion.

Listeria monocytogenes causes invasive disease by crossing the intestinal epithelial barrier. This process depends on the interaction between the bacterial surface protein Internalin A and the host protein E-cadherin, located below the epithelial tight junctions at the lateral cell-to-cell contacts. We used polarized MDCK cells as a model epithelium to determine how L. monocytogenes breaches the tight junctions to gain access to this basolateral receptor protein. We determined that L. monocytogenes does not actively disrupt the tight junctions, but finds E-cadherin at a morphologically distinct subset of intercellular junctions. We identified these sites as naturally occurring regions where single senescent cells are expelled and detached from the epithelium by extrusion. The surrounding cells reorganize to form a multicellular junction that maintains epithelial continuity. We found that E-cadherin is transiently exposed to the lumenal surface at multicellular junctions during and after cell extrusion, and that L. monocytogenes takes advantage of junctional remodeling to adhere to and subsequently invade the epithelium. In intact epithelial monolayers, an anti-E-cadherin antibody specifically decorates multicellular junctions and blocks L. monocytogenes adhesion. Furthermore, an L. monocytogenes mutant in the Internalin A gene is completely deficient in attachment to the epithelial apical surface and is unable to invade. We hypothesized that L. monocytogenes utilizes analogous extrusion sites for epithelial invasion in vivo. By infecting rabbit ileal loops, we found that the junctions at the cell extrusion zone of villus tips are the specific target for L. monocytogenes adhesion and invasion. Thus, L. monocytogenes exploits the dynamic nature of epithelial renewal and junctional remodeling to breach the intestinal barrier.

Journal Article↗
PubMed2006

[Structural-functional analysis of diffusion in glucose absorption by rat small intestine enterocytes].

To elucidate mechanisms providing transport of sugars across intestinal epithelium, on taking into account the current hypotheses (active transport, participation of paracellular transport and passive component of transcellular transport), it was important to reveal structural changes of tight junctions and distribution of the carriers of facilitated diffusion of GLUT2 and protein kinase C during absorption of glucose. On using confocal and electron microscopy, ultrastructural and immunocytochemical studies of enterocytes after perfusion of isolated rat small intestine fragment with 75 mM glucose (chronic experiment) have shown: 1) fluorescent labels of transporter GLUT2 and PKCbetaII are located in the apical area of enterocytes situated at the upper half of the villus. Antibodies against GLUT2, conjugated with gold, are revealed at the microvilli or apical membrane and in the area of terminal network; 2) no ultrastructural changes of the tight junction are detected on ultrathin sections and freeze--fracture replics. At the same time, fluorescent and gold labels against actin are concentrated in the vicinity of the lateral membrane in the tight junction area. The results obtained can serve a confirmation of a hypothesis that at high glucose concentrations GLUT2 participates in its transfer across the apical membrane.

Animals↗
PubMed1986

The permeability of the primary decidual zone in the rat uterus: an ultrastructural tracer and freeze-fracture study.

The rat primary decidual zone (PDZ) is a transitory avascular region of transformed fibroblasts surrounding the implanting embryo. Studies using fluorescein-labeled tracers have shown that the PDZ is selectively permeable to macromolecules, permeability decreasing with increasing molecular weight. In the present study we investigated the morphologic basis of the permeability barrier. Horseradish peroxidase (HRP) or HRP-labeled immunoglobulin G (IgG-HRP) was administered i.v. to rats on Day 7 of pregnancy, and the animals were killed 30 min to 2 h later. The reaction product of HRP was the same density in uterine blood vessels as in the intercellular spaces of the endometrium and PDZ at 30 min and 1 h after administration. Two hours after administration, the reaction product of IgG-HRP was dense in uterine blood vessels, much less dense in the interstitial spaces of the endometrium, and was not detected in the PDZ. There was an abrupt change in the density of the IgG-HRP reaction product at the intercellular clefts between endothelial cells, where cellular junctions were observed in control tissue. This suggests that the passage of large macromolecules from blood to the implantation chamber is limited initially by cellular junctions between capillary endothelial cells. The exclusion of IgG-HRP from the PDZ indicates that an additional barrier(s) to macromolecules in this region. Lanthanum nitrate tracer was uniformly present throughout the intercellular spaces of the PDZ except at tight junctions between decidual cells. Freeze-fracture replicas of the PDZ showed tight junctions that varied from single strands to interconnected networks of strands oriented mainly parallel to the long axis of the PDZ. Some strands were discontinuous. The tight junctions between decidual cells appear to be functionally discontinuous because HRP readily penetrated the PDZ, but such junctions may retard larger macromolecules such as IgG-HRP. The biological significance of the permeability barrier of the PDZ is discussed.

Animals↗
PubMed1976

Vitamin-A-induced mucous metaplasia. An in vitro system for modulating tight and gap junction differentiation.

Stratified squamous epithelia from 14-day chick embryo shank skin contain rare tight-junctional strands and only small gap junctions. Exposure of this tissue to retinoic acid (vitamin-A) (20 U/ml) in organ culture, however, induces mucous metaplasia, accompanied by tight-junction formation and gap-junction growth; untreated specimens continue to keratinize. To investigate sequential stages of junctional assembly and growth, we examined thin sections and freeze-fracture replicas at daily intervals for 3 days. During the metaplastic process, tight junctions assemble in midepidermal and upper regions, beginning on day 1 and becoming maximal on day 3. Two tight-junctional patterns could be tentatively identified as contributing to the emergence of fully formed zonulae occludentes: (a) the formation of individual ridges along the margins of gap junctions; (b) de novo generation of continuous ramifying strands by fusion of short strand segments and linear particulate aggregates near cellular apices. Gap junction enlargement, already maximal at day 1, occurs primarily three to four cell layers deep. Growth appears to occur by annexation of islands of 20-40 8.5-nm particles into larger lattices of islands separated by particle-free aisles. Eventually, a single gap junction may occupy much of the exposed membrane face in freeze-fractured tissue, but during apical migration of the cells such junctions disappear. The vitamin- A chick-skin system is presented as a responsive model for the controlled study of junction assembly.

Animals↗
PubMed1988

Evaluation of different procedures for the dissociation of retinal pigmented epithelium into single viable cells.

Retinal pigmented epithelium (RPE) from 7-day-old chicken embryos (stages 29 to 31) was isolated and dissociated into single cells using different procedures. The results were assessed in two ways. (1) The yield of single RPE cells per embryo was determined, and their ability to form pigmented colonies in clonal culture was tested. The most efficient and gentle procedure included isolation of the RPE in EDTA solution, trypsinization at low temperature and low enzyme concentration in the presence of EDTA, followed by incubation in culture medium for up to 4 hr. The completely dissociated cells thus obtained had a much higher plating efficiency and more uniform pattern of colony growth and differentiation than those obtained under any other conditions tested. (2) The effects of different treatments on cell junctions and morphological integrity of the cells were determined by transmission electron microscopy. EDTA solution yielded excellent separation of the epithelial sheet from the mesenchyme by dissociating it from Bruch's membrane, but had little effect on the junctions between adjacent RPE cells. Trypsinization of the epithelium under various conditions separated the basal lateral cell borders and caused loss of gap junctions, but left many cells still joined by apical tight junctions. Final disruption of the tight junctions occurred during recovery of the trypsinized cells in culture medium and was accompanied by dedifferentiation of the RPE cells.

Animals↗
PubMed1990

Warner-Lambert/Parke-Davis Award lecture. Pathobiology of the intestinal epithelial barrier.

The major route of passive permeation across intestinal epithelia is paracellular. The intercellular tight junction lies in and serves as the rate-limiting barrier in this paracellular pathway. Once viewed as static, it is now clear that the structure and permeability of the tight junction is highly dynamic. Not only may inflammatory events (cytokines, neutrophil transmigration) reversibly effect the tight junction but this key barrier also is regulated by physiologic events such as activation of absorptive cell Na(+)-nutrient cotransporters. Such physiologic regulation of the junction is of major importance to the absorption of nutrients via parcellular solvent drag.

Animals↗
PubMed1979

Ultrastructure of canine urinary bladder carcinoma.

Luminal and intraepithelial asymmetric unit membrane plaques were found in the urinary bladder urothelium of normal dogs. Tight junctions were found only at the apical poles of the luminal cells. In four dogs with spontaneous urinary bladder carcinomas the asymmetric unit membrane plaques were replaced by symmetric unit membrane. In the neoplastic luminal cells the tight junctions were partially attenuated. Invasive and metastatic neoplastic cells had some tight junction at the stromal interface. Some gap junctions were seen in the normal urothelium but not in the neoplastic cells. The amount of desmosomes in the neoplastic cells varied according to their direction of differentiation (transitional, squamous or glandular).

Animals↗
PubMed1989

Intercellular communication between rat anterior pituitary cells.

Cell-to-cell communication within the rat anterior pituitary was investigated in 60-day-old male rats with immunohistochemistry, scanning electron microscopy, freeze-fracture electron microscopy, and conventional transmission electron microscopy. A dense cytoreticular network of cytoplasmic processes from the folliculostellate cells was found to contain immunoreactive S-100 protein and was observed throughout the anterior pituitary. Nonimmunoreactive cells, which were granular, were situated in the center of each network. Almost all of the granulated cells were situated in close proximity to the folliculostellate cells. Scanning electron microscopy revealed that the gland consisted of microlobules enclosed by a basal lamina. On the surface of the microlobules were blood vessels whose branches invaded its internal structures. Cytoplasmic processes from folliculostellate cells projected outside the microlobule. Freeze-fracture electron microscopy demonstrated the presence of numerous intramembranous particles on the P-face of the plasma membrane. Scattered on the cell surface were groups of particles forming gap junctions. Meshworks of ridges which were representations of tight junctions were also observed near clusters of microvillous fragments. Clusters of particles forming small gap junctions were located between the meshworks of tight junctions. Small gap junctions were clearly observed by conventional electron microscopy between junctional complexes in a manner similar to that seen by freeze-fracture electron microscopy. Slender cytoplasmic processes of folliculostellate cells came in contact near the basal lamina and were adjoined by small gap junctions. The ratio of nongranular cells which contained gap junctions to those in which the junctions were absent was about 1:1. The size of the gap junctions ranged from 50 nm to 3 microns. No gap junctions were observed along the plasma membranes of the granular cells. The significance of an intercellular communication system within the anterior pituitary gland of the rat is to establish a mechanism for rapid transmission of information in an organ which lacks direct innervation.

Animals↗
PubMed2001

[Ultrastructural studies of hepatoblast junctions and liver hematopoiesis of the mouse embryo].

To clarify the morphological changes in hepatoblast connections during the development of fetal liver hematopoiesis, ICR mouse livers of 11 to 19 days of gestation were studied by means of three-dimensional reconstruction, immunohistochemistry, electron microscopy and freeze fracture replica method. Embryonic liver weight showed rapid increase until 19 days of gestation, and an initial steep increase, due to hematopoietic development, was observed at 13 to 15 days of gestation. Hepatoblast volume appeared to be constant until 13 days of gestation, and, thereafter, showed a gradual increase. An 11-day primitive hepatic cord contained a few immature hematopoietic cells among hepatoblasts, and the hepatoblasts made contact with one another by short cytoplasmic projections. The area of the contact surface had a diameter of 4-5 microns, where E-cadherin-mediated adherens junctions were found. At 12-13 days of gestation, hepatoblasts surrounded large ellipsoidal hematopoietic foci, with long cytoplasmic projections. In addition to the adherens junctions, small desmosomes appeared to bind hepatoblasts together, and biliary canaliculi could be recognized between hepatoblasts. At peak stage of liver hematopoiesis at 14 days of gestation, both tight junctions and gap junctions appeared around the biliary canaliculi, and four types of specialized junctions, i.e., adherens junctions, desmosomes, tight junctions and gap junctions, appeared to be fully developed. After 15 days of gestation, hepatocyte volume showed rapid increase, and the surface areas between adjacent hepatocytes were markedly enlarged. As a result, the involuted hematopoietic foci were forced to move from interhepatocytic spaces to perisinusoidal space at the end of the intrauterine life.

Animals↗
PubMed1998

Cell lines of pulmonary and non-pulmonary origin as tools to study the effects of house dust mite proteinases on the regulation of epithelial permeability.

BACKGROUND: Allergenic and non-allergenic proteinases from house dust mites (HDM) cause loss of adhesion between airway epithelial cells that may result in a loss of functional cohesion between the cells and thus assist in allergen presentation. Improved cellular assay systems are needed to ascertain the mechanisms involved. OBJECTIVES: To survey a series of epithelial cell lines (Calu-3, 16HBE14o-, NCI-H292 and A549 from human airways, and MDCK from dog kidney) and establish their utility for studies of the effects of HDM proteinases from D. pteronyssinus on epithelial permeability. To develop an improved method for measuring changes in epithelial permeability induced by HDM proteinases and other provocants. METHODS: The permeability of epithelial monolayer cultures to mannitol was calculated from measurements of clearance using a technique that permits mathematical estimation and reduction of non-cellular diffusional constraints. Permeability was studied under control conditions and after perturbation of monolayers with HDM proteinases (separated into serine- and cysteine-proteinase classes) or chelation of extracellular Ca2+. Fluorescent antibody staining was used to investigate whether the cells expressed tight junctions (staining of ZO-1), desmosomes (staining of desmoplakin) and zonulae adherentes (staining of E-cadherin). RESULTS: The Calu-3 line was identified as an airway cell line that expressed functional tight junctions, desmosomes and zonulae adherentes. Calu-3 monolayers exhibited a low clearance and permeability to mannitol, similar to that seen in the extensively characterized MDCK cell line. Clearance and permeability were significantly increased by treatment with either HDM proteinase fraction or by calcium chelation. 16HBE14o- cells also had a low permeability to mannitol under control conditions and expressed a similar repertoire of functional proteins from major intercellular junctions. In contrast, NCI-H292 and A549 cell lines were functionally deficient in tight junctions, although they did express desmosomes and zonulae adherentes to a greater extent. Epithelial permeability was found to be a more appropriate and sensitive index of epithelial perturbation than was tracer clearance. CONCLUSION: These results suggest that the Calu-3 and 16HBE14o- cell lines are useful tools in studying the mechanism of HDM proteinases on airway epithelial cell function. HDM proteinases of both cysteine and serine mechanistic classes were found to perturb epithelial adhesion and function.

Adult↗
PubMed2005

Zinc protects renal function during cadmium intoxication in the rat.

This study investigates the effect in the rat of chronic CdCl2 intoxication (500 microg Cd2+/kg, daily i.p. injection for 5 days) on renal function and the changes in tight junction proteins claudin-2, claudin-3, and claudin-5 present in rat kidney. We also studied the effect of coadministration of ZnCl2 (500 microg Zn2+/kg) during chronic CdCl2 intoxication. Our results indicate that 1) most of the filtered Cd2+ is reabsorbed within the kidney; 2) chronic Cd2+ intoxication can induce a change in renal handling of ions without altering glomerular filtration rate; 3) a delayed nephropathy, showing Fanconi-like features, appears more than 5 days after the end of CdCl2 exposure; 4) epithelial integrity is altered by chronic Cd2+ intoxication affecting the expression and localization of claudin tight junction proteins; and 5) cotreatment with Zn2+ protects against the renal toxic effects of Cd2+, preventing altered claudin expression and inhibiting apoptosis. In conclusion, these results show that Cd2+ toxicity and cellular toxic mechanisms are complex, probably affecting both membrane transporters and tight junction proteins. Finally, Zn2+ supplementation may provide a basis for future treatments.

Animals↗
PubMed1992

Effect of cadmium chloride on transepithelial electrical resistance of Sertoli cell monolayers in two-compartment cultures--a new model for toxicological investigations of the "blood-testis" barrier in vitro.

The effect of various doses (0.75-24 microM) of cadmium chloride (CdCl2) on the development of intercellular tight junctions by immature rat Sertoli cells (Sc) was investigated in vitro using the two-compartment culture system. The status of tight junctions was monitored by repeated measurements of the transepithelial electrical resistance (TER). For defining the specificity of CdCl2 effects, the TER changes were correlated with Sc secretory activity (immunoactive inhibin), the cell number (DNA content), and viability (MTT test). The effects of CdCl2 depended on the concentration of the toxicant as well as on the onset and duration of exposure (4 and 18 hr on Day 1 or 5 of culture). The observed effects could be divided into four categories: (1) At highest doses employed, the TER values decreased significantly and irreversibly during 13 days of culture, and the decrease was accompanied by a significant and irreversible drop in inhibin secretion, cell viability, and cell number. (2) Within a narrow range of doses, the irreversible, or only partially reversible, decrease of TER was accompanied by a transient decrease, or no change, of the secretory activity and no significant changes in Sc cell number and/or viability. (3) With still lower doses, the TER values rapidly decreased and then returned to control level within 3-4 days. In this group, no changes in either inhibin secretion or cell viability were observed. (4) Exposure to the lowest doses of CdCl2 caused a delayed, but significant increase in TER. This increase was not accompanied by noticeable changes in other parameters evaluated. These data suggest that CdCl2 may selectively compromise, at least in vitro, the development and maintenance of the inter-Sc tight junctions, without affecting the secretory activity or the cell number and viability. However, increasing cumulative doses of CdCl2 (concentration multiplied by the time of exposure) led to decreased inhibition secretion and cell viability and then, finally, to irreversible cell damage and death. We believe that the experimental model and approach reported in this paper should be very useful for investigating the mechanism of action of known or potential testicular toxicants, particularly those suspected to compromise the integrity of the "blood-testis" barrier.

Animals↗
PubMed2004

Developmental regulation of claudin localization by fetal alveolar epithelial cells.

Tight junction proteins in the claudin family regulate epithelial barrier function. We examined claudin expression by human fetal lung (HFL) alveolar epithelial cells cultured in medium containing dexamethasone, 8-bromo-cAMP, and isobutylmethylxanthanine (DCI), which promotes alveolar epithelial cell differentiation to a type II phenotype. At the protein level, HFL cells expressed claudin-1, claudin-3, claudin-4, claudin-5, claudin-7, and claudin-18, where levels of expression varied with culture conditions. DCI-treated differentiated HFL cells cultured on permeable supports formed tight transepithelial barriers, with transepithelial resistance (TER) >1,700 ohm/cm(2). In contrast, HFL cells cultured in control medium without DCI did not form tight barriers (TER <250 ohm/cm(2)). Consistent with this difference in barrier function, claudins expressed by HFL cells cultured in DCI medium were tightly localized to the plasma membrane; however, claudins expressed by HFL cells cultured in control medium accumulated in an intracellular compartment and showed discontinuities in claudin plasma membrane localization. In contrast to claudins, localization of other tight junction proteins, zonula occludens (ZO)-1, ZO-2, and occludin, was not sensitive to HFL cell phenotype. Intracellular claudins expressed by undifferentiated HFL cells were localized to a compartment containing early endosome antigen-1, and treatment of HFL cells with the endocytosis inhibitor monodansylcadaverine increased barrier function. This suggests that during differentiation to a type II cell phenotype, fetal alveolar epithelial cells use differential claudin expression and localization to the plasma membrane to help regulate tight junction permeability.

1-Methyl-3-isobutylxanthine↗
PubMed2005

Intestinal absorption enhancement via the paracellular route by fatty acids, chitosans and others: a target for drug delivery.

Peroral delivery of hydrophilic drugs is one of the greatest challenges in biopharmaceutical research. Hydrophilic drugs usually present low bioavailability after oral administration. One of the causes of this low bioavailability is their poor intestinal permeation through the paracellular pathway. This pathway is actually restricted by the presence of tight junctions at the apical side of the enterocytes. In the last few years, great interest has been focused on the structure and cellular regulation of tight junctions, materializing in more in-depth knowledge of this intestinal barrier. Simultaneously, and on the basis of this understanding, continuous efforts are being made to develop agents that can modulate tight junctions and magnify the paracellular permeability of hydrophilic compounds without causing significant intestinal damage. This review focuses on strategies to improve the paracellular permeation of poorly absorbed drugs as a way to enhance their bioavailability after oral administration. Most of the research on this subject has been carried out using in vitro models (mainly Caco-2 cell monolayers), which yield useful information on the potential effects and mechanisms of action of absorption-enhancing compounds. However, in vivo studies, which are much more scarce, are needed to confirm the effects of potential enhancers and to evaluate the suitability of including these compounds as excipients in drug formulation. We review the in vitro and in situ studies involving the most promising paracellular permeation enhancers (e.g., medium chain fatty acids and chitosan and its derivatives), analyzing the degree of drug absorption enhancement achieved, as well as the potential associated toxicity. The few studies performed in vivo are also presented. In addition, the findings of recent absorption enhancers, such as zonula occludens toxin or thiolated polymers, are reviewed.

Adjuvants, Pharmaceutic↗
PubMed2005

Epidermal growth factor-mediated growth control of confluent mammary epithelial cells cultured on artificial basement membrane.

Local epithelial cell growth is involved in physiological and pathological processes such as development, morphogenesis and carcinogenesis. Cell growth is triggered by the binding of growth factors, such as epidermal growth factor (EGF) to their own receptors (i.e. EGFR). In confluent states, EGFRs are distributed on the basal-lateral side of polarized cells. Therefore, the delivery of EGF to EGFR is thought to be regulated by both tight junctions between the cells, as well as by the basement membrane to which the cells are attached. This research constructed a new culture device with which EGF can be delivered to either the basal-lateral or apical side of confluent epithelial cells that are cultured on an artificial Matrigel basement membrane. Cells in a confluent state started to regrow as a result of incubation with basal medium containing EGF, but not as a result of incubation with apical medium containing EGF. The rate of confluent epithelial cell regrowth depended on EGF concentrations supplied via the basement membrane. In contrast, cells in which tight junctions were disrupted by pre-treatment with EGTA displayed regrowth as a result of incubation with apical medium containing EGF. These results suggest that EGF signaling from the basal-lateral side is regulated by the basement membrane, while that from the apical side is blocked by the tight junctions. Thus, this culture model can be readily used to study the control of local growth of epithelial cells in physiological and pathological processes.

Blotting, Western↗
PubMed2005

Cationic albumin conjugated pegylated nanoparticle with its transcytosis ability and little toxicity against blood-brain barrier.

Our newly developed drug delivery carrier, cationic bovine serum albumin (CBSA) conjugated with poly(ethyleneglycol)-poly(lactide) (PEG-PLA) nanoparticle (CBSA-NP), was designed for brain drug delivery. CBSA, as a brain specific targetor, was covalently conjugated with the maleimide function group at the distal of poly(ethyleneglycol) (PEG) surrounding the nanoparticles. To evaluate its blood-brain barrier (BBB) transcytosis and toxicity against the BBB endothelial tight junction, we have explored a method of coculture with brain capillary endothelial cells (BCECs) on the top of micro-porous membrane of cell culture insert and astrocytes on the bottom side. The permeability of 14C-labeled sucrose was determined. For the CBSA-NP transcytosis study, a lipophilic fluorescent probe, 6-coumarin, was incorporated into nanoparticles. The BBB permeability of CBSA-NP in vitro was calculated and compared with native bovine serum albumin (BSA) conjugated pegylated nanoparticles (BSA-NP). As the coculture model, the transendothelial electrical resistance reached up to 313+/-23 ohms cm2. The tight junction between BCECs in the coculture could be visualized by scanning electron microscopy and transmission electron microscopy. The unchanged permeability of 14C-labeled sucrose comparing to that in the appearance of 200 microg/ml of CBSA-NP proved that CBSA-NP did not impact the integrity of BBB endothelial tight junctions. CBSA-NP also showed little toxicity against BCECs. The permeability of CBSA-NP was about 7.76 times higher than that of BSA-NP, while the transcytosis was inhibited in the excess of free CBSA. It was concluded that CBSA-NP preferentially transported across BBB with little toxicity, which offered the possibility to deliver therapeutic agents to CNS.

Animals↗
PubMed2005

Multiple pathways are involved in the oral absorption of BMS-262084, a tryptase inhibitor, in rats: role of paracellular transport, binding to trypsin, and P-glycoprotein efflux.

BMS-262084 is a potent and selective beta-lactam tryptase inhibitor with therapeutic potential for treating asthma. The oral bioavailability of BMS-262084 was low in rats (4% at a dose of 0.5 mg/kg) due to poor absorption. BMS-262084 was excreted mainly unchanged in the urine, suggesting minimal metabolism in rats. The objective of this study was to investigate the mechanisms of oral absorption of BMS-262084 in rats. Modulation of intestinal tight junctions, binding to trypsin, and involvement of the intestinal dipeptide transport system and P-glycoprotein (P-gp) in the absorption of BMS-262084 were examined. Coadministration of BMS-262084 with SQ-29852, a substrate of the intestinal dipeptide transport system, did not change the oral absorption of BMS-262084. An increase in the dose of BMS-262084 from 0.5 to 50 mg/kg resulted in a 3.7-fold increase in its oral absorption. Inulin absorption was enhanced upon coadministration with BMS-262084, suggesting the opening of tight junctions in the intestinal epithelium. Coadministration of aprotinin, a trypsin inhibitor, increased the oral absorption of BMS-262084 several fold. In vitro, using Caco-2 cells, BMS-262084 appeared to be a P-gp substrate, with an efflux ratio of 14. These results suggest that absorption of BMS-262084 is mediated by several concurrent mechanisms. At higher doses of BMS-262084, increased absorption may be primarily due to opening of tight junctions in the intestinal epithelium and consequent absorption via the paracellular pathway, while at lower doses, binding to trypsin may contribute to limiting its absorption. P-gp efflux may also play a role in influencing the absorption of BMS-262084. The intestinal dipeptide transporter system does not appear to be involved in the absorption of BMS-262084.

ATP Binding Cassette Transporter, Subfamily B, Mem↗